Posts Tagged 'ecology'

Project Daspletosaurus 2013

finalwide-on-white

I’m sure a goodly number of readers are already aware of this as I’ve been tweeting and facebooking it quite a lot, but I have a science kick-starter project running on the Microryza site. It sounds almost too contrived to be honest, but it’s a project aimed at looking at possible cannibalism in Daspletosaurus based on material Darren Tanke has worked on at the Tyrrell.

Obviously Darren and I have form when it come to tyrannosaurs, both with our own research interests and in particular with the Gorgosaurus preparation project. Here though it’s a skull of Daspletosaurus with bite marks attributable from another large tyrannosaurine. I’m looking for funding to get me out to Alberta and check out this and related material and work to write this all up and hopefully learn something about tyrannosaur behaviour and ecology.

Daspleto rt lat edited skull

I’ll skimp on the details here because it’s all up on the Microryza site, so do follow this link and take a look. More specifically, if you can spare a small amount towards the total, it would be very much appreciated and do please blog and tweet this – the model only really works if people know about it and are intrigued or excited so spreading the wrod is very important (and free!). Obviously I’ll be blogging the project and putting as much information out as I am able, so I hope to make this as open as I can and get the audience involved.

My thanks to Microryza for supporting this, and to David Orr for the fantastic logo up top and Matt van Rooijen for help with the project video (featuring much Matt artwork).

 

 

Some dinosaur ecology to digest

In the last couple of weeks I’ve had two papers come out in PLoS ONE tackling different aspects of dinosaur ecology. In rather different ways both look at the morphology of various living clades and use that to build up an idea of what patterns are present and how dinosaurs fit into this.

The Musings is set more or less to idle these days, so I don’t want to say anything too extensive here, not least when I have blogged the most recent paper already on the Lost Worlds and Darren Naish has some very extensive coverage of the first one. Still, I don’t want this one to dry up entirely and with a dinosaur-keen audience, it seemed a good idea to get up at least a quick post on the two.

First off there’s a paper on claw shape and how this might, or might not, relate to possible climbing functions. The major results are somewhat equivocal. Perhaps unsurprisingly, there is a lot of variation in claw shape (curvature and midpoint dorsoventral height) and that means the boundaries are blurred between those animals that climb from those that are predatory or based on the ground. In short, for most it’s hard to make any kind of confident predictions off of our analysis at least, but there is a lot of scope for further work, and at least some dinosaurs plot out clearly in one behavioural category and well away from the others.

Second, there’s the piece on dinosaur body size distribution. Here non-avian dinosaurs are shown to have a different pattern of body size distribution to various vertebrate clades both living and extinct, with dinosaurs having relatively few small species and a high number of large ones. This nicely fits with the idea that dinosaurs filled multiple niches as part of their ontogeny, with niches for small species being filled by juveniles.

I’ll keep it short and sweet with both being freely available to read as obviously all the details are in there.

Birn-Jeffery, A.V., Miller, C., Naish, D., Rayfield, E.J. & Hone, D.W.E. 2012. Pedal claw curvature in birds, lizards and Mesozoic dinosaurs – complicated categories and compensating for mass-specific and phylogenetic control. PLoS ONE, 7: e50555, 11p.

O’Gorman, E. & Hone, D.W.E. 2012. Body size distribution of the dinosaurs. PLoS ONE, 7: e51925.

More on dromaeosaurs vs azhdarchids

Yesterday I covered the basic introduction to my new paper about a Velociraptor specimen with an azhdarchid element preserved in it’s gut. Today I want to move on from the basics (what is there) to what this potentially means and how this is inferred. Most of my recent research is based around theropod ecology and behaviour (like this, this and this for example) and specimens like this one can provide new information and evidence for how these animals were acting. The obvious question here is why is this inferred as scavenging and not predation? As usual with such questions going so far back in time, it’s hard to be definitive, but this is the better supported inference.

