Thursday, 12 January 2012

Daspletosaurus is the Key


Southern Alberta, 77 million years ago and beside a large tract of marshland, feeding on the carcass of an adult Brachylophosaurus, are three adult daspletosaurs. All three tyrannosaurs consume everything they can rip away from the carcass with their powerful jaws and great swathes of meat, tendon and bone are swallowed whole – nothing is disregarded.

There are frequent disputes over dominance of the carcass and although the snarling displays of aggression rarely amount to much, they do, on occasion, snap at each other’s head and bite down hard. These clashes are only brief – instinct tells the tyrannosaur that this form of interaction can cause severe damage and infection if prolonged.
Suddenly, all three tyrannosaurs become aware that they are not alone and each one, in turn, notices movement in the undergrowth and in the surrounding treeline. This merely stimulates them to eat faster and now copious amounts of hadrosaur disappear down their gullets with hardly any thought. All that matters is to eat as much as you can as fast as you can.
A troodontid, almost casually, steps into view but although the daspletosaurs are already aware of him, they give him short  shrift and carry on feeding – they know they still have some minutes remaining. Eventually other troodontids appear and then another, then another until there several of them surrounding the feeding carnivores. A sudden movement behind them causes one of the tyrannosaurs to look behind him and he sees other predators approaching – this time they are dromaeosaurs. He knows it is nearly time.
The troodontids slowly approach the carcass and, as they do, the daspletosaurs raise their heads, snap their jaws and issue a very deep low frequency growl from within. The intruders both front and rear stop and take a step back but it does not put them off for long and this game is played out again and again over the coming minutes and still the daspletosaurs continue to feed as much as possible.
Eventually the intruders almost reach the carcass and then one of them takes a quick bite out of the carcass. This time one of the daspletosaurs quickly reacts and issues a large roar and takes a step forward toward the impudent troodontid. Again this temporarily halts the advance but not for long. Soon other troodontids, as well as the dromaeosaurs, begin nipping at the remnants of the hadrosaur and now, as their stomachs become full, the tyrannosaurs eventually begin to give way and allow the smaller predators to keep darting in and out, taking scraps of flesh.
All of a sudden the harassment becomes too much for one daspletosaur and he tears off a huge haunch of hadrosaur and carries it away into some trees. The remaining two daspletosaurs continue to feed but, in the end, they too break away from the feast and move off leaving what is left of the carcass for their tormentors and the carcass almost disappears from sight as the seething mass of small predators’ attack what’s left with abandon.
The daspletosaurs go their own ways for this was not a structured, coordinated kill – rather it was mutually advantageous to bring the hadrosaur down as a threesome as opposed to an individual attacking on their own. Each will return several times to the spot of the kill in the days ahead to see if anything remains and what can be scavenged. If they meet up with each other again, they will give their opposites a wide berth since they do not usually interact unless it is time to mate or if the opportunity to join a kill arises again.

