Posts Tagged 'evolution'

Kulindadromeus images

While I’m sure huge parts of the internet are currently going mad over the new ornithischian Kulindadromeus and the implications for fuzzy dinosaurs (or otherwise) there current crop of pictures available isn’t that great. Inevitably those in the paper are small and crammed into the limited space (in the main paper at least, I’ve not yet got hold of the supplementary files and am writing this before the paper is released) and the press images are focused on the beautiful life reconstructions. However, Pascal Godefroit was kind enough to pass onto me a pile of images that he said I could use. Many have made their way onto my Guardian piece on the subject, but even there they have to stay small to fit the website’s style and some of the detail is lacking, so I’ll put them up here instead.

Obviously these images come directly from Pascal and are copyright to him and his team and should not be reproduced without his direct permission. Anyway, they do show some nice details of various parts of these specimens and the different integumentary structures (both scales and filaments) rather well and I imagine will be of some interest. I won’t add any more description here since I’ve already written a couple of thousand words on this animal today and I suspect most readers will be angling for the paper to do their detailed reading anyway. Enjoy.

feathers on femur 3Multiple filaments associated with the femur

 

SONY DSCMultiple filaments associated with the humerus.

 

foot + scalesSmall scales associated with the pes.

 

head+integumentSmall filaments associated with the skull.

 

integument on proximal tibia 2Filaments at the proximal tibia.

 

scales on distal tibia 2Scales on the distal tibia.

 

SONY DSCClose up of tooth series.

 

Huge thanks to Pascal for lending me these images and letting me put them online and obviously my congratulations on the discovery.

A new German ‘Darwinopterid’ pterosaur

Regular readers of the Pterosaur.net blog will have already seen this post and might well have put two and two together and realised that this is ‘Darwinopterus’-like pterosaur from the Solnhofen. We are still waiting some kind of proper description on this (and it’ll need a name too) but it has had a mention in the literature and been on show a number a times. It’s incomplete and disarticulated, but it’s far from a bad specimen and very obviously has the classic features one would expect – a combined nasoantorbital fenestra, a big head, and yet some rather more basal features in the wings and feet.

Darwinopterus is the key taxon that helps us join up the basal pterosaurs and pterodactyloids, and there’s been a series of taxa named from the Chinese Daohugou beds that lived alongside this genus (a number of which are probably synonyms to be honest) as had made China the centre for this. Still, a couple of specimens from the UK have been found (or rather, rediscovered) that suggest these forms might have been more widely distributed and once they appeared in China, the Solnhofen and surrounding beds then became an anomaly – they were full of both pterodactyloids and basal forms, so surely the intermediates might have also hung around and been present given the numbers seen in China.

Now though a second one has turned up in Germany and it’s a lovely specimen of what is a small, and juvenile animal. The preservation is superb, and as Helmut Tischlinger has been working on it, there’s obviously some exceptional images, but there’s also some interesting features.

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The short paper covering this animal is in German, so I might well be repeating things already said in the manuscript, but I’m going from only the English abstract and figure captions and my own thoughts, so this might be badly mangling or even completely replicating things already written. If so, my apologies to the authors or anyone else who has read the paper.

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For me the more obviously interesting features all lie in the back end of the animal. First off as you can see below the distal phalanx of one wing had had a nasty break and then healed with a mass of bone that least the end at a rather major angle compared to the proximal part. There are a few pterosaur pathological wings out there, but this is quite a big one.

Secondly the tail is rather short. In my paper on pterosaur tails with Lu Junchang we suggested that Darwinopterus might have a tail of rather intermediate length between the classic ‘long’ and ‘short’ tails and this specimen might be going the same way. Not only that, but the tail also seems to have relatively short zygopophyses that are barely as long as the abutting centrum, whereas Darwinopterus at least has very Rhamphorhynchus-like ones that are very long.

The fifth toe also seems to be something of an intermediate – it is not a small nub like the pterodactyloids, but nor is the second phalanx that long and it’s not curved either as in other basal forms. Finally, the wing metacarpal looks to my eye to be rather longer than in other non-pterodactyloids. In other words, at least some of these features look to me not just to lie between the non-pterodactyloids and pterodactyloids, but actually somewhere between what we see in Darwinopterus-like animals and the pterodactyloids.

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In short, this is not just a lovely-looking and intriguing specimen, but it certainly helps to fill in the ‘missing’ part of the Solnhofen and surrounding beds (this one is from Painten). Moreover, at first glance at least, it offers some tantalising prospects for looking at the evolution of characters towards the origin of the pterodactyloids and the changes especially to the wing metacarpals, tail and feet (all key characters for wings / control surfaces) and what this may have meant for their biology. More on this and other specimens is coming, so there’s some interesting work to be done and much to find out.

Tischlinger & Frey. 2014. A new pterosaur with mosaic characters of basal and pterodactyloid pterosauria from the Upper Kimmeridgian of Painten (Upper Palatinate, Germany). Archaeopteryx, 31: 1-13.

