Palaeontographica, Abt. A: Palaeozoology – Stratigraphy Article Vol. 315, Issues 1 – 4: 67–119 E Stuttgart, January 2020 Bisonalveus gracilis n. sp. (Pentacodontidae, Cimolesta): novel dental adaptations and their paleobiological implications in a small Paleocene mammal by Richard C. Fox1, * and Craig S. Scott2, ** With 7 plates, 1 text-figure, and 2 tables The LSID for the publication is: zoobank.org:pub:9F9E7BDE-9183-4077-9BC5-A28DDAAF2203 LSID for the species is: zoobank.org:act:70548CEF-C1FD-4817-A-20B23798CD5E44F Abstract A new species of shrew-sized late Paleocene (middle Tiffanian) eutherian mammal, Bisonalveus gracilis (Pentacodontidae, Ci- molesta), is described from the DW-2 locality and correlative sites in the Paskapoo Formation, central Alberta, Canada. B. grac- ilis differs from the genotypic species, B. browni Gazin, in having a less robust cheek dentition and a reduced, single-rooted p2, and from B. holtzmani Gingerich in having substantially smaller molars. Previously published evidence implies that B. gracilis possessed a venomous bite, indicated by vertically emplaced, dagger-like upper canines (C) containing a well-defined channel for conveying venomous saliva, a Venom Delivery System (VDS) analogous to that of the extant Caribbean eulipotyphlan mammal Solenodon Brandt. Further research has revealed that the third upper incisor (I3) of B. gracilis closely resembles the upper canine in these novel features, strengthening the hypothesis that parts of the dentition of the species were adapted for this specialized function. Moreover, the molars of B. gracilis exhibit sharply pointed major cusps and well-developed, vertical shearing crests, some of which are neomorphic, while aspects of M2 are convergent on the shearing M1 of Carnivora. Collec- tively, the unique dental features of B. gracilis appear to be adaptations for consuming animal tissue and imply that B. gracilis was a tiny predator, employing a venomous bite in securing its energy requirements from animal protein. Recent alternatives to this interpretation of the paleobiology of B. gracilis are discussed but are shown to be lacking in their factual support, from either the fossil evidence or from modern analogues. Keywords: Bisonalveus; Eutheria; faunivore; Paleocene; venom Contents Abstract ������������������������������������������������������������������������������������������� 67 6. Discussion ��������������������������������������������������������������������������������� 90 1. Introduction ����������������������������������������������������������������������������� 68 6.1 Criticisms of the evidence . 90 2. Geological setting and localities ������������������������������������������� 68 6.2 Alternative functions . 94 2.1 General geology . 68 6.3 Paleobiology of Bisonalveus gracilis ����������������������������� 97 2.2 Locality information ������������������������������������������������������� 68 7. Conclusions ������������������������������������������������������������������������������� 99 3. Material and methods ������������������������������������������������������������� 70 Acknowledgments . 100 4. Systematic paleontology . 70 References ��������������������������������������������������������������������������������������� 100 5. Function of molariform teeth in Bisonalveus gracilis ������� 87 Plates 1–7 and explanation of plates ����������������������������������������� 106 Author’s addresses: 1 Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9 * [email protected] 2 Royal Tyrrell Museum of Palaeontology, P. O. Box 7500, Drumheller, AB, Canada T0J 0Y0 ** Corresponding author: [email protected] © 2020 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/pala/2020/0087 0375-0442/2020/0087 $ 23.85.