Dental homologies and evolutionary transformations in Caviomorpha (Hystricognathi, Rodentia): new data from the Paleogene of Peruvian Amazonia

ABSTRACT

Dental homologies and evolutionary transformations within caviomorph rodents have long been disputed. Here, we participate in these debates in providing new insights from the dental morphology of Paleogene caviomorphs from Peruvian Amazonia (Contamana and Shapaja). Their analyses and comparisons with many hystricognaths allow (1) to generalize some hypotheses previously proposed about occlusal morphology of caviomorph cheek teeth, and (2) to propose new ones. In caviomorphs, the third crest of upper teeth would correspond either to a mesoloph or to a mesolophule or to a combination of both. The transformation from a pentalophodont pattern to a tetralophodont pattern would be explained by the disappearance of the metaloph. Likewise, the transformation from a tetralophodont pattern to a trilophodont pattern is observed by the loss of the third crest. A direct transformation from a pentalophodont pattern to a trilophodont pattern is also observed. Concerning lower teeth, discrepancies of homologies are centered on the mesial cristids, which can be notably distinguished depending on their compositions and connections with other structures. The ancestral patterns of caviomorph lower molars and dp4s were likely tetralophodont and pentalophodont, respectively. However, schemes with five and four (even three) transverse cristids cannot be ruled out for the two loci, respectively.

KEYWORDS:

• Caviomorph rodents
• Peru
• South America
• dental morphology
• homology hypotheses

Acknowledgments

We especially thank P.-O. Antoine (ISE-M, France), members and supporters of the international team who contributed to the discovery and exploitation of the caviomorph-bearing localities from Peruvian Amazonia. F. Catzeflis (ISE-M), S. Jiquel (ISE-M), B. Marandat (ISE-M), C. Argot (MNHN, France), G. Billet (MNHN), V. Nicolas (MNHN), A. Verguin (MNHN), C. Chacaltana (INGEMMET, Peru), L.M. Tejada-Medina (INGEMMET), A. Kramarz (MACN, Argentina), M. Reguero (MLP, Argentina), I. Olivares (MLP) and B. Mamani Quispe (MNHN-Bol, Bolivia) kindly granted access to the osteological collections under their care. Many thanks to F. Pujos (IANIGLA, Argentina) for his help and long standing investment in our collaboration with the MNHN-Bol; R. Andrade Flores (MNHN-Bol) and C. Robinet (MLP) for their precious help during our journey at the MNHN-Bol; L. Defend (ISE-M) for the inventory and conditioning of the UM collections of Salla rodents. We thank L. Hautier (ISE-M), P.-H. Fabre (ISE-M), A. Candela (MLP), and C. Robinet for providing us the photographs of several collection specimens. Many thanks to A.-L. Charruault (ISE-M), S. Jiquel, S. Unal (ISE-M), P. Coster (UK, USA), H. Sallam (Mansoura University, Egypt) and M.G. Vucetich (MLP) who kindly made and/or provided us casts of fossil rodents. We are particularly indebted to M. Arnal (MLP, Argentina), A. Candela, A.G. Kramarz, M.E. Pérez (MPEF, Argentina) and M.G. Vucetich for fruitfull discussion on rodent dental homologies. We are particularly grateful to P.-O. Antoine, V. Barriel (MNHN), A. Candela, A. Kramarz, E. Seiffert (USC, USA) for their well-appreciated reading of this work, and their sensible remarks and advices. Lastly, we also thank the Editor in Chief of Historical Biology (G. Dyke, UD, USA) and the two anonymous revierwers, who provided formal reviews of this manuscript that enhanced the final version. This is ISEM publication 2018–152.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplementary data for this article can be accessed here.

Additional information

Funding

Parts of this work were supported by the L.S.B. Leakey Foundation; the National Geographic Society; the LabEx CEBA under Grant ‘Agence Nationale de la Recherche’ - ‘Investissements d’Avenir’ (ANR-10-LABX-0025-01; SOURCE and NEOTROPHYL projects); by the CoopIntEER CNRS/CONICET 252540 program; and the ECOS-SUD/FONCyT program.