 

Edit: Helmut has asked me to clarify that in the paper he and Dino do not say this is an animal likely to be specifically part of the Wukonogpteridae (i.e. Darwinopetus and kin) but suggest it is closer to the pterodactyloids.

The filamented Psittacosaurus

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By now most people with even a passing interest will be aware of the fact that there are now a number of specimens (and indeed species) of ornithischian dinosaurs that are preserved with some form of filament-type structure which, superficially at least, bear some resemblance to primitive feathers. However when the first candidate was announced, this specimen of Psittacosaurus housed in Frankfurt, it inevitably causes something of a furore with many suspicious of the data and suggestions that the filaments were simply coincidentally preserved plant stems or something similar.

The discovery of multiple specimens of Tianyulong inevitably make this rather more plausible as a real find, though of course a few more filamented Psittacosaurus would be nice. A third taxon is apparently now know but sadly illness led to a no-show at SVP so few have seen anything of this new find. Still, the original find is an impressive specimen, but doesn’t seem to have really been thoroughly described or illustrated too well and as I’m in a position to at least partially rectify that, here’s some photos I took of the specimen on my recent trip.

I have actually seen this before years ago but extremely briefly, and have also seen a superb cast of it in the Carnegie (my photo of which actually popped up in a dinosaur text book recently, [with permission I should add] such was the quality of the copy). However, I’d never really *looked* at it properly and actually spending a few minutes (even through a glass case) reveals some lovely details.

First off, it’s big. The biggest specimen I’ve seen by far for this genus, though the head is not that large compared to the rest of the body. Then there is skin pretty much everywhere – this does turn up in Liaoning not too infrequently, but rarely to this extent or quality. It covers large chunks of the animal and even completely covers large chunks of the bones in places (just look at the femur) and it looks like there’s a pile of gastroliths in the gut that are also covered.

While I’d be very cautious about interpreting the extent of the skin as being directly linked to other soft tissues, the extensive ‘flap’ behind the hindlimb would correspond with what you might expect from large retractor muscles there and so might well be genuine. Not only that, but there’s quite a bit of texture to the skin and in a couple of places it appears to have a different surface texture to others (see the underside of the base of the tail, and the area around the toes), which could also be genuine. On top of that, both the individual scales are clear in some places, and are even coloured differently (the larger ones are black) implying at least the possibility of this representing a pattern on the animal, and this changes along the body (look a the concentration in the tail, compared to the legs) though again:caution. It does look rather like this little patch that I featured years ago which is rather neat. Finally, this pattern also extend onto bones that are not obviously covered with skin (see the distal forelimb for example) with apparently the stains or some other taphonomic artefact of the scales left on the bones themselves.

And yes, then there are the filaments. Sprouting up off the base of the tail and extending most of the way along its (incomplete) length. They are rather thick and clearly somewhat stiff, but also flexible enough to bend under their own weight. While not a common reference, they look a lot to me in terms of  their apparent properties like the tail hairs of giraffe (though much, thicker). It’s a real shame they are at least in part cut off the edge of the slab, but certainly appear to have stopped appearing well short of the end of the tail, so their full extent does appear to have been preserved.

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I think that’s everything I can reasonably (or even unreasonably) speculate about this specimen without, yknow, actually going back and reading the original paper and associated commentary. However, the really key thing is of course that here’s some nice pictures of this and it gives a welcome opportunity to revisit this important and interest specimen.

More on the 11th Archaeopteryx

DSCF9843Continuing my collection / database of Archaeopteryx images, it’s time to increase it a little further. Last week I helped out at the Natural History Museum’s ‘open evening’ called “Science Uncovered”. I was there basically to be a scientist for people to talk to, but there were whole stands from other universities with research connected to the NHM and of course a raft of curators, researchers and other staff bringing the behind-the-scences stuff to the front of house. One special had been laid on that really drew the crowds – the 11th Archaeopteryx specimen.

Although it has appeared on here before, this is the first time I had seen it and was able to take some notes of features and indeed get a few photos. The lighting was absolutely nightmarish, but between tons of photos and a bit of tweaking of balance levels I have produced at least a few that are not too terrible, though at not very high resolution and mostly taken at a pretty low angle. Enjoy (as far as you can).

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An appeal for data on dinosaur tail data

Regular readers should be familiar with my 2012 paper on the lengths of tails in non-avian dinosaurs (those who you who missed it, for shame! can catch up with my post here). In this I looked at the general lack of complete tails in the fossil record, but also showed that tail length varies considerably in dinosaurs, and thus should not be included in length estimates or mass estimates derived from length.Collecting data for the paper I scoured a number of museum collections, went through as much of the dinosaur literature as I felt able, and also contacted numerous researchers and curators to ask for any ideas and things I might have missed or undescribed specimens hidden in basements and drawers. Many people were generous with their time and knowledge and by the end of it, I was really pleased with what I had in terms of a dataset.

