Dracoraptor

Dracoraptor Temporal range: Early Jurassic, 201–199 Ma PreЄ Є O S D C P T J K Pg N ↓
Skeletal reconstructions
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Clade:	Neotheropoda
Genus:	†Dracoraptor Martill et. al, 2016
Type species
†Dracoraptor hanigani Martill et. al, 2016

Dracoraptor is a genus of carnivorous neotheropod dinosaur from the Hettangian age of the Early Jurassic period of Wales.

Discovery

Right and left premaxilla

The Dracoraptor fossils were discovered in 2014 and 2015 near the Welsh town of Penarth. In March 2014, brothers and amateur palaeontologists Nick and Rob Hanigan, while searching for ichthyosaur remains at Lavernock Point, the large cape south of Cardiff, found stone plates containing dinosaur fossils which had fallen off the seven metres high cliff face. Judith Adams and Philip Manning of the University of Manchester made X-ray pictures and CAT-scans of the fossils. The remains were donated to the Amgueddfa Cymru – National Museum Wales. They were prepared by Craig Chivers and Gary Blackwell. On 20 July, 2015, student Sam Davies found additional plates with foot bones.^[1]

The type species, Dracoraptor hanigani, was named and described in 2016 by David M. Martill, Steven U. Vidovic, Cindy Howells, and John R. Nudds. The generic name combines the Latin draco, "dragon", a reference to the Welsh Dragon, with raptor, "robber", a usual suffix in the names of theropods. The genus name was suggested by the Hanigan brothers. The specific name honours Nick and Rob Hanigan as discoverers although to be grammatically correct it should be haniganorum.^[1]

The holotype, NMW 2015.5G.1–2015.5G.11, was discovered in the lower Bull Cliff Member of the Blue Lias Formation in the United Kingdom. More precisely, it came from a layer just meters below the first occurrence of Jurassic ammonite Psiloceras and above the Paper Shales that represent the lithological Triassic-Jurassic boundary, precisely dating the dinosaur to the earliest Hettangian, 201.3 million years ago ± 0.2 million years.^[1]

The holotype consists of a partial skeleton with skull. It contains both praemaxillae, both maxillae, teeth, a lacrimal, a jugal, a postorbital, een squamosal, a supraoccipital, parts of the lower jaws, a possible hyoid, two neck vertebrae, neck ribs, rear back vertebrae, at least five front tail vertebrae, chevrons, ribs, belly ribs, the lower parts of a left forelimb, a furcula, both pubic bones, a left ischium, a right thighbone, a shinbone, the upper part of a calf bone, a left astragalus, three tarsals and three metatarsals. About 40% of the skeletal elements is presented. Some bones have been preserved as natural moulds. The specimen in 2016 represented the most complete Mesozoic theropod known from Wales.^[1]

Description

Restoration

Size and distinguishing traits

Dracoraptor was a biped, much like its relatives. The fossil discovered in Wales is a 7-foot-long (2.1 metre) juvenile with a hip height of seventy centimetres; adults may have been ten feet (three meters) long.

In 2016, some distinguishing traits were established. The praemaxilla carries only three teeth, a basal trait. The jugal has a thin front branch running to the maxilla. The bony external nostril is large and has a thin branch beneath it. The pubic bone is obliquely directed to the front and is considerably longer than the ischium. The fourth tarsal has a process at the upper side.^[1]

Skeleton

Hand elements and the furcula at the extreme right

In the front of the snout each praemaxilla embraces the front of a very large nostril. The skull bears three premaxillary 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. 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 an antorbital 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.^[1]

Neck vertebra

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 low neural spines. Their undersides are slightly convex and their cross-sections are rectangular. At the front side the vertebral body is pierced by a pleurocoel, a depression with a pneumatic opening for the air sac to enter the inside of the vertebra. The tail vertebrae have two parallel keels at their undersides, which peter out towards the front. Their side processes are flat and broad.^[1]

The presence of a furcula was reported. Furculae have only rarely been recovered from early theropod fossils; other examples include those of Segisaurus and Coelophysis. The lower arm bones, the ulna and the radius, have a length of about seven centimetres. Hand elements are present but a formula of the phalanges could not determined.^[1]

In the pelvis, the pubic bone has 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 the ischium 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.^[1]

On the thighbone, the lesser trochanter has about two thirds of the height of the greater trochanter and is separated from it by a V-shaped cleft. A clear fourth trochanter is present. In the foot, the third metatarsal has a length of 116 millimetres.^[1]

Evolutionary relationships

A cladistic analysis in 2016 determined that Dracoraptor was a basal member, positioned low in the evolutionary tree, of the Neotheropoda. It was the basalmost coelophysoid.^[1]

The precise affinities of Dracoraptor are indicated by its various traits. The build of the pelvis shows it was a saurischian dinosaur. Among dinosaurs, the dagger-shaped transversely flattened teeth are only found with Theropoda. A membership of the clade Neotheropoda is proven by the shallow depression around the fenestra antorbitalis, the forward position of a pleurcoel on the neck vertebrae and the presence of an obturator notch in the ischium. The position in the Coelophysoidea is more uncertain. Dracoraptor does not clearly share many of the synapomorphies 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 its phylogeny.^[1]

Paleobiology

Close up of a tooth

At the end of the Triassic Period roughly half of Earth's species became extinct in the Triassic-Jurassic extinction event. This extinction event allowed dinosaurs to become the dominant land animals. The largest land predators at the end of the Triassic were Rauisuchia, large quadrupedal reptiles which disappeared in the extinction, paving the way for carnivorous dinosaurs to become the dominant land predators.

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.^[2] In the early Jurassic, Lavernock Point was a small island and the cadaver of Dracoraptor had probably been washed into the sea. Despite the lack of data regarding its ecology, the authors in 2016 had it tentatively illustrated as a "shore-dwelling predator and scavenger".^[1]

Dracoraptor is the oldest known Jurassic dinosaur.^[1] S. Vidovoc 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 from Jurassic Park, books and TV" and "Dinosaurs diversified and populated the ecological niches in the Early Jurassic."^[2] 

References

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