Skeletogenesis of the pelvic girdle and members in embryos of Caiman yacare (Crocodylia: Alligatoridae)

Abstract

Caiman yacare embryos were collected and subjected to the bone cleared and Alizarin staining to analyze the ontogenic patterns of the skeletal ossification of the pelvic girdle and members. Ossification of C. yacare pelvis begins at 36 days of incubation. The femur, tibia and fibula present simultaneous stain retention at 30 days. It has four tarsal bones, the calcaneus, the talus, distal III and distal IV. Their ossification starts with the calcaneus from the 40th day of incubation, followed by the talus. At 54 days, the distal tarsal IV is conspicuous, as is the outline of the distal III. Each foot has five metatarsi (MT) and 13 phalanges (phalangeal formula 2:3:4:4). Ossification of the metatarsi begins at 36 days and follows the sequence MTI=MTII=MTIII=MTIV>MTV. The first phalanges begin the ossification process on the 36th day and continue up to the last day of incubation. The sequence of ossification of the proximal phalanges is PPI=PPII=PPIII>PPIV, while that of the medial phalanges is MPII> MPpIII>MDpIII>MPpIV>MDpIV and that of the distal phalanges is DPI>DPII>DPIII>DPIV, and the ontogenic pattern of the bones of the pelvic girdle and members of C. yacare differs from that of other reptiles, albeit with a few similarities. INTRODUCTION Vertebrates have a unique skeleton that is composed of a set of plastic structures that are able to grow, adapt and repair themselves due to the wide morphological and architectural diversity of the skeletal tissue (White et al., 2003; Hildebrand and Goslow, 2006). This trait is conservative to the point that its general pattern displays in the tetrapods lineages. Its evolutionary pattern also enables this structure to respond to the particular habits of each species (Withers, 1992). In some reptiles, the ossification patterns are well known. Several anatomical studies of the skeletons of reptiles have been conducted, as demonstrated by the.