Junk in the Trunk Redux

Today I’ve got another interview from Scott Persons! Scott’s going to tell us all about his new paper on the tail of Carnotaurus, which follows his paper on the tail of Tyrannosaurus published last year. Enjoy!

1. What inspired you to conduct this study?

This was a case where no inspiration was required, just thoroughness . . . and a pinch of luck. My work on Carnotaurus was part of my Master’s thesis, which looked at the tail morphology of a wide range of carnivorous dinosaurs. Carnotaurus, a member of the unusual abelisaurid group, was on my list of potential dinosaurs to examine. The first Carnotaurus material that I saw was a cast at the Natural History Museum of Los Angeles County. Examining the L.A. Carnotaurus cast fit in nicely with my schedule, but I was in California primarily to measure the tail of a Dilophosaurus skeleton at Berkley.

Fortunately, it only takes one look at a Carnotaurus tail vertebra to realize that something dramatically weird is going on with the animal’s tail.  On a “normal” theropod tail vertebra (or, for that matter, a “normal” anything-else tail vertebra), boney projections, called the caudal ribs, stick out horizontally and have a simple rod-like shape. In Carnotaurus, the caudal ribs of the basal tail vertebrae project more vertically than horizontally, and their shape is complex – with tips that are thin and shaped like half-crescents. After examining the specimen in California, I realized how interesting a Carnotaurus tail study would be, and it became a major focus of my research (which meant Dilophosaurus and several other theropods had to take a backseat).

The 6th tail vertebra of Carnotaurus, as seen from the side (upper left), the front (upper right), and from above (lower center).

2. Why “speed demon”?

The title of the Carnotaurus tail paper (published in the online scientific journal PLoS ONE) is “Dinosaur Speed Demon”. It is an unusual title. Supernatural fiends (fast or otherwise) and peer-reviewed natural history literature don’t usually mix. But the explanation is straightforward:

Carnotaurus is famous for its ugly mug and two large conical horns that stick out from its forehead in an indisputably devilish style (hence “Demon”).  As for “Speed”, the conclusion that I and Dr. Phil Currie came to was that the vertically oriented caudal ribs and their bizarre half-crescent-shaped tips (which interlocked with those adjacent in the vertebral series) provided an expanded and ridged framework for one super-sized tail muscle: the caudofemoralis. The caudofemoralis is a locomotive muscle that attaches to the femur and lends considerable force to the power strokes of the legs. Except for some birds, all dinosaurs had caudofemoral muscles (that’s a major reason why dinosaurs have big tails), but I estimate that, relative to its body-size, Carnotaurus had the biggest.

A new Carnotaurus illustration created for the paper by artists Lida Xing and Yi Liu.

Big locomotive muscles mean more locomotive power, which means Carnotaurus was adapted for speed.  Some puns are too good to pass up.

3. So…could Carnotaurus outrun the Jeep in Jurassic Park?

Estimating the maximum running speed of a dinosaur or any other extinct animal is hard. (So hard that in the published paper, I stick to offering a qualitative rather than a quantitative assessment of Carnotaurus running performance.) There are lots of important variables besides absolute muscle mass that determine how fast an animal can run.

As I said in my previous blog post, just keeping pace with the JP Jeep would require a speed of 30-40 mph (48-64 kph) (remember, the black-leather-clad rump of a certain chaotician was preventing the driver from switching into high gear).  So, achieving Jeep-catching speed would mean a charging Carnotaurus was roughly 30% faster than a charging black rhinoceros – a scary thought, but not an implausible one. If I had to guess, I would say: Yes, Carnotaurus was fast enough to outrun the Jeep. Just the same, I don’t think Carnotaurus would have caught it. Here’s why:

The tree branch doesn’t move, and the T. rex doesn’t appear to see it.

Jurassic Park fans will recall that in the chase scene, just as the T. rex is getting close enough for Jeff Goldbloom to feel its hot breath, the Jeep drives under a low tree branch. Being the colossus that it is, the Tyrannosaurus just smashes through the branch and stays on course. At roughly one third T. rex’s size, Carnotaurus probably couldn’t do that. Instead, the abelisaurid would have had to avoid the collision. While my study indicates that Carnotaurus was evolutionarily engineered for speed, it also indicates that this speed came at the cost of turning performance.

The rigid framework provided by the interlocking caudal ribs would have limited sinuous motions, which would have disadvantageously increased the animal’s effective rotational inertia. When turning, Carnotaurus would have been forced to awkwardly swing its hips and the front half of its tail all at once, like a single stiff board. The set of a tropical Hawaiian forest just isn’t the ideal hunting ground for Carnotaurus, and I think having to swerve around the foliage would have slowed Carnotaurus down considerably.

