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Surveying Mass Extinctions - Part 2

Postosuchus, one of the crocodylomorphs of the Triassic (FunkMonk, Public Domain)

Continuing my overview of the Earth's extinction events! Part 1 covered the 'Precambrian' and Paleozoic, and so Part 2 will conclude with the Mesozoic and Cenozoic Eras.

Smithian-Spathian Boundary Event

When? - ~249.9 Million Years Ago (Olenekian Age, Early Triassic)

Cause - The Siberian Traps still had a little juice in them, and briefly experienced a few more eruptions which were enough to recharge ocean anoxia and an increase in volcanic carbon leading to global warming (Du, etal. 2022).

Victims - Life was on the road to recovery following the Great Dying, even following a massive spike in global temperatures facilitated by the loss of forests (Xu, et al. 2025). Surveys of fossil communities point to the Smithian-Spathian being particularly disruptive to regrowth: many species survived the destruction only to perish almost immediately afterward. Lystrosaurus, one of the most common of the dicynodont protomammals, went extinct, as did contemporaneous tetrapods like the archosauriform Proterosuchus. In the seas, life was hit equally hard, with losses among conodonts, ammonoids, bivalves, and other marine invertebrates, while radiolarians (amoeba-like, shelled plankton) suffered extinctions.

Survivors - It appears that bony fishes and the ancestors of marine reptiles survived through the harsh conditions, and it's widely understood that ichthyosaurs and sauropterygians (placodonts & proto-plesiosaurs) experienced an adaptive radiation afterward, preying on the many newly evolving fishes. They would become some of the major marine vertebrates of the Mesozoic Era. Among marine invertebrates, the start of the Triassic marks the origin of the "Modern Fauna", mainly composed of bivalves, gastropods, echinoderms, and crustaceans.

Carnian Pluvial Episode

When? - ~234-232 Million Years Ago

Cause - Climate warming coincides with increased moisture in the atmosphere, and it appears that the hot-house conditions of the Triassic Period facilitated the appearance of megamonsoons which dumped rains across the Pangaean supercontinent for roughly 2 million years. Such persistent rainfall affected the rock and water cycles and turned large areas of the land into humid, wetland environments (Corso, et al. 2020).

Victims - Such a change in the water cycle shifted both marine and freshwater communities, and there were extinctions among mollusks, crinoids (isocrinids died out), corals, bryozoans, conodonts, bony fishes, and planktonic forms. On land, tetrapods experienced losses, primarily among herbivorous varieties like rhynchosaurs and dicynodonts.

Survivors - The spread of wetlands encouraged the growth of new forests, and ferns, conifers, and cycadeoids (stem-angiosperms) experienced increased biodiversity. Fossil evidence points to the rise of dinosaurs, crocodylomorphs, turtles, lepidosaurs (lizards & tuataras) and mammaliaforms during the Carnian Pluvial Episode, meaning that essentially all the modern land vertebrate groups evolved, perhaps, in response to the changes (Corso, et al. 2020). In the oceans new life took root with the first scleractinian corals (the group to which modern stony corals belong), though it wasn't until several million years later when they formed a symbiotic relationship with zooxanthellae algae that coral reefs developed. Importantly, zooxanthellae belong to the dinoflagellate group, which also shared an origin during the Carnian alongside the chalk-forming coccolithophore plankton. Neopterygians - ray-finned fishes with lightened scales and skeletons - and the proto-sharks and rays (or neoselachians) experienced an adaptive radiation as well.

End Triassic Mass Extinction

When? - 201.4 Million Years Ago

Cause - Pangaea was in the beginning stages of break-up, and one of the first areas of release was between the future continents of North America and Eurasia. In the proto-North Atlantic, massive lava flows marked the boundaries of separation and are recorded in the rock record as the Central Atlantic magmatic province or CAMP (Whalen, et al. 2015). Correlations between geologic dating and the timing of extinctions have pointed strongly to CAMP being one of the leading causes of the mass extinction (Deenen, et al. 2010; Bond & Grasby, 2017). As much as 720,000 cubic-miles of lava may have pooled across the northern hemisphere (Benton, 2023). Such enormous volcanic outpourings would have contributed to climatic warming and ocean acidification & anoxia as they erupted over an estimated 600,000 year period in four pulses (Bond & Grasby, 2017).

Victims - In the oceans, the scleractinian corals faced their harshest extinction event before the present. Among the other marine losses was the total extinction of the lamprey-like conodonts, and ammonoid diversity plummeted so much that only one lineage survived to give rise to the famous ammonites of the Jurassic & Cretaceous oceans. Conulariids, a bizarre group related to jellyfish, also went extinct after having lived through the entire Paleozoic Era. On land, plants suffered a drop in biodiversity across several regions, and the CAMP was a decisive turning-point in amniote evolution. This extinction event was the death-nail for many of the crocodylomorphs and remaining therapsid protomammals (specifically dicynodonts and therocephalians), whose lines ended before the Triassic closed out. The giant temnospondyls would never recover their past diversity: metoposaurs and pelagiosaurids would go extinct. Many marine or coastal reptile groups died out, including the placodonts and long-necked tanystropheids. Reptiles as a whole were severely reduced in diversity, with parareptiles, many archosauromorphs, and the other so-called "Triassic weirdos" going extinct.

Survivors - It would be the dinosaurs who would take up the major terrestrial niches on land for the remainder of the Mesozoic, having outlasted the other reptile groups and having their own adaptive radiation. Of the therapsids, only the mammaliaforms survived to give rise to crown mammals in the Jurassic Period. Of the temnospondyls, the lissamphibians (frogs, salamanders, caecilians) would diversify across forested and wetland ecosystems. Of the marine reptiles, only the plesiosaurs and ichthyosaurs survived. Pterosaurs, the flying reptiles closely related to dinosaurs, had evolved prior to CAMP, and would go on to rule the skies.

Toarcian Oceanic Anoxic Event

When? - ~183 Million Years Ago (Early Jurassic Period)

Cause - A minor extinction event that occurred in about six pulses as a result of volcanic activity and ocean anoxia (Caruthers, et al. 2013). The eruptions of the Karoo and Ferrar Traps in South Africa have been linked, which may have also released methane as well as CO2 into the atmosphere. There is evidence to suggest extensive wildfires and acid rain affected life on land (Reolid, et al. 2022).

Victims - As a result of ocean anoxia, this event was particularly rough for shelled marine invertebrates, like ammonites, bivalves brachiopods, and ostracods. Forams, radiolarians, and dinoflagellate plankton were hit hard. Marine reptiles experienced severe losses, with a number of plesiosaur and ichthyosaur clades going extinct (including the giant predatory temnodontosaurids). Dinosaur and plant diversity appears to have been impacted by the Traps eruptions: fossil sites show a decline in gymnosperms, cycadeoids, seed ferns, true ferns, and lycopods, and there are notable extinctions of many lineages of early sauropodomorphs (traditionally known as "prosauropods") and thyreophorans (e.g. Scelidosaurus) as well as the coelophysoid predators who preyed on them (in addition to the related, double head-crested Dilophosaurus).

Survivors - Thalattosuchians, ocean-adapted crocodylomorphs seem to have taken over some of the niches of the lost marine reptile groups. Terrestrial ecosystems experienced a shift from the earlier high-diversity communities to substantially lower-diversity forests primarily composed of conifers and cycads (Slater, et al. 2019). Dinosaurs experienced a turnover in diversity, with the earlier predatory forms being replaced by allosauroids, megalosauroids, and tyrannosauroids; while the herbivores were replaced by larger and more derived sauropods, stegosaurs, and ankylosaurs (Reolid, et al. 2022). Recent evidence shows that insects may have benefited from the anoxic event by feasting on the dead fish corpses and newly-evolved plants (Swaby, et al. 2024).

Tithonian Extinction

When? - ~143 Million Years Ago (Late Jurassic Period)

Cause - An area of ongoing and controversial research, there is growing evidence of one or a number of events occurring at the end of the Jurassic Period that could be regarded as an extinction event, as there is evidence of both environmental change and faunal turnover at this time (Tennant, et al. 2016). Proposed causes include volcanic activity and even bolide impacts, which contributed to falling sea levels and a general cooling & drying of the global climate.

Victims - There is evidence of diversity loss at regional levels across many taxa, from marine mollusks to dinosaurs. Scleractinian coral reefs were badly hit, and there was a large decline in decapod crustaceans, ammonites, and bivalves; among the latter, heteroconchs (the cockle & unionid mussle clade) and lucinids (hatchet clams) experienced losses. Lineages of freshwater fishes, turtles, and plesiosaurs died out. The long-tailed pterosaurs (traditionally known as "rhamphorhynchoids") died out. Among dinosaurs, there was a particularly noticable turnover in forms: predatory ceratosaurids, megalosaurids, and allosaurids went extinct; many clades of sauropods suffered losses; and the stegosaurs lost considerable diversity.

Survivors - Rudists, a clade of bivalves, replaced the scleractinians as the ocean's major reef-building organisms for the remainder of the Mesozoic Era. Both gastropods and brachiopods seemed to have been unaffected by the changes. Marine fishes, and sharks & rays as a whole, seemed to do well, as did the reptilian ichthyosaurs and thalattosuchians. Notosuchian crocodylomorphs evolved right after the Jurassic extinction, encompassing a diverse group of land-living forms. Pterodactyloids - the short-tailed pterosaurs - persisted and underwent a burst in evolutionary change. Though the major groups of dinosaurs were more or less established long before the end of the Jurassic, it wasn't until afterward that they experienced another burst of evolution. New species of ceratopsians, ornithopods, ankylosaurs, titanosaurs, allosauroids, megalosauroids, and coelurosaurs (including new lineages of birds) evolved across the continents.

Cycadeoid, a type of stem-angiosperm (Matteo De Stefano/MUSE, CC BY-SA 3.0)

Aptian-Albian Extinction

When? - ~117-113 Million Years Ago (Early Cretaceous Epoch)

Cause - Volcanic eruptions in the South Asian Rahjamal Traps appear to have spurred a period of high global temperatures and ocean anoxia, designated at "OAE1" (Benton, 2023). The oceans, at least, experienced a cooling trend by the early Albian Age (Balestra, et al. 2025).

Victims - The Aptian Event is said to have been one of the major die-offs of foraminifera in the Earth's history, impacting populations from the Atlantic to the Tethys (Balestra, et al. 2025). Extinctions on land appear to have been more regional in scope and mainly affected plant communities: a number of ginkgo, conifer, and cycadeloid genera went extinct (Archangelsky, 2001).

Survivors - While gymnosperms, cycadeoids, and ferns as a whole did not suffer tremendous losses, the early angiosperms (flowering plants) would ultimately experience a burst in biodiversity. By 100 million years ago, the "Angiosperm Terrestrial Revolution" would bring a significant shift in the ecological relationships between plants and animals, particularly among insects and herbivorous tetrapods (Benton, et al. 2021).

