Ontogeny of the Appendicular Skeleton inMelanosuchus niger(Crocodylia: Alligatoridae)

Abstract

The objective of the present study was to analyze chondrogenesis and the ossification pattern of the limbs of Melanosuchus niger in order to contribute with possible discussions on homology and the fusion pattern of autopodial elements and phylogeny. In the Reserva Extrativista do Lago Cuniã, Rondônia, Brazil, six nests were marked and two eggs removed from each nest at 24-hour intervals until hatching. Embryos were cleared using KOH; bone tissue was stained with alizarin red S and cartilage with Alcian blue. Routine staining with HE was also performed. In the pectoral girdle, the scapula showed ossification centers before the coracoid process. In the pelvic girdle, the ilium and the ischium were condensed as a single cartilage, although ossification took place through two separate centers, forming distinct elements in the adult. The pubis developed from an independent cartilaginous center with free end, which reflects its function in breathing. In the initial stages, the stylopodium and the zeugopodium developed from the condensation of a Y-shaped cartilage in the limbs, and differentiation of the primary axis and digital arch were observed. The greatest changes were observed in the mesopodia. In their evolution, Crocodylia underwent a vast reduction in the number of autopodial elements as a consequence of fusions and ossification of some elements. This study shows that the chondrogenesis and ossification sequences are dissociated. Moreover, the differences between M. niger and other species show clear variation in the patterns for these events in Alligatoridae.

Ossification Pattern in Forelimbs of the Siamese Crocodile (Crocodylus siamensis): Similarity in Ontogeny of Carpus Among Crocodylian Species

“…In stage 24 ( Fig. 3) distal carpals 3 1 4 1 5 fuse and they are clearly visible as a single structure similar to stage 15 in Melanosuchus niger (Vieira et al, 2016). In stage 25, the center of ossification arises already in the last element of the carpus-the pisiform.…”

“…The reason why is still questionable in avians (Xu and Mackem, 2013) as well as in crocodylians (this work). However, it seems that in extant crocodylians both chondrogenesis (M€ uller and Alberch, 1990) as well as ossification (Rieppel, 1993b;Lima et al, 2011;Vieira et al, 2016) have the similar patterns.…”

“…In stage 25, the center of ossification arises already in the last element of the carpus-the pisiform. Ossification of the distal carpal 3 1 4 1 5 is supposed to start after the beginning of ossification in the pisiform, as was described for the Caiman yacare (Lima et al, 2011;Vieira et al, 2016). The rest of distal carpals and centrale should be cartilaginous (M€ uller and Alberch, 1990).…”

“…The rest of distal carpals and centrale should be cartilaginous (M€ uller and Alberch, 1990). Generally, ossification starts earlier in metacarpals than in the carpus itself similarly to Alligator mississippiensis (Rieppel, 1993b), Caiman yacare (Lima et al, 2011), and Melanosuchus niger (Vieira et al, 2016). After stage 25, ossification occurs in the entire carpus as well as in all the digits and long bones and continues until the adulthood.…”

Ontogeny of the Postcranial Axial Skeleton of Melanosuchus niger (Crocodylia, Alligatoridae)

“…Other organogenesis aspects, including the postcranial axial skeleton, were reviewed by Ferguson (1985). Limb development in crocodilians was studied by Steiner (1934), M€ uller and Alberch (1990), and Vieira et al (2016b). Rieppel (1993) also analyzed the ossification pattern in the species A. missisipiensis.…”