Heretical dinosaurs?

19 04 2007

Last night I managed to finish Bob Bakker’s landmark work, The Dinosaur Heresies, and I have to say I don’t think I’ve ever read a better book about science for both the general public and those with a vested interest in the Dinosauria. Along with the easy-to-understand text, the book is lavishly illustrated with diagrams and action-packed dinosaur portraits, visually appealing as well as mentally fulfilling. I was especially interested to see the differing depictions of Deinonychus, Bakker’s version bearing feathers and appearing sleek and deadly, while the same dinosaur in The Illustrated Encyclopedia of Dinosaurs (and the cover of the first edition of The Dinosauria) seem somewhat grotesque. Even so, sometimes Bakker’s dinosaurs seem a little hyperactive (somersaults, backflips, and other acrobatics abound in his illustrations), but this is the point; to portray dinosaurs as active, warm-blooded animals.

It’s also interesting to note that the cover image of the book, a Daspletosaurus attempting to pin down or slice open a Styracosaurus, is a running theme with Bakker; the front page for the “Leo Project” features a cgi-rendered snapshot of a few seconds after the cover image, and Bakker’s Tyrannosaurus rex mount seems to taking the same pose. This is just a minor point, but I did find it interesting to find this “logo” appear so often.

Anyway, as far as the actual content of the book there is much that piqued my curiosity, but of course there are also a few errors given the book is about 20 years old. There may be other mistakes, and of course the number of dinosaurs we now know (especially from South America, parts of Africa, and Asia) has skyrocketed, but the biggest one I saw was the positioning as Deinonychus as a potential ancestor to Archaeopteryx and birds. This is never explictly stated, but Bakker has no reservations explaining how Deinonychus would be the perfect avian ancestor. The only problem is, however, that Deinonychs lived after Archaeopteryx, making it an unsuitable candidate for an ancestor. As Gregory S. Paul and others have hypothesized, perhaps the dromeosaurids were secondarily flightless, some split occurring during the evolution of flight that led later dinosaurs to have more advanced characters than Archaeopteryx itself. We’re going to need more fossils and data if we’re going to solve this puzzle, but for a while the “Deinonychus as ancestor” idea confused me.

Specifically, I remember a PBS documentary series (played several times, but at least once around Thanksgiving I think) that featured beautiful animation and was all about advances in dinosaur science. One particular scene featured a dromeosaurid running, eventually growing feathers, turning into a dino-bird, and eventually (if I remember correctly) a Canada Goose. Such confusion still abounds, as last semester I visited the American Museum of Natural History with my evolution class and had to explain the evolution of birds using the mounts available. While everyone was with me while I went over changes in hip structure, I needed a few extra minutes because the question came up again; how could a Cretaceous dinosaur be the ancestor of a Jurassic one? The mystery is far from solved, but the relationship of dromeosaurs and birds seems now far more complicated than what has previously been expected.

This aside, I found Bakker’s treatment of “duckbilled” dinosaurs most rewarding; they’ve been placed in swamps for far too long. Indeed, while they may have swum from time to time or crossed rivers, they appear to have been poorly adapted to life in the swamp, their deep and rigid tails offering them little propulsive power and their small feet did little to spread their weight over soft ground. If we look at modern herbivores that live in swampy habitats and use water for an escape (like the Lechwe of the Okovango Delta) we see adaptations to spread their weight out over soft ground so they don’t sink in. Hadrosaurs don’t appear to have any such adaptation, and if they fled into the water to avoid big land predators they would essentually be serving themselves up to large crocodilians of the time. Again, this isn’t to say they never went into the water, but it seems that they were poorly adapted to be in or around a swamp or water source for an extended period of time. Just because they have a superficially duck-like beak doesn’t mean it required the same habitat.

Bakker also makes a good case for active, warm-blooded dinosaurs, although work still needs to be done on the subject; I agree with Bakker, but it’s hard to articulate why other than “That’s what my observations tell me,” which isn’t very scientific in of itself. I am curious, however, why the possibility of being “warm-bodied” hasn’t come up in these discussions. Some modern fish like Great White Sharks and Tuna have the ability to keep their body temperatue several degrees C higher than the surrounding seawater, allowing them to live very active lifestyles for fish. Unfortunately, the secret to this adaptation lies in tissues and vessels that do not fossilize, but couldn’t it be possible that if not fully warm-blooded that dinosaurs had the ability to have a higher body temperature than their surroundings? Perhaps there is some flaw in this logic and that’s why it hasn’t been discussed, but I think it’s an idea that has at least some merit for determining (at least) the origins of warm-bloodedness.