Cenomanian-Turonian Extinction

When? - ~94.5-90.3 Million Years Ago (Late Cretaceous Epoch)

Cause - As in the Aptian-Albian, the oceans underwent another anoxic event - "OAE2" - that was paralleled by a sharp rise in global sea levels and temperatures (Petrizzo, et al. 2022; Arthur, et al. 1988). These are linked to volcanic lava flows in both the newly-forming Caribbean Sea and in Madagascar as it separated from the Indian Subcontinent (Kuroda, et al. 2007), but other areas of the world seem to have contributed with their own eruptions (Petrizzo, et al. 2022). The transition from the Early to Late Cretaceous Epochs was thus marked by a dynamic shift in the Earth's climate and oceans.

Victims - There was a significant turnover of Mesozoic marine life, particularly among plankton (many coccoliths, forams, radiolarians, and dinoflagellates went extinct), mollusks (many rudists and ammonites went extinct), and sea-going reptiles (ichthyosaurs and the large-headed plesiosaurs called pliosaurs went extinct). So far as can be deduced, there were no significant extinctions on land at a global level.

Survivors - The Cenomanian-Turonian would be the last time in Earth's history that a major ocean-anoxia event occurred across the world's oceans (Petrizzo, et al. 2022). Mosasaurs, a lineage of paddle-limbed lizards, would evolve to take over the role of the ocean's great predators from the pliosaurs and ichthyosaurs. On land, the drying of the climate facilitated the spread of mid-latitude open forest environments dominated by flowering trees of the Fagales clade (the oaks, birches, alders, etc) while closed-conifer araucaria & cypress forests reduced in size (Heimhofer, et al. 2018).

Impression of the K-Pg Bolide Hitting the Earth (Donald Davis, Public Domain)

End-Cretaceous Mass Extinction Event

When? - ~66.043 Million Years Ago

Cause - Since the pioneering research done by the Alvarez team in 1980, the sheer volume of studies on the world of the very latest Cretaceous Period have converged on one major consensus: a ~6.2 mile-long bolide (space rock) collided with the Earth and it was this that ultimately caused a mass extinction (Chiarenza, et al. 2020). It struck the Yucatán Peninsula with the power of over a billion nuclear bombs, landing in an area rich in carbonate and sulfate minerals (Schulte, et al. 2010). Immediate effects from the blast included enormous earthquakes and megatsunamis. It is argued that the rain of returning debris in the form of superheated glass may have triggered surface conditions comparable to an oven, and the land would have cooked and burned under a global firestorm (Robertson, et al. 2013). All this would have occurred on the first day of the impact. By having landed in carbonate & sulfate-rich terrain, particularly strong aerosols had also been ejected across the atmosphere to produce a blanket against solar radiation. This then shifted the atmosphere from fire to ice, and a prolonged impact winter would unfold over a period of years to decades (Brugger, et al. 2016). The release of aerosols also contributed to ocean acidification through acid rains. Though there is evidence of intensive and substantial volcanism on the Indian Subcontinent at the end of the Cretaceous - these being the Deccan Traps eruptions - its effects on extinctions appear to have been minimal, and in fact they may even have helped life survive in the wake of the devastation (Chiarenza, et al. 2020).

Victims - The species losses span the entire breadth of the tree of life. The most prominent extinctions were, of course, among the non-avian dinosaurs (including all but one lineage of birds), marine reptiles, and pterosaurs. There were also losses among modern reptile groups, with lizards, tuataras, and crocodylomorphs being hard hit. Mammals - typically thought of as hardy survivors - actually suffered significant extinctions too, with marsupials and multituberculates experiencing the biggest die-offs. There were broken connections between plants and insects, leading to a decline in numbers for both (Labandeira, et al. 2022). Several clades of oceanic sharks and rays, and bony fishes, went extinct. The great rudist bivalves and the reefs they formed died out, and there were large losses among the scleractinian corals too. Fellow marine invertebrates suffered both declines and extinctions, most notably the inoceramid clams (now extinct), the squid-like belemnites (now extinct), and the ammonites (extinct within about a million years of the event). As with most mass extinctions, planktonic forms suffered greatly, with coccoliths and forams experiencing another wave of extinctions.

Survivors - Freshwater animals, particularly turtles, frogs, and bony fishes, seem to have buffered against the devastation, with some forms growing exceptionally large fairly soon into the Paleogene Period. In the seas, many marine forms survived by either retreating to the depths or seeking shelter in refugia. On land, all major animal groups ultimately survived, including the dinosaurs: neornithine birds (the group to which our living forms belong) seem to have made it out against the other bird clades because they were ground-dwelling generalists. Mammals and other small tetrapods also survived by being generalists, as well as having burrowing or subsurface behaviors that allowed them to ride out the head & cold. Total recovery is estimated to have taken a few hundred thousand years as global temperatures climbed back to hothouse conditions, and the increased ash from the global wildfires appear to have fertilized the soil enough to spur a rapid growth in broadleaved angiosperms. The bolide impact gave birth to the first tropical rainforests (Carvalho, et al. 2021).

Eocene Marine Events

When? - ~41.5-37.71 Million Years Ago (Eocene Epoch)

Cause - Two little known extinction events, which appear to be linked to changes in ocean circulation (MacLeod, 2015). In the first at the Lutetian-Bartonian boundary, there is evidence of a brief period of global warming which increased runoff into the oceans, though there is as yet no evidence of increased CO2 outgassing (Intxauspe-Zubiaurre, et al. 2018). During the second at the Bartonian-Priabonian boundary, cooler waters from temperate zones flooded into warmer, tropical waters (MacLeod, 2015).

Victims - The first thermal maximum period appears to have wiped out a large diversity of gastropods, bivalves, and foraminifera, while the latter saw extinctions among foraminifera (including the last Nummulites), gastropods, bivalves, and echinoids (the urchin clade) (Less & Özcan, 2012). There are correlated extinctions on land during these times, particularly with the loss of various placental mammal groups (e.g. dinoceratans, hyopsodontids), and these may be tied to possible changes in sea levels (MacLeod, 2015).

Survivors - Beyond the losses of mollusks and plankton, most marine life appears to have made it through this period. Fossil records at European sites point to remarkable fish diversity in the following ages.

The "Grande Coupure"

When? - ~33.9-33.4 Million Years Ago (Eocene-Oligocene Epoch)

Cause - At the end of the Eocene Epoch, Antarctica had begun to acquire its permanent ice sheets following its separation from the other southern hemisphere continents and the beginnings of circumpolar ocean currents. This would have cascading effects down through the Cenozoic Era, as the Earth's average global climate would gradually shift towards cooler temperatures and more marked seasonality. Research supports a link between the increasingly rapid seasonal changes (including colder winters) and a high rate of extinctions (Ivany, et al. 2000). As sea-levels shrunk due to the expanding ice sheets, the Turgai Strait which had separated the European and greater Eurasian landmasses closed up, allowing different animals and plants to spread into new lands.

Victims - The name "Grande Coupure" means "Great Cut" and refers to a clear turnover in mammalian diversity in Europe, as their original faunas were replaced by greater-Eurasian migrants (Costa, et al. 2011). European artiodactyls or even-toed hoofed mammals (e.g. xiphodontids, amphimerycids), perissodactyls or odd-toed hoofed mammals (e.g. palaeotheres), early primates (e.g. adapids & omomyids), rodents, and lipotyphlans all suffered extinctions. There is evidence in North America of a significant turnover in smaller animals like reptiles and snails (Zanazzi, et al. 2007). In the oceans, there was a notable decline in the diversity of mollusks and other marine invertebrates (Ivany, et al. 2000), and several varieites of stem-whales (like Basilosaurus) went extinct likely as a result of poor catches.

Survivors - In Europe, the new mammals that tookover and diversified include rhinoceroses, anthracotheres & entelodonts (clades related to hippos), ancestral hedgehogs, and various rodent lineages (e.g. cricrtids, castorids), while several of the native European forms also survived relatively unscathred. In the oceans where was an increase in predatory shell-drilling snail species upon the surviving bivalves (Kelly & Hanson, et al. 1996). Both toothed and baleen whales evolved and diversified in astonishing variety.

Middle Miocene Disruption

When? - ~14 Million Years Ago

Cause - Throughout the Earth's history, Milankovitch cycles have shifted the axis and orbital eccentricity of the planet, and these shifts become noticeably pronounced when there are large areas of surface ice. It's widely believed that the most famous Ice Ages of the Quaternary Period were influenced by these cycles, but in earlier periods they had similar power (Halbourn, et al. 2005). During the preceding Neogene Period, such orbital changes shifted the circulation of ocean currents, which in-turn shifted heat transfer and spurred increased global cooling (Shevenell, et al. 2004). Further influence on ocean currents was the final closure of the Tethys, which once linked separate oceans (Hamon, et al. 2013).

Victims - Statistically, it has been argued that this was one of the largest extinction events of the Cenozoic Era (at least regarding regional extinctions) but so far concrete evidence has been lacking for many groups (MacLeod, 2015). The warm-living faunas of the northern hemisphere suffered die-offs, with losses among crocodylomorphs, turtles, and lizards (Böhme, 2003). Tundra ecosystems in Antarctica, some of the last major land communities on the continent, experienced their last breath (Lewis, et al. 2008). In the oceans, a number of foram genera went extinct, but there is little evidence for marine invertebrate extinctions.

Survivors - Those plants and animals that could migrated to more accomdating clines and adapted to the cooling of the climate, eventually giving rise in a few million years time to extensive grassland ecosystems and their herding and pack-hunting faunas.

Pliocene-Pleistocene Extinction

When? - ~3-2 Million Years Ago

Cause - As the Neogene passed into the Quaternary, and the dawn of the last Ice Age was approaching, there was a time of dynamic climatic and environmental changes. The Greenland Ice Sheet and the greater Arctic Polar Cap were forming, and the Antarctic glaciers had by then more-or-less formed. Much like in the Middle Miocene, there were shifts in ocean circulation and heat-exchange which affected the globe, and shallow coastal seas were diminished (Pimiento, et al. 2017). This was assisted by the closing of the Isthmus of Panama, which connected North and South America and further closed off ocean currents.

Victims - Marine invertebrates suffered tremendous losses, particularly in the Atlantic and Pacific Oceans as cooler conditions took over warm-adapted species. In the Caribbean Sea, coral reefs declined in spread and diversity after 2 million years ago (Budd, 2000). Recent work shows that large marine vertebrates experienced a dramatic extinction of species, with losses among whales, sharks, penguins, and sea turtles (Pimiento, et al. 2017). The connection of the western hemisphere facilitated a prolongued exchange of animals and plants between the two Americas, the Great American Biotic Interchange, which contributed to the eventual turnover (and decline) of native South American mammals by incoming North American species. In the newly-formed Afro-Eurasian landmass, there were also an increased extinction of proboscideans and other mammal groups (Cantalapiedra, et al. 2021).

