Craniodental and postcranial morphology of Indohyaenodon raoi from the early eocene of india, and its implications for ecology, phylogeny, and biogeography of hyaenodontid mammals

ABSTRACT

New remains of the early Eocene hyaenodontid Indohyaenodon raoi are described from the Vastan Lignite Mine in Gujarat, western India, including the first known rostrum, upper dentition, and postcrania, substantially expanding our knowledge of the species and providing insights into its functional morphology and relationships. Craniodental morphology suggests that I. raoi had a broad diet, including non-vertebrate material as well as flesh of a diversity of prey species. Postcranial morphology is broadly similar to that of other early hyaenodontids and suggests a scansorial locomotor repertoire. Dental morphology indicates that I. raoi is closely related to other South Asian hyaenodontids, with shared features including strong cingula, narrow premolars, and a reduced P4 protocone. We present the most comprehensive phylogenetic analysis of Hyaenodontidae to date, which corroborates this relationship but finds South Asian hyaenodontids to be the stem of a group that includes most African hyaenodontids. This and other higher-level relationships within Hyaenodontidae are, however, weakly supported, and substantially different alternative hypotheses of relationships are not significantly less parsimonious, reflecting strong character conflict. Factors contributing to this conflict include the isolation of hyaenodontid faunas on different continents during much of the Eocene, canalization and simplification of carnivorous dentitions, and a lack of non-dental material for critical hyaenodontid groups. The new phylogeny is consistent with either an African or an Asian origin for the group.

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ACKNOWLEDGMENTS

The authors thank all the institutions and agencies that supported this research—grants from the Department of Science & Technology, Government of India, to R.S.R.; National Geographic Society grants 6868-00, 7938-05, 8356-07, 8710-09, 8958-11, and 9240-12 to K.D.R. and A.S.; grant from the Director, Wadia Institute of Himalayan Geology, Dehradun, to K.K.; CSIR-ES scheme grant number 560 (21/EMR-II) and INSA SS grant no. SP/SS/2006/2841 to A.S.; and Belgian Federal Science Policy Office Research grant BR/121/A3/PALEURAFRICA to T.S. and F.S. The facilities and support provided by the general manager and staff of the Vastan Lignite Mine (Gujarat Industries Power Company Limited) are gratefully acknowledged. We thank other members of our field team, including H. Ahrens, R. Dunn, A. Folie, F. Gould, H. Singh, and G. McKusick Voegele. We are also grateful to N. Egi and P. Holroyd who helpfully answered queries on hyaenodontid morphology and phylogeny. We are grateful to A. Friscia and P. D. Polly and an anonymous reviewer for comments that have substantially improved this contribution.