Almost inevitably though, without hours of publication and my blog post on the subject, people started contacting me with new leads. Many were things I had looked at and decided were not complete, but some were things I had missed and represented additional data. Great though this was, there was not a lot I could do with even a handful of new data – the paper was done. However, inspired I did dive back into the literature and had another look and did find a few more and as you may have guessed, have now got as far as I, or rather we, can. This time out I’m collaborating with Scott Persons (who has been doing a lot of his own tails stuff) and a mathematically inclined colleague Steve Le Comber.

Scott and I have pooled our resources and have now found nearly 50 dinosaur specimens with complete tails, though we have this time out also been including specimens with ‘nearly’ complete tails. Obviously subjective, but we’re working on that.

Anyway, we’re appealing for more data. If you are aware of a dinosaur that has a truly complete (every single caudal vert, down to the last nub) tail, that’s not on the list, then do please let us know. If you know of something that’s near complete (maybe just a tip missing, or a couple in the middle or similar) do also let us know. Please be as specific as possible – “I think I saw a hadrosaur with a good tail in the AMNH” isn’t going to win you any prizes or get us anywhere, and we have at this point checked out a lot of material. On that note, all we can really offer is a mention in the acknowledgements for good leads that yield datapoints, and this may also include some limited measure of gratitude, or even a pint at the next conference where you catch us. Maybe.

Here are the lists of what we have to date.

Complete tails:

Othneilosaurus SMA 0010
Jeholosaurus IVPP V 12529
Scleidosaurus NHM R1111
Scutellosaurus MNA PI. 175
“Saichania” MPC 100/1305
Pinacosaurus PIN 614
Dyoplosaurus Arbour et al., 2009
Dryosaurus YPM 1884
Tethyshadros Dalla Vecchia, 2009
Edmontosaurus Lull and Wright, 1942
Lambeosaurus ROM 1218
Corythosaurus ROM 845
Hadrosauridae indet TMP 1998.58.01
Centrosaurus Brown, 1917
Psittacosaurus Sereno, 1987
Psittacosaurus IVPP V 120888
Coelophysis AMNH 7229
Sinocalliopteryx JMP-V-05-8-01
Gorgosaurus Currie, 2003
Gallimimus Osmólska et al., 1972
Ornithomimus TMP 1995.11.001
Caudipteryx IVPP V 12430
Nomingia Barsbold et al., 2000
Microraptor IVPP V 13352
Mei Xu and Norell, 2004
Jinfengopteryx CAGS IG 040801
Archaeopteryx Wellnhofer, 1974
Epidexipteryx IVPP V 15471
Lufengosaurus Young, 1941
Camarasaurus Gilmore, 1925
Opisthocoelicaudia Borsuk-Bialynicka, 1977
Protoceratops Fastovsky et al. 2012
Protoceratops Fastovsky et al. 2012
Leaellynasaura Herne pers comm
Chasmosaurine Mallon, 2010
Stegosaurus SMA 0092
Archaeoceratops IVPP V11115
Parksosaurus ROM 804
Anchiceratops CMN 8547
Microraptor Li et al 2012
Anchiornis IVPP
Sinusonasus Xu & Wang 2004
Spinophorosaurus Remes et al 2009
Kentrosaurus Holotype
Ornithomimid TMP 90.26.01
Tenontosaurus OMNH data

Near complete tails:

Epidendrosaurus IVPP V 12653
Sinornithoides IVPP V9612
Ceratosaurus USNM 4735
Khaan IGM 100/1127
Corythosaurus Lull & Wright, AMNH 5240
Anatosaurus Lull & Wright 8399
Anatosaurus lull & wright
Tianyuraptor Zheng et al 2009
Apatosaurus Gilmore 1936
Juravenator Chiappe & Goehlich, 2010
Sciurumimus Rauhut et al 2012
Psittacosaurus sinensis IVPP V 738
Psittacosaurus IVPP V14341.1
Psittacosaurus IVPP V14341.2
Psittacosaurus IVPP V14341.3
Psittacosaurus IVPP V14341.4
Sinocalliopteryx Ji et al 3007
Sinosauropteryx Currie & Chen 2001
?Heterodontosaurus MCZ 4188

Any other suggestions (specimens or papers), please do add them to the comments below. All help is most gratefully received.

Species recognition in dinosaurs? Not so much

Those with an interest in dinosaur cranial crests and exaggerated structures (which should really be everyone since they turn up in pretty much every major lineage one way or the other) will probably be aware of the exchanges going on in the literature over these features. Although myself and colleagues have been advocating that sexual selection (and or socio-sexual signaling: the two can be hard to separate) is a likely strong candidate as the prime driver for many of these features, others have been advocating that this is not the case and instead the answer lies in species recognition. The latest to delve into this area is a paper I’ve done with Darren Naish and is the first time we’ve addressed this issue directly. While we have written or contributed to a number of efforts looking at support for sexual selection in dinosaurs, this is the first time we have tackled the other side of the problem.

