Қазылған кесіртке - Скелидозавр

Genus of reptiles (fossil)

Scelidosaurus (,/s//ɛ//l//ᵻ//d//oʊ /'/s//ɔːr//ə//s/; with the intended meaning of "limb lizard", from Greek skelis/σκελίς meaning 'rib of beef' and sauros/σαυρος meaning 'lizard') is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of England. Scelidosaurus lived during the Early Jurassic Period, during the Sinemurian to Pliensbachian stages around 191 million years ago. This genus and related genera at the time lived on the supercontinent Laurasia. Its fossils have been found in the Charmouth Mudstone Formation near Charmouth in Dorset, England, and these fossils are known for their excellent preservation. Scelidosaurus has been claimed as one of the earliest complete dinosaur, and is among the most completely known dinosaur of the British Isles. Despite this, a modern description only materialised in 2020. After initial finds in the 1850s, comparative anatomist Richard Owen named and described Scelidosaurus in 1859. Only one species, Scelidosaurus harrisonii named by Owen in 1861, is considered valid today, although one other species was proposed in 1996. Scelidosaurus was about long. It was a largely quadrupedal animal, feeding on low scrubby plants, the parts of which were bitten off by the small, elongated head to be processed in the large gut. Scelidosaurus was lightly armoured, protected by long horizontal rows of keeled oval scutes that stretched along the neck, back and tail. One of the oldest known and most "primitive" of the thyreophorans, the exact placement of Scelidosaurus within this group has been the subject of debate for nearly 150 years. This was not helped by the limited additional knowledge about the early evolution of armoured dinosaurs. Today most evidence suggests that Scelidosaurus is the most derived of the known basal thyreophorans, either closely related to Ankylosauria or Stegosauria+Ankylosauria.

A full grown Scelidosaurus was rather small compared to most later non avian dinosaurs, but it was a medium sized species in the Early Jurassic. Some scientists have estimated a length of 4 metres (13 ft). Scelidosaurus was quadrupedal, with the hindlimbs longer than the forelimbs. It may have reared up on its hind legs to browse on foliage from trees, but its arms were relatively long, indicating a mostly quadrupedal posture.

