Posts Tagged 'paleontology'

Pteranodon vs Cretoxyrhina

Shark vs Pterosaur. By Mark Witton.

Over the last 10 years I have published quite a few papers on various feeding traces, shed teeth and stomach contents that help demonstrate and refine some understandings about who ate who in the Mesozoic. These are often very interesting but also frustratingly incomplete and it can be hard to identify one, let alone both, of the protagonists and in any case these are often isolated examples that may or may not represent wider trends. Still, at least sometimes there can be a good set of marks with repeated patterns and enough data to be quite confident about a relationship.

One such is that between the classic giant pelagic pterosaur Pteranodon and various sharks from the Cretaceous, most notably Squalicorax. This is no big surprise, these pterosaurs were spending a large amount of time out over the water and could probably dive and swim after prey, even if they didn’t likely sit for long on the surface when they did so. Even aside from the possibility of being caught, at least some pterosaurs must have died while out over the water or been stranded and ill or injured on the surface and that would inevitably attract large predators to come for a meal. Given the huge numbers of Pteranodon bones we have, it should not then be a surprise that there are a good number of them described with various bite marks that can be confidently attributed to large sharks. Pterosaurs were generally lightweight for their size but that doesn’t mean there was not some decent muscle on them and modern seabirds are not infrequently eaten by sharks providing a nice analogy too.

‘Complete’ Pteranodon at the LACM.

Such data though is limited to marks on bones and it’s always nice to have something more detailed than this. Although mentioned before in several previous papers, one outstanding Pteranodon specimen in LA has never been described or illustrated properly and so when I got my hands on it while visiting Mike Habib a few years ago, it was rather inevitable that something would happen, and the paper on that, with the healthy addition of Mark Witton as a collaborator, is now out.

The indivdual in question is mounted as a lovely complete (and sort of 3-D) pterosaur on display in the Los Angeles County Museum but it is a composite of somewhat indeterminate origin and it’s not entirely clear how many individuals were used to make it or how complete any of them were. What is clear though is that there is a short series of articulated cervical vertebrae and that these have the tooth of a decently sized shark with them. It’s trapped under a prezygopophysis so it’s hard to think it just drifted in there by chance onto a skeleton at the very bottom of the sea, and while the tooth doesn’t look like it penetrates the bone it is a reasonable interpretation that this is a shed tooth from a bite.

The tooth is diagnostic of the large pelagic shark Cretoxyrhina and we have a good enough idea of where in the mouth it sat which means we can get decent estimates of the sizes of each of the two animals here. The Pteranodon clocks in at around 5 m in wingspan with the shark being 2.5 m in length, but despite this apparent discrepancy, the shark would have been by far the heavier animal and in the water it would swim rings round the pterosaur. In short, while we don’t know quite what happened here (was it predation or scavenging) it looks like a decent sized shark took a chunk out of a pterosaur and lost a tooth in the process.

This is the first record of sucha trophic relationship between these two genera, though of course various unattributed bites that are already known might also have been made by Cretoxyrhina. However, despite the large numbers of Pteranodon specimens known, apparent bites on them turn up in only about 1% of cases. In some ways this may sound like a lot but there’s perhaps a 6% rate of carnivore-consumed interactions known for Rhamphorhynchus, so the open ocean (perhaps unsurprisingly) might have had fewer incidences of large predators getting to grips with large pterosaurs than near shore ones with much smaller animals.

All in all though, this adds a nice new point to the dataset on pterosaurs and their position in various food chains. We have a healthy record of them eating things, and being eaten, and each new bit of data like this helps us get a better and better handle on how pterosaurs fitted into ecosystems and how they might have lived, and died, in the Mesozoic.


The paper is fully OA and available here.


Constructing hypotheses on behaviour in the fossil record

Those keeping up with papers on palaeoethology may well have noticed that a number of papers have gone online in the Journal of Zoology of late with a common theme. Darren Naish has a paper on the behaviour of fossil birds, Andy Farke has one on combat in ornithischians, and Pete Falkingham has a paper on interpretation of trackways. This is not a coincidence, but part of a special issue of the journal out today on behaviour in the fossil record and all of these contributions will eventually be published together with a number of others in a collection I have assembled as a guest editor. The volume has ended up rather dinosaur-biased which is unfortunate as a number of other papers were promised from other fields (including on whales and the Burgess shale) which never appeared and giving the set a more dino-centric appearance than I had planned or hoped for.

