| Dubreuillosaurus | |
|---|---|
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| Reconstructed skull | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Megalosauridae |
| Genus: | †Dubreuillosaurus Allain, 2005 |
| Species: | †D. valesdunensis |
| Binomial name | |
| †Dubreuillosaurus valesdunensis (Allain, 2002 [originallyPoekilopleuron]) | |
| Synonyms | |
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Dubreuillosaurus is agenus of carnivorousdinosaur from the middleJurassic Period. It is amegalosauridtheropod. Its fossils were found inFrance. The only named species,Dubreuillosaurus valesdunensis, was originally described as a species ofPoekilopleuron,Poekilopleuron? valesdunensis, which is still formally thetype species of the genus. It was later renamedDubreuillosaurus valesdunensis when, in 2005, Allain came to the conclusion that it was not part of the genusPoekilopleuron. Its type specimen, MNHN 1998-13, is only rivalled in the number of preserved elements in this group by that ofEustreptospondylus.Dubreuillosaurus is considered to a sistertaxon ofMagnosaurus. It did not show signs of insular dwarfism even though it was uncovered on an island.
In 1994, the mayor ofConteville inNormandy, André Dubreuil, noted that duringland rehabilitation of the old quarry ofPierre de Caen, dinosaur bones had surfaced. He secured a partial skull and some ribs and notified the ParisMuséum national d'Histoire naturelle. However, professional excavations only started in 1998 when the rock of the collapsed quarry face had already been spread by a bulldozer over a considerable surface. It proved necessary to dig up and sieve many cubic metres of rubble over several years, ultimately salvaging about two thousand bone fragments, varying in size between one and ten centimetres. From these scraps a more complete skeleton had to be reassembled.
In 2002, when this process had not yet been completed,Ronan Allain, after having dedicated a thesis to it,[1] named the find as a new species ofPoekilopleuron:Poekilopleuron? valesdunensis. Thespecific name referred to the nearby ancient battlefield of theBattle of Val-ès-Dunes, whereWilliam the Conqueror had in 1046 defeated his enemies. The naming paper also contained a description of the skull.[2] The question mark after the generic name already indicated the assignment toPoekilopleuron was tentative. By 2005, Allain had come to the conclusion that the new species was not part ofPoekilopleuron. He therefore created the new genus nameDubreuillosaurus for this species, the name honouring the Dubreuil family. Thetype species of the genus is the originalPoekilopleuron valesdunensis, thecombinatio nova isDubreuillosaurus valesdunensis. The 2005 paper also contained a description of the postcranial skeleton.[3]
Theholotype,MNHN 1998-13, has been uncovered in a layer of theCalcaire de Caen dating from the middleBathonian. It consists of a fragmentary skeleton with skull. Preserved parts include: the majority of the skull; the splenial and angular of the lower jaw, a natural mold of the surangular, two cervical vertebrae, cervical ribs, seven dorsals, ribs, gastralia, three sacrals, ten caudals, a chevron, a piece of the scapula, a claw of the hand, a partial thighbone, the upper part of a shinbone, a partial fibula, a fifth metatarsal and the first phalanx of the third toe. Considering the incompleteness of most other megalosaurids, this genus is exceptional in having a significant percentage of the skeleton been found. Thetype specimen ofDubreuillosaurus is in the number of preserved elements only rivalled in this group by that ofEustreptospondylus. The holotype represents a subadult individual.[3]
Dubreuillosaurus was physically comparable toEustreptospondylus. The holotype was an individual byGregory S. Paul estimated to measure 5 metres (16 ft) long and to weigh 250 kilograms (550 lb).[4] However, this was a subadult; the adult length is uncertain, though it has been indicated as high as 9 metres (30 ft).
In 2005, Allain established some distinctive traits.Dubreuillosaurus has an unusually low and long skull, with a length three times the height. In the upper corner of the front edge of the nasal branch of the maxilla, a kink is present, separating a convex curvature below from a concave curvature above. The descending branch of the postorbital has a U-shaped cross-section. The parietal bones are not visible in side view. The supratemporal fenestra has a straight inner edge. A paraquadratic fenestra is lacking. A well-developed process is present on the underside of the jugal branch of the ectopterygoid. The rear edge of the jugal branch of the ectopterygoid, in front of the infratemporal fenestra, is deeply grooved. The lower jaw has a large external mandibular fenestra. Theforamen mylohyoideum is largely oriented to the front and below. The head of the thighbone is directed to the inside and below. The front underside of the thighbone has a concave surface.[3] In 2012Matthew Carrano added oneautapomorphy: on the rear of the braincase there is a notch between the basioccipital and the bone surface formed by the exoccipitals and the opisthotic.[5]
Dubreuillosaurus seemed to lack any sort of crest or horns, but the only known specimen is a juvenile, and it is possible that these structures developed in later life. Like its relatives,Dubreuillosaurus probably had short, powerful arms with three-fingered hands.[6]
In 2002,Poekilopleuron? valesdunensis was assigned to theMegalosauridae.[2] In 2012, Carranoet al. refined this to theAfrovenatorinae, in which it would be thesister species ofMagnosaurus within theclade.[5]
The phylogenetic position ofDubreuillosaurus according to Carranoet al. is shown by this cladogram:[5]
Cau (2024) called the diagnosis ofDubreuillosaurus into question, considering it ajunior synonym of the contemporaryPoekilopleuron, attributing the skeletal differences as positional and individual variation, as seen inAllosaurus. Thus,Dubreuillosaurus would represent a less mature individual thanPoekilopleuron.[7]
During the Middle Jurassic much of Europe consisted of a number of islands. Thefossil ofDubreuillosaurus was discovered in sedimentary rocks that were laid down in coastal, mangrove swamps at the east coast of theArmorican Massif. This suggests that it might have hunted fish and other marine prey.[6]Allain in 2002 describedP? valesdunensis as a fish eater orpiscivore but this was influenced by the fact that the holotype ofPoekilopleuron bucklandii had been found together with fish remains.[2] Though uncovered at an islandDubreuillosaurus did not show the effects ofinsular dwarfism; like withEustreptospondylus its small size is due to its being a subadult.
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