The skull of Daspletosaurus
Image by AStrangerintheAlps

Of course, all the above is purely conjecture on my part but there is some palaeontology in there as well. The age, terrain and fauna are all correct as are some other details such as face biting and the crushing and swallowing of bone. But it is really my way of discussing what I consider to be, not only the most fascinating, but also looks like turning out to be probably one of the most important tyrannosaurids in the next few years – Daspletosaurus.
Daspletosaurus torosus was named in 1970 by Dale Russell. The holotype CMN 8506 essentially consisted of the skull and skeleton but there were no hind limbs recovered save for one femur. The specimen was recovered by Charles Sternberg in 1921 from the Late Cretaceous Oldman Formation in Alberta, Canada. When first collected, Sternberg initially thought the skeleton represented Gorgosaurus or indeed, as it turned out, to be a new species.
Daspletosaurus has a number of things going for it which make it such an intriguing object of study. Firstly, it is a tyrannosaurine and is closely related to Tyrannosaurus although its actual systematic relationship within tyrannosaurinae remains unclear for now.  Secondly, there are multiple species of Daspletosaurus with the majority of these still to be diagnosed, formally described and named. Just what this will mean for tyrannosaurine systematics and synonymy is unclear.
Another fascinating issue is the fact that, in the Dinosaur Park Formation in Alberta, Daspletosaurus sp. actually co-existed with Gorgosaurus which has been taken as suggestive of niche partitioning between large theropods, since Daspletosaurus is a much more robust animal than the lightly built Gorgosaurus. This was considered a somewhat unusual occurrence at first but now more formations around the world are demonstrating similar co-occurrences of large theropods co-existing and this further blurs the issue.
There is even a little legend surrounding Daspletosaurus and that is that, not only did it have proportionately the biggest forelimbs of any tyrannosaurid, but it also had the biggest teeth, proportionately, of any tyrannosaur – including T.rex. But I have never been able to find a reference for the statement about the teeth and if you are aware of the origin of this “fact” then I would very grateful if you would let me know.  
Daspletosaurs are also known from bone beds and a site in the Two Medicine Formation in Teton County, Montana has revealed the remains of over three individuals, including a juvenile, and may be suggestive of gregarious tyrannosaurs similar to the albertosaurs of the Dry Island bone bed. This is still a matter of conjecture, however, and the Teton County site also contains multiple remains of hadrosaurs.
Daspletosaurus, as a species, is undoubtedly of crucial importance in our understanding of faunal endemism and isolation in Late Cretaceous North America, the origins and dispersal of tyrannosaurines and our overall understanding of tyrannosaurid systematics. Essentially, Daspletosaurs are very cool animals and are, for me, the quintessential tyrannosaurid – they are uber-cool.
Incidentally, Anthony Maltese, over at the Rocky Mountain Dinosaur Resource Center (RMDRC), has published a number of times on his blog about preparation of two daspletosaurs known as Sir William and Pete 3. Sir William has finished being prepped now  but Pete 3 is undergoing preparation right now and, with the main jacket still to come,  I would expect more posts in the future about the project. A lot of the material is truly awful and they are performing miracles in restoring this important specimen. Head over there now and take a look if you have not already done so.
Daspletosaurus in the Field Museum
Image by brianbrarian 

Reference

Russell, D.A. 1970. Tyrannosaurs from the Late Cretaceous of Western Canada. National Museum of Natural Sciences Publications in Palaeontology 1:1-30.

8 comments:

protohedgehog said...

Has anyone looked at the possibility that Gorgosaurus and Daspletosaurus might represent an ontogenetic series, or possibly even sexual morphs of the same species? It's odd that there is just one case of sympatry in large theropods (or are there more..?)

Anthony Maltese said...

Thanks for the plug, Mark! A for your facts: Daspletosaurus does indeed have very long forelimbs for a tyrannosaur. Pete III's arms are about as long as Sue's, however they are less robust. As for the teeth: I can't tell who said that. We see a few teeth (shed) in the JRF that are pretty close to being tyrannosaurus-sized. Who knows though...

Mark Wildman said...

Thanks for the comments guys. Jon, I think you may have a point regarding sexual dimorphism – to a degree. I confess that I am unaware of any specific work regarding dimorphism in Daspletosaurus, Albertosaurus or Gorgosaurus although there has been plenty of study regarding Tyrannosaurus eg Larson 2008 which is highly indicative of sexual morphotypes within the genera.

It seems unlikely that Daspletosaurus and Gorgosaurus are ontogenetic variants of the same taxa since the cranial differences between the two are subtle but marked. However, there is still so much data to be published that anything is possible which is why I suggest that Daspletosaurus, as a genera, is going to be crucial in our understanding of diversity within Tyrannosauridae.

Always glad to point others in the direction of the RMDRC Anthony. The comparative images of the humeri of Pete 3 and Peck’s Rex were really interesting and, as you point out, the rex humerus is quite robust, as highlighted by the deltoid ridge.

Marc Vincent said...
This comment has been removed by the author.
Steven said...

Apparently a second specimen has been found in the Oldman Formation. I happened to read that today from here: http://www.calgaryherald.com/travel/Phil+Currie+continues+break+ground+hunt+dinosaurs/5994627/story.html

Mark Wildman said...

Hi Steven. Yes I saw that article doing the rounds - very interesting. It should be D. torosus, of course, which is really excellent to have a second specimen of this important tyrannosaur to study.

Hadiaz said...

I always enjoy a good "day in the life of" story about dinos, hence why this blog post is 1 of my favorites from you.

Out of curiosity, any particular reason why the troodonts appeared b-4 the dromaeosaurs?

Mark Wildman said...

None whatsoever I'm afraid - they were the first ones that sprang to mind when I wanted something small and agile to aggravate the tyrannosaurs.

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