| Dracoraptor | |
|---|---|
 | |
| Skeletal reconstruction, with present bones in green, external moulds in orange, and provisionally identified bones in blue | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Coelophysoidea |
| Genus: | †Dracoraptor Martillet al.,2016 |
| Type species | |
| †Dracoraptor hanigani Martillet al., 2016 | |
Dracoraptor (meaning "dragon thief") is agenus ofcoelophysoiddinosaur that lived during theHettangianstage of theEarly JurassicPeriod of what is nowWales dated at about 201 million years ago.[1][2] The fossil was first discovered in 2014 by Rob and Nick Hanigan and Sam Davies at theBlue Lias Formation on the South Wales coast. The genus nameDracoraptor is fromDraco, referring to theWelsh dragon, andraptor, meaning robber, a commonly employed suffix for theropod dinosaurs, with thetype species beingDracoraptor hanigani. It is one of the oldest known Jurassic dinosaurs and is the first dinosaur skeleton from the Jurassic of Wales.[1]
The firstDracoraptorfossils were discovered in 2014 near the Welsh town ofPenarth. In March 2014, brothers and amateurpalaeontologists Nick and Rob Hanigan, while searching forichthyosaur remains atLavernock Point, a large cape south ofCardiff, found stone plates containing dinosaur fossils which had fallen off the 7-metre (23 ft) high cliff face. Judith Adams and Philip Manning of theUniversity of Manchester took X-ray pictures andCAT-scans of the fossils. The remains were donated toAmgueddfa Cymru – Museum Wales, and prepared by Craig Chivers and Gary Blackwell. In 2015, student Sam Davies found additional rock plates at the dig site which contained foot bones assigned toDracoraptor.[3]
Thetype species,Dracoraptor hanigani, was named and described in 2016 by British palaeontologists David Martill, Steven Vidovic, Cindy Howells, and John Nudds. The generic name combines theLatindraco, "dragon", a reference to theWelsh Dragon, withraptor, "robber". Thespecific name honours Nick and Rob Hanigan as discoverers.[3]
Theholotype, NMW 2015.5G.1–2015.5G.11, was discovered in the lowerBull Cliff Member of theBlue Lias Formation in the United Kingdom. More precisely, it came from a layer just metres below the first occurrence ofJurassicammonitePsiloceras and above the Paper Shales that represent thelithologicalTriassic-Jurassic boundary, precisely dating the dinosaur to the earliestHettangianstage, 201.3 million years ago ± 0.2 million years.[3]
The holotype consists of a partial skeleton with skull. It contains bothpraemaxilla (frontmost upper jaw bones), bothmaxillae (main upper jaw bone), teeth, alacrimal, ajugal, apostorbital, asquamosal, asupraoccipital, parts of the lower jaws, a possiblehyoid, twocervical (neck)vertebrae (backbones),cervical ribs, reardorsal (back) vertebrae, at least five frontcaudal (tail) vertebrae,chevrons,ribs,gastralia (or "belly ribs"), the lower parts of a left forelimb, afurcula (wishbone), bothpubic bones, a leftischium (lower and rearmost hip bone), a rightfemur, atibia (shin bone), the upper part of afibula (calf bone), a leftastragalus (ankle bone), threetarsals, and threemetatarsals. About 40% of the skeleton is presented.Dracoraptor is thus the most completeMesozoic non-birdtheropod dinosaur known from Wales.[3]
Dracoraptor was a biped, much like its relatives. The fossil discovered in Wales is a 2.1-metre (6.9 ft) juvenile with a hip height of 70 centimetres (28 in); adults may have been 3 m (9.8 ft) long.[citation needed]
In 2016, someautapomorphies (distinguishing traits) were established forDracoraptor. The praemaxillae carried only three teeth, abasal trait. The jugal had a thin front branch running to the maxilla. The bony externalnostril is large and had a thin branch beneath it. Thepubic bone is obliquely directed to the front and is considerably longer than theischium. The fourthtarsal had a process at the upper side.[3]
In the front of the snout each praemaxilla embraces the front of a very large nostril. The skull bears three praemaxillary teeth per side and at least seven maxillary teeth. The teeth are recurved or dagger-shaped. The edges of the tooth crown are serrated with six to eight denticles per millimetre (0.03 in). On the trailing edge these serrations run all the way to the root, on the leading edge they end at a higher position. Towards the tip of the tooth, these denticles become gradually somewhat smaller. The maxilla borders anantorbital fenestra with a shallow depression. The jugal is a slender element with a straight lower edge, a thin front branch overlapped by the rear branch of the maxilla and an ascending process towards the lacrimal that is thin but not pointed. The lacrimal is rectangular and pinched in the middle.[3]
