''Velocisaurus'' ("swift lizard") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

noasaurid Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other ther ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

period of

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 List of South American countries by area, second-largest ...

Description

''Velocisaurus'' was probably around long, based on a

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...

length of . This makes it the smallest noasaurid, after '' Berthasaura''. The foot is unique in that the middle (third)

metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

has become the main weight-bearing element. Its upper end has thickened whereas the shafts of the adjoining second and fourth metatarsals have thinned considerably. Such a configuration is unknown for other theropods, including birds. Bonaparte explained it as an adaptation for a cursorial (running) lifestyle. The high speed would have been necessary to escape larger theropods; Bonaparte suggested that ''Velocisaurus'' was itself an

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

, as indicated by the fact that the sole claw found, of the fourth toe, was not trenchant but relatively straight. ''Velocisaurus'' can be characterized by several traits unknown in other Abelisauroids. These include: * A subtriangular cross section of the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...

, with the medial and lateral sides converging to form a thick crest pointing anteriorly (a subtriangular cross section of the femur is also known in '' Masiakasaurus''). * A long and slender

with a large anteriorly flat distal end to accommodate a large ascending process of the

astragalus ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...

(reminiscent of derived coelurosaurs and ornithomimids). * Very thin and rod-like metatarsals II and IV (metatarsal II is reduced to a lesser extent in other noasaurids and some

abelisaurids Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...

as well). * An anteroposteriorly short and dorsoventrally tall subtriangular pedal

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly ...

IV-1, with a narrow dorsal surface.

History of discovery

In 1985 Oscar de Ferrariis and

Zulma Brandoni de Gasparini Zulma Nélida Brandoni de Gasparini (born 15 May 1944) is an Argentinian paleontologist and zoologist. She is known for discovering the fossils of the dinosaur '' Gasparinisaura'', which was named after her. Work Born in the city of La Plata, ...

uncovered fossils at Boca del Sapo in

Neuquén province Neuquén () is a province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west. It also meets La Pampa Provinc ...

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

from layers of the

Bajo de la Carpa Formation The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that crops out in northern Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the oldest of two formations belonging to the Río Colorado Subgr ...

, dating from the

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...

. Among them was the right lower hind limb of a small theropod. In 1991 this dinosaur was described and named by

José Bonaparte José Fernando Bonaparte (14 June 1928 – 18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists . One of the best-known Argentine paleo ...

as ''Velocisaurus unicus''. The generic name is derived from

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

''velox'', "swift", a reference to the fact that the hind leg and foot show adaptations for running. The specific name means "unique" in Latin, referring to the exceptional build of the foot. The genus and species are based on the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

MUCPv 41, a nearly complete right leg which is part of the collection of the Museo de la Universidad Nacional del Comahue.Bonaparte J.F. (1991). "Los vertebrados fósiles de la Formación Rio Colorado, de la Ciudad de Neuquén y Cercanías, Cretácico Superior, Argentina" he fossil vertebrates of the Rio Colorado Formation, of the city of Neuquén and surroundings, Upper Cretaceous, Argentina ''Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" e Instituto Nacional de Investigación de las Ciencias Naturales. Paleontología'' 4: 17-123 A somewhat complete left leg, specimen MPCN-PV-370, was described in 2016.

Classification

Bonaparte originally assigned ''Velocisaurus'' to a family of its own, the Velocisauridae. A study of theropod relationships by

Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina.

and Sebastian Apesteguia in 2003 showed that ''Velocisaurus'' was a close relative of the strange ceratosaur '' Masiakasaurus''. These two may form a subfamily, the Velocisaurinae. In 2004 this subfamily was assigned to the

Noasauridae Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other th ...

within the more inclusive

Abelisauroidea Abelisauroidea is typically regarded as a Cretaceous group, though the earliest abelisauridae remains are known from the Middle Jurassic of Argentina (classified as the species Eoabelisaurus mefi) and possibly Madagascar (fragmentary remains o ...

.F. E. Novas, F. L. Agnolin, and S. Bandyopadhyay, 2004, "Cretaceous theropods from India: a review of specimens described by Huene and Matley (1933)", ''Revista del Museo Argentino de Ciencias Naturales, nuevo serie'' 6(1): 67-103

Palaeobiology

In a 2001 study conducted by Bruce Rothschild and other paleontologists, 12 foot bones referred to ''Velocisaurus'' were examined for signs of

stress fracture A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or ...

, but none were found.Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

References

{{Portal bar, Dinosaurs, Cretaceous Abelisaurs Santonian life Late Cretaceous dinosaurs of South America Cretaceous Argentina Fossils of Argentina Bajo de la Carpa Formation Fossil taxa described in 1991 Taxa named by José Bonaparte

Description

History of discovery

Classification

Palaeobiology

See also

References