Megaraptora
| Megaraptorans Temporal range: Early Cretaceous - Late Cretaceous, 130–84 Ma | |
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| Diagram showing the skull and skeleton of Murusraptor | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Family: | †Neovenatoridae |
| Clade: | †Megaraptora Benson, Carrano & Brusatte, 2010 |
| Subgroups | |
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Megaraptora is a group of large carnivorous theropod dinosaurs.
Evolution and origin
The origins of megaraptorids have recently been determined. Studies by paleontologists Phil Bell, Steve Salisbury et al. of a newly discovered, as-yet-unnamed megaraptorid (referred to by the public media as "Lightning Claw," and most likely synonymous with Rapator) from opal fields southwest of Lightning Ridge, Australia, dating back 110 million years ago reveals that megaraptorids likely evolved in Australia, then spread to the rest of Gondwana in an episode of evolutionary radiation. The specimen also allowed for alternative phylogenitic testing as to the placement of megaraptorans as either tyrannosauroids or carcharodontosaurids.[2][3]
Classification
Megaraptora has historically been a group with highly controversial relationships.
Early phylogenetic studies of the group's relationships conducted by Benson, Carrano and Brusatte in 2010 and Carrano, Benson and Sampson in 2012 recovered the group as a branch of the allosauroids (specifically within the family Neovenatoridae), part of a large group of theropods that also includes the metriacanthosaurids, carcharodontosaurids, and allosaurids. This would make megaraptorans the last surviving allosauroids; at least a few megaraptorans, including Orkoraptor, lived near the end of the Mesozoic era, dating to the late Santonian stage of the late Cretaceous period, about 84 million years ago.[4][5] Another study published later in 2010 found the Australian theropod Rapator to be a megaraptoran extremely similar to Australovenator.[6]
On the other hand, Novas et al. published a study in 2012 which, while confirming that Neovenator was closely related to carcharodontosaurids, also found Megaraptor and its relatives to be coelurosaurs closely related to tyrannosaurids.[7] Study of the skull anatomy of a juvenile specimen of Megaraptor also suggested to Novas and his colleagues that it was a tyrannosauroid.[8] Analysis of the theropod Gualicho published by Apesteguía and colleagues in 2016 recovered megaraptorans as either allosauroids or basal coelurosaurs, and depended on whether Gualicho's anatomy was plugged into Carrion's analysis or Novas' analysis. This suggested that the controversial placement of megaraptorans was more of a consequence of incomplete analyses than to their actual anatomy.[9]
Later in 2016, Novas and colleagues published a study of megaraptoran hand anatomy, in an attempt to help settle the question of their classification. They found that megaraptorans lacked most of the key features in the hands of derived coelurosaurs including Guanlong and Deinonychus. Instead, their hands retain a number of primitive characteristics seen in basal tetanurans such as Allosaurus. Nevertheless, there are still a number of traits that support megaraptorans as members of the Coelurosauria.[10]
The cladogram below follows Coria & Currie (2016), based on the Carrano et al. (2012) dataset.[11]
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References
- ↑ Matías J. Motta, Alexis M. Aranciaga Rolando, Sebastián Rozadilla, Federico E. Agnolín, Nicolás R. Chimento, Federico Brissón Egli, and Fernando E. Novas (2016). "New theropod fauna from the Upper Cretaceous (Huincul Formation) of northwestern Patagonia, Argentina". New Mexico Museum of Natural History and Science Bulletin. 71: 231–253.
- ↑ Bell, P. R., Cau, A., Fanti, F., & Smith, E. (2015). A large-clawed theropod (Dinosauria: Tetanurae) from the Lower Cretaceous of Australia and the Gondwanan origin of megaraptorid theropods. Gondwana Research.
- ↑ New dinosaur is Australia’s largest carnivore Australian Geographic.
- ↑ Benson, R.B.J.; Carrano, M.T; Brusatte, S.L. (2010). "A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic". Naturwissenschaften. 97 (1): 71–78. Bibcode:2010NW.....97...71B. doi:10.1007/s00114-009-0614-x. PMID 19826771.
- ↑ Matthew T. Carrano, Roger B. J. Benson and Scott D. Sampson (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300. doi:10.1080/14772019.2011.630927.
- ↑ Agnolin, Ezcurra; Pais; Salisbury (2010). "A reappraisal of the Cretaceous non-avian dinosaur faunas from Australia and New Zealand: Evidence for their Gondwanan affinities". Journal of Systematic Palaeontology. 8 (2): 257–300. doi:10.1080/14772011003594870.
- ↑ F. E. Novas; F. L. Agnolín; M. D. Ezcurra; J. I. Canale; J. D. Porfiri (2012). "Megaraptorans as members of an unexpected evolutionary radiation of tyrant-reptiles in Gondwana". Ameghiniana. 49 (Suppl.): R33.
- ↑ Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. (2014). "Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation.". Cretaceous Research. 51: 35–55. doi:10.1016/j.cretres.2014.04.007.
- ↑ Apesteguía, S.; Smith, N.D.; Juárez Valieri, R.; Makovicky, P.J. (2016). "An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina.". PLoS One. 11 (7): e0157793. doi:10.1371/journal.pone.0157793.
- ↑ Novas, F.E.; Rolando, A.M.A.; Agnolin, F.L. (2016). "Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy." (PDF). Memoirs of Museum Victoria. 74: 49–61.
- ↑ Coria RA, Currie PJ (2016) A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLoS ONE 11(7): e0157973. doi:10.1371/journal.pone.0157973