For those who are regular readers this post clears up the mystery of the Thursday post –my new paper is out. It’s time for me to be a bit self indulgent on here as I have a new paper out that I imagine will be of interest to quite a few people on the web. My interests in palaeontology have always veered strongly towards behaviour and ecology and this is my first paper that deals with it in some depth, so please allow me to expound on this at length and forgive the excesses. Right, onto the actual content!
A quick skim through the palaeontological literature (in all its manifestations) would suggest that the big carnivorous dinosaurs spent their time trying to get their teeth and claws into all manner of big adult herbivores. Tyrannosaurs tackling giant ceratopsians, allosaurs slicing into huge sauropods and carcharodontosaurs picking on the great hadrosaurs among others are commonplace. While I’ll happily admit that most of these scenarios usually come from book covers, palaeoart and the odd life reconstruction rather than detailed descriptions in technical papers, these do crop up in proper papers from time to time and certainly very few people have ever challenged them to any serious degree, so they have prospered unchallenged.
Well, I’ve taken a fair pop at them in this paper, and I rather suspect there will be a backlash by those who misread, misunderstand, over interpret, misinterpret or simply have not read my words, so I’m going to try and get my revenge in first. This is a new and as yet untested hypothesis and there are lots of caveats that I detail and lots of ifs, buts and maybes, so if you want to ask a question do please read this carefully first (and the paper too, obviously there’s loads more in there that I don’t cover here), it covers quite a lot of ground. The long and short of it is that I think that the concept of big theropods tackling comparably sized large adult prey would have been a rare event – the exception not the rule. There are a fair number of reasons to support this contention and some more to suggest possible problems and I’ll go through them at tedious length. So hang onto your hats, it’s a thrill a minute here! Possibly.
The thesis set out in the paper (written with Oli Rauhut [L], my boss from my time in Munich I should mention at this point) is that in the main theropods stuck to predating on juveniles and largely left the adults alone. I’m only really referring here to big theropods on the grounds that small one would probably not have been able to trouble big herbivores (though many of the concepts would probably apply to small theropods tackling comparatively small prey too). The real concern here is the idea of bringing down multi-ton plant eating giants, so we’ll stick to the bigger theropods (themselves ton and multi-ton animals). There is also a blurred distinction between the adults of small species and the juveniles of big ones as prey, though in addition to their size as a whole juvenile animals suffer several penalties in the face of defence towards predators.
When we look at the fossil record for theropod predation we first off see that there is only a very limited amount of it. That is, while there are famous incidents of theropods leaving bite marks on bones or having wounded or eaten other animals, the record is really pretty limited. This is odd in a sense, as given that there were a great many theropods out there, and lots of prey, they have to eat and really should be leaving more of a mark (so to speak) on the bones of their prey species. While one might think that of course any animal that was killed for food would simply be eaten and this could not be fossilised this can’t be the whole truth of the matter – it’s hard to see any theropod crunching its way through a brachiosaur femur and actually eating it for example – but you would expect to at least see some tooth marks when they stripped the flesh from it. Even in an open environment like the African savannah with plenty of predators and scavengers you will often see half bones and skulls sitting in the open which of course at least have the potential to be buried and preserved. Certainly the fossil record has all kinds of biases and a dead and half-eaten animal is not necessarily going to be buried or found (and see below) but the record is still remarkably low considering the numbers of specimens we have and the relative rates of bone damage seen in mammalian faunas, both extant and recently extinct. In short, if theropods are going after big animals, we should see the damage wrought on big bones, and that is quite rare.
This suggests that perhaps we are missing such traces because theropds were exceptionally good at destroying bones in the fossil record either through exceptional bone consumption or digestion or both. This doesn’t really stand up though. While the big tyrannosaurs certainly seem to have some adaptations towards attacking and breaking up bones the others do not, and obviously some bones would be too big and too robust for any theropod to tackle effectively (brachiosaur femora again). In terms of digestion, both birds and mammals tend to pass out pretty significant amounts of bone that they consumed, whereas at least some crocodiles can pretty much eliminate all bone in their digestive system, or at least turn it into a liquid and not leave any recognisable fragments. Theropods would seem to be closer to the former than the latter however. Despite evidence of acid etching on bones and fish scales in theropod stomachs we can still identify these fragments (they have not been destroyed) and there are also coprolites containing identifiable bits of bone (in the sense that we can tell femurs from vertebrae and what clade they came from, even if crunched up and acid worn). If even the biggest, most bone-crunching, best adapted bone feeder like T.rex can eat a small juvenile hadrosaur and still pass out bits that we can identify then one would expect that if they were chowing down on whole vertebrae or humeri or just bits of adult bones we’d find these too as stomach contents, but we don’t. They just don’t seem to be eating big bits of bone, or for that matter big bones. In fact on the rare occasions we find anything what we do find are bits of juvenile dinosaurs as stomach contents.
Hatchling Triceratops - easier to kill than an 8 ton adult.