First off there is the relative sizes of the animals. While it’s not unknown for predators to tackle other predatory animals, or relatively big prey it’s certainly not normal. Lions don’t routinely hunt leopards or bears go after wolves. This is relevant here since azhdarchids were most likely active predators themselves and so a potentially dangerous animal to attempt to kill. Moreover, the azhdarchid in question was most likely 9 kg in weight with a 3 m wingspan (and could have been considerably larger), while the Velociraptor was a sub-adult of around 13 kg. In short if this was a predation it was no mean feat – perhaps the equivalent of a small coyote bringing down a big eagle. Sure it’s possible, but it’s not unreasonable to think this was really very unlikely. It’s more likely this was a young carnivore scavenging on the carcass of a dead pterosaur, as indeed was inferred for a similar previous specimen from Canada.

Even if we assume that it was a kill, other things don’t add up well to support this. Theropods don’t tend to consume large amounts of bone like this. They might consume relatively large items (like a whole small prey item) but not large chunks of bone like this. And it is a pretty big chunk of bone, probably the same length as the skull of the dromaeosaur. Moreover, we also know that theropods can be really quite delicate feeders, including other velociraptorines. The tendency seems to be to scrape meat free of the bones, now chew up and swallow whole ones (like modern birds of prey, they’ll swallow a mouse, but will pull chunks off of rabbit or sheep). Carcass consumption patterns by modern vertebrates also show that whole big bones like that don’t tend to be swallowed. Finally, the pterosaur weighted at least half and potentially more than the dromaeosaur. Given their apparent skill at stripping a carcass of meat I don’t think I dromaeosaur would be swallowing whole bones (and ones that would be pneumatic, not filled with marrow) when much of it’s own weight was sitting there in muscle and viscera.

In short, predators don’t normally predate other predators. Predators (including theropods) don’t usually seek out large prey. Predators (including theropods) don’t usually consume large bones of large prey unless they are a bone specialist or there’s nothing left. Even when there’s not much meat left, theropods tend to scape this free to eat rather than swallow bones. Sure all of these could hit the ‘least likely’ option and it’s a who-knows-what to 1 chance that a small dromaeosaur took on a big azhdarchoid, killed it and started swallowing big bones. But it’s far more reasonable to infer that it scavenged the last bit of a carcass it chanced across.

We are then left with scavenging as the most likely explanation as to why this animal was swallowing whole bones. Interestingly, we do also see shed teeth being a common feature of dromaeosaur (and indeed theropod in general) feeding yet here every tooth in the skull is intact. That is admittedly merely a soupscon of evidence for scavenging, but one might well expect a tooth or two to be lost during a fight with such a big adversary. or even biting through bones to swallow them again suggesting it just picked up and swallowed what it could find without much or any oral processing.

Uncoloured version of Velociraptor feeding. Courtesy of, and copyright to Brett Booth.

Moving on from this issue then, what does this tell us about the ecology of dromaeosaurs? Well to  degree, not much we didn’t know already. There’s already evidence for both predation and scavenging in the dromaeosaurs, and indeed already evidence they were eating pterosaurs. Even so, more evidence is always good, and it does at least reinforce the existing evidence we have. It also therefore takes us a little further away (sadly) from the idea that dromaeosaurs were some kind of hyper-carnivorous super-predator that spent their time knocking down huge prey items with all their claws and teeth. I say sadly, because it’s a great idea and a wonderfully romantic notion, but sadly these animals were every bit as opportunistic as other carnivores and clearly were not beyond taking the odd, or indeed regular, free meal through scavenging. Indeed given the number of specimens we now have supporting a scavenging interpretation, this does seem to have been a pretty common part of their behavioural repertoire as carnivores.

Velociraptor scavenging an azhdarchid pterosaur

Image courtesy of, and copyright to Brett Booth.

So yesterday at short notice I rushed up this teaser post which seemed to do the trick, and now I’ve got a bit more time on my hands, I can start putting down a proper post on the subject. Yep, I have a new paper out and this time featuring dromaeosaurs and pterosaurs. Long time readers will remember that almost exactly 2 years ago I had another paper out on dromaeosaur scavenging featuring shed teeth and bite marks on some Protoceratops material. Coupled with the famous fighting dinosaurs specimen we have pretty good evidence for dromaeosaurs, and specifically Velociraptor for feeding on this dinosaur. The record of dromaeosaur predation and feeding is actually pretty good compared to other theropods groups and there is also an isolated pterosaur wing bone from Canada with shed dromaeosaur teeth and bite marks.

