Saturday, April 21, 2007

Maximum bite force in Tyrannosaurus rex

I'm on a roll today. Might as well post another.

So obviously, this is a Tyrannosaurus rex. It's so famous I'm afraid I don't really know what else to write about. Oh well, I'll just ramble on about bite forces then.

T. rex has been the focus of many biomechanical studies. Bite force is no exception. However, as much of a celebrity T. rex is, as far as I'm aware, there have only been two studies so far that have attempted to estimate the bite force of T. rex: Erickson et al. (1996) and Meers (2002).

Erickson et al. (1996) had an interesting approach of reproducing bite marks using cast replicas of a T. rex tooth and ramming it into a cow bone. They recorded the forces needed in order to penetrate the bone to different depths. The depths of T. rex bite marks found on a Triceratops ilium was compared to this relationship of puncture depth and forces needed. As a result they found out that a bite force of 6.4 kN were needed in order to to make that bite mark. From the shape and size of the tooth, Erickson et al. (1996) suggested that the bite may have been made from a mid maxillary tooth. So they extrapolated a possible bite force for the posterior-most tooth position. Further, they suggest that up to 30% of the original bite force may have been lost due to several layers of soft tissues that the tooth would have had to penetrate before it reached the bone. In conclusion, they proposed a maximum bite force of 13.4 kN.

Mason Meers (2002) on the other hand employed a much simpler approach. He regressed bite force against body mass and extrapolated the relationship to a 5 tonne T. rex. As a result, his maximum bite force was 183 to 235 kN, an order of magnitude higher than Erickson et al.'s (1996).

So which is closer to the truth?

I would say somewhere in between the two.

Through my own studies, I'm confident to say that Erickson et al.'s (1996) bite force estimate is not really a maximal value. This isn't restricted to just Erickson et al.'s (1996) estimates but for other theropods as well (Rayfield et al. 2001; Mazzetta et al. 2004a, b). With Rayfield et al. (2001) and Mazzetta et al. (2004a, b), their methods in bite force estimation may have the tendency to underestimate. Erickson et al. (1996) on the other hand probably estimated their bite force fairly accurately. The only problem is that the T. rex that produced the bite mark may not have exerted its maximum bite force. The position of the bite on the Triceratops (in the pelvic region) strongly suggests that these bite marks were produced post-mortem and were probably not killing bites but feeding bites. It is unclear just how hard it was biting, but the safe bet is, it was probably just happily munching away at a leisurely (or necessary) bite. I had a chat with Greg Erickson at a conference and he seems to have an opinion along this line as well.

Meers (2002) on the other hand may have overestimated maximum bite force. This is mostly because his slope on the regression equation is closer to 1, or proportional increase of bite force with increasing body mass. So the bigger the animal the stronger the bite. However, my own studies suggest that this slope may actually be significantly lower than 1, so in other words, the bigger the animal, the progressively weaker the bite gets relative to its increase in body mass.

So this puts maximum bite force for T. rex with various body mass estimates at somewhere between 50 to 80 kN.

References:
  • Erickson, G. M. , Van Kirk, S. D., Su, J., Levenston, M. E., Caler, W. E. and Carter, D. R. 1996. Bite- force estimation for Tyrannosaurus rex from tooth-marked bones. Nature, 382:706-708.
  • Gerardo V. MAZZETTA, Adrián P. CISILINO y R. Ernesto BLANCO. 2004a. Distribución de tensiones durante la mordida en la mandíbula de Carnotaurus sastrei Bonaparte, 1985 (Theropoda: Abelisauridae). Ameghiniana 41: 605-617.

  • Gerardo V. MAZZETTA, R. Ernesto BLANCO y Adrián P. CISILINO. 2004b. Modelización con elementos finitos de un diente referido al género Giganotosaurus Coria y Salgado, 1995 (Theropoda: Carcharodontosauridae). Ameghiniana 41: 619-626.

  • Rayfield EJ et al, 2001, Cranial design and function in a large theropod dinosaur, Nature 409: 1033-7
Images from National Geographic and BBC.

Coelophysis bauri

I'm going to start using this blog not only for my technical comments but also to introduce my attempts at life-restorations of theropod dinosaurs. Left is the famous Coelophysis bauri. Coelophysis is one of the best preserved theropods with numerous complete specimens.

