A basal tetanuran theropod dinosaur from the Middle Jurassic of Argentina: implications for the early evolution of tetanuran theropods
Final Report Abstract
Tetanurae is the most successful clade of theropod dinosaurs, which also includes modern birds. Early in their evolutionary history, tetanurans are considered to have split into three major clades: Megalosauroidea, Coelurosauria, and Allosauroidea. The oldest tetanurans occur in the earliest Middle Jurassic, but the early fossil record of the clade is still poor, especially as most of the known basal taxa are extremely fragmentary. In the frame of the project, we studied one of the oldest known and most complete pre-Late Jurassic representatives of Tetanurae, a new species of basal allosauroid from the latest Early to early Middle Jurassic Cañadón Asfalto Formation of Patagonia, Argentina. The new taxon has an unusual character combination, uniting features currently considered to be apomorphic of different tetanuran lineages with characters that are plesiomorphic for the clade as a whole. A phylogenetic analysis of basal tetanurans resulted in a monophyletic Carnosauria (Allosauroidea + Megalosauroidea, to the exclusion of Coelurosauria), and the inclusion of the new taxon significantly changes topology within carnosaurs. An analysis of the distribution of homoplasy in theropod phylogeny shows high levels of homoplasy concentrated in proximal nodes at the base of Tetanurae, after the Pliensbachian-Toarcian extinction event. These results highlight the complex morphological evolution in the early radiation of tetanuran theropods, in which convergences and parallelisms were extremely common. This pattern seems to be a common feature in rapid radiation events of major clades of vertebrates and might explain the common difficulties to unravel phylogenetic relationships of important lineages at the base of major clades.
Publications
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2016. A new megalosaurid theropod dinosaur from the late Middle Jurassic (Callovian) of north-western Germany: Implications for theropod evolution and faunal turnover in the Jurassic. Palaeontologia electronica 19.2.26A: 1-65
Rauhut, O.W.M., Hübner, T.R. & Lanser, K.-P.
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2016. New discoveries and the radiation and faunal replacements in tetanuran theropod dinosaurs during the Jurassic. Zitteliana 88: 40
Rauhut, O.W.M.
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2017. A theropod dinosaur from the Late Jurassic Cañadón Calcáreo Formation of Chubut, Patagonia, and the evolution of the theropod tarsus. Ameghiniana 54: 506-538
Rauhut, O.W.M. & Pol, D.
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2017. Die Cañadón-Asfalto-Formation in Argentinien: Einmalige Einblicke in die Wirbeltierevolution im mittleren Jura. Freunde der Bayerischen Staatssammlung für Paläontologie und Historische Geologie e.V., Jahresbericht und Mitteilungen, 45: 49-82
Rauhut, O.W.M.
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2018. An allosauroid from the Early-Middle Jurassic of Patagonia and phylogenetic uncertainty at the base of Allosauroidea. XVI Annual Meeting of the European Association of Vertebrate Palaeontologists, Caparica June 29th July 1st 2018; Abstract Book: 159
Rauhut, O.W.M. & Pol, D.
