Say hello to Aardonyx

The skull of Aardonyx, courtesy Adam Yates.

Hopefully you have now said you ‘hellos’ so we can actually talk about the animal. Published today, Aardonyx was described by a team led by Adam Yates of Dracovenator fame. The beast in question is a new sauropodomorph dinosaur from the Early Jurassic of South Africa and has a few rather neat things to tell us about the evolution of sauropods. As ever I don’t want to simply rehash the paper as I’m sure a number of bloggers will cover most of the things going on and I’m not sure it serves a huge purpose for everyone to say the same things! There’ll be plenty of discussion I’m sure online, so I’ll try to be specific.

Behold the (possibly) mighty Deinocheirus

There is a tradition in archosaur palaeontology to refer to things we don’t know much about as ‘enigmatic’, and while an appropriate term much of the time, it is annoyingly overused. Basically if something is interesting and very incomplete it is left as ‘enigmatic’ which is often a euphemism for “I’m going to speculate wildly because there is no good evidence to contradict me” or “I’m not going to say anything about it at all”. Deinocheirus, in the public eye at least, sits firmly in the former camp and one can see why.

Recovered from Late Cretaceous rocks the specimen consists of just a partial pair of arms. Very, very large arms to be sure, and certainly a theropod but after that things get murky. Most researchers seem happy with the idea that these likely belonged to some form of giant ornithomimid it has previously suggested to belong to a theirizinosaur. As a result of that lack of information (a pair of partial arms, described quite sometime ago, and in Russian as I recall) Deinocheirus seems to have entered into popular palaeo folklore as the great unknown theropod, thought I would have thought something like Gigantoraptor and the presence of other giant therizinosaurs would have left it without much potential glamour even if a complete one ever turned up. Still, it IS rarely figured and I have Max Langer to thank for this image from Warsaw (though it’s not clear if this is the original or a cast).

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The tyrannosaur overbite

Many thanks to Darren Tanke today for loaning me this photograph of a Gorgosaurus, one of a number of tyrannosaurs from the Late Cretaceous of North America. This is a great photo as it really shows off one outstanding feature of tyrannosaurs (and indeed theropods in general) namely the fact that the teeth and jaws of these animals do not meet together as they do for humans (and other mammals, and lots of other things). Instead, the  lower jaw slots inside the upper one so that the teeth move past each other rather than coming together.

However you almost never see this. In mounted skeletons the jaws are inevitably open to give a dramatic gape and this is mimicked in a huge amount of palaeoartworks. Even in scientific drawings the jaw is typically half open to show the anatomy of the mandible, or missing entirely. As a result, this is very rarely illustrated and thus I imagine appreciated by many people. So here you have it, the tyrannosaur overbite, with the teeth of the upper jaw being clearly visible as they overlie the mandible. Incidentally this is not an extreme version, I know of (but sadly have not seen) a Ceratosaurus where the teeth in the upper jaw are so long that they finish below the bottom edge of the mandible when the jaws are shut! Toothy.

 

 

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What is an arctometatarsal?

There are a great deal of technical words in science that people often dismiss as jargon, but as I have said (perhaps even more than once or twice) science writing is about brevity and clarity and technical terms are useful when properly defined. In stead of writing ‘that odd situation where the middle metatarsal of a foot is compressed proximally’ you can talk about arctometatarsals for example.

And with that horribly contrived introduction and definition under our belts we can move on. Arctometatarsals (sometimes referred to as ‘the arctometatarsalian condition’) are indeed as I described an unusual feature of some theropods whereby the central metatarsal of the three that the animal stands on (and thus number III) is constricted and covered by the flanking bones such that they splay out at the base. (For those who have missed out the metatarsals are the bones on the foot between the ankle and the toes – in humans at least the majority of the foot, though since theropods walk on their toes only, the metatarsal effectively add to the length of the leg).

You can see a nice example of an arctometatarsal here on this not great photo of Tarbosaurus and I’ve done my best to badly ink in the outlines of the other two bones in red. It should be clear that at the bottom of the middle metatarsal appears the same as the others but further up is appears to shrink and disappear behind the others. In fact is disappears *between* the others – it’s not behind them, but stuck between them. In some cases it can flare out a little at the other end, but usually it is reduced to a very fine splint of bone at the upper end.

This condition has actually evolved a number of times and is present in tyrannosaurs, the wonderfully weird alvarezsaurs (of which much more soon I hope), ornithomimosaurs, troodontids and even a couple of oviraptorosaurs. Among the more derived theropods it is then quite common and worth looking out for. Its exact function is not really known, but has been thought to correlate with running (and with the exception of the giant tyrannosaurs these animals are all good runners).

