Deciduous dentition and dental eruption of Hyainailouroidea (Hyaenodonta, “Creodonta,” Placentalia, Mammalia)

Deciduous dental morphology and the sequence of permanent dental eruption offer developmental and phylogenetic insights into mammalian evolution. Early life history in Hyaenodonta, a morphologically diverse and biogeographically widespread clade of carnivorous mammals known from the Paleogene and early Neogene, has only been examined closely in one genus: Hyaenodon. Here we describe the deciduous dental morphology for six hyainailouroids, a clade of hyaenodonts distantly related to Hyaenodon that dominated early Cenozoic meat-eating niches of Afro-Arabia for nearly 20 Ma. Results suggest significant variation among hyainailouroids in expression of the dP3 and dP4 protocone, paracone, and metacone and in expression of the dP3 and dP4 paraconid, metaconid, and talonid. Deciduous dental characters were incorporated into a Bayesian phylogenetic analysis. The topology was congruent with earlier systematic examinations of hyaenodont evolution, suggesting that deciduous dental features can be phylogenetically informative and that taxa known only from deciduous teeth can be incorporated into studies of mammalian systematics. Based on the specimens described herein, the dental eruption sequence of Hyainailouroidea is reconstructed. P4 and P3 erupt after M3, evidence that the deciduous carnassial complex formed between dP3 and dP4 was retained until late in development, permitting hyaenodonts to heavily wear shearing blades on these teeth before replacement. This differs from Carnivora, a group that tends to replace deciduous dentition earlier in development, effectively limiting carnivorans to a single set of carnassials throughout most of their lifespan. This developmental difference between carnivorans and hyaenodonts can now be examined in a larger systematic and ecological context. Matthew R. Borths. Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio 45701, USA; Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio 45701, USA. borths.1@gmail.com Nancy J. Stevens. Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio 45701, USA; Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio 45701, USA. stevensn@ohio.edu Borths, Matthew R. and Stevens, Nancy J. 2017. Deciduous dentition and dental eruption of Hyainailouroidea (Hyaenodonta, “Creodonta,” Placentalia, Mammalia). Palaeontologia Electronica 20.3. 55A: 1-34. https://doi.org/10.26879/776 palaeo-electronica.org/content/2017/2056-deciduous-hyaenodont-teeth Copyright: November 2017 Society for Vertebrate Paleontology. This is an open access article distributed under the terms of Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0), which permits users to copy and redistribute the material in any medium or format, provided it is not used for commercial purposes and the original author and source are credited, with indications if any changes are made. creativecommons.org/licenses/by-nc-sa/4.0/ BORTHS & STEVENS: DECIDUOUS HYAENODONT TEETH