Abrictosaurus

Abrictosaurus (/əˌbrɪktəˈsɔːrəs/; "wakeful lizard") is a genus of heterodontosaurid dinosaur from the Early Jurassic Period of what is now southern Africa. It was a small bipedal herbivore or omnivore, approximately 1.2 meters (4 feet) long, and weighing less than 45 kilograms (100 pounds).

This dinosaur is known from the fossil remains of only two individuals, found in the Upper Elliot Formation of Qacha's Nek District in Lesotho and Cape Province in South Africa. The Upper Elliot is thought to date from the Hettangian and Sinemurian stages of the Early Jurassic Period, approximately 200 to 190 million years ago.[1] This formation is thought to preserve sand dunes as well as seasonal floodplains, in a semiarid environment with sporadic rainfall. Other dinosaurs found in this formation include the theropod Megapnosaurus, the sauropodomorph Massospondylus, as well as other heterodontosaurids like Heterodontosaurus and Lycorhinus. Remains of terrestrial crocodylomorphs, cynodonts and early mammals are also abundant.[2]

Abrictosaurus
Temporal range: Early Jurassic, 199–196 Ma
Abrictosaurus
Specimen NHMUK RU B54
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Family: Heterodontosauridae
Subfamily: Heterodontosaurinae
Genus: Abrictosaurus
Hopson, 1975
Species

Description

Abrictosaurus dinosaur
Illustration

Heterodontosaurids like Abrictosaurus were small, early ornithischians, named for their markedly heterodont dentition. They are best known for the large, canine-like tusks (often called caniniforms) in both upper and lower jaws. There were no teeth in the front of the jaws, where a hard beak was used to crop vegetation. There were three premaxillary teeth, with the first two small and conical and the third enlarged to form the upper caniniform, counterpart to the even larger lower caniniform, which was the first dentary tooth. In the upper jaw, a large gap (or diastema) accommodated the lower caniniform tooth and separated the premaxillary teeth from the wider chewing teeth of the maxilla. Similar teeth lined the remainder of the lower jaw.[2]

Abrictosaurus is usually considered the most basal member of the family Heterodontosauridae.[1][2] Lycorhinus and Heterodontosaurus both had high-crowned cheek teeth, which overlapped each other in the jaw, forming a continuous chewing surface analogous to those of Cretaceous hadrosaurids. Abrictosaurus had more widely separated cheek teeth, with lower crowns, more similar to other early ornithischians. It has been suggested that Abrictosaurus lacked tusks and that this is another primitive feature.[3] However, caniniforms were clearly present on one of the two specimens of Abrictosaurus. The upper caniniform measured 10.5 millimeters (0.4 inches) high, while the lower reached 17 mm (0.67 in). These caniniforms were serrated only on the anterior surface, unlike those of Lycorhinus and Heterodontosaurus, which were serrated on both anterior and posterior edges.[4][5] Abrictosaurus also had smaller, less powerful forelimbs than Heterodontosaurus and one fewer phalanx bone in both the fourth and fifth digits of the forelimb.[6]

History and naming

Both specimens of Abrictosaurus are housed in the collection of University College London. The holotype specimen was discovered in Lesotho and consists of a partial skull and skeleton (UCL B54). Paleontologist Richard Thulborn, who first described the specimen in 1974, considered it a new species of Lycorhinus and named it L. consors, using the Latin word consors which means 'companion' or 'spouse'. As UCL B54 lacked the caniniforms which had been found in the type species, Lycorhinus angustidens, Thulborn believed it to be female.[6] Neither the skull nor the skeletons of Abrictosaurus have been fully described in the literature. A tooth from the latest Triassic of Switzerland has been assigned to Abrictosaurus sp., but this has not been supported, as the specimen does not have unique characteristics of Abrictosaurus, heterodontosaurids, or ornithischians in general.[7]

In 1975, James Hopson redescribed a fragmentary heterodontosaur skull (UCL A100) found in South Africa that Thulborn had previously assigned to Lycorhinus angustidens.[4] After showing that UCL A100 could not belong to L. angustidens but was instead more similar to UCL B54, Hopson erected a new genus to contain both specimens. The generic name Abrictosaurus (from the Greek αβρικτος/abriktos meaning 'wakeful' and σαυρος/sauros meaning 'lizard') refers to Hopson's disagreement with Thulborn's hypothesis that heterodontosaurids underwent periods of aestivation (hibernation during hot and/or dry seasons). The specific name was retained, creating the new binomial Abrictosaurus consors.[5] Despite Hopson's renaming, Thulborn continued to consider Lycorhinus angustidens, Heterodontosaurus tucki, and Abrictosaurus consors to be three species of the genus Lycorhinus. Most paleontologists maintain all three genera separately, although there is no precise definition of a species or genus in paleontology.[1]

