Designed by Paul Smith 2006. This website is copyrighted by law.
Material contained herewith may not be used without the prior written permission of FAUNA Paraguay.
Photographs on this web-site were taken by
Paul Smith, Hemme Batjes, Regis Nossent,
Alberto Esquivel, Arne Lesterhuis, Josť Luis Cartes, Rebecca Zarza and Hugo del Castillo and are used with their permission.
The Infraorder Archosauria contains extinct groups such as the dinosaurs and pterosaurs. The only living representatives are the Order Crocodylia (see below), though recent molecular and genetic evidence suggests that the birds may also belong in this infraorder. Archosaurians are an ancient lineage.
The upper and lower temporal fossae are present and both arches are complete. There is parietal foramen and the supratemporal bone is absent. The external nares (nostrils) are located close together near the midline of the snout. A well-developed lachrymal separates the pre-orbital opening from the orbit. The quadrate is large and fixed. There are no palatal teeth, but thecodont teeth are present in the maxilla and premaxilla. A secondary palate is present. The vertebrae are holochordal with no intercentra. The hind limbs are enlarged and in many extinct groups (and the extant birds) there is a tendency towards bipedalism, not exhibited by the modern day Crocodylia.

The Paraguayan Crocodylia are represented by a single family, the Alligatoridae (see below). The skull is broad and flattened posteriorly with a long snout and is usually sculptured. The upper temporal fossa is small. The secondary hard palate is well-developed with choanae located far back. The maxillae, palatines and pterygoids all meet in the midline of the palate enclosing the narial canal. Vertebrae are procoelous and the sternum is cartilaginous. Abdominal ribs are present and the pubis is excluded from the acetabulum. Teeth are conical, numerous and restricted to the margins of the jaws. . An interclavicle is present but there is no clavicle. Presacral vertebrae number 23 or 24. Heart includes two atria and two separate ventricles. A fleshy transverse fold is present on the posterior margin of the tongue and on the palate. A diaphragm separates the thoracic and abdominal cavities. Dermal armour is present. Forelimbs shorter than hindlimbs and digits number 4/5. Cloacal opening is longitudinal and males possess a single protrusible penis. They are oviparous, laying shelled eggs in a nest guarded by the female. Two pairs of scent glands are present, one on the throat and one on the cloacal lips.

Three species in this family occur in Paraguay, classified into two genera Caiman and Paleosuchus. Compared to other Crocodylia the snout is not particularly elongated. The fourth tooth of the lower jaw fits into a pit on the upper jaw so that it is not visible when the jaws are closed. The fourth maxillary tooth is the largest and the lower tooth row sits inside the upper tooth row. Horns of the hyoid are vertical and spread caudally. Dermal plates present both dorsally and ventrally.

Fouquette MJ (unpublished) - Synopsis of Recent Reptiles to Genus - Arizona University
Whitfield P Ed.
1984  - Longman Illustrated Animal Encyclopedia - Guild Publishing, London.