One of my most favourite dinosaurs has always been Ceratosaurus but, given that I mostly work on Lower Cretaceous dinosaurs, I’ve never had the chance to look at it much (Ceratosaurus is Upper Jurassic). Imagine my surprise then when, during a recent visit to Glasgow (Scotland), I was confronted with a complete mounted (replica) skeleton of this neat beast at Kelvingrove Art Gallery and Museum. First named by Othniel Marsh in 1884, Ceratosaurus is best known for the type species, C. nasicornis from the Morrison Formation of Colorado…
Less well known is that two additional Morrison Formation species were named in 2000: C. magnicornis, named for its particularly big horns, and C. dentisulcatus, characterised by unusual elongate pockets located next to the keels on its teeth (Madsen & Welles 2000). These two might be distinct species, but it’s also possible that C. magnicornis at least might simply be a growth phase (a big male for example) of C. nasicornis. Furthermore, Ceratosaurus is not unique to the USA, but is also known from Upper Jurassic deposits in Portugal, Switzerland and Tanzania. The Portugese remains have most recently been identified as referable to C. dentisulcatus (Mateus et al. 2006) meaning that – if correctly identified – this species had an intercontinental range during the Tithonian. That’s a really big deal for lots of reasons. Several other species names have been proposed for Ceratosaurus specimens, but none are currently regarded as valid.
Often regarded as phylogenetically isolated (albeit close to the ancestry of abelisaurs), it was recently argued that Genyodectes serus from the Aptian-Albian Cerro Barcino Formation of Chubut Province in Argentina might be a close relative of Ceratosaurus, the two forming a clade Ceratosauridae (Rauhut 2004). Sarcosaurus from England, once mooted as a small, Lower Jurassic ceratosaurid, has more recently been argued to be a coelophysoid (Carrano & Sampson 2004, Naish & Martill 2007) [adjacent image is old photo showing C. nasicornis as mounted in the Smithsonian Institution].
Why is Ceratosaurus so cool? It doesn’t just have a nasal horn; it also sports large preorbital horns, and note that its nasal horn is actually positioned quite far back relative to the snout tip. Its skull is particularly deep and its maxillary teeth are particularly big, as are the dentary teeth. In a recently discovered, but as yet undescribed, juvenile specimen, the teeth are reported to be so long that their tips extend beyond the ventral edge of the lower jaw when the mouth is closed (similarly proportionally long teeth are present in some other theropod juveniles actually). These features all imply that Ceratosaurus was an adept macropredator, and perhaps it avoided competition with the more abundant Allosaurus by specialising on different (larger?) prey (Henderson 2000). Paradoxically though, the back of the skull looks very lightly constructed, with an immense laterotemporal fenestra; the postorbital bar (formed by the postorbital and jugal) is really gracile, and the mandible is both shallow and slightly curved along its length.
Uniquely amongst theropods, Ceratosaurus had a continuous row of bony scutes running along its neck, back and tail. It wasn’t that big – less than 7 m long and less than a ton in weight. Because Ceratosaurus is, morphologically, an archaic theropod compared to its tetanuran contemporary Allosaurus, Greg Paul (1988) likened it to a thylacine* surrounded by dingoes, which I kind of like. Incidentally, as a kid I recall reading a book which argued that Ceratosaurus and Allosaurus were the same species, with the smaller, horned Ceratosaurus being the male. This idea is patently ludicrous (the two are totally different animals, anatomically disparate in every conceivable detail), and unfortunately – or fortunately – I cannot recall the book in question [in adjacent image of the display at Kelvingrove, note how narrow the skull is. You can also see the furcula].
* Thylacine is spelt ‘thycaline’ in the relevant bit of text however (p. 276).
Finally, why on earth is Ceratosaurus displayed at a Scottish museum? Various bits and pieces from Jurassic rocks of Scotland have been identified as belonging to coelophysoids. Coelophysoids and ceratosaurids (and abelisaurs) have been united by some theropod workers in a group termed Ceratosauria. So whereas it would have been most appropriate to showcase a Coelophysis skeleton, the museum – I assume – went for the most charismatic member of Ceratosauria. New data, new analyses and new taxa nowadays seem to show that Ceratosauria is not monophyletic… nor is Coelophysoidea… but I’ll have to leave that to another time [very nice image below borrowed from wikipedia].
Refs – –
Carrano, M. T. & Sampson, S. D. 2004. A review of coelophysoids (Dinosauria: Theropoda) from the Early Jurassic of Europe: with comments on the late history of the Coelophysoidea. Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 2004, 537-558.
Henderson, D. M. 2000. Skull and tooth morphology as indicators of niche partitioning in sympatric Morrison Formation theropods. Gaia 15, 219-226.
Madsen, J. H. & Welles, S. P. 2000. Ceratosaurus (Dinosauria, Theropoda) a revised osteology. Utah Geological Survey Miscellaneous Pubication 00-2, 1-80.
Mateus, O., Walen, A. & Antunes, M.T. 2006. The large theropod fauna of the Lourinhã Formation (Portugal) and its similarity to the Morrison Formation, with a description of a new species of Allosaurus. New Mexico Museum of Natural History and Science Bulletin 36, 1-7.
Naish, D. & Martill, D. M. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London 164, 493-510.
Paul, G. S. 1988. Predatory Dinosaurs of the World. Simon & Schuster, New York.
Rauhut, O. W. M. 2004. Provenance and anatomy of Genyodectes serus, a large-toothed ceratosaur (Dinosauria: Theropoda) from Patagonia. Journal of Vertebrate Paleontology 24, 894-902.