New theropod dinosaur from the late Cretaceous of Brazil improves abelisaurid diversity

Abstract

The Late Cretaceous Marília Formation (Bauru Group, Bauru Basin) is a geological unit that occurs on São Paulo, Minas Gerais, Goiás, and Mato Grosso do Sul states, Brazil. This formation consists predominantly of paleosols developed in a semiarid/arid environment and recent reappraisal of its formerly known members reduced its lithological composition and geographical distribution. Hence, the Marília Formation has a very sparse vertebrate fossil record without named species so far. In this contribution we describe a new abelisaurid theropod (Dinosauria) from this unit, namely Kurupi itaata gen. et sp. nov., discovery in the Municipality of Monte Alto, western São Paulo State. The holotype MPMA 27-0001/02 consists of three caudal vertebrae and the partial pelvic girdle. Kurupi itaata gen. et sp. nov. shares with other South American abelisaurids fused ischia and caudal vertebrae with long and laterodorsally oriented transverse processes, with fan-shaped distal ends. Autapomorphies of the new theropod include the variation of ∼15° of the inclination of the transverse process between the first (C1) and seventh (C7) caudal vertebra; C1 with anterolaterally projected triangular process placed below the proximodistal mid-portion of the transverse process, and a notch at the anterodistal portion of the transverse process, between a shelf-like process and the anterodistal corner of the transverse process; and anterior caudal vertebrae (present in C1 and C7, inferred in the others) with a cuneiform process, anterodorsally projected, located on the dorsal surface of the transverse process. Phylogenetic analysis recovered Kurupi itaata gen. et sp. nov. among abelisaurid theropods, but was nested in an unresolved massive polytomy of the entire clade. Taphonomic traits on the studied specimens corroborate previous proposals for the paleoenvironmental context of the Marília Formation. Kurupi itaata gen. et sp. nov. was about 5 m long, with a rigid tail, and cursorial locomotion as indicated by its a muscles attachment and bones anatomy. This new taxon contributes to the knowledge of the Maastrichtian continental fauna of Brazil and increases the diversity of medium-sized abelisaurids in western Gondwana.