One interesting thing about this animals is the supposed evidence of cannibalism. Two specimens have been long considered to have
remains of members of its own species in their thoracic cavities. This view has been recently challenged by Sterling Nesbitt et al. A closer reinspection of the specimens revealed that in one specimen (AMNH FR 7223) the gut contents were actually not even inside the ribcage but underneath it. The second specimen (AMNH FR 7224) on the other hand was shown to actually have bone materials within its thoracic cavity. However, detailed histological study has shown that none of these bones had any diagnostic characters to suggest they were Coelophysis but were more likely to be from a small crocodylomorph.

So, there is no compelling evidence of cannibalism in Coelophysis.

Friday, April 20, 2007

Terrestrial-style feeding in Acanthostega


Although the very early tetrapod Acanthostega possesses many adaptations for an aquatic lifestyle, recent work by Molly Markey and Charles Marshall of Harvard University suggests it had a more terrestrial-style feeding. This is a pretty cool piece of work as suture morphologies on the skull roof of a modern fish Polypterus was correlated with suture functions during feeding. Stain gauge measurements in the skull of Polypterus show tension in the anterior and compression in the posterior parts of the skull. The cross-sectional morphology of these sutures seem to be correlated well with the strain patterns. (image left taken from here)

The authors then went on to quantify suture morphology in fossil forms, a sarcopterygian Eusthenopteron, an early tetrapod Acanthostega, and a fully terrestrial Phonerpeton. The cross-sections revealed that while Eusthenopteron showed similar suture morphology to Polypterus, Acanthostega and Phonerpeton did not. Extrapolating the relationship between suture function and suture morphology would suggest that Eusthenopteron had a similar strain pattern to Polypterus, indicating a similar feeding pattern, in this case, suction feeding. The suture morphology of Phonerpeton on the other hand was not consistent with the 'tension anteriorly, compression posteriorly' but compression both anteriorly and posteriorly. Since Phonerpeton is fully terrestrial, this form of strain pattern is presumably associated with a feeding style where biting prey is the main source of load.

So what's it like in Acanthostega?

Interestingly enough, Acanthostega is reported to have suture morphology reflecting compression at both the anterior and posterior margins of the skull. This suggests that the skull of Acanthostega did not experience the same kind of strains associated with suction feeding as seen in Eusthenopteron or Polypterus. Rather, it is more consistent with the patterns observed for Phonerpeton.

Conclusions: Acanthostega probably employed a biting-type feeding.

So my two cents are as follows:

This is a nicely done piece of work. It's nice and simple and compelling, mostly because of strain gauge measurements in Polypterus - man, I love it when people actually back things up with extant animals.

However, there are a couple of things I'd noticed.

First of all, I think it would be more compelling if strain gauge measurements were also taken from a fully terrestrial extant animal. That way you know for a fact that certain strain patterns are associated with terrestrial-style feeding. The paper only assumes that the strain patterns observed in Phonerpeton would be associated with a terrestrial-style feeding, an assumption that is understandable but should be taken with care as Phonerpeton is another fossil taxon. But I'm just guessing that peeling off the skin of an iguana or some poor amphibian to stick strain gauges directly onto the skulls is not going to be easy. But acquring cross-sections of modern tetrapod skulls should be possible at the least.

Secondly, it seems to me that the locations where cross-sections were taken are not entirely consistent across the species used. Only the interfrontal (IF) and interparietal (IP) sutures are figured for the two fish species while additional locations, the nasofrontal (NF), frontoparietal (FP), and interpostparietal (IPP) are considered for Acanthostega and Phonerpeton. I wonder what the cross-sections of these locations would show in Polypterus and Eusthenopteron.

Overall, I liked this paper for many reasons. I think this is a pretty cool study, as far as functional morphology goes.

Wednesday, April 18, 2007

DinoBase Launch


So I am managing an online resource called DinoBase. DinoBase was set up by Mike Benton of University of Bristol about 7 years ago, but had recently undergone a complete make-over. While the old DinoBase used to be literaly tens and hundreds of html pages, the new DinoBase features a dynamic system. It's pretty much a relational database, where all the different categories of information (e.g. genus, location, reference, etc.) are stored in separate tables but link to other tables. This enables data entry to become very quick and easy.

