La familia Atoposauridae: una aproximación a la historia de los cocodrilos enanos

Abstract

The Family Atoposauridae: an Approach to the History of Dwarf Crocodiles
The family Atoposaridae consists of four taxa of dwarf crocodiles whose paleogeographic distribution and fossil record are restricted to the Upper Jurassic-Lower Cretaceous of Western Europe (Portugal, England, Spain, France and Germany). The recent phylogenetic approaches to the family placed it at the base of the Neosuchia dade, far from being considered as the sister group of the Eusuchia. Some metric characteristic shared by most of the Atoposauridae (length of the ulna with respect to the humerus and radius, length of the tibia with respect to the femur, body size etc.) are the primitive condition found in the base of the crocodylomorphs. Thinking about the metric features, we evaluate a character associated to the ecological niche (the home range) regarding the body size of dwarf crocodiles. Two hypotheses that have been compared with the phylogenetic proposal of the crocodylomorphs, are suggested: 1) the Atoposauridae keeps the primitive home range, as a simplesiomorphy within the crocodylomorpha 2) The Atoposauridae occupied a vacant space in a specific faunistical assemblaje, being in this case a convergent home range (due to reversal). The second hypothesis is preferred (more parsimonious), noticing that the distribution of the character-states in the home range require less a priori assumptions. A possible phenomenon of competition between lizards and Atoposaurs is also suggested, due to an hypothetical correlation of sizes, which would occur in the Western Europe outcrops (smallest lizards and Atoposaurs are together associated in France and Germany, and the same for the largest ones in Portugal, England and Spain).