Posts Tagged 'sauropods'

Academics on Archosaurs: Jeff Wilson

Jeff Wilson, University of Michigan
I’m interested in sauropod dinosaurs, the fossil reptiles of the Indian Subcontinent, and ichnofossils.

1. What first got you interested or involved in your research field?
I was never interested in dinosaurs (or fossils, for that matter) as a child. I’m still not crazy about them. I loved anatomy from an early age, which manifested itself in unsupervised frog dissections and me following around my uncle, a surgeon, in hopes of getting into the operating room (which I did). This interest in anatomy led me to believe I should be a doctor, and so I took the MCAT and worked for a year as a surgical technician – only to find that I didn’t like the clinical atmosphere or dealing with patients. I didn’t really know what to do with myself at that point. I ran into my advisor at Kalamazoo College, Paul Sotherland, who recommended Gould’s book ‘Wonderful Life’ to me. That book changed everything. It brought together anatomy, evolution, history, and adventure in a way that I hadn’t thought about before. I wondered who could be doing that sort of work nearby and eventually wrote Paul Sereno, who in 1992 was fresh from his second trip to Ischigualasto. I drove down to Chicago to visit him, and he showed me the skull of Herrerasaurus, which was mysterious to me. I don’t remember much about what Paul and I talked about, but after a couple of weeks he called to invite me to spend three months in the Sahara excavating a sauropod graveyard. I remember him telling me we were driving there from London. I said yes.

2. What is your favourite piece of research?
I will take a ‘pass’ on this question, but I will say that the most fun I ever had working on a manuscript was when Matt Carrano and I put together the ‘response to reviewers’ for our 1999 paper on wide-gauge sauropod trackmakers. We were graduate students then, and we were reviewed by the formidable R. McNeill Alexander, Martin Lockley and Tony Thulborn. Thulborn alone had 80+ marginal annotations specifically about word choice and composition. He was so charming in the way he flayed the paper, one had to laugh. Example: we used the word “freer” in the original to refer to titanosaur vertebral articulations, to which he wrote something like (from memory, not a direct quote), “Gentlemen, there is no ‘freer’ ? one is either free or not, just like one cannot be ‘partially pregnant’ or ‘somewhat dead’.” Ha! There’s more to the story, but I’ll end here.

3. What do you think is the most interesting or important discovery in your field in recent years?
I really admire some recent work on saurischian dinosaurs, but it is difficult to pick one discovery. Perhaps I’ll go with a technique. I was really blown away by Steve Gatesy’s recent SVP talk on 3-D motion analysis in birds.

4. What do you think is the biggest unanswered question in your field right now?
Sample sizes are typically quite low for sauropod dinosaur species, many of which are represented by a single exemplar. We have become habituated to describing all (or most) morphological variation in our exemplars as differentiating species or genera, often without entertaining the possibility of within-individual, within-population, and within-species variation. Discriminating among these sources of variation is to me one of the most important questions facing us.

5. What advice would you give to students about research?
Philip Gingerich wrote this nice paper ‘George Gaylord Simpson: Empirical Theoretician’ in which he examined and categorized the nearly 13,000 pages of Simpson’s primary output. Although he was thought of as a ‘theoretician’, much of Simpson’s work, especially his early work, was empirical. I think that collecting careful, quality empirical data is important, and I would encourage students build their datasets with a question in mind. Bigger is not necessarily better; the dataset should be small enough that it can be managed and mastered.

Mamenchisaurus ungual

I can’t be the only person with a soft spot for certain anatomical features and I really do like unguals. They are after all, an important (perhaps the most important) between an animal and it’s environment and we see numerous adaptations and modifications to unguals accordingly. Sauropods are rather cool in this regard often having rather outsized unguals on the manus or pes that in some cases look rather more suited to a theropod. This is from the Mamenchisaurus mount in Chengdu University of Technology though as I don’t have the full original set of photos I took I have to go by memory and I think this was a pedal claw.