Turning to living animals we see two intertwining patterns that are common throughout not just the amniota, but really across metazoans as a whole (at least as far as they have been studied and as far as I can track them through the literature). First we see that in general predators prefer to take juvenile prey over adult prey (and indeed juveniles are, for a variety of reasons more vulnerable to predators than adults, and not just the most obvious ones like being small and lacking big horns or whatever amking thme safer for predators to attack) and indeed predators still prefer a juvenile of a big taxon over an adult of a small one. Secondly, (and unsurprisingly to anyone even vaguely familiar with the basic principles of natural selection) there are generally large numbers of juveniles in any given animal population and they tend not to survive to reproduce. Indeed the classic animal population structure is crucially one of large numbers of juveniles, few intermediates (‘subadults’ or adolescents), and large numbers of adults. Each year many new juveniles are born, yet the subadult population remains stable and low because most juveniles don’t make it past the early part of their lives. They are being killed, and ecological studies show that the vast majority of this loss is through predation. Overall, predators take juvenile prey first and foremost and there is no reason to think theropods were any different. In fact the records of bite marks, stomach contents and coprolites rather suggest that they fitted this pattern (even if that evidence is sparse).
Finally turning back to the fossil record, what we see of dinosaur populations would also support this hypothesis. Despite their size, dinosaurs produced very large number of offspring – compare the ability of an elephant to give birth once every few years with a sauropod or hadrosaur that could potentially lay dozens of eggs at a time, perhaps several times a year. Dinosaurs were producing juveniles at a fantastic rate and they were not all making it to adulthood, and nor were they all dying from falling into lakes or under rockslides (and thus turning up in the fossil record) – they were being eaten. There is a clear and obvious bias against finding juvenile animals in the fossil record (see below) but given the extraordinary reproductive ability of dinosaurs can we really attribute the strong absence of juvenile dinosaurs in the fossil record to this alone? We do actually have some good collections of juvenile animals, but perhaps pertinently these actually are often the result of a catastrophic death assemblages. We only find them when they died in a manner unlikely to make them vulnerable to scavenging (like mud traps). Of course unlike big adult skeletons with bigger (and better mineralised) bones and all those awkward horns and plates and spikes, juveniles were small, easy to consume whole, with bones that could be crunched and digested easily and leave little or no trace to ever be found.
It all adds up to a fairly coherent picture of population structures, reproductive rates, digestion, feeding, hunting strategy and even the raw ability of theropods to even bite bone (or otherwise) and combines data from the fossil record and living animals. It certainly fits the current data better than the idea that theropods targeted big adult animals while somehow juveniles avoided getting preserved and theropods fed without leaving bite marks or having stomachs full of big bones. However, as ever this is obviously not the whole story.
So now come the inevitable exceptions and cop-out clauses which are exactly the kind of thing the media don’t report on and then people assume you never thought of or ignored or bypassed. I don’t pretend for a moment that this is a watertight case (the data is too limited in quite a few ways) but based on the available evidence, I do think that as a general rule and based on the currently available evidence, it’s plausible and, yes, even likely. That is, in most ecosystems large theropods preferentially targeted juvenile prey and as such played a significant role in eliminating juvenile dinosaurs from entering the fossil record.
OK first off, as I say on here repeatedly, the biological world in incredibly diverse and varied and there is no way at all that *every* big theropod only ever hunted juveniles or made them its primary target. Even casting aside possible dedicated scavengers, or those eating other things like fish, there were doubtless a few theropods that had very different behavioural / ecological patterns and were dedicated adult hunters. Equally, even the ‘dedicated’ juvy killers would take the opportunity to attack an unwary or sick adult. Plenty of adults would still get dispatched by theropods and indeed those that were very old or ill were more likely to die at the hands of a carnivore than ‘natural causes’. This is a rule of thumb I’m presenting here, not a law of absolutes.
Secondly, yes the data is a bit thin, very thin actually. I am essentially advocating an ‘absence of evidence’ hypothesis. While there are those who stick to “‘absence of evidence is not evidence of absence” as a mantra, there are limits. If you search for a needle in a haystack for a few days and check as many pieces of hay as possible, sift it, run a magnet through it, and burn what’s left and still don’t find a needle, there’s probably none there. No, you can’t say it for sure, but you can have a pretty good idea, and you can’t look forever: we must be practical and pragmatic as scientists, especially as palaeontologists! The old canard ‘more research is needed’ is genuinely true in this case – there is no good record / catalogue in the literature of feeding traces, or stomach contents, or a record of how many juvenile specimens we have, and many have probably been missed. There might be sufficient evidence already out there to turn this concept over, or it might yet be found in the future, but we do have some pretty good collections and some studies of these incidences and they do seem to support these contentions.
Bone taphonomy - awkward
Similarly, it is of course very hard, if not impossible, to separate out the possible distinction between an absence of juveniles via theropods or from taphonomic biases. Juvenile skeletons are smaller, less ossified and at greater risk of loss in the fossil record (and harder to find) so maybe we are just missing them rather than their being eaten. Again, further research might alleviate this, but it may never be possible to tell the difference. I think that the supporting evidence (especially from extant organisms’ behaviour) tips the balance in favour of predation but this is certainly the biggest drawback here. Certainly I would not rule this aspect out – taphonomy is certainly going to be important and I am not suggesting that *all* juveniles are killed and eaten, nor that theropods were the only factor at play – merely that they were an important one.
Finally, there is of course the possibility that theropod were just doing something weird and really didn’t act like any other terrestrial predators, or that the dinosaurs themselves as a whole had some odd physiological or ecological quirks that we have not yet spotted or thought of which would switch things around. However, this does seem pretty unlikely and would require special pleading as an argument and if anything is one of the most intensely researched areas of dinosaur palaeontology right now, so if this is the case we’ll probably see something turn up quite quickly.