The paper originally started as a long section that was included in our paper on mutual sexual selection with Innes Cuthill, but as we were later forced to cut down the length of the submission, this was a section that was relatively easy to prune as tangential to the main issue. However, we felt it needed saying and with new data coming out and the discussion ramping up, we revived and revised the work and it is now out. (Well, it has been in press and available for a while but is now properly out).

This is an important area for discussion – after all, the horns, crests, frills, plates, bosses and the rest (not least feathers) are key features and adaptations in various dinosaur lineages and trying to work out how they might have been used and what this means for evolutionary drivers and patterns is going to be a major issue. It’s hard to really understand stegosaurs or ceratopsians say if you can’t say that much with confidence about their ‘bonus’ features. While obviously each clade, or even each genus / species probably needs to be taken on a case-by-case basis when it comes to detailed analyses, some gross patterns can be seen or at least discussed. In the case of species recognition, is it even an actual ‘thing’ when it comes to exaggerated structures, and if it is, how is it supposed to work. The hypothesis has enjoyed some support in the literature for some unusual dinosaur features so it’s well worth examining.

Species recognition (in the context of exaggerated structures) for those who don’t know, is the idea that individuals of a species use these features to help them recognise cospecifics with to ensure they mate with the right species, or to maintain herd coherence. In short, carry round a key feature and you should be able to make it easier to stay in touch with the right animals and avoid the wrong ones. Various lines have been put forward to support this idea (in general and specifically towards dinosaurs) but we feel that none of them actually stack up and some have some serious problems.

First off is a pretty big issue – to our knowledge there is no evidence of any living species using some form of crest or exaggerated structure for species recognition. Individuals of species do recognise each other (not a big shock) but actually things like antlers or casques don’t seem to form part of the pattern that conspsecifics recognise. This may not be a big shock, after all, you can recognise a species by the overall appearance (size, shape, colour), their smell or specific sounds they make, behaviour, and other features. On top of this, some species are very varied in appearance for the big features (antlers of deer look very different as they grow, and are different between males and females and between juveniles and adults etc.) so relying on one feature is a bad idea at best, and a plastic one an especially bad call.

Plus of course, you often get closely related taxa that are sympatric. Is some big set of horns going to help you correctly identify conspecifics if there are half a dozen similarly-looking species also in the area? Look at things like African antelope and gazelle, or more extreme examples like tyrant flycatchers. We have trouble telling them apart sometimes based on their morphology, yet they seem to have no trouble. If this is so critical to dinosaurs, why to the iguanodonts seem relatively free of crests, but the hadrosaurs go nuts with them? And why are they all so similar in general form between species when they are supposed to help separate them out? Surely they should be divergent, not all similar in appearance. And why do we see things like Wuerhosaurus or Spinosaurus running around with all this weight to make sure they don’t mate with the wrong species when there are no other members of their clade to get confused with?

In some cases we see both issues coming together. If we look at the various small protoceratopsians of China / Mongolia, we see disagreement between researchers as to how many species (or genera) there may be. What is notable however, is that the characters being used to separate them out don’t typically involve the frill or bosses of the skull, and where they do, may be things that are not externally visible (e.g. the width of the media bar in the frill). In short – if there are multiple species here, the frills are apparently similar enough that we can’t separate them and so are unlikely to be part of the identity concept of the animals. If however, there is only one species present, then we are back to the paradox of a large frill being carried around but with no other species that could confound any signals.

On top of that, is it really worth it? After all, while you do want to stay in touch and make sure you mate with the right species, bolting on a good few kilos of bone to your head, and then the extra muscle to support it, and then lugging that around for your entire life is a lot of effort. When you can probably already identify conspecifics by their colour, patterns, scent and calls (of simply because nothing else like them at all is on the same continent) surely these would experience strong negative selective pressures if they didn’t have any other support.

Furthermore, how would such features ever evolve? If the populations / species were allopatric then we return to the situation of them not having another group to get confused with and crests are unnecessary for recognition. If they were sympatric though, how would this work? Pretty much the definition of a natural biological population is one that is breeding within itself, but here we’d have to have a population diverging because some don’t recognise each other as conspecifics even though we would expect, pretty much by definition, there not to be too much difference in structure shape between them (e.g. a tiny crest vs no crest). Now some animals might prefer each other, but that’s mate choice, not recognition, and there would have to be enough individuals for this to work – one mutant with a crest when no one else has one is not going to start forming a new species, and if there were a bunch of the with the new crest they’d also have to identify each other as different and avoid mating or hanging around with the others. So how would a large feature that’s for correct recognition allow a population to split in this way? To us at least it appears most unlikely to occur at all, let alone repeatedly.

In addition to this, there is rampant hybridization of closely related species in the natural world (and indeed in captivity). Even extravagantly ornamented species like pheasants with numerous adornments and bright colours and patterns hybridise regularly – clearly no matter how extreme the cue, at least some animals regularly have problems with them or are indiscriminate, but either way they are not that effective.

