Skeletogenesis of the pectoral girdle and forelimbs in embryos of Caiman yacare (Daudin, 1802) (Crocodylia, Alligatoridae)

ABSTRACT

Embryos of Caiman yacare were collected and subjected to the bone clearing and staining protocol in orderto analyze the ontogenetic patterns of ossification of the pectoral girdle and forelimb skeleton. The osseousstructure of the girdle and forelimbs of C. yacare begins to ossify starting at 30 days of incubation, withthe presence of dye retention in the scapula, coracoids, humerus, radius and ulna bones. During embryonicdevelopment, the autopodio of C. yacare has four bones in the carpus, the radial, ulnar, pisiform and carpaldistal 4+5 bone. Their ossification begins at 39 days of incubation with the radial, followed by the ulnar, and at54 days, the pisiform and the distal carpal 4 + 5. Each mesopodio has 5 metacarpi and are present 15 phalanges,two in digits I and V, three in digits II and IV, and four in digit III (phalangeal formula 23432). Ossificationof the metacarpi starts at 27 days of incubation, following the sequence MCII=MCIII=MCIV>MCI>MCV.The first phalanges begin the process of ossification on day 36, continuing up to the last day of incubation.The sequence of ossification of the proximal phalanges is PPI=PPII=PPIII>PPIV=PPV, that of the medialphalanges is MPII>MPpIII>MPdIII>MPIV, and that of the distal phalanges is DPI>DPII>DPIII>DPV>DPIV.The ontogenetic pattern of the bones of the forepaw of C. yacare generally differs from that of other reptiles,although there are some similarities.