Birds stand out from other egg-laying amniotes by producing relatively small numbers of large eggs with very short incubation periods (average 11-85 d). This aspect promotes high survivorship by limiting exposure to predation and environmental perturbation, allows for larger more fit young, and facilitates rapid attainment of adult size. Birds are living dinosaurs; their rapid development has been considered to reflect the primitive dinosaurian condition. Here, nonavian dinosaurian incubation periods in both small and large ornithischian taxa are empirically determined through growthline counts in embryonic teeth. Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles. Developmental and physiological constraints would have rendered tooth formation and incubation inherently slow in other dinosaur lineages and basal birds. The capacity to determine incubation periods in extinct egg-laying amniotes has implications for dinosaurian embryology, life history strategies, and survivorship across the Cretaceous-Paleogene mass extinction event.Dinosauria | teeth | embryology | Neornithes | extinction

Triceratops developed complex dental morphology, allowing it to become a dominant herbivore in the late Mesozoic era.

In most mammals and a rare few reptilian lineages the evolution of precise dental occlusion led to the capacity to form functional chewing surfaces due to pressures generated while feeding. The complex dental architectures of such teeth and the biomechanics of their self-wearing nature are poorly understood. Our research team composed of paleontologists, evolutionary biologists, and engineers have developed a protocol to: (1) determine the histological make-up of grinding dentitions in extant and fossil taxa; (2) ascertain wear-relevant material properties of the tissues; (3) determine how those properties relate to inter-tissue-biomechanics leading the dental functionality using a threedimensional Archard's wear model developed specifically for dental applications; (4) analyze those data in phylogenetic contexts to infer evolutionary patterns as they relate to feeding. Finally we discuss industrial applications that are emerging from our paleontologically-inspired research.

The cranial casques of modern cassowaries (Casuarius) have long intrigued researchers; however, in‐depth studies regarding their morphological variation are scarce. Through visual inspection, it has been recognized that casque variability exists between conspecifics. Understanding casque variation has both evolutionary and ecological importance. Although hypothesized to be targeted by selection, intraspecific casque variation has not been quantified previously. Through a large sample of C. casuarius (n = 103), we compared casque shape (lateral and rostral views) between sexes and between individuals from non‐overlapping geographical regions using two‐dimensional (2D) geometric morphometrics. We found no statistically significant differences between the casque shape of females and males and few substantial shape differences between individuals from different geographic areas. Much of the intraspecific variation within C. casuarius is due to casque asymmetries (77.5% rightward deviating, 20.7% leftward deviating, and 1.8% non‐deviating from the midline; n = 111), which explain the high variability of southern cassowary casque shape, particularly from the rostral aspect. Finally, we discuss how our non‐significant findings implicate social selection theory, and we identify the benefits of quantifying such variation for further elucidating casque function(s) and the social biology of cassowaries.

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Many vertebrates (e.g., chameleons, bovids, hornbills) possess cranial elaborations; however, studies investigating the morphological variation of these structures are rare. For example, the conspicuous cranial casques of modern cassowaries have long been hypothesized to perform a number of functions (e.g., physical ramming, vocalization, thermoregulation, visual display) despite an absence of quantitative methodologies to determine whether ornament shape variation within the group aligns with proposed biological roles. In order to fill this data gap, we compared casque shape between sexes and native geographic regions in a large sample of adult southern cassowaries (Casuarius casuarius; n = 103). We quantified casque shape in lateral and rostral views using elliptical Fourier analysis, ordinated the shape data, and used multivariate analysis of variance to address specific comparisons. We hypothesized that casques would be sexually dimorphic and regionally specific, consistent with proposed display functions. However, we found no significant differences in casque shape between female and male C. casuariusand few significant shape differences between individuals from specific geographical areas. Much of the intraspecific casque shape variation, particularly from the rostral aspect, is due to asymmetries across the midline. In our sample, casques were 77.5% rightward deviating, 20.7% leftward deviating, and 1.8% non‐deviating. Although it is unclear if this directional casque asymmetry provides a functional advantage, future studies may elucidate this feature. Altogether, two‐dimensional shape analysis does not support a role for the casque as a de factodiscriminator between sexes nor regional sub‐populations in C. casuarius. These findings stand in contrast to those of other ornamented birds (e.g., Numida meleagris) and potentially point towards alternative biological functions.

No abstract

During gnathostome diversification modifications to dental form and mineralized tissues (enamel, dentines, and cementum) facilitated the exploitation of novel food resources, leading to the occupation of an unprecedented variety of ecological trophic niches. Generally, it has been assumed that the intra‐tissue biomechanics of these constituents had little bearing on whole‐tooth functionality, aside from mammalian enamel in occluding dentitions. Many mammals, for example, possess teeth that self‐wear to a functional topography with a diversity of derived tissues—some which possess unique mechanical attributes to resist wear and fracture. Here we formally test the hypothesis that gnathostome dental tissue material properties were static prior to the cladogenesis of Mammalia. Hardness (a proxy for wear resistance) and elastic modulus (proxy for structural rigidity and relevant to whole tooth rigidity) were tested using two standardized material science techniques, microindentation and nanoindentation, as well as a novel approach for quantifying fracture propagation patterns from indentation cracks. These data were analyzed in an ecological context using modern phylogenetic comparative methods. The results show these material properties to be highly variable within and between major groups of gnathostomes, with enamel and orthodentine hardnesses ranging from ~2.1 gigapascals (GPa) to ~6.1 GPa and ~0.5 GPa to ~1.5 Gpa, respectively. Elastic modulus values measured spanned ~34.6 GPa to ~112.5 Gpa in enamel, and from ~15.6 GPa to ~33.4 GPa in orthodentine. Lissamphibia display the lowest hardness and elastic modulus values of both enamel and orthodentine while the higher hardness and elastic modulus values are found in specific taxa from chondrichthyans, mammals, and some squamates. Aside from enamel hardness, there is no significant relationship between most material properties and assigned dietary classes. An ancillary goal of this work is also to glean initial insights about how dental attributes for non‐mammalian and mammalian taxa more generally may contribute to whole‐tooth form, function, performance, and diet. Clade‐specific complex fracture patterns in the enamels of mammals and chondrichthyans, for example, show that gnathostome lineages independently evolved traits that function to control fracture and minimize damage associated with catastrophic failure. Overall, this study suggests that selection operated at the tissue level primarily in enamel to bring about shifts in whole‐tooth functionality across Gnathostomata.Support or Funding InformationNSF EAR 0959029 awarded to Gregory M EricksonSigma Xi GIAR awarded to David Ian KayThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.