Martin Ezcurra & Federico Agnolin (2017)
The research ofMesozoic theropods in Gondwana: a brief historical overview.
Ameghiniana 54(5):Â 483â487
The study of Gondwanan non-avian theropods has been outstandingly prolific in the last three decades and has shown that the taxonomic and morphological diversity of the group is comparable to that of Laurasia. As a consequence of this diversity, the Gondwanan non-avian theropod record has been crucial to understand the evolution and global biogeography of dinosaurs during the Mesozoic. However, the history of the research of the southern theropods has been heterogeneous in the last century and only in 2004 we reached the 50% of all the valid Gondwanan theropod species currently known. Here we propose that the history of the Gondwanan theropod research can be divided in three different stages.
Ricardo N. MartÃnez & Cecilia Apaldetti (2017)
A Late Norian-Rhaetian coelophysid neotheropod (Dinosauria, Saurischia) From The Quebrada Del Barro Formation, Northwestern Argentina.
Ameghiniana 54(5): Â488â505
Coelophysoids are the most abundant theropod dinosaurs known from the Late Triassic through Early Jurassic and represent the earliest major radiation of Neotheropoda. Within Coelophysoidea sensu lato, the most stable clade is Coelophysidae, which are small theropods characterized by long necks, and light and kinetic skulls. Coelophysids are the most abundant basal non-Tetanurae neotheropods known world- wide; however, until recently, they were unknown from South America. We report here a new coelophysid neotheropod, Lucianovenator bonoi gen. et sp. nov., from the late NorianâRhaetian Quebrada del Barro Formation, northwestern Argentina. A phylogenetic analysis recovered Lucianovenator bonoi nested into the monophyletic group Coelophysidae in an unresolved clade, together with Coelophysis rhodesiensis and Cam- posaurus arizonensis. The presence of Lucianovenator in the late NorianâRhaetian of Argentina increases the poor and scarce record of Triassic South American neotheropods, suggesting that the virtual absence of theropods in the fossil record during the Rhaetian is probably a tapho- nomic/stratigraphic bias instead of a decline in diversity and abundance after the Norian. Finally, the new finding corroborates the American en- demism of coelophysid neotheropods in the Late Triassic and their worldwide distribution during the Early Jurassic, supporting the extreme faunal homogeneity hypothesized for Early Jurassic continental biotas.
Martin Ezcurra (2017)
A new early coelophysoid neotheropod from the Late Triassic of Northwestern Argentina.
Ameghiniana 54(5): Â506â538
Neotheropoda represents the main evolutionary radiation of predatory dinosaurs and their oldest members are Late Triassic in age. The Triassic neotheropod record is restricted to North America and Europe with the exception of a few specimens from South America, which includes a single species âZupaysaurus rougieriâ and a yet unnamed form. Here, the South American record of the group is enriched with the description of the new genus and species Powellvenator podocitus from the middle Norian Los Colorados Formation (Ischigualasto-Villa UniÃn Basin) of northwestern Argentina. The new taxa are represented by previously undescribed partial hindlimbs collected by J. F. Bonaparte and associated to the hypodigm of the pseudosuchian Riojasuchus tenuisceps. In addition, a specimen originally interpreted by Bonaparte in 1972 as an indeterminate coelurosaur is here referred to the new species. Powellvenator podocitus differs from other basal dinosaurs in character-states that include an astragalus with a distinctly sigmoid posterodorsal margin and a rounded dorsal expansion on the anteromedial portion of the astragalar body in anterior view, calcaneum with a laterally projected flange, and strongly reduced shaft of metatarsal II. The phylogenetic relationships of the new species were tested in one of the most comprehensive analyses focused on early neotheropods, which recovered Powellvenator podocitus within Coelophysoidea and as the sister-taxon of Coelophysidae. Powellvenator podocitus represents the first coelophysoid from South American together with a preliminary reported form from the Marayes-El Carrizal Basin.
Pandoravenator fernandezorum gen. et sp. nov.
Oliver Rauhut & Diego Pol (2017)
A theropod dinosaur from The Late Jurassic CaÃadÃn CalcÃreo Formation of Central Patagonia, and the evolution of the theropod tarsus.
