Wednesday, July 27, 2016

[Paleontology • 2016] Phylogenetic Relationships of the Cretaceous Gondwanan Theropods Megaraptor and Australovenator: the Evidence Afforded by Their Manual Anatomy

General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e., proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and II long and slender), and one derived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of metacarpal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea. 

Keywords: Dinosauria, Theropoda, Megaraptoridae, Cretaceous, Argentina, Australia, morphology.
Figure 3. Left manus of Megaraptor namunhuaiquii (MUCPv 341) in dorsal view
 (A) and schematic representation (B) . Scale bar: 1 cm. 

Figure 6. Left manus in dorsal view of A, Dilophosaurus (modified from Welles, 1980); B, Allosaurus; C, Megaraptor; D, Sinocalliopteryx; E, Tanycolagreus (modified from Carpenter et al., 2005); F, Deinonychus (modified from Ostrom, 1969); G, Scipionyx (modified from Dal Sasso and Maganuco, 2011); H, Guanlong (modified from Xu et al., 2009); and I, Sinosauropteryx (modified from Currie and Chen, 2001). Not to scale. 

Abstract Novas, F.E., Aranciaga Rolando, A.M. and Agnolín, F.L. 2016. Phylogenetic Relationships of the Cretaceous Gondwanan Theropods Megaraptor and Australovenator: the Evidence Afforded by Their Manual Anatomy. Memoirs of Museum Victoria. 74: 49–61.