Spondylosoma

Spondylosoma (meaning "vertebra body") is a genus of avemetatarsalian archosaur belonging to the clade Aphanosauria from the late Ladinian-age Middle Triassic Lower Santa Maria Formation in Paleorrota Geopark, Brazil.

Spondylosoma
Temporal range: Middle Triassic
Spondylosoma aphanosaur skeletal
Skeletal restoration showing known material, with a mostly hypothetical outline
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Aphanosauria
Genus: Spondylosoma
Type species
Spondylosoma absconditum
von Huene, 1942

History

Friedrich von Huene based the genus on a fragmentary postcranial skeleton held at the University of Tübingen. This skeleton includes two teeth, two cervical vertebrae, four dorsal vertebrae, three sacral vertebrae, scapulae, part of a humerus, part of a femur, and part of a pubis. At the time, he thought it was a prosauropod.[1]

Spondylosoma skeletal Headden
Known bones on a silhouette of a basal dinosaur, an outdated classification scheme

With the discovery of the basal dinosaur Staurikosaurus, Spondylosoma drew attention as a possible relative. Authors went back and forth on the question, considering it either as a basal dinosaur, or as a "thecodont" or other basal archosaur. In 2000, Peter Galton noted that it lacks dinosaurian characteristics and was probably a rauisuchian more closely related to rauisuchids,[2] whereas in 2004 Max Langer disputed this and included Spondylosoma as a possible basal dinosaur similar to the herrerasaurs (but did not firmly rule out raisuchian affinities).[3] In his 2009 thesis on archosaur evolution, Sterling Nesbitt placed Spondylosoma at Archosauria incertae sedis, noting that the characters used by Galton to tentatively place the genus in Rauisuchidae are also found in Aetosauria, and that the holotype lacks characters to place it in either Pseudosuchia or Ornithodira.[4]

The redescription of Teleocrater[5] revealed numerous similarities between Spondylosoma and a few other Triassic taxa leading to their referral to a new clade of archosaurs, Aphanosauria, which is the sister to Ornithodira within Avemetatarsalia.

References

  1. ^ von Huene, F. (1942). Die fossilen Reptilien des südamerikanischen Gondwanalandes. C.H. Beck:Munich, 342 p. [German]
  2. ^ Galton, P.M. (2000). Are Spondylosoma and Staurikosaurus (Santa Maria Formation, Middle-Upper Triassic, Brasil) the oldest saurischian dinosaurs? Paläontologische Zeitschrift 74(3):393-423.
  3. ^ Langer, M.C. (2004). Basal Saurischia. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (second edition). University of California Press:Berkeley, 25-46. ISBN 0-520-24209-2
  4. ^ Sterling J. Nesbitt (2009). "The early evolution of archosaurs: Relationships and the origin of major clades". Columbia University (open access dissertation): 1–632.
  5. ^ Nesbitt et al. 2017. The earliest bird-line archosaurs and the assembly of the dinosaur body plan. Nature. doi:10.1038/nature22037
1942 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1942.

Aphanosauria

Aphanosauria ("hidden lizards") is group of reptiles distantly related to dinosaurs (including birds). They were at the base of a group known as Avemetatarsalia, one of two main branches of archosaurs. The other main branch, Pseudosuchia, includes modern crocodilians. Aphanosaurs possessed features from both groups, indicating that they are the oldest and most primitive known clade of avemetatarsalians, at least in terms of their position on the archosaur family tree. Other avemetatarsalians include the flying pterosaurs, small bipedal lagerpetids, herbivorous silesaurids, and the incredibly diverse dinosaurs, which survive to the present day in the form of birds. Aphanosauria is formally defined as the most inclusive clade containing Teleocrater rhadinus and Yarasuchus deccanensis but not Passer domesticus (House sparrow) or Crocodylus niloticus (Nile crocodile). This group was first recognized during the description of Teleocrater. Although only known by a few genera, Aphanosaurs had a widespread distribution across Pangaea in the Middle Triassic.They were fairly slow quadrupedal long-necked carnivores, a biology more similar to basal archosaurs than to advanced avemetatarsalians such as pterosaurs, lagerpetids, and early dinosaurs. In addition, they seemingly possess 'crocodile-normal' ankles (with a crurotarsal joint), showing that 'advanced mesotarsal' ankles (the form acquired by many dinosaurs, pterosaurs, lagerpetids, and advanced silesaurids) were not basal to the whole clade of Avemetatarsalia. Nevertheless, they possessed elevated growth rates compared to their contemporaries, indicating that they grew quickly, more like birds than modern reptiles. Despite superficially resembling lizards, the closest modern relatives of aphanosaurs are birds.

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.