Sexual dimorphism

The hypothesis of sexual dimorphism in heterodontosaurids has long centered on Abrictosaurus. Tusks are a sexually dimorphic trait in many modern mammals, including musk deer, walrus, Asian elephants and many pigs, with tusks being present primarily in males. The lack of tusks in UCL B54 led to suggestions that it was female; perhaps even a female of another species.[6] The discovery of caniniforms in UCL A100 showed that A. consors also has this 'male' characteristic, suggesting that it is at least a valid species in its own right. However, UCL B54 may actually be a juvenile, based on its short face and unfused sacral (hip) vertebrae. Therefore, the lack of tusks could be a juvenile trait instead of a secondary sexual characteristic, weakening the case for sexual dimorphism.[2]

References

  1. ^ a b c Norman, D.B., Sues, H.-D., Witmer, L.M., & Coria, R.A. 2004. Basal Ornithopoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd edition). Berkeley: University of California Press. Pp. 393-412.
  2. ^ a b c d Weishampel, D.B. & Witmer, L.M. 1990. Heterodontosauridae. In: Weishampel, D.B., Dodson, P., and Osmolska, H. The Dinosauria (1st edition). Berkeley: University of California Press. Pp.486-497.
  3. ^ Sereno, P.C. 1986. Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). National Geographic Research 2: 234-256.
  4. ^ a b Thulborn, R.A. 1970. The systematic position of the Triassic ornithischian dinosaur Lycorhinus angustidens. Zoological Journal of the Linnean Society 49: 235-245.
  5. ^ a b Hopson, J.A. 1975. On the generic separation of the ornithischian dinosaurs Lycorhinus and Heterodontosaurus from the Stormberg Series (Upper Triassic) of South Africa. South African Journal of Science 71: 302-305.
  6. ^ a b c Thulborn, R.A. 1974. A new heterodontosaurid dinosaur (Reptilia: Ornithischia) from the Upper Triassic Red Beds of Lesotho. Zoological Journal of the Linnean Society of London. 55: 151-175.
  7. ^ Irmis, Randall B.; Parker, William G.; Nesbitt, Sterling J.; Liu, Jun (2007). "Early ornithischian dinosaurs: the Triassic record". Historical Biology. 19 (1): 3–22. CiteSeerX 10.1.1.539.8311. doi:10.1080/08912960600719988.
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.

Dracovenator

Dracovenator () is a genus of dilophosaurid theropod dinosaur that lived approximately 201 to 199 million years ago during the early part of the Jurassic Period in what is now South Africa. Dracovenator was a medium-sized, moderately-built, ground-dwelling, bipedal carnivore, that could grow up to an estimated 7 m (23.0 ft) long. Its type specimen was based on only a partial skull that was recovered.

Echinodon

Echinodon (pronounced eh-KY-no-don) meaning "hedgehog tooth" in reference to the spines on its teeth (Ancient Greek: εχινος, romanized: echinos, lit. 'hedgehog', + ὀδών, odṓn, 'tooth'), occasionally known as Saurechinodon, is a genus of small European dinosaur of the early Cretaceous Period (Berriasian age), 140 million years ago.

Fruitadens

Fruitadens is a genus of heterodontosaurid dinosaur. The name means "Fruita tooth", in reference to Fruita, Colorado (USA), where its fossils were first found. It is known from partial skulls and skeletons from at least four individuals of differing biological ages, found in Tithonian (Late Jurassic) rocks of the Morrison Formation in Colorado. Fruitadens is the smallest known ornithischian dinosaur, with young adults estimated at 65 to 75 cm (26 to 30 in) in length and 0.5 to 0.75 kg (1.1 to 1.7 lb) in weight. It is interpreted as an omnivore and represents one of the latest-surviving heterodontosaurids.

Heterodontosauridae

Heterodontosauridae is a family of early ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Although their fossils are relatively rare and their group small in numbers, they lived across all continents except Australia for approximately 100 million years, from the Late Triassic to the Early Cretaceous.

Heterodontosaurids were fox-sized dinosaurs less than 2 metres (6.6 feet) in length, including a long tail. They are known mainly for their characteristic teeth, including enlarged canine-like tusks and cheek teeth adapted for chewing, analogous to those of Cretaceous hadrosaurids. Their diet was herbivorous or possibly omnivorous.

Heterodontosaurinae

Heterodontosaurinae is an extinct subfamily of heterodontosaurid ornithischian dinosaurs from the earliest to the mid Middle Jurassic (Hettangian - Bajocian) of Africa and South America. Currently, the basalmost known heterodontosaurine is Lycorhinus angustidens from the Early Jurassic of Cape Province, South Africa. Heterodontosaurines are small-bodied ornithischians characterized by their cheek tooth crowns that are taller than wide, and jaw joint set below the axis of occlusion between maxillary and dentary teeth. Heterodontosaurinae was implicitly named in 1966 by Oskar Kuhn as he is the author of the family Heterodontosauridae. It is a stem-based taxon defined phylogenetically for the first time by Paul Sereno in 2012 as "the most inclusive clade containing Heterodontosaurus tucki Crompton and Charig 1962 but not Tianyulong confuciusi Zheng et al. 2009, Fruitadens haagarorum Butler et al. 2010, Echinodon becklesii Owen 1861."

