Ignotosaurus

Ignotosaurus is an extinct genus of silesaurid dinosauriform known from the Late Triassic (Carnian) Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina.[1] It was therefore contemporary with early dinosaurs such as Herrerasaurus, and lived in the same place.

Ignotosaurus
Temporal range: Carnian
~231.7–231.1 Ma
Ignotosaurus illium
The holotype ilium, seen in dorsal and lateral view
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dracohors
Clade: Silesauridae
Genus: Ignotosaurus
Martínez et al. 2013
Type species
Ignotosaurus fragilis
Martínez et al. 2013

Etymology

The name, meaning 'unknown lizard' from the Latin 'ignotus' 'unknown' and the Greek 'σαυρος' '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 70 millimetres (2.8 in) long, but it is difficult to say accurately how large Ignotosaurus was.[1]

Description

The ilium is slender, and its blade has an extremely thin central portion (only 1 millimetre (0.039 in) 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 has a back wall created by a ventral flange and this closes a socket as it is in contact with the ischium and pubis. The supraacetabular crest is laterally oriented and forms part of the articulation for the femur. A ridge rises from the dorsal edge of this crest and joins the preacetabular process, as in the close relative Silesaurus. 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 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.[1]

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, which are not preserved).[1]

It is thought that the Ischigualasto Formation at this time was a river basin habitat with abundant vegetation. As Ignotosaurus was probably a herbivore, like other silesaurids, it would probably have flourished here, competing for food with rhynchosaurs, cynodonts and possibly some early dinosaurs.[1]

References

  1. ^ a b c d e Martínez et al., 2013

Bibliography

Anchisauria

The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.

However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.

Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Avetheropoda

Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.

Cerapoda

Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.

Dinosauriformes

Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.

Haya griva

Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.

Jeholosauridae

Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Melanorosauridae

The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.

Neotheropoda

Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.

Orionides

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Orodrominae

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Raeticodactylidae

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Riojasauridae

Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).

Silesauridae

Silesauridae is an extinct clade of Triassic dinosauriformes consisting of the closest known relatives of dinosaurs. As indicated by coprolite contents, some silesaurids such as Silesaurus may have been insectivorous, feeding selectively on small beetles and other arthropods.

Unaysauridae

Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.

Xixiposaurus

Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.

Yueosaurus

Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.

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