4. Does this tell us anything about the evolution of abelisaurids?

Yes, but exactly what it tells us is a matter of debate.

Abelisaurids are known from Africa, India, Madagascar, and South America. Carnotaurus is from South America. If you look at the tails of older South American abelisaurids, you will see what I think is a clear evolutionary sequence of adaptations in the vertebrae that leads to the advanced form of Carnotaurus. I would argue this shows that, over time, South American abelisaurids were getting faster. I would also argue this strongly suggests that Carnotaurus is more closely related to other abelisaurids from South America than it is to abelisaurids from Africa, India, or Madagascar (all of which lack special tail-vertebrae adaptations). The argument is important, and a matter of contention, because it has been previously asserted (by paleontologists much more experienced than myself) that Carnotaurus is most closely related to abelisaurids from outside South America.

The evolution of South American abelisaurid tail vertebrae through time (each vertebra is depicted in frontal and top-down views, numbers are millions of years from now).

5. Carnotaurus may not be as famous as Tyrannosaurus, but it has popped up occasionally in film and TV. What are your favorite portrayals of Carnotaurus?

Yeah, Carnotaurus has had its chance in the spotlight, probably because its striking facial profile makes it a natural fill for villainous roles. Picking my favorite portrayals is hard . . . because most have been so terrible.

In Michael Crichton’s second Jurassic Park novel, a Carnotaurus pack poses a threat to the inexplicably resurrected character of Ian Malcolm. The book gives Carnotaurus cuttlefish-like powers of camouflage, but the dinosaurs ultimately prove no match for the tactic of annoyingly waving flashlights (really, that’s what Crichton wrote).

A pair of marauding Carnotaurus played the bad guys in Disney’s Dinosaur. But these red menaces had to suffer an anatomical redesign and wound up looking more like tyrannosaurs with horns.

By giving some of the Iguanodon a nose horn, the Mickey Mouse organization set paleontology back to the days of Gideon Mantell. The big red Carnotaurus, or “Carnotaur”, wasn’t much better.

A Carnotaurus had the starring dinosaur role in the 2008 animated movie Turok: Son of Stone. This was a film that managed to be offensive at an artistic, intellectual, and social level (kind of like Transformers 2 [Victoria’s note: don’t get me started on Transformers 2…]), but the Carnotaurus does get some good (though ridiculously over-the-top) action scenes.
Turok and his trusty steed prepare to go all Stone Age on a gang of Neanderthal sumo wrestlers.

Most recently, Fox TV’s Terra Nova series showed us a new CGI Carnotaurus. Terra Nova’s Carnotaurus has its flaws (though, perhaps no more so than any of its other cast members), but I enjoyed seeing it in action.
 Outside the Terra Nova compound, a Carnotaurus squares off against what I thought was a beige version of the new Batmobile.

I would have to say my favorite media portrayal of Carnotaurus is in the absurd Japanese cartoon series Dinosaur King. In the show, a Carnotaurus named Ace is the loyal companion of a young boy and helps him fight evil.

Ace and Rex take the bus (the pet dinosaur is named “Ace” and the boy is named “Rex”).

The Dinosaur King’s CGI cartoon Carnotaurus actually suffers from fewer anatomical inaccuracies than ether Disney’s or Terra Nova’s, and it’s nice to see a theropod get to play the hero for a change. From what I’ve seen, Dinosaur King is a something of a Pokemon rip-off, and all the dinosaurs get special super powers — some of the dinos breathe fire, others cause earthquakes, etc. And what is Ace’s special power? Super speed!

Valiantly defending us from alien invaders, mad scientist, and temporal paradoxes, Ace (seen here in his grownup form) is a two-horned, purple, people protector.

Persons WS, Currie PJ. 2011. Dinosaur speed demon: the caudal musculature of Carnotaurus sastrei and implications for the evolution of South American abelisaurids. PLoS ONE 6(10): e25763.

6 thoughts on “Junk in the Trunk Redux

  1. If Carnotaurus's speed came at a cost of turning ability would it have been better adapted to hunt in plains-type environment as opposed to a more densely-vegetated environment? Is that congruent with the paleoecology of the areas the fossils have been found in?


  2. In the evolution diagram:

    “…numbers are millions of years from now.”

    Strange, I thought abelisaurs lived eons AGO. 🙂 Jessica raises some interesting questions; hope I can address them soon.


  3. The fact that Carnotaurus was apparently such a speed demon brings up another question. Is is possible, in some of the more derived abelisaurs at least, that the tiny arms of these theropods were used as balancing organisms.


  4. How could they have been effective at balancing if they were tiny?
    I recall an author in The Complete Dinosaur opined that dinosaurs did not fit in forests but lived just outside them. So I suppose even in the titanosaur dominated environments, trees wouldn't have gotten in the way of a “speed demon” predator.


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