This ‘new’ specimen marks the first record of gut contents for Velociraptor and the first record of a pterosaur bone as gut content in a theropod. (The ‘new’ is becuase this specimen was actually found in the 1990s, but has yet to be described, though I’m told there’s a photo of it in Luis Chiappe’s recent birds book). Thus we do have rather exceptional evidence for a Velociraptor chowing down on an azhdarchid.

Velociraptor specimen with a pterosaur bone as gut content (black arrows). From Hone et al., 2012

And here it is, well part of it. The Velociraptor in question was remarkably well preserved and complete which allowed the preparation of it with the chest cavity as a single articulated piece with the vertebrae, sternum, ribs, gastralia and even uncinate processes all intact and in their original positions. The bones are really well preserved and much of the material has been prepared free of the matrix entirely. One obviously example is the skull which, bizarrely, is on display in Barcelona so at least some reader might have already seen that, though sadly I haven’t and had to rely on some superb photos kindly sent by Fabio Dalla Vecchia. It’s hard to show the bone off properly what with the whole ribcage in the way (which is, incidentally, a broken ribcage, one of the ribs took a huge battering and shows a healed break – white arrow in the above picture). S you’ll be delighted to know there are also some close-ups in the paper like this one (below) and even some CT scans in the supplementary data.

Close up of the bone. From Hone et al., 2012

As you can see the bone is incredibly thin-walled which is the major reason that it’s inferred to be an azhdarcid pterosaur, though their presence in the Late Cretaceous, including a related formation, and the general absence of other pterosaurs in the Late Cretaceous helps support this identity. Given what is around and the thinness of the bones, it’s pretty unambiguous as indeed is the identification of the dromaeosaur as Velociraptor given that we have basically the whole thing. In short, this is about as convincing a case as one could make that a Velociraptor had eaten an azhdarhid. But was it really scavenging? Well that and other issues I’ll be talking about tomorrow, as there’s quite a lot more to say on this. Stay tuned.

Finally, my thanks to Brett Booth for more awesome artwork for me to use, and you can see more of this and my interview with him on his dinosaurs here.

Hone, D.W.E., Tsuhiji, T., Watabe, M. & Tsogbataar, K. Pterosaurs as a food source for small dromaeosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology, in press. Horrible uncorrect proof and behind a paywall, but the abstract, figures and other bits are visible to all.

Guest Post: Dinosaurs and the latitudinal biodiversity gradient

Today Phil Mannion returns to the Musings with a guest post on his recent paper on dinosaur diversity patterns and their relationships to latitude. Take it away Phil:

The presence of a latitudinal biodiversity gradient (LBG), whereby species richness is highest in the tropics and declines polewards, is a pervasive pattern affecting the majority of life on Earth today, and was recognised by early naturalists such as Charles Darwin and Alexander von Humboldt (whose foundation coincidentally partly supported the research outlined below). Despite its near ubiquity (on both land and in the sea), the causes of the gradient are less well established, with numerous hypotheses proposed over the last fifty or so years. Most of these have been refuted, leaving climate and the distribution of area as the two most likely causes. Understanding the cause and evolution of the gradient is vital to predicting biodiversity loss driven by present-day climate change and explaining geographical variation in biodiversity; as such the fossil record offers a unique perspective on this issue.

Previous work investigating the deep time LBG focused on marine invertebrates – these studies tended to find support for a modern type pattern throughout the Phanerozoic (approximately the last 530 million years). Little prior work has been carried out on terrestrial species, but the few studies to look at the deep time LBG on land found no evidence for a modern pattern until after the Eocene (approximately 30 mya).

Along with colleagues from the UK (Roger Benson, Paul Upchurch, Richard Butler and Paul Barrett) and USA (Matt Carrano), we looked at the LBG in Mesozoic dinosaurs (including birds). Using a number of different methods to mediate for sampling biases in the fossil record, we found no evidence for a modern type pattern at any point in the 160 million year evolutionary history of Mesozoic dinosaurs; instead we found dinosaur diversity to peak at palaeotemperate latitudes (30-60° North and South). The consistency of this result across analyses for different time slices indicates that this pattern is not controlled by climatic fluctuations – evidence suggests that the climatic gradient was “flatter” in the Mesozoic than today (i.e. there was less of a difference in temperature between tropical and temperate regions) – but was instead driven by the amount of available land area in latitudinal belts.

