Trees from Teeth: Investigating the Potential of Dental Microstructure for Phylogeny Reconstruction
Open AccessDespite decades of research, the evolutionary relationships among hominin fossils remain poorly understood. One reason for this is that uncovering the phylogeny of fossil taxa depends on hard tissue morphology and whether morphological traits carry a phylogenetic signal that is strong enough to be detected among the “noise” of recent functional adaptation. Characters chosen for a phylogenetic analysis need to be from morphological regions that are well represented in the hominin fossil record, and there must be evidence that the morphology is likely to have a strong phylogenetic signal. Given these criteria, the dentition is an obvious region to investigate. Teeth comprise the majority of the fossil record and teeth are unaffected by remodeling, so that once they are formed they are only subject to wear and attrition. Most importantly, teeth preserve a record of growth in the form of incremental features found in the microstructure of the hard tissues that compose a tooth. These traits are understood to be homologous across mammalian taxa and their use in phylogenetic hypotheses remains untested. This project investigates dental microstructure traits (daily secretion rate, decussation factor, striae of Retzius-EDJ angle, enamel prism-EDJ angle, cuspal enamel thickness, periodicity, total number of striae of Retzius, lateral formation time, cuspal formation time, cusp-specific formation time, enamel extension rate) in a large sample of extant primates which includes Catarrhini (apes and Old World Monkeys), Platyrhinni (New World Monkeys), and Strepsirrhini (Lemurs, Lorises, and Galagos) to determine whether these traits can reconstruct the primate molecular consensus phylogeny. This project uses new morphological data and combines phylogenetic comparative methods to evaluate these traits within a phylogenetic context. The aims of the project are 1) Evaluate and describe enamel growth in non-hominoid primates, 2) Establish the proportion of inter- to intraspecific variation in dental microstructure traits in the apes, 3) Test whether there is a shared pattern of phylogenetic signal in these traits, 4) Determine whether these traits can reconstruct phylogeny. The enamel growth patterns observed throughout the non-hominoid primates suggest that they retain the ancestral state of enamel secretion, however there are other aspects of enamel growth that were found across taxa that correspond with what is known about growth and life history in individual primates. For example, the Colobinae taxa, which are largely leaf-eating monkeys, were found to have rapid enamel formation timed. This rapid growth reflects their early dental eruption schedule. Enamel growth patterns observed in non-hominoids are not shared with patterns observed in the great apes. Dental microstructure traits had a higher proportion of inter- to intraspecific variation, which is important for character selection in a phylogenetic analysis. These traits were found to have high phylogenetic signal. Body mass can distort the signal in morphological traits, and thus body mass and tooth size were accounted for, and once tested, traits that were measured in the lateral region of enamel showed high signal. Ultimately, these traits did not reconstruct the primate phylogeny. In several analyses, the traits did cluster taxa based on the taxonomic level of family, suggesting these traits may be useful for studies of higher taxonomy.
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