The evolutionary origin(s) of the trunk in Proboscidea (Mammalia, Afrotheria) based on Osteology

Nxumalo, Mpilo
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To date, no quantitative assessment of the evolution of the trunk in elephant ancestors has beenundertaken. This study aims to quantify the dimensions of the infraorbital canal (volume andsurface area of the infraorbital foramen) and retraction of the naris, to test how these metrics correlate with the dimensions of the nose/trunk in some selected modern mammals and apply these assessments to the fossil record to determine the evolutionary origin (s) of the trunk in Proboscidea. The gross morphology of the infraorbital canal in these species is described in detail for the first time. The results indicate that there is a significant and strong correlation between the surface area of the infraorbital foramen and the dimensions of the snout. The dimensions of the infraorbital canal increase with the size of the facial appendage. There is no correlation between the degree of narial retraction and dimension of the snout in extant taxa. There is a strong taxonomic and phylogenetic signal in the morphology of the infraorbital canal. The application to fossils suggests that Numidotherium possessed a trunk shorter than that of tapirs, and Deinotherium amore tapir-like trunk length. Gomphotheres, Anancus and E. rackei possessed snout lengths shorter than proposed in the literature. The trunk did not originate as a single event at the root of Proboscidea but is a result of a long evolution that spanned the proboscidean phylogenetic tree for at least 60 My, between the last common ancestor of Proboscidea and that of Sirenia.
A dissertation submitted to the Evolutionary Studies Institute, University of the Witwatersrand, in partial fulfilment of the requirements for the degree Master of Science (Palaeontology), 2022