The first modern diagnosis was provided by David Bruce Norman in 2020. In a first article, Norman provided autapomorphies, unique derived characters, of the skull. The front snout bones, the premaxillae, have a common central rough extension, in life bearing a small upper beak. The nasal bone has on its upper outside a facet touching the inner side of the ascending branch of the premaxilla. The antorbital fenestra is present as a bean shaped depression, its lower edge formed by a sharp ridge. The central parietal crest on the skull roof is formed by two parallel crests separated by a narrow trough on the midline. The roof of the nasal cavity is formed by special plates above the vomers, called the "epivomers". The epipterygoid bone is shaped as a small conical vertical structure of which the base connects to the upper side of the pterygoid bone by means of a lateral flat surface. The basioccipital has large oblique facets on the lower sides. The opisthotic has an expanded pedicel with facets on its underside. Elongated epistyloid bones project obliquely to the rear and below, from the back of the skull. A small spur like structure on the upper edge of the paroccipital process encases the posttemporal fenestra. The rear of the skull is fused on its upper edge with a pair of large curved horn shaped osteoderms. The lower jaw shows only little exostosis, limited to the angular, and lacking an attached osteoderm. The premaxilla, the bone forming the snout tip, was short and no predentary, the bone core of the lower beak on the tip of the stout lower jaws, has been found, so the horny beak that is assumed present with all ornithischians was likely very short. Its teeth were longer and more triangular in side view than in later armoured dinosaurs. Between these main series, one or two rows of smaller oval keeled scutes were present. There were in total four rows of large scutes on the tail: one at the top midline, one at the midline of the underside, and one at each tail side. Whether the midline tail scutes continued over the torso and neck to the front is unknown and unlikely for the neck, though Scelidosaurus is often pictured this way. The neck had at each side two rows of large scutes. The osteoderms of the lower neck row were very large, flat and plate like. The first osteoderms of the top neck rows formed a pair of unique three pointed scutes directly behind the head. These points seem to have been connected by tendons to the rear joint processes, the postzygapophyses, of the axis vertebra. Between the large scutes, very small (5 10 millimetres [0.2 0.4 in]) flat "granules" of bone were perhaps distributed within the skin. In the later Ankylosauria, these small scutes may have developed into larger scutes, fusing into the multi osteodermal plate armour seen in genera such as Ankylosaurus. The lemma text contained a diagnosis, implicating that the genus was validly named and was not a nomen nudum, despite the fact that the definition was vague and no specimens were identified. Owen intended to call the dinosaur "hindlimb saurian" but confused the Greek word σκέλος, skelos, "hindlimb", with σκελίς, skelis, "rib of beef". The name was inspired by the strong development of the hind leg. Afterwards Harrison sent a knee joint, a claw (GSM 109561), a juvenile specimen and a skull to Owen, that were described in 1861. On that occasion the type species Scelidosaurus harrisonii was named, the specific name honouring Harrison. British palaeontologist David Bruce Norman has stressed how remarkable it is that Owen, who previously had propounded that dinosaurs were active quadrupedal animals, largely neglected Scelidosaurus though it could serve as a prime example of this hypothesis and its fossil was one of the most complete dinosaurs found at that time. Norman explained this by Owen's excessive workload in this period, including several administrative functions, polemics with fellow scientists and the study of a large number of even more interesting newly discovered extinct animals, such as Archaeopteryx. Norman also pointed out that Owen in 1861 suggested a lifestyle for Scelidosaurus that is very different from present ideas: it would have been a fish eater and partially sea dwelling. perhaps he was motivated by their larger size. Unfortunately, mixed in with the Scelidosaurus fossils had been the partial remains of a theropod dinosaur and the femur and tibia thus belonged to such a carnivore; this was not discovered until 1968 by Bernard Newman. The same year, B. H. Newman suggested to have Lydekker's selection of the knee joint as the lectotype officially rescinded by the International Commission on Zoological Nomenclature, as the joint was in his opinion from a species related to Megalosaurus. Eventually, after Newman had already died, Alan Jack Charig actually filed a request in 1992. The knee joint was in 1995 by Samuel Welles et al. informally assigned to a "Merosaurus", which name has not yet been validly published. It more likely belongs to some member of the Coelophysoidea or Neoceratosauria. The new lectotype skeleton had been uncovered in the Black Ven Marl or Woodstone Nodule Bed, marine deposits of the Charmouth Mudstone Formation, dating from the late Sinemurian stage, about 191 million years ago. It consists of a rather complete skeleton with skull and lower jaws. Only the snout tip, the neck base, the forelimbs and the tail end are missing. Hundreds of osteoderms were found in connection with the skeleton, many more or less in their original position. From the 1960s onward, this fossil was further prepared by Ronald Croucher using acid baths to free the bones from the surrounding matrix, a method perfected for the Charmouth fossils. In 1992, Charig reported that only a single block had yet to be treated,