Dongusuchus

Dongusuchus (meaning Donguz River crocodile in Greek, for the area where the type specimen was found) is an extinct genus of archosauriform. Fossils have been found from the Donguz Formation outcropping on the banks of the Donguz River in the Orenburg Oblast of Russia. They are associated with a fossil assemblage called the Eryosuchus Fauna, named after the capitosaurid Eryosuchus, the most common organism found from the assemblage. The locality dates back to the Anisian and early Ladinian stages of the Middle Triassic.Sennikov (1988) and Gower and Sennikov (2000) suggested that Dongusuchus was a gracile rausuchian with a long, sigmoidally curved neck, unlike the more typical robust short-necked rauisuchians that appear later in the Triassic. More recently, Nesbitt (2009) argued that Dongusuchus most probably represents a non-archosaurian archosauriform. According to Nesbitt (2009), the poorly-defined crista tibiofibularis and the absence of a distinct anteromedial tuber of the proximal portion in Dongusuchus suggest that it is not a member of Archosauria. Although Gower and Sennikov (2000) suggested that the distinct sigmoidal shape of Dongusuchus femur is unique, a similar shape is present in the femora of some phytosaurs. A paratype tibia was also found to be more closely related to Euparkeria and phytosaurs, on the basis of its convex and rounded distal surface. Additionally, the proximal surface of the tibia lacks a trait present in nearly all pseudosuchians, a depression on its lateral condyle. Nesbitt assigned Dongusuchus to Archosauriformes on the basis of the following traits: its femur has a low fourth trochanter, and the distal condyles do not expand markedly beyond the shaft. These traits suggest that Dongusuchus was an archosauriform more derived than Erythrosuchus.Dongusuchus was also excluded from Archosauria by Niedźwiedzki et al. (2014) and a new large cladistic analysis of archosauromorphs by Ezcurra (2016) found Dongusuchus to be the sister taxon to the Indian Yarasuchus. Both Dongusuchus and Yarasuchus were recovered in a clade with Spondylosoma and Teleocrater by Nesbitt et al. (2017) at the base of Avemetatarsalia, making them more closely related to bird-line archosaurs.

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.

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.

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).

Teleocrater

Teleocrater (meaning "completed basin", in reference to its closed acetabulum) is a genus of avemetatarsalian archosaur from the Middle Triassic Manda Formation of Tanzania. The name was coined by English paleontologist Alan Charig in his 1956 doctoral dissertation, but was only formally published in 2017 by Sterling Nesbitt and colleagues. The genus contains the type and only species T. rhadinus. Uncertainty over the affinities of Teleocrater have persisted since Charig's initial publication; they were not resolved until Nesbitt et al. performed a phylogenetic analysis. They found that Teleocrater is most closely related to the similarly enigmatic Yarasuchus, Dongusuchus, and Spondylosoma in a group that was named the Aphanosauria. Aphanosauria was found to be the sister group of the Ornithodira, the group containing dinosaurs and pterosaurs.

A carnivorous quadruped measuring 7–10 feet (2.1–3.0 m) long, Teleocrater is notable for its unusually long neck vertebrae. The neural canals in its neck vertebrae gradually become taller towards the back of the neck, which may be a distinguishing trait. Unlike the Lagerpetidae or Ornithodira, the hindlimbs of Teleocrater are not adapted for running; the metatarsal bones are not particularly elongated. Also unlike lagerpetids and ornithodirans, Teleocrater inherited the more flexible ankle configuration present ancestrally among archosaurs, suggesting that the same configuration was also ancestral to Avemetatarsalia but was lost independently by several lineages. Histology of the long bones of Teleocrater indicates that it had moderately fast growth rates, closer to ornithodirans than crocodilians and other pseudosuchians.

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.

Yarasuchus

Yarasuchus (meaning "red crocodile") is an extinct genus of avemetatarsalian archosaur that lived during the Anisian stage of the Middle Triassic of India. The genus was named and described in 2005 from a collection of disarticulated but fairly complete fossil material found from the Middle Triassic Yerrapalli Formation. The material is thought to be from two individuals, possibly three, with one being much more complete and articulated than the other. The type and only species is Y. deccanensis. Yarasuchus was a quadruped roughly 2–2.5 metres (6.6–8.2 ft) long, with an elongated neck and tall spines on its vertebrae. Unlike other quadrupedal Triassic reptiles, the limbs and shoulders of Yarasuchus were slender, and more like those of ornithodirans.

Yarasuchus has had a complicated taxonomic history, after originally being described as a "prestosuchid rauisuchian", it was later variously recovered as a poposauroid pseudosuchian and a non-archosaurian archosauriform of unstable position. In 2017 it was determined to be related to the similarly enigmatic Triassic reptiles Teleocrater, Dongusuchus and Spondylosoma. Together, they belong to a group called Aphanosauria and are placed at the base of Avemetatarsalia, sister to Ornithodira, making Yarasuchus one of the earliest diverging bird-line archosaurs known. The relative completeness of Yarasuchus and its evolutionary position helps to shed light on the origins of later, well known bird-line archosaurs such as the dinosaurs and pterosaurs.

Yueosaurus

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

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