Eustreptospondylus

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Eustreptospondylus
Temporal range: Late Jurassic (Oxfordian), 163–154  Ma
Eustreptospondylus skeleton (incomplete skull).JPG
Mounted holotype skeleton
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: Megalosauridae
Subfamily: Eustreptospondylinae
Paul, 1988
Genus: Eustreptospondylus
Walker, 1964
Species:
E. oxoniensis
Binomial name
Eustreptospondylus oxoniensis
Walker, 1964
Synonyms

Eustreptospondylus ( /jˌstrɛptspɒnˈdləs/ yoo-STREPT-o-spon-DY-ləs; [1] meaning "true Streptospondylus" or "well curved vertebra") is a genus of megalosaurid theropod dinosaur, from the Oxfordian stage of the Late Jurassic period (some time between 163 and 154 million years ago) in southern England, at a time when Europe was a series of scattered islands (due to tectonic movement at the time which raised the sea-bed and flooded the lowland).

Discovery and naming

Nopcsa's 1905 skeletal restoration Eustreptospondylus.jpg
Nopcsa's 1905 skeletal restoration

In 1870, workers at the Summertown Brick Pit, just north of Oxford, England, found the skeleton of a theropod. The remains were acquired by the local bookseller James Parker, who brought them to the attention of Oxford Professor John Phillips. Phillips described the bones in 1871, but did not name them. [2] At the time, the remains represented the most complete skeleton of a large theropod ever found. Eustreptospondylus is still the most complete of any large Jurassic European theropod. In 1890, the skeleton was bought by Oxford University, and Arthur Smith Woodward examined it and referred it to Megalosaurus bucklandi. In 1905 and 1906 Baron Franz Nopcsa reassigned the skeleton to the species, Streptospondylus cuvieri, which had been first described by Sir Richard Owen in 1842, based on a now lost vertebra from the Bathonian stage of the Jurassic period. [3] The reason for this assignment was that the type species Streptospondylus altdorfensis from France, was a clearly related form, and Nopcsa decided to subsume all British material of this nature under a single Streptospondylus species, for which then the name S. cuvieri could not be avoided. [4] [5] The assignment of a rather complete find to a species based on very poor remains was troublesome. This was compounded by German palaeontologist Friedrich von Huene, who sometime referred to the specimen as Streptospondylus cuvieri and at other times considered it a species of Megalosaurus: Megalosaurus cuvieri . [6]

In 1964, Alick Donald Walker clarified matters by erecting a separate genus and species for the Oxford specimen: Eustreptospondylus oxoniensis. The genus name Eustreptospondylus, was intended to mean "true Streptospondylus". Streptospondylus means "turned vertebra", and is derived from the Greek words streptos (στρεπτος) meaning "reversed" and spondylus (σπονδυλος), a reference to the fact that its dorsal vertebrae were opisthocoelous, in contrast to the typical procoelous vertebrae of crocodiles. [7] The specific name "oxoniensis", refers to its provenance from Oxford. [8]

Von Huene's 1923 restoration of Streptospondylus cuvieri, which actually depicts Eustreptospondylus Streptospondylus cuvieri.jpg
Von Huene's 1923 restoration of Streptospondylus cuvieri, which actually depicts Eustreptospondylus

The holotype, OUM J13558, was recovered by W. Parker from claystone in a marine layer of the Stewartby Member of the Oxford Clay Formation, which dates to the Callovian stage of the Jurassic period, approximately 162 million years ago. It consists of a rather complete skeleton, with a skull which is missing elements including the nasal bones, the jugals, the rear ends of the lower jaws, the lower arms and the end of the tail. It represents a subadult individual. The only other specimen ever referred to Eustreptospondylus oxoniensis is OUMNH J.29775, a left ilium. The holotype was fully prepared and exhibited in 1924, in a rather erect position. In the early twenty-first century a new display changed this to a horizontal position of the body.

Modern skeletal restoration Eustreptospondylus oxoniensis skeleton.png
Modern skeletal restoration

In 2000, Oliver Walter Mischa Rauhut found that only minor differences in the hip bones — a more upward extending fusion of the "feet" of the pubic bones — make Eustreptospondylus different from a previously known megalosaurid called Magnosaurus , [9] and in 2003 he proposed that they should be the same genus, which would make the full species name Magnosaurus oxoniensis. [10] In 2010, Gregory S. Paul considered the species identical to Streptospondylus altdorfensis. [11]

The first detailed description of the Eustreptospondylus material was in 1906 by Nopcsa. A modern description was published in 2008 by Rudyard Sadleir e.a. [12] In 1964, Walker also named a second species of Eustreptospondylus: Eustreptospondylus divesensis, based on a French find. [8] In 1977 this became the separate genus Piveteausaurus .

