Analysis of the longitudinal variation in the axial skeleton of Serpentes (Squamata) using geometric morphometrics techniques

Author(s)

Fabio de Andrade Machado

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2010-11-29

Examining board members

Hussam El Dine Zaher; Tiana Kohlsdorf; Luis Fábio Silveira

• Advisor: Hussam El Dine Zaher

Abstract

Snakes are an extremely successful group of vertebrates. Despite their apparent morphological simplicity, they managed to occupy a great diversity of habitats. The axial skeleton of snakes has relationships with various aspects of their life history that could have had direct influence in the evolutionary success of these animals. Furthermore, the shape of the vertebrae is recognized as being of taxonomic value, a fact that elicits a special interest, since the majority of the fossil record of this group is composed of disarticulated vertebral elements. Geometric morphometrics methods use information about the position of landmarks in two or three dimensions, placed over anatomical structures for statistical analyses of shape variation. This group of techniques has been shown to identify shape variations that would not be diagnosed through traditional methods. The present work sought to evaluate the vertebrae of the pre-cloacal skeleton of Serpentes in the context of geometric morphometrics, evaluating the influences of ecology and phylogeny over the shape of these structures, and also investigating the taxonomic usefulness of vertebral shape. Results presented here suggest the existence of a patterning of the axial skeleton that is conserved throughout the evolutionary history of the group. An ecomorphological analysis demonstrates that the vertebral shape is highly influenced by life-history traits such as fossoriality and constriction. Despite the absence of phylogenetic signal, analyzes of classification of dissociated vertebral elements show that the vertebral shape can be used to diagnose isolated vertebrae. These results reiterate the necessity of performing studies of longitudinal variation in order to correctly identify fossil material associated with this group. (AU)

• FAPESP's process: 07/52144-5 - Analysis of the longitudinal variation of the axial skeleton in serpents (Squamata) using tools of geometric mophometry
• Grantee: Fábio de Andrade Machado
• Support Opportunities: Scholarships in Brazil - Master