Heterodontosaurus

Heterodontosaurus is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic, 200–190 million years ago. Its only known member species, Heterodontosaurus tucki, was named in 1962 based on a skull discovered in South Africa. The genus name means "different toothed lizard", in reference to its unusual, heterodont dentition; the specific name honors G. C. Tuck, who supported the discoverers. Further specimens have since been found, including an almost complete skeleton in 1966.

Though it was a small dinosaur, Heterodontosaurus was one of the largest members of its family, reaching between 1.18 m (3 ft 10 in) and possibly 1.75 m (5 ft 9 in) in length, and weighing between 2 and 10 kg (4.4 and 22.0 lb). The body was short with a long tail. The five-fingered forelimbs were long and relatively robust, whereas the hind-limbs were long, slender, and had four toes. The skull was elongated, narrow, and triangular when viewed from the side. The front of the jaws were covered in a horny beak. It had three types of teeth; in the upper jaw, small, incisor-like teeth were followed by long, canine-like tusks. A gap divided the tusks from the chisel-like cheek-teeth.

Heterodontosaurus is the eponymous and best-known member of the family Heterodontosauridae. This family is considered one of the most primitive or basal groups within the order of ornithischian dinosaurs. In spite of the large tusks, Heterodontosaurus is thought to have been herbivorous, or at least omnivorous. Though it was formerly thought to have been capable of quadrupedal locomotion, it is now thought to have been bipedal. Tooth replacement was sporadic and not continuous, unlike its relatives. At least four other heterodontosaurid genera are known from the same geological formations as Heterodontosaurus.

Hettangian

The Hettangian is the earliest age and lowest stage of the Jurassic period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassic period) and is followed by the Sinemurian.In European stratigraphy the Hettangian is a part of the time span in which the Lias was deposited. An example is the British Blue Lias, which has an upper Rhaetian to Sinemurian age. Another example is the lower Lias from the Northern Limestone Alps where well-preserved but very rare ammonites, including Alsatites, have been found.

Jingshanosaurus

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

List of African dinosaurs

This is a list of dinosaurs whose remains have been recovered from Africa. Africa has a rich fossil record, but it is patchy and incomplete. It is rich in Triassic and Early Jurassic dinosaurs. African dinosaurs from these time periods include Coelophysis, Dracovenator, Melanorosaurus, Massospondylus, Euskelosaurus, Heterodontosaurus, Abrictosaurus, and Lesothosaurus. In the Middle Jurassic, the sauropods Atlasaurus, Chebsaurus, Jobaria, and Spinophorosaurus, flourished, as well as the theropod Afrovenator. The Late Jurassic is well represented in Africa, mainly thanks to the spectacular Tendaguru Formation. Veterupristisaurus, Ostafrikasaurus, Elaphrosaurus, Giraffatitan, Dicraeosaurus, Janenschia, Tornieria, Tendaguria, Kentrosaurus, and Dysalotosaurus are among the dinosaurs whose remains have been recovered from Tendaguru. This fauna seems to show strong similarities to that of the Morrison Formation in the United States and the Lourinha Formation in Portugal. For example, similar theropods, ornithopods and sauropods have been found in both the Tendaguru and the Morrison. This has important biogeographical implications.

The Early Cretaceous in Africa is known primarily from the northern part of the continent, particularly Niger. Suchomimus, Elrhazosaurus, Rebbachisaurus, Nigersaurus, Kryptops, Nqwebasaurus, and Paranthodon are some of the Early Cretaceous dinosaurs known from Africa. The Early Cretaceous was an important time for the dinosaurs of Africa because it was when Africa finally separated from South America, forming the South Atlantic Ocean. This was an important event because now the dinosaurs of Africa started developing endemism because of isolation.

The Late Cretaceous of Africa is known mainly from North Africa. During the early part of the Late Cretaceous, North Africa was home to a rich dinosaur fauna. It includes Spinosaurus, Carcharodontosaurus, Rugops, Bahariasaurus, Deltadromeus, Paralititan, Aegyptosaurus, and Ouranosaurus.

Lycorhinus

Lycorhinus is a genus of heterodontosaurid ornithischian dinosaur hailing from the Early Jurassic (Hettangian to Sinemurian ages) strata of the Elliot Formation located in the Cape Province, South Africa.

Manidens

Manidens is a genus of heterodontosaurid dinosaur from the Middle Jurassic of Patagonia. Fossils have been found in the Cañadón Asfalto Formation in Chubut Province, Argentina, dating to the Bajocian.

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.

Sinemurian

In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic epoch or series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian.In Europe the Sinemurian age, together with the Hettangian age, saw the deposition of the lower Lias, in Great Britain known as the Blue Lias.

Tianyulong

Tianyulong (Chinese: 天宇龍; Pinyin: tiānyǔlóng; named for the Shandong Tianyu Museum of Nature where the holotype fossil is housed) was a genus of heterodontosaurid ornithischian dinosaur. The only species was T. confuciusi, whose remains were discovered in Jianchang County, Western Liaoning Province, China.

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