Adding to this is in fact my own paper in the volume. This was something I had been working on for a while before being asked to compile the special issue (indeed the fact that I was working on it, and it was intended got the journal may have precipitated the invitation) and in the context was the perfect home for the paper. As with similar cases I had nothing to do with my own manuscript and it was submitted separated and edited and refereed independently by the journal, and only after acceptance could it be added to the list. Most of the papers are reviews of one form or another, and in my case the paper written with my friend Chris Faulkes looks primarily at issues of hypothesis creation on behaviours for fossil taxa.

Our main contention is that in the past palaeontologists have been a bit over zealous in the production of hypotheses and the way in which they have been generated has made them difficult to assess or even simply discuss and in at least a few cases hould probably not have been suggested at all. We don’t think it inappropriate to generate hypotheses that cannot be immediately tested, or those that are difficult generally to assess, but a hypothesis must have at least some support behind it to make it valid in the first place, and poor uses of terms, lack of specificity, or even use of fundamentally flawed concepts have meant that there are problematic ideas in the scientific literature.

Mutual sexual selection is perhaps a good example here. I’ve now penned a number of papers with various authors about the issues surrounding this idea and how it may fit into archosaur evolution. The point is not whether or not we are right about this, but more the fact that this was something hinted at by Darwin, written about by Huxley and extensively studied by numerous ethologists for decades, and yet many palaeontological papers discussed sexual selection purely in terms of dimorphism, or the fact that sexually selected features should feature on only one gender, or indeed that sexual selection should be mutually exclusive of other functions. None of these things are true, so hypotheses that rely on one of these as are starting point are going to be fundamentally flawed, or at least problematic.

Thus the paper sets out to identify some key areas where we feel mistakes have tended to be made (myself drawing on examples from dinosaurs and pterosaurs, Chris from his area of expertise the mammals) and to also then try to find a set of guidelines that might help the better generation of hypotheses allowing for reduced confusion and better testing. Naturally we think this is going to benefit researchers, but given the rampant hypothesising that often accompanies any online discussions of the behaviours and ecology of extinct animals online and in other informal venues, it might just help clean up some of the more egregious suggestions that can be put forwards based on the most tenuous of links. Some of it may sound excessively simple and even obvious, but that doesn’t mean it hasn’t been an issue in the past. I actually had a chat with an ecologist the other day who bemoaned a similar set of problems in her field, and I think the issue is more one of advancement and general improvement that systematic errors or poor science.

Naturally we did try hard not to pick on individual papers (or people) but we did also want to point to some specific examples of the kinds of problems we were discussing and so a few things get the finger pointed at them, but they have mostly had specific rebuttals in the literature already, or were very much generic issues. Hopefully then, we’ve not bent any noses out of joint. I was certainly grateful to Andy Farke for reading an earlier version to check for overall tone and to see if it was working the way we wanted. Anyway, here are a few of the things we looked at.

Terms need to be more specific. Talking about ‘parental care’ say in general terms isn’t very helpful when this can encompass pre- or post-natal care, or both, and differing degrees of commitment from parents over very different timescales. So a statement like ‘X showed parental care and Y didn’t’ may not mean much if the parental care shown was minimal, or two papers might say this where one is referring to all parental care, and the other only post-natal, making them hard to compare.

Overlooking counterexamples or complexity. Descriptions of species or clades as ‘social’ has been creeping into the literature on dinosaurs and yet even if you do somehow have super evidence for sociality in a species, applying that to other taxa, or even other member of the same species is not necessarily a great idea. While we do have highly social species that basically can’t function when not in a group (like some molerats) even famously social animals like lions often spend part or much of their time apart, and some like cheetahs can be incredibly plastic, switching from social to solitary multiple times in their lives, and yet it would be a big mistake to suggest tigers are fundamentally social because their nearest relatives the lions are.