Survivors - The shift to the Quaternary Ice Age promoted the evolution and adaptation of cold-adapted organisms, both on land and in the oceans. It's not until after this time that the great rorquals and other baleen whales evolved in response to the decline in larger marine predators (Slater, et al. 2017).

Late Pleistocene Megafaunal Extinctions

When? - Began roughly 80,000 Years Ago

Cause - Homo sapiens evolved across Africa by 300,000 Years Ago and there is evidence of periodic dispersals into Eurasia since that time, but it isn't until between 80 and 50,000 years ago that a wave of humans migrated from East Africa, into the Iranian Plateau, and out across the rest of the world. In contrast to other hominins like Neanderthals, early Homo sapiens lived in extensive social networks, could adapt remarkably fast to unique environments, bred fast, and relied on domestic dogs as hunting assistants. This made them very effective predators, and organisms which bred slow & few or were previously unaccustomed to a human presence (as was the case in regions like the Americas or Oceania) were the most vulnerable. Though it is true that there was a shift from glacial to interglacial conditions between the Pleistocene and Holocene epochs, so far as can be discerned from the patterns of extinction, it was human beings who ultimately wiped out the world's megafauna, the largest animals of a given ecosystem (Lemoine, et al. 2023).

Victims - Far from being considered a mass extinction, the decline consisted mainly of giant mammals, birds, and assorted non-avian reptiles. Wherever a firm human presence was established, within a few thousand years, giant marsupials, mammoths, mastodons, ground sloths, glyptodonts, horses, camels, bovids, bears, big cats, flightless birds, giant tortoises, and meiolaniid turtles went extinct. Islands were also particularly hard-hit and a tenuious link with the extinction of the New Zealand moa and Madagascan hippos, giant lemurs, and elephant birds to these earlier human dispersals, even though they occurrred within the last 2,000 years.

Survivors - Though there is even evidence of significant declines among mammals which survived into the present day (Bergman, et al. 2023), ultimately the factors in their favor were many. Some wild mammals dispersed alongside humans and settled where now-extinct forms roamed, like the moose (Meiri, et al. 2020). Others had co-evolved with humans or other hominins in the first place: hence the lack of die-offs in Africa or South Asia (Turvey, et al. 2021). Subsequent environmental changes unfolded in a world depleted of large animals, given their extensive influence on ecosystem engineering, and habitats that survived were a shell of their former selves (Svenning, et al. 2024).

Earth System Trends of the last 300 Years (Bryanmackinnon, CC BY-SA 4.0) Larger Image

Late Holocene Mass Extinction

When? - At least 500 Years Ago, but arguably earlier

Cause - As human populations increased and the need/desire for resources like food, minerals, and territory increased, the global environment took on greater and greater stresses. While there is ample evidence of positive and negative ecological management across human history, the last 500 years of global capitalism and colonialism have had a proportionally-devastating effect on habitat destruction, defaunation, and extinction. Particularly strong drivers include (and have included) intensive agriculture, overhunting, overfishing, overharvesting, the wildlife trade, pollution & runoff, added input from CO2 & methane emissions, and widespread ignorance or apathy about any of these things (Bradshaw, et al. 2021). The conditions being created on the Earth as you read this have been compared to and understood in the context of past mass extinctions, especially in light of recent revelations: for example, it has been demonstrated that ocean anoxia, acidification, and the formation of "dead zones" is occurring in parts of the ocean today (Gobler & Baumann, 2016; Mancini, et al. 2024).

Victims - Though the extent of calculated losses has been contentious and disputed (MacLeod, 2015), recent surveys show without a doubt that a significant defaunation and extinction of lineages is occurring across all biological lineages and that we are in the beginning pains of a mass extinction event (Cowie, et al. 2025; Ceballos & Ehrlich, 2018). A 2023 analysis estimated that ~1.97 million species could become threatened with extinction due to various human activities (Hochkirch, et al. 2023), while the contributions from anthropogenic (human-induced) climate change could further accelerate extinctions with a excess of 1.5°C global average temperatures (Urban, 2024). In the oceans, in freshwater systems, and on terrestrial habitats, life is being impacted. Surveys estimate that 40.7% of amphibians, 21.1% of non-avian reptiles, 13.6% of birds, and 25.4% of mammals are threatened with extinction (Cox, et al. 2022). >40% of insects - usually outliers in past extinction events - are at risk (Sánchez-Bayo & Wyckhuys, 2019). 26% of freshwater fishes & 30% of freshwater crayfish, shrimp, and crabs are at risk (Sayer, et al. 2025). 12.7% of marine fishes are at risk (Loiseau, et al. 2024), with sharks, rays, and large bony fishes especially depleted. 44% of coral species are at risk (IUCN, 2024) and complex reef ecosystems are vulnerable to total collapse. Among mollusks, it is estimated that between 7.5-13% of described snails and clams have been wiped out since 1500 (Régnier, et al. 2017); land snails & freshwater bivalves have been especially vulnerable. Roughly 39% of vascular plants (angiosperms, gymnosperms, ferns, & lycopods) are at risk (Lughadha, et al. 2020). Overall, it has been estimated that ~30% of known species have either been killed off or threatened with extinction within the last 500 years (Isbell, et al. 2022).

Survivors - A 2023 study reported that "49% and 3% of species currently remain stable or are increasing, respectively" and that this survivability shows "a tendency to expand towards temperate climates" (Finn, et al. 2023). That said, the sheer scale of biological destruction and its multifacited human causes will almost certainly have uncalculated consequences and affect these numbers. We must recognize one key fact: this is the only extinction event in Earth's history whose definite cause (humanity) is also its solution. The very same power that has allowed humans to change the surface of the planet is the very same that can end the devastation and safeguard biodiversity (including our own wellbeing). We need only choose to do so.

Closing Thoughts

This has been a worthwhile exercise, and I have learned a lot in researching and preparing this summary of extinction events, and I have tried to be comprehensive in scope (however imperfect I might have been).

I have gathered a few key lessons in outlining the history of extinctions, and here's what I've taken to heart:

Plankton and marine invertebrates have been the backbone of understanding extinction events. In fact, their very nature as common, easily-preserved fossils is what allowed geologists and paleontologists to create the time scale of the Earth, whose major divisions have been marked by the loss or appearance of specific invertebrate fossils. They are particularly vulnerable to extinctions, and many major lineages have succumbed to death, thus altering the foundations of oceanic food webs.

Plate tectonics have been one of the major driving forces of extinction events. While the hypothesis of a "cyclicity of mass extinctions" due to cosmological phenomena has been heavily debated, there is a clear correlation between the movements of the continents and extinction events. Volcanic eruptions are usually the result of tectonic activities, and it is through them that significant ocean anoxia and climatic warming/cooling occur. As well, the closing or opening of isthmi due to continental drift have helped regulate the positions of oceanic currents. All these phenomena have been involved in the majority of the Earth's extinction events. Bolide impacts, for all their popularity as research subjects, have only truly been confirmed as harbingers of extinction for the End Cretaceous Event.

Life is resiliant, but not all-powerful. Though our fellow organisms have survived all the previously described events, it is clear that today's sample is the exception: >99% of all the species that have ever lived are now extinct. The threats to their wellbeing have been many and without warning, and the loss of even a few species or clades has upset whole ecosystems. This is all the more reason why we must do everything we can to preserve and cherish the life that still exists on the Earth. The Holocene Mass Extinction has been particularly severe and all-encompasing, and it is a fact that diversity enhances survivability in the long-term. The Great Dying took millions of years for life to fully recover, and we're basically playing out this extinction event on a significantly shorter timescale, with no clear guarantee of the outcome; we are truly living in unprecedented times. If we want to have a future worth living, we must embrace this understanding of past extinction events and rebuild our connections with life on Earth.

Special thanks to @albertonykus & @otussketching for productive conversations on the nature of extinction events.

Book Citations

Michael J. Benton. Extinctions (Thames & Hudson, 2023)

Peter Brannen. The Ends of the World (Ecco, HarperCollins, 2017)

Norman MacLeod. The Great Extinctions (Firefly Books, 2015)

Paper Citations

Luis W. Alvarez, et al. 1980. Extraterrestrial Cause for the Cretaceous-Tertiary Extinction (Science)

Sergio Archangelsky, 2001. The Ticó Flora (Patagonia) and the Aptian Extinction Event (Acta Paleobotanica)

Michael A. Arthur, et al. 1988. Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary (Nature)

Barbara Balestra, et al. 2025. Benthic foraminiferal Mg/Ca response across the Aptian-Albian Boundary Interval at DSDP Site 511 (Falkland Plateau) (Palaeogeography, Palaeoclimatology, Palaeoecology)

Michael Benton, et al. 2021. The Angiosperm Terrestrial Revolution and the origins of modern biodiversity (New Phytologist)

Juraj Bergman, et al. 2023. Worldwide Late Pleistocene and Early Holocene population declines in extant megafauna are associated with Homo sapiens expansion rather than climate change (Nature Communications)

Madelaine Böhme, 2003. The Miocene Climatic Optimum: evidence from ectothermic vertebrates of Central Europe (Palaeo)

David P. G. Bond & Stephen E. Grasby, 2017. On the causes of mass extinctions (Palaeogeography, Palaeoclimatology, Palaeoecology)

Corey J. A. Bradshaw, et al. 2021. Underestimating the Challenges of Avoiding a Ghastly Future (Frontiers)

Julia Brugger, et al. 2016. Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous (Geophysical Research Letters)

A. F. Budd, 2000. Diversity and extinction in the Cenozoic history of Caribbean reefs (Coral Reefs)

Juan L. Cantalapiedra, et al. 2021. The rise and fall of proboscidean ecological diversity (Nature Ecology and Evolution)

Andrew H. Caruthers, et al. 2013. The Pliensbachian–Toarcian (Early Jurassic) extinction, a global multi-phased event (Palaeogeography, Palaeoclimatology, Palaeoecology)

Mónica R. Carvalho, et al. 2021. Extinction at the end-Cretaceous and the origin of modern Neotropical rainforests (Science)

Gerardo Ceballos & Paul R. Ehrlich, 2018. The misunderstood sixth mass extinction (Science)

Alfio Alessandro Chiarenza, et al. 2020. Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction (PNAS)

Jacopo Dal Corso, et al. 2020. Extinction and dawn of the modern world in the Carnian (Late Triassic) (Science Advances)

