Correlation structure of the cheek teeth enamel crown patterns in the genus Equus (Mammalia: Equidae): an analysis by geometric morphometrics with outline points

Abstract

Correlation structure of the cheek teeth enamel crown patterns i n he genus Equus was studied by means of geometric morphometrics using outline points as descriptors to reveal the levels of morphological integration of the toothrow elements. Crown patterns in 34 upper and 31 lower toothrows (260 teeth in total) from 30 horse species were analyzed, the respective sets of 70 to 150 outline points were processed using the elliptic Fourier, principal component, and cluster analyses. The most correlated were shown to be the serial homologous crown elements within premolar and molar toothrow portions and less across the total toothrow. Correlation between occluding upper and lower teeth was shown to be low. Such correlation structure allowed identifying several levels of integration of the cheek teeth crown patterns in the genus Equus. A possibility of considering the serial homologous crown elements as the modules of the evolutionary developmental structure of the equine toothrows was discussed. Certain perspectives of similar studies in the specialized artiodactyles were emphasized.