There are however new things that might support this work, or at least help to provide auxiliary evidence that may help sort out the varying possibilities that are discussed above. As I have lamented before on here, we don’t know that much about many extant animals, and this makes it hard to extrapolate to extinct ones. More research on predatory habits of living animals, how they damage bones (and which bones, and how much leaving what kinds of traces) and when and where they strike what kinds of prey would flesh out the story. Similarly, a better understanding of how bones are buried and preserved would assist the interpretation of the picture in the fossil record – are juveniles really biased against being preserved, and by how much? Can we create some kind of correlation to correct for this bias? Turning to the dinosaurs themselves if we can get a better handle on their reproductive rates and growth we might see patterns that support this hypothesis (like lots of eggs being laid and very fast growth towards adulthood, some of which is starting to appear in the literature) and a better understanding of how their populations were divided (adults, juveniles and intermediates and predators vs prey) would greatly enhance our understanding of their ecological pressures and interactions.
That largely wraps it up, (and well done for making it this far, this is nearly as long as the original paper) so I’ll summarise. Giant theropods probably took juvenile prey for preference over adults, and healthy adults would have been generally avoided. This matches what (admittedly little) we know of dinosaurian reproductive rates and population ecology and can be reflected in both the fossil record for dinosaur feeding traces (bites, gut contents and coprolites) and for the manner in which extant organisms of all kinds hunt their prey. This is collectively hard to separate out from taphonomic effects and baises but now we have a hypothesis we can try to test it. Doubtless on occasion a Tyrannosaurs would face off with a Triceratops bull in a fantastic one-on-one combat the like of which films are based on, but it would be a once in a lifetime experience for at least one on them, and that’s why a T.rex would avoid the possibility and simply snap up something a fraction of the size and lacking the horns and spikes and most importantly, nous, to know better.
HONE, D., & RAUHUT, O. (2009). Feeding behaviour and bone utilization by theropod dinosaurs Lethaia DOI: 10.1111/j.1502-3931.2009.00187.x
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Dave Hone's Archosaur Musings 
I don’t really have a problem with the basic premise. I agree that the titanic battle paradigm is a bit more Hollywood than what we see today in Nature. So the predictions are reasonable. But I do have one question and a nit to pick.
The question is about the support for your statement about dinosaur fecundity. Is this statement based on nests and eggs? Would not taphonomic issues be involved? I’m not saying that dinosaurs were necessarily k-selected here, I just want to know what the evidence for your claim is.
My nitpick is not with your essay specifically, but is, rather, a more general pet peeve of mine. I hate the use of “predate” as a verb synonymous with “prey upon”. But that use has become too ubiquitous for it to ever lose traction now.
It’s a statement based on eggs and nests – there are huge numbers of them, despite what you might expect of a taphonomic bias against them (they are fragile and many nests would be kept well away from places where they might be destroyed by e.g. flooding). There is generally pretty good evidence that dinosaurs tended to lay lots of eggs (e.g. whole nests with large numbers of eggs in, identifiable to a given genus). The paper contains only a very brief discussion of this though of course there are a bunch of references to back the point up.
Hi Dave,
Congrats on the paper.
With regard to your suggestion that juvenile dinosaurs are scarce in the fossil record, I’m a bit worried about the fact that the only reference in the paper cited in support of this is from 1965 and doesn’t actually contain any raw abundance data. My impression of the dinosaur fossil record, particularly ornithischians, is that actually a very large component of it is made-up of juveniles and subadults, and this is being increasingly supported by current histological approaches to establishing ontogenetic stage. Do you know of any hard data to support this part of your argument (i.e. a census of ontogenetic stage within a formation)?
It was a concern for me too I’d agree. The problem comes from the lack of material on this in the literature. The Dodson paper i cite is the only one that Oli or I could find that has ever dealt with the issue. While one might expect that the ratio of adults to juveniles has not changed much over the years I suspect is has (and certainly a couple of big finds like the recent ones of whole groups of ornithomimids and psittacosaurs might skew this a bit in terms of numbers). Sadly I got hold of the recent ‘Bonebeds’ book far too late to include any of it.
We really need a systematic review of the literature / collection on this front (not just in terms of this hypothesis but also generally useful information it will give us on population structures etc.). Even if they were more common that we suggest here, I’m not sure it is necessarily a problem for the hypothesis since in at least some formations juvenile mammals are still common yet are still under the same general selection issues (juvies getting targeted out by predators even if lots of others still make it into the fossil record through other means [like a tar pit say]). It’s a question of sorting out what is taphonomic and what is predatory. It’s probably impossible, but we might be able to get a handle on ti with thorough surveys of both bone beds and extant faunas / extant bone collections.
Oli with a tie, no beard, no long hair? Well THAT’s unusual. 😉
Congrats on the paper.
Yeah, excellent picture of Oli!
Came courtesy of Adrianna at the launch of the pterosaur exhibition, hence Oli being dressed up to give a talk.
Great post and congratulations on your new paper with D and Rahut.
“Hatchling triceratops – easier to kill than an 8 ton adult.”
On that note however I would wonder if this is correct. Are you aware of the recent study that claims that dinosaurs would have weighed half as much as once believed? I assume that you have not had a lot of time to read papers on account of your trip and the new paper that you have published. Or do you not believe that the paper I told of is correct?
I have read that paper and while the work is fine, the report of that work is somewhat off kilter. They found that according to one method of scaling (mostly used back in the 80’s) *some* estimates were out by up to half, which is nothing like the same as ‘all dinosaur estimates are double what they should be’. Certainly mroe recent and more detailed analyses of many taxa have confirmed relatively high mass estimates (e.g. Don Henderson’s superb work). OK, 8 t might be a bit over, but probably not by too much, and certainly not by 4 t.
