Australovenator

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Australovenator
Temporal range: Late Cretaceous,[1] 95 Ma
Banjo Australovenator.jpg
Reconstructed skeleton, Australian Age of Dinosaurs Museum, Winton, Australia
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Megaraptora
Genus: Australovenator
Hocknull et al., 2009
Species: A. wintonensis
Binomial name
Australovenator wintonensis
Hocknull et al., 2009

Australovenator (meaning "southern hunter") is a genus of megaraptoran theropod dinosaur from Cenomanian (Late Cretaceous)-age rocks (dated to 95 million years ago[1]) of Australia. It is known from partial cranial and postcranial remains which were described in 2009 by Scott Hocknull and colleagues, although additional descriptions and analyses continue to be published. It is the most complete predatory dinosaur discovered in Australia.

Description[edit]

Life restoration

According to Hocknull, it was 2 m (6.6 ft) tall at the hip and 6 m (20 ft) long, with a weight of about 500–1000 kg. Because it was a lightweight predator, he coined it as the "cheetah of its time".[2] Like other megaraptorans, Australovenator would have been a bipedal carnivore.[3]

History of discovery[edit]

Australovenator is based on a theropod specimen (AODF 604), affectionately nicknamed "Banjo" after Banjo Paterson[4]), which was found intermingled with the remains of the sauropod Diamantinasaurus matildae at the "Matilda site" (AODL 85). The parts of the holotype as it was initially described, which are held at the Australian Age of Dinosaurs Museum of Natural History, consists of a left dentary, teeth, partial forelimbs and hindlimbs, a partial right ilium, ribs, and gastralia. Australovenator was described in 2009 by paleontologist Scott Hocknull of the Queensland Museum, and colleagues. The type species is A. wintonensis, in reference to nearby Winton.[5]Although the holotype was first described in 2009, the process of excavating the "Matilda site" is still ongoing and papers describing new elements of the holotype are still being published.

Silhouette with known skeletal elements.

Additional arm elements of the holotype were described in 2012,[6]more leg elements were described in 2013,[7] and a right dentary was described in 2015.[8]

Rapator was described by Huene for a first metacarpal from Australia. When Australovenator was described, it was considered either an alvarezsaurid, or an intermediate theropod. Hocknull et al. (2009) identified a few distinguishing characters between the taxa, based on a poorly preserved metacarpal I from the holotype of Australovenator.[5] Agnolin et al. (2010), reclassified Rapator, instead finding it a megaraptoran, potentially sister taxon to Australovenator. They mentioned that Megaraptor, the only other taxon also preserving metacarpal I, was less similar to Rapator than Australovenator. However, there were no clear differences between the two latter taxa.[9] The metacarpals of both taxa were redescribed in White et al. (2014), who determined that they were not synonymous, adding multiple features two the potential characters identified by Hocknull et al. and Angolan et al.[1]

Classification[edit]

Dentary

A phylogenetic analysis found Australovenator to be an allosauroid carnosaurian, with similarities to Fukuiraptor and carcharodontosaurids. In the initial analysis, it was shown to be the sister taxon of the Carcharodontosauridae.[5] More detailed studies found that it formed a clade with several other carcharodontosaurid-like allosaurs, the Neovenatoridae.[10] Recent phylogenetic analysis suggests Australovenator is a tyrannosauroid, like with all other megaraptorans.[11] A phylogenetic analysis in 2016 focusing on the new neovenatorid Gualicho found that Australovenator and other megaraptorids were either allosauroids or basal coelurosaurs as opposed to being tyrannosauroids.[12]

The ankles of Australovenator and Fukuiraptor are similar to the Australian talus bone known as NMVP 150070 that had previously been identified as belonging to Allosaurus sp., and this bone likely represents Australovenator or a close relative of it.[5][13] Alternatively, this bone could belong to an abelisaur.[14]

The cladogram below follows the 2010 analysis by Benson, Carrano and Brusatte.[10] Another study published later in 2010 also found the Australian theropod Rapator to be a megaraptoran extremely similar to Australovenator.[9]

Sculpture in Winton
Neovenatoridae

Neovenator


unnamed

Chilantaisaurus


Megaraptora
unnamed

Siats meekerorum[15]




Australovenator



?Rapator



Fukuiraptor



unnamed

?Orkoraptor




Aerosteon



Megaraptor






Australovenator holding prey

The cladogram below follows the 2014 analysis by Porfiri et al. that finds megaraptorans to be tyrannosauroids.[16]

Megaraptora

Fukuiraptor


Megaraptoridae

Australovenator



Aerosteon


unnamed

Orkoraptor



Eotyrannus



Megaraptor




Palaeobiology[edit]

With very comprehensive and well-preserved hand and foot remains, Australovenator has been made a topic of various research papers studying the dynamics of theropod appendages.