Elisenda Costa, et al. 2011. The age of the “Grande Coupure” mammal turnover: New constraints from the Eocene–Oligocene record of the Eastern Ebro Basin (NE Spain) (Palaeogeography, Palaeoclimatology, Palaeoecology)

Robert H. Cowie, et al. 2025. Denying that we may be experiencing the start of the Sixth Mass Extinction paves the way for it to happen (Trends in Ecology & Evolution)

Neil Cox, et al. 2022. A global reptile assessment highlights shared conservation needs of tetrapods (Nature Portfolio)

M.H.L. Deenen, et al. 2010. A new chronology for the end-Triassic mass extinction (Earth and Planetary Science Letters)

Yong Du, et al. 2022. A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction (Global and Planetary Change)

Catherine Finn, et al. 2023. More losers than winners: investigating Anthropocene defaunation through the diversity of population trends (Biological Reviews)

Christopher J. Gobler & Hannes Baumann, 2016. Hypoxia and acidification in ocean ecosystems: coupled dynamics and effects on marine life (Biology Letters)

Ann Holbourn, et al. 2005. Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion (Nature)

L. Hamon, et al. 2013. The role of eastern Tethys seaway closure in the Middle Miocene Climatic Transition (ca. 14 Ma) (European Geosciences Union)

Ulrich Heimhofer, et al. 2018. Vegetation response to exceptional global warmth during Oceanic Anoxic Event 2 (Nature Communications)

Axel Hochkirch, et al. 2023. A multi-taxon analysis of European Red Lists reveals major threats to biodiversity (PLOS One)

Beñat Intxauspe-Zubiaurre, et al. 2018. The last Eocene hyperthermal (Chron C19r event, ~41.5 Ma): Chronological and paleoenvironmental insights from a continental margin (Cape Oyambre, N Spain) (Palaeogeography, Palaeoclimatology, Palaeoecology)

Forest Isbell, et al. 2022. Expert perspectives on global biodiversity loss and its drivers and impacts on people (Frontiers in Ecology and the Environment)

IUCN Red List Press Release, 2024. Over 40% of coral species face extinction (IUCN)

Linda C. Ivany, et al. 2000. Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary (Nature)

Patricia H. Kelley & Thor A. Hansen, 1996. Recovery of the naticid gastropod predator-prey system from the Cretaceous-Tertiary and Eocene-Oligocene extinctions (Geological Society, London)

Junichiro Kuroda, et al. 2007. Contemporaneous massive subaerial volcanism and late cretaceous Oceanic Anoxic Event 2 (Earth and Planetary Science Letters)

Conrad C. Labandeira, et al. 2002. Impact of the terminal Cretaceous event on plant–insect associations (PNAS)

Rhys Taylor Lemoine, et al. 2023. Megafauna extinctions in the late-Quaternary are linked to human range expansion, not climate change (Anthropocene)

György Less & Ercan Özcan, 2012. Bartonian-Priabonian larger benthic foraminiferal events in the Western Tethys (Austrian Juurnal of Earth Sciences)

Adam R. Lewis, et al. 2008. Mid-Miocene cooling and the extinction of tundra in continental Antarctica (PNAS)

Nicolas Loiseau, et al. 2024. Inferring the extinction risk of marine fish to inform global conservation priorities (PLOS Biology)

Eimear Nic Lughadha, et al. 2020. Extinction risk and threats to plants and fungi (Plants, People, Planet)

A. M. Mancini, et al. 2024. The past to unravel the future: Deoxygenation events in the geological archive and the anthropocene oxygen crisis (Earth-Science Reviews)

Meirav Meiri, et al. 2020. Population dynamics and range shifts of moose (Alces alces) during the Late Quaternary (Journal of Biogeography)

Maria Rose Petrizzo, et al. 2022. Biotic and Paleoceanographic Changes Across the Late Cretaceous Oceanic Anoxic Event 2 in the Southern High Latitudes (IODP Sites U1513 and U1516, SE Indian Ocean) (Paleoceanography and Paleoclimatology)

Catalina Pimiento, et al. 2017. The Pliocene marine megafauna extinction and its impact on functional diversity (Nature Ecology and Evolution)

Claire Régnier, et al. 2017. Measuring the Sixth Extinction: what do mollusks tell us? (The Nautilus)

M. Reolid, et al. 2022. Impact of the Jenkyns Event (early Toarcian) on dinosaurs: Comparison with the Triassic/Jurassic transition (Earth-Science Reviews)

Douglas S. Robertson, et al. 2013. K-Pg extinction: Reevaluation of the heat-fire hypothesis (JGR Biogeosciences)

Francisco Sánchez-Bayo & Kris A.G. Wyckhuys, 2019. Worldwide decline of the entomofauna: A review of its drivers (Biological Conservation)

Catherine A. Sayer, et al. 2025. One-quarter of freshwater fauna threatened with extinction (Nature)

Peter Schulte, et al. 2010. The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary (Science)

Amelia E. Shevenell, et al. 2004. Middle Miocene Southern Ocean Cooling and Antarctic Cryosphere Expansion (Science)

Graham J. Slater, et al. 2017. Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynamics (Proceedings of the Royal Society B)

Sam M. Slater, et al. 2019. Substantial vegetation response to Early Jurassic global warming with impacts on oceanic anoxia (Nature Geoscience)

Felisa A. Smith, et al. 2018. Body size downgrading of mammals over the late Quaternary (Science)

Jens-Christian Svenning, et al. 2024. The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene (Extinction)

Emily J. Swaby, et al. 2024. The fossil insect assemblage associated with the Toarcian (Lower Jurassic) oceanic anoxic event from Alderton Hill, Gloucestershire, UK (PLOS One)

Jonathan P. Tennant, et al. 2016. Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover (BRCPS)

Samuel T. Turvey, et al. 2021. Late Quaternary megafaunal extinctions in India: How much do we know? (Quaternary Science Reviews)

Lisa Whalen, et al. 2015. Supercontinental inheritance and its influence on supercontinental breakup: The Central Atlantic Magmatic Province and the breakup of Pangea (Geochemistry, Geophysics, Geosystems)

Zhen Xu, et al. 2025. Early Triassic super-greenhouse climate driven by vegetation collapse (Nature Communications)

Mark. C. Urban, 2024. Climate change extinctions (Science)

Alessandro Zanazzi, et al. 2007. Large temperature drop across the Eocene–Oligocene transition in central North America (Nature)

[joanjournal]

Surveying Mass Extinctions - Part 1

Patterns of Extinction, taken from Marshall, 2023

Mass extinctions are when a large sample of biological clades undergoes a geologically-brief period of die-off that is statistically higher than the background rate of extinction (Marshal, 2023). Most of the organisms that have ever lived died out through the regular trials of natural selection, but on occasion the Earth's conditions changed so rapidly that many different species could not adapt in time.

These extinction events were some of the driving forces that shaped the evolution of life, typically be "reshuffling the deck" or weeding out a few key taxa, thus paving the way for new life to flourish. So what are these mass extinctions and just how did they change the world?

In this post, I will be providing a brief account of our current understanding of each extinction event: when they occured, their causes, and the victims and survivors. As you'll come to discover, the pop-science view of "five big mass extinctions" is complicated by evidence suggesting that some singular events are best seen as two or three, while others have been neglected by mainstream coverage.

Great Oxidation Event

When? - ~2.4-2 Billion Years Ago (Paleoproterozoic Era)

Cause - When photosynthesizing bacteria evolved the Earth's atmosphere did not contain free oxygen, being mainly CO2 and nitrogen. The process of photosynthesis converts sunlight into sugars which takes in CO2 and expels oxygen. The abundance of prokaryotes engaged in this chemistry released oxygen in enormous quantities. While much of it initially was absorbed by dissolved iron on the seabed, the rest rose into the atmosphere. This increase in free oxygen changed the air content and triggered global cooling (perhaps spawning glacial periods).

Victims - It has been generally proposed that the newly oxygenated atmosphere had negative effects on the then-common anaerobic bacteria & archaea, who should have suffered a mass extinction due to oxygen poisoning. While direct evidence for this had been lacking for some time, recent geochemical work suggests "a rapid reduction in primary productivity of >80%" that "imply a collapse in primary productivity" (Hodgskiss, 2019).

Survivors - Aerobic prokaryotes would have flourished in the aftermath of the Oxidation Event, while anaerobic forms would have migrated and adapted into areas still free of oxygen. It has been argued that the evolution of eukaryotes was spurred by the changes, but so-far this is controversial (Fakhraee, 2013).

End-Ediacaran Extinction Event

When? - ~541 Million Years Ago

Cause - An event little-studied and sometimes doubted (MacLeod, 2015), recent work posits that Ediacaran communities were generally low-diversity and "quiet"-ecologically (Darroch, et al. 2015). The gradual evolution of new animal life (a.e. not an explosion as typically described) at the bridge of the Cambrian corresponds with ecosystem-engineering that simply pushed many of the Ediacaran species to extinction.

Victims - The mysterious "Ediacaran fauna": a collection of soft-bodied, basal-animals. Dipleurozoans (e.g. Dickinsonia), trilobozoans, and cephalozoans (e.g. Spriggina) went extinct.

Survivors - Petalonamids like Charnia, frond-shaped stem-eumetazoans (animals with tissues, nerves, and muscles) were the only classic Ediacaran forms to make it through. Genetic and fossil evidence shows that the ancestors of many living animal groups were around at the time: they likely contributed to the extinction in the first place. This event marks the transition towards the so-called "Cambrian Fauna" of marine invertebrate biodiversity that characterized the next 40 million years.

Archaeocyathids (Stanton F. Fink, CC BY 2.5)

End-Botomian Extinction Event

When? - ~513-509 Million Years Ago (Middle Cambrian Period)

Cause - Recent work points to roughly 4-pulses of the "Cambrian Explosion" (Benton, 2023). By 513 MYA, this had ceased, and marine invertebrate faunas were abundant in the world's oceans. Evidence from sulphur isotopes suggests that volcanic eruptions in present-day north Australia led to a rise in CO2 and anoxic conditions on the continental shelves (Hough, et al. 2006). Such shifts are prime conditions for disrupting and destroying reef ecosystems; the early Cambrian saw the rise of archaeocyathids, reef-building relatives of sponges, that supported marine communities.

Victims - The last of the petalonamids died out. Archaeocyathids and the reefs they built perished. There were losses among brachiopods (obolellates died out), trilobites (the spiny olenellids in particular), and it has been proposed that the halkieriids & Wiwaxia - potential stem-mollusks - were victims but there are some issues with stratigraphic-dating and there is tentative evidence they survived into the Ordovician.

