The new issue December issue of National Geographic, a Dracorex peering at me from the cover, arrived in the mailbox today, and I can't say that I was a big fan of the dinosaur feature that I blogged about a few days ago. While the main body of the article, an essay by John Updike, is alright, the thing that first grabbed my attention was the mention that perhaps Spinosaurus was "buffalo-backed," the elongated neural spines along its back supported masses of fat or muscle rather than a sail. Some pencil sketches illustrate the differing hypotheses, although I have to say that the "hump" version looks a bit silly. The notion, proposed by J.B. Bailey in the paper "Neural Spine Elongation in Dinosaurs: Sailbacks or Buffalo-Backs?" in 1997 (and echoed by Hans-Dieter Sues in the NG article), has been (admittedly) difficult for me to take seriously, the hypothesis that Spinosaurus and other dinosaurs with tall neural spines having humps rather than sails owing more to the superficial comparison with the skeletons of animals like buffalo than anything else. Indeed, properly detecting and analyzing convergence can be a tricky thing. This is a relatively minor point, but I was surprised to see that the hypothesis was still being floated as a contender for the possible function of neural spine elongation in dinosaurs.
Moving on to the essay by John Updike, the piece is a quick tour of a few of the featured specimens, mixing ideas of improvement and progress with not being too hasty in laying value judgments on fauna that have gone before. The ending of the piece, however, struck a bit of a sour note for me. After recounting his son's fondness for dinosaurs, Updike concludes;
They were eventual losers, in a game of survival our own species is still playing, but new varieties keep emerging from the rocks underfoot to amuse and amaze us.
My own bias is that I am one of the many who is enthralled by dinosaurs and their implications for understanding life on earth (which should be no surprise to readers of this blog), and it's hard for me to see them, or any group of animals, as losers. Some lineages survive and others go extinct, but I think the term "losers" and the allusion to a great biological "game" present a sort of value judgment that stems from a view that dinosaurs are primarily biological curiosities, a notion brought forth by the final words. Indeed, it is hard to speak of dinosaurs to the public without invoking something of a circus-like atmosphere, the animals being strange aberrations more than creatures to be understood and integrated into what we know about the history of our own planet. Even in my own personal experiences, it's difficult to discuss paleontology with those who lack such an interest without being thought of as something of an immature adult who wants to chase dragons in the dust for a living, someone who pursues science but not in a respectable lab-bench way (this, of course, being far from the truth). I think Updike realizes this prehistoric mystique, but overall his essay seems to grapple a bit with the concept of dinosaurs as curiosities and dinosaurs as once-living organisms that have real implications for our understanding of evolution.
What disappointed me most, however, was the lack of hand-drawn artwork and photography of the actual specimens involved in the article. The CGI-rendered dinosaurs took a prominent place in the piece, and while I definitely enjoyed Jason Poole's sketches (almost as if they had been made on an expedition to seek the dinosaurs themselves), I felt that the computer-generated dinosaurs didn't do justice to the bones themselves, the fossils being relegated to something of a sidebar. Perhaps the trend of "bringing dinosaurs to life" via computers ignited by Jurassic Park and Walking With Dinosaurs is hear to stay, but I must say that I prefer the more "traditional" mediums of paintings, drawings, and photography of actual skeletons to what looks like a bestiary from the latest Xbox game. (If you'd like to read more about the depiction of "strange dinosaurs" in art, please read Matt's wonderful piece at the HMNH.)
Overall I thought the article had some interesting bits of information, but the almost sideshow like flair of "bizarre" dinosaurs didn't appeal to me as much. Evolution was surely invoked, but there were no phylogenetic diagrams or larger explanations of how evolution is relevant to dinosaurs (and vice versa) in the text, and while I do appreciate that the piece probably introduced readers to creatures that they otherwise would have never heard of, I still felt a little let down by how everything was put together. Then again, maybe I'm just cranky and others have a more positive impression. Of more value, I think, was commentary on NG dinosaur illustrations from 1942 - 2000 by paleontologist (and frequent contributor to the comments on this blog) Thomas R. Holtz, Jr., reviewing various aspects of how our ideas have changed and the scientific basis for many illustrations.
