Ontogeny of the plastron of the giant Amazon River turtle, Podocnemis expanse (Schweigger, 1812) (Testudines, Podocnemididae).

Podocnemis expanse, known popularly as the giant Amazon river turtle, is widely exploited. This makes specimens available for various studies, and we used this opportunity to investigate aspects of the development of the plastron. We examined several stages of pre- and post- hatching development in embryos and hatchlings collected starting from day 18 of natural incubation. Embryos and hatchlings were cleared and double stained for cartilage and bone. The epiplastron, endoplastron, hyoplastron, hypoplastron, xiphiplastron, and mesoplastron bones form the complete plastron of this turtle. In stage 16, bone centers become visible in most of the bones of the plastron. Alizarin Red stain retention indicated that the sequence of bone ossification is as follows: first the hyoplastron and the hypoplastron, then the endoplastron followed by the xiphiplastron, and lastly the mesoplastron. The epiplastron bone shows an ossification center only in stage 20. All these elements have independent ossification centers and join together only later. The plastron closes completely seven months after hatching.