Sauropod haemal arches: morphotypes, new classification and phylogenetic aspects

ALEJANDRO OTERO; PABLO A. GALLINA; JUAN I. CANALE; ALEJANDRO HALUZA

Historical Biology

Taylor & Francis

Lugar: Londres; Año: 2011 vol. 24 p. 243 - 256

0891-2963

Abstract. Sauropod haemal arches are caudal bony structures that traditionally have been incorporated into two different types observed in different anatomical views: Y-shaped (anterior view) and forked (lateral view). This research proposes a classification combining information observed in anterior and lateral views. Four types of ?Y-shaped? and six types of ?V-shaped? chevrons were recognized. Complete chevron series in some eusauropods allows the comparison of topological equivalent structures along the tail and also among taxa. A basal titanosaur from Argentina exhibits mid-caudal chevron morphology in which more than one cranial and caudal process is present, arising from the distal blades as well as from the proximal rami, a condition not seen before in a sauropod dinosaur. The morphological variability seen in sauropod chevrons along the tail is in close relationship with the development and distribution of M. caudofemoralis longus, as seen in extant crocodiles and as previously proposed for non-avian theropods and for caudal centra and transverse processes of sauropod dinosaurs. Two new characters related to middle chevrons are here proposed, in which the transitional morphology is described.