Also worthy of note is the upcoming NG documentary Dino Death Trap set to air on December 9th. I'll probably miss this one as I don't have television, but it appears that it'll focus on recent discoveries in the Gobi like Guanlong. A blurb at the end of the magazine also says that Dino Autopsy will air in December featuring the analysis of an juvenile Edmontosaurus using CT scans, and even though I know there are some here who might consider hadrosaurs boring, the program sounds interesting.
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Jaime Headden and I had a hideously arduous debate about the hump/sail issue on the Dinosaur Mailing List. Here's a post from it- http://dml.cmnh.org/2003Apr/msg00360.html . What I concluded was that Spinosaurus had neural spines of similar construction to Bison except it lacks spine tables. I think a big problem is that people think Bailey's idea demands a broad, heavy structure, but there's no reason to think that intermediates in width between Bison humps and stereotypic skin sails couldn't exist.
I'd like to know details of what you find unsatisfactory in in Red Queen. (We already know Matt R.'s not a biologist.) I found the presentation very engaging; in each chapter he demonstrates how the seemingly-persuasive argument in the previous chapter collapses -- sometimes on logic, sometimes on further evidence. It seemed good training for a non- (or not-yet-) biologist in not getting too attached to clever ideas, and an adventure too.
I've missed out on the hump debate. Catching up just a bit, this looks more like turf wars than serious objections. Why shouldn't a spinosaurus pack some fat up there for hard times? If you think they cared how silly it looked, let me offer you the hornbill for consideration.
Okay, from a functional point of view I can see how a Spinosaurus neural spine could be compared with a Bison spine, and because we have little else to go on comparative anatomy is a favoured tool. But there are quite a few mammals who store fat, and the metabolic processes of storing fat are, I believe, well understood. However, if Spinosaurus was not endothermic, and even if it was, we are probably dealing with a very different metabolism. What other examples are there of ectotherms storing fat like this? If there are no other cases, then it would seem more parsimonious to conclude there was no fatty store present than that there was a fat reserve. Other examples notwithstanding, I think it's a little dangerous to suppose Spinosaurus had a fat store just because the spines look a bit like Bison's. But then I don't work on either theropods or mammals...
I agree with you, I always get irritated when people refer to dinosaurs as being "failures" because of their extinction...the human race has not been around for nearly a fraction of the time that many dinosaur lineages existed, how do we know we won't end up "losers" in terms of longevity? Also, people overlook the derived theropods flying over our heads every day...
I also already dealed a lot with this topic. I am no absolutely sure that Spinosaurus and other dinosaurs or reptiles with similar elongated dorsal spines had no sailbacks. Spinosaurus is often compared with Dimetrodon, but they have in fact really no similarity, despite being both long. I looked at the skeletons of different animals, including hump-backed bovines like bisons (not only photos, but also living animals and their skeletons). If you look at the elongated spines without having the all-present image of a sail-backed Spinosaurus in your mind, you will see that there is nearly nothing unusual about them, only the fact that they are very long. The sides of such spines are normally covered with muscles, no matter it is the back of a human, a crocodile or a buffalo. If the dorsal spines grow longer, all structures around them will grow to. I see really no reason why they should be only covered by skin. In fact this would be much stranger than some kind of hump. I think the main reason why Spinosaurus was from the very beginning shown with a sail was because it was a reptile. Most people automatically think about such structures at reptiles, what you can see at many old dinosaur-movies, despite the fact that only very very few living reptiles have actually some kind of sail. If the vertebras of Spinosaurus would exactly the same way, but come from a mammal, nobody would ever think about a sail.
