The evolution of jaw mechanism and dental function in heterodont crocodyliforms

Abstract

Heterodont dentition sometimes including multicuspid crowns appeared in numerous fossil forms through all main lineages of the Crocodyliformes. Teeth in these complex dentitions frequently bear wear facets that are exclusive indicators of tooth–tooth occlusion. Besides, dental features, specialisations of the jaw apparatus, jaw adductors and mandibular movement can be recognised, all reflecting a high variability of jaw mechanism and of intraoral food processing. Comparative study of these features revealed four main types of jaw mechanism, some of which evolved independently in several lineages of Crocodyliformes. Isognathous orthal jaw closure (precise jaw joint, rough wear facets) is characteristic for heterodont protosuchians and all forms possessing crushing posterior teeth. Proal movement (protractive powerstroke) occurred independently in Malawisuchus and Chimaerasuchus is supported by the antagonistic, vertically oriented carinae. Developed external adductors are the main indicators of palinal movement (retractive powerstroke) that evolved at least two times in various South American taxa. The fourth type (in Iharkutosuchus) is characterised by lateromedial mandibular rotation supported by extensive horizontal wear facets. This evolutionary scenario resembles that of the masticatory system of mammals and suggests that the ecological roles of some mammalian groups in North America and Asia were occupied in Western Gondwana by highly specialised crocodyliforms.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:D6CE962F-2B38-47F8-BD4B-B9E035917F20

Keywords::

• Crocodyliformes
• heterodont dentition
• dental wear
• jaw adductors
• complex jaw mechanism
• dental occlusion

Acknowledgements

I am really grateful to M. Delfino and an anonymous reviewer for their critical comments and suggestions that greatly improved this manuscript. I am very grateful to E. Prondvai for her critical comments and questions. I thank the following colleagues and institutes to the access the crocodyliform material in their care: I. Souza de Carvalho and T. Marinho (Federal University of Rio de Janeiro, Rio de Janeiro, Brazil); A. Celso, F. Iori and S. Aparecida (Monte Alto Museum, Sao Paolo State, Brazil); A. Carvalho (University of Sao Paolo, Sao Paolo, Brazil); A. Kellner, D. Dias Rego Henriques, L. Carvalho (National Museum, Rio de Janeiro, Brazil); S. Chapman, P. M. Barrett, C. McCarthy (Natural History Museum, London, UK); O. Rauhut (Paläontological Institute, München, Germany); N. Micklich and M. Blume (Darmstadt, Germany); D. Schwarz-Wings (Humboldt-Universität zu Berlin Museum für Naturkunde, Berlin, Germany); X. Xu and J. Li (Institute for Vertebrate Paleontology and Paleoantropology, Beijing, China); Patrick and Annie Mechin (Vitrolles, France); T. Tortosa (Natural History Museum, Aix-en-Provence, France); U. Göhlich and R. Gemel (Natural History Museum, Vienna, Austria); S. Apesteguía, P. Gallina, F. Novas (Natural History Museum, Buenos Aires, Argentina); J. Company (Polytechnic University of Valencia, Valencia, Spain).

I thank J. Sertich (Denver Musuem of Natural History, Denver, CO, USA), P. O'Connor (Ohio University College, Athens, OH, USA), J. Clark (George Washington University, Washington, DC, USA), I. Carvalho (UFRJ), Z. Csiki (University of Bucharest), E. Buffetaut (CNRS, Paris, France), E. Frey (Staatliches Museum für Naturkunde, Karlsruhe, Germany) and D. Schwarz-Wings (Humboldt-Universität zu Berlin Museum für Naturkunde, Berlin, Germany), P.M. Barrett (Natural History Museum, London, UK), L. Chiappe, (Natural History Museum, Los Angeles, USA), C. Holliday (University of Missouri, Columbia, USA), M. Delfino (University of Torino, Torino, Italy), E. Prondvai, M. Rabi and L. Makádi (MTA–ELTE Lendület Dinosaur Research Group, Budapest, Hungary) for useful consultations, comments and suggestions. I am grateful to J. Sertich, D. Pol, A. Turner, P. O'Connor, M. Delfino and F. Novas for providing me photographs on various crocodyliform specimens.

I thank E. Hankó and Zs. Hajdu for digital work on the illustrations. F. Varriale (Johns Hopkins University, Baltimore, MD, USA) showed me preparation of moulds taken from the teeth. I am grateful to Á. Görög and K. Bóka (Eötvös University, Budapest, Hungary), K. Buczkó (Hungarian Natural History Museum, Budapest, Hungary) and P. Ozsvárt (MTA–MTM Research Group for Paleontology, Budapest, Hungary) for help with the SEM. I thank P. Ungar (University of Arkansas, Fayetteville, AR, USA) for sending us the Microware software.

I thank Bolyai Fellowship, OTKA (PD 73021, NF 84193), MTA–ELTE Lendület Dinosaur Research Group, Hantken Foundation, The Jurassic Foundation, National Geographic Society, Hungarian Natural History Museum, European Union ‘Synthesys’ Grant for their financial support. I would like to thank G. Dyke for inviting me to submit this work to Historical Biology.