Cranial ontogenetic variation in Mapusaurus roseae (Dinosauria: Theropoda) and the probable role of heterochrony in carcharodontosaurid evolution

The carcharodontosaurid theropod Mapusaurus roseae (Cenomanian of Neuquén Province, Argentina) is represented by at least seven disarticulated individuals from a monospecific bonebed, all of different sizes and presumably different stages of maturity. We report a series of anatomical differences between repeated skull bones of Mapusaurus , which we interpret as produced by peramorphic heterochronic processes. The materials analyzed include maxillae, lacrimals, dentaries, and isolated teeth. Most of the differences were recorded in the maxilla, the most noticeable change being the reduction of the pneumaticity. We found that some of the synapomorphic characters of derived carcharodontosaurids appear to be the result of peramorphic heterochronies, as in the strongly ornamented facial bones, and the single opening in the anteroventral corner of the antorbital fossa in the maxilla.