Diversity and convergences in the evolution of feeding adaptations in ankylosaurs (Dinosauria: Ornithischia)^*

* Research was conducted at the Eötvös Loránd University, Budapest, Hungary.

Abstract

Ankylosaurian dinosaurs were low-browsing quadrupeds that were traditionally thought of as simple orthal pulpers exhibiting minimal tooth occlusion during feeding, as in many extant lizards. Recent studies, however, have demonstrated that effective chewing with tooth occlusion and palinal jaw movement was present in some members of this group. Qualitative and quantitative analysis of feeding characters (i.e. craniodental features, tooth wear patterns, origin and insertion of jaw adductors) reveal at least three different jaw mechanisms during the evolution of Ankylosauria. Whereas, in basal members, food processing was restricted to simple orthal pulping, in late Early and Late Cretaceous North American and European forms a precise tooth occlusion evolved convergently in many lineages (including nodosaurids and ankylosaurids) complemented by palinal power stroke. In contrast, Asian forms retained the primitive mode of feeding without any biphasal chewing, a phenomenon that might relate to the different types of vegetation consumed by these low-level feeders in different habitats on different landmasses. Further, a progressive widening of the muzzle is demonstrated both in Late Cretaceous North American and Asian ankylosaurs, and the width and general shape of the muzzle probably correlates with foraging time and food type, as in herbivorous mammals.

Keywords:

• Ankylosauria
• feeding characters
• tooth wear
• dental occlusion
• palinal jaw movement
• herbivory

Acknowledgements

We thank Victoria Arbour and Ralph Molnar for their constructive comments that highly improved the MS. The authors thank Juri Miyamae and Daniel L. Brinkman (PMNH, Yale University, New Haven, Connecticut, USA) for images on the Sauropelta teeth, Joshua Schmerge (UKNHM, Lawrence, USA) for pictures on Silvisaurus, Ken Carpenter (USU EPM, USA) for sending the cast of Peloroplites tooth, Jim Kirkland (UGS, Salt Lake City, Utah, USA) for pictures on Gastonia. We are grateful to Tibor Pecsics (Eötvös University, Budapest, Hungary) for the illustrations on ankylosaur skulls. We thank Magdalena Borsuk-Białynicka (PAS, Warsaw, Poland), Tatiana Tumanova (PIN, Moscow, Russia), Mark Norell (AMNH, New York, USA), Michael Brett-Surman (USNM, Washington DC, USA), Carl Mehling (AMNH, New York, USA), Kieran Shepeard, Alan McDonald, and Margaret Currie (CMN, Ottawa, Canada), Kevin Seymour and David Evans (ROM, Toronto, Canada), Jim Gardner, Don Henderson, Brandon Strilisky and Becky Sanchez (TMP, Drumheller, Canada), Mike Caldwell and Victoria Arbour (University of Edmonton, Edmonton, Canada), Luis Alcala and Eduardo Espínez (Dinopolis, Teruel, Spain), Suzanne Jiquel and Laurent Marivaux (UM2, Montpellier, France) for access to specimens. We are grateful to Gábor Botfalvai (MTA–ELTE Lendület Research Group, Budapest, Hungary), Ádám Kocsis (MTA-MTM-ELTE Paleontological Research Group) and Bob Sullivan (Harrisburg, PA, USA) for useful consultations, Péter Gulyás, Réka Kalmár, Zsófia Hajdu and Dóra Csengődi (MTA–ELTE Lendület Research Group) for preparation of the specimens, and Krisztina Buczkó (MTM, Budapest, Hungary) for help with the SEM.

Notes

* Research was conducted at the Eötvös Loránd University, Budapest, Hungary.