While some data like the apparent rapid growth of structures late in ontogeny has been used to support the idea that they are characteristics involved in socio-sexual signaling, it’s also a problem for the herd coherency part of the model. After all, lots of juvenile dinosaurs are known from aggregations suggesting they spent a lot of time together, even when the adults did not appear to. If these features were key, we’d expect juveniles to have them, and adult perhaps to shun them when they were no longer needed, but instead the opposite is true. In general the herd coherency argument is a bit odd anyway, again you have lots of ways of identifying and keeping in touch with conspecifics and some are clearly better than visual aids. Scent can have a temporal component, and vocalizations can be interactive beyond line of sight (especially useful in forests, or when things are behind you, or you are foraging and looking down etc.). No matter how big they are, visual structures are not always going to be that useful, even if they are unique.

In the increasingly infamous issue of Torosaurus and Triceratops, if these animals are truly conspecific then for a start we are back to the issue of ‘lone’ taxa (I don’t think Leptoceratops is going to be much of an issue here) and the pointlessness of crests where none are needed. On the other hand, this is also potentially a problem for the mate recognition idea. We know that at least some dinosaurs were sexually mature before they were osteologically mature and this could be the case for these animals too. If so, then the alleged transformation between one morph and the other would create confusion – both the Triceratops morph and the Torosaurus morph (or indeed anything in between) would be viable mates.

In short, we really have no clear evidence for species recognition in any living species, and that alone should make it unlikely to have been a key player across dinosaurs for the whole Mesozoic. Such structures would be costly, and yet not necessarily do the job it is supposed to with other signals being cheaper and just as effective, or more effective in many circumstances. It’s not clear why it should be so important for some clades and not other similar forms (iguanodotids vs hadrosaurs for example) and is clearly either redundant for some taxa, or would not actually reduce confusion. Nor is it clear quite how this would evolve in the first place, or why it would be sustained, and hybridization suggests that crests alone would not even prevent incorrect matings. Put this all together and we feel that there really is no good support for the idea of crests and other structures being primarily used in species recognition. They did of course likely have an effect – it would be odd if Stegosaurus or Corythosaurus didn’t use their respective features as part of how they identified one another. But that does not make them the prime, or only, driving force of all these different features in all these different lineages.

There was a fashion in dinosaur palaeo to write off any odd structure as simply sexual selection and leave it there. This was rightly railed against, but what was often criticised was the fact that sexual selection seemed undiagnosable in the fossil record and so the problem was that it was untestable rather than the fact that such throwaway remarks devoid of context or explanation do little for the subject. Now we are in the odd position where rarely you see very similar comments (in terms of their style) about species recognition popping up in the literature about exaggerated structures despite the lack of support for it, and the now (well, we think), strong cases made for sexual selection, or at least it’s assessment. Although previously the case for sexual selection was pretty weak, it is at least an extremely common phenomenon in living taxa and with obvious powerful effects on anatomy and behaviour. Species recognition has not yet even been shown (in relation to exaggerated structures) in any living clade, and while offhand one-line explanations are not the way to go, it seems odd that one has been replaced with the other.

 

Hone, D.W.E., & Naish, D. 2013. The ‘species recognition hypothesis’ does not explain the presence and evolution of exaggerated structures in non-avialan dinosaurs. Journal of Zoology, 290: 172-180.

Sexual selection in the fossil record

Regular readers will know that for the last few years I’ve been slowly building a research profile concentrating on the behaviour and ecology of dinosaurs and pterosaurs. While the various papers on feeding behaviour, stomach contents, predation and niche partitioning in theropods has been the more high profile, I think the work on sexual selection is arguably more important as it potentially has profound implications for how we interpret all manner of fossils and how they may (or may not) relate to one another. After all, there’s a major ecological and taxonomic difference between identifying two species of a clade, and one species that exhibits major sexual dimorphism.

My colleagues and I have already looked at the idea that sauropod necks were driven by sexual selection, and after much strife, finally got a paper published discussing mutual sexual selection and the implications that has for diagnosing taxa in the fossil record and what it might mean for parental care and other aspects of behaviour. There’s more to come in these areas as I have further work planned and am involved in some other areas linked to this, so the area is growing rapidly and, I hope, ripe for a general revisit in the literature. However, while these papers have in large part being about drawing out some false assumptions in the literature and providing new hypotheses about sexual selection that could be looked at in the fossil record, they were a bit short on how this could be done, and were if anything, narrow in focus (not that Ornithodira is a small group, but its got nothing on Animalia).

So then to a paper in TREE that came out yesterday online. Led by entomologist Rob Knell, it also includes  Darren Naish and myself and attempts to provide a review of the entire question of sexual selection in the fossil record. We look at ways in which this could be diagnosed, some false dichotomies and assumptions that have been put forwards in the past, try to identify some key features that may help diagnose sexual selection and look at some of the more convincing cases for this that have been put together to date. Clearly there’s a limit to what we can get into under 10 pages for what is supposed to be a review, but I think there’s some nice synthesis in there and a bit more “we can try doing this”-type stuff, that just covering what has been said before. Anyway it’s out and available (though behind a paywall, sorry) so go take a look.