As far as the user is concerned, the information on these individual tables are pulled out and compiled onto a single page, just like any webpage, only that that particular page doesn't exist online as an individual page. So type in a dinosaur genus, species, year of description or author, click on the one you want to view and all the relevant information about that dinosaur will be presented in a single page. This, I think is a very cool system.

DinoBase also has features aside from the database itself. The forum is the newest addition to DinoBase which has quickly become promising. This takes up quite a bit of my energy as I always am on the look out for new dinosaurs to post under the 'Recent Discoveries' Forum or dinosaur-related news to introduce.

Just yesterday, we had a media-event (which I'm not really sure how much the media actually picked up on) where we invited children to explore DinoBase, work on some activity sheets downloadable from the site, look at some cool casts of dinosaur bones, or have a chat with Bristol palaeontologists. So that was the 'Official Launch'. Hopefully, we'll get more attention within the next few days...

Monday, April 9, 2007

Robotic salamander

I know this isn't about dinosaurs but it's more to do with scientific methods in palaeontology. Recently, in the journal Science, there was a paper about a robotic salamander where its gaits are controlled by a spinal cord model. The spinal cord model gives out signals that oscillates the trunk. The team confirmed that the more intense the signal, the higher the frequency of the oscillation gets. This higher frequency oscillation produces a swimming gait similar to that of real salamanders. On top of that, they found that limb oscillation saturates at a lower frequency and the robot switches from walking to swimming.

According to the authors, the main significance of this study is 'to show how a tetrapod locomotion controller can be built on top of a primitive swimming circuit and explain the mechanisms of gait transition, the switch between traveling and standing waves of body undulations, and the coordination between body and limbs'.

This work has been taken up pretty frequently as a possible scenario of evolution of walking gaits from swimming in early tetrapods. Though, I have heard criticisms that since salamanders are derived amphibians, modelling their locomotory switches from swimming to walking does not necessarily show how this might have happened in basal tetrapods. This is true from a certain perspective, like trying to figure out the biomechanics of basal birds (without all the adaptations of flight), using advanced birds (with highly specialised flight adaptations) as models. However, as the authors stated, the significance of this study is that the neural control of walking can be based on a primitive swimming neural control such as those seen in lampreys.

If this isn't convincing, then even from a purely biomechanical point of view, it is still significant in that they provided a good model to understand the locomotory switch from swimming to walking in a modern salamander. If we don't even understand how modern animals work, how are we to understand how extinct animals may have worked.

Originally posted on DinoBase

Friday, April 6, 2007

Ultrasaurus and Ultrasauros

This is an ancient topic, but I was just thinking about it the other day.

Do you remember that whole thing about Ultrasaurus?

In 1979, James Jensen of Brigham Young University found what he believed to be the largest sauropod ever. The press went mad and widely publicised the dinosaur under the name Ultrasaurus. I remember as a kid that Ultrasaurus (along with Supersaurus) was always depicted as a huge brachiosaur dwarfing even Brachiosaurus.

However, it took another 6 years before Jensen finally published his findings. By then, a Korean palaeontologist, Haang Mook Kim, had already named a sauropod with the name Ultrasaurus because he thought it belonged to the same genus that Jensen had found. But it turned out that Kim's Ultrasaurus was something different, and when Jensen wanted to use Ultrasaurus, his first preference, he couldn't because it was 'preoccupied'. So he instead named his dinosaur Ultrasauros with an 'o'.

Funnily enough, Kim's Ultrasaurus later became a nomun dubium or a dubious name because there wasn't enough information to assign it to any dinosaur family. Jensen's Ultrasauros had also become a junior synonym of Supersaurus because it turned out that the type of Ultrasauros was in fact a chimera comprised of bones from Supersaurus and a very large brachiosaur. Since Supersaurus was named earlier, Ultrasauros unfortunately had no right to be a recognised genus name.

So despite the huge confusion they caused, both Ultrasaurus and Ultrasauros are now invalid taxa.

Originally posted on DinoBase