The relationship between diet and tooth complexity in living dentigerous saurians

Abstract

Living saurian reptiles exhibit a wide range of diets, from carnivores to strict herbivores. Previous research suggests that the tooth shape in some lizard clades correlates with diet, but this has not been tested using quantitative methods. I investigated the relationship between phenotypic tooth complexity and diet in living reptiles by examining the entire dentary tooth row in over 80 specimens comprising all major dentigerous saurian clades. I quantified dental complexity using orientation patch count rotated (OPCR), which discriminates diet in living and extinct mammals, where OPCR-values increase with the proportion of dietary plant matter. OPCR was calculated from high-resolution CT-scans, and I standardized OPCR-values by the total number of teeth to account for differences in tooth count across taxa. In contrast with extant mammals, there appears to be greater overlap in tooth complexity values across dietary groups because multicusped teeth characterize herbivores, omnivores, and insectivores, and because herbivorous skinks have relatively simple teeth. In particular, insectivorous lizards have dental complexities that are very similar to omnivores. Regardless, OPCR-values for animals that consume significant amounts of plant material are higher than those of carnivores, with herbivores having the highest average dental complexity. These results suggest reptilian tooth complexity is related to diet, similar to extinct and extant mammals, although phylogenetic history also plays a measurable role in dental complexity. This has implications for extinct amniotes that display a dramatic range of tooth morphologies, many with no modern analogs, which inhibits detailed dietary reconstructions. These data demonstrate that OPCR, when combined with additional morphological data, has the potential to be used to reconstruct the diet of extinct amniotes. J. Morphol. 278:500-522, 2017. © 2017 Wiley Periodicals, Inc.

Multiple evolutionary origins and losses of tooth complexity in squamates

“…Despite the lack of a similar large-scale phylogenetic assessment, studies suggest relatively few mammalian lineages experienced reversals towards reduced tooth complexity (including complete tooth loss) 10,11,29 , and even fewer re-evolved cusps once lost 30 . We confirm here across the whole of Squamata the link noted previously between plant-eating squamates and a specialized, typically more complex dentition 20 , similar to those hypothesized or discovered for early tetrapods 13 , crocodyliforms 14 , and mammals 4 . The generality of these findings suggests similar ecological and dietary selective pressures for complex dental phenotypes operate across all tetrapods.…”

“…A regularized phylogenetic multivariate analysis of variance (MANOVA) on principal component scores confirm statistically significant differences between diets overall ( p -value = 0.001; Fig.1c) with negligible phylogenetic signal in the model’s residuals (Pagel’s λ = 0.03). Herbivore teeth differ from both the insectivorous and omnivorous morphospace regions (Fig.1c, Extended Data Table 2), similarly to observations from mammals and saurians 4,20 . Furthermore, we find support for shifts in the rate of evolution of tooth shape outline independent of cusp number among the 75 species examined (log Bayes Factor = 319), with particularly high rates characterising Iguanidae (Extended Data Figure 2).…”

“…To understand the repeated origin of dental-dietary adaptations and their role in vertebrate evolution, we investigated tooth complexity evolution in squamates, the largest tetrapod radiation. Squamata is recognized for including species bearing complex multicuspid teeth within heterodont dentitions 20 , and squamate ecology spans a broad range of past and present niches. Squamates express dental marker genes broadly conserved across vertebrates 18 , with varying patterns of localization and expression compared to mammals, and structures at least partially homologous to mammalian enamel knots (non-proliferative signalling centres of ectodermal cells) determine tooth shape in some squamate clades 19,21,22 .…”

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

“…A strictly carnivorous diet has been proposed for derived troodontids with folidont teeth (Zanno and Makovicky, 2011;Torices et al, 2018), yet a folidont dentition appears to be characteristic of herbivorous and/or omnivorous extant animals. Among lepidosaurs, small constricted crowns with a low number of relatively large mesial and distal denticles, as seen in therizinosaurids and derived troodontids, is clearly present in herbivores such as Sauromalus and Iguana (Melstrom, 2017).…”

“…The heterodont dentition displayed by some coelurosaurs has been interpreted as an indicator of a dietary shift from faunivory to herbivory or omnivory (Zanno and Makovicky, 2011). A heterodont dentition with simple conical teeth in the mesial portion of the jaws, in fact, characterizes non-carnivorous lepidosaurs such as iguanids (Barrett, 2000;Melstrom, 2017).…”