Discovery and speciesEdit
Cetiosauriscus was first named by German palaeontologist Friedrich von Huene in 1927, from Early Callovian age remains, the specific name of the genus being Cetiosauriscus leedsi. Its generic name means "whale-like lizard (i.e. Cetiosaurus-like)". In 1887 John Whittaker Hulke had named the species Ornithopsis leedsii, based on specimen BMNH R.1984-1988, a set of bones from the Leeds collection. After a suggestion by Harry Govier Seeley, in 1905 this species was renamed to Cetiosaurus leedsi by Arthur Smith Woodward, who referred a second specimen from the same collection to the species: BMNH R.3078. The specimen was mounted for many years and was exhibited in the Dinosaur Gallery of the Natural History Museum in London. Both specimens were assigned to Cetiosauriscus leedsi by von Huene. In 1929 von Huene also renamed Ornithopsis greppini, a species found in Switzerland, "Cetiosauriscus" greppini.
In 1980 A.J. Charig concluded that BMNH R.3078 could not be referred to BMNH R.1984-1988, due to a lack of comparable bones, and created a new species for the former: Cetiosauriscus stewarti. The specific name honours Sir Ronald Stewart, the chairman of the London Brick Company which owned the clay pit the fossils had been found in. Furthermore he considered both C. leedsi and "C." greppini nomina dubia.
Phillips (1871) based Cetiosaurus glymptonensis on nine middle-distal caudal centra from the Forest Marble Formation of Oxfordshire, England. Upchurch and Martin (2003) reexamined this material and concluded that it was potentially a diplodocid and was distinct from both Cetiosaurus oxoneinsis and Cetiosauriscus. The centra are elongated, as occurs in many diplodocids. The lateral surfaces of the centra bear two parallel horizontal ridges, causing the centra to be octagonal in transverse cross-section. The upper ridge is also present in Cetiosauriscus but the lower ridge is unique. This was later renamed into Cetiosauriscus.
In 1990 John Stanton McIntosh renamed two more species of Cetiosaurus into Cetiosauriscus. They were Cetiosauriscus longus and "Cetiosauriscus" glymptonensis. Neither, however, was sufficiently complete to determine whether they possess the characteristic autapomorphy. Both were again considered nomina dubia by Charig, who, in 1993, petitioned the ICZN to make Cetiosauriscus stewarti the type species instead of the original Cetiosauriscus leedsi. This was done in 1995, making BMNH R.3078, already the holotype of the species C. stewarti, the genoholotype (holotype) of Cetiosauriscus.
BMNH R.3078 was found at Peterborough, Cambridgeshire, in strata of the Upper Oxford Clay and consists of a series of vertebrae from the rear half of the skeleton. Other remains, including a front leg with fossilized cartilage in its joint, a hind leg, a possible whiplash tail, and a partial sacrum have been referred to C. stewarti. With that much material, Cetiosauriscus is one of the most complete sauropods from the United Kingdom.
A few species have, over the years, been assigned to Cetiosauriscus. Only one is certainly referable to it though. Most species have been recombined from or into Ornithopsis or Cetiosaurus, historically a wastebasket taxon.
In 1980, Charig named a mostly complete specimen previously identified as Cetiosauriscus leedsi into its own species, Cetiosauriscus stewarti. After Cetiosauriscus leedsi, the type species, was proven to not be a species of Cetiosauriscus, Charig sent a petition to the ICZN to identify Cetiosauriscus stewarti as the type species. Cetiosauriscus stewarti is a possible senior synonym of Cetiosauriscus leedsi, Cetiosaurus leedsi and Ornithopsis leedsi.
