Vertebral Comparative Anatomy and Morphological Differences in Anguine Lizards with a Special Reference to Pseudopus apodus.

The paper reports on the first detailed vertebral and rib morphology of anguine taxon Pseudopus apodus using micro-computed tomography. A comparison shows significant morphological differences of vertebrae of Pseudopus relative to those of Anguis and Ophisaurus. Usually, there are 55 presacral vertebrae, two sacral and 95-97 caudal vertebrae. Pseudopus apodus can be defined by 23 diagnostic features concerning the vertebral column. Although zygapophyseal articulation between atlas and axis is well developed in limbed anguid gerrhonotine lizards like Abronia or Barisia, it is absent in the extant representatives of the clade Anguinae, which are limbless. Thus, our study brings further support to the hypothesis about the complete reduction of this articulation in forms with reduced or absent limbs. Comparison of adult and juvenile morphology of vertebrae of P. apodus was also analysed. Heterochrony in the evolution of this taxon was previously confirmed by its skull morphology and it can be also documented on the basis of vertebrae. Our data suggest that a peramorphic heterochronic process played a role in the evolution of this largest extant anguine species. Geometric morphometric analyses revealed a pattern of high vertebral disparity among species. We found a clear separation of limbless forms in morphospace. Pseudopus apodus always clusters within Ophisaurus-species confirming molecular and some morphological phylogenies. Only the first tail vertebra shows a distinct difference to those of other anguids, which might be related to altered locomotion associated to the larger body size in this species. This article is protected by copyright. All rights reserved.