Monday, April 28, 2008

Allosaurus fragilis 3: Allosaurus yet again...

Yes it is, it's Allosaurus fragilis yet again! The point is, Allosaurus is by far the easiest theropod to draw...I don't know why, but perhaps it's because you see images of Allosaurus skulls everywhere, being depicted as the "generic" theropod. Of course it is one of the most abundant theropods ever so we do have a good idea of its morphology and to a certain extent its ontogeny - the vast majority of fossils are of adults or subadults while juveniles and hatchlings are very rare.

I use Allosaurus when I am testing out new ideas, whether it be biomechanics or just new angles to draw...certainly this is the case of the latter. It's not entirely a ground-breakingly new angle at all but one that I have attempted in numerous previous accounts and have never really gotten right. Though, I think I've got it almost right this time. I find angled shots really difficult - as you may have noticed, most of my drawings have got the skulls captured in a lateral aspect or just slightly angled. Depth perseption in dinosaur drawings are quite hard - I find, at least...

Saturday, April 26, 2008

Ceratosaurus nasicornis

One of my all-time favourite theropod is for some reason Ceratosaurus nasicornis. You might think its the horns but I'm actually more drawn to the overall skull morphology. I can't remember now why but Ceratosaurus was one of the first theropods that I attempted to draw the skull of. So I guess it was the first theropod that I actually paid attention to the skull morphology in some detail...

In any case, Ceratosaurus is still a taxon of significance. It represents the diverse group of basal theropods otherwise known as Ceratosauria, though what constitutes the group has never been stable. Aside from Ceratosaurus, Ceratosauria has traditionally included such taxa as Elaphrosaurus, Dilophosaurus, Coelophysis, Syntarsus, abelisaurids and other "ceratosaurs". Recent work however seem to show Ceratosauria in this traditional sense to be unsupported. Most recent phylogenies would separate coelophysoids (Coelophysis, Syntarsus, possibly Dilophosaurus, etc.) from Ceratosauria but the exact taxonomic make up of Ceratosauria is still controversial. Thus a more inclusive definition is preferred - that is, Ceratosauria is all dinosaurs sharing a more recent common ancestry with Ceratosaurus than with birds.

Even then, the vast majority of ceratosaurs are abelisaurs anyway so I can't see why they can't just be called basal abelisaurs or something...Ceratosaurus itself seems to be very closely related to abelisaurs, an enigma as all abelisaurs (with the exception of Tarascosaurus) are known from the Cretaceous of Gondwana. But then again, Ceratosaurus is basal to abelisaurs and its earlier presence may just be that basal abelisaurs weren't necessarily restricted to Gondwana...but who knows, maybe we'll never know.

Sunday, April 20, 2008

More on jaw muscle reconstructions

I have some more old images of mine, this one is of the jaw muscle reconstructions in Deinonychus. The skull is reconstructed from Ostrom's (1969) original figures. And jaw muscles are based on personal observations in numerous modern bird species. Off the bat it's obvious I've only referred to birds and not crocodilians or other diapsids because of the way I've reconstructed the MAMES attaching with a tendonous attachment onto the coronoid process. The muscle attached to the dorsal and medial surfaces of the surangular just medial and posterior to the MAMES is the MAMEM. In contrast, the MAMES in crocodilians attach along the dorsal surface of the surangular with the MAMEM attaching just medial to that. I suspect given the arrangement of cranial bones that the muscles arrangements in theropods would be more similar to crocs (and other diapsids) than to birds. The MPT is reconstructed as wrapping around the ventral side to attach to the lateral surface of the angular as in crocs.

Another picture I drew of muscle reconstructions in theropods, or rather another one of them hypothetical dissections, is one in Allosaurus. Again it is evident the muscles are based on birds from the MAMES attachment. Like in a previous post, the skin is peeled off halfway and the tongue and hyobranchial apparatus have been removed to reveal just the jaw adductor muscles. I just think this is a rather comical drawing, more so than the last one.

You might think that all this is pointless and we will never know what the muscles in theropods were like, but a large part of biomechanics actually rely on muscle data and the more we know about them the better it is.

Saturday, April 19, 2008

Centrosaurus

I've broken my routine and drew a Centrosaurus instead of a theropod. I couldn't decide what theropod I wanted to draw but I was getting a bit bored of theropods.