- Cetiosauriscus stewarti Charig, 1980 (type) = Cetiosauriscus leedsi? (Hulke, 1887) Huene, 1927 (nomen dubium) = Cetiosaurus leedsi? (Hulke, 1887) Huene, 1932 (nomen dubium) = Ornithopsis leedsi? Hulke, 1887 (nomen dubium)
In 1927, von Huene recombined Cetiosaurus leedsi into Cetiosauriscus as Cetiosauriscus leedsi, the type species. Cetiosaurus leedsi was originally named by Hulke in 1887 as a species of Ornithopsis. The specimen BMNH R3706, including some ribs, may belong to a pliosaur but was originally noted as Cetiosaurus leedsi. In 1905, Woodward moved it into the genus Cetiosaurus. These classifications are no longer accepted and Ornithopsis leedsi is thought to be an indeterminate Brachiosaurid. Cetiosauriscus leedsi is a possible junior synonym of Cetiosauriscus stewarti. Two years later, in 1929, von Huene renamed another species of Ornithopsis as a Cetiosauriscus species, Cetiosauriscus greppini. "Cetiosauriscus" greppini was later renamed Cetiosaurus greppini by von Huene in 1932, a junior synonym of "Cetiosauriscus" greppini. "Cetiosauriscus" greppini is from the Reuchenette Formation, a formation of Early Kimmeridgian age. It is known from three individuals, the holotype being the most complete. "Cetiosauriscus" greppini differs from Cetiosauriscus stewarti by having caudal transverse processes that are anteroposteriorly flat and have a distinct dorsal wing-like expansion. It also differs in having anterior posterior centrodiapophyseal laminae situated ventrally from the anterior caudal transverse process, a coracoid with a rounded outline and with a notch ventrally to the glenoid articular face, remarkably straight shafts of humerus and femur, a distal end of the humerus with a higher medial than lateral hemicondyle, a more proximally placed 4th trochanter, and a longer and straighter ischium shaft. These characters certify that both taxa differ on the generic level. The discovery of cartilaginous tissue relatively proximal to the end of the humerus of "Cetiosauriscus" greppini has suggested that the cartilage caps of sauropods may have been larger than predicted by an Alligator CCF and that the cartilage caps extended fairly far onto the metaphysics of some long bones. "Cetiosauriscus" greppini is now considered to be Eusauropoda incertae sedis. Cetiosaurus longus, in 1990, was recombined as a species of Cetiosauriscus, Cetiosauriscus longus by McIntosh. This classification is not accepted and Cetiosauriscus longus is a junior objective synonym of Cetiosaurus longus because it cannot be proven to possess any characteristic autapomorphies. In the same year, McIntosh also renamed Cetiosaurus glymptonensis as "Cetiosauriscus" glymptonensis. "Cetiosauriscus" glymptonensis is considered to be Eusauropoda incertae sedis, in need of a new genus.
"Cetiosauriscus" greppini is known from a femur with bite marks on it. The marks strongly match the teeth of Machimosaurus, meaning that Machimosaurus scavenged or possibly regularly preyed on animals like Cetiosauriscus. "Cetiosauriscus" glymptonensis is diagnosed by middle-distal caudal centra having a distinct horizontal ridge approximately one-third the way up the lateral surface.
- Cetiosauriscus leedsi (Hulke, 1887) Huene, 1927 (nomen dubium) = Ornithopsis leedsi Hulke, 1887 (nomen dubium) = Cetiosaurus leedsi (Hulke, 1887) Woodward, 1905 (nomen dubium) = Cetiosauriscus stewarti? Charig, 1980
- "Cetiosauriscus" greppini (Huene, 1922) Huene, 1929 (nomen dubium) = Ornithopsis greppini Huene, 1922 (nomen dubium) = Cetiosaurus greppini Huene, 1932 (nomen dubium) = non Cetiosauriscus
- Cetiosauriscus longus (Owen, 1842) McIntosh, 1990 (nomen dubium) = Cetiosaurus longus Owen, 1842 (nomen dubium)
- "Cetiosauriscus" glymptonensis (Phillips, 1871) McIntosh, 1990 = Cetiosaurus glymptonensis Phillips, 1871 (nomen dubium) = non Cetiosauriscus
The only overlapping material between BMNH R3078 and the holotype of Cetiosauriscus leedsi was an ilium. In both specimens the ilium was preserved in insufficient ways. Since the only overlapping material was impossible to compare, Charig found that BMNH R3078 was of a different species and he named it Cetiosauriscus stewarti.
Huene felt the vertebrae of BMNH R3078 had proportions different enough from Cetiosaurus to warrant its own genus. Also, the fusion of centra with minimal osseous proliferation is manifest in the caudal vertebrae of Cetiosauriscus. The Cetiosaurus specimen OUMNH J13695 has a low horizontal ridge on each of its lateral surfaces, creating a slightly subhexagonal tranverse cross-section, and is also seen on Cetiosauriscus, as well as the anterior caudals of Haplocanthosaurus, and caudals 15 to 30 of Omeisaurus. Also, the area around the periphery of each articular face is flattened, creating a 'bevelled' appearance, and also occurs in Cetiosaurus and Haplocanthosaurus. A whiplash tail was apparently found in the same deposits but it is not certain it belongs to the same individual. Since there is no overlapping material, this assignment to Cetiosauriscus should be treated with caution.
Since the proportions of the limbs in BMNH R3078 differed enough from Cetiosaurus, Huene found that it warranted a new genus. Metacarpal 1 is short and massive, with the prominent process on the lower part of the posterior margin of the lateral face, a characteristic of the diplodocoids Diplodocus, Apatosaurus, Cetiosauriscus and Dicraeosaurus.
A characteristic that distinguishes Cetiosauriscus is that it has axially concave summits on the cranial and middle caudal neural spines. Barosaurus differs from it in having a more complex sculpting laterally and ventrally in the caudals; in having a larger humerus-femur ratio; and in having differently developed chevrons.