So there you have it – the arctometatarsal. It’s amazing just how much information you can cram into one word really – long live technical terms.

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Guest post: a new tyrannosaur – Alioramus altai.

Those of you at SVP will have already been aware of this new critter and I get to be smug and say that Steve Brusatte (formerly a guest poster on here with Shaochilong) showed me the photos months ago. However the paper is now out and Steve has been kind enough to write up another post for the Musings on his next groovy Asian theropod. Take it away please:

Anchiornis and the temporal paradox

So after the original Anchiornis paper and now the follow up things should be pretty clear about the identity of this animal – it’s a troodontid that looks an awful lot like a basal bird. This is no surprise given that birds and troodontids are very close relatives and that Anchiornis is an especially basal troodontid and thus is probably closer in appearance to other basal birds than many others of its kind, and of course the original specimen in lacking a head did not have all the characters that might have helped us solve this earlier. So now onto the issue of time and evolution which is nicely demonstrated here by the new find – the oft quoted and very misleading temporal paradox.

Anchiornis – again

Anchiornis. Modified from Hu et al., 2009.

OK by now the ‘secret’ is probably out and the ‘new basal avialian’ that my colleagues and I described earlier this year, Anchiornis, turns out not to be an avialian (or avian if you prefer) at all, but in fact is a very basal troodontid. Those new specimens I mentioned at the time brought in a ton of extra detail and information that allowed researchers to firm up the diagnosis of this animal and show conclusively that it is indeed a troodontid. There are some important and interesting lessons to take from this, both in terms of theropod and bird relationships and how new information changes perspectives. To try and avoid me rambling on and keeping the issues clear, I have listed them:

Pssst – wanna be a palaeontologist?

My target audience on the Musings is, at least in my mind, are those people who are not experts in dinosaurs or even necessarily that interested in the past world but still find life (prehistoric and otherwise) of general interest but perhaps find the mainstream media too lightweight and full on technical papers and blogs too detailed. However, if you ever wanted to make the step up and actually, you know, be a scientist here’s your chance.

Andy Farke, Matt Wedel and Mike Taylor have got together and perhaps insanely created the Open Dinosaur Project (which to me sounds like a veterinary issue). What is the wondrous concept I hear you ask? Well a lot of dinosaur research at the coalface simply revolves around collecting data – most notably measurements. How big each individual bone was in various dimensions can potentially tell you a huge amount about an animal: not just did it have long legs, but were they longer than it’s relatives, absolutely longer or proportionally longer, where they all longer or just the front legs, was this linked to their habitats or predators? This is great in theory but as I can testify, when you want to compare a few hundred animals, scattered in a few dozen collections worldwide and described in a thousand different journal articles it can take months of work to produce the data to make one graph that will support one paragraph in a published paper. It is, in short, labour intensive.

The solution? Open source palaeontology – if you have an hour to spare, pick up a scientific journal, get some data for them and enter it on their online database. And then, this is the good bit, not only will you be directly contributing to palaeontological research but they will invite you to be an author on the paper. Yes, you too can become a real published scientist with a real academic paper to your name. And the website contains ALL the information you need – it matters not if you have never read a paper before or don’t know your humeri from your femora, it’s all there. And don’t worry about access to the papers either – most of them are freely available online these days. All you need is a few *minutes*, an internet connection and a bit of motivation / interest in dinosaurs and if you are reading this blog you probably have all of them already. So head on over there and become a real researcher.

Since they have also asked me to try to generate a bit of discussion I will say this – I think they are going to run into some huge problems for all kinds of reasons and while I sincerely hope for the best and wish them well, I strongly suspect this may end in time consuming frustration. However (and this a ten storey ‘However’ with wall to wall carpeting throughout, chandeliers and a large sign outside says “This is a large ‘However’”) this would in itself be a good thing (the attempt, not the failure) – this kind of collaborative project whether between many academics or recruiting the public is likely to increase in science. More and more projects like this will appear (there are some like it on a much smaller scale) and learning how to do it, what the problems are and how to get past them will make the next attempt infinitely easier no matter how much of a failure this might be (and despite the pessimism above, they have a good shot at making this work). Good luck guys (you’ll probably need it).

And if you were wondering as I forgot to say so, their project is on ornithischian limb bones, hence the appearance of an iguanodontid in the middle of the text.

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Archaeoceratops

Well I’m back from a very busy week in Seoul and while I’m clearing out e-mails and so fourth, you’ll have to make do with a couple of quick picture posts to satisfy any archosaur related cravings you may have. Here we have the interesting little basal ceratopsian Archaeoceratops from Liaoning. Proper posts coming soon, promise – I have big series lined up on the problems facing vertebrate palaeontologists with the taxonomy of archosaurs. Won’t that be fun? (Probably not, but it might be educational, which is kinda the point).