Anyway, I guess this would be Centrosaurus apertus Lambe, 1904 because of the cranial ornamentation. C. apertus and C. brinkmani Ryan et Russell, 2005 differ in their cranial ornamentations with C. apertus having larger parietal ornamentations. C. brinkmani is also restricted to the Oldman Formation of southern Alberta.

I don't really know enough about ceratopsians to write anything interesting (I just think they look great!) but I might as well comment on the forelimb posture...for the longest time, there has been a debate regarding the forelimb posture of ceratopsians. Some argued for an erect parasaggital posture while others argued for a sprawling posture with the humerus averted laterally. Anatomically, the sprawling posture seems to make sense. However, this left a discrepancy with ceratopsian trace fossils that had shoulder-width manual trackways. The manual impressions are also directed laterally unlike sprawling reptile manual impressions that are directed medially.

As Paul and Christiansen (2000, Paleobiology 26: 450-465) pointed out, this bipolar reconstruction of erect versus sprawling posture is misleading, as "fully erect" is suggestive of columnar elephantine limbs, while most large mammals don't even have this posture. "The issue of forelimb posture in ceratopsians is primarily a question of whether the humerus operated in a largely parasagittal fashion or employed significant mediolateral rotation during locomotion" (Paul and Christiansen 2000, p.451). Manual trackways would enforce the hands to be directly beneath the shoulder - the humerus likely operated in a largely parasagittal fashion but with the elbows slightly averted, instead of a "sprawling" manner. The elbows were probably flexed, so that takes care of the anatomy.

The problem, as I've heard from a friend who's worked on ceratopsian forelimb posture, is as mentioned above that the manual impressions are directed outward but most reconstructions force the hands to face forwards. Now, anatomically, that would rotate the whole forelimb laterally hence the sideways averted humerus and sprawling posture. But if the hands were to face sideways, as the trackways suggest, then the whole forelimb rotates so that it is pretty much underneath the body in an "erect" posture but with the elbows flexed, not the elephantine columnar fully erect posture.

So to summarise, I believe ceratopsians held their forelimbs pretty much underneath their shoulders with their elbows flexed and hands facing slightly outwards.

Dromaeosaur head dissection

I was going through my older drawings and came across this. It's quite comical but its a dromaeosaur head midway through dissection. The skin has been peeled off to reveal the jaw adductor muscles, jaw depressor muscle, parts of the neck muscles, and trachea. I got this idea from my own numerous dissections of bird heads. Minus the fact that this looks like a dinosaur, the initial phases of dissections in bird heads also look something like this...

Even in birds there really isn't much of a subdermal layer of muscles, except some really thin sheets that presumably control the feathers. But other than that, archosaurs don't have facial muscles seen in mammals and the skin is pretty much attached directly to the skull and mandibles in most parts, especially the rostrum.

The jaw adductors visible in this phase are the M. adductor mandibulae externus (MAME) superficialis (MAMES) filling the lateral temporal fenestra, MAME medialis (MAMEM) occupying the supratemporal fenestra, and M. pterygoideus (MPT) attaching on the ventral/medial side of the mandible and inserting/originating at the pterygoideus/palatine/quadrate on the upper jaw. The M. depressor mandibulae (MDM) is the slim body of muscle attaching on the back of the skull down to the retroarticular process if there is one or the posterior edge of the mandible.

Be the Dinosaur: a travelling museum exhibit

For some time now, I have been working as a scientific consultant on a travelling museum exhibit called Be the Dinosaur. The main attraction to this exhibit is the virtual simulation of the Late Cretaceous Hell Creek Formation. Visitors can navigate through the environment as a Tyrannosaurus rex or a Triceratops and try and complete some tasks, such as gathering food, or crossing a river, etc. However, in order to survive these simulations, the visitor must be very keenly aware of what they need to do and where to look for necessary stuff such as energy-rich food - the dinosaurs have a virtual digestive system and need to stock up energy for severe tasks like fording rivers. These information are provided in the panel-based education kiosks located throughout the exhibit so you can't skip the kiosks and go straight into the simulator pods - because you won't be prepared to survive. I think this is a clever way to educate visitors in various fields of science associated with dinosaur palaeobiology, including hunting behaviours, social behaviours, nutrition, energetics, biomechanics, etc.