Apart from the lectotype, other fossils are known of Scelidosaurus. In 1888 Lydekker catalogued a large number of single bones, largely limb elements, and osteoderms, that had been acquired by the NHMUK from the Norris collection. that had already been reported in 1959. Found by geologist James Frederick Jackson (1894–1966) of Charmouth, it is from a slightly younger layer, the Stonebarrow Marl Member dating to the early Pliensbachian, about 190 million years old. which was sold to the Bristol Museum where it is registered as specimen BRSMG CE12785. Specimen CAMSMX.39256 is part of the collection of the Sedgwick Museum at Cambridge. In 2020, Norman denied this. However, in 2024, Satchell reidentified the proximal femur fragment (BELUM K3998) as an indeterminate dinosaur remain, not belonging to a Scelidosaurus or an ornithischian. In 2000, David Martill et al. announced the preservation of soft tissue in a specimen referred to a cf. Scelidosaurus sp. (that is, material tentatively referred to the genus Scelidosaurus but not to any specific species). The fossil, with inventory number BRSMG CF2781, was in the early 1990s, in an already prepared state, discovered in the legacy of the late Professor John Challinor, who had used it to illustrate his lectures. Its provenance is unknown. It consists of a series of eight caudal vertebrae in a cut slab of carbonate mudstone, which was judged to date from the late Hettangian to Sinemurian stages. Parts of the fossil were preserved in such a way that an envelope of preserved soft tissue is visible around the vertebrae, and show the presence of an epidermal layer over the scutes. Although the fossils are fragmentary, this reassessment has not been accepted, and S. oehleri is today once again recognized as Tatisaurus. In 1989, scutes which were found in the Kayenta Formation (Glen Canyon Group) of northern Arizona, were by Kevin Padian referred to a Scelidosaurus sp., and used to determine that the age of the strata was around 199.6 196.5 million years ago, at a time when it was still thought that Scelidosaurus harrisonii dated to the early Sinemurian. These scutes established a geographic tie in between Arizona's Glen Canyon and Europe, where fossils of Scelidosaurus had previously been discovered. In 2016, Peter Malcolm Galton and Kenneth Carpenter identified it as a nomen dubium, instead once again placing the specimens as Thyreophora indet.

Scelidosaurus was placed in the Dinosauria by Owen in 1861. In 1868/1869 Edward Drinker Cope proposed a family Scelidosauridae in a double lecture but this was only published in December 1871; therefore it was Thomas Henry Huxley who validly named the Scelidosauridae in 1869. In the nineteenth century almost any armoured dinosaur then known has been considered a member of the Scelidosauridae. In the later twentieth century, the term was used for an assembly of "primitive" ornithischians close to the ancestry of ankylosaurs and stegosaurs, such as Scutellosaurus, Emausaurus, Lusitanosaurus and Tatisaurus. The family was resurrected by Chinese paleontologist Dong Zhiming in his 2001 description of Bienosaurus, a thyreophoran sharing close affinities with Scelidosaurus. Scelidosaurus was an ornithischian. It was the oldest ornithischian known until the description of Geranosaurus in 1911. though this concept then encompassed all armoured forms. In a 1968 paper, Romer argued it was an ankylosaur. or basal to the ankylosaur stegosaur split. The stegosaur classification has fallen out of favor, but is seen in older dinosaur books. Cladistic analyses have invariably recovered a basal position for Scelidosaurus, outside of the Eurypoda. In the 2022 monograph on Scelidosaurus by David Norman, a different relationship amongst thyreophorans was found, with Stegosauria being the most basal group, and Scelidosaurus being most closely related to Ankylosauria. Fossil records of thyreophorans more basal than Scelidosaurus are sparse. The more "primitive" Scutellosaurus, also found in Arizona, was an earlier genus which was facultatively bipedal. A trackway of a possible early armoured dinosaur, from around 195 million years ago, has been found in France. Ancestors of these basal thyreophorans evolved from early ornithischians similar to Lesothosaurus during the Late Triassic. In this aspect, it resembled the stegosaurids, which also bore primitive teeth and simple jaws. Its diet would have consisted of ferns or conifers, as grasses did not evolve until late into the Cretaceous Period, after Scelidosaurus was long extinct. Another similarity with the stegosaurs is the narrow head, which might indicate a selective diet consisting of high quality fodder. However, Barrett pointed out that for an animal the size of Scelidosaurus, with a large gut allowing efficient fermentation, the intake of easily digestible food of high energetic value was less important than with smaller animals, that are often critically dependent on it. Norman concluded that Scelidosaurus fed on low scrubby vegetation, with a height up to one metre. Raising itself on its hindlimbs alone, could have vertically increased the feeding envelope and was perhaps anatomically possible, but Norman doubted it was a relevant part of its behaviour.