65 - New Species of Dryolestoid from Allen Formation (Patagonia, Argentina) and Phylogenetic Context

Poster Board Number: 65
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Abstract Body : Dryolestoids are a group of ancient mammalians that share a distant common ancestor with modern marsupials and placentals (and therefore also humans). Late Cretaceous (approximately 100-66 My) localities in northwestern Patagonia have yielded important fossils from this group, along with those of multituberculates and stem therian mammals. Here, we describe a new collection of isolated dryolestoid dental elements. This collection represents both previously unknown taxa and novel material of known mammals. It therefore allows refinement of our interpretations regarding the morphology and evolution of these enigmatic forms.
The remains were collected, screen washed, and hand picked at the Cerro Tortuga locality (Rio Negro province, Argentina). Specimens were curated, mounted, photographed, and illustrated. Preliminary taxonomic hypotheses were then formed based on diagnostic characters.
We identify a new genus and species of dryolestoid based on 3 isolated lower molariforms. Several morphological characters - particularly cusp arrangement, root shape, presence of cingulids, and trigonid basin shape - diagnose this species and differentiate it from related forms. We also refer 18 isolated specimens to previously described dryolestoid taxa, completing their anatomy and testing previous hypotheses.
The remains in this collection allow for more complete reconstructions of the dentitions of several species and support earlier hypotheses of dryolestoid phylogeny. We hypothesize that this newly described species is closely related to the South American dryolestoid radiation known as meridiolestidans. We also posit that the morphology present in this new species represents a dietary shift within dryolestoids from insectivory to herbivory. This morphology supports earlier hypotheses that mesungulatids were likely derived from more generalized and insectivorous meridiolestids.