Evolutionary history of tooth attachment systems in Archosauromorpha: understanding the origin and ontogeny of Archosaurian thecodonty

• Grant number: 22/00171-9
• Support type: Scholarships in Brazil - Doctorate
• Effective date (Start): June 01, 2022
• Effective date (End): October 31, 2025
• Field of knowledge: Biological Sciences - Zoology - Paleozoology
• Principal researcher: Max Cardoso Langer
• Grantee: Gabriel Mestriner da Silva
• Home Institution: Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (FFCLRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Associated research grant: 20/07997-4 - Dinosaur diversity and associated faunas in the Cretaceous of South America, AP.TEM

Abstract

The recently published paper of Mestriner et al. (2022) challenged the idea that Silesauridae had a simple permanent ankylothecodont dentition, because their teeth spend considerable time attached to the jaws via a non-mineralised periodontal ligament (gomphosis) prior to being fused in place. This condition is known as "delayed ankylosis", with teeth passing through an extended stage in which the teeth are suspended in sockets by soft periodontal ligament, followed by posterior mineralisation and fusion to the jaws. The tooth attachment development in silesaurids could be a promising model to understand the ancestral condition in the sister group of dinosaurs and, possibly, crocodylians. Yet, a broader study of dental tissues is necessary to shed light on the evolution of tooth attachment in Archosauromorpha, testing if heterochrony is in fact responsible for the emergence of a permanent gomphosis stage in crocodylians and dinosaurs. In any case, a transition from ankylothecodonty to thecodonty appears to be an oversimplification of a more complex evolutionary history. In recent years, a lot of information regarding tooth attachment in early archosaurs, non-archosaurian archosauromorphs, and non-dinosaurian Dinosauromorpha entered the literature without the requered support of histological studies. For this PhD project, I thus aim to study the evolutionary history of the "Archosauromorph Tooth Attachment System" (ATAS) using traditional histology and micro-computed tomography of tooth-bearing bones, within the time frame of the past 300 million years, reconstructing the ancestral tooth attachment over major archosauromorph clades. The proposal will be the first histology-based research to sample a large variety of such reptiles, aiming to clarify the fundamental shifts from the ancestral ankylosis to the gomphosis of Crocodylomorpha and Dinosauria. Moreover, the study will shed light on the functionality of the dental ontogenetic phases in Archosauromorpha. (AU)