Description

Size comparison of E. oxoniensis Eustreptospondylus Size Comparison by PaleoGeek.svg
Size comparison of E. oxoniensis

The main specimen of Eustreptospondylus was not fully grown, and according to an estimate by Paul in 1988 was about 4.63 metres (15.2 ft) long and weighed about 218 kilograms (481 lb). [13] Various estimates suggest that Eustreptospondylus was an "average-sized" theropod, with a hypothetical adult length of around 6 metres (20 ft), and a mass of 0.5 tonnes (0.49 long tons; 0.55 short tons). [1] [11]

The skull of Eustreptospondylus has a rather pointed snout in side view, with a large horizontally oriented nostril. There is no lacrimal horn. The skull roof is relatively thick. Oblique grooves in the jaw joints caused the gape of the mouth to be widened when the lower jaws were opened. These jaws at the front are rather tall and wide. No teeth have been preserved in either the upper or lower jaws, but the size of its toothsockets proves that the third tooth of the lower jaw was enlarged. Though not keeled, the front dorsal vertebrae have paired hypapophyses at their undersides, just as with Streptospondylus altdorfensis.

Distinguishing anatomical features

Skull fragments, NHM Eustreptospondylus skull fragments (39152089754).jpg
Skull fragments, NHM

Sadleir et al. (2008) established several traits that distinguish Eustreptospondylus from its direct relatives. In the corner of the lacrimal a shallow depression is present, which is pierced by a smaller foramen. The descending branch of the postorbital has a groove in its outer rear corner. The outer side of the squamosal has a well-developed drooping flange covering, in side view, the upper rear part of the lateral temporal fenestra. The tenth neck vertebra has a clear depression on its front underside. The neck and dorsal vertebrae are not keeled. [12] In 2012 Matthew Carrano added to these traits. The peduncle of the ilium to which the pubic bone is attached, is as transversely wide as it is long from front to rear. With the rear blade of the ilium, the lower edge of the outer blade side is turned upwards to an almost horizontal position, creating and denuding over its total length a bone surface, the "brevis shelf", forming the internal face of the inner blade side — this shelf with dinosaurs functions as an attachment area for a tail muscle, the Musculus caudofemoralis brevis. [14]

Reconstructed skull, showing known remains of the holotype in white Eustreptospondylus reconstructed skull.png
Reconstructed skull, showing known remains of the holotype in white

Sadleir also found additional traits proving that Eustreptospondylus differed from Magnosaurus nethercombensis in more than a single detail. The interdental plates reinforcing the back of the teeth are longer from front to rear than they are tall; with M. nethercombensis the opposite is true. Seen from above, the pubic bone forms transversely a more narrow part of the lower rim of the hip joint. Seen from behind, the upper part of the inner side of the thighbone is straight. The cnemial crest of the upper shinbone has no ridge running to the front and below, on its outer side. [12]

Classification

In 1964, Walker assigned Eustreptrospondylus to the Megalosauridae, which was historically included in a paraphyletic "Carnosauria", though sometimes a separate Eustreptospondylidae was recognised. [15] Today Eustreptospondylus is commonly considered a member of the Eustreptospondylinae, clade within the Megalosauridae.

A possible position of Eustreptospondylus in the evolutionary tree is given by this cladogram based on a cladistic analysis by Carrano et.al.: [14]

Megalosauroidea

Paleobiology

Eustreptospondylus feeding on an ichthyosaur Eustrept1DB1.jpg
Eustreptospondylus feeding on an ichthyosaur

Diet

Eustreptospondylus, like many other theropods, fed on smaller dinosaurs and pterosaurs, or scavenged the carcasses of fishes, marine reptiles, and other dinosaurs. [1] It might have foraged on shorelines for carcasses and marine life. [16]

Swimming

Eustreptospondylus is known from a fossil from what was an island, at a time when Europe consisted mostly of archipelagos. This suggests that it might have been able to swim short distances. Eustreptospondylus has been considered a good swimmer, strong enough to swim from island to island like the modern day Komodo dragon. Not all palaeontologists agree with the swimming hypothesis. The opposing theories hold that the fossil of Eustreptospondylus was either swept out to sea during a flood after the animal died on the mainland, or it was carried to the ocean after it died in a river. [1]

Insular dwarfism

Eustreptospondylus has been portrayed as a genus that evolved insular dwarfism. In 2000, David Martill and Darren Naish pointed out that the portrayal of the animal as an island-dwelling dwarf species was caused by not realizing that the holotype specimen represented a subadult. [17]

Related Research Articles

<i>Megalosaurus</i> Genus of Jurassic-aged theropod dinosaur

Megalosaurus is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic Epoch of southern England. Although fossils from other areas have been assigned to the genus, the only certain remains of Megalosaurus come from Oxfordshire and date to the late Middle Jurassic.

