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Detecting taxonomic and phylogenetic signals in equid cheek teeth: towards new palaeontological and archaeological proxies.

ABSTRACT: The Plio-Pleistocene evolution of Equus and the subsequent domestication of horses and donkeys remains poorly understood, due to the lack of phenotypic markers capable of tracing this evolutionary process in the palaeontological/archaeological record. Using images from 345 specimens, encompassing 15 extant taxa of equids, we quantified the occlusal enamel folding pattern in four mandibular cheek teeth with a single geometric morphometric protocol. We initially investigated the protocol accuracy by assigning each tooth to its correct anatomical position and taxonomic group. We then contrasted the phylogenetic signal present in each tooth shape with an exome-wide phylogeny from 10 extant equine species. We estimated the strength of the phylogenetic signal using a Brownian motion model of evolution with multivariate K statistic, and mapped the dental shape along the molecular phylogeny using an approach based on squared-change parsimony. We found clear evidence for the relevance of dental phenotypes to accurately discriminate all modern members of the genus Equus and capture their phylogenetic relationships. These results are valuable for both palaeontologists and zooarchaeologists exploring the spatial and temporal dynamics of the evolutionary history of the horse family, up to the latest domestication trajectories of horses and donkeys.

SUBMITTER: Cucchi T

PROVIDER: S-EPMC5414255 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Detecting taxonomic and phylogenetic signals in equid cheek teeth: towards new palaeontological and archaeological proxies.

Cucchi T T Mohaseb A A Peigné S S Debue K K Orlando L L Mashkour M M

Royal Society open science 20170405 4

The Plio-Pleistocene evolution of <i>Equus</i> and the subsequent domestication of horses and donkeys remains poorly understood, due to the lack of phenotypic markers capable of tracing this evolutionary process in the palaeontological/archaeological record. Using images from 345 specimens, encompassing 15 extant taxa of equids, we quantified the occlusal enamel folding pattern in four mandibular cheek teeth with a single geometric morphometric protocol. We initially investigated the protocol ac ...[more]

PMID: 28484618

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Project description:Background: It has been suggested that fissures of the occlusal surface of equine cheek teeth may develop into crown fractures. Objectives: To examine the evolution of fissures present on the occlusal surface of cheek teeth. Furthermore, to investigate the presence of a fissure as a risk factor for the development of a subsequent crown fracture. Study Design: Observational longitudinal study. Methods: Bi-annual dental examinations were performed on 36 horses for 3 years. Video-recordings were made to evaluate the evolution of detected fissures. The effect of possible predictors on the development of tooth fractures was investigated by regression analysis. Results: The evolution of 785 fissures (467 type 1a, 271 type 1b, 47 type 2) was recorded. Fissure characteristics were observed to remain unchanged, disappear, become longer, shorter, change in configuration or change in color. Partial crown fractures (22 maxillary, 50 mandibular) were recorded in 52 cheek teeth in 22/36 horses. Fifty-nine of these fractures evolved from previously observed fissures (24 type 1a, 29 type 1b, 6 type 2). All fissure types proved to be a significant risk factor for the development of a crown fracture (p < 0.001), with the highest odds for type 2 fissures (OR = 14.27; 95% CI = 4.88-41.71). Other significant risk factors were the time of follow-up (p < 0.001), mandibular teeth (p < 0.001) and the lingual side of a tooth (p < 0.001). All fractures were non-complicated. Main Limitations: Some horses were prematurely lost for follow-up, which perhaps influenced the results. A longer follow-up period would have also allowed an evaluation of the risk for pulp disease on the long term subsequent to partial crown fractures. Conclusions: The presence of a fissure of any type, mandibular cheek teeth, the lingual side of cheek teeth, and time of follow-up proved to be significant risk factors for development of a cheek tooth crown fracture. Type 2 fissures showed the highest odds followed by type 1b fissures. The observed partial crown fractures demonstrated a low clinical impact whereby no tooth showed signs of development of endodontal disease.

