Monday, July 28, 2008
Monographs aint dead
A common lament amongst the vertebrate palaeontology community is the trend toward quick, brief publications in high-impact journals with long delayed to non-existant followup with detailed descriptions. The problem is a symptom of today’s ‘publish or perish’ academic climate where the cost of spending a lot of time producing a monograph that will inevitably appear in a low impact journal can actually harm an early career. I am guilty of adding to the problem myself. Five years after my publication of Antetonitrus in the Proceedings of the Royal Society the descriptive osteology is still in preparation (though not because I don’t wish to produce it, it is just that so many other projects have pushed their way to the front of my to do list). Fortunately more organised and focused researchers have not forgotten the value of a thorough descriptive osteology for the good of the science, if not the individual. One of these crossed my desk last week. “Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco” does exactly what it says on the cover and how sorely was this needed! Tazoudasaurus is a relatively newly named Moroccan sauropod from the Early Jurassic. It is significant because it is rather completely represented non-eusauropod. For those only cursorially interested in dinosaurs eusauropods are the 'classic' sauopods with enormous bodies, long necks, tiny heads with large retracted nostrils, unique tubular, fingerless hands atop elephantine limbs and lightweight vertebrae constructed from thin laminae. In all the construction of the eusauropod 'bauplan' is one of the great transformations in dinosaur, if not vertebrate, evolution equal in my mind to the evolution of birds. Sadly our understanding of this evolution has been severely hampered by the extremely fragmented nature of pre-eusauropod sauropods. The usual standard basal taxon is Vulcanodon which is hopelessly fragmentary as you can see in the diagram below. There is enough of Vulcanodon to show that it is clearly outside Eusauropoda but it tells us nothing about the evolution of dorsal vertebrae (which must really bother these guys), hands or the skull. Help is now at hand: Tazoudasaurus is clearly a close relative of Vulcanodon (the monograph adds new derived character states which shores up the monophyly of Vulcanodontidae) and it preserves some skull bones along with good neck and dorsal vertebrae and a complete articulated hand.
It is apparent that vulcanodontids are actually quite close to Eusauropoda and are distinctly more advanced than the fragmentary rabble of basal sauropods that has been steadily accreting to the base of Sauropoda in recent years (e.g. dinosaurs like Antetonitrus, Gongxianosaurus and Isanosaurus). For instance the dorsal vertebrae have transversely expanded laminar neural spines, unlike the transversely flattened, plate-like affairs seen in the aforementioned trio. The hand is really cool. The palm is not wrapped into the semitubular arrangement seen in eusauropods, and the fifth metacarpal is still quite a bit shorter than the others (as in prosauropods) but the fingers are reduced right down to mere clawless stumps.
Given the high number of synapomorphies linking vulcanodontids and eusauropods over the more 'prosauropody' taxa like Antetonitrus, Allain and Aquesbi go ahead and erect a new higher level taxon: Gravisauria ('the heavy lizards'), an action I support.
The authors also discuss faunal turnover at the end of the Early Jurassic but I want to save that for another post, not least because I had come to identical conclusions and even have the idea in press (where it will probably linger for another year). If you like sauropods get a hold of this paper (no I do not have a pdf).
Allain, R., Aquesbi, N. (2008). Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas, 30(2), 345-424.