Survivors - Paleontologists recognize a "Cambrian Dead Interval" following the Botomian in which marine biodiversity was low for a while (Brannen, 2017). The climate was fairly cool and geologists have found evidence of coastal ice within tropical zones that likely kept surviving invertebrates in check (Runkel, et al. 2010). For context, the Burgess Shale community is thought to have come into being following the extinction event.

Early Dresbachian & Franconian Extinction Events

When? - ~502 & 497 Million Years Ago (Late Cambrian Period)

Cause - A series of extinction pulses that are little known. Attention has been drawn to the Steptoean Positive Carbon Isotope Excursion or SPICE, a return to anoxic conditions due this time to coastal upwelling (Bond & Grasby, 2017).

Victims - Trilobites experienced particularly high losses, with the flat-bodied redlichiids dying out and the genera-records of North America and Australia lowering over time (Bond & Grasby, 2017).

Survivors - Marine invertebrate communities remained low in diversity compared to earlier times.

Cambrian-Ordovician Extinction Event

When? - ~485 Million Years Ago (Late Trempealeauan Age)

Cause - The culmination of punctuated Cambrian extinctions, with eruptions in southern Africa contributing to even-lower anoxic conditions in the oceans.

Victims - Among other invertebrate losses, trilobites were reduced in clade-diversity to such levels that they never recovered from their peak in the Cambrian.

Survivors - Despite the losses among trilobites, modelling suggests that a few clades may have entered symbiotic relationships with sulphur-bacteria, ensuring their survival in hard times (John & Walker, 2016). Brachiopods radiated into entirely new groups following the extinction event, while conodonts (lamprey-like early vertebrates) truly began to flourish afterwards. Evidence from Morocco and the United Kingdom show that some of the Cambrian marine fauna survived into the Ordovician (Botting, et al. 2023).

Anatomy of a Bryozoa zooid (SLP456, CC BY-SA 4.0)

Late Ordovician Extinction Events

When? - ~445-444 Million Years Ago (Mid & Late Ashgill Epochs)

Causes - Following the various Cambrian extinctions, marine invertebrate faunas underwent a radical shift called the Great Ordovician Biodiversification Event: the new "Paleozoic Fauna" constituted mainly of brachiopods, bryozoa, echinoderms, graptolites, and cephalopods and remained in place for roughly 230 million years. Two pulses of extinction are recognized at the end of the period, having commonly been attributed to the rise in the Gondwanan Ice Sheet in the southern hemisphere (a sort of proto-Antarctica), which caused a drop in coastal sea levels while simultaneously chilling the tropical oceans. Additional factors have been proposed, including a convergence in volcanic activity that reduced oxygen-levels in the seas and further cooled the climate. Recovery of black shales in North Africa and Arabia indicate that this rapid icehouse cooling was just as rapidly followed by severe greenhouse warming (Brannen, 2017). This is not consensus, however, and other proposals have been work-shopped including volcanic global warming (with no glaciation involved) and extraterrestrial events (Bond & Grasby, 2017, Benton 2023).

Victims - The first wave of extinctions primarily hit free-swimming and planktonic forms, and "multi-branched" graptolites were hit very hard. The second wave of extinctions was less severe, but overall both periods saw significant loses in sessile (fixed to the ocean floor) organisms (including crinoids, "inarticulate" brachiopods, and bryozoa). The iconic giant nautiloid cephalopods like Endoceras died out.

Survivors - Evidence points to a lessening in regional marine faunal diversity but a broadening of geographic ranges for particular organisms. Trilobites, brachiopods, and bryozoa did survive, but now they were a shell of their former variety. Perhaps the most remarkable post-catastrophe boost was in the early vertebrates: jawless fishes had evolved in the Cambrian, but following the Ordovician they radiated, developed paired fins, and gave rise to jawed fishes or gnathostomes.

Silurian Extinctions

When? - Between 432 and 420 Million Years Ago

Cause - A series of three little-known pulses of extinction during the Middle and Late Silurian Periods. The first (the Ireviken Event) seems to correspond to deep-ocean anoxia, while the second and final (the Mulde & Lau events) follow a drop in sea levels

Victims - In the strata in which these extinction events occurred, there were significant losses among trilobites, graptolites, and conodonts. There is evidence to suggest a fall in plantkonic-productivity (Bond & Grasby, 2017)

Survivors - Rugose and tabulate reef-builders remained unaffected

Zlichov, Daleje, Chotec, Kačák & Taghanic Extinctions

When? - Between 410 and 386 Million Years Ago

Cause - Five minor pulses of regional extinctions throughout the Early and Middle Devonian Periods, attributed to sea level rises and oceanic anoxia

Victims - Goniatites and agoniatitids, relatives of ammonites, suffered losses, as did trilobites, conodonts, brachiopods, bryozoa, and a little-known group of lophophorates called tentaculitids. An additional group of reef-builders - the stromatoporoid sponges - also experienced declines along with certain rugose and tabulate coral taxa

Survivors - While there were losses among marine invertebrate clades, no major groups died off altogether.

Devonian Reef, showcasing rugose & tabulate corals (James St. John, CC BY 2.0)

Late Devonian Extinctions

When? - Between 372.2-358.9 Million Years Ago

Cause - Long recognized as a singular extinction event (and one of the "Big Five", the Late Devonian is better understood to have encapsulated perhaps two pulses of extinction. The first was largest of the two, the Kellwasser Event, followed millions of years later by the Hangenerg Event which closed out the period. There have been issues with poorly-dated strata, and this has led to conflicting data suggesting times of global cooling and warming (Brannen, 2017). A leading contender for the two pulses had been the rise and spread of terrestrial plants: the evolution of root-systems lead to widespread weathering of rocks and soil run-off, which triggered a particularly deadly combination of ocean anoxia and poisonous planktonic blooms akin to red-tides (Smart, et al. 2023). There is also evidence to suggest volcanic activity played a role in at least the Kellwasser Event (Benton, 2023).

Victims - This was the peak for reef-building organisms during the Devonian, and these events led to such a great loss in rugose & tabulate corals, with the stromatoporoids going extinct, that these ecosystems never recovered. Overall marine life suffered tremendous extinctions across invertebrate and vertebrates groups. Trilobite diversity was cleaved once again, e.g. lichids, corynexochids, harpetids, odontopleuridans, and phacopids. Cystoid echinoderms went extinct. Pentamerid brachiopods went extinct. Most of the jawless fishes and all of the jawed and armored "placoderms" went extinct (think of Dunkleosteus & Bothriolepis).

Survivors - Trilobites only barely made it through the extinction event, with only the proetid clade surviving. Bivalve and gastropod mollusks - originally minor elements of the marine fauna - began to experience a rise and spread of variety. Fish diversity, though severely depleted, did eventually recover under new adaptive radiations, particularly among cartilaginous and lobe-finned groups. There is little evidence to suggest that land floras and faunas were effected by the changes.

Serpukhovian Extinction

When? - Between 330 and 325 Million Years Ago

Cause - A significant mass extinction at the end of the Mississippian or Early Carboniferous Period. Recent isotopic studies point to (you guessed it) deepwater anoxia spreading to shallow coastal waters (Hu, 2022).

Victims - The Mississippian seas were originally home to massive groves of crinoid forests supplemented by surviving rugose corals, but following the Serpukhovian Event these environments experienced a major turnover. Major brachiopod groups suffered losses, as did conodonts.

Survivors - Marine invertebrate faunas remained low throughout the rest of the Carboniferous Period.

Carboniferous Rainforest Collapse

When? - ~305 Million Years Ago

Cause - The famous coal forests full of giant arthropods and reptilian-esque stem-amphibians were only a Pennsylvanian or Later Carboniferous phenomena. The fossil record points to a widespread span of these forests across present-day Europe and North America, which at the time strode the equator (Benton, 2023). On the paleo-continent of Gondwana in the southern hemisphere, glaciers spread and facilitated a massive drop in global sea levels. The coal forests were situatied in low-lying wetlands, and so the great majority of these environments collapsed as the world cooled and dried.

Victims - Coal forests were primarily formed of lycopods, which suffered losses and declines. Within the forests, early tetrapods experienced a drop in species richness (Dunne, et al. 2018).

Survivors - There is evidence of a transition in flora between the coal forest lycopods and tree ferns, which in turn led to a shift in the development of "fixed-channel" floodplains and river systems (Davies & Gibling, 2011). Despite the declines, coal forests did survive in small pockets, with ecological members like Lepidodendron and the giant griffinflies making it to the end of the Permian Period.

Olson's Extinction

When? - 273 Million Years Ago

Cause - Recent research supports a small extinction event occuring at the end of the Early Permian Period (Brocklehurst, 2020). The causes are still being studied, although a rise in global temperatures has been implicated based on the taxa that were effected, whom primarily inhabited wetter environments.

Victims - Among the synapsid "protomammals", most of the early-branching forms went extinct, including edaphosaurids, ophiacodonts, and sphenacodontids (e.g. Dimetrodon). Reptiliomorphs and temnospondyls also experiences losses, as did the fern-dominated floras they relied upon.

Survivors - Therapsids, derived synapsids with more mammalian-traits survived and radiated into several new clades. Seed-bearing plants, including ancestral conifers and ginkgoes, survived and later flourished.

Carnivorous gorgonopsian preying on herbivorous pareiasaurs (Dmitry Bogdanov, CC BY 3.0)

The Great Dying or End Permian Extinctions

When? - Between 259 and 251 Million Years Ago

Causes - Statistically this was the largest mass extinction event in Earth's history, but recent work points to it unfolding in two massive pulses: the Capitanian Event and the Changhsingian Event (Bond & Grasby, 2017; Benton, 2023). An increase in research over the last decade has shed new light on the multifaceted causes of this extinction event. Both events were encapsulated by a spike in volcanic emissions, with the Capitanian perhaps centered on the Emeishan Traps eruptions of South China and the Changhsingian centered on the Siberian Traps eruptions of Russia. Such activity lead to spikes in ocean anoxia and acidification, and the Changhsingian in particular had additional baggage. The Siberian Traps emissions were enormous, on the order of 1.8 million cubic miles of lava flows which are preserved today as flood basaltic deposits 1,300-9,840 feet thick (MacLeod, 2015). Such devastating volcanic activity over several hundred million years pushed C02 levels in the atmosphere and blotted out the sun, triggering a runaway greenhouse effect. This global warming was assisted by the melting of deep ocean methane and underground salts, and the release of sulfates from the volcanoes (which chipped away at the ozone layer). The oceans became choked with acid and were heated to 93-104°F (Benton, 2023), and the land was boiling and suffocating under an sky filled with 2,500 ppm of CO2 (Wu, et al. 2021). The only organisms to really flourish were sulphur-eating bacteria.

