Metriacanthosaurus

Metriacanthosaurus
Live reconstruction (mainly based on better known representatives of the metriacanthosaurids)
Temporal occurrence
Upper Jurassic (lower Oxfordium )
164 million years
Locations
England
Systematics
Lizard dinosaur (Saurischia) Theropoda Tetanurae Metriacanthosauridae Metriacanthosaurus
Scientific name
Metriacanthosaurus
Walker , 1964
species
Metriacanthosaurus parkeri ( from Huene , 1923)

Metriacanthosaurus is a monotypic genus of the Metriacanthosauridae ( Sinraptoridae ) from the lower Upper Jurassic (lower Oxfordian , approx. 164 million years ago) of England. The known material of the only species Metriacanthosaurus parkeri is limited to only a few postcranial bones.

etymology

The name of the genus is a compound of the Greek words μέτριος metrios 'moderate, moderate', ἄκανθα akantha 'sting' and σαῦρος sauros 'lizard'. It therefore means something like "moderately prickly lizard" and refers to the moderately elongated spinous processes of the vertebrae. The specific epithet of the only kind described so far honors the amateur paleontologist James Parker. The holotype (OUM (NH) J.12144) comes from his collection, which was transferred to the Oxford University Museum in 1914, and is also the only known specimen of this type to date.

Find location and taphonomy

Type and so far only locality of Metriacanthosaurus found : cliff in the northeastern part of Weymouth Bay (Bowleaze Cove)

The location of the holotype of Metriacanthosaurus is a cliff in the channel coast at Weymouth in Dorset in South West England, in which the upper Jurassic upper part (Weymouth member, Cardioceras cordatum zone) Oxford Clay formation digested is.

The Oxford Clay ("Oxford Clay") is a marine sedimentary rock , which means that the bones were not embedded in the sediment where the animal in question lived and died, but that they were transported into the sea, presumably by a river were only embedded there. This also explains the incompleteness of the material. The fact that an oyster-like mussel of the species Gryphaea dilatata had grown attached to one of the pelvic bones was indicative of the stratigraphic position of the find layer .

Taxonomic history

In 1923, the leading German paleontologist at the time, Friedrich von Huene, published a short treatise on the European theropods of the Jurassic and Cretaceous periods . In this work he mentioned a copy of the "Parker Collection" from Weymouth's Oxford Clay, which included an incomplete pelvis, a thigh bone (femur), the proximal ("upper") end of a lower leg bone (tibia) and parts of the trunk and tail spine . He found similarities, but also differences to the species Megalosaurus bucklandii and " Megalosaurus (Streptospondylus) cuvieri " known from the higher Central Jurassic of England and therefore declared this specimen to be the holotype of a new Megalosaurus species, which he called Megalosaurus parkeri .  

In his monograph on the lizard-basin dinosaurs, von Huene (1932) was no longer entirely sure about his original assignment and classified the fossil bones from Weymouth as a transition form to the genus " Altispinax " from the English Wealden, which he himself established in 1923, due to the height of the spinous processes ( Lower chalk ) a.

In 1964, Alick Walker found in a paper on the presumed ancestry of the great theropods that the bones from Weymouth were so different from those of " Streptospondylus cuvieri  " and Megalosaurus bucklandii that he established the genus Metriacanthosaurus especially for them . Apart from the relatively high spinous processes with which he justified the choice of name, he saw no similarities with the Unterkretazischen forms " Altispinax " and Acrocanthosaurus .

features

Reconstruction of the outline of the iliac bone of the holotype and the only known specimen of Metriacanthosaurus parkeri (left cranial, right caudal; after Walker, 1964)

According to Walker's (1964) reconstruction of the ilium, its dorsal (“upper”) edge has a relatively sharp kink: While the caudal (“rear”) section of the dorsal edge rises slightly towards the middle, it falls relatively from the middle abruptly to the cranial ("front") end of the ilium, and that rises significantly more than the rear section. Walker (1964) uses this feature, among other things, to generically distinguish Metriacanthosaurus from Megalosaurus . However, the correctness of Walker's (1964) reconstruction has been confirmed by Carrano et al. (2012) have been questioned, and they consider this characteristic as questionable, without, however, questioning the validity of M. parkeri as a formal taxon. In addition to the kink in the upper edge of the ilium, Molnar (1990) mentions the presence of a lateral (lateral) ridge on the proximal (“iliac”) part of the ischium, already mentioned by Huene, as a delimiting feature ( autapomorphy ). In his dissertation on Megalosaurus , Benson (2009) ^* names the following two diagnostic features for Metriacanthosaurus : the ventral ("lower") side of the posterior vertebral bodies flat, and the width of the torso vertebrae about 3/4 of their height in the rear part.

