January 30, 2014 | 42
One of my favourite ichthyosaurs is the generally large, archaic, long-snouted Temnodontosaurus, and if you have an especially good memory you’ll recall it being mentioned here and there on Tet Zoo over the years (see links below). We have lots of Temnodontosaurus fossils here in southern England and I feel pretty familiar with the ‘genus’ (cough cough) – I haven’t published anything on it yet but work is in progress. Here are assorted words.
Temnodontosaurus is among the most archaic of the parvipelvian ichthyosaurs – Parvipelvia being the clade whose members are united by the presence of a strongly reduced pelvic girdle, a tibia and fibula that are about similar in form and position with respect to the end of the femur, and other characters (Maisch & Matzke 2000). Within Parvipelvia, phylogenetic studies have generally found Temnodontosaurus to be close to (but outside) the clade that includes the superficially billfish-like leptonectids and the most familiar parvipelvians of the Jurassic and Cretaceous, the thunnosaurians (Maisch & Matzke 2000, McGowan & Motani 2003). Sander (2000) used the name Neoichthyosauria for this Temnodontosaurus + leptonectid + thunnosaurian clade. However, a novel result was recovered in the phylogeny we recently published as part of our study of the Iraqi parvipelvian Malawania: we found Temnodontosaurus and leptonectids to group together (Fischer et al. 2013). As I said last time, this is “an intuitively pleasing discovery, given the similar gestalt of these often big, often especially long-snouted, long-flippered ichthyosaurs”.
Characterising Temnodontosaurus is difficult. For now, the name is used for a selection of Lower Jurassic neoichthyosaurians from England, France and Germany, all of which combine a distinctive humerus (it’s proportionally short, distally wide and has a waisted shaft) with a long body and tail where more than 80 vertebrae are present anterior to the tailbend. However, better features that unite them have yet to be published and my strong suspicion (and that of several other ichthyosaur workers) is that they’re grouped together because they’re of about the same ‘grade’, not because they share derived characters.
In general, Temnodontosaurus specimens are large, usually exceeding 6 m and sometimes exceeding 12 m. Their orbits are proportionally smaller than those of leptonectids and most thunnosaurians but are still literally enormous, in cases exceeding an incredible 26 cm in width. Substantial variation in temnodontosaur skull and tooth shape suggests diverse feeding adaptations within the group. A short-snouted, orca-like skull shape is present in Temnodontosaurus eurycephalus, a markedly elongate, pointed rostrum is present in T. acutirostris and a markedly gracile, possibly edentulous rostrum is present in T. azerguensis, for example. This variation is consistent with the idea that taxonomic revision of the group is required: the named taxa may not be close relatives at all.
T. eurycephalus is one of the most incredible of ichthyosaurs. Only a single skull, discovered at Lyme Regis, is known, the basisphenoid of a far smaller ichthyosaur preserved clenched between its teeth! (did the T. eurycephalus really die while eating another ichthyosaur, were these remains vomited up during death, or is the association just a fluke?). An interesting historical snippet is that this specimen (its length exceeding 1 m) was originally referred to Ichthyosaurus breviceps, a short-nosed thunnosaurian universally regarded as a diminutive ichthyosaur that rarely exceeds 2 m in total length.
More on ichthyosaurs later this year. For previous Tet Zoo articles on ichthyosaurs, see…
Refs – -
Clark, R. 1989. The Charmouth Ichthyosaur. A Dorset Giant. Bristol City Museum and Art Gallery, Bristol.
Fischer, V., Appleby, R. M., Naish, D., Liston, J., Riding, J. B., Brindley, S. & Godefroit, P. 2013. A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs. Biology Letters 9, 20130021 http://dx.doi.org/10.1098/rsbl.2013.0021
Hungerbühler, A. & Sachs, S. 1996. Ein grosser Ichthyosaurier aus dem Pliensbachium von Bielefeld. Ber. Naturwiss. Verein Bielifeld u. Umgegend 37, 15-52.
Maisch, M. W. & Matzke, A. T. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298, 1-159.
McGowan, C. & Motani, R. 2003. Handbook of Paleoherpetology Part 8 Ichthyopterygia. Verlag Dr. Friedrich Pfeil, München.
Sander, P. M. 2000. Ichthyosauria: their diversity, distribution, and phylogeny. Paläontologische Zeitschrift 74, 1-35.