Victims - Life across all clades experienced declines and total extinctions, hence the designation of "The Great Dying". In the seas, all the trilobites, rugose & tabulate corals, eurypterids ("water scorpions"), goniatites, and strophomenid & orthid brachiopods went extinct. Fusulinid foraminifera (forams are shelled amoeba-like microbes) went extinct. Receptaculitid marine algae went extinct, and there were sharp losses among land plants, including the Glossopteris forests. This is the only major extinction event to affect insects, and five clades died out including the paleodictyopterids and giant griffinflies (meganisopterans). Many groups of therapid protomammals went extinct, including gorgonopsians, dinocephalians, and biarmosuchians. The parareptiles - early diverging forms with the anapsid-skull condition - also mostly perished. Lepospondyls, amphibian-like stem reptiles, went extinct, while only some temnospondyl groups perished (e.g. the gharial-like archegosaurids).

Survivors - It is estimated that life took several million years to recover, and the earliest Mesozoic Era was for the most part an empty place for some time. Surviving marine invertebrates were all smaller than their ancestors, and many aquatic vertebrates may have survived the devastation by retreating to the deeper ocean depths. Overall, therapsids, reptiles, and temnospondyls survived and would jockey for available land and freshwater niches, the outcome of which would be determined by further catastrophies.

This survey will conclude with the Mesozoic and Cenozoic mass extinctions in the next post...

Book Citations

Michael J. Benton. Extinctions (Thames & Hudson, 2023)

Peter Brannen. The Ends of the World (Ecco, HarperCollins, 2017)

Norman MacLeod. The Great Extinctions (Firefly Books, 2015)

Paper Citations

David P. G. Bond & Stephen E. Grasby, 2017. On the causes of mass extinctions (Palaeogeography, Palaeoclimatology, Palaeoecology)

Joseph P. Botting, et al. 2023. A Middle Ordovician Burgess Shale-type fauna from Castle Bank, Wales (UK) (Nature Ecology and Evolution)

Neil Brocklehurst, 2020. Olson's Gap or Olson's Extinction? A Bayesian tip-dating approach to resolving stratigraphic uncertainty (PNAS)

Simon A. F. Darroch, et al. 2015. Biotic replacement and mass extinction of the Ediacaran biota (PNAS)

Neil S. Davies & Martin R. Gibling, 2011. Evolution of fixed-channel alluvial plains in response to Carboniferous vegetation (Nature Geoscience)

Emma M. Dunne, et al. 2018. Diversity change during the rise of tetrapods and the impact of the ‘Carboniferous rainforest collapse’ (PNAS)

Mojtaba Fakhraee, et al. 2023. Earth's surface oxygenation and the rise of eukaryotic life: Relationships to the Lomagundi positive carbon isotope excursion revisited (Earth-Science Reviews)

Ashley P. Gumsley, 2017. Timing and tempo of the Great Oxidation Event (PNAS)

Michelle Hough, et al. 2006. A major sulphur isotope event at c. 510 Ma: A possible anoxia-extinction-volcanism connection during the Early-Middle Cambrian transition? (Terra Nova)

Malcolm S. W. Hodgskiss, et al. 2019. A productivity collapse to end Earth's Great Oxidation (PNAS)

Dongping Hu, et al. 2022. Multiple S-isotope constraints on environmental changes during the Serpukhovian mass extinction (Earth and Planetary Science Letters)

Douglas L. John & Sally E. Walker, 2016. Testing symbiotic morphology in trilobites under dysoxic and oxic conditions from Cambrian to Early Ordovician Lagerstätten (Palaeogeography, Palaeoclimatology, Palaeoecology)

Charles R. Marshall, 2023. Forty years later: The status of the "Big Five" mass extinctions (Cambridge Prisms: Extinction)

Anthony Runkel, et al. 2010. Tropical shoreline ice in the late Cambrian: Implications for Earth’s climate between the Cambrian Explosion and the Great Ordovician Biodiversification Event (GSA Today)

Matthew S. Smart, et al. 2023. The expansion of land plants during the Late Devonian contributed to the marine mass extinction (Nature Communications Earth & Environment)

Yuyang Wu, et al. 2021. Six-fold increase of atmospheric pCO2 during the Permian–Triassic mass extinction (Nature Communications)

[joanjournal]

How Many Continents? Should We Care?

Physical World Map with tectonic boundaries (Eric Gaba, CC BY-SA 3.0) - Larger Image

I'm sure many of you would probably answer the question "what is a continent?" quite simply: it's a large landmass surrounded by water. And the question of "how many of them?": well it's seven!

Right?

It's easy to think that there is some common sense when it comes to defining a continent and their number, but it turns out that this is a matter that's fairly multifaceted. I've been curious about this myself many times before and it's something I've discussed with friends, and they've brought a number of perspectives to the table. So for this post, I'd like to break down the definition of continent and the number of proposed continents and see whether we can make sense of them in a way that can be mutually-agreed. And if we can't agree, why not?

First of all, who came up with the concept of continents? As Josephine Quinn explained in her 2024 book How the World Made the West, "Ionian Greek scholars invented the continents". The Ancient Greeks of the 6th Century BC split their world into Europe and Asia based upon the liquid-divisions of the Mediterranean Sea through the west coast of Anatolia and on to the Black Sea. The question of Africa was conflicting for a time, as some scholars recognized the achievements of the Phoenicians under Necho II of Egypt in circumnavigating Africa, while others subsumed Africa into Asia. Whatever their dimensions, to the Greeks these landmasses had political and cultural connotations from the very beginning: as the wars with Persia dawned, they believed that the different continents produced different temperaments and conditions, resulting in conflicting views about the nature of "Europeans" and "Asians" (Quinn 2024).

Of course, as the centuries rolled by and people began to make longer journeys overseas, they became more familiar with their homelands. And with the European discoveries of "New Worlds", of course, played a roll in shaping opinions. However, as late as the 18th Century, geographers were still in discourse about the nature of continents: some questioned the traditional ideas of antiquity in subdividing the "Old World" into distinct landmasses, and others preferred a looser definition that included sizable islands. In any case, many geographers and nonspecialists in the 21st Century still refer to "Europe", "Asia", and "Africa", so the shadows of the Ionians have remained over us to this day.

In their landmark 1997 book The Myth of Continents, Martin W. Lewis & Karen E. Wigen argued comprehensively that this long history of continental discourse simply reflects cultural conventions. Whatever scientific arguments the ancients had about the nature and number of continents was never really scientific to begin with, riddled as they were in ethnocentric bias and the western need to label and categorize.

That said, is there a way to define and delineate continents from a scientific perspective that focuses solely on geology and not culture?

When looking upon the planet Earth, geologists recognize that there is a distinction between land and sea (and I'm not talking about the dividing-line being the water): the key is in the rocks of the crust.

Geologic age of oceanic crust (FCrameri, CC BY-SA 4.0) - Larger Image

The ocean floor consists mainly of basaltic and gabbroic rocks. These igneous rocks form a series of layers going down about 4-6 miles (7-10 kilometers) deep and are composed of dark-colored mafic minerals like iron and magnesium. As a rule, basaltic rocks form the upper layers while gabbroic rocks form the lower layers that neighbor the top of the mantle.

The lands of the continents consist mainly of a foundation of granitic rocks: also igneous and composed of light-colored felsic minerals like aluminum and silicon. Due to the rock cycle, many areas of the continental crust have been frequently recycled and changed and so consist of sedimentary or metamorphic rocks, and can vary in height from 12 miles (20 km) to 44 miles (km) in thickness. As well, sea-level changes can expose or submerge this continental crust, and the true scale of these granite-pedestals can be seen in the continental shelves of the oceans today.

So this could be one piece of criteria to work with: a continent consists of a distinct granitic crust base.

But we must remember that the Earth's crust is not one uniform layer. Since the formation of Alfred Wegener's hypothesis of continental drift and the subsequent modern scientific consensus of plate tectonics by the late 1960s, geologists have recognized that the lithosphere is cracked like an egg into constantly moving plates. Tectonic plates essentially float above the mantle due to being comprised of lighter minerals. They move through a combination of convection currents in the mantle, gravitational forces, and the rising of magma at mid-ocean ridges, which causes these plates to divide, collide, and shape the Earth's crust.

Earth's Tectonic Plates (M. Bitton, CC BY-SA 3.0) - Larger Image

The map shown above is a generally accepted representation of the Earth's tectonic plates. As you look, you can make out certain plates that correspond to conventionally-recognized continents, but as you continue looking you also find that things aren't straightforward. Europe is not considered a distinct plate but rather belongs to a larger Eurasian plate. Yet, this Eurasian plate doesn't correspond to how people would subsume Europe & Asia: there are separate Arabian, Indian, and Philippine plates, and part of Siberia is included in the North American Plate! As well, there are many tectonic plates that are composed mainly of the oceanic basaltic crust and not the continental granitic crust we're looking for.

That's not even the half of it. For the last decade or so there has been a growing body of research into plate tectonics, and many researchers have argued strongly for a rethink of how we look at the Earth's crust. One 2022 paper by Derrick Hasterok and colleagues proposed that there are 16 major plates and 54 "microplates", while another 2023 paper by Janpieter van Dijk culminated in a division of the Earth into 1,180 plates (see below).

Janpieter van Dijk's global tectonic map (CC BY-SA 4.0)

With such a more refined understanding of tectonic forces comes newer and newer interpretations of how geologists should look at the world. Much news was made about Zealandia in 2017, when Nick Mortimer and colleagues formerly designated an area of undersea continental crust - comparable in size to South Asia - as "Earth's hidden continent". And more recently, Luke Longley and colleagues argued that the geologic boundary separating the North American and Eurasian plates along Iceland have not fully separated yet (Longley, et al. 2024). This Rifted Oceanic Magmatic Plateau would essentially mean that North America and Eurasia still consist of a single continent connected along the northern Atlantic.

So it seems that one possible second criteria that a continent must be separated by the divergent or convergent boundaries which surround tectonic plates - as some geologists have proposed in the past - is far less stable.

The Mortimer, et al. 2017 paper is fascinating to me in that they also set about the task to try to understand continents scientifically and give a concise definition. After reviewing past criteria, the team agreed with the designations that continents should have a base of granitic felsic crust. They argue that the elevation of the land should play a key role, and this makes sense given that continental crust is substantially thicker than oceanic crust. And they push for a size minimum of >386,102 square miles (one million square kilometers). Tectonic divisions do not appear to play a big role in their schema, as Zealandia is not on a separate plate but borders the Australian and Pacific plates.

As hinted above, there are smaller subdivisions of the Earth's crust, including microcontinents which have broken away from larger landmasses (think Madagascar), but these I suppose can be considered as distinct from continents in the way that plutoids and other dwarf planets are different from true planets.

All this said, there is one dimension that could very well throw a wrench into this whole discussion: deep time.