Extreme examples or oddities are useful to provide context or even limits on ideas. Some species have incredibly specific requirements or only live in certain environments, while others are much more adaptable. You don’t really find sand cats outside of deserts or dry environments, and while lions show up in quite a few places, you can get puma in everything from high mountains to praries, deserts and rainforests, yet there’s not especially obvious about their osteological anatomy that they could occupy so many more environments.

Make sure the analogy or reasoning behind it is actually correct. Not too long ago it was suggested that azhdarchids had long necks to reach into carcasses of large dinosaurs. However, given that the heads of the biggest azhdarchids (estimated at getting on for 2 m) are longer already than the longest sauropod ribs we know of (2 m) then any kind of neck is redundant in this context, let alone a long one, and vultures do fine with absolutely short necks and heads while feeding on carcasses of animals many times their size. The analogy that the hypothesis is being based on is fundamentally false and if that is the sole support for it as a concept, then it’s really not much of a hypothesis.

The short version of much of this could well be summarised as “look more at the behaviour of extant organisms”. I know Darren bangs this drum a lot on TetZoo and I’ve said it in plenty of talks and to lots of people if less so online. It is confounding when people say that such-and-such behaviour isn’t seen in reptiles when it plainly is, or that only animals with feature Y can do this behaviour when it’s known in numerous species, that are just less specialised towards it (or even show no obvious adaptations – like tree-climbing crocs). True this may not be common or normal, but to assume that it’s impossible, or that there is a perfectly consistent correlation is incorrect.

Part of the difficulty is a lack of good data on many of these things. Ethologists can simply observe behaviours and therefore don’t necessarily go looking for osteological or other correlates that we might be able to detect in the fossil record. That does make things harder, but we need to try and avoid getting trapped by ‘we don’t know if this correlates therefore this hypothesis is valid since we don’t know’. I am actually not against (in principle) hypotheses that are difficult if not currently impossible to test, but as with the azhdarchid neck example, there is a difference between something that can’t be tested, and something which is not even supported at the most basic of level. A hypothesis has to have some support, and some specificity about that will go a long way to making things much more clear and amenable to testing and allow a great fit of existing and future data.

What is most remarkable is how far things have come so quickly. So many modern analyses are using things like FEA and functional morphological analyses, are looking for correlates of behaviour (or aspects of ecology that link to behaviour), and more and better comparisons to extant forms and their anatomy are being used. Such important work or our understanding of the biology of extinct animals should not be let down by poor hypotheses and we do hope that, while things are improving already, this will help better communication and understanding of ideas.


D. W. E. Hone and C. G. Faulkes 2014 A proposed framework for establishing and evaluating hypotheses about the behaviour of extinct organisms (292: 260–267)





Darren Tanke’s Gorgosaurus preparation 15: finishing touches

The Gorgosaurus has entered its final phase of preparation on this side. All the bones are being worked on in a systematic fashion now. Glue that stabilized them mostly went inside the bones, but some is on the outside and rough in appearance or dirty with embedded sand/dust. All this “old glue” is carefully scrapped off and a final clean coat of thin glue applied to the surface where needed. Rough rock areas are being smoothed down. As said in an earlier update, the specimen will be molded in latex rubber. This will likely be done in one piece and how that is made will be covered in future updates if Dave Hone and the followers of this blog are interested [Edit: I most definitely am, it would be great to cover this too! Dave]. It is technically not fossil preparation but an important and often overlooked aspect of the technical side of vertebrate paleontology.