Project description:In the absence of independent observational data, ecologists and paleoecologists use proxies for the Eltonian niches of species (i.e., the resource or dietary axes of the niche). Some dietary proxies exploit the fact that mammalian teeth experience wear during mastication, due to both tooth-on-tooth and food-on-tooth interactions. The distribution and types of wear detectible at micro- and macroscales are highly correlated with the resource preferences of individuals and, in turn, species. Because methods that quantify the distribution of tooth wear (i.e., analytical tooth wear methods) do so by direct observation of facets and marks on the teeth of individual animals, dietary inferences derived from them are thought to be independent of the clade to which individuals belong. However, an assumption of clade or phylogenetic independence when making species-level dietary inferences may be misleading if phylogenetic niche conservatism is widespread among mammals. Herein, we test for phylogenetic signal in data from numerous analytical tooth wear studies, incorporating macrowear (i.e., mesowear) and microwear (i.e., low-magnification microwear and dental microwear texture analysis). Using two measures of phylogenetic signal, heritability (H2) and Pagel's λ, we find that analytical tooth wear data are not independent of phylogeny and failing to account for such nonindependence leads to overestimation of discriminability among species with different dietary preferences. We suggest that morphological traits inherited from ancestral clades (e.g., tooth shape) influence the ways in which the teeth wear during mastication and constrain the foods individuals of a species can effectively exploit. We do not suggest that tooth wear is simply phylogeny in disguise; the tooth wear of individuals and species likely varies within some range that is set by morphological constraints. We therefore recommend the use of phylogenetic comparative methods in studies of mammalian tooth wear, whenever possible.

Project description:Background: Ex vivo fracture models are frequently used in human dentistry to provide insights in the fracture mechanisms of teeth. Equine cheek teeth fractures are an important dental pathology, but there has been no research performed to examine the fracture resistance ex vivo. Objective: To evaluate the fracture resistance of equine cheek teeth and identify anatomical predictors that might influence fracture resistance in healthy teeth. It was further evaluated if the presence of a fissure caused a decrease in fracture resistance. Study design: Ex vivo experimental design. Methods: Individual cheek teeth were subjected to a compression load in a universal testing machine until fracture occurred. Testing was performed in two study groups. A first group of healthy cheek teeth was tested to examine anatomical predictors on fracture resistance. A second group comprised cheek teeth with occlusal fissures and an equal number of age- and size-matched fissure-free teeth as controls. The effect of possible predictors on fracture resistance was investigated by regression analysis. Results: In the first group, fracture resistance was significantly influenced by the location on the tooth where testing was performed in both maxillary (p < 0.001) and mandibular teeth (p < 0.001). Additional significantly associated factors were Triadan number in mandibular (p = 0.009) and the mesiodistal length of the occlusal surface of maxillary teeth (p = 0.01). Experimentally induced crown fractures that extended below the simulated bone level were more frequently associated with pulp horn exposure (p < 0.001). In the second group, significant lower fracture loads were recorded in teeth with fissures (mandibular p = 0.006; maxillary p < 0.001), compared to fissure-free teeth. Main limitations: This ex vivo model does not imitate the in vivo masticatory forces and lacks the shock-absorbing properties of the periodontal ligament. Conclusions: The methodology used in this study provides an ex vivo experimental set-up to test fracture resistance of equine cheek teeth enabling evidence-based research to examine the potentially weakening effects of tooth pathology and its treatments. Crown resistance to fracture differed along the occlusal surface of healthy equine cheek teeth, and the presence of fissures further decreased fracture resistance.

Dataset Information

Detecting taxonomic and phylogenetic signals in equid cheek teeth: towards new palaeontological and archaeological proxies.

Publications

Detecting taxonomic and phylogenetic signals in equid cheek teeth: towards new palaeontological and archaeological proxies.

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