Silesaurus

Silesaurus is a genus of silesaurid dinosauriform from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now Poland.

Fossilized remains of Silesaurus have been found in the Keuper Claystone in Krasiejów near Opole, Silesia, Poland, which is also the origin of its name.[1] The type species, Silesaurus opolensis, was described by Jerzy Dzik in 2003. It is known from some 20 skeletons, making it one of the best-represented of the early dinosauriformes.

Silesaurus
Temporal range: Late Triassic, 230 Ma
Silesaurus szkielet
Reconstructed skeleton
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauriformes
Clade: Dracohors
Clade: Silesauridae
Genus: Silesaurus
Dzik, 2003
Species
  • S. opolensis Dzik, 2003 (type)

Description

Silesaurus opolensis
Size compared to a human

Silesaurus measured approximately 2.3 meters (7.5 feet) in length, and was facultatively bipedal. Lightly built, it was probably a fast and agile animal with an active lifestyle. The snout was narrow with forward-pointing nostrils, and the large orbits likely provided Silesaurus with acute vision.

Initially, Silesaurus was thought to be strictly herbivorous, but later research on coprolite contents indicates that it may have been insectivorous.[2] The teeth of the animal were small, conical, and serrated, and were distributed irregularly in its jaws. The tip of the dentary had no teeth, and evidence suggests that it was covered by a keratinous beak.[1]

Classification

Silesaurus1
S. opolensis restored without feather-like filaments
MEPAN silezaur rauizuch
Silesaurus opolensis and Polonosuchus silesiacus models in Poland

Scientists think that Silesaurus was not a dinosaur, but rather a dinosauriform. Dinosaurian features lacking in Silesaurus include an enlarged deltopectoral crest (a muscle attachment on the humerus), and epipophyses (enlarged tendon attachment above the postzygapophysis) on the cervical vertebrae.

However, Silesaurus has some dinosaurian characteristics as well:

As a result, alternative hypotheses place Silesaurus at or near the base of the ornithischian dinosaurs. Other scientists propose a basal link between the basal sauropodomorphs and ornithischians.[1]

Systematic position after Nesbitt (2011):[3]

Ornithodira 
 Pterosauromorpha 

Scleromochlus

Pterosauria

 Dinosauromorpha 
 Lagerpetonidae 

Lagerpeton

Dromomeron

 Dinosauriformes 

Marasuchus

 Silesauridae 

Lewisuchus/Pseudolagosuchus

Asilisaurus

Eucoelophysis

Sacisaurus

Silesaurus

 Dinosauria 
 Saurischia 

Theropoda

Sauropodomorpha

Ornithischia

Palaeoecology

Silesaurus lived in a subtropical environment similar to the modern Mediterranean basin with alternating summer monsoons and dry winters. The animal shared its environment of extensive swamplands and fern vegetation with a wealth of invertebrates as well as dipnoan and ganoid fishes, temnospondyls, phytosaurs and early pterosaurs.[4]

Palaeobiology

Beetle elytra and other arthropod remains have been found in coprolites which have been recovered in the vicinity of Silesaurus fossil occurrences. The size and shape of the coprolites combined with the peculiar beaked architecture of Silesaurus's skull may suggest that this animal produced the coprolites and that it could have been wholly or partially insectivorous.[5] It might have fed on insects and other small arthropods by pecking, using the beak-like tip of the snout to accurately target prey in a way similar to modern birds.[6] If so, this would represent the earliest known occurrence of this highly derived mode of feeding and have implications for the understanding of the evolutionary adaptations that would eventually lead up to the origin of dinosaurs.

References

  1. ^ a b c Dzik, J. (2003). "A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland." Journal of Vertebrate Paleontology, 23(3): 556-574.
  2. ^ Martin Qvarnström; Joel Vikberg Wernström; Rafał Piechowski; Mateusz Tałanda; Per E. Ahlberg; Grzegorz Niedźwiedzki (2019). "Beetle-bearing coprolites possibly reveal the diet of a Late Triassic dinosauriform". Royal Society Open Science. 6 (3): Article ID 181042. doi:10.1098/rsos.181042. PMC 6458417.
  3. ^ Nesbitt, 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History. 352, 292 pp.
  4. ^ John W. M. Jagt, Grzegorz Hebda, Sławomir Mitrus, Elena Jagt-Yazykova, Adam Bodzioch, Dorota Konietzko-Meier, Klaudia Kardynał, Kamil Gruntmejer. 2015. Field Guide, Conference Paper, European Association of Vertebrate Palaeontologists XIII Annual Meeting.
  5. ^ Martin Qvarnström; Joel Vikberg Wernström; Rafał Piechowski; Mateusz Tałanda; Per E. Ahlberg; Grzegorz Niedźwiedzki (2019). "Beetle-bearing coprolites possibly reveal the diet of a Late Triassic dinosauriform". Royal Society Open Science. 6 (3): Article ID 181042. doi:10.1098/rsos.181042. PMC 6458417.
  6. ^ Martin Qvarnström; Joel Vikberg Wernström; Rafał Piechowski; Mateusz Tałanda; Per E. Ahlberg; Grzegorz Niedźwiedzki (2019). "Beetle-bearing coprolites possibly reveal the diet of a Late Triassic dinosauriform". Royal Society Open Science. 6 (3): Article ID 181042. doi:10.1098/rsos.181042. PMC 6458417.
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.

