Dental replacement in Mesozoic birds: evidence from newly discovered Brazilian enantiornithines

Yun-Hsin Wu,Luis M. Chiappe,Agustín G. Martinelli,William Nava,David J. Bottjer

doi:10.1038/s41598-021-98335-8

Abstract

Polyphyodonty—multiple tooth generations—in Mesozoic birds has been confirmed since the nineteenth century. Their dental cycle had been assessed through sparse data from tooth roots revealed through broken jawbones and disattached teeth. However, detailed descriptions of their tooth cycling are lacking, and the specifics of their replacement patterns remain largely unknown. Here we present unprecedented µCT data from three enantiornithine specimens from the Upper Cretaceous of southeastern Brazil. The high resolution µCT data show an alternating dental replacement pattern in the premaxillae, consistent with the widespread pattern amongst extinct and extant reptiles. The dentary also reveals dental replacement at different stages. These results strongly suggest that an alternating pattern was typical of enantiornithine birds. µCT data show that new teeth start lingually within the alveoli, resorb roots of functional teeth and migrate labially into their pulp cavities at an early stage, similar to modern crocodilians. Our results imply that the control mechanism for tooth cycling is conserved during the transition between non-avian reptiles and birds. These first 3D reconstructions of enantiornithine dental replacement demonstrate that 3D data are essential to understand the evolution and deep homology of archosaurian tooth cycling.

Highlights

Polyphyodonty—multiple tooth generations—in Mesozoic birds has been confirmed since the nineteenth century
In an attempt to understand the pattern of dental replacement of these birds, Edmund[1] reviewed previous findings in avian dentition and concluded that the evidence was consistent with the presence of “replacement waves” in which stimuli moving in an anterior–posterior direction, generate waves of tooth replacement
Our observations strongly suggest the presence of an alternating pattern of dental replacement for these enantiornithines

Summary

Introduction

Polyphyodonty—multiple tooth generations—in Mesozoic birds has been confirmed since the nineteenth century. Dumont et al.[13] utilized CT imaging techniques to make inferences on the implantation, attachment, and formation time of the teeth of Hesperornis and Ichthyornis Based on these results, Dumont et al.[13] suggested that in these stem birds the replacement teeth first formed at the lingual side of functional teeth, invading them through lingual resorption pits, and in the end expelling and replacing them. Dumont et al.[13] suggested that in these stem birds the replacement teeth first formed at the lingual side of functional teeth, invading them through lingual resorption pits, and in the end expelling and replacing them These authors provided important data on aspects of dental replacement in some of the most immediate toothed outgroups (the ornithurines Hesperornis and Ichthyornis) of living birds but the preservation of the scanned specimens limited the data available on the tooth cycling and replacement pattern throughout the jaw. These data allow testing specific hypotheses of dental replacement patterns in stem birds

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Conclusion