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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Symposium: Mechanisms of whole dentition patterning in extant and extinct amniotes 4

Room: Salon B   4:30 pm–6:00 pm

Moderator(s): J. Richman, L. Hlusko, & T. Grieco
DEN4-1  4:30 pm  Tissue-level analysis of ziphodont teeth in terrestrial animals. Brink K.S.*, University of British Columbia; Reisz R.R., University of Toronto Mississauga
Abstract: Tooth morphology and development can provide valuable insights into the feeding behaviour and evolution of extinct organisms. A predominant tooth morphology in terrestrial carnivorous animals over the past 290 million years is ziphodont. These teeth are labio-lingually compressed, distally recurved, and have mesial and distal carinae bearing denticles. Known today only in varanid lizards, ziphodonty is much more pervasive in the fossil record. The first occurrence of ziphodonty is in the Early Permian non-mammalian synapsid Dimetrodon and several groups of therapsids, and convergently became widespread in archosaurs, especially theropod dinosaurs. This study aims to document the structural differences in tooth tissues of ziphodont teeth of different terrestrial carnivores through time. The teeth of synapsids, phytosaurs, crocodilians, dinosaurs, and modern varanid lizards were examined histologically. Results show that some teeth considered as ziphodont based on the external morphology of the denticles are in fact ornamented with serrations composed of enamel only, as in some species of Dimetrodon and the canines of Smilodon. True denticles possess a dentine core with an enamel cap, thereby increasing the surface area available for enamel and strengthening the tooth. Among those taxa with teeth bearing true denticles, the internal structure of the teeth differs. Theropod dinosaurs have specialized structures composed of globular and sclerotic dentine between each denticle, which are absent in synapsids, phytosaurs, and varanid lizards. These structures, previously hypothesized to prevent tooth breakage, are now suggested to have first evolved to shape and maintain the characteristic denticles through the life of the tooth. The convergent evolution of the ziphodont tooth morphology in several taxonomic groups reveals the efficiency of ziphodont teeth in facilitating a carnivorous lifestyle.

DEN4-2  5:00 pm  Morphological integration of deciduous and permanent dentitions in carnivorans. Tomiya S.*, Field Museum of Natural History; Reuter D.M., University of Oregon; Sulser R.B., University of Chicago
Abstract: In many mammals, the milk teeth are transient yet crucial structures for processing food during their early stages of life. Selection on the morphology of milk teeth may have important influence on the evolution of replacement teeth through shared developmental pathways. We investigated the patterns of morphological integration of deciduous and permanent dentitions at macroevolutionary scales, focusing on the order Carnivora. We collected ecomorphological data (based on linear measurements) for the milk (DP3-4/dp3-4) and replacement teeth (P4-M1/p4-m1) of 49 extant species representing eight families. Analyses of this data set have led to four key observations: (1) the morphology of carnivoran milk teeth, while diverse, is significantly less disparate than that of replacement teeth, supporting earlier, qualitative observations by Leche (1909, 1915); (2) nevertheless, the sizes and, to lesser extent, shapes of milk teeth are significantly correlated with those of their functional counterparts in the permanent dentition among all the species in the data set; (3) milk-tooth morphology preserves relatively deep (tribe- to family-level) phylogenetic relationships more faithfully than replacement-tooth morphology; (4) different families tend to show characteristic deciduous-to-permanent transitions in the morphospace. We interpret these results to suggest that milk teeth evolve in similar directions to replacement teeth but at slower rates. Overall, our findings are consistent with the hypothesis that morphological evolution of deciduous dentition is an important catalyst for that of permanent dentition at relatively fine phylogenetic scales. Dramatic evolutionary transformation of replacement teeth, however, appears to require additional modification of the shared developmental pathway between deciduous and permanent dentition.

DEN4-3  5:30 pm  Voles, molars, and molecules: integrating quantitative morphology, genetics, and evo-devo to study evolutionary processes. Burroughs R.W.*, University of Chicago
Abstract: The innate biases of the fossil record dictate that certain anatomical systems offer unique insight into the process of evolution. Dentition is one such anatomical system. Teeth are complex anatomical structures displaying a wide-range of ecomorphologies, they are relatively abundant in the fossil record, and they have a long history of detailed study. The intersection of the genetic and developmental mechanisms underlying tooth development, and the evolutionary history of those mechanisms, provide opportunities to explore mechanistic and philosophical/conceptual questions within evolutionary biology. For example, dissecting the conceptual framework of how we integrate mechanisms of dental patterning and their evolutionary history with material data from the fossil record highlights areas where modern evolutionary constructs conflict or resolve one another. I describe an empirical system focused on a proposed anagenetic change in the dental morphology of the Sagebrush Vole, Lemmiscus curtatus. This study integrates quantitative morphology, phylogeography, quantitative genetics, and evo-devo to understand how dental patterning within L. curtatus evolved over time. Beyond reconstructing the evolution of dentition in L. curtatus, I also explore how the paradigms of emergent morphology (developmental biology) and transformational morphology (paleontology) may inform and/or conflict with one another. For example, can developmental mechanisms cause true convergent evolution, i.e., the origination of the same morphological feature, from the same genetic architecture, in separate populations or species? Because a detailed understanding of the evolutionary history and genetic architecture for dental patterning is available for Lemmiscus, the system offers the opportunity to synthesize these micro- and macroeolutionary phenomena.

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