Osteologia de Melanosuchus niger (Crocodylia: Alligatoridae) e a evidência evolutiva

Abstract

RESUMO.-O objetivo foi realizar a descrição anatômica do esqueleto de Melanosuchus niger, com o intuito de contribuir com informações evolutivas sobre a espécie. Utilizaram-se três espécimes adultos de M. niger, com comprimento médio de 2,40m, provenientes da coleção biológica do Lapas-UFU. Na cintura peitoral, a escápula é maior do que o coracóide. Já nos elementos da cintura pelvina, o púbis não participa da formação do acetábulo, o contato com o ilío, ocorre por ligamentos, e sua articulação com o ísquio, permite movimentos dorso-ventrais. The objective was an anatomical description of the skeleton of Melanosuchus niger, in order to contribute with evolutionary information about the species. Three adult specimens of M. niger with an average length of 2.40m were used, originating from the biologic collection of Lapas-UFU. In the forelimb, the scapula is bigger than the coracoid. Regarding the hindlimbs, the pubic does not participate in the formation of the acetabulum; the contact with the ilium is made by ligaments, and its articulation with the rump allows dorsal-ventral movements. Regarding the forelimbs, the humerus is a stylopodium element, and the ulna and radius a zeugopodium element. The carpus exibits the ulnar-radial+intermedium fusion, fusion of the distal carpals 3+4+5, and the pisiform. It has five metacarpals, numbered lateromedially as metacarpal 1, 2, 3, 4, and 5. The phalangeal formula is 2:3:4:3:2. Regarding the pelvic limbs, the stylopodium is formed by the femur, and the zeugopodium by tibia and fibula. In tarsus has four bones: fusion of the intermedium+centrale, fibulare, distal tarsal 3, and distal tarsal 4. It has four long metatarsals I, II, III and IV, with metatarsal II and III being relatively longer than the others. Metatarsal V is a very small bone; the feet have the phalangeal formula 2:3:4:4. At the skull, the nasal opening is only the palatine bones, vomer, pterygoid, premaxilla and maxilla forming the bone structure of the secondary palate; the parietal bone is the only element on the cranial roof. In the pos-axial skeleton ist distinct pairs of ribs which articulate with the cervical, dorsal, lumbar, sacral and caudal vertebrae. The gastralia consists of seven rows of fine bone located between the pubic bone and caudal part of the sternum.

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

“…In M. niger we noted the presence of these sutures in the sacral and caudal ribs of recently hatched offspring. In skeletons of adult M. niger specimens, Vieira et al () described this occurrence only in the most cranial vertebrae, and reported that the most caudal region these sutures are not visible any more. Besides, other changes may be observed in the adult skeleton, such as the transverse process originating more ventrally to the zygapophysis, at the level of the neurocentral suture.…”

“…The ventral ribs in M. niger are little ossified projections that extend caudoventrally originating in the distal end of the dorsal ribs (Vieira et al, ). These structures are found in most of the living birds (Bellairs and Jenkin, ), and are also found in some theropod dinosaurs (Paul, ).…”

“…The presence of a median element in the pectoral waist is a plesiomorphic characteristic. In Crocodylia, including M. niger , this element is identified as the interclavicle (Rieppel, ; Vickaryous and Hall, ; Vieira et al, ); in Testudines, as the endoplastron (Lane, ); and in birds, as the furcal bone (Russell and Joffe, 1985). In the histological sections of the interclavicle of M. niger , in several development stages, it was possible to observe that this element was developed as an intramembranous structure (Fig.…”

“…It is worthy emphasizing that in M. niger, and in C. yacare (Lima et al, 2011c), the odontoid process is found cranially to the vertebral body showing a very clear ossification center separated from the body of the axis. In the M. niger skeletons that were prepared and analyzed in the current study, it was possible to clearly see the suture between these elements of the axis (Vieira et al, 2016a), which is a result of the individual development of the odontoid process, both in cartilage and bone development (Fig. 5).…”

“…For identification of cartilage condensations of postcranial skeleton and the ossification pattern, the terminology proposed by Burke and Alberch (1985), Shubin and Alberch (1986), M€ uller and Alberch (1990), and Bellairs and Kamal (1981) was used. Embryonic stages were determined using external morphological characteristics, following the methods proposed by Vieira et al (2011) and structures of skeleton description were based in studies of Mook (1921), Iordansky (1973), Romer (1956), and Vieira et al (2016a).…”