Oh I see, well thanks for setting me straight on that regard.
No problem. it’s an interesting paper and their point was well made, but somewhat inevitably the reports were a bit overblown and essentially interpreted ‘some’ as ‘all’. It’s actually particularly interesting as it’s not just the one allometry method that gets critcised that has produced high estimates for dinosaur masses and several very varied methods have converged on similar results at times that this paper still suggests are too high. We need to work out where this discrepancy is coming from, though of course the problems of working out how heavy something was from a 100 million year old skeleton makes this tricky.
I have to admit, I was going to file this paper under “redundant” when I first read the abstract. Given what we see in current ecosystems, I always thought it was a given that the young, and very old would be the most likely prey of large predators. I kind of just “wrote off” all the various epic illustrations out there, as they are more likely to reflect what the artist would like to see, rather than what really happens.
Have you received a lot of resistance to the paper since it was published?
It’s kind of funny; the argument posited in this paper actually lends support to all those scenes in the Jurassic Park films where large theropods are chasing after people. I guess they weren’t a waste of energy after all. 🙂
Well I’ve not received any opposition yet since the paper has only been out for 18 hours, though I have had some lively ‘discussions’ with some of my colleagues over it. I am expecting some resistance, but I would reiterate that this is a new hypothesis really and as such needs to be tested. *I* think we are right, but I can’t really say that as such and we do need more evidence to test it properly. Let’s see where the data takes us.
Hi, Dave, good stuff — congratulations. Two questions: first, could you please shove a PDF my way? And second, do you see the same age-range distribution (lots of juveniles, few subadults, many adults) in non-dinosaurian fossil assemblages such as the basal-synapsid-dominated Permian fauna and the various mammal-dominated post-Mesozoic faunas? And, and a third question: is that also what we see in extant systems? Based on the answer to that, you should be able to say something about the strength of the taphonomic bias
Hi Mike.
1. Yes, when I get a copy back from Lethaia myself. I only have the proofs knocking around at the moment.
2. I don’t know about the Permian / post Mesozoic stuff, since I didn’t look into it. I didn’t look into it because you would be left with the same problem as the dinosaurs (i.e. trying to spot a bias without a baseline value). I did look at extant faunas however and yes that population structure is very, very common. If you think about your basic evolution principles it fits there of course – there are many births but not many of them ever get to reproduce and make it to adulthood. If you combined a better understanding of this for dinosaurs (for which we do need more work on egg production, seasonality etc.) and taphonomy of juveniles vs adults we could well sort out some of the likely magnitude of each factor though it would be tricky and of course there would still be a fair bunch of unknowns (it makes quite a difference if a Diplodocus lays 10 or 1000 eggs a year and either is probably possible).
This is good. I don’t see anything about packs of theropods taking on bigger prey, which I would not see as contradicting the premise, but which would muddy the evidential water. Smaller theropods hunting in packs cooperatively might do better to cooperate by having some harass mom, with no expectation of eating her, while the rest raid the nest.
It must have been frustrating, anyway, to bring down an enormous beast and find it full of balloons and prickly packing foam. The wee ones were, well, wee-er, but hadn’t pneumatized yet. They must have been more satisfying, crunch-wise.
Well in the paper we fairly specifically deal with large theropods only and exclude the idea of packs of small ones attacking big targets because it would make the situation more complex. Not that I don’t think it didn’t happen, but when you are trying to organise a review / new hypothesis like this you simply can’t consider every possible alternative as the whole things just baloons to an unwieldy size with all kinds of endless caveats and cross references (what about deserts, what about prey near water, what about adolescents, what about spinosaur like teeth etc. etc.). \
While I think some small theropods probably were pack hunters and did tackle large prey at the moment, the evidence is pretty inconclusive and far from definite right now so it was easier just to leave it out until such time as it becomes clear that this was happening and in such numbers that it might affect the data we see in the fossil record.
Hi Dave,
Congratulations on the paper! Interesting reading. With regard to testing your hypotheses, you talk about careful study of bone fragments found around theropod skeletons which could be stomach contents. I would have thought that stomach acid would result in changes in bone microstructure that should be observable histologically, more easily than acid etching. It would be interesting to take histological samples of bone fragments to see if the activity of stomach acid can be seen.
Are there any tooth microwear studies on extant carnivores that commonly bite bone, and are there any microwear features commonly attributable to bone processing? A study comparing the microwear of extant carnivores and theropod teeth to try to identify features specifically caused by bone processing would be interesting.
Finally, I know Emily has carried out FEA on several theropod skulls and shown that they could have inflicted a bone crushing bite, but has any FEA work been carried out specifically on stress and strain in theropod teeth? An FEA study of the teeth of different theropods and their abilities to withstand stresses of biting bone would be interesting too.
BTW I downloaded a pdf so I’ll send one to Mike (if I can find his email address) and if anyone else wants one let me know.
Susie
Hi Susie, thanks for that.
There’s a lot there and I’ll try and deal with it all. Bits are covered in the paper but not necessarily in a way that’s easy to pick out in conjunction with these questions, plus other people are likely interested so I’ll try and answer it all here.
