Geometric morphometrics of madtsoiid snake vertebrae: assessing intracolumnar position and taxonomic identity

GÓMEZ, R.O.; SOTO, E.M.

Trelew

Congreso; XXIII Jornadas Argentinas de Paleontología de Vertebrados; 2007

Museo Paleontológico Egidio Feruglio

The taxonomy of fossil snakes has been usually based on qualitative and subtle differences of shape, proportion, and location of traits on vertebrae of the same region of the column; hence, determination of the intracolumnar position of isolated vertebrae is the first step leading to taxonomic comparisons. With this aim in mind, we applied geometric morphometric techniques to a supposedly multispecific assemblage of sixty-five madtsoiid precloacal vertebrae from the Upper Cretaceous of Patagonia, which we previously had separated into six putative monospecific samples. To determine the position of the vertebrae, as morphometric model we used a boid vertebral column that was partitioned into equal sized sections, each serving as an identification sample. The madtsoiid vertebrae were digitized and iteratively superimposed with the boid sections through Generalized Procrustes Analysis (GPA). Once the position of each element was determined, we subjected vertebrae of the same portion of the column to GPA and discriminate function analysis to test the taxonomic identity of each sample. Results from analyses to determine intracolumnar position showed significant morphological differences among identification samples and cross-validation values between 72% and 100% accuracy in identification of control individuals, and a high agreement of GPA and traditional assignments of the fossil vertebrae. Additionally, the results from taxonomic identity analyses showed re-classification values of 100% correct attributions for each group. It is suggested that these techniques could provide an excellent method for the determination of intracolumnar position and a test for taxonomic assignments of fossil snake vertebrae.