Ixalerpeton

Ixalerpeton (meaning "leaping reptile") is a genus of small, bipedal dinosauromorphs in the lagerpetid family, containing one species, I. polesinensis. It lived in the Late Triassic of Brazil alongside the sauropodomorph dinosaur Buriolestes.[1]

Ixalerpeton
Temporal range: Carnian
~237–228 Ma
Ixalerpeton models
Models
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Family: Lagerpetidae
Genus: Ixalerpeton
Cabreira et al. 2016
Species:
I. polesinensis
Binomial name
Ixalerpeton polesinensis
Cabreira et al. 2016

Description

Ixalerpeton was similar to other lagerpetids (namely Dromomeron and Lagerpeton) in having long hindlimbs with well-developed muscle attachments on the femur; in particular, its fourth trochanter was quite large and formed a crest (which is unlike Dromomeron).[1] However, the last few dorsal vertebrae of Ixalerpeton do not have the forward-inclining neural spines of Lagerpeton (which were associated with the latter's hopping, or saltatory, lifestyle).[1][2] In addition to the enlarged fourth trochanter, a suite of other traits differentiate Ixalerpeton from all previously-described lagerpetids; there is an antitrochanter on the ilium; the end of the shaft of the ischium is tall; there is no ambiens process on the pubis; the medial condyle on the femur is relatively flat at the front end but sharply angled at the back end; and the back face of the top end of the tibia has a deep groove.

The head and forelimbs found with Ixalerpeton are the first of these elements that have been found among lagerpetids.[3] Unlike dinosauriforms, the posttemporal fenestra at the back of the skull is large and unreduced; there is an extra bone, the postfrontal, bordering the eye socket; there is no supratemporal fossa, which is an indentation found on the frontal bone in dinosauriforms; and the glenoid cavity on the scapula, where the scapula-humerus joint is located, faces slightly sideways instead of backwards. On the other hand, there is an anterior tympanic recess on the braincase, and the deltopectoral crest on the humerus is long, both of which are common among basal dinosauromorphs.[1]

Discovery and naming

The holotype specimen of Ixalerpeton, numbered ULBRA-PVT059, consists of parts from the skull, vertebral column, and all four limbs. The specimen comes from the Carnian Santa Maria Formation of Brazil, and it was found alongside two individuals of Buriolestes as well as a set of femora belonging to second individual of Ixalerpeton. The genus name of Ixalerpeton combines the Greek words ixalos ("leaping") and erpeton ("reptile"), and the species name polesinensis references the town of São João do Polêsine, where the dig site is located.[1]

Classification

A 2016 phylogenetic analysis found that Ixalerpeton was the closest relative of Dromomeron. The phylogenetic tree recovered is partially reproduced below.[1]

Eucrocopoda

Euparkeria

Lagerpetidae

Lagerpeton

Ixalerpeton

Dromomeron

Dinosauriformes

Marasuchus

Pseudolagosuchus

Lewisuchus

Saltopus

Dinosauria

Paleoecology

Similar to the Ischigualasto[4] and Chinle[5] Formations, the Santa Maria Formation preserves both Ixalerpeton (a non-dinosaur dinosauromorph) and Buriolestes (a dinosaur). This indicates that dinosaurs did not rapidly replace their dinosauromorph ancestors.[1]