Residual dinosaur diversity after controlling for sampling, plotted against non-marine area (NM area) and palaeogeographical reconstructions for the Late Triassic (bottom), Jurassic (middle) and Cretaceous (top). From Mannion et al., 2012

Given that living birds conform to the modern day pattern, a significant change must have occurred at some point in the last 65 million years. Evidence from molecular phylogeny (and work on fossil insects) suggests that this change occurred at the end of the Eocene (34 mya), following the strengthening of the climatic gradient and an increase in seasonality. As such, there is no evidence for a modern type LBG on land before the last 30 million years.

Mannion, P. D., Benson, R. J. B., Upchurch, P., Butler, R. J., Carrano, M. T. and Barrett, P. M. 2012 (Published online). A temperate palaeodiversity peak in Mesozoic dinosaurs and evidence for Late Cretaceous geographical partitioning. Global Ecology and Biogeography, doi: 10.1111/j.1466-8238.2011.00735.x

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.

 

The ecological implications of Zhuchengtyrannus

OK, I admit there’s not actually too much to say about this, but what little there is, is quite important. Zhuchengtyrannus is really rather big – a little smaller than Tyrannosaurus, about the same size as Tarbosaurus and thus as a theropod perhaps bigger than anything except these two, Spinosaurus, Mapusaurus and Giganotosaurus (and more coming on that tomorrow). It was certainly a serious customer.

More boringly, in a way, Zhuchengtyrannus is really quite a normal large tyrannosaurine –the anatomical differences are sufficient for taxonomic purposes but would probably make no real difference to the overall appearance of the animal – that is, as far as we can tell it would look in life very much like Tarbosaurus and Tyrannosaurus. While there isn’t that much of it, what we have is quite normal and it’s reasonable to infer that this animal was occupying a similar niche to the other giant tyrannosaurines (and that means predation and scavenging).

That is in itself a bit of a novelty. As I’ve noted before when discussing spinosaurs, it’s actually quite common to find multiple, similarly-sized large theropods in the better-known dinosaurian faunas. We find Allosaurus, Torvosaurus and Ceratosaurus together, Sinraptor and Monolophosaurus, Charcarodontosaurus and Spinosaurs and so on. Even when it comes to tyrannosaurines we find the smaller Daspletosaurus and Albertosaurus together (not to mention our old favourite Gorgosaurus). However, Tyrannosaurus seems to have lived alone as it were (and you can argue Nanotyrannus, but it’s quite a bit smaller) and Tarbosaurus may not have been really troubled by Alioramus. While we have no direct evidence that Tarbosaurus and Zhuchengtyrannus overlapped directly their fossils are being recovered from very similar times and only a few hundred kilometers apart. It’s really quite likely that they met and of course ZT is itself accompanied by another large tyrannosaur from the same quarry so there could have been quite a party going down.

To employ a much overused phrase, this does rather leave T. rex as the exception that proves the rule – it’s increasingly looking like the only big theropod which doesn’t come with at least one accompanying near-equally sized alternate carnivorous theropod. Despite the ever increasing similarities between the Late Cretaceous faunas of North America and Asia, T. rex does still seem to be, in at least one way, still the undisputed king of his own backyard.

A last bit of Limusaurus – theropod diets and herbivory

Limusaurus - not predatory (compare with Ceratosaurus below)

Limusaurus - not predatory (compare with Ceratosaurus below)

Well I had said I was all Limusaurus-ed out, but then that stuff was written a month ago, so I do have a bit more Limusaurus left in me right now. This post is odd in a couple of ways as it covers something that is not mentioned in the paper, and also something that I would like to write about in the future myself (something I’d normally avoid blogging about). I have not spoken in detail to my co-authors but I rather think the point I am going to make here didn’t get into the paper because we simply didn’t think of it, rather than not having the space to include it. While the point itself is simple enough the potential caveats and explanations that surround it are complex, so bear with me.

In short Limusaurus seems to be unusual not just because it is a basal herbivorous theropod, but because it is so profoundly different to the other members of its clade (the ceratosaurs) that are so obviously carnivorous. The other theropod lineages that yield herbivorous / omnivorous taxa are pretty uniform in their dietary approach so this appears to be a quite an exception. Continue reading ‘A last bit of Limusaurus – theropod diets and herbivory’


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