Eustreptospondylus

Eustreptospondylus oxoniensis Temporal range: Middle Jurassic, 165–161Ma PreЄ Є O S D C P T J K Pg N ↓
Mounted holotype skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Theropoda
Family:	†Megalosauridae
Subfamily:	†Eustreptospondylinae Paul, 1988
Genus:	†Eustreptospondylus Walker, 1964
Species:	† E. oxoniensis
Binomial name
Eustreptospondylus oxoniensis Walker, 1964
Synonyms
Magnosaurus oxoniensis (Walker, 1964) Rauhut 2003

Eustreptospondylus ("true Streptospondylus") is a genus of megalosaurid dinosaur, from the Callovian stage of the Middle Jurassic period (165 to 161 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). It might have foraged on shorelines for carcasses and marine life.^[2]

The main fossil of Eustreptospondylus was found in 1870. At first it was assigned to other genera. In 1964 it was made a separate genus. Eustreptospondylus was about six metres long as an adult. It was carnivorous, bipedal and had a slightly stiffened tail. It was a typical theropod, with powerful hind limbs, and small forelimbs.

Discovery and naming

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

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.^[3] At the time the remains represented the most complete skeleton of a large theropod ever found; they still are the most complete of any large Jurassic European theropod. In 1890, after the skeleton had been bought by Oxford University, it was referred to Megalosaurus bucklandi by Arthur Smith Woodward. In 1905 and 1906 Baron Franz Nopcsa referred the skeleton to a different species: Streptospondylus cuvieri which had been described originally by Sir Richard Owen, in 1842, based on a now lost vertebra from the Bathonian.^[4] The reason for this was that the type species of Streptospondylus, 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.^[5][6] The association of a rather complete find with a species based on very poor remains however, created a very confusing situation. German palaeontologist Friedrich von Huene added to the confusion by sometimes accepting the name Streptospondylus cuvieri, at other times considering it another species of Megalosaurus: Megalosaurus cuvieri.^[7]

In 1964, Alick Donald Walker decided to clarify matters by naming a separate genus and species for the Oxford specimen: Eustreptospondylus oxoniensis. The generic name was derived from Streptospondylus. It can be literally read as "well-turned vertebra" — Streptospondylus, "turned vertebra", itself referring to the fact that the dorsal vertebrae with this dinosaur were opisthocoelous, contrary to the typical procoelous vertebrae of crocodiles — but the intended meaning was "true Streptospondylus". The specific name refers to the provenance from Oxford.^[8]

Modern skeletal restoration

The holotype, OUM J13558, was found in a marine layer of the Stewartby Member of the Oxford Clay Formation dating from the late Callovian. It consists of a rather complete skeleton with skull. The most important missing elements are 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.

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] Neither of both opinions has gained much acceptance.

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

Eustreptospondylus feeding on an ichthyosaur

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 218 kilogrammes heavy.^[13] In 2010, Paul estimated the adult length at six metres, the weight at half a tonne.^[11]

Puppet head that was used in Walking With Dinosaurs at the Oxford University Museum of Natural History^[1]

Several traits have been established by Sadleir, distinguishing Eustreptospondylus from its direct relatives. In the corner of the lacrimal bone a shallow depression is present, 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 or 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]

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]

The skull of Streptospondylus 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.

Phylogeny

Walker in 1964 assigned Eustreptrospondylus to the Megalosauridae. Though sometimes a separate Eustreptospondylidae was recognised,^[15] today Eustreptospondylus is more commonly seen as a member of a Eustreptospondylinae within Megalosauridae.

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

In popular culture

Eustreptospondylus was featured in episode 3 of BBC's Walking with Dinosaurs, "Cruel Sea". One is eaten by a Liopleurodon while fishing. At the end of the episode, two adult Eustreptospondylus eat a beached and dying Liopleurodon. The episode also portrayed Eustreptospondylus as being able to swim short distances in shallow water. It was also featured in the Primeval novel Fire and Water, where it is portrayed as the top predator of the Middle Jurassic, and was also shown to have swum to small islands. In 2000, David Martill and Darren Naish pointed out that the portrayal of Eustreptospondylus as an island-dwelling dwarf species was caused by not realising that the holotype specimen represented a subadult.^[16] The marine layers in which Eustreptospondylus was found, at the time were located off the west coast of the London-Brabant Massif, a terrane of considerable size.

Footnotes

References

• Haines, Tim & Chambers, Paul. (2006) The Complete Guide to Prehistoric Life. Canada: Firefly Books Ltd.