inatungulates

[inatungulates]

American elk Cervus canadensis canadensis

Observed by kevinricker, CC BY-NC

[inatungulates]

Gemsbok Oryx gazella

Observed by markuslilje, CC BY-NC-ND

[inatungulates]

Columbian black-tailed deer Odocoileus columbianus columbianus

Observed by manlivesingrimsby, CC BY-NC

[inatungulates]

Red hartebeest Alcelaphus caama

Observed by plantamigo, CC BY-NC

[inatungulates]

Offshore spotted dolphin Stenella attenuata attenuata

Observed by airvillanueva, CC BY-NC

[inatungulates]

Limpopo bushbuck Tragelaphus sylvaticus roualeynei

With grey-footed chacma baboon Papio ursinus griseipes

Observed by rooikat_, CC BY-NC

[inatungulates]

Vicuña Vicugna vicugna

With Andean gull Chroicocephalus serranus, middle background, and Andean flamingo Phoenicoparrus andinus, far background

Observed by slunky, CC BY

[inatungulates]

African bush elephant Loxodonta africana

Observed by hirons, CC BY-NC

[inatungulates]

African forest elephant Loxodonta cyclotis

Observed by simben, CC BY-NC-ND

[inatungulates]

West African elephant Loxodonta "cyclotis"

Observed by ngltaylor, CC BY-NC

For the past few decades, two species of African elephants Loxodonta have been recognized: the larger African bush elephant Loxodonta africana, found predominantly in open country, and the smaller African forest elephant Loxodonta cyclotis of the Congolian forest block in Central Africa. Separated from the Congolian forest bloc by the dry savannas and scrublands of the Dahomey Gap is the Guinean forest block of West Africa.

In West Africa, the Guinean forest block provides the lowland rainforest habitat favored by African forest elephants, but at the edges of the drier woodlands and scrublands of the Dahomey Gap, elephants also live. On iNaturalist, elephants in West Africa - all clearly of the same type - are variously identified by users as bush elephants, forest elephants, or simply IDed to the genus level owing to some ambiguity as to the nature of these animals. The observation above shows a good example of the somewhat odd appearance of these elephants. Basically, these are forest elephants with the characteristics typical of the species visible: rounded ears, rounded head, fairly good definition between the base of the trunk and the tusk margins, relatively gentle concavity to the back, fairly straight or gently-curved tusks that are directed downward as they emerge from the upper jaw. Compared to the typical forest elephants of the Congolian forest block, though, these West African elephants often show a stockier build, a broader head, more robust tusks, and more deeply-developed skin wrinkles; all features that are at least superficially bush elephant-like.

Genetic work over the past quarter-century or so recovers two distinct lineages of forest elephants which correspond to a Central African/Congolian forest block clade, and a West African/Guinean forest block clade. Divergence between the West and Central clades occurred sometime in the early or middle Pleistocene: estimated to have occurred more than 2.3 million years ago (Eggert et al., 2002; Roca et al., 2015), or, more in a more recent study, between 609,000-463,000 years ago (Palkopoulou et al., 2018); Lin and colleagues (2023) follow the later split date in their text, but their mitochondrial cladogram shows a median age of 1.73 million years ago for this split. Regardless of exactly when the two lineages diverged, there seems to be consensus that it was no later than the middle Pleistocene. In addition, there is another component to the genetic story, involving the now-extinct straight-tusked elephants Palaeoloxodon spp. Straight-tusked elephants have long been considered close relatives of Asian elephants Elephas maximus, but genetics show they are in fact originally derived from the same common ancestor as the African elephants. Subsequent to the split between the ancestral straight-tusked elephants and ancestral African elephants, the straight-tusked lineage underwent extensive hybridization with one of the forest elephant lineages - specifically, the West African clade, sharing derived alleles to the exclusion of the Central African forest elephant clade.

What does this all mean for the taxonomy of the elephants found in West Africa? Contra the sometimes-rather-fervent assertions of numerous iNat users, they are not African bush elephants, though they may be found in bush country. The simplest answer, favored by most scientists, is that they are African forest elephants, though with the caveats that (A) they are not strictly tied to rainforest habitats and (B) they represent a deeply-diverged lineage within that species that has not had any real contact with the typical Central African form for something like half a million years at minimum. To me (a born splitter, admittedly) this seems somewhat unsatisfying: while there is no hard-and-fast rule on how long ago a split has to have occurred for it to be called speciation, a divergence in the early (perhaps earliest) Pleistocene would certainly be recognized as a species-level split in many mammal groups; to let such a split go without taxonomic recognition also feels as though it is not emphasizing the unique genetic history of the elephants concerned. Though their positions has not been widely taken up, this passage from Eggert and colleagues (2002) takes good stock of the situation and sums up my feelings nicely:

"[...]these West African populations have been on a different evolutionary trajectory for more than 2 Myr [though, again, more recent work suggests a potentially younger date]. As human conversion of habitat now precludes significant gene flow into these populations, they should be considered a separate taxon."

The ongoing genetic history of elephants, living and extinct, is fascinating, complicated, and surely full of as-yet-undiscovered stories. On this blog, the West African elephant will be catalogued as Loxodonta "cyclotis" in reference to its clear affinity to, but deep divergence from, the typical form of L. cyclotis from the Congolian forest block. In time, I hope to revisit this topic with new insights.

Ref:

Eggert, LS, CA Rasner, and DS Woodruff. 2002. The evolution and phylogeography of the African elephant inferred from mitochondrial DNA sequence and nuclear microsatellite markers. Proceedings: Biological Sciences 269(1504):1993-2006.

Lin, H, J Hu, S Baleka, J Yuan, X Chen, B Xiao, S Song, Z Du, X Lai, M Hofreiter, and G Sheng. 2023. A genetic glimpse of the Chinese straight-tuskes elephants. Biology Letters 19:20230078.

Palkopoulou, E, M Lipson, S Mallick, S Nielsen, N Rohland, S Baleka, E Karpinski, AM Ivancevic, T-H To, RD Kortschak, JM Raison, Z Qu, T-J Chin, KW Alt, S Claesson, L Dalén, RDE MacPhee, H Meller, AL Roca, OA Ryder, D Heiman, S Young, M Breen, C Williams, BL Aken, M Ruffier, E Karlsson, J Johnson, F Di Palma, J Alfoldi, DL Adelson, T Mailund, K Munch, K Linblad-Toh, M Hofreier, H Poinar, and D Reich. 2018. A comprehensive genomic history of extinct and living elephants. Proceedings of the National Academy of Sciences 115(11):E2566-E2574.

Roca, AL, Y Ishida, AL Brandt, NR Benjamin, K Zhao, NJ Georgiadis. 2015. Elephant natural history: A genomic perspective. Annual Review of Animal Biosciences 3:20.1-20.9.

[inatungulates]

Baird's tapir Tapirus bairdii

Observed by oscar_wainwright, CC BY-NC

[inatungulates]

Southern white rhinoceros Ceratotherium simum simum

Observed by xbbt, CC BY-NC

[inatungulates]

Chapman's zebra Equus quagga chapmani

Observed by simben, CC BY-NC-ND

[inatungulates]

Risso's dolphin Grampus griseus

Observed by anudibranchmom, CC BY-NC

[inatungulates]

Naisa short-finned pilot whale Globicephala macrorhynchus macrorhynchus

Observed wayneosborn, CC BY-NC

[inatungulates]

Ross Sea killer whale Orcinus orca

Observed by whale_nerd, CC BY-NC

[inatungulates]

Common hippopotamus Hippopotamus amphibius

Observed by gaell, CC BY-NC-ND