Sauropod gauges

Those familiar with sauropod trackways (and who of us isn’t?) will know that these are often described as ‘wide gauge’ or ‘narrow gauge’ depending on the separation between the left and right sets of prints of a given animal. Obviously sauropods would have had trouble swinging their legs under the midline of the body when walking so they leave two parallel sets of tracks, though the gap between these can be low or high.

This is something I’ve read many times and certainly have no truck with the idea. But it’s hard to *see* such a possible difference on a single sauropod specimen when you have nothing else to compare it to. Thus once more we turn to the Carnegie and their pair of giants. Conveniently, these animals are of pretty similar gross dimensions so the comparison is easier to make and look at the difference and, wow. You can probably walk though the legs of Apatosaurus (upper) quite easily, but you’d have to turn sideways or squeeze a little to get though those of Diplodocus. It’s quite a difference for two animals that are fairly close relatives and of such similar size.

Camarasaurus cranium

A little more sauropod goodness to help stretch out the week. Here a complete Camarasaurus skull and mandible seen in anterior view. As you can see, the skull has undergone a little deformation, though given the fragility of the average sauropod skull it’s pretty minimal and this really is a superb example. Certainly if there is one thing we do need it is more sauropod skulls, they are really rather rare for such a diverse and long-lived clade.

Sauropodan flotsam

This is very nearly the last photo I have from the Carnegie, such a shame, I’ll just have to go again. As noted before the museum does a nice line in small cabinets and displays of elements alongside and this little collection sits below the wonderfully mounted Diplodocus. I assume all of the material here represents that genus but I may have kinda forgotten to take a photo of the label so I don’t know for sure, though the skull at least is a bit of a give away.

Small but beautiful (and tasty)

Over the last few days I’ve given a couple of presentations about my work on the feeding ecology of theropods and in particular their apparent preference for juvenile prey. It seemed appropriate (well to me at least) to post up these photos of the very young Apatosaurus in the Carnegie dinosaur hall. I’m rather assuming it’s a pure sculpture since I’m not aware of any very young material of this genus, though I could have missed it, and foolishly I didn’t check the signs. Anyway, my time in Pittsburgh is drawing to a close, but I have, quite literally, nearly a hundred photos of things I want to post and talk about from my visit (and then there’s the zoo and aviary!) so expect to see a lot more stuff in the coming weeks.

My thanks to Mike Habib and Matt Lamanna for hosting my time here. Cheers guys!

A pair of giants

So obviously these guys got a decent look in yesterday, but this pair of photos hopefully shows off how nicely the two have been mounted and the way in which they have been matched in their respective poses to provide a nice mirror-image effect. For me though it’s nice to be able to compare them – I’ve seen mounts of Diplodocus before (indeed of this Diplodocus), and of Apatosaurus, but never the two together and it genuinely does make a difference to have them put together like this for comparison.

Camarasaurus heads young and old

Here’s a pair of skulls (well casts I think, but I’m not 100% sure) of the sauropod Camarasaurus. We really are very short of cranial material when it comes to sauropods so to have these and for them to represent both an adult (below) and a pretty small juvenile (above) is even better. In fact they appear, to me at least, surprisingly similar in form with very little in the way of ontogenetic changes to the skull as the animal heads towards adulthood, though of course it’d be nice to have a tiny baby for comparison.

Nigersaurus

Yes I *still* have more photos to come from the Tokyo Dino Expo 2011, and it’s nice to get back to the sauropods. More specifically this sauropod, the rarely seen Nigersaurus. One of the rare and unusual rebbachisaurs the characteristic lawn-mower type skull s really rather obvious here, and the neck is pretty short and reminiscent of the dicraeosaurs. For me this was really nice to see as I’d yet to encounter any material or a mount of any member of this group, so even just a general feel for the proportions and to see a few details was nice.

Sauropod Jaws

While there is obviously some variation in the teeth and jaws of sauropods, they are on the whole pretty conservative when compared to the theropods or ornithischians (none of them have beaks for starters!). Rather peg-like clippers of one form or another seem to be the main theme. This nice set of jaw piece though does show that if nothing else, the size and number of the teeth can be dramatically different across a jaw of otherwise similar size.

