Mythbusting Palaeoloxodon Evolution: The Story So Far… | Hanwen (Steven) Zhang

Mythbusting Palaeoloxodon Evolution: The Story So Far…

The Early-Middle Pleistocene Transition interval saw the emergence of Palaeoloxodon in Africa and its subsequent dispersal into Eurasia, thereby becoming a keystone megaherbivore for Pleistocene palaeoenvironmental retrodiction across vast parts of Afro-Eurasia. The underlying phylogenetic mechanism of this bio-event recently became the centre of heated controversy, with ancient DNA evidence supporting the apparent closeness of Palaeoloxodon to Loxodonta (African elephants); in contrast to the hitherto established “Elephas recki” model of Palaeoloxodon origin from an ancestor associated with Elephas (Asian elephants). A reappraisal of the problem cannot be detached from revisiting some deep-rooted complications in understanding the fossil history of Palaeoloxodon. A survey of skull materials reveals that the characteristic parieto-occipital crest (POC) of Palaeoloxodon to be an ontogenetically variable trait that exhibits salient character polarity across phylogeny. This facilitated the recent re-identification of a Middle Late Pleistocene skull from northern India with poorly developed POC as belonging to Palaeoloxodon turkmenicus, an obscurely known taxon bridging the morphological gap between the archetypal P. recki known from East Africa, and derived Eurasian Palaeoloxodon species. A novel cladistic analysis of craniodental characters falls palpably short of supporting a Palaeoloxodon-Loxodonta clade, but strongly indicates supposed time-successive evolutionary stages within the “E. recki” complex to represent phylogenetically distinct crown-group elephantid lineages. whereas the nominotypical recki from late Early Pleistocene East Africa is morphologically consistent with Palaeoloxodon (thus Palaeoloxodon recki), other earlier remains attributed to recki exhibit far greater cranial disparity than can be explained by anagenesis in a single lineage. The Late Pliocene skull from southern Ethiopia attributed to brumpti is most morphologically similar to the contemporary “Elephas” planifrons of the Siwaliks and Phanagoroloxodon from southeastern European Russia; whereas the Early Pleistocene atavus shares substantial similarities with the contemporary Siwalik E. hysudricus.