Knell, R., Naish, D., Tompkins, J.L. & Hone, D.W.E. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution, in press.

Variation of tail length in dinosaurs

So I have a new paper out and inevitably I’m going to talk a bit about it on the Musings. While I’ve had a few abstracts and the odd short paper out as sole author, this is pretty much my first proper effort in a major journal where I’m the only author. Not that I didn’t have help of course (which is what the acknowledgements are for) and I do especially want to take the opportunity up front to thank various people for their contributions and help, but most especially Susie Maidment for her help in data collection.

Right, onto the actual paper. Way back in 2010 I was looking at pterosaur tails in connection to an anuroganthid that turned up with (for one of them) an unusually long tail. This got me thinking about dinosaur tails and it struck me that while we obviously had some taxa with short tails (like Caudipteryx) and some looked pretty long (like Diplodocus) that no one seemed to have looked at just what kind of variation there was. Moreover, the more I thought about it, and the more I looked through papers and collections (and then later on asked various colleagues) the more often I came across ‘complete’ specimens that were nothing but when it came to the distal caudals. And so began my investigation into the tail lengths of the non-avian dinosaurs (though admittedly Archeopteryx sneaks into the paper as do the scansoriopterigids). Obviously the paper is there to be read, but hopefully this will serve as a quick summary and discussion of the basic points for those who can’t get it or don’t want to read it.

The first thing to note is that actually we really do have very few dinosaur fossils with complete tails. Despite a good hunt through the literature, a couple of collections, and exchanges with a number of colleagues I was able to track down very few specimens where every caudal was known. Even in things from localities like the Jehol and Solnhofen where skeletons are preserved in beautiful condition and soft tissues are common, there are actually very few specimens with every caudal vertebra preserved. Sure the sauropods might expect to do badly given how incomplete they always seem to be, and we’ve got more than a few dinosaurs known from only fragmentary remains. However, on the other hand we now have thousands of dinosaur fossils, and some species are known from dozens or even hundreds of good specimens and many of these are from sites of excellent preservation. But for all my searching and asking, I found less than 20 dinosaur specimens in total that have every caudal preserved. That’s really very low. Even things like ankylosaurs and dromaeosaurs with those lovely reinforced tails don’t seem to do any better either, complete tails are really, really rare.

Now there are a good number that are probably close to being complete with only a few distal ones missing, but obviously quite how true this may be is hard to determine. Sure there tends to be a general tapering of the size of the caudals which can give you a reasonable guess as to where it likely ends, especially if they are very small when they stop, but things like Diplodocus with it’s near endless rod-like caudals or the sudden stop in Nomingia means you could easily be wrong. In short, while a specimen like Sue we can probably have a pretty good guess how long the tail was and quite how much was missing, for plenty of other species it’s not going to be so easy. And things get worse from here.

Not only are there few dinosaurs with complete tails, but in one wonderfully illustrative case we have some major intraspecific variation. Two specimens of Leptoceratops are preserved side by side and so we can be confident that these aren’t just the same species, but are even from the same population. The problem is, one has 10 more caudals than the other, and their tails are proportionally rather different in length too. There’s quite a bit of intraspecific variation there, and indeed a look across other amniotes suggests that this is quite common – caudal counts and caudal lengths can vary a lot in tetrapod species. Tail length is sexually dimorphic in some snakes for example, and can vary a lot even in mammals.

Interspecific variation can be high too, which means it may not be safe to reconstruct missing tails from even close relatives. The wonderful little Epidexipteryx has the joint shortest tail known for any dinosaur that I found, but it’s sister taxon, Epidendrosaurus, has one of the longest tail known (and that one is incomplete and would have been longer still). While this might be an unusual case, there’s a decent bit of variation seen in a couple of other clades too.

All of this means that we need to be a fair bit more careful when talking about dinosaur tails and especially when it comes to recounting their size in terms of length. The length of a dinosaur is absolutely ubiquitous in the media as a measure of size and it turns up in a few papers too. However while some taxa are of course known absolutely in terms of their length, and many are probably about right despite being not entirely complete, others would seem to be little more than a best guess – and a best guess based on not very much to be honest. The data for sauropods in particular seems to be incredibly sparse and accounting for the inter- and intraspecific variation seen, I don’t think I’d be confident in reconstructing the tail of something like Argentinosaurs to within even a 50% error – it could be really long or very short and there’s no way of picking one over the other. Even ignoring some of the outliers, there’s a fair bit of variation there and can have quite an effect on the appearance of an animal.