Carnian

The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian Pluvial Event) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.

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.

Dinosauromorpha

Dinosauromorpha is a clade of archosaurs that includes the clade Dinosauria (dinosaurs), and all animals more closely related to dinosaurs than to pterosaurs. Birds are the only surviving dinosauromorphs.

Epipophyses

Epipophyses are bony projections of the cervical vertebrae found in archosauromorphs, particularly dinosaurs (including some basal birds). These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. Their morphology is variable and ranges from small, simple, hill-like elevations to large, complex, winglike projections. Epipophyses provided large attachment areas for several neck muscles; large epipophyses are therefore indicative of a strong neck musculature.The presence of epipophyses is a synapomorphy (distinguishing feature) of the group Dinosauria. Epipophyses were present in the basal-most dinosaurs, but absent in the closest relatives of the group, such as Marasuchus and Silesaurus. They were typical for most dinosaur lineages; however, they became lost in several derived theropod lineages in the wake of an increasingly S-shaped curvature of the neck.Several scientific papers have observed that epipophyses were present in various non-dinosaur archosauromorphs. These include several pseudosuchians (Batrachotomus, Revueltosaurus, Xilousuchus, Effigia, Hesperosuchus), basal avemetatarsalians (aphanosaurs) non-archosaur archosauriforms (Vancleavea, Halazhaisuchus), rhynchosaurs, several tanystropheids, and allokotosaurs. Sauropod-oriented paleontologist Mike Taylor has informally suggested that epipophyses were also present in the vertebrae of certain pterosaurs.

Eucoelophysis

Eucoelophysis (meaning "true hollow form") is a genus of dinosauriform from the Late Triassic (Norian) period Chinle Formation of New Mexico. It was assumed to be a coelophysid upon description, but a study by Nesbitt et al. found that it was actually a close relative of Silesaurus, which was independently supported by Ezcurra (2006), who found it to be the sister group to Dinosauria, and Silesaurus as the next most basal taxon.However, the relationships of Silesaurus are uncertain. Dzik found it to be a dinosauriform (the group of archosaurs from which the dinosaurs evolved), but did not rule out the possibility that it represents a primitive ornithischian.

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. It was therefore contemporary with early dinosaurs such as Herrerasaurus, and lived in the same place.

Jingshanosaurus

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

Lutungutali

Lutungutali (meaning "high hip" in the Bemba language) is an extinct genus of silesaurid dinosauriform from the Middle Triassic of Zambia. The single type species of the genus is Lutungutali sitwensis. Lutungutali was named in 2013 and described from a fossil specimen, holotype NHCC LB32, including hip bones and tail vertebrae. The specimen was collected in 2009 from the upper Ntawere Formation, which dates to the Anisian stage of the Middle Triassic. Lutungutali is the first known silesaurid from Zambia and, along with the Tanzanian silesaurid Asilisaurus and dinosauriform Nyasasaurus, the oldest bird-line archosaur known from body fossils (i.e. parts of the skeleton).

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.

Pseudolagosuchus

Pseudolagosuchus (meaning "false Lagosuchus") is a genus of dinosauromorph from the Middle Triassic (Ladinian) Chañares Formation of Argentina. It may be a junior synonym of Lewisuchus, but there is very little overlapping material. It was a small reptile which was probably about 1 meter (3.3 ft) long, 30 centimeters (1 ft) tall, and weighed approximately 2 kilograms (4.4 lb). It is known only from a pubis, a femur, a tibia, and vertebrae. Both Sterling Nesbitt, Christian Sidor et al. (2010) and Matthew Baron, David Norman and Paul Barrett (2017) treated this taxon as being synonymous with Lewisuchus.

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.

Soumyasaurus

Soumyasaurus is a small silesaurid dinosauriform from the Late Triassic (Norian) Cooper Canyon Formation of western Texas.

Technosaurus

Technosaurus (meaning "Tech lizard", for Texas Tech University) is an extinct genus of Late Triassic dinosauriform, from the Late Triassic Bull Canyon Formation (Dockum Group) of Texas, United States.

For about 20 years after its description, it was thought to be a basal ornithischian dinosaur, but better remains of other Triassic archosaurs have cast doubt on this interpretation. As named, it was a chimera of different animals.

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.

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