A 2015 study tested the range of motion of Australovenator's arms using computer models and found that it had flexible arms, with the forearms capable of making an angle of 144 to 66 degrees with the humerus, an elbow range of motion similar to that of maniraptoriformes. Unusually, its radius could slide independently of the ulna when its arm was flexed, similar to that of birds but unlike most non-avian dinosaurs. However, the study also found that Australovenator's fingers were capable of extension far beyond those of any other sampled theropod, with only Dilophosaurus having capabilities even near it. This study concluded that Australovenator's flexibility, facilitated by a combination of traits in both primitive and advanced theropods, played a role in prey capture, giving it the ability to grasp prey towards its chest to make it easier for its weak jaws to disemboweling food.[17]

A 2016 study used CT scans of an emu foot to digitally reconstruct the musculature and soft tissue of an Australovenator foot, as well as determine how soft tissue affects flexibility. The study determined that muscular range of motion is often overestimated when not accounting for soft tissue, and that soft tissue reconstruction is vital for making future analyses of theropod flexibility more accurate. A review of hindlimb elements described in 2013 re-identified several phalanges which were initially positioned incorrectly. In addition, it noted that Australovenator's phalanx II-3 was splayed, a pathology that may have resulted from the impacts of kicking motions. Some modern birds, such as the cassowary, are known to use their second toe as weapons in defensive or territorial fights.[18]

A 2017 followup to the 2016 study used a 3-D printed model of the reconstructed foot to make footprints in a matrix of clay and sand in an effort to understand the creation of dinosaur footprints. The study specifically was designed to clarify the identity of particular controversial footprints from Lark Quarry, which may have been left from either a large theropod (like Australovenator) or an ornithopod (like Muttaburrasaurus). The study found that the artificial Australovenator footprints were similar to those at Lark Quarry, concluding that the trackways in question were likely those of a theropod. The writers of the study expressed interest in creating a reconstruction of a Muttaburrasaurus foot as an extension of the study, although unfortunately no Muttaburrasaurus pedal material is known.[19]

Palaeoecology[edit]

Life restoration of Australovenator feeding on carcass of Diamantinasaurus

AODL 604 was found about 60 kilometres (37 mi) northwest of Winton, near Elderslie Station. It was recovered from the lower part of the Winton Formation, dated to the late Cenomanian. AODL 604 was found in a clay layer between sandstone layers, interpreted as an oxbow lake, or billabong, deposit. Also found at the site were the type specimen of the sauropod Diamantinasaurus, bivalves, fish, turtles, crocodilians, and plant fossils. The Winton Formation had a faunal assemblage including bivalves, gastropods, insects, the lungfish Metaceratodus, turtles, the crocodilian Isisfordia, pterosaurs, and several types of dinosaurs, such as the sauropods Diamantinasaurus and Wintonotitan, and unnamed ankylosaurians and hypsilophodonts. Plants known from the formation include ferns, ginkgoes, gymnosperms, and angiosperms.[5]

References[edit]