Continents have a history going back at least 4.4 billion years (Hazen 2012), when evidence from zircon crystals hints that mineral evolution had produced the first granitic crust. Interestingly, one hypothesis for the origin of continents is that as the early basalt crust cooled in the newborn oceans, it pressed the lower basaltic layers against the upper mantle, which melted and changed the mineral composition into granite. These rocks, being lighter in composition, floated and pushed up to the surface, eventually forming small islands of land which eventually collided into cratons.

Cratons are considered the grand progenitors of the continents and are the oldest surviving geologic structures on Earth, calculated in billions of years. They can be considerably large and much of the remaining continental land area of the Earth essentially merged around them, slowly forming the landmasses we recognize today.

The North American Craton or Laurentia (U.S. Geological Survey, Public Domain)

Because of plate tectonics, our perception of stable continents shatters as we wind back the clock. Land bridges connect landmasses. Supercontinents form and break apart. Microcontinents abound and then collide into continents, becoming subsumed. It's only for the past 100 million years or so that the outlines of the modern continents can become discernible, beyond that, boundaries are blurred. One wonders how humans would've divided the planet's continents had we first emerged in, say, the Ordovician Period of 460 million years ago?

With this in mind, we run into a similar problem in biology: how to define species. When Linnaeus devised his System of Nature in the 18th Century, he had only living animals and plants to rely on when he coined the species-level in taxonomy. Since that time, every living thing has been given a binomial name. Humans are Homo sapiens, gray wolves are Canis lupus, etc, etc. These were essentially fixed categories, as the early naturalists of the time were mainly creationists. But once scientists understood evolution, deciphered its mechanisms, and recognized the volumes of history in deep time, suddenly species were no longer fixed but constantly changing entities. Wind back the clock and Homo sapiens eventually submerges into Homo erectus or some related form; go back even further and there are no longer hundreds of primates or rodents or whales but earlier placental mammals that belonged to their own unknown species.

This revolutionary shift in thinking has transformed how biologists classify species. They no longer rely on a simple system of comparing morphology but could use any of 16-32 different definitions, and they can now refer back to the fossil record or compare genomic sequences for clues about how living forms changed over time. Animals and plants that we once defined as concrete taxa have been split into multiple species and, conversely, many have been lumped into a single species.

Maybe we should be looking at continents in this way? Instead of creating a list of criteria and comparing the different living landmasses together, we should be thinking temporally, and considering multiple definitions for continent. The big side-effect of this would be that "continent" is a fluid, ever-changing category much like species. No one would have a single answer, because deep time renders these divisions as near-meaningless in the grand scheme of things. That's not to say that plate boundaries or cratons or granitic vs. basaltic crusts don't matter or can't tell us anything, it's just that this is another way the natural world rejects attempts at being subdued by rigid classification.

What is a continent? How many continents are there? Maybe these are the wrong questions to ask and the wrong ways to think, and it would be best to shake off the last few shackles those Ionian Greeks left us over 2,500 years ago.

What do you think?

Book Citations

Philip Eales, et al - The Science of the Earth (DK, 2022)

Robert M. Hazen - The Story of Earth (Penguin Books, 2012)

Josephine Quinn - How the World Made the West (Random House, 2024)

Martin W. Lewis & Karen E. Wigen - The Myth of Continents (University of California Press, 1997)

Paper Citations

Janpieter van Dijk, 2023. The new global tectonic map - Analyses and implications (Terra Nova)

Derrick Hasterok, et al. 2022. New Maps of Global Geologic Provinces and Tectonic Plates (Earth-Science Reviews)

Luke Longley, et al. 2024. The David Strait proto-microcontinent: The role of plate tectonic reorganization in continental cleaving (Gondwana Research)

Nick Mortimer, et al. 2017. Zealandia: Earth's Hidden Continent (GSA Today)

[joanjournal]

Dingoes - an origin story in the making

Fraser Island Dingo (Newretreads CC BY-SA 4.0)

One of the most charismatic of Australia's placental mammals is the dingo, and their presence on the continent has always retained an air of mystery in the scientific community. The earliest European colonists noted the relationship between these dogs and First Nations peoples, where it was recognized as a "domestic animal" (Tench, 1789).

Subsequent ethnographic and field records show a more complicated picture. Dingoes occurred in both wild and human-centered conditions, and could freely move between these two states, sometimes leaving to roam the countryside while their human companions were away. People treated dingoes as lapdogs and cuddle-buddies, relied on them to ward off enemies on the physical and spiritual planes, and valued them as companions during hunting and gathering work; as well traditional Aboriginal knowledge includes multiple references to dingoes (Shipman, 2021).

That said, when it comes to the question of origins - how the dingo got to Australia - more questions have been raised than answers.

To start with, let's look at the zooarchaeological record. The oldest remains of a dingo come from Madura Cave on the Nullarbor Plain in southwestern Australia, which have recently been re-dated to between 3,348-3,081 years ago (Balme, et al. 2018).

Human beings have been on the continent for far longer than this, with conflicting results from archaeology and ancient DNA studies hinting at potentially multiple expansions between 65,000 and ~40,000 years ago (Sümer, et al. 2024; Clarkson, etal. 2017). There is no evidence to suggest that the ancestors of First Nations Australians brought dogs with them to the continent, and the sheer lack of dingo remains between this period and the site at Madura Cave would imply then that these animals arrived at a far later date.

Turning now to genetics, evolutionary biologists have been able to shed far more light onto this matter.

Put it simply, most zoologists agree that the dingo belongs to the same species as the domestic dog, Canis lupus familiaris. The ancestors of our furry friends belong to a now-extinct population of gray wolves that seem to have inhabited central Eurasia and was domesticated by Ancient North Eurasians by 23,000 years ago (Perri, et al. 2021, Bergström, et al. 2020).

A paper by Matt A. Field and colleagues in 2022 demonstrated that most modern domestic dogs contain an increased number of copies of a gene called AMY2B, which creates copious amounts of the enzyme amylase in the pancreas to aid in the digestion of starches. It seems clear in this that the transition to agriculture across the world in the starting millennia of the Holocene Epoch was followed closely by domestic dogs. However, the dingo was found to lack this genetic change, indicating that its lineage branched off before the radiation of ancestral breeds by 11,000 years ago (Bergström, et al. 2020).

New Guinea Singing Dog (Patti McNeal, CC BY 2.0)

The closest living relative of the dingo is the New Guinea singing-dog which, like its Australian relative, exists along a spectrum of wild and domestic populations. These animals are near identical in appearance, and the most recent studies have revealed that their relationship is far more complex than being sister species: it appears that the dingo may be a subgroup of the New Guinea varieties, more closely related to the domestic forms than the wild ones (Surbakti, et al. 2020). These and similar findings also show evidence of admixture between New Guinea dogs and the separate later-diverging lineage of Oceanian dogs which accompanied the Austronesian-speaking Lapita peoples that populated Southeast Asia and the Pacific Islands. This is reflected in one paper which found that the New Guinea singing dog samples derived 58% of their genome from ancient East Eurasian breeds (Bergström, et al. 2020). In contrast, it appears that dingoes have never interbred with other domestic dogs during their tenure in Australia as has long been believed (Weeks, et al. 2024).

So, it is clear that a source of answers to the origin of dingoes lay with their New Guinea cousins. At some point, a population was separated and settled in Australia without prior admixture from other dog lineages. When did this happen?

One comprehensive genetic study has suggested that the introduction of the dingo occurred further back in time than the earliest archaeological sites would suggest. Between 8,300 and 7,800 years ago - and at least on two occasions according to one proposed hypothesis - dingoes diverged from the New Guinea dogs and found their way onto Australia (Cairns & Wilton. 2016). Subsequent work on historic dingo remains adds support to this model, showing a gradient in dingo diversity that had already been established by 2,000 years ago (Souilmi, et al. 2024, Koungoulos, et al. 2024).

This creates somewhat of a disconnect between the genetic data and the archaeology, as no older dingo remains have been found beyond 3,300 years ago. In her 2021 book Our Oldest Companions, Pat Shipman drew two possible conclusions from this research: if these findings were valid, then dingoes simply did not interact with people when they first reached the continent until thousands of years later, or if these findings were not valid, it's because the proposed dates are over-estimates of mutation rates, which could have varied in their speed and so give the impression of phylogenetic antiquity.

It must also be considered that this early split from New Guinea dogs does not necessarily mean that introduction to Australia happened immediately afterward. For all we know, these new populations remained on the island for thousands of years before they were properly introduced. Shipman recounted the remarkable speeds at which dogs spread into new regions when introduced by people in historic times, and it's likely that it only took a few hundred years for dingoes to arrive and spread across the continent before 3,300 YA (Shipman, 2021).

These questions all tie into perhaps the biggest mystery in dingo origins: who brought them to Australia?

One immediate candidate would be the Austronesian-speaking peoples, who have a fairly clear archaeological record of moving through Southeast Asia and into New Guinea and onto the outer western Pacific islands. It would be a matter of picking up the ancestral dingoes and landing them on Australian shores. In his landmark 1994 book The Future Eaters, Tim Flannery felt it "personally... quite likely" that the Lapita people would have become rather familiar with northeast Australia, citing evidence as disparate as Maori oral traditions and the genetics of parasitic lice. He even credits them with introducing the dingo. There is some very recent evidence further adding support to an idea of contact and familiarity: comparisons of pottery shards on offshore Jiigurru island on the Great Barrier Reef point to contact between Lapita people and First Nations Australians around 2,950 and 1,815 years ago (Ulm, et al. 2024).

Another proposed candidate are the Toaleans of south Sulawesi. Evidence of their society ranges far beyond the Austronesians, having lived on the island for around 9,000 years. They share genetic ancestry with the Indigenous Peoples of Australia, New Guinea, and greater island Melanesia. The Toaleans were also sea-fairing people, and evidence of similar tool technologies between them and Borneo point to extensive marine trade networks (Fillios & Taçon, 2016).

At the moment, the issues with these and other candidates are a lack of evidence and an inconsistency with dates. We must recall there is a minimum date of 3,300 YA for the presence of dingoes in Australia, plus a few hundred years perhaps. While the Lapita were certainly present in and around New Guinea by that point, there is a lack of evidence to show that their presence near Australia extended beyond influencing coastal pottery use by the First Nations in the Great Barrier Reef. And besides, while they had domestic dogs, these belonged to a different lineage than the dingo (which shows no evidence of admixture with other dogs). Fillios & Taçon, 2016 argued strongly for the Toaleans as the right candidate, as they were a foraging society and so would have conceivably owned dogs that lacked the AMY2B gene copies seen in agricultural breeds. To date, however, there has been no evidence they had domestic dogs or that they reached Australia.