1. I think we spoke more about fragments that might be *in* theropods than around them as possible fragments (though a disarticulated skeleton might well have bits around the corpse as opposed to in in certainly) but the point is well made. I’m not aware of any (i.e. I haven’t seen them,but then didn’t look for them) papers on histological changes as opposed to acid etching and that might well add another line of evidence, or rather provide potentially a better / different test for some bone pieces. Wother considering certainly.
2. There are some microwear studies for mammals, but the problem here is that these marks don’t show up that often (even in bone biters) and when you consider than mammals keep their teeth but theropods shed theirs regularly (I recall one paper suggesting T.rex might have had complete turnover of all its teeth every few months, though I can’t recall which now) means that you may only very very arely see these marks in theropods. I don’t know of any checks by people on theropod teeth, but it is worth considering. However they might be marginally more common that in at least some mammalian carnivores as some of these are very delicate feeders wheras I suspect most large theropods were not. Between the two factors (care in tooth-bone contact vs shed teeth) getting any meaningful signal and interpreting it right will be tricky, though soimething like large tyrannosaurs which may well have been serious bone breakers combined with large numbers of teeth known would be worth looking at.
3. I don’t know of any direct FEA studies on tooth power / resistance, though Greg Erickson did soem estiamtes in 1996 based on the mauled Tric pelvis and the depth of the bites. Other measurable bites (e.g. the bitten stegosaurus plate) could be used as proxies for other taxa, but of course it can be tricky to work out which animal left the traces and what the likely dimensions of the teeth were, plus how the power was applied. It could be done I’m sure (FEA or other methods) and would be interesting. It could add to his discussion certainly if you factor in the strengths of various bones too which is another area we’d need to look into (just how much stronger is an adult bones vs a juvenile one, given the differences in ossification etc.).
Thanks for the comments and I hope this largely covers it!
Just a few random thoughts here–combined with it being more than a bit late right now, they may be more disorganized than I’d like. 😉
I wish I could find some detailed studies in the area, but it seems to me that (for example) a singular lion would be far more likely to snag a juvenile prey item when given the chance, since its first and foremost goal is to feed itself–and the less energy it can spend at any given time to acquire that food the better. But if an animal is part of a larger social group, it will often hunt for the energetic interests of both the group it’s tagging along with and those of itself–so larger prey is on menu far more frequently (a pride of lions attacking giraffes, water buffalo, and elephants etc.).
The same idea applies to hyenas when hunting–except when in a pack, juveniles will be targeted more frequently than full grown adults of the various local herbivores due to the hyena’s smaller size (enough food with less risk of injury). Though in many instances they’ve been shown to dispatch fully grown healthy adults if the occasion calls for it.
So in a nutshell, I’d imagine that a solitary carnivorous dinosaur would almost certainly be more likely to attack the smaller animals of a group of potential prey than would be the same dinosaur if it lived and hunted in a group which would tend to prefer much larger kills to spread the metabolic love around.
-Tor
Hi Tor, thanks for your comments. I would agree that packs of theropods (or any carnivores) can *potentially* target larger prey but there are several other facors here that still come into play.
1. You can still target juveniles and hunt large animlas simulataneously, or to put it anotherway, not all juveniles are small! Even a young water buffalo or elephant is a big animal relatively so even a pack of lions can get a good meal from one while still sargeting ‘babies’ and not adults. You can see especailly how this might scale with dinosaurs where even a young sauropod would be one hell of an animal.
2. Young animals are (in general) so much more vulnerable that it is still probably worth targeting them. You might as a pack get individually less meat for taking on a juvenile than an adult prey item, but if you are successful 1/3rd of the time hunting juveniles but only 1/10th of the time hunting adults and a juvie is 1/3rd or the adult mass it’s still a worthwhile endeavour. (those numbers are made up just to make the point). Juveniles would also likely be more numberous than adults for many dinosaur faunas too which would make them a more avialble resource as well as a more vulnerable one.
3. Sticking with this point, your hunting success will be higher and it will also be safer with less risk of injury (again, this might be emphasised in some dinosaurs e.g. Triceratops).
4. Even in the examples you give (lions and hyenas, but also wolves and other group predators) while they can and do tackle adult prey, where studies have been done they still prefer juneviles for the reasons outlined in the paper.
As such I would agree with the point that adult theropods in a group could have taken on bigger and more dangerous prey than alone, but I still do not necessarily think they necessarily would, or that it would be their prey of choice.
Great points!
Thinking back on it, I’m absolutely inclined to agree. Especially considering that (though the record is almost certainly a bit distorted) predator/prey ratios were roughly similar to those of today, whereas the number of dinosaurs born in a given clutch far outnumbered the limited number of offspring modern day mammals create.
So not only would it be less risky for them to target juveniles, various carnivores would just plain be more likely to find them than in current ecosystems.
Cool stuff–glad to change my view on the subject!
Thanks Tor. We do, as I have been saying everywhere, need to get a much better handle on the evidence, but I *do* think that currently it points towards our hypothesis. We need more work, but I think what we have done so far demonstrates that it’s a valid hypothesis and well worth the investment of checking it out properly.
Hi Dave,
Got some answers for Susie’s FEA question. Mazzetta et al. published a cool finite element analysis of a carcharodontosaurid tooth:
Mazzetta GV, Blanco RE, Cisilino AP. 2004. Finite element modelling of a tooth referred to the genus Giganotosaurus Coria and Salgado, 1995 (Theropoda : Carcharodontosauridae). Ameghiniana 41:619-626.