The neck vertebrae are elongated, opisthocoelous, i.e. with a vertebral body that is convex in front and concave at the rear, and crowned by lowneural spines. Their undersides are slightly convex and their cross-sections are rectangular. At the front side the vertebral body is pierced by apleurocoel, a depression with a pneumatic opening for theair sac to enter the inside of the vertebra. The tail vertebrae had two parallel keels at their undersides, which peter out towards the front. Their side processes are flat and broad.[3]
The presence of afurcula was reported. Furculae have only rarely been recovered from early theropod fossils; other examples include those ofSegisaurus andCoelophysis. The lower arm bones, theulna and the radius, had a length of about seven centimetres. Hand elements are present but a formula of the phalanges could not determined.[3]
In the pelvis, thepubic bone had a length of 212 millimetres. It points obliquely to the front. The pubic foot is moderately broadened in side view, bot at the front and at the rear. The shaft of theischium is with a length of 129 millimetres markedly shorter than the pubic shaft. On the upper front edge a rectangular obturator process is present, forming a clear obturator notch with the ischial shaft. The shaft fan out to below, into an ischial foot.[3]
On the thighbone, the lesser trochanter had about two thirds of the height of thegreater trochanter and is separated from it by a V-shaped cleft. A clear fourth trochanter is present. In the foot, the third metatarsal had a length of 116 millimetres.[3]
Acladistic analysis in 2016 determined thatDracoraptor was a basal member, positioned low in the evolutionary tree, of theNeotheropoda. It was the basalmostcoelophysoid.[3]
The precise affinities ofDracoraptor are indicated by its various traits. The build of the pelvis shows it was asaurischian dinosaur. Among dinosaurs, the dagger-shaped transversely flattened teeth are only found with Theropoda. A membership of theclade Neotheropoda is proven by the shallow depression around the antorbital fenestra, the forward position of a pleurocoel on the neck vertebrae and the presence of an obturator notch in the ischium. The position in theCoelophysoidea is more uncertain.Dracoraptor does not clearly share many of thesynapomorphies of the group, such as a rounded jugal branch towards the lacrimal. This accounts for its basal position in the analysis. Further preparation of the fossils might provide additional information about itsphylogeny.[3]
At the end of the Triassic Period roughly half of Earth's species became extinct in theTriassic-Jurassic extinction event.[4] Thisextinction event allowed dinosaurs to become the dominant land animals. The largest land predators at the end of the Triassic wereRauisuchia, largequadrupedal reptiles which disappeared in the extinction, paving the way for carnivorous dinosaurs to become the dominant land predators.[5]
Dracoraptor had pointed and serrated teeth, indicating it was a meat-eater. But the teeth were small, about one centimetre long, showing it ate small vertebrate animals.[6] In the early Jurassic, South Wales was a coastal area with several small islands in a warm shallow sea. The area which is now Lavernock Point was offshore, so the cadaver ofDracoraptor had probably been washed into the sea from the land to the north. Despite the lack of data regarding itsecology, the authors in 2016 had it tentatively illustrated as a "shore-dwelling predator and scavenger".[3]
Dracoraptor is the oldest known Jurassic dinosaur.[3] Vidovic stated: "So this dinosaur starts to fill in some gaps in our knowledge about the dinosaurs that survived the Triassic extinction and gave rise to all the dinosaurs that we know fromJurassic Park, books and TV" and "Dinosaurs diversified and populated the ecological niches in the Early Jurassic."[6]
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