Unenlagia
Encyclopedia
Unenlagia is a genus
of, possibly dromaeosaurid, theropod dinosaur
from the Late Cretaceous
of Argentina
.
The genus Unenlagia has been assigned two species: U. comahuensis, the type species described by Novas and Puerta in 1997, and U. paynemili, described by Calvo et al. in 2004.
province of Argentina a skeleton of a theropod was discovered in the Sierra del Portezuelo and reported the same year. In 1997 Fernando Emilio Novas and Pablo Puerta named and described Unenlagia comahuensis. The generic name is derived from Mapuche
uñen, "half", and lag, "bird", in reference to the fact that the describers considered the species to be a link between birds and more basal theropods. The specific name refers to the Comahue
, the region the find was made.
The holotype
specimen, MCF PVPH 78, was uncovered in layers of the Portezuelo Formation
dating to the Coniacian
. It consists of a partial skeleton lacking the skull but including vertebrae, a sacrum, ribs, chevrons, a scapula, a humerus, a partial pelvis, a femur and a tibia.
In 2002 near the Lago Barreales a second skeleton was uncovered and reported in 2003. In 2004 it was named and described by Jorge Calvo, Juan Porfiri and Alexander Kellner
as a second species: Unenlagia paynemili. The specific name honours Maximino Paynemil, the chief of the Paynemil community. The holotype is MUCPv-349, a partial skeleton consisting of a humerus and two pubes. Several paratype
s were also assigned: MUCPv-343, a claw; MUCPv-409, a partial ilium; MUCPv-415, a phalanx and MUCPv-416, a vertebra.
Some researchers consider Neuquenraptor
to be a junior subjective synonym of Unenlagia.
and Austroraptor
.
Unenlagia was very birdlike. Novas and Puerta found its pelvic region, especially the form of the ilium
, to be very similar to that of the early bird Archaeopteryx
. The shoulder girdle of Unenlagia was originally interpreted as if it was adapted for flapping, with a flat scapula
positioned on top of the ribcage, making the shoulder joint point more laterally. However, in 2002 Kenneth Carpenter
pointed out that this would imply that the shoulder-blade was dorsoventrally flattened instead of laterally as with other theropods and that it thus were more likely the scapula was located on the side of the ribcage. This conformed to a later hypothesis by Philip Senter that non-avian theropods like Unenlagia were unable to lift their forelimbs above their back, as even would still have been the case for the basalmost bird Archaeopteryx
. South-American workers have remained unconvinced though, countering that a laterally positioned scapula would make the coracoid of Unenlagia jut into its ribcage, which seems anatomically implausible.
At at least two meters (6.6 ft long), Unenlagia was probably too big to fly; scientists thus consider that it either evolved from flying ancestors, or Rahonavis (if an unenlagiine) evolved flight from adequately pre-adapted (but too large; see also exaptation
) dromaeosaurids independently of the Archaeopteryx lineage, at a time when a multitude of bird lineages had already undergone vigorous adaptive radiation
.
sensu Gauthier 1986.
However, in 1999 Mark Norell and Peter Makovicky stated that Unenlagia was a member of the Dromaeosauridae
. Unenlagia would have belonged to the strange and extremely bird-like Gondwana
n clade
of dromaeosaurids called the Unenlagiinae
, and be closely related to species such as Buitreraptor
and Neuquenraptor
(which might be the same species as Unenlagia). Makovicky et al. in 2005 also recovered the 'flying raptor' Rahonavis
as a member of this group, which would mean that either Unenlagia is secondarily flightless, having evolved from flying, Rahonavis-like ancestors, or that bird-like flight evolved at least twice. Norell et al. in 2006 also found Rahonavis to be the sister taxon of Unenlagia.
This position has not been unanimously accepted. In 2011 Novas and Federico Agnolín published a study in which an Unenlagiidae was positioned within Avialae.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of, possibly dromaeosaurid, theropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
.
The genus Unenlagia has been assigned two species: U. comahuensis, the type species described by Novas and Puerta in 1997, and U. paynemili, described by Calvo et al. in 2004.
Discovery and naming
In 1996 in the NeuquénNeuquén
Neuquén is the name of the following things:* Neuquén, Argentina* Neuquén Province* Neuquén River* Neuquén Group...
province of Argentina a skeleton of a theropod was discovered in the Sierra del Portezuelo and reported the same year. In 1997 Fernando Emilio Novas and Pablo Puerta named and described Unenlagia comahuensis. The generic name is derived from Mapuche
Mapuche
The Mapuche are a group of indigenous inhabitants of south-central Chile and southwestern Argentina. They constitute a wide-ranging ethnicity composed of various groups who shared a common social, religious and economic structure, as well as a common linguistic heritage. Their influence extended...
uñen, "half", and lag, "bird", in reference to the fact that the describers considered the species to be a link between birds and more basal theropods. The specific name refers to the Comahue
Comahue
.Comahue is a sub-region of Argentina slightly to the south of the country's centre that covers the northern part of Argentine Patagonia and includes the provinces of Neuquén and Río Negro....
, the region the find was made.
The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen, MCF PVPH 78, was uncovered in layers of the Portezuelo Formation
Portezuelo Formation
The Portezuelo Formation is a geologic formation outcropping in the Mendoza, Río Negro and Neuquén provinces of Argentina. It is the fourth-oldest formation in the Neuquén Group and the older of the two formations in the Río Neuquén Subgroup...
dating to the Coniacian
Coniacian
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...
