Ecomorphology and ecology of the grassland specialist,Rusingoryx atopocranion(Artiodactyla: Bovidae), from the late Pleistocene of western Kenya

Abstract

Rusingoryx atopocranion is an extinct alcelaphin bovid from the late Pleistocene of Kenya, known for its distinctive hollow nasal crest. A bonebed of R. atopocranion from the Lake Victoria Basin provides a unique opportunity to examine the nearly complete postcranial ecomorphology of an extinct species, and yields data that are important to studying paleoenvironments and human-environment interaction. With a comparative sample of extant African bovids, we used discriminant function analyses to develop statistical ecomorphological models for 18 skeletal elements and element portions. Forelimb and hindlimb element models overwhelmingly predict that R. atopocranion was an open-adapted taxon. However, the phalanges of Rusingoryx are remarkably short relative to their breadth, a morphology outside the range of extant African bovids, which we interpret as an extreme open-habitat adaptation. It follows that even recently extinct fossil bovids can differ in important morphological ways relative to their extant counterparts, particularly if they have novel adaptations for past environments. This unusual phalanx morphology (in combination with other skeletal indications), mesowear, and dental enamel stable isotopes, demonstrate that Rusingoryx was a grassland specialist. Together, these data are consistent with independent geological and paleontological evidence for increased aridity and expanded grassland habitats across the Lake Victoria Basin.

Migratory behavior in the enigmatic Late Pleistocene bovid Rusingoryx atopocranion

“…This behavior would be advantageous to animals traveling long distances to maintain communication with conspecifics. Its postcranial morphology also indicates that this species was exceptionally adapted for open environments, with some limb structures outside the range of variation in modern African Bovidae, including shorter relative phalanx length than any other taxon (Kovarovic et al, 2021). This is consistent with animals traveling across open grasslands seasonally.…”

“…Though primarily grazing, Rusingoryx atopocranion incorporated more browse into its diet than any modern eastern African alcelaphin, including its closest relative in the region, Connochaetes taurinus (Figure 5). The relatively low δ 13 C values of R. atopocranion may seem contradictory to the morphology of this species, being highly hypsodont (Faith et al, 2011) and open-adapted postcranially (Kovarovic et al, 2021). Additionally, Faith et al (2011) find that its mesowear clusters with other grazers.…”

“…For this reason, we hypothesize that the demise of R. atopocranion in the Lake Victoria Basin may be linked to its migratory behavior. Finally, as argued by Kovarovic et al (2021), the re-establishment of Lake Victoria would have been associated with increased humidity and precipitation in the region, possibly leading to expansion of woodier environments that may have further impeded migratory pathways.…”

The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene

“…Further, many island environments also experienced total to near-total extinctions of their larger native fauna within this period or later (Stuart, 2015). Sub-Saharan Africa is often presented as having an intact megafauna, but actually lost a number of species in the late Quaternary, including an elephant species (Palaeoloxodon iolensis), a giant buffalo (Pelorovis antiquus), various antelopes (e.g., Rusingoryx atopocranion) and a giant warthog (Metridiochoerus compactus) (Faith, 2014;Manthi et al, 2020;Kovarovic et al, 2021). Similarly, mainland southern Asia also lost an elephant (Palaeoloxodon namadicus), another proboscidean (Stegodon orientalis), a hippopotamus (Hexaprotodon sivalensis), an equid (Equus namadicus), several orangutans (Pongo spp.…”

“…There is widespread evidence that Late Pleistocene Homo sapiens populations targeted large game and were sophisticated, efficient megafauna hunters in the varied environments they colonized, for example: mammoths in northern Siberia as early as 45,000 years ago (Pitulko et al, 2016), diverse large mammals at the initial colonization of Europe north of the Alps at the same time (Smith et al, 2024), and a diversity of gomphotheres, giant ground sloths, giant armadillos, equids, bears, cervids, and camelids across South America (Bampi et al, 2022). In fact, numerous megafauna kill sites for a large number of extinct species exist in Africa (Kovarovic et al, 2021), Eurasia (Shipman, 2015;Pitulko et al, 2016), North America (Sanchez et al, 2014;Waters et al, 2015), and South America (Bampi et al, 2022). Kill sites are so far missing from the limited record for Australia and New Guinea (Hocknull et al, 2020).…”