EVOLUTION OF TITANOSAURID SAUROPODS. 1:PHYLOGENETIC ANALYSIS BASED ON THE POSTCRANIAL EVIDENCE

Abstract

"The phylogenetic relationships of titanosaurid sauropods are examined by means of a clodistic parsimony analysis based on postcranel features. Eusauropoda tBarapasaurus tagorei + Neosauropoda) have, at least, two synapomorphies. The Camarasauromorpha (Camarasauridae + Titanosauriformes) have five synapomorphies. The Titanosauriformes [Brachiosaurus brancai + tChubunsaurus insignis + Titanosauria)] share six derived characters (e.g., presence of medial prespinallamina in posterior trunk vertebrae, neural arches positioned anteriorly in mid and posterior caudal centra, c1aw on manual digit 1reduced or absent). Chubutisaurus insignis Del Corro shares with Titanosauria one apomorphy. Titanosauria is rediagnosed based on five synapomorphies (e.g., eye-shape pleurocoels in trunk vertebrae, anterior caudals procoelous, pubis considerably longer than ischium). Titanosauridae comprises titanosaurids with: absence of hyposphene-hypantrum articulation in posterior trunk vertebrae, six sacral vertebrae, anterior caudals strongly procoelous having ""ball and socket"" articular faces, mid and posterior caudals strongly procoelous, semilunar sternal plates, claw on manual digit I absent, manual phalanges absent and preacetabular lobe of ilium nearly horizontal, outwardly projected. Titanosaurids more derived than Epachthosaurus sciuttoi Powell and Malawisaurus dixeyi Haughton have medial prespinal lamina formed down to the base of neural spine in posterior trunk vertebrae and quadrangular coracoids. Argentinosaurus huinculensis Bonaparte and Coria, Opisthocoelicaudia skarzynskii Borsuk-Bialynicka and Titanosauridae indet*(DGM ""Serie B"") form a monophyletic group characterized by presence of accesory spino-diapophyseallaminae in trunk vertebrae. Aeolosaurus Powell shares with Alamosaurus sanjuanensis Gilmore and the Saltasaurinae biconvex first caudal and presence of dorsal prominence on inner face of scapula. Alamosaurus sanjuanensis is the sister-taxon of the Saltasaurinae."