Currently, the simulation features Tyrannosaurus rex, Triceratops, some insects for the background and lots of plants but will in the future include other animals such as fishes, turtles, lizards, crocs, and other species of Hell Creek dinosaurs possibly including birds.

You can view a few sample movies on Youtube
Wildlife Documentary
It's good to be King
Visitor response

60mb version of Wildlife documentary:
Wildlife documentary large

"this is the test article and as such is a work of progress, improvements, refinements are constantly being added in both graphics and technology - and will constantly be added during the lifespan of the exhibit" - from the developers.

The "Wildlife documentary" and "It's good to be King" are both basically a nature documentary in that the camera is just placed strategically to capture the actual behaviours of the animals. In that, I mean that their behaviours are not preprogrammed or part of a scenario, but are completely governed by their AIs. The interractions between the rexes and coordinated hunting you see in "Wildlife Documentary" are completely spontaneous. The AIs only have a few simple and basic drives and needs and "some universal information that any animal that would know about its environs". So the rexes are responding to each other the way they are through whatever the AIs decided was desirable under those circumstances.

The background movements like leaves swaying in the wind or water currents plus all physical interactions are generated by a physics engine and all animals have separate AIs governing their behaviour. All of these simulations are occurring real time and thus it is virtually a new experience every single simulation. Because all events are unfolding real time, the above videos are in essence a documentary and the cameras have to be placed in a good position to actually capture anything interesting.

In the actual simulator pods though, it is not just watching a nature documentary but actually getting involved as a T. rex or a Triceratops. You can be part of a hunting party or a member of a large herd in search of fresh vegetation...

The exhibit will premiere at the Louisville Science Center in mid May and then go on tour.

Tuesday, April 15, 2008

Suchomimus tenerensis: colour

Phew...so this is an Adobe Illustrator version of the Suchomimus drawing from a few days ago. As always, I used Illustrator to trace out the outline and then use different layers to colour, shade, and add a bit of effect. The stripes took me forever to do...

Sunday, April 13, 2008

DinoBase, 1 year anniversary coming up!

Well, it's almost a whole year since the launch of the new DinoBase. The actual one-year anniversary for the relaunch is the 17th of April (see here for my post on the launch day last year). I'm sure most of my readers are already aware, DinoBase is an online resource hosted by the Department of Earth Sciences, University of Bristol which I just happen to be the administrator of. The main feature of DinoBase is as the name suggests, its online database of dinosaurs. Visitors can search for dinosaurs using a number of search criteria such as genera, species, author, or year of description. I'll just go through the basic search function here.

Let's say we want to search for Tyrannosaurus rex but can't be bothered to spell out the whole name so we type in "tyranno".


Now we click on "search" and DinoBase will return the following list:


Note that DinoBase returns all records alphabetically, so the first few are the ones of interest, in this case, Tyrannosaurus bataar and Tyrannosaurus rex. Now to view the record we don't want to click on the dinosaur names because that will research the database under a new search criterion, i.e. the name you just clicked as the new keyword, so we want to click on the magnifying glass icon to the right of the names. When you place your cursor over it, a little pop-up comes up with "View Record".


Now we can view the information as a new window. Incidentally, Tyrannosaurus bataar is listed twice once as Tyrannosaurus and again as Tarbosaurus. This is due to a glitch in the system that doesn't let me delete entries so it stays for the moment. The only solution around this problem is to state its synonymous situation and redirect the user to the correct name, i.e. Tarbosaurus bataar, though I'm sure some people would prefer Tyrannosaurus bataar...

We do try to keep the information up to date as possible but currently there are only two of us doing data entry and management on the side (as we are both students) so there is a bit of a limit. New entries are stored on the waitlist until approved by myself - which is quite harsh as we need size data for taxa that is known from a single vertebra...so you can imagine why I'm reluctant to just approve every single new entry - I want to get as much as an accurate size estimate as possible, motly because information on DinoBase is supposed to be "academically approved".