Scott Hartman has been good enough to make this for me – a Spinosaurus with a short, ‘normal’ and long tail. All of these kinds of lengths can be seen in various theropods and to my mind are all plausible – indeed, we’ve been quite conservative here and could easily have copped off another hatful of caudals or plugged on a good few more and the results would still be quite plausible and within the bounds seen by other theropods. Of course note that while the length of that tail in each varies enormously, and as such, so too does the total length of the animal, the mass would not change that much. A 16 m long Spinosaurus sounds massive compared to a 12 m one, but if the only difference is in tail length, then in terms of mass there might not be much in it, just a few tens of kilos in a multi-ton animal.

So, estimating the length of a dinosaur without a mostly complete tail could give you a rather inaccurate number. There does seem to have been a fair bit of inaccurate information out there in the literature in the past with people giving ranges of caudal counts for groups when individuals were known with much higher values, and clades being described as having ‘long’ tails when they didn’t (or there was no real way to tell). However, there is a little more to this, I also did an analysis where (as far as possible, which admittedly wasn’t that far) the variation in tail length was compared to snout-vent length.

When examining living species, most biologists use snout-vent length as a proxy for how large animals are. After all, the tail length can vary a lot as we’ve seen, and even weight isn’t a great measure for a lot of living animals as it can fluctuate a lot on an annual basis, and of course isn’t available for specimens in museums. So a measure from the tip of the snout to the vent / anus is a common measure of size but we don’t seem to use it much in palaeontology (and certainly not for dinosaurs). In short therefore, we’re using a measure which not only includes a lot of variation in the tail that might screw up the results (and that most of the time we don’t know for sure anyway), but it’s not compatible with other datasets on extant taxa. The question is though, would the equivalent be any better for dinosaurs?

My simple analysis suggests so – that from the available data, tails are rather more variable in dinosaurs than the body. As for the vent, well, that we obviously don’t know exactly as a decidedly soft tissue structure so I plumped for the last sacral being a point that would be close to the vent and an unambiguous point on the skeleton that would be easily identified and would likely be preserved. This measure (snout-sacrum) is one I suggest we should start using when we want to talk about dinosaurs sizes in terms of length.

So there you have it. We don’t seem to have too many dinosaur tails, those we have suggest much inter- and intraspecific variation and so estimates of total length or using total length may not be very reliable. Snout-sacrum length is probably more reliable and in any case would bring the data in line with that used by most biologists. My final note though is an appeal – despite the work I did trying to uncover dinosaurs with complete tails, I’m sure I’ve missed some. Perhaps they’ve simply not been described, or are squirreled away in obscure journals, or are only listed as paratypes etc. I have seen a couple of things published since this work was finalised that look like the tail is complete but where the paper doesn’t actually say and it’s not entirely clear from the figures. I can’t believe that some of those massed ranks of undescribed Psittacosaurus, Protoceratops and various massed ranks of hadrosaurs and iguanodontians don’t have a few more complete ones lying around that can be measured. So if you do know of any specimens out there with complete tails (and better yet, totally complete specimens in terms of the skull and vertebral column) do please let me know. I’ve exhausted all the easily available avenues to date, but I’d love to do the analysis again with much more data. One day.

Hone, D.W.E. 2012.Variation in the tail length of non-avian dinosaurs.Journal of Vertebrate Paleontology, 32: 1082-1089.

Archaeopteryx

It was suggested to me not too long ago that I might well have the best and most extensive collection of images of Archaeopteryx specimens online. Between having seen quite a few of these on display and having taken photos myself, plus the near endless collection generously sent on by Helmut Tischlinger of his UV works, nearly every specimen is on here and most with multiple views, close-ups and in UV. I am still missing a couple, but I’d have to agree that I’ve yet to see any online collection that can rival mine. Still, they are scatted around all manner of posts and so aren’t necessarily that easy to find. No more, here’s they are all are for convenience.

Cast of the London specimen

The Berlin specimen

The Berlin specimen returns

The Munich specimen

Mayr with the Eichstaett specimen

Eichstaett, Thermopolis and Berlin in UV

Solnhofen, Eichstaett and ‘chicken-wing’ specimens

Close-ups of the Solnhofen specimen

Solnhofen specimen in black and white

The Thermopolis specimen

The Daiting specimen (and in UV)

The most recent (11th) specimen (and in UV)

More on the 11th specimen

Yet more Archaeopteryx – Chicken Wing, Haarlem and Maxberg

If you have others you are happy to share and have permission to distribute, do please let me know and send them on. This is simply there as a reference collection for people to learn and work with, but obviously more (or better, not all of these are great) would be lovely to have and make this still more useful. I know there are some scans and images out there and it’d be great to round this out as a clearing-house for people who want to see and compare these specimens.

Brunn – not the Solnhofen

At the end of my last post I raised a most significant point – Bellubrunnus isn’t a Solnhofen pterosaur. While it’s easy to think that those Jurassic lithographic beds from Bavaria are the Solnhofen, it’s not the case. Like all rock records, different divisions are known and are grouped in various hierarchical clusters. The Solnhofen is home to a lot of important species (Archaeopteryx for starters, not to mention all the pterosaurs and insects and plants and fishes) and a good deal of work has gone into working out the stratigraphy of all these different fossil-bearing beads, but not all lithographic limestones lie in the Solnhofen.

