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

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 2:3:4:3:2). 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.

Description of embryonic stages in Melanosuchus niger(Spix, 1825) (Crocodylia: Alligatoridae)

The determination of embryonic stages is very useful in comparative and evolutionary anatomy, experimentalresearch and ecological studies. Although tables of development stages already exist for some crocodilianspecies, no table has yet been published for Melanosuchus niger. Therefore, the aim of this work is to monitorthe development of this species of Alligatoridae and characterize its stages based on the main morphologicaltransformations the embryo undergoes during the incubation process. Under natural conditions, two sampleswere collected daily in the Lake Cuniã Extractive Reserve in Rondônia, Brazil, making a total of 186 eggs.The incubation period was 90 days at an ambient temperature varying from 25.2 to 31.7 °C. We established24 embryonic stages between the formation of the pharyngeal arch and hatching. Primordia for the sensoryorgans and somites were observed in the early stages. The buds of the pelvic and thoracic limbs emergedsimultaneously, also in the early stages. An analysis of these structures showed evidence of considerableevolutionary modifications when compared with embryos of different species. In stage 12 we observed subtlepigmentation in the region of the head and, in stage 25, the pigmentation and striped pattern were typical ofthe newly hatched specimen. The eyetooth was visible in stage 18, disappearing within the first few weeks afterhatching. The vitellus was completely absorbed in the penultimate stage. Direct comparisons of the table ofembryonic stages were made between M. niger and other crocodilian taxa, and the main differences identifiedwere chronological variations.

Ontogeny of scleral ossicles of giant amazon river turtles Podocnemis expansa Schweigger, 1812(Testudines, Podocnemididae)

Scleral ossicles are bony plates in the eye sockets of many vertebrates, whose morphology, development and position differ in distinct groups of vertebrates. To investigate the development, number, shape and arrangementof the scleral ossicles of Podocnemis expansa, 15 embryos were collected, starting from the 18th day of natural incubation and 16 adult specimens belonging to the LAPAS collection, whose eye sockets were removed. The embryos and eye sockets were subjected to bone diaphanization and staining techniques. The scleral ossicles in this species of Testudines were found to be quadrangular, varying in number from 10 to 13, with 11.25 ± 0.93 in the right eye and 11.43 ± 0.81 in the left eye, occupying a position close to the anterior edge of the sclera. The ossicles develop intramembranously and begin to present ossification centers at stage 21, with ten ossification centers in the right eye and eight in the left eye. In stage 23, all the ossicles of the sclerotic ring increase in length and approach the adjacent ossicles, forming a ring. In stage 26, the scleral ossiclesare already arranged in their definitive form.