 

Here we have the multiple and very small teeth of Nigersaurus (top), rather more robust, but still ultimately long, thin and quite numerous teeth of Apatosaurus (middle), and finally the much larger and more robust teeth of Camarasaurus (bottom). Nigersaurus is especially nice and odd as you can see the huge numbers of replacement teeth sitting in situ the gives this an appearance that’s something like a dental battery of a derived ornithischian.

 

Diplodocus skulls again

I did feature one of these a while back – though one that was bolted onto a Mamenchisaurus skeleton. Here we have a cast from the same collections in Ireland as yesterday’s Stegosaurus cranium. This has the mandible separate from the skull, but I’ve put in back on for some shots to show off how they fit together. Diplodocus has a rather iconic skull shape when seen side on, but actually the dorsal view is the one I always find most interesting. It’s so regular with very square sides and just a slight curve to the very front. It seems almost too geometric to be quite natural.

Neck multifunctionality

Following on from my post on sauropod neck lengths (and indeed that of the SV-POW! boys and Tet Zoo too), at the end I made the inevitable comment that necks (and indeed other structures) can be multifunctional. A long neck can be an indicator of sexual selection at the same time as providing increased reach for food. As noted before, analogy plays an important role in working out (or at least hypothesising) palaeo behaviour, so are there any animals out there that seem to do this. Indeed there are, so step forward, the Galapagos giant tortoise.

Tortoise neck use - above, reaching for food, below, challenging rivals. By Darren Naish, from Taylor et al., 2011.

Research shows that those animals with longer necks do gain a distinct advantage in reaching higher placed food. The neck provides a genuine basis for natural selection based on neck length. However, it has also been shown that when tortoises stand off in dominance battles, the individual with the longer neck tends to win. So, necks would also appear to be under some measure of sexual selection / dominance as well.

So what about the giraffes? They have long necks and the males fight with their heads, so what’s going on there. Well males do have longer necks than females, but there’s not really anything to say that longer necked males do better. Bigger males do better (no surprise) but not through a longer neck per se. Plus of course the males are actively fighting with their heads. (And tortoises can be quite vicious if you’ve ever seen them fight, then bite and butt with their shells).

Posturing only gets you so far in nature. Sure, there are cheats out there (false cleaner fish, milk snakes, female mimic salmon etc.), but they can only prosper as long as they are in the minority. This is because sooner or later someone is going to square up to you in one way or another and find out if you really can back the bark with bite. If you can’t, you’re going to lose. And if say most of the population were lying, once a dominant animal (or predator etc.) finds out, then that is going to take over damned fast. So lying only works when there are few liars, and most things are honest. In other words, if they are advertising that they can win a fight, it’s because they can and will.

What does this mean for sauropods? Well is has been suggested in the past that sauropods might fight one another, with their necks. Now if this was going to happen you’d expect to see some evidence of this in sauropods. Like the especially tough and thick skulls of male giraffe, or the prow-shaped rams of some tortoises, or robust necks and heads in male sauropods and you’d see injuries from some serious sauropod neck-on-neck action. Only of course there aren’t any.

Instead sauropod skulls are incredibly weak and fall apart if you look at them funny, let alone ram them into something else at speed. And while the neck as a single unit might be quite tough, it has those lovely wafer-like lamina and those oh-so-thin cervical ribs. If they were fighting we’d see breaks, pathologies, healed bones and the rest. And you can’t cheat by just having a big neck and expecting the others to back down, you have to back that up or someone will realise it’s all talk.

I’m sure sauropods did fight on occasion, sooner or later animals of pretty much any species will come into competition and of course it is members of the same species that tend towards the fiercest competition. There will come times when accessing that water hole, or harem, or territory is critical and combat becomes inevitable. But was it with the neck? No. The neck might have been a *symbol* of the power of the individual even if it wasn’t used (pheasants and cockerels show off their colours to demonstrate their fitness, but they fight with their spurs).


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