''Ignotosaurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of silesaurid dinosauriform known from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

) Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

.Martínez et al., 2013 It was therefore contemporary with early dinosaurs such as ''

Herrerasaurus ''Herrerasaurus'' is likely a genus of saurischian dinosaur from the Late Triassic period. Measuring long and weighing around , this genus was one of the earliest dinosaurs from the fossil record. Its name means "Herrera's lizard", after the ...

,'' and lived in the same place.

Etymology

The name, meaning 'unknown lizard' from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

'ignotus' 'unknown' and the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

'' 'lizard', is quite apt as there is only one specimen known and this specimen is only known from the right ilium. This ilium is approximately long, but it is difficult to say accurately how large ''Ignotosaurus'' was.

Description

The ilium is slender, and its blade has an extremely thin central portion (only thick), hence the specific name 'fragilis'. It has the saddle-shaped lateral profile of most silesaurids, and is longer than it is deep. The

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

has a back wall created by a ventral flange and this closes a socket as it is in contact with the

ischium The ischium (; : is ...

and pubis. The supraacetabular crest is laterally oriented and forms part of the articulation for the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

. A ridge rises from the dorsal edge of this crest and joins the preacetabular process, as in the close relative ''

Silesaurus ''Silesaurus'' is a genus of silesaurid dinosauriform from the Late Triassic, of what is now Poland. Discovery and naming The Krasiejów claypit near Opole, Poland, was first discovered as a fossil locality in the 1980s after quarrying for ...

''. The preacteabular process is flattened anteroposteriorly and is angled at 90° to the iliac blade, pointing anterolaterally - these are the diagnostic features of this species. The end of the process has a

rugose Rugose means "wrinkled". It may refer to: * Rugosa, an extinct order of coral, whose rugose shape earned it the name * Rugose, adjectival form of rugae Species with "rugose" in their names * ''Idiosoma nigrum'', more commonly, a black rugose tra ...

growth, but it is less extensive than that of ''Silesaurus''. The postacetabular process is long and has a brevis fossa present on the ventral side. It has a thick rectangular cross-section and a rugose area at the end. The pubic peduncle is long and stout, with a prominent dorsal margin. ''Ignotosaurus'' is thought to be most closely related to ''Silesaurus, Sacisaurus'' and '' Eucoelophysis,'' but as only one of the three characteristic features for silesaurids is preserved this is not certain (the other features are on the femur and

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

, which are not preserved). It is thought that the Ischigualasto Formation at this time was a

river basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, th ...

habitat with abundant vegetation. As ''Ignotosaurus'' was probably a

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

, like other silesaurids, it would probably have flourished here, competing for food with

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s and possibly some early dinosaurs.

References

Bibliography

* {{Taxonbar, from=Q16753928 Carnian genera Late Triassic reptiles of South America Triassic Argentina Fossils of Argentina Ischigualasto Formation Fossil taxa described in 2013 Taxa named by Paul Sereno Silesauridae