Wednesday, March 19, 2008

The taxonomic status of Megalosaurus bucklandii

A new paper by Roger Benson of Cambridge University and colleagues discuss the taxonomic status of Megalosaurus bucklandii.

Every dinosaur fan knows of Megalosaurus, the first dinosaur to be named by William Buckland in 1824. Megalosaurus is also historically significant as being one of the taxa that Richard Owen based his Dinosauria in 1842, the other taxon obviously being Iguanodon. The type species M. bucklandii was erected by Gideon Mantell in 1827. Buckland's original description of Megalosaurus in 1824 is based on a series of syntypes, one of which is the famous dentary (fig). Over the years, many other large theropod specimens from the Middle Jurassic were "unjustifiably (Benson et al. 2008)" attributed to M. bucklandii. Over the years, many authors noted the possibility that the syntype series and all subsequent referred specimens may belong to different taxa all together. Thus M. bucklandii is suggested to only refer to the lectotype dentary.

According to Benson et al. (2008) the lectotype dentary allows for a diagnosis of M. bucklandii thus making it a valid taxon. Although the systematic position of M. bucklandii is unresolved, Benson et al. (2008) regard it as a possible member of the clade comprising of Ceratosauria and Tetanurae but not an abelisaurid or coelophysoid. Further, the characteristic dentary morphology present in all known spinosauroids is absent in the lectotype dentary. Thus, Benson et al. (2008) recommend the discontinuation of allying Megalosaurus with Spinosauroidea and also the practice of referring any other taxa as "megalosaurid".

So I guess we should stop using Megalosauridae and "megalosaurids" and start referring to these taxa (with the exclusion of Megalosaurus) as spinosauroids...

In my opinion, just because of its historical importance to dinosaur research, the most significant discovery in the future would be the discovery of a more complete specimen indisputably assignable to Megalosaurus bucklandii - that is, the associated specimen of a M. bucklandii dentary with other cranial and postcranial materials. The discovery of such a specimen is probably the only way to resolve the systematic position of M. bucklandii and the taxonomy of all other unassociated materials previously referred to M. bucklandii.

Reference:
Benson, R. B. J., P. M. Barrett, P. Powell, and D. B. Norman. 2008. The taxonomic status of Megalosaurus bucklandii
(Dinosauria, Theropoda) from the Middle Jurassic of Oxfordshire, UK. Paleontology 51: 419-424


Abstract: The lectotype of the Middle Jurassic theropod dinosaur Megalosaurus bucklandii, a right dentary, can be diagnosed on the basis of two unique characters: a longitudinal groove on the ventral part of the lateral surface of the dentary and a slit-like anterior Meckelian foramen. This taxon, the first dinosaur to be scientifically described, is therefore valid. Currently, however, no further material can be referred to this species with any certainty. Megalosaurus bucklandii occupies an uncertain systematic position but is not an abelisaurid or coelophysoid. Additionally, it does not possess the diagnostic dentary characters that are present in all known spinosauroids. Owing to this uncertainty, use of the family Megalosauridae should be discontinued until such time as its systematic position becomes clearer.

Happy birthday, Raptor's Nest!

March seems to be a popular month to be born...both my parents are born in March, my friends' birthdays are in March, Ask a Biologist just recently had its first year anniversary, and now, today (19 March) is a whole year from my first blog post on Raptor's Nest - Woohoo!

And coincidentally, it's actually my real birthday today as well - and I had only realised this coincidence last week! I've survived 28 years and been in school in one way or another for 25 of those years...As my name wich means "to learn" in Japanese suggests, I have so far led most of my life as a student (of science) and will probably do so for the rest of my life

Sunday, March 16, 2008

Deinosuchus

I was recently asked a question about the possibility of Deinosuchus being in the Hell Creek and interacting with Tyrannosaurus rex. Since the Hell Creek is well-sampled and there are no Deinosuchus fossils it is safe to assume that it was absent from the Hell Creek. However, the person asking the question was fully aware of that so the question actually was, "if Deinosuchus were to be known from surrounding areas of the same age, would it be scientifically plausible to infer its presence in the Hell Creek?" To be perfectly honest, I had no idea of the temporal and geographic range of Deinosuchus and so it turned out to be an interesting afternoon of researching this.

As far as I can gather from the literature and also from colleagues that work on fossil crocs, there are no peer-reviewed scientific articles that ever state the presence of Deinosuchus in strata younger than the late Campanian. Lucas et al. (2006) include a review of Deinosuchus occurrences in one of their papers and they conclude the temporal range of Deinosuchus as being ~73-80 Ma, the younger of the range being about 12 Ma prior to the Hell Creek environment. David Schwimmer (not Ross from friends) states in his book that the supposed Maastrichtian (70.6 - 65.5 Ma) Deinosuchus remains (unpublished accounts) may be a misidentification of large (marine?) crocs. As I only had access to an on-line preview of the book, I couldn't track down the exact identity of this mystery croc...These are also supposed to be from the Atlantic Coastal Plain.

