Thursday, June 5, 2008

The story of Dracovenator - part II

James Kitching and his field assistant Regent ‘Lucas’ Huma found Dracovenator on a farm called ‘Upper Drumbo’ in the Barkly East District of the Eastern Cape Province. This district is almost entirely covered by thick lava flows of the Drakensberg Group that also make up the highlands of nearby Lesotho. Fortunately the Kraai River, and some of its tributaries have cut deep enough through the lava to get down to the underlying sediments of the Clarens and Elliot Formations. And this is where you find dinosaurs. Well a few anyway. The area can hardly be described as brimming. A recent international expedition led by Oliver Rauhut and ably assisted by yours truly, had ten or so palaeontologists crawling up and down every inch of available outcrop on Upper Drumbo. We eventually found two worthy specimens but this is quite a low haul for the Elliott (sadly neither were Dracovenator).
Anyway back to Dracovenator. I gave it the species name ‘regenti’ to honour James’ long-term field assistant and friend, Regent Huma. As Regent was a black man in apartheit South Africa he never got the recognition he deserved.
What do the bones look like? Firstly there is an odd combination of characters in the premaxilla. The snout was clearly long and low (a ‘coelophysoidy’ condition) with the external nostrils retracted posterior to the premaxillary teeth but the shape of posterior margin of the premaxilla seems to indicate a subrectangular anterior ramus of the maxilla (an advanced theropod condition). The next-most informative piece was the back end of the lower jaw, which looked just plain weird with all sorts of lumps and bumps growing out of it. However after seeing the original Dilophosaurus wetherilli specimens it became clear that Dilophosaurus also had the same morphology, only a little more subdued. Anyway desperately incomplete as the known remains are there is enough to distinguish the new species from all other known theropods.
Well almost. The known parts of Dracovenator barely overlap with the much better known dilophosaurid, Cryolophosaurus ellioti from Antarctica, and where they do overlap (just the posterior end of the maxilla and the posterior end of the dentary[edit: that should be 'mandible' not 'dentary']) they are essentially identical. So it may well be that Dracovenator is the same as Cryolophosaurus or an exteremly close relative. This isn’t so unusual as many of the species in earlier Triassic deposits of the Karoo Basin are also found in Antarctica. It does go against Nate Smith and colleagues (2007a) dilophosaurid topology. He found that the Chinese dilophosaur (‘Dilophosaurus’ sinensis) was basal to a clade consisting of Dracovenator, Dilophosaurus wetherilli and Cryolophosaurus (with D. wetherilli and Cryolophosaurus being each other’s closest relatives). This topology is strongly at odds with geography and suggests dilophosaurids were jumping all over Pangaea as they diversified (perfectly possible given that this happened before the breakup of Pangaea) (Smith et al. 2007b). Having seen both species of Dilophosaurus (the photograph is of the holotype of D. sinensis) though, I really don’t think much of the supposed differences and am impressed by strong similarities not seen in other theropods. Thus I am happy to include them in the same genus (contra some other opinions). Thus I think there may be some geographic separation of dilophosaurids after all, with a northern D. wetherilli/D. sinensis clade and a southern Crylophosaurus/Dracovenator clade. With luck permitting, new fossils should be able to test this idea.


Smith ND, Makovicky PJ, Hammer WR and Currie PJ. 2007a. Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society 151, 377–421.

Smith ND, Makovicky PJ, Pol D, Hammer WR and Currie PJ. 2007b. The dinosaurs of the Early Jurassic Hanson Formation of the Central Transantarctic Mountains: Phylogenetic Review and Synthesis. U.S. Geological Survey and The National Academies, Short Research Paper 003; doi:10.3133/of2007-1047.srp003

Yates AM. 2006 (for 2005). A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods. Palaeontologia africana 41: 105-122.


Darren Naish said...

Great to see a photo of 'D'. sinensis at last - I've only ever seen diagrams. sinensis always looks to be more robust-snouted that wetherilli, with a much shorter prenarial region to the premax - are these differences genuine? Is also seems that sinensis has shorter crests, as in wetherilli they extend to the postorbital.

By the way - what do you think of the kayentakatae crests? I wonder if they're not crests at all: it looks like one of the nasals has flipped up so that we're seeing it in dorsal view. I say this without having looked at the specimen however.

Darren Naish said...

Bugger, loads of typos in previous message, sorry.

Adam Yates said...

I could say quite a bit about D. sinensis but probably shouldn't. I understand Phil Currie has a paper redesribing it in the pipeline. Anyway the premax is shorter than in wetherilli but the preservation at the tip of the snout of this specimen is pretty crappy (I couldn't make out exactly how many pmx teeth there were but the usual four seems likely. As for the size of the crest, I get the impression this is pretty variable from individual to individual. I'm impressed by the fairly close match of small details between the Chinese and North American species, even down to the individual rugae on the surface of the crests (it doesn't help that wetherilli has not been well figured). You may have noticed a little prong-like spike sticking backwards from the base of the crest inwetherilli. That I am sure is just the bottom edge of a rounded posterior lobe, just like the one seen in sinensis.
As for kayentakatae, I think it is highly likely that (as was the case in Zupaysaurus) the crests are indeed just displaced nasals. However I haven't seen the specimen either.