If you look at the skeletons of different living and extinct animals, you will see that many of them has or had highly elongated dorsal spines. You will find such structures at all places. Some animals had them over the shoulders, some more in the region of the hips. Interestingly many animals have for example very long dorsal spines at their tail vertebras, even such unexpected animals like beaked whales. If the elongated spines of all known animals are covered with muscles, even the very long ones, why should Spinosaurus be an exception? There are other spinosaurids with prominent but much shorter elongated dorsal spines. I saw several reconstructions, which did not show it as a short sail, but as a muscle-covered structure with a triangular cross-section. I saw some time ago a very nice reconstruction of Arizonasaurus, which also rivals Spinosaurus in the prominence of the dorsal spines. The reconstruction showed no sail, but a narrow hump, and it looked very realistic. Many people think about the big mass of meat when they hear the word hump. But even the humps of buffalos are not that wide, but as they are normally covered with fur, they look much wider.
The idea that that such a "hump" would be a storage for fat shows an abscence of knowledge about disctinct anatomical features. Most bone structures are places to attach muscles, but you don?t need bones to hold fat. There is no structure in the spines of camels which would indicate one or even two dorsal fat stores, because they are not necessary. Reptiles often stores fat at the tail, birs often at many different regions under their skin. The humps of zebus are also a very bad comparison, because they consits only of a very strangely enlarge Musculus rhomboideus and have no elongated spines under them at all.
I don?t know why Spinosaurus actually had such elongated dorsal spines. After a longer discussion I came to a possible result. Perhaps there was no very specific reason. If you look at large living and extinct bovines, you will find that some of them have nearly no elongated dorsal spines, some have medium-elongated dorsal spines, some long dorsal spines and Bison antiquus had huge ones. This is not always synonymous with increasing body size, and there is no direct anatomical reason why an american bison should develop a large shoulder hump and for example the same-sized or even larger aurochs not. Spinosaurids had also elongated dorsal spines in different length variations.
Thanks for the long and informative comment, Sordes. I'm actually working on a post all about "sail-backs" in the fossil record, so I appreciate the input. Personally, I don't buy the hump idea for Spinosaurus and Arizonasaurus because of the way the spines are arranged in a sort of "bell curve" and their height; they would be carrying a lot of mass on their backs, and many animals with the "humps" have the tallest spines oriented more towards the anterior portion of the spine. Perhaps some forms like Acrocanthosaurus and Irritator had more of a hump, but a "sail" elongate neural spines show up again and again in various groups of dinosaurs (as well as some other extinct taxa), which makes me think there's something different going on than what we see in modern day mammals. Obviously I'll have more on this later.
Nathan; I'm actually writing up a long post all on spines & sails to more fully explain things for those new to the debate (I just didn't want to go into a long discussion here). As for The Red Queen, I obviously still have to read the bulk of the book so I don't want to jump to any conclusions, but there were just some early clues that it was more in line with a "selfish gene" view of human reproduction and evolution, a view that I don't entirely agree with. Nothing outrageous has shown up so far, just some clues that the way he's approaching the problem is a bit different than the way I would so I'm trying to be mindful of that as I read the rest.
Well, I think the problem of most people with the idea of hump-backed reptiles is the idea that such a hump has to look very massive, and the whole animal would be covered with huge masses of flesh. But this don?t have to be so. I posted some photos of the Arizonasaurus-reconstruction I have seen some time ago at Stuttgar at my blog:
http://bestiarium.kryptozoologie.net/artikel/arizonasaurus-das-scheinkr…
It looks really very naturalistic, and I can very well imagine, that this animal actually looked so, and that for example Spinosaur had a similar narrow "hump". One reason why I don?t buy anymore the idea of sailbacks (except Dimetrodon and Edaphosaurus) is the anatomy of the vertebras. There is really nothing which would indicated that they were covered with skin, and nothing which would speak against muscle-attachments. I once wrote a long blog-post about this topic, but as it is in german, I suppose most readers hear won?t be able to read it:
http://bestiarium.kryptozoologie.net/artikel/hatte-spinosaurus-wirklich…
> One reason why I don?t buy anymore the idea
> of sailbacks (except Dimetrodon and Edaphosaurus)
Sordes,
when speaking of Permian sailbacks, don't forget *Platyhistrix*, the temnospondyl.
Damn, always forget the name of this critter...but I remember it very well, there is a wonderfull drawing of this animal from John Sibbick.