I also enjoyed Bakker’s analysis of the “boneheads,” Pachycephalosaurus and its kin. These dinosaurs are often shown butting heads for dominance, but a dome-shaped skull doesn’t seem to be efficient for head-to-head combat; all the force would be put on one part of the skull instead of spreading it out across a wider area (like a bighorn sheep) or providing only glancing blows. As Bakker notes, such a design might be better at butting flanks than other domed heads, and if I could I would like to do a study. Why not reconstruct some heads from Pachycephalosaurus and ram them together at varying speeds/forces to see how well they could take blows or if they really even could butt their heads together effectively. Such tests might give us some clues to possible skull trauma we could look for. Further, why not look at the ribs/flanks/hips/femurs of these dinosaurs and see if they have any blunt-force fractures (including how many and whether they healed). I would imagine such a trend would have been noticed already, but I am indeed skeptical of the head-to-head combat hypothesis for these dinosaurs (although it might have worked for some of their broader-skulled kin).

Bakker’s discussion of extinction is also interesting, and while I think that the impact in the Yucatan 65 million years ago (along with the activity of the Deccan Traps in India, which I wonder if their activity is resultant from the meteor impact) finished off the dinosaurs and many other times of life, I think more work needs to be done one the potential decline of the dinosaurs prior to the event. We shouldn’t forget how the Western Interior Seaway recded and habitats changed, and as Bakker notes species diversity seemed to decline. Given that fact that large contiguous populations are more likely to be in stasis than evolve new forms, having the land be dominated by Triceratops might have signalled significant changes that wouldn’t allow dinosaurs to cope with the impending disaster. This, of course, is speaking primarily for North America and I would like to see a new study done, in the spirit of those done by David Raup, about how many dinosaurs (both in diversity and number) there were in different parts of the world, especially since South America seems to have been so different from North America in its dinosaur diversity during the Cretaceous.

There are other items I could go on about but I think I’ve spent enough time giving my opinion here; Bakker’s book is absolutely engrossing and there are few books I have enjoyed more. So many science books are stale and spend so much time on history, whereas Bakker takes you on an intellectual field-trip laden with evidence from personal experience and observation; science writers would do well to learn from Bakker’s example. If you don’t have the book already, I highly suggest you get your hands on a copy, and if you do and haven’t read it in a while perhaps it’s time to revisit it.




4 responses

19 04 2007

This sounds like a great book–I’ll need to check it out. My creationist father-in-law has recently been throwing around the idea that “museums are having to totally redo their dinosaur exhibits ’cause they got it all wrong” and I’d like to have some specific examples to back up my rejoinder that “that’s because science, unlike religion, is a self-correcting endeavor.” (Actually, I’d rather just not have the argument and go drive go-karts with him instead. Go-karts are fun; arguing with bible-thumpers is less so.)

19 04 2007

Yeah, go-karts sound like a lot more fun to me too (in fact I’ve never driven one; it’s on my to-do list).

The sad thing is that many museums still haven’t corrected the mistakes Bakker talks about, i.e. the Triceratops at the American Museum of Natural History still has sprawling front arms even though we know this isn’t the case. He goes into a lot of detail about how scientists had the “right idea” about dinosaurs around the turn of the century until the 1920’s when suddenly everything got messed up.

You might also want to look into Gould’s “Essay on a Pig Roast” in the collection “Bully For Brontosaurus.” It’s all about “Nebraska Man”, or a pig tooth that ended up causing a big stir about North American hominids and such, but Gould makes the important point at the end that this story isn’t as much about faulty science as science at its best; correcting mistakes and falsifying bad hypotheses. If I can dig up any more resources I’ll let you know. šŸ™‚

28 04 2007

Re: Ceratopsian mounts- according to Peter Dodson, all attempts to mount *Triceratops* and related critters wind up having to deal with the fact that ceratopsian anataomy won’t allow erect forelimbs. The sprawl, according to Dodson, is something that everyone who attempts to mount a ceratopsian has to come to accept, thought they usually set out with a more “updated” pose in mind.
(Source- “The Horned Dinosaurs: A Natural History” Peter Dodson )

Nonetheless, Bakker’s book is still a great read, and, speaking as someone who read it a loooong time ago, it was fun watching a lot of his predictions being born out by new discoveries!

29 04 2007

Thanks for the correction Phil; shortly after reading Bakker’s work I read about some more recent studies (i.e. trying to mount a Torosaurus where the legs wouldn’t work unless they were at least slightly sprawling. I’ve tried to find some ceratopsian trackways as well being that most illustrations seem to have them more or less sprawling depending on who the author is.

What I would be interested in is when the transition from legs-under-the-body to semi-sprawl happened; did it change because of the increasing weight of the skull? When I got to thinking about it, it made sense that the front legs would be at least a little out to the side so as to support the massive heads of these animals. That being said, some mounts I’ve seen have their front legs in an almost lizardlike sprawling position, so the actual amount of bend at the elbows for each genus of ceratopsian dinosaur should be looked into more carefully (if it hasn’t already been done by people like Dodson that is, who I actually had the pleasure to meet when I was 10). Thanks again Phil; I’ll likely do some more digging and post a correction in the coming days.

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