  1. ^ a b c White, M. A.; Falkingham, P. L.; Cook, A. G.; Hocknull, S. A.; Elliott, D. A. (2013). "Morphological comparisons of metacarpal I for Australovenator wintonensis and Rapator ornitholestoides: Implications for their taxonomic relationships". Alcheringa: an Australasian Journal of Palaeontology. 37: 1. doi:10.1080/03115518.2013.770221. 
  2. ^ Scientists discover 3 new Aussie dinosaurs. ABC News. July 3, 2009
  3. ^ Holtz, Thomas R., Jr.; Molnar, Ralph E.; Currie, Philip J. (2004). Weishampel, David B.; Dodson, Peter; Osmólska Halszka (eds.), eds. The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 71–110. ISBN 0-520-24209-2. 
  4. ^ Australovenator on prehistoric-wildlife.com
  5. ^ a b c d e Hocknull, Scott A.; White, Matt A.; Tischler, Travis R.; Cook, Alex G.; Calleja, Naomi D.; Sloan, Trish; Elliott, David A. (2009). Sereno, Paul, ed. "New Mid-Cretaceous (Latest Albian) Dinosaurs from Winton, Queensland, Australia". PLoS ONE. 4 (7): e6190. Bibcode:2009PLoSO...4.6190H. PMC 2703565Freely accessible. PMID 19584929. doi:10.1371/journal.pone.0006190. 
  6. ^ White, M. A.; Cook, A. G.; Hocknull, S. A.; Sloan, T.; Sinapius, G. H. K.; Elliott, D. A. (2012). Dodson, Peter, ed. "New Forearm Elements Discovered of Holotype Specimen Australovenator wintonensis from Winton, Queensland, Australia". PLoS ONE. 7 (6): e39364. Bibcode:2012PLoSO...739364W. PMC 3384666Freely accessible. PMID 22761772. doi:10.1371/journal.pone.0039364. 
  7. ^ White, Matt A.; Benson, Roger B. J.; Tischler, Travis R.; Hocknull, Scott A.; Cook, Alex G.; Barnes, David G.; Poropat, Stephen F.; Wooldridge, Sarah J.; Sloan, Trish (2013-07-24). "New Australovenator Hind Limb Elements Pertaining to the Holotype Reveal the Most Complete Neovenatorid Leg". PLOS ONE. 8 (7): e68649. ISSN 1932-6203. doi:10.1371/journal.pone.0068649. 
  8. ^ White, Matt A.; Bell, Phil R.; Cook, Alex G.; Poropat, Stephen F.; Elliott, David A. (2015-12-15). "The dentary ofAustralovenator wintonensis(Theropoda, Megaraptoridae); implications for megaraptorid dentition". PeerJ. 3. ISSN 2167-8359. doi:10.7717/peerj.1512. 
  9. ^ a b 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. 
  10. ^ a b 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. PMID 19826771. doi:10.1007/s00114-009-0614-x. 
  11. ^ 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. 
  12. ^ http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0157793
  13. ^ Molnar, Ralph E.; Flannery, Timothy F.; Rich, Thomas H.V. (1981). "An allosaurid theropod dinosaur from the Early Cretaceous of Victoria, Australia". Alcheringa. 5 (2): 141–146. doi:10.1080/03115518108565427. 
  14. ^ Agnolin, F. L.; Ezcurra, M. D.; Pais, D. F.; Salisbury, S. W. (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. 
  15. ^ Zanno, L. E.; Makovicky, P. J. (2013). "Neovenatorid theropods are apex predators in the Late Cretaceous of North America". Nature Communications. 4: 2827. Bibcode:2013NatCo...4E2827Z. PMID 24264527. doi:10.1038/ncomms3827. 
  16. ^ Juan D. Porfiri; Fernando E. Novas; Jorge O. Calvo; Federico L. Agnolín; Martín D. Ezcurra; Ignacio A. Cerda (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. 
  17. ^ White, Matt A.; Bell, Phil R.; Cook, Alex G.; Barnes, David G.; Tischler, Travis R.; Bassam, Brant J.; Elliott, David A. (2015-09-14). "Forearm Range of Motion in Australovenator wintonensis (Theropoda, Megaraptoridae)". PLOS ONE. 10 (9): e0137709. ISSN 1932-6203. doi:10.1371/journal.pone.0137709. 
  18. ^ White, Matt A.; Cook, Alex G.; Klinkhamer, Ada J.; Elliott, David A. (2016-08-03). "The pes ofAustralovenator wintonensis(Theropoda: Megaraptoridae): analysis of the pedal range of motion and biological restoration". PeerJ. 4. ISSN 2167-8359. doi:10.7717/peerj.2312. 
  19. ^ White, Matt A.; Cook, Alex G.; Rumbold, Steven J. (2017-06-06). "A methodology of theropod print replication utilising the pedal reconstruction of Australovenator and a simulated paleo-sediment". PeerJ. 5. ISSN 2167-8359. doi:10.7717/peerj.3427.