Ecological signal in the size and shape of marine amniote teeth

Abstract

Amniotes have been a major component of marine trophic chains from the beginning of the Triassic to present day, with hundreds of species. However, inferences of their (palaeo)ecology have mostly been qualitative, making it difficult to track how dietary niches have changed through time and across clades. Here, we tackle this issue by applying a novel geometric morphometric protocol to three-dimensional models of tooth crowns across a wide range of raptorial marine amniotes. Our results highlight the phenomenon of dental simplification and widespread convergence in marine amniotes, limiting the range of tooth crown morphologies. Importantly, we quantitatively demonstrate that tooth crown shape and size are strongly associated with diet, whereas crown surface complexity is not. The maximal range of tooth shapes in both mammals and reptiles is seen in medium-sized taxa; large crowns are simple and restricted to a fraction of the morphospace. We recognize four principal raptorial guilds within toothed marine amniotes (durophages, generalists, flesh cutters and flesh piercers). Moreover, even though all these feeding guilds have been convergently colonized over the last 200 Myr, a series of dental morphologies are unique to the Mesozoic period, probably reflecting a distinct ecosystem structure.

Armed to the teeth: the underestimated diversity in tooth shape in snakes and its relation to feeding behavior and diet.

“…We obtained one tooth per specimen, so 63 dentary teeth. Com-parisons between single teeth (from different bones) in phylogenetically diverse samples have demonstrated an ecological signal (Fischer et al, 2022), and the interspecific shape variation is larger than intraspecific variation in our sample, validating the use of one tooth per species (see Supplementary Material 2b).…”

“…Our sample is composed of adult or sub-adult specimens from museums (AMNH, MNHN, Jerusalem University) and private collections (details in Supplementary Material 1 & 2). While comparisons of the shape of the teeth from different bones show a significant ecological signal in some clades (Fischer et al, 2022) we here decided to focus only on the dentary bone to ensure functional homology. In snakes, the dentary is involved in capturing, restraining, and manipulating the prey; so, it endures loads related to both prey characteristics (e.g., hardness) and feeding behavior (e.g., holding a vigorous prey, extracting a snail from its shell).…”

“…Rounded teeth, for example, allow to crush hard prey items, they are tough, can barely bend and consequently are susceptible to fragmentation (Crofts et al, 2020). Because of their tight and reliable relationship with diet and their abundance in the fossil record, teeth have been suggested to be good indicators of past climate and paleoenvironments (e.g., Evans, 2013), and are used to make inferences on the ecology of extinct species (Bellwood et al, 2014;Evans & Pineda-Munoz, 2018;Fischer et al, 2022;Frederickson et al, 2018;Massare, 1987). By extension, tooth morphology could also be used to infer the feeding habits of secretive species that are sometimes only known from museum specimens, providing the link between tooth shape and food properties has been established.…”

Armed to the teeth: The underestimated diversity in tooth shape in snakes and its relation to feeding behavior and diet

“…Our sample is composed of adult or subadult specimens from museums (AMNH, MNHN, Jerusalem University) and private collections (details in Datas S1 and S2 ). While comparisons of the shape of the teeth from different bones show a significant ecological signal in some clades (Fischer et al, 2022 ) we here decided to focus only on the dentary bone to ensure functional homology. In snakes, the dentary is involved in capturing, restraining, and manipulating the prey; so, it endures loads related to both prey characteristics (e.g., hardness) and feeding behavior (e.g., holding vigorous prey, extracting a snail from its shell).…”

“…Rounded teeth, for example, allow to crush hard prey items, they are tough, can barely bend, and consequently are susceptible to fragmentation (Crofts et al, 2020 ). Because of their tight and reliable relationship with diet and their abundance in the fossil record, teeth have been suggested to be good indicators of past climate and paleoenvironments (e.g., Evans, 2013 ), and are used to make inferences on the ecology of extinct species (Bellwood et al, 2014 ; Evans & Pineda‐Munoz, 2018 ; Fischer et al, 2022 ; Frederickson et al, 2018 ; Massare, 1987 ). By extension, tooth morphology could also be used to infer the feeding habits of secretive species that are sometimes only known from museum specimens, providing the link between tooth shape and food properties has been established.…”