Part of the Gorgosaurus‘s final phase of preparation is getting it ready for latex molding. Molding a fossil is like chess- if you do something to the specimen, it will affect how the mold will be removed in the future? You always have to think ahead. For example a deep undercut under a bone can be molded, but once the latex cures how will it be removed from that deep undercut? Will it come off easy, or (more likely) will it be “stuck” and in the efforts to remove the mold, the bone above is damaged or possibly destroyed. With these thoughts in mind, the Gorgosaurus is being gone over section by section, looking for potential problem areas for molding and demolding as well as general areas of support. Bad undercuts are being fixed. Any low spots are obvious “weak” areas for support and latex will stick more firmly to them than a flat of slightly convex surface. These low areas are filled in. To do this, I first take leftover waste rock matrix from the Gorgosaurus and with a hammer break it up into sand grain consistency. The hole or depression to be fixed is glued and then enough loose sand it sprinkled into the low spot. A dry brush steers the sand in to small undercuts. Larger undercuts can be filled by using a small funnel made out of a piece of paper. The funnel’s tip is put under the undercut (usually meaning the funnel is angled somewhat) and pinches of sand dropped into the funnel until the problem area is filled up- this works great for microcracks only a sand grain wide too. Once this is all done, a very gentle puff of air administered by mouth gently blows away any brush marks in the loose sand. Then the loose sand is glued with acetone-based glue- the same used to stabilize the bones. Being acetone-based, it can be reversed at any time in the future if need be.

The final effect looks fairly good, but never adopts the same color as the untreated rock, but this can be rectified with paint later if wanted. The procedure is shown here in one small area and then a picture of an overall area after treatment is shown. The long and narrow belly ribs in the overall view on the right side are much better stabilized now. You may ask why not just leave the rock in there to begin with and that is usually the plan, but sometimes it is not there (due to a wide crack), or crumbled away into loose unstable pieces, or was deliberately removed for some reason (such as the removal of the postorbital from the antorbital fenestra in an earlier post) and needed to be refilled. We are hoping to start molding the Gorgosaurus block by mid February.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

Darren Tanke’s Gorgosaurus preparation 10: filling the cracks and a foot uncovered

Following hot on the heels of our little Q & A session, Darren gets us back to the real action of tyrannosaur prep work:

This update is for November 19, and November 21-26. Much more progress has been made on the Gorgosaurus. The left hind foot and much of the major limb bones are now uncovered. The whole left hind limb is complete and articulated, but the bone very splintery and requiring lots of glue. Next week I will use a homemade glue dispensing system, akin to an IV drip bag used in a hospital. This will glue not only the splintered bones of the leg but the flaky matrix as well. A recent meeting regarding this specimen has concluded that once this specimen is prepared on this side, it will be flipped over and worked from the other (original top) side. There are several reasons for this, one of which is that the skull is wanted for study by several researchers and will be CT scanned once finished. There appears to be no neck on the Gorgosaurus so this may be quite easy to separate from the rest of the body. All this added work will add several months to the preparation time.

In this update I will address some issues involving crack repair on the Gorgosaurus block. Cracks are unstable areas and can expand or allow nearby rock to fall in further destablizing an already weak spot. It is often required to fill these cracks in as a temporary or permanent fix. Such cracks can be simply filled with epoxy glue which is airscribed or ground down with a high speed rotary tool with a wire brush. Or, the top of the glue can be airscribed to give it some rough rock-like texture and then reglued and loose sand from the block sprinkled on top when that glue is wet. Once dry, the leftover loose sand is brushed away and the crack is well hidden. In the attached before, during and after pictures, one can see the crack virtually disappears. It is barely visible to you and I because we know where it was, but to a viewing public, the crack cannot be seen at all. The camouflaging of the crack can be further achieved (if necessary) by regluing some random areas of the fixed crack and sprinkling a slightly different colored sand on top, and/or augmented by acrylic paints. In the series of four photographs here, the crack is seen at the beginning, filled with tissue paper which is then glued, loose sand from block is sprinkled on top, and finally brushed away. This is another quicker technique that works very well. This crack was fixed when it was believed that the head would remain in the rock as found. Now that it has been decided to take the skull out, the fixed crack is no longer needed. When work resumes there, I can simply rehydrate the glue with acetone and my fix job will come apart easily. The fix job shown here took all of 2 minutes to do.

The other photographs show the preparation progress on the hind foot (top) and shoulder girdle region (below). The runny plaster of Paris poured in at the beginning of the project saved the day in a couple spots, stabilizing the loose rock long enough to be airscribed away.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

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