Assuming a femur length of 80 centimeters, Metriacanthosaurus must have been a relatively large theropod (especially for its time) , with an estimated weight of one ton. The genus was named after its elongated spinous processes, but these are no longer or higher than in many comparable large, relatively closely related and almost contemporary theropods, but, similar to Megalosaurus , Sinraptor and Ceratosaurus, more than 1.5 times as high as the vertebral body (vertebral center).

^* cited in Carrano et al. (2012)

classification

Metriacanthosaurus is a relatively original theropod and as such is one of the "primitive" representatives of the Tetanurae . Its characteristics suggest a close relationship with a line of development known mainly from China. Paul (1988) even came to the conclusion that Metriacanthosaurus was identical to the genus Yangchuanosaurus , a view that was not accepted. In addition, Paul (1988) coined the name Metriacanthosaurinae for a subfamily (the Eustreptospondylidae within its "palaeotheropods") specifically to accommodate this genus. In a comprehensive survey of British dinosaurs (Naish & Martill, 2007), Metriacanthosaurus is classified as the geologically oldest representative of the Sinraptorids in Europe, older than Lourinhanosaurus from the Upper Jurassic of Portugal, which was first described as Sinraptoride in 1998 .

A relatively current hypothesis on the closer relationship of Metriacanthosaurus is shown in the following cladogram (after Carrano et al., 2012: p. 249, Fig. 8B). The name Metriacanthosauridae is used here as an allegedly older synonym for Sinraptoridae. ^**

Allosauroidea	Metriacanthosauridae  Yangchuanosaurus zigongensis     CV 00214 ***     Yangchuanosaurus shangyouensis  Metriacanthosaurinae  Shidaisaurus     Metriacanthosaurus     "Sinraptor" hepingensis     Sinraptor dongi     Siamotyrannus     Allosauria

^** Carrano et al. (2012: p. 250) claim that Paul (1988) coined the name Metriacanthosauri d ae for a newly established family, which is not true. Instead, he coined the name Metriacanthosauri n ae for a newly established subfamily, which he placed in the also newly established family Eustreptospondylidae.

^*** CV 00214 is an incompletely preserved postcranial skeleton from the Shangshaximiao Formation (Oxfordium to early Kimmeridgian ) by Zigong , which was previously assigned to the species Szechuanosaurus campi , which is only based on tooth finds and is therefore considered a noun dubium . The results of the analysis by Carrano et al. (2012) according to CV 00214 to a representative of the genus Yangchuanosaurus .

Individual evidence

1. ↑ Christopher White: Museums and art galleries. Pp. 485-498 in: Brian Harrison (Ed.): The History of the University of Oxford: Volume VIII: The Twentieth Century. Clarendon Press, Oxford 1994, ISBN 0-19-822974-7 , p. 492.
2. ↑ ^{a b c d e} Alick Walker: Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. In: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 248, 1964, pp. 53-134, doi: 10.1098 / rstb.1964.0009 , p. 109 (Fig. 16e, f), 116 f.
3. ↑ ^{a b c d e f g} Matthew T. Carrano, Roger BJ Benson, Scott D. Sampson: The phylogeny of Tetanurae (Dinosauria: Theropoda). In: Journal of Systematic Palaeontology. 10, No. 2, 2012, pp. 211-300, doi: 10.1080 / 14772019.2011.630927 .
4. ^ ^{A b} Friedrich von Huene: Carnivorous Saurischia in Europe since the Triassic. In: Bulletin of the Geological Society of America. 34, 1923, pp. 449-458, doi: 10.1130 / GSAB-34-449 (alternative full text access : BHL ), p. 453.
5. ↑ ^{a b c} Friedrich von Huene: The fossil reptile order Saurischia, its development and history. In: Monographs on Geology and Palaeontology, Series 1, No. 4. Leipzig 1932, p. 231.
6. ↑ Ralph E. Molnar: Problematic Theropoda: “Carnosaurs”. Pp. 306-317 in: David B. Weishampel, Peter Dodson, Halszka Osmólska (eds.): The Dinosauria. University of California Press, Berkeley 1990, p. 314.
7. ^ ^{A b c} Gregory S. Paul: Predatory dinosaurs of the world. Simon and Schuster, 1988, ISBN 0-671-61946-2 ( archive.org ), p. 289 ff .
8. ^ ^{A b} Darren Naish, David M. Martill: Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia . In: Quarterly Journal of the Geological Society . 164, 2007, pp. 493-510.
9. ^ Roger BJ Benson, Jonathan D. Radley: A New Large-Bodied Theropod Dinosaur from the Middle Jurassic of Warwickshire, United Kingdom . In: Acta Palaeontologica Polonica . 55, No. 1, 2010, pp. 35-42. doi : 10.4202 / app.2009.0083 .