References

  1. ^ a b c d e f g Cabreira, S.F.; Kellner, A.W.A.; Dias-da-Silva, S.; da Silva, L.R.; Bronzati, M.; de Almeida Marsola, J.C.; Müller, R.T.; de Souza Bittencourt, J.; Batista, B.J.; Raugust, T.; Carrilho, R.; Brodt, A.; Langer, M.C. (2016). "A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet". Current Biology. 26 (22): 3090–3095. doi:10.1016/j.cub.2016.09.040. PMID 27839975.
  2. ^ Sereno, P.C.; Arcucci, A.B. (1994). "Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis". Journal of Vertebrate Paleontology. 13 (4): 385–399. doi:10.1080/02724634.1994.10011522.
  3. ^ Cell Press (10 November 2016). "Dinosaurs' rise was 'more gradual,' new fossil evidence suggests". Phys.org. Retrieved 11 November 2016.
  4. ^ Martínez, R.N.; Apaldetti, C.; Alcober, O.A.; Colombi, C.E.; Sereno, P.C.; Fernandez, E.; Malnis, P.S.; Correa, G.A.; Abelin, D. (2013). "Vertebrate succession in the Ischigualasto Formation". Journal of Vertebrate Paleontology. 32 (Supplement 1: Memoir 12: Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian–Norian) of Argentina): 10–30. doi:10.1080/02724634.2013.818546.
  5. ^ Irmis, R.B.; Nesbitt, S.J.; Padian, K.; Smith, N.D.; Turner, A.H.; Woody, D.; Downs, A. (2007). "A Late Triassic Dinosauromorph Assemblage from New Mexico and the Rise of Dinosaurs". Science. 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
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.

Buriolestes

Buriolestes (meaning "Buriol's robber") is a genus of early sauropodomorph dinosaurs from the Late Triassic Santa Maria Formation of the Paraná Basin in southeastern Brazil. It contains one species, B. schultzi, named in 2016. The type specimen was found alongside a specimen of the lagerpetid dinosauromorph Ixalerpeton.

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.

Lagerpetidae

The Lagerpetidae (; originally Lagerpetonidae) is a family of basal dinosauromorphs. Members of the family are known from Late Triassic of Argentina, Arizona, Brazil, New Mexico, and Texas. Lagerpetids were typically small, although some, like Dromomeron gigas, were fairly large. Lagerpetid fossils are very rare, the most common finds are of the hindlimbs, which possessed a number of unique features.

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

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.

Raeticodactylidae

Raeticodactylidae is a family of eudimorphodontoid eopterosaurian pterosaurs that lived in Switzerland during the Late Triassic. The family includes Caviramus, and the type genus Raeticodactylus, which are both known from the Kössen Formation, around 205 mya. Raeticodactylidae was first used in 2014 by Andres et al., as a group of all pterosaurs closer to Raeticodactylus than Eudimorphodon. The following phylogenetic analysis follows the topology of Andres et al. (2014).

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).

Santa Maria Formation

The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a Late Anisian to Early Norian age (Early to Late Triassic), and is notable for its fossils of early dinosaurs and other dinosauromorphs, including the herrerasaurid Staurikosaurus, the basal sauropodomorphs Buriolestes and Saturnalia, and the lagerpetid Ixalerpeton. It received this name because it was discovered first in the city of Santa Maria, on the central region of Rio Grande do Sul state.

The distinguished English paleontologist Arthur Smith Woodward determined the age of Santa Maria Formation dated Mesozoic Era, Upper Triassic period (about 220 million years). A U-Pb (Uranium decay) dating of a locality of the Upper portion of the Santa Maria Formation dated around 233.23±0.73 million years ago, putting that locality 1.5 million years older than the Ischigualasto Formation, instead being in the temporal range of the Los Chañares Formation, and making the two formations (Santa Maria and Ischigualasto) approximately equal as having the earliest dinosaur localities.The Santa Maria Formation is part of the Candelária Sequence, and is biostratigraphically subdivided into Dinodontosaurus (latest Ladinian-earliest Carnian), Santacruzodon (earliest Carnian-middle Carnian), and Hyperodapedon (middle Carnian-latest Carnian) Assemblage Zones (from the oldest to youngest). Moreover, the Hyperodapedon Assemblage Zone is subdivided into Hyperodapedon Acme Zone (most of the zone, where the rhynchosaur Hyperodapedon is widely reported) and Exaeretodon Sub-Zone (restricted to 3 known and sampled localities, where Hyperodapedon is almost absent, but the traversodontid cynodont Exaeretodon is widely reported). These subdivisions are also known as Lower and Upper Hyperodapedon Assemblage Zone, respectively.

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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