Posts Tagged 'tails'

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.

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.

Sauropod tails: up or down?

By now even the media (well most of it) has cottoned onto the fact that sauropods did not drag their tails along the ground like giant lizards, but instead held them off the ground behind them. Except, well, not quite always.

While sauropod footprints are common, there are the occasional set of tracks that also show a mark that is interpreted as (and can only really be) that left by a tail dragging on the ground behind. So what’s going on, is the tail up or down?
Continue reading ‘Sauropod tails: up or down?’


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