Austroraptor

Austroraptor Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N
Maxilla and dentary of the holotype
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Dromaeosauridae
Subfamily:	†Unenlagiinae
Genus:	†Austroraptor Novas et al., 2008
Species:	†A. cabazai
Binomial name
†Austroraptor cabazai Novas et al., 2008

Austroraptor (

The type specimen of Austroraptor cabazai,

It is the largest

The skull is low and elongated, much more so than that of other dromaeosaurs, and measures 80 cm (31 in). Austroraptor has conical, non-serrated teeth, which Novas et al. compared to those of spinosaurids, based on how the enamel of the surface of its teeth is fluted.^[1] Austroraptor shares a trait that is unique to it and to Adasaurus: the descending process of the lacrimal bones curves anteriorly to a large degree.^[5] Austroraptor has a bizarre morphology in its toes, which are strangely disproportionate. The 4th toe is over twice the width of the 2nd toe, and nearly three times the expected width based on similarly sized members of its taxonomic family. This has suggested to some researchers that the holotype specimen is a paleontological chimera; however, there is no uncertainty about the affinity of the taxon, so a chimera hypothesis can not be assured.^[5]

Several of Austroraptor's skull bones bear some resemblance to those of the smaller

However little of the entire skeleton was found, the bones that are available for analysis possess some distinct characteristics that differentiate Austroraptor from other dromaeosaurs. Austroraptor is particularly notable because of its relatively short forearms, which are much shorter in proportion when compared to the majority of the members of Dromaeosauridae. According to Novas et al. 2008, Austroraptor can be distinguished based on the following characteristics:[1]

• A lacrimal that is highly pneumatized, with the descending process strongly curved rostrally, and with a caudal process flaring out horizontally above the orbit.
• The lack of a dorsomedial process on the postorbital bone for articulation with the frontal bone, and with the squamosal process extremely reduced.
• The maxillary and dentary teeth are small, conical, devoid of serrations and fluted.
• The humerus is short, at approximately 46% of length of the femur.
• The pedal phalanx II-2 is transversely narrow, contrasting with the extremely robust phalanx IV-2.^{[Note 1][Note 2][Note 3][Note 4]}

In 2012, comparison with a second specimen showed that the fourth toe was not especially broad; the purported second phalanx had in fact been a first phalanx.^[2]

Classification

A

The following cladogram is based on the phylogenetic analysis conducted by Turner, Makovicky and Norell in 2012, showing the relationships of Austroraptor among the other genera assigned to the taxon Unenlagiinae:^[5]

Cau et al. 2017 published a phylogenetic analysis of the Dromaeosauridae during the description of Halszkaraptor, in which members of the Unenlagiinae are classified as:^[7]

In 2019, during the description of

Unenlagiinae	Austroraptor Buitreraptor Pyroraptor Pamparaptor Rahonavis Ornithodesmus Dakotaraptor Unenlagia

In 2021, Brum and colleagues classified

sister taxon to Austroraptor.^[9]

Unenlagiinia	Halszkaraptorinae Unenlagiinae Buitreraptor Neuquenraptor Unenlagia comahuensis Unenlagia paynemili Austroraptor Ypupiara

Paleobiology

It has been suggested that unenlagiines had better capacities for running and pursuit predation than other dromaeosaurids. While

Laurasian dromaeosaurids (Eudromaeosauria) were more stocky and had shorter legs and had an active predatory lifestyle, unenlagiines could likely maintain high speeds for extended amounts of time because they were more gracile. Unenlagiines have modified metatarsals that resemble those of microraptorines: they are relatively thin and lengthened. Based on these adaptations, it is likely that unenlagiines preyed on small, fast animals, although the exact animals are unknown. Buitreraptor features particular traits that can be attributed to specific hunting methods.^[10]

Models for Buitreraptor propose that it hunted by traveling large distances in pursuit of prey, which may explain the long-legged trait shared by various genera of Unenlagiidae. Buitreraptor is characterized by its long forelimbs and hands; it likely relied on them to restrain prey and the curved claw of the second pedal digit would have injured or killed the victim. Buitreraptor probably swallowed its prey whole due to its lack of serrated teeth with flesh-tearing capabilities; the teeth functioned to simply hold prey.^[10]

The same model was proposed for the much larger Austroraptor with few exceptions:^[10]

• It would not have used its arms to handle prey, due to their relatively small size.
• Its teeth were conical and probably stronger, so it may have been able to use them for hunting larger prey.

The teeth of Austroraptor are conical and lacking denticles, similarly to those of

anhanguerids, etc.^[9]

Paleoecology

The holotype specimen was found in terrestrial sediments that were deposited during the

abelisaurids such as Quilmesaurus, Aucasaurus and Carnotaurus.^[1]

During his description of

herbivorous dinosaurs.^[13] Other contemporaneous paleofauna includes the titanosaurs Laplatasaurus, Rocasaurus and Saltasaurus, the bird Limenavis,^[11] and the hadrosaurids Bonapartesaurus, Kelumapusaura, and Lapampasaurus.^[14][15]

See also

• Allen Formation
• Timeline of dromaeosaurid research
• 2008 in paleontology

Notes

1. ^ This condition differs from that Laurasian Dromaeosaurids, but is unknown for other Unenlagiines
2. ^ A condition also observed in Buitreraptor
3. ^ A smaller ratio than in other Dromaeosaurids and Paravians
4. ^ This condition differs from that of other Dromaeosaurids including Unenlagiines, but resembles the condition observed in advanced Troodontids

References

1. ^
   PMID 19129109
   .
2. ^
   S2CID 129058582
   .
3. ^ Paul, G. S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 138.
4. ^ ^{a b} Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Supplementary Information 2012
5. ^
   S2CID 83572446
   .
6. ^ "Researchers find short-armed raptor in Argentina". Reuters. 2008-12-16. Retrieved 2010-11-10.
7. S2CID 4471941
   .
8. PMID 31333906
   .
9. ^
   doi:10.1002/spp2.1375
   .
10. ^
    PMID 32023660
    .
11. ^ ^{a b} Weishampel, D. B.; Dodson, P.; Osmolska, H. (2007). The Dinosauria, Second Edition. University of California Press. p. 604.
12. ISSN 1851-8044
    .
13. S2CID 55411436
    .
14. S2CID 90963879
    .
15. S2CID 131521822
    .

External links

• Media related to Austroraptor at Wikimedia Commons
• Data related to Austroraptor at Wikispecies