Exceptionally simple, rapidly replaced teeth in sauropod dinosaurs demonstrate a novel evolutionary strategy for herbivory in Late Jurassic ecosystems

Evolution of postcanine complexity in Gomphodontia (Therapsida: Cynodontia)

Gomphodonts form a Triassic radiation of small to medium-bodied (<0.5-2.5 m in length) quadrupedal cynodonts characterized by labiolingually expanded gomphodont postcanines. They were the dominant cynodont group in Middle and Late Triassic ecosystems from the Southern Hemisphere and the first predominantly herbivorous cynodonts to evolve. Gomphodonts were also the first therapsids to develop hypsodonty and a dentition with complex occlusal patterns, and their highly diagnostic upper and lower postcanines show many different morphologies. Here, we explored dental complexity in gomphodont cynodonts through time using geographic information system analysis and orientation patch count applied on 3D crown surfaces of upper and lower gomphodont postcanines belonging to 32 gomphodont taxa. This study reveals that the peak in postcanine complexity was reached early in the evolution of gomphodonts with the emergence in the Early Triassic of omnivorous or insectivorous forms with postcanines made of well-separated cusps and cingular cuspules. Traversodontids evolved simpler postcanines via coalescence of cusps into crests and the development of large occlusal basins, and the Middle Triassic radiation of traversodontids led to a sharp decrease in mean postcanine complexity. Simplification of the postcanines in traversodontids is interpreted as being related to a gradual increase in the consumption of plant material. Interestingly, the trend of insectivory/omnivory high postcanine complexity and herbivory low dental complexity in gomphodonts is opposite to the trend of dental complexity reported in some extant mammals, with omnivorous having low dental complexity and herbivorous higher. Postcanine complexity remained relatively stable throughout the evolution of traversodontids and only slightly diminished in the Late Triassic due to the presence of minute forms with particularly simple postcanines in the Rhaetian. The major phylogenetic diversity and taxonomic richness of Gomphodontia are represented in two periods of time: at the end of the Anisian, an age in which the postcanine complexity is simplifying, and at the early Carnian when the postcanine complexity in traversodontids, the only Gomphodontia represented, is stable.

Dental complexity and diet in amniotes: A meta-analysis

Tooth morphology is among the most well-studied indicators of ecology. For decades, researchers have examined the gross morphology and wear patterns of teeth as indicators of diet, and recent advances in scanning and computer analysis have allowed the development of new and more quantitative measures of tooth morphology. One of the most popular of these new methods is orientation patch count (OPC). OPC, a measure of surface complexity, was originally developed to distinguish the more complex tooth crowns of herbivores from the less complex tooth crowns of faunivores. OPC and a similar method derived from it, orientation patch count rotated (OPCR), have become commonplace in analyses of both modern and fossil amniote dietary ecology. The widespread use of these techniques makes it possible to now re-assess the utility of OPC and OPCR. Here, we undertake a comprehensive review of OPC(R) and diet and perform a meta-analysis to determine the overall difference in complexity between herbivores and faunivores. We find that the relationship between faunivore and herbivore OPC or OPCR values differs substantially across studies, and although some support the initial assessment of greater complexity in herbivores, others do not. Our meta-analysis does not support an overall pattern of greater complexity in herbivores than faunivores across terrestrial amniotes. It appears that the relationship of OPC or OPCR to diet is taxon-specific and dependent on the type of faunivory of the group in question, with insectivores often having values similar to herbivores. We suggest extreme caution in comparing OPC and OPCR values across studies and offer suggestions for how OPCR can constructively be used in future research.

Technical note: A freeware, equitable approach to dental topographic analysis

Dental topographic analysis has proved a valuable tool for quantifying dental morphology. Established workflows often use proprietary software for pre-processing dental surfaces, rendering the method expensive and inaccessible to many. This study explores the use of freeware pre-processing alternatives. We tested 4 decimation tools and 13 smoothing tools across 7 different freeware packages. Surfaces generated via proprietary software could not be replicated, but it was possible to obtain statistically similar measurements using freeware. Based on this investigation, we propose a freeware workflow for researchers to conduct dental topographic analysis, with the expectation that their results will be comparable to that obtained through proprietary methods.

Multi-proxy dentition analyses reveal niche partitioning between sympatric herbivorous dinosaurs

Dentitions of the sympatric herbivorous dinosaurs Hungarosaurus (Ankylosauria, Nodosauridae) and Mochlodon (Ornithopoda, Rhabdodontidae) (Santonian, Hungary) were analysed to investigate their dietary ecology, using several complementary methods-orientation patch count, tooth replacement rate, macrowear, tooth wear rate, traditional microwear, and dental microwear texture analysis (DMTA). Tooth formation time is similar in Hungarosaurus and Mochlodon, and traditional and DMTA microwear features suggest low-browsing habits for both taxa, consistent with their inferred stances and body sizes. However, Mochlodon possesses a novel adaptation for increasing dental durability: the dentine on the working side of the crown is double the thickness of that on the balancing side. Moreover, crown morphology, enamel thickness, macrowear orientation, and wear rate differ greatly between the two taxa. Consequently, these sympatric herbivores probably exploited plants of different toughness, implying dietary selectivity and niche partitioning. Hungarosaurus is inferred to have eaten softer vegetation, whereas Mochlodon likely fed on tougher material. Compared to the much heavier, quadrupedal Hungarosaurus, the bipedal Mochlodon wore down more than twice as much of its crown volume during the functional life of the tooth. This heavy tooth wear might correlate with more intensive food processing and, in turn, could reflect differences in the metabolic requirements of these animals.