Some of the entries will have pretty pictures like this one for T. rex. But a lot of them don't so if you're reading this and you're an active palaeoartist and want to use this chance to promote your dinosaur reconstructions, then please do contribute. We are always looking for good images of minor or rare dinosaurs!

Sinraptor dongi

Second drawing of the day...though the date has changed already. This is Sinraptor dongi an allosauroid from the Jurassic of Xinjiang, China. There are two recognised species of Sinraptor, S. dongi and S. hepingensis. S. hepingensis was initially described as the third species of Yangchuanosaurus after Y. shangyouensis and Y. magnus (Gao 1992 Vertebrata PalAsiatica 30: 313-324) but was subsequently assigned to the genus Sinraptor (Currie and Zhao 1993 Canadian Journal of Earth Sciences 30: 2037-2081). Compared to Yangchuanosaurus, Sinraptor has a relatively longer and lower skull. The two genera are united as Sinraptoridae. One of the distinchuishing features of sinraptorids is the high number (more than two) of accessory openings in the antorbital fossa. Another interesting feature of Sinraptor is the tall plate-like neural spines of the dorsal vertebrae. This is quite similar to Metriacanthosaurus such that Paul (1988 Predatory Dinosaurs of the World) synonymised Yangchuanosaurus with Metriacanthosaurus - he used M. shangyouensis instead of Y. shangyouensis.

I had two opportunities of studying the specimen of S. dongi at the IVPP. S. dongi is stored in an offsite warehouse about an hour's drive out from the IVPP. It is really a warehouse and mounted specimens of Sinraptor, Monolophosaurus, and a prosauropod (I forgot what it was) are just standing there amongst wooden crates and discarded packing materials, literally collecting dust. And it was damn cold...

Saturday, April 12, 2008

Suchomimus tenerensis

Ok. Back to my usual passion - drawing theropods. This time, it's Suchomimus tenerensis. As always, I ran out of paper but this time, I scotch-tapee another piece of paper to fit the tail...however, the extra length made it too big for my scanner so I had to scan it in twice and stitch them together using Photoshop...

Anyway, a bit about Suchomimus - though this dinosaur is really famous that I probably won't have anything unique to comment on. Suchomimus is a spinosaurid dinosaur from the Lower Cretaceous (Aptian) of Niger (Sereno et al. 1998). It is quite distinctly different from the other famous African spinosaur Spinosaurus in snout morphology and in the lack of the giant sail - although Suchomimus also has elongated neural spines along the posterior dorsal, sacral, and anterior caudal vertebrae. The elongation is most pronounced in the sacral vertebrae but it is nowhere as long as those seen in Spinosaurus.

Along with the slightly older Baryonyx from the UK and contemporary Cristatusaurus of Niger, Suchomimus is phylogenetically distinct from Spinosaurus and Irritator of Brazil - the former three forming the subfamily Baryonychinae and the latter forming the subfamily Spinosaurinae. However, it has been suggested that Suchomimus is congeneric with Cristatusaurus as well as with Baryonyx. In which case, both Cristatusaurus and Suchomimus should be sunk into Baryonyx because of senior priority...whatever - I don't really know much about taxonomy but personal observations of the skull elements of Baryonyx and a cast replica of the same elements in Suchomimus lead me to believe that this may be the case - at least with Suchomimus and Baryonyx. Suchomimus is just slightly bigger than Baryonyx. Then again it is believed that Baryonyx is a sub-adult anyway, so if they were the same genus then we could just be observing an ontogenetic sequence...

Thursday, April 10, 2008

Evolutionary theories...hurt my head

It's been some time since my last post...

Anyway, I've been busy trying to write a manuscript on the evolution of bite forces using finches and cats as case studies. One thing I've found out through this process is that, it doesn't matter how sophisticated a method you use, nor does it matter how great you think your results look, what matters is your ability to tie that into a broader perspective of evolutionary theory. And I've sadly realised, that either I don't have the brains, or the imagination, or the creativity, to write anything remotely interesting in the grand scheme of evolutionary theory. Evolutionary theory's the interesting end-product of all this functional morphology and phylogenetic comparative methods anyway, and if you can't do that, then you're screwed...

But I don't intend to be lazy and give up. At the same time I've been trying to be greedy. So I've been trying to read as much evolutionary theories as I can...


....and my head hurts...