The last remaining evidence we can look at are First Nations oral traditions and history. As Pat Shipman recounts: "Traditional knowledge, expressed in dances (corroborees) and myths, ... asserts that dingoes were transported to Australia — accidentally or purposefully — by coastal boat-using peoples..." (Shipman, 2021).

Indigenous Australians retained memories of their first encounter with dingoes as animals with some familiarity to humans. Shipman has argued that the fluidity of these dogs between "wild" and "domestic" states is evidence that from the beginning the dingo and its New Guinea ancestors were behaviorally unique from all other dog breeds by having lived in a sort of intermediate-state: they were not as wild as gray wolves, nor were they as tamed and reared as hounds and terriers. That they seemed to stick around with people anyway and benefit reminds me somewhat of domestic cats, who have never been as fully-domesticated as most of our other pets and livestock.

Clearly, we know more about the origins of dingoes than we did a few decades ago, but there are still missing puzzle pieces. A currently undocumented people from Southeast Asia or the Western Pacific introduced dingoes (perhaps more than once) onto the Australian continent prior to 3,300 years ago, descended from dogs in New Guinea many thousands of years earlier (who, themselves, are descended from an ancient pre-agricultural lineage of dogs).

Given the recent advances in ancient DNA research and an increasing sample size of Southeast Asian sites prior to the spread of farming Austronesian-speaking peoples, I have little doubt that these gaps will be filled in the coming years. Pre-colonial Australia was clearly not as isolated from the rest of humanity as is typically portrayed in pop-history texts, even ignoring dingoes, but by finding out more about the curious origin of these sandy-colored companions and wanderers, we will continue to break that stereotype and further align Australia to the rest of the ancient world.

Book Citations:

Tim Flannery, The Future Eaters (Grove Press, 1994)

Pat Shipman, Our Oldest Companions (Harvard University Press, 2021)

Watkin Tench, A Narrative of the Expedition to Botany Bay (London, 1789)

Paper Citations:

Jane Balme, et al. 2018, New dates on dingo bones from Madura Cave provide oldest firm evidence for arrival of the species in Australia (Nature Scientific Reports)

Anders Bergström, et al. 2022, Grey wolf genomic history reveals duel ancestry of dogs (Nature)

Anders Bergström, et al. 2020, Origin and genetic legacy of prehistoric dogs (Science)

Chris Clarkson, et al. 2017, Human occupation of northern Australia by 65,000 years ago (Nature)

Matt A. Field, et al. 2022, The Australian dingo is an early offshoot of modern breed dogs (Science Advances)

Loukas G. Koungoulos, et al. 2024, Phenotypic diversity in early Australian dingoes revealed by traditional and 3D genomic morphometric analysis (Nature Scientific Reports)

Anna-Sapfo Malaspinas, et al. 2016, A genomic history of Aboriginal Australia (Nature)

Angela R. Perri, et al. 2021, Dog domestication and the duel dispersal of people and dogs in the Americas (PNAS)

Yassine Souilmi, et al. 2024, Ancient genomes reveal over two thousand years of dingo population structure (PNAS)

Arev P. Sümer, et al. 2024, Earliest modern human genomes constrain timing of Neanderthal admixture (Nature)

Suriani Surbakti, et al. 2020, New Guinea highland wild dogs are the original New Guinea singing dogs (PNAS)

Melanie A. Fillios & Paul S.C. Taçon. 2016, Who let the dogs in? A review of the recent genetic evidence for the introduction of the dingo to Australia and implications for the movement of people (Journal of Archaeological Science: Reports)

Sean Ulm, et al. 2024, Early Aboriginal pottery production and offshore island occupation on Jiijurru (Lizard Island group), Great Barrier Reef, Australia (Quaternary Science Reviews)

Andrew R. Weeks, et al. 2024, Genetic structure and common ancestry expose the dingo-dog hybrid myth (Evolution Letters)

Kylie M. Cairns & Alan N. Wilton, 2016, New insights on the history of canids in Oceania based on mitochondrial and nuclear data (Genetica)

[joanjournal]

Reviews: Riley Black - When the Earth was Green

I've been fond of Riley Black's writing for many years now, ever since I picked up a copy of My Beloved Brontosaurus as I was starting college. I appreciate the sense of wonder she brings into her paleo-literature, especially when she is explaining scientific research or breaking down complex subjects. Not only that, her ability to remain as up-to-date as possible with the latest research and discourse had made her a go-to source of information for me for years.

So I was absolutely delighted when I heard that she was going to tackle plant evolution in her new book When the Earth was Green! Not long after its release I quickly snagged a copy.

When it comes to understanding plant life, one of the things you have to recognize is that they do not exist in a vacuum. They are intimately woven with all the other organisms in their environment, and that environment itself is more-or-less underpinned by the plants that live there. Right away Black makes this point known, and emphasizes that plants are living things. She then continues by investigating the curiosities of deep time in relation to plants, and the kinds of things people often neglect to think about when it comes to visualizing past ecosystems.

From then on the book devotes most of its pages to different snapshots of the Earth's past from 1.2 billion years ago onwards, telling the story of plant evolution in small narrative episodes. Each chapter highlights a key change or lineage in the story of plants and its relation to the story of animal evolution.

To be completely honest, I had struggled with this format during the first half of the book. I do not know what on earth was going on with my head, but I seem to have had a different vision for what this book would be like vs. what Black actually wrote. Like I wanted something more... academic and more nitty-gritty with details? But I took some time and sat with my thoughts, and then went back to her previous book The Last Days of the Dinosaurs (which I adored and read in less than a week). This style of "narrative nonfiction" - to quote Goodreads - was how Black formatted this last book, so what was my problem here? I had stopped following the Late Cretaceous chapter and decided to continue on with a more open mind. Sure enough, as I read through the Cenozoic chapters, I gained much more appreciate and love for the book.

I absolutely loved the Cenozoic chapters and Black's choices of subject material. I had relearned and felt sheer fascination with our understandings of, say, how modern tropical rainforests became a post-Mesozoic phenomena or how autumn foliage ensured the survival of microfauna in northern latitudes. I wonder if this actually means I'm more of a Cenozoic-slut than the other geologic eras, but can't say that's a fair assessment of my paleontological interests. Living in a world with rainforests and deciduous trees means that I'm curious about how these environments and ecological relations developed, so perhaps Black was tapping into my love of big history connections?

Anywho, I'm very glad I followed the book through to the end, because I was rewarded with some beautiful reflections to ponder about. True to her style, Black flips our stereotypes of paleontology on their head, and she ends the book giving some praise to the fact that the fossil record is so patchy and full of gaps. It's these gaps that have helped scientists easily study relations between taxa and understand the evolution of life, because otherwise the seemless blending of species and environments would literally break the foundations of biology and force us to rethink how we look at nature. Which... I mean, that sounds awesome and vibes with my anarchist thinking, but I do agree that we probably wouldn't have developed our understanding of big concepts in evolution and deep time as clearly as we have had things turned out that way. So I definitely appreciate those gaps and have shifted how I think about them.

Before I end this review, I just want to say that Riley Black's fusion of her gender-journey with her love of Earth's prehistory spoke to me in ways that I haven't truly recovered from. Her writing makes me want to be louder and prouder and more comfortable in my own skin than I've ever been.

Um... I don't really care about giving rankings or ratings on this blog, as I feel many people will only look at stars or numbers and not care about nuance. I'll say that, in the end, I ended up absolutely enjoying When the Earth was Green and encourage anyone with an interest in deep time to pick it up and share it with their friends. It's beautifully written and is sure to spark your imagination in some way or another. You'll certainly never look at plants the same way again...

Buy it here! And check out Riley Black's page here!

[joanjournal]

Welcome to My Blog!

Greetings! My name is Joan, and I'm a digital artist and somewhat amateur naturalist. I graduated with a BA in Anthropology and have mainly been involved in online science communication. For those who may be aware, my most recent involvement was as a co-creator with @albertonykus of Through Time and Clades: a YouTube Natural History series in which we discussed relevant topics in zoology, paleontology, and anthropology through lectures and news-sharing.

Recently, we said goodbye to our channel due to scheduling conflicts with life/work as well as loss of energy maintaining TTC the way we had. This was never an easy decision to make, and we have always figured that our spark for sharing our interests in the world around us would always be around in some way. In our finale episode, I had pondered about continuing my journey from this show with a blog of sorts. So here we are.

Joan's Journal will serve as a hub for... well, anything and everything that comes to my interests and that I feel like sharing. Unlike TTC, however, my blog will be less structured and often stray into topics that I have interest in but actively chose to underplay in the former series. Things like politics, belief systems, and philosophy. Sounds fun!

There will still be plenty of discussion on evolutionary history, human prehistory, the diversity of life on Earth, etc. If anything I can see this blog being an archive of all the information I've gathered and learned (and will continue to actively do so) in my readings and discussions with others.

So, essentially, that's why I chose to call this blog a "journal". It's a log of my thoughts, at the end of the day. It just so happens that my thoughts will often include citations and references and be supported by science and scholarship, as well as being a vessel for my personal opinions, reflections, and beliefs.

If you enjoyed Through Time and Clades, then I hope you find some value in spending time with me and listening to what I have to say. This won't be a reboot, more of a spin-off :)

For now, I'll leave you all with something to ponder:

This is a photo I took back in 2021 at the Florida Museum of Natural History, in the Powell Hall exhibit Northwest Florida: Waterways and Wildlife.

This is part of a diorama which depicts a trading exchange at Chattahoochee Landing along the Apalachicola River in southern Florida, between two Native American nations around 1300 AD. Here are representatives of Etowah (located today in NW Georgia), one of the many towns of the Mississippian Culture that held sway in Eastern North America from the 900s AD to the dawn of European contact in the continental United States. The tall noblewoman depicted here is opening the exchange with a gift (an embossed plate) to representatives of the Fort Walton culture, an archaeological term used for the ancestral Apalachee nation whose ancestral lands are near the Apalachicola River (at left, but not shown in this photo).

This museum diorama is a window into another time, and a very beautifully and accurately depicted one at that. I often like to place my senses into scenes like this: what words were exchanged? What were did the people of either nation think about the other? Did these exchanges happen often, and, if so, how did the people plan such occasions? How formal was everything? Did people crack jokes, exchange memories, cause drama?

It's thoughts like these which make the study of the human past so fascinating to me. It's easy to see depictions like this of unnamed, long-gone peoples - whether in museums or nonfiction books - and forget that behind every face was a fully-fledged human being with all the complexity that entails. Perhaps if you lived at the time, they could be as familiar to you as your family, friends, and neighbors...

This scene took place over 700 years ago. The cultures depicted have long since changed beyond present recognition. Also consider that this diorama no longer exists. The hall underwent major renovations and reshaping back in 2023, and to my knowledge this exhibit was removed after decades on display.

So, in a sense, this is a snapshot of the past in more ways than one...