Unenlagiinae is a subfamily of long-snouted
paravian
Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the aviala ...
theropods. They are traditionally considered to be members of
Dromaeosauridae, though some authors place them into their own family,
Unenlagiidae, alongside the subfamily
Halszkaraptorinae
Halszkaraptorinae is a basal ("primitive") subfamily of Dromaeosauridae (or possibly Unenlagiidae) that includes the enigmatic genera ''Halszkaraptor'', ''Natovenator'', ''Mahakala'', and ''Hulsanpes''. Halszkaraptorines are definitively known o ...
. Unenlagiines are known from
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, with possible unenlagiines being known from North America, Madagascar, Europe, and even Australia.
Description
![Austroraptor Restoration](https://upload.wikimedia.org/wikipedia/commons/6/6f/Austroraptor_Restoration.png)
Most unenlagiines have been discovered in
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. The largest was ''
Austroraptor
''Austroraptor'' ( ) is a genus of large dromaeosaurid dinosaur that lived during the Late Cretaceous Period in what is now Argentina.
''Austroraptor'' was a large-sized, moderately-built, ground-dwelling, bipedal carnivore, estimated at in len ...
'', which measured up to 5–6 m (16.4–19.7 ft) in length, making it also one of the largest dromaeosaurids.
The subfamily is distinguished from other dromaeosaurids by a tail stiffened by lengthy chevrons and superior processes, a reduced second pedal ungual, a posteriorly oriented pubis and very elongated snouts. Unenlagiines also had elongated, slender hindlimbs with a subarctometatarsalian metatarsus, which is characterized by the pinched metatarsal III at the upper end. Their distinct anatomy from
Laurasian dromaeosaurids was likely a consequence of the breakup of
Pangaea into
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
and Laurasia, where the geological isolation of unenlagiines from their relatives resulted in
allopatric speciation
Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...
.
[
]
Classification
During the description of ''Halszkaraptor
''Halszkaraptor'' (; meaning " Halszka's seizer") is a genus of waterfowl-like dromaeosaurid dinosaurs from Mongolia that lived during the Late Cretaceous period. It contains only one known species, ''Halszkaraptor escuilliei''.
The type speci ...
'' in 2017, Cau ''et al.'' published a phylogenetic analysis of the Dromaeosauridae, in which, members of the Unenlagiinae are classified as:
In 2019, during the description of ''Hesperornithoides
''Hesperornithoides'' (meaning "western bird form"; nicknamed "Lori") is a genus of troodontid theropod dinosaur that lived in North America during the Late Jurassic period.
Discovery
Although several Troodontid teeth were found, with the trood ...
'', many Paravian
Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the aviala ...
groups were examined for the inclusion of this new genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
, including the Unenlagiinae. The analysis ended in the inclusion of ''Rahonavis
''Rahonavis'' is a genus of bird-like theropods from the Late Cretaceous (Maastrichtian, about 70 mya) of what is now northwestern Madagascar. It is known from a partial skeleton ( UA 8656) found by Catherine Forster and colleagues in Maevarano ...
'', '' Pyroraptor'' and ''Dakotaraptor
''Dakotaraptor'' (meaning “thief from Dakota”) is a potentially chimaeric genus of large dromaeosaurid theropod dinosaur that lived in North America during the Late Cretaceous period. The remains have been found in the Maastrichtian stage of ...
'' to the Unenlagiinae.
Paleobiology
A study performed by Gianechini and colleagues in 2020 indicates that unenlagiine dromaeosaurids of Gondwana possessed different hunting specializations than the eudromaeosaurs from Laurasia. The shorter second phalanx in the second digit of the foot of eudromaeosaurs allowed for increased force to be generated by that digit, which, combined with a shorter and wider metatarsus, and a noticeable marked hinge‐like morphology of the articular surfaces of metatarsals and phalanges, possibly allowed eudromaeosaurs to exert a greater gripping strength than unenlagiines, allowing for more efficient subduing and killing of large prey. In comparison, the unenlagiine dromaeosaurids possess a longer and slender subarctometatarsus, and less well‐marked hinge joints, a trait that possibly gave them greater cursorial
A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often u ...
capacities and allowed for greater speed than eudromaeosaurs. Additionally, the longer second phalanx of the second digit allowed unenlagiines fast movements of their feet's second digits to hunt smaller, faster types of prey. These differences in locomotor and predatory specializations may have been a key feature that influenced the evolutionary paths that shaped both groups of dromaeosaurs in the northern and southern hemispheres, respectively.
See also
* Timeline of dromaeosaurid research
*Halszkaraptorinae
Halszkaraptorinae is a basal ("primitive") subfamily of Dromaeosauridae (or possibly Unenlagiidae) that includes the enigmatic genera ''Halszkaraptor'', ''Natovenator'', ''Mahakala'', and ''Hulsanpes''. Halszkaraptorines are definitively known o ...
References
{{Taxonbar, from=Q1258292
Dromaeosaurs