Also, Miriam Reichel (University of Alberta) is doing her PhD on theropod tooth biomechanics, with lots of innovative FE modeling. At SVP this year, she and Aaron LeBlanc are presenting on FEA of mosasaur enamel microstructure. You can track Miriam down for her insights on theropods.
Cheers,
Eric
Sounds great Eric, many thanks. I’ll make sure I find them. Will you be coming over?
Nice shirt, Dave!
Little bit late, but I read a paper the other day in which it was hypothesized that the cranial kinesis of Carnotaurus was designed to allow it to swallow whole small dinosaurs–thought it fairly relevant.
That is handy yes. Since the paper went in I have found a half dozen references I could have included that would have helped strengthen my case and a whole small subsection I should have written but did not think of, prompted by queries from colleagues. I’m planning on turning that into a paper in itself at some point so there is still room for expansion. That’s the way it goes really. I scoured the literature but you can’t read *everything* even over several years.
Paper’s name is ‘A New Close Relative of Carnotaurus Sastrei–Bonaparte 1965–(Theropoda: Abelisauridae) From the Late Cretaceous of Patagonia’ if you’re interested.
Thanks for that, b ut I actually have it already – I’ve ene read it. Sorry I wasn’t too clear before: I have actually read that paper, I just hadn’t remembered that part of it and thus it never made it into the paper. Sadly I can’t remember every detail of every paper i have read – I have sure there are relevant bits of the papers I *did* cite that should have gone in and did not. It happens really unless you have a photographic memory for research papers.
Gotcha, quite understandable!
Sent an e-mail with a few thoughts on the paper–on the whole it was a really cool read.
I have a tough time imagining T. Rex and similarly sized theropods being able to subsist mostly off little baby dinosaurs. Certainly adult dinosaurs would provide more meat to supply the big predators’ bodies. You might also want to consider that tyrannosaurids in particular are overbuilt for animals you’re saying mostly ate youngsters. Why would they evolve jaws with thousands of pounds of bite force if they weren’t frequently hunting fairly large, aggressive animals as opposed to bite-sized, defenseless infants?
I don’t want to go on for ever so I’ll try to keep this short, but I would suggest you read the paper as I cover some of this there. However to try and deal with these points in order:
Plenty of living animals do just that (live of small / juvenile prey) it’s just a question of scaling things up (for an extreme example, anteaters do OK despite the small size of their individual prey items but lots of birds only east small things, foxes eat tons of worms and beetles etc.). If the predator is bigger but the prey is also bigger it should be no problem. You have to consider quality (prey size) *and* quantity.
The tyrannosaur problem is a non sequiteur – just because tyrannosaurs primarily ate small juveniles (assuming they did, for the sake of argument here) does not mean they don’t need those jaws for who knows what other reason – they might still occasionally have taken big adults as an essential (if minor) part of the diet and thus needed big jaws, they might need them for scavenging, or intraspecific combat etc. As long as having huge jaws is occasionally beneficial and does not penalise another aspect of their lives then they will be selected for. If they *specialised* in juveniles then you might expect weaker jaws, but that is not what I am advocating and indeed in the paper we have a special section devoted to tyrannosaurs because they are different to other theropods.
“they might still occasionally have taken big adults as an essential (if minor) part of the diet and thus needed big jaws”
I would think natural selection would have encouraged big bone-crushing jaws if they were attacking big game at least fairly frequently. Certainly such force would be unnecessary for scavenging as all they would have to do was to strip the meat off the bone.
Also, the argument that big theropods were the culprits behind the lack of baby dinosaurs in the fossil record fails to consider that there were smaller theropods around. What were the raptors, compies, and their ilk eating?
Brandon, sorry to be whiny, but you really have to read the paper – I don’t want to have to keep answering things I have already answered. Still to continue:
“I would think natural selection would have encouraged big bone-crushing jaws if they were attacking big game at least fairly frequently.”
Not so, many birds mate just once a year but still seem to find carrying huge ornaments around with them the rest of the time to be worthwhile. A big difference, even only very occasionally to your survival will propagate a selective force.
“Certainly such force would be unnecessary for scavenging as all they would have to do was to strip the meat off the bone.”
That assumes they only want the meat. The bones themselves contain calcium, phosphorous etc. that are useful, plus the bone marrow itself is very nutritious – there is a good reason to attack the bones themselves. It’s also probably tricky for theropods to strip the meat off of a big carcass or bones like vertebrae.
“What were the raptors, compies, and their ilk eating?”
The prey of smaller dinosaur perhaps (it’s not all brachiosaurs and triceratops-es, or other small prey (mammals, pterosaurs, lizards [Compsognathus has one in it’s gut], small crocs) or they may have gone after the same prey. A lone deinonychus could probably have tackled a hatchling titanosaur for example. There are lots of possibilites here, few of which have been tackled in the literature. This paper never intended to answer that question, so it’s hardly a flaw in the argument.
Well, it’s pretty odd that dinosaurs had so many young; so then, since the maiasauras and the Auca Mahuevo saltasaurs suggest, as well as Oviraptor, they were good parents.
So, if that’s the case, why did the predators get SO gigantic? Is it just to sneak in past super-size parents guarding their young, in the case of a charcharodonto attacking a titanosaur kind of thing,but it’s reasonable to say that some predators did go for the youngsters. An allosaurus can’t risk getting injured by a herd of adult diplodocus, can it?
But then, that doesn’t explain why Spinosaurus got so huge, while Irritator and Baryonyx remained pretty decent. Okay, the Bahariya Oasis had Paralititan and Aegyptosaurus, but could it hunt them?
