Eustreptospondylus

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.[1]

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
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; 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.[3] 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.[4][5] 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.[6]

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.

Description
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.[12] In 2010, Paul estimated the adult length at six metres, the weight at half a tonne.

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.[11] 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.[11]

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.