Obviously this doesn’t mean that an animal from one layer right above or below the Solnhofen didn’t overlap in time with other strata – the rocks don’t delineate when and where species lived. However, Brunn is rather older than even the oldest Solnhofen beds and from the Kimmeridgian rather than the Tithonian. While the rocks are of a similar kind and were put down in a similar manner in similar ecosystems, the two are different.

Work on the Brunn beds are still very new and I must confess I’ve not looked into it in any great detail (not least as all the literature seems to be in German) and have had to rely heavily on my colleagues here. Still, the two do seem to contain different taxa as a whole and while to date the higher vertebrates at Brunn have been few and far between, given the quality of the preservation, I don’t think there’s any reason to expect that we won’t get a lot more in the future. Moreover this does suggest that Brunn is different to the Solnhofen and so we might expect a different (if closely related) fauna to be present. In short, the fact that we now have literally hundreds of pterosaurs from the Solnhofen and no record of Bellubrunnus there, supports the idea that this is a different genus, and also the idea that there might be many more new pterosaur species in there to be found. At the very least, there is a lot more to learn from the Brunn biota.

One last point to address here lies in the temporal distribution of rhamphorhycnhines. The recently described Qinlongopterus is also known from a single, small, and young specimen, though it heralds from the Middle Jurassic of China. As described this taxon is really rather similar to Rhamphorhynchus and it was suggested that as such, the rhamphorhycnhines might be really rather stable as a group and went long periods of time with little morphological change. Obviously Bellubrunnus interrupts this apparent trend, as compared to the Middle Jurassic of China, it’s much closer in time and space to Rhamphoprhynchus, yet does have quite a few differences. This is probably due to that fact that unlike Bellubrunnus, Qinlongopterus is really badly preserved, and morphological information is rather limited. What can be seen in Qinlongopterus is very Rhamphorhynchus-like, but that’s not saying much since the condition of it means that not all the many details can be seen. Plus of course the young of species tend to be much harder to tell apart than the adults, since, well they don’t have all their adult features yet and typically the younger they are the harder that will be. So in fact this ‘stability’ is illusory based on the age and condition of Qinlongopterus and in any case is interrupted by the emergence of Bellubrunnus and its differing anatomy.

And on that subject, next up, that interesting tail…

Sciurumimus

Readers will remember a beautiful fossil from the Solnhofen being shown on here back in November of last year. People who have access to the internet will probably now now that yesterday the first formal publication on this animal came out. It’s now named Sciurumimus – the squirrel mimic – on account of the rather bushy tail. There’s already a ton of discussion on this online and quite some hefty coverage so I’m not going to dive into the ins and outs of feather distribution in theropods or the phylogenetic position of it. It is worth comparing it to Juraventor of course – sister-taxon to Sciurumimus in the analysis and from the same beds. Despite the obvious gross similarities, the authors do note a ton of small differences between the two that suggest they are genuinely distinct.

Of much more interest to the readers though will be the fact that once more Helmut Tischlinger has been generous enough to send me a variety of nice images with permission to publish them here. At least one of these isn’t in the paper and the res is pretty good so even those of you who’ve been able to peruse the PNAS paper might do well here, so enjoy. As usual my thanks to him for this very generous act and a reminder that these are his images and should not be reproduced without permission etc.

 

 

 

 

Issues on understanding evolution

A couple of things intersected over the last week or so that have had me thinking a bit more about evolution and how it’s presented. More specifically, I’ve increasingly noticed a phenomenon that seems to get little attention and might be worth a bit more consideration. In short, there do seem to be a good number of people who, for whatever reason, are really quite happy with the concept of evolution as a whole (species arise, natural selection happens, common ancestry etc.) but seem to profoundly misunderstand how and why it works.

It’s perhaps understandable that a lot of focus goes into winning over the people who don’t accept that evolution even exists, but we should not ignore those who are happy enough with the idea, but actually don’t understand it at all well. After all, they might well be vulnerable to misinformation or further misunderstandings, when in fact they should be the kind of people who would be resistant to such things. I’ve heard or come across all sorts of basic mistakes and misunderstandings like the idea that evolution is directed (or has some predetermined outcome), that mankind is all but inevitable, that evolution occurs at the individual level, that X is the exact and direct ancestor of Y and so on.

All of these things are the kinds of fallacies that creationists use to undermine evolution or promote confusion about how it really operates, yet these are also errors made by those who have no problem with the concept. While these mistakes are not ignored when it comes to public outreach in science, I do wonder if in part, we are paying too little attention to a sizable number of people who would benefit from knowing more and having a better understanding and appreciation of evolution, and likely be interested in learning more. We’re not talking about deep and complex evolutionary theory, merely some fairly basic concepts that should be easy and simple enough to explain quickly and effectively, the question is, are we doing that for the people who need it?

 


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