Ameghiniana 54(5): Â539â566
A fragmentary postcranial skeleton from the Late Jurassic (OxfordianâTithonian) CaÃadÃn CalcÃreo Formation of Chubut, Argentina,represents a new taxon of theropod dinosaur, which is here described as Pandoravenator fernandezorum gen. et sp. nov. This material representsthe first Late Jurassic theropod known from Argentina. Pandoravenator fernandezorum is characterized by strongly elongated postzygapophyses in the caudal vertebrae and an unusual tarsal joint, with the astragalus showing two distal tubercles and a very low and laterally inclined ascending process. Phylogenetic analyses indicate that the new taxon is a basal tetanuran, although its exact phylogenetic position within basal tetanurans remains uncertain, due to the fragmentary nature of the remains and the lack of consensus among the different phylogenetic analyses. The tarsus of P. fernandezorum shows an intermediate morphology between that of basal theropods and more derived tetanurans. It is especially noteworthy for the presence of a suture between the distal astragalar condyles and the anteroproximal extension ofthe astragalus, including the ascending process. This indicates that a separate ossification of the ascending process of the astragalus was present in this taxon, and, in a phylogenetic context, thus provides evidence that the origin of the ascending process and the astragalar body from separate ossifications was already present at the base of Averostra.
NicolÃs Roberto Chimento, Federico Lisandro Agnolin, Fernando Emilio Novas, Martin Daniel Ezcurra, Leonardo Salgado, Marcelo Isasi, Manuel Suarez, Rita De la Cruz, David Rubilar-Rogers & Alexander Vargas (2017)
Forelimb posture in Chilesaurus diegosuarezi (Dinosauria, Theropoda) and its behavioral and phylogenetic implications.Â
Ameghiniana 54(5): Â567â575
Many dinosaur skeletons show evidence of behavior, including feeding, predation, nesting, and parental care. The resting posture of the forelimbs has been studied in some theropod species, in relation to the acquisition of flight in advanced maniraptoran theropods. Chilesaurus diegosuarezi is a bizarre tetanuran recently described from the Toqui Formation (latest Tithonian) of southern Chile that is represented by multiple well-preserved and articulated specimens. The aim of the present work is to analyze the forelimb posture of four articulated specimens of Chilesaurus: SNGM-1935 (holotype), SNGM-1936, SNGM-1937, SNGM-1938; focusing on its anatomical description, and phylogenetic and behavioral implications. All the preserved specimens of Chilesaurus show strongly ventrally flexed arms with the hands oriented backwards, an arraignment that closely resembles those in dinosaur specimens previously described as preserving resting posture, such as Mei long, Sinornithoides youngi, and Albinykus baatar. As a result, it seems that individuals of Chilesaurus have been in passive activity (e.g. feeding, resting) when they were buried quickly, allowing their fossilization in life position and preserving the forelimb resting posture. The arraignment of the forelimb bones in Chilesaurus could show the first evidences of the structures linked to the muscles that flex the forearms, features related with the acquisition of flying control in advanced maniraptorans.
Afromimus tenerensis gen. et sp. nov.
Paul C. Sereno (2017)
Early Cretaceous ornithomimosaurs (Dinosauria: Coelurosauria) from Africa.
Ameghiniana 54(5): Â576â616
A new genus and species of ornithomimosaur, Afromimus tenerensis, is described based on a partial skeleton from the Lower Cretaceous (Aptian-Albian) El Rhaz Formation of Niger. The holotype and only known individual preserves caudal vertebrae, chevrons and portions of the right hind limb. Derived ornithomimosaurian features include the broad, peanut-shaped articular surfaces of mid caudal centra, parasagittal fossae on mid caudal centra for reception of the postzygapophyses of the preceding vertebra, and a raised, subtriangular platform on the ventral aspect of the pedal phalanges. New information is given for, and comparisons made to, the basal southern African ornithomimosaur Nqwebasaurus thwazi. Ornithomimosaurs are unusual among coelurosaurian clades with major radiations on northern landmasses; the oldest undoubted member and now another basal form are known from a southerrn landmass, Africa.
Ariana Paulina-Carabajal & Philip J. Currie (2017)
The braincase of the theropod dinosaur Murusraptor: osteology, neuroanatomy and comments on the paleobiological implications of certain endocranial features.
Ameghiniana 54(5): Â617â640
A detailed description of the neuroanatomy of Murusraptor barrosaensisâa mid-sized non-maniraptoran theropod from the Late Cretaceous of north Patagoniaâis based on the exceptionally preserved type braincase. CT scans provide new information on the braincase, brain, cranial nerves, encephalic vasculature, and inner ear of this taxon. Worldwide, relatively few non-maniraptoran theropod braincases have been described in detail and the new information reported here is important to better understand the variability of braincase characters within the clade. This study suggests that megaraptorids have a particular brain pattern that is different from those of other non-coelurosaur theropods, such as allosauroids and ceratosaurs, and different from that of some coelurosaurs, such as tyrannosaurids, although sharing more similarities with the latter. The Reptile Encephalization Quotient of Murusraptor is within a range between those of Allosaurus and Tyrannosaurus; the Olfactory Ratio is, however, smaller than the observed in tyrannosaurids and allosauroids. The paleobiological implications on gaze stabilization, hearing, and olfaction in the Argentinean taxon are still poorly understood.