<i>Ceratosaurus</i> Genus of theropod dinosaur from the Late Jurassic period

Ceratosaurus was a carnivorous theropod dinosaur that lived in the Late Jurassic period. The genus was first described in 1884 by American paleontologist Othniel Charles Marsh based on a nearly complete skeleton discovered in Garden Park, Colorado, in rocks belonging to the Morrison Formation. The type species is Ceratosaurus nasicornis.

<i>Afrovenator</i> Extinct genus of dinosaurs

Afrovenator is a genus of megalosaurid theropod dinosaur from the Middle or Late Jurassic Period on the Tiourarén Formation and maybe the Irhazer II Formation of the Niger Sahara region in northern Africa. Afrovenator represents the only properly identified Gondwanan megalosaur, with proposed material of the group present in the Late Jurassic on Tacuarembó Formation of Uruguay and the Tendaguru Formation of Tanzania.

<i>Cetiosauriscus</i> Genus of reptiles (fossil)

Cetiosauriscus is a genus of sauropod dinosaur that lived between 166 and 164 million years ago during the Callovian in what is now England. A herbivore, Cetiosauriscus had — by sauropod standards — a moderately long tail, and longer forelimbs, making them as long as its hindlimbs. It has been estimated as about 15 m (49 ft) long and between 4 and 10 t in weight.

<span class="mw-page-title-main">Megalosauridae</span> Extinct family of dinosaurs

Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relatively primitive group of basal tetanurans containing two main subfamilies, Megalosaurinae and Afrovenatorinae, along with the basal genus Eustreptospondylus, an unresolved taxon which differs from both subfamilies.

<i>Elaphrosaurus</i> Ceratosaurian theropod dinosaur genus from the Late Jurassic Period

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<i>Monolophosaurus</i> Extinct genus of dinosaurs

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).

<span class="mw-page-title-main">Megalosauroidea</span> Extinct superfamily of Dinosaurs

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<i>Dubreuillosaurus</i> Extinct genus of dinosaurs

Dubreuillosaurus is a genus of carnivorous dinosaur from the middle Jurassic Period. It is a megalosaurid theropod. Its fossils were found in France. The only named species, Dubreuillosaurus valesdunensis, was originally described as a species of Poekilopleuron, Poekilopleuron? valesdunensis, which is still formally the type species of the genus. It was later renamed Dubreuillosaurus valesdunensis when, in 2005, Allain came to the conclusion that it was not part of the genus Poekilopleuron. Its type specimen, MNHN 1998-13, is only rivalled in the number of preserved elements in this group by that of Eustreptospondylus. Dubreuillosaurus is considered to be the sister species of Magnosaurus. It did not show signs of insular dwarfism even though it was uncovered on an island.

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<i>Piveteausaurus</i> Extinct genus of dinosaurs

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<i>Streptospondylus</i> Extinct genus of dinosaurs

Streptospondylus is a genus of tetanuran theropod dinosaur known from the Late Jurassic period of France, 161 million years ago. It was a medium-sized predator with an estimated length of 6 meters (19.5 ft) and a weight of 500 kg (1,100 lbs).

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<i>Poekilopleuron</i> Extinct genus of dinosaurs

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<i>Duriavenator</i> Genus of theropod dinosaur

Duriavenator is a genus of theropod dinosaur that lived in what is now England during the Middle Jurassic, about 168 million years ago. In 1882, upper and lower jaw bones of a dinosaur were collected near Sherborne in Dorset, and Richard Owen considered the fossils to belong to the species Megalosaurus bucklandii, the first named non-bird dinosaur. By 1964, the specimen was recognised as belonging to a different species, and in 1974 it was described as a new species of Megalosaurus, M. hesperis; the specific name means 'the West' or 'western'. Later researchers questioned whether the species belonged to Megalosaurus, in which many fragmentary theropods from around the world had historically been placed. After examining the taxonomic issues surrounding Megalosaurus, Roger B. J. Benson moved M. hesperis to its own genus in 2008, Duriavenator; this name means "Dorset hunter".

<i>Leshansaurus</i> Extinct genus of dinosaurs

Leshansaurus is a genus of theropod dinosaur from the Late Jurassic Shaximiao Formation of what is now China. It was described in 2009 by a team of Chinese paleontologists. The type species is Leshansaurus qianweiensis. Fossils of Leshansaurus were discovered in strata from the Shangshaximiao Formation, a formation rich in dinosaur fossils. Li et al. referred this taxon to Sinraptoridae – a group of carnosaurian theropods, but it may belong to Megalosauridae instead.

References

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  15. S.M. Kurzanov, 1989, "O proiskhozhdenii i evolyutsii infraotryada dinozavrov Carnosauria", Paleontologicheskiy Zhurnal1989(4): 3-14
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