There was one thing that baffled me though, the exact age of the Black Creek Group, where the holotype material of Deinosuchus rugosus is from, and this took a bit of digging around the interweb and stratigraphy literature. Although according to Lucas et al. (2006) citing Schwimmer (2002), the Deinosuchus-bearing horizon of the Black Creek is supposed to be ~73-74 Ma, I couldn't find support for this figure mostly because there is no mention of exactly which formation of the Black Creek Group the holotype is from. This presents a bit of a problem, as according to this website, the Black Creek Group of North Carolina has three formations spanning from Early Campanian (Tar Heel Formation), Upper Campanian (Bladen Formation), and to the Early Maastrichtian (Donoho Creek Formation). So depending on which formation of the Black Creek Group the holotype material is from, the upper range of Deinosuchus can be as young as the Early Maastrichtian. The overlying marine strata, the Peedee Formation, is regarded as being Late Maastrichtian and dated at 66.7 Ma (Schwimmer 2002). D. rugosus is supposed to be from the upper part of the Black Creek thus placing it relatively younger than other Deinosuchus-bearing strata with an absolute younger bound at >66.7 Ma.

Fortunately, I stumbled across a PhD thesis that pretty much resolved this issue. According to Mitra (2002), Elizabethtown, the locality of the type specimen of D. rugosus, belongs to the Tar Heel Formation and Early Campanian in age. Further, the Phoebus Landing locality, where some referred D. rugosus specimens are known from, is supposed to be Campanian. So I've finally managed to find support for the ~73-74 Ma age of the Deinosuchus-bearing horizon of the Black Creek (Lucas et al. 2006, citing Schwimmer (2002)). Perhaps if I actually had read Schwimmer (2002) and not just the on-line previews, I wouldn't have had to go through all this effort but I wouldn't know if it's discussed in the book because our library doesn't have a copy....In any case, N Carolina would have been on the eastern side of the Western Interior Seaway anyway and all Deinosuchus specimens from Montana are definitively Campanian in age.

So in summary, all known Deinosuchus materials are from the Campanian, temporally ranging between ~73 and 80 Ma, thus making its presence in the Late Maastrichtian and in particular in the Hell Creek unlikely.

One thing that I thought was quite interesting is that Deinosuchus seems to be abundant in places and times where large theropods are absent or rare.

References:
Lucas, S. G., R. M. Sullivan, and J. A. Spielman. 2006. The giant crocodylian Deinosuchus from the Upper Cretaceous of the San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin 35:245-248.

Mitra, M. 2002. Paleopalynology of the Tar Heel Formation of Atlantic Coastal Plain of North Carolina, United States. North Carolina State University.

Schwimmer, D. R. 2002. King of the crocodylians: the paleobiology of Deinosuchus. Indiana University Press. 220 pages.

Saturday, March 15, 2008

Velociraptor mongoliensis

I've been fooling around again toying with the idea of a Velociraptor mongoliensis perching atop a recently deceased carcass and intimidating its competitors, presumably other Velociraptor individuals. As a few of us have discussed here, according to Roach and Brinkman (2007), the evidence for pack-hunting behaviour in dromaeosaurs is pretty slim. The authors are casting doubt over Deinonychus regularly hunting large prey in a highly coordinated pack-hunting style, mainly based on the loose cooperative hunting styles seen in extant archosaurs (a couple of species of crocodiles and plenty of examples of predatory birds) and the komodo dragon.

Komodo dragons are known to solitarily take down prey as much as 10 times its own size. On this basis, the authors mention that it would be possible for a 70 - 100 kg Deinonychus to solitarily take down a Tenontosaurus anywhere between 700 - 1000 kg.

The fossil sites are reexamined as well. The Deinonychus skeleton(s) found with the Tenontosaurus may have been victim to intraspecific fighting and were killed and eaten by larger adult Deinonychus as frequently observed in komodo dragons and some predatory birds. The large degree of disarticulation of the Deinonychus skeleton as opposed to the more articulated Tenontosaurus seem to indicate that the freshly killed Deinonychus may have been more apetising for the aggregated Deinonychus individuals. The other individuals probably aggressively tore apart and consumed the dead Deinonychus, leaving only the bony bits with not much meat like the manus, pes and tail.

That was pretty much recycling my DinoBase post but I thought it was a pretty cool study. Here, I envisage Velociraptor in a similar fashion - Velociraptor and Deinonychus are pretty closely related even within dromaeosaurs so we could infer something similar. I just like the idea of dromaeosaurs having something like a furry crest so I overdid it and gave this guy a lot of hair - or perhaps its ruffling its "feathers". Anyway, note that this raptor's got its sickle claw dug into the carcass to firmly hang on.

Reference:
Brian T. Roach and Daniel L. Brinkman 2007. A Reevaluation of Cooperative Pack Hunting and Gregariousness in Deinonychus antirrhopus and Other Nonavian Theropod Dinosaurs. Bulletin of the Peabody Museum of Natural History 48: 103–138

Monday, March 10, 2008

Happy birthday, Ask a Biologist!

Well, it's actually this coming Friday (the 14th) but since this is a good chance to promote the site, why not start early?







Ask a Biologist is a Q&A website started up by University of Bristol graduate, Dr. Dave Hone. The unique thing about AAB is that unlike many Q&A forums around the internet, AAB's answerers are all either qualified PhDs, PhDs in training, or have a similar level of experience or qualifications. So there is a certain level of quality and authenticity to the answers provided. The questions are either answered by someone in the field or someone decently knowledgeable in the field with proper scientific research and citations to back it all up.

As with many forums, absolutely anyone can ask questions on AAB, sometimes even the contributors ask the other experts for opinions. But it is primarily aimed towards children and young persons still in school. So if you know of any kids aching to get some of their burning questions regarding biology, then please use this chance to direct them to http://www.askabiologist.org.uk.

I am a regular contributor to AAB as well and if you are aware of the DinoBase Forum then you will find the layout almost identical - in fact they were both designed by the same web-designer and software engineer.