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The other side of the Marginocephalia

Since I covered pachycephalosaurs the other day, it seem pertinent to put up a picture of a ceratopsian – the other group of dinosaurs that comprise the Marginocephalia. These are likely more familiar to many of you as in addition to ‘classics’ like Triceratops, I have also covered Protoceratops and Psittacosaurus on here at various times. Here however is the large ceratopsian Chasmosaurus, again taken from the Fukui Prefectural Dinosaur Museum. I’m off to Korea at rather short notice tomorrow, then off with a National Geographic film crew to Liaoning again and then off to the UK for SVP. As such the Musings may be a bit sparse over the next month, but I do have a fair few posts in waiting and I’ll have sufficient internet access to keep them coming, but my usual rate of one a day may go down a fair bit.

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Pachycephalosaur head butting

Despite my interests in dinosaur behaviour I have rather managed to avoid the question of pachycephalosaurs so far and with a couple of nice photos on cue it seemed a good time to discuss this at least superficially. I don’t think this clade has actually even been mentioned here at any point so this is longer overdue.

Since I try to cover even the basics of archosaur palaeontology on here I should probably give a bit of background to these bone heads (as they are occasionally know – the literal translation of the name being thick headed reptiles). Pachycephalosaurs are a group of ornithischian dinosaurs closely allied to the ceratopsians (the horned dinosaurs) and with them make up the large and important clade the Marginocephalae. They were herbivorous bipeds that only spanned a relatively small range of sizes from small to medium (compared to many of their relatives) with the largest genus, Pachycephalosaurus, being up to around 5 m long.

Obviously their most prominent characteristic is the massively thickened skull roof and the occasional fringe of spines and knobs that run around the crown of the skull. What these were actually used for has long been contested with the most obvious suggestion being that these were used to fight with, either with each other or to attack other animals (like predators). Evidence has gone backwards and forwards over this with papers saying the head could not have absorbed impacts of fighting, or could have done, that they would clash heads or would not and would target flanks and that these were ornamental or not. In short, the only real consensus is that there is no real consensus as yet.

This may come as a surprise as despite the obvious controversial nature of many questions in palaeontology many are at least close to a consensus or the evidence has started to tip decisively but here this is not really the case. Part of the problem is likely to be the sparsity of material – pachycephalosaurs are not known from many good specimens at all (half a dozen are known from only skulls, partial skulls, or just the domes) and some aspects of their anatomy are thus not well understood. Combined with the relative lack of interest in this clade (since almost everyone seems to prefer theropods) it is perhaps less of a surprise.

The lack of material in Europe especially and the fact that the group is not half as well known as the ‘classics’ like tyrannosaurs and ceratopsians, and their relative small size means that they rarely make it into dinosaur halls outside North America so I was pleased to see two different displays of them in Japan – the first time I’d actually seen any. At the top we have a butting pair from Tokyo and below the front/side and back of a skull from Fukui (both images used with permission). I hope more research goes into this area as it is genuinely fascinating and covers various aspects of mechanics, ecology and behaviour that integrate well and of course the application of data and studies from living animals would be especially useful.

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Reversing the hallux

The reversed hallux has long been an important aspect of the discussion of dinosaur habits, and more specifically the origin of flight though it might not seem so at first glance. The hallux is basically the technical term for what most people would call the big toe, that is, the first digit on the foot and its reversal (or otherwise) basically relates to the orientation it holds – does it point forwards with the other toes, or sideways, or has it reversed to point behind?

The reason this point is so often contested or debated lies in two simple truths. Firstly, birds with a reversed hallux are mostly perching birds – those that live in trees and perch on branches and by extension are generally decent fliers. Secondly, the orientation of the hallux is incredibly difficult to determine in flat 2-D fossils such as those we generally get for things like early birds and close relatives in the non-avian dinosaurs.

The result as you might have guessed is that palaeontologists are incredibly interested in reversed halluces since this may allow us to determine if early birds and (perhaps more importantly) their likely ancestors were hanging around (so to speak) in trees. However between the tendency for the hallux to come free from the rest of the toes and the fact that compression can lead to it lying in a misleading orientation on a slab means that reconstructing the original position accurately is difficult at best.

It will be no surprise therefore to learn that this has been controversial at best and for things like Archaeopteryx with multiple good, and conflicting, specimens know the debate has been long and remains (largely) unresolved. The picture here is of a birds from Liaoning that I saw recently and clearly shows the hallux facing behind on each foot with no obvious signs of dislocation. Convincing is this case, but unhelpfully this is rarely in the more interesting taxa.

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