''Lucianovenator'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 ...

coelophysid Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of C ...

theropod

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 ...

which lived 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 ...

during the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

. The genus name ''Lucianovenator'' translates to "Luciano's hunter", in reference to Don Luciano Leyes, who first reported the remains. The species name ''bonoi'' refers to Tulio del Bono, a local scientific authority who collaborated on the describers' research. It is one of the few

neotheropods Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the e ...

known from South America.

Discovery

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 several ...

(PVSJ 906) of ''Lucianovenator bonoi'' was found in the "Quebrada del puma" locality of the

Quebrada del Barro Formation The Quebrada del Barro Formation is a geological formation of the Marayes-El Carrizal Basin in San Juan Province, Argentina. This formation is the most fossiliferous portion of the Triassic Marayes Group, and is also the youngest unit of the gro ...

in Argentina, which is estimated to be from the late

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

in age, approximately 210 to 202 million years ago. PVSJ 906 represents an articulated vertebral sequence from the third

cervical In anatomy, cervical is an adjective that has two meanings: # of or pertaining to any neck. # of or pertaining to the female cervix: i.e., the ''neck'' of the uterus. *Commonly used medical phrases involving the neck are **cervical collar **cervic ...

to fourth dorsal

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

, as well as a

sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

and a partial

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. In addition, three more specimens were referred to ''Lucianovenator''. These include PVSJ 899 (a sacrum and partial pelvis), PVSJ 1013 (a sacrum), and PVSJ 1084 (a sacrum and partial pelvis). PVSJ 1004, the proximal end of a right

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 connects ...

, may also belong to the species.

Description

As with other neotheropods, the cervical vertebrae of ''Lucianovenator'' possess a complex system of fossae (pits) and laminae (ridges) that connect the main body of each vertebra (centra), front and rear joint plates (pre- and post- zygapophyses), and top and bottom rib facets (diapophyses and pleurapophyses) to each other. Although the cervicals of ''Lucianovenator'' possess many fossae, four particular examples of paired fossae (four on each side of the vertebrae) can be used to distinguish it from other neotheropods. The first of these is deep pit located directly at the base of each prezygapophysis, and the second is a larger pit is located immediately behind it. These two pits are obscured by a ridge known as a prezygapophyseal centrodiapophyseal lamina, which connects each prezygapophysis to the each diapophysis, and each diapophysis to the rear portion of the centrum. A third fossa is located at the rear portion of the vertebra. It too is obscured from the side, this time by the centropostzygapophyseal lamina which connects each postzygapophysis to the rear portion of the centrum. Each of the third fossae connects to a pair of large internal cavities which lie adjacent to the canal for the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

. This combination of features is unique to ''Lucianovenator,'' as no other coelophysoid possesses all of these features at once. The first and third pairs of fossae are similar to those of '' "Syntarsus" kayentakatae'', but the second pair is not. The third pair does connect to internal cavities in '' Coelophysis bauri'', but so does the first pair, unlike the case in ''Lucianovenator''. Another of ''Lucianovenator'''s distinguishing traits is that the anterior cervical ribs are very long (more than five times as long as the cervical centra). The fourth diagnostic pair of cervical fossae in ''Lucianovenator'' is also the only

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

(unique distinguishing trait) of the genus''.'' ''Lucianovenator'' is unique in the fact that the edge of each centrodiapophyseal lamina (which connects each diapophysis to the centrum) acquires a long and deep pit, which becomes progressively longer and deeper towards the base of the neck. In cervical 9, the pit is nearly the entire length of the centrodiapophyseal lamina, and is so deep that it is not completely visible from the side.

Classification

A phylogenetic analysis published along with the description of ''Lucianovenator'' assigned it to the

Coelophysidae Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of C ...

, in a clade with '' Coelophyis rhodesiensis'' and '' Camposaurus''. This clade is supported by a single feature, the fact that the zygapophyses of the sacral vertebrae are fused. The authors of the paper suggested that the relative rarity of theropods in Rhaetian deposits compared to Norian deposits may be the result of

taphonomic bias Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...

rather than a decline in diversity.

References

{{Taxonbar, from=Q30116769 Coelophysoids Late Triassic dinosaurs of South America Triassic Argentina Fossils of Argentina Fossil taxa described in 2017

Discovery

Description

Classification

See also

References