. It consists of a partial skeleton lacking the skull but including vertebrae, a sacrum, ribs, chevrons, a scapula, a humerus, a partial pelvis, a femur and a tibia.
In 2002 near the Lago Barreales a second skeleton was uncovered and reported in 2003. In 2004 it was named and described by Jorge Calvo, Juan Porfiri and Alexander Kellner
Alexander Kellner
Alexander Wilhelm Armin Kellner is a Liechtensteinian/Brazilian paleontologist, a leading expert in the field of the study of pterosaurs....
as a second species: Unenlagia paynemili. The specific name honours Maximino Paynemil, the chief of the Paynemil community. The holotype is MUCPv-349, a partial skeleton consisting of a humerus and two pubes. Several paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
s were also assigned: MUCPv-343, a claw; MUCPv-409, a partial ilium; MUCPv-415, a phalanx and MUCPv-416, a vertebra.
Some researchers consider Neuquenraptor
Neuquenraptor
Neuquenraptor is a dromaeosaurid theropod dinosaur of the Late Cretaceous of Argentina, one of the first dromaeosaurids found in the Southern Hemisphere....
to be a junior subjective synonym of Unenlagia.
Description
The body length of Unenlagia has been disputed, due to the fact that only the leg length is well known and an uncertainty whether this should be extrapolated using the proportions of the low-slung Dromaeosauridae or the long-legged basal birds. Estimates have thus varied between a length of 3.5 metres and a weight of 75 kilogrammes on the one hand, and a length of just two metres on the other. Likewise, the interpretation of the head form has changed from a shorter-snouted dromaeosaurid condition to the elongated shape known from the later discovered related genera BuitreraptorBuitreraptor
Buitreraptor is a predatory dromaeosaurid theropod dinosaur from the Cretaceous of Argentina.Buitreraptor was described in 2005. The type species is Buitreraptor gonzalezorum...
and Austroraptor
Austroraptor
Austroraptor was a genus of dromaeosaurid dinosaur that lived about 70 million years ago during the Cretaceous period in what is now modern Argentina. The type species for the genus, Austroraptor cabazai, was described in late 2008 by Fernando Novas of the Museo Argentino de Ciencias Naturales...
.
Unenlagia was very birdlike. Novas and Puerta found its pelvic region, especially the form of the ilium
Ilium
-Places:* Ilion or, Latinized, Ilium, another name for the legendary city of Troy, hence the title of Homer's Iliad*Ilium , an ancient city in Epirus...
, to be very similar to that of the early bird Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
. The shoulder girdle of Unenlagia was originally interpreted as if it was adapted for flapping, with a flat scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
positioned on top of the ribcage, making the shoulder joint point more laterally. However, in 2002 Kenneth Carpenter
Kenneth Carpenter
Kenneth Carpenter is a paleontologist. He is the museum director of the USU Eastern Prehistoric Museum and author or co-author of a number of books on dinosaurs and Mesozoic life...
pointed out that this would imply that the shoulder-blade was dorsoventrally flattened instead of laterally as with other theropods and that it thus were more likely the scapula was located on the side of the ribcage. This conformed to a later hypothesis by Philip Senter that non-avian theropods like Unenlagia were unable to lift their forelimbs above their back, as even would still have been the case for the basalmost bird Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
. South-American workers have remained unconvinced though, countering that a laterally positioned scapula would make the coracoid of Unenlagia jut into its ribcage, which seems anatomically implausible.
At at least two meters (6.6 ft long), Unenlagia was probably too big to fly; scientists thus consider that it either evolved from flying ancestors, or Rahonavis (if an unenlagiine) evolved flight from adequately pre-adapted (but too large; see also exaptation
Exaptation
Exaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour...
) dromaeosaurids independently of the Archaeopteryx lineage, at a time when a multitude of bird lineages had already undergone vigorous adaptive radiation
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
.
Phylogeny
Novas and Puerta in the original description considered Unenlagia a sister taxon of the birds, which would make it a basal member of the AvialaeAvialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
sensu Gauthier 1986.
However, in 1999 Mark Norell and Peter Makovicky stated that Unenlagia was a member of the Dromaeosauridae
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
. Unenlagia would have belonged to the strange and extremely bird-like Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of dromaeosaurids called the Unenlagiinae
Unenlagiinae
Unenlagiinae is a subfamily of Dromaeosauridae. Unenlagiines are one of the most basal lineages of dromaeosaurids. Unenlagiines are known from South America and Madagascar....
, and be closely related to species such as Buitreraptor
Buitreraptor
Buitreraptor is a predatory dromaeosaurid theropod dinosaur from the Cretaceous of Argentina.Buitreraptor was described in 2005. The type species is Buitreraptor gonzalezorum...
and Neuquenraptor
Neuquenraptor
Neuquenraptor is a dromaeosaurid theropod dinosaur of the Late Cretaceous of Argentina, one of the first dromaeosaurids found in the Southern Hemisphere....
(which might be the same species as Unenlagia). Makovicky et al. in 2005 also recovered the 'flying raptor' Rahonavis
Rahonavis
Rahonavis is a genus of bird-like dinosaur from the Late Cretaceous of what is now northwestern Madagascar. It is known from a partial skeleton found in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province...
as a member of this group, which would mean that either Unenlagia is secondarily flightless, having evolved from flying, Rahonavis-like ancestors, or that bird-like flight evolved at least twice. Norell et al. in 2006 also found Rahonavis to be the sister taxon of Unenlagia.
This position has not been unanimously accepted. In 2011 Novas and Federico Agnolín published a study in which an Unenlagiidae was positioned within Avialae.