Well that is 2 specimens that suggest *some* brooding. Don’t forget that crocs have lots of young and some are excellent parents (at least early on in their lives) but we are not drowning in crocs – most of them still die and don’t make it to adulthood.
The thing is there are multiple factors at play here – I’m sure not *all* theropods hunted juveniles exclusively (or even mainly) – there will have been exceptions. I’m trying to provide a general rule of thumb and I can’t account for every exception (different climates, environments, prey species available, competitors etc.) that would have driven selection of prey and prey size vs theropod body size. Picking individual examples won’t get you very far since even a few dozen possible exceptions or awkward correlates would not necessarily negate the *general* hypothesis here.
As for theropod body size there are still good reasons to be big – you can compete better for the best territories, mating rights, attack biiger (if still juvenile) prey, take adults, scavenge bigger kills and yes on occasion, tackle adults. Primary prey alone will not necessarily determine how big you are – anteaters are big and eat ants.
Another thing; did sauropods have such fast growth rates just to be safefrom the theropods? Anyway, that’s what I think; anyhow, if sauropods did protect their young until they reached a certain size, and they were alone afterwards (which is basically the point of view I have of these animals)what’s the point of certain theropods getting so big? Not all sauropods were as big as blue whales as adults…ANYWAy
Well I think that’s a possibility certainly. But you have to remember that in terms of finding causality it’s very hard in the fossil record. Large size may have been a good defence against many predators, but there might have been other (stronger) influences on body size like female preference, they type and amount of food around, what water was available, the terrain, migration or climate patterns etc. In short, this is just one variable and determining if it was the *dominant* variable that drove sauropod body size (or even just a significant one) is pretty much impossible. If we look, we may find a correlation between sauropod body size and theropod body size but we haven’t even looked yet, so it’s hard to predict let alone verify.
I get it. Well, nobody exactly has found a mother sauropod of ny kind with her babies, so it might be reasonable, considering how quickly ideas change.
Anyhow, an adult sauropod had a tiny head on a multi-ton body. If the hatchling had a bigger head, and was eating much more food in comparison to tis body weight, than an adult, it may be, or may not be plausible, or possible. Anyway, they did have the smallest EQ of all dinosaurs, but then again, since birds and crocs are the closest relatives of dinosaurs, then it doesn’t seem unlikely that sauropods protected their young until at least they were of breeding age, or a little smaller. It seems as if they filled two different niches i nthe smae ecosystem, but they belonged to the same genus.
Anyhow, I personally believe in my head, at least, that supergiant sauropods laid eggs singly, and smaller, saltasaurus-sized ones laid them in groups (all small sauropods, to be exact). So, with so many young in the area, it’s obviously not surprising that they’d be eaten by big and small carnivores, or wven be trampled accidentally by the adults, maybe even their own parents.
Well, thanks, and bye.
Well there are some large nests containing large sauropod eggs so there is a suggestion there that even big animals had full multi-egg nests. As for parental care which is something else again there is no direct evidence for it (like whole mutli-age herds together, parentds close to nests, nests with older-than-hatchlings in, nests with brought in food etc.). That doesn’t mean that it did not happen, just that it I hard to argue much convinvingly either way at the moment. Just being big with a (relatively) small brain doesn’t make you incapable of complex behaviours (look at whales or at another scale, ants – I’m sure they had the capacity to have provided some simple care, it’s just not clear if they did).
I would not be surprised if they did occupy different niches in an ecosystem (juveniles vs adults) just based on size (a hatchling sauropod cannot reach 30 feet into the trees) if nothing else. It’s a separation seen in a great many species.
Another amazing example of complex behaviors in simple organisms can stretch even further–mold without a neurological network ‘preparing’ for stimuli.
“Single-celled slime molds demonstrate the ability to memorize and anticipate repeated events, a team of Japanese researchers reported in January. The study clearly shows “a primitive version of brain function” in an organism with no brain at all.
In their experiment, biophysicist Toshiyuki Nakagaki of Hokkaido University and colleagues manipulated the environment of Physarum slime-mold amoebas. As the cells crawled across an agar plate, the researchers subjected them to cold, dry conditions for the first 10 minutes of every hour. During these cool spells, the cells slowed down their motion. After three cold snaps the scientists stopped changing the temperature and humidity and watched to see whether the amoebas had learned the pattern. Sure enough, many of the cells throttled back right on the hour in anticipation of another bout of cold weather. When conditions stayed stable for a while, the slime-mold amoebas gave up on their hourly braking, but when another single jolt of cold was applied, they resumed the behavior and correctly recalled the 60-minute interval. The amoebas were also able to respond to other intervals, ranging from 30 to 90 minutes.”
http://discovermagazine.com/2009/jan/071
Click to access PhysRevLett_100_018101.pdf
What I mean here, is that young and adults ate different foods, and adult sauropods may only have guarded their young, not brought them any food.
Another thing; among my favorite dinos are the Neuquen Portezuelo-age critters, and the sauropods themselves are among my favorite even among them.
