Isaberrysaura

Isaberrysaura is a genus of ornithischian dinosaur from the Early Jurassic Los Molles Formation of Patagonia, Argentina. The genus contains a single species, I. mollensis, described by Salgado et al. in 2017 from a single specimen. Although initially classified as a basal neornithischian, subsequent analysis has allied it with the Stegosauria; the morphology of its skull resembles those of other members of the group.

Isaberrysaura
Temporal range: Bajocian
~168 Ma
Isaberrysaura mollensis skull
Skull and teeth
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Clade: Genasauria
Genus: Isaberrysaura
Salgado et al. 2017
Type species
Isaberrysaura mollensis
Salgado et al. 2017

Description

The teeth of Isaberrysaura are heterodont, with recurved premaxillary teeth and lanceolate maxillary and dentary teeth. In extant iguanid lizards, similar dentition is correlated with omnivorous diets, indicating that Isaberrysaura might too have been omnivorous. Isaberrysaura is also estimated to have measured around 5 to 6 m (16 to 20 ft) long, making it of moderate size.[1]

The skull in particular is very unusual; it is estimated to be 52 cm long and 20 cm wide across the orbits, and it is almost as high as it is wide. The snout slopes anteroventrally from the posterodorsal corner of the infratemporal fenestra to what is seemingly the maxillary-premaxillary contact and the infratemporal fenestra is dorsoventrally deep. In contrast, the orbit is subcircular, not quite as dorsoventrally tall as anteroposteriorly long, smaller than the infratemporal fenestra, and only visible in lateral view. The anterolateral sector of the left supratemporal fenestra is relatively well preserved and it is visible only in dorsal view. The skull's antorbital fossa is roughly triangular, with its base longer than the other two sides. The jugal is triradiate and the anterior process of the jugal forms the posteroventral corner of the antorbital fossa and surpasses anteriorly the base of the lacrimal, a feature seen in basal thyreophorans and stegosaurs. The dorsal process of the jugal is proportionally long. The quadratojugal is very broad and the premaxilla is incompletely preserved while the post-cranial material is as-yet-undescribed at present. The dentition is heterodont, with six premaxillary teeth and thirty maxillary teeth. The genus' overall appearance is highly similar to that of stegosaurians, though lacking the characteristic plates and likely possessing a bipedal stance.[1]

Discovery

Isaberrysaura map
Map showing where the holotype was found

The holotype specimen of Isaberrysaura was discovered in the marine to deltaic sediments of the Los Molles Formation, which is of Bajocian age, by Isabel Valdivia Berry, who is honoured in the generic name. The holotype, known as MOZ-Pv 6459 consists of a partial skeleton with a nearly complete skull (the post-cranial material of which is still unprepared), six cervical vertebrae, fifteen dorsal vertebrae, a sacrum with a partial ilium and an apparently complete pubis, nine caudal vertebrae, part of a scapula, ribs, with the addition of unidentifiable fragments.[1]

Classification

Isaberrysaura as neornithischian
Initial reconstruction of Isaberrysaura as a neornithischian, with gut contents in red

Isaberrysaura's classification is problematic at best; the holotype specimen shares traits with both thyreophorans and neornithischians. For this reason, it has been placed in the Genasauria. Three datasets within the same study by Salgado et al indicated that while it possessed the characteristics of the neornithischians and thyreophorans, it did not fit within either of those groups, representing a previously unknown morphotype within the Ornithischia as a whole.[1] Subsequently, the phylogenetic analysis conducted by Han et al. (2018) recovered Isaberrysaura as one of the basalmost known stegosaurs.[2]

Paleobiology

Gut content of Isaberrysaura mollensis
Gut contents

The holotype specimen of Isaberrysaura has been preserved with fossilized stomach contents. Within the rib cage, a mass of fossilized seeds was discovered; the first preserved meal uncovered in a basal ornithischian. Two types of seeds were recovered close to the posterior ribs of Isaberrysaura, distinguished according to their size. The largest seeds preserved three layers: an outer fleshy sarcotesta, the sclerotesta, and the inner layer (possibly corresponding to the nucellus). These seeds are cycadales of the family Zamiineae on the basis of a well-defined coronula in the micropylar region, whereas the smaller, platyspermic seeds are still indeterminate. The intact nature of the sarcotesta in the largest seeds suggests that Isaberrysaura swallowed the seeds whole without chewing and that they were in the first stages of digestion based on their position in the gut. Based on its teeth, it is possible that the dinosaur had an omnivorous diet, but as no trace of animal remains have been found alongside the seeds, this remains speculative at best. It also remains possible that there were enzyme-producing bacteria present in the dinosaur's gut to aid in digesting tougher plant material as seeds.[1]

See also

References

  1. ^ a b c d e Salgado, Leonardo; Canudo, José I.; Garrido, Alberto C.; Moreno-Azanza, Miguel; Martínez, Leandro C. A.; Coria, Rodolfo A.; Gasca, José M. (2017). "A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents". Scientific Reports. 7: 42778. Bibcode:2017NatSR...742778S. doi:10.1038/srep42778. PMC 5311864. PMID 28202910.
  2. ^ Fenglu Han; Catherine A. Forster; Xing Xu; James M. Clark (2018). "Postcranial anatomy of Yinlong downsi (Dinosauria: Ceratopsia) from the Upper Jurassic Shishugou Formation of China and the phylogeny of basal ornithischians". Journal of Systematic Palaeontology. 16 (14): 1159–1187. doi:10.1080/14772019.2017.1369185.
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.

Neornithischia

Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.

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

Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.

Orodrominae

Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.

Powellvenator

Powellvenator is an extinct genus of coelophysoid theropod dinosaur that lived during the latter part of the Triassic Period in what is now northwestern Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin. The type species, Powellvenator podocitus, was named by Martin Ezcurra in 2017.

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).

Thescelosaurinae

Thescelosaurinae is a subfamily of ornithischian dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America.

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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