Anyhow, I’ve reconstructed Rinconsaurus nesting behavior in my head and in a sketch, and it shows two mums standing in an area full of eggs. If a Rinconsaurus baby took ten years to grow up from an 18-inch runt coming from an egg as big as a small melon, to a 36-foot 7-ton beast that ate from the branches of conifers. Furthermore, the ‘guard-only’ scenario is pretty stupid, as I thought it would be. As you earlier said, you’re right; king cobras themselves build nice nests and guard their eggs. If adult rincons had such tiny heads and such big bodies, and if their kids grew up in a mere decade or so, then their food demands would’ve been very, very, very different. I can just envision a Rinconsaurus nesting site; adults busily going to and fro from forest to nest, bringing back plenty of leaves for insulation and food for the young, as well as feeding themselves. Of course, unenlagias and small notosuchid crocs take some eggs and hatchlings, but Megaraptor packs occasionally attack the adults as well-end of babies. Yet, maybe they took turns in guarding the hatchlings…
However, like I said that the super-sauropods nested alone, and my biggest brainwave comes up as the biggest of the big-Futalongkosaurus. How many 100-foot 60-ton mums can one place hold? That’s how it struck me that anything in that range were lone nesters that behaved more like a king cobra, and built a proper leafy nest, and that the young stayed in the area with the mother for some time. The nest would’ve been made like that of the big snake’s, and they may have nested, say…in a ferny, open grove of araucarias. Then, once tje young left, they went and formed herds with other juveniles, after whcih they lived alone. That’s the way I see it, and king cobras are. after all, the biggest poisonous snakes of all.
As I say it is possible, but soem ecosystems can support huge numbers of animals (like a million bison, or a million wildebeest, plus zebra, hartebeest and gazelle), so i do not think herds of vast multi-tonne sauropods are impossible, or them nesting together. THe offspring might well scatter immediately, or herds separate after nesting, or who knows what. In short, I think there are far too many reasonable possibilities at stake and far too little data to select any one from the huge mass as being more ikely that the others. Many things are possible, none are certain, and in this case none can easily be evaluated.
That’s true, I guess…
Another idea of mine. Do you know that when you look at a titanosaur, the thing you notice is that some are awfully vast, and others are awfully small?Well, about gigantism, it’s possible for a whale to get as big as he wants becuase the water bears and supports its weight. Correct?
Then, a diplodocid can grow as big as a whale since its bonesare light with pleurocoels in them that keep the weight down. Yet, titanosaurs, mostly, have primitive, cetiosaur-like bones with no hollows in them, and yet, they must still walk on land, on four legs. How did they do it? Well, I’m not sure if this suggestion has been forwarded previously (it might’ve) but I think the wide-gauge stance of a titanosaur helped it in this endeavor. Yes, it makes sense; look at the lillytrotter birds; their toes and claws are widely spread out on a huge area, so that when they step on a lillypad, they won’t sink. The biggest titanosurs themselves, therfore, might’ve bbeen able to spread their weight out on a wider area since they had wider bodies and stances than their precursors. It makes sense, doesn’t it?
I think you are confusing several things here. Whales are not unlimited in maximum size as there are still constraints of heart muscles and oxygen absorption in the lungs etc. On land thing are different and while diplodocoids did get very big, they will still run into size limits – the leg bones are not hollow and have to carry the weight of the whole animal and there is a limit to how much mass bones can support (plus of course the cartilge in the joints, muscles to move the legs etc.) and if they get too heavy the legs would be so vast as to meet each other.
As for the lilly-trotter argument, the issues there is transmitting force to the ground. It works becuase it has big, spreading feet, not because the toes are far apart. Thus the wide-gague of titanosaurs is irrelevant here as they still have small feet.
Hmmm….that would make perfect sense. sauropods didn’t have giant, clwed feet, and the water-living sauropod idea was flushed down the toilet long ages ago. It’s pitiful, you see. Anyhow, thanks for the advice and the new blog site. Well, anyhow, you know, I think it’s also quite irrevalent to put sauropod stats in a theropod page! THEY’D BE KILLED!!!Ha-Ha-just kidding!
Anyhow, the sauropods really do stretch the limits of comprehension, even though they’re my favourite dinosaurs, and, very recently, I did (I’m still doing, actually) a big sketched-out drawing, showing a pack of deltadromeus attacking a very small-about 18 feet, actually-Paralititan, and the adult has its mouth open, bellowing to try and see them off. It’s a pity that paralititans are not known, as is the commonest-from very good remains. I’ve seen plenty of paralititan pics, and one looks totally different from another. DI’ve seen a picture of a paralititan that looks like a brachiosaur with short legs, and one by National Geographic (in the magazine with the dracorex on the cover) looks more titanosaur-ish. So, I added some hypothetical sexual dimorphism as well, and…I’m still in the progres now. I think it really supports your idea, Dave. The baby killer idea, I mean. It’s nicely in there. Thanks! I guess the idea of mine showing the rearing of their offspring sounds far more plausible- I’m an idealist.
Glad you like my work and the blog!
Hey there! I haven’t been in for some time, and, as I don’t want to burden you guys with too many long questions, I’d like to ask you one last thing.
Okay, this is about sauropods (as usual) and apparently, it concerns growth rates.
Isn’t there any other site where I can get some info about this question:
Can an animal’s thermoregulatory abilities change during its lifetime?
Can there be anything on SVPOW about this?
Well, there’s no ‘guys’ just me really…
Websites with information? Probably not, you’ll need to go to the scientific literature. Martin Sander has done quite a bit on this especially.
“Can an animal’s thermoregulatory abilities change during its lifetime? ”
Quite probably, though I can’t think of any examples off the top of my head of animals that do (aside from hibernation / torpor).
“Can there be anything on SVPOW about this?”
Ask them, not me.
Uh…..yeah! Yeah…thanks.
Well sorry, not much I can so really.