Archive for March, 2010

Linheraptor – another new dromaeosaur

Linheraptor life reconstruction. Courtesy of Matt van Rooijen.

One of the most exciting things that our excavations uncovered at Bayan Mandahu in the last two years can finally be revealed. Alvarezsaur expert Jonah Choiniere gets the credit for spotting a curved claw poking out of the sand back in 2008 while out prospecting with Mike Pittman. A quick dig revealed there was quite a bit more bone present of some theropod or other. However, as with many such events, the specimen was dug out and put in a plaster jacket without uncovering it so that it was protected from damage. Therefore it was only months later back at the lab when the jacket was opened and preparation of the specimen done that it was clear what was inside. It was this:
Continue reading ‘Linheraptor – another new dromaeosaur’

IVPP Crates

In a sense this picture post manages to avoid showing dinosaurs but I rather like it. The IVPP has a large number of casts of various Chinese dinosaurs and these are often sent around the country as part of travelling exhibitions on fossils and palaeontology. In order to help the locals keep track of which bits go in which boxes for shipping they have these little icons of theropods, ornithopods and sauropods. I think they are both quite fun and actually rather stylish and though it would be nice to include them here. I’ve shown the theropod here before, but here are some others.

Coming very soon, exciting new theropod goodness!

Superb article on science communication

Well worth five minutes of anyone’s time. Go read it. And here’s a nice satirical view of (sadly) what usually happens.

Both via Bad Science.

And while we’re on the subject, I’m still looking for nice archosaur photos for the Musings, and nice ‘anything biological at all’ photos for the new and improved (and very nearly here) Ask A Biologist. E-mails to the usual address please.

Ossification and preservation

While obviously working on dinosaurs means that you are primarily looking at fossil bones, these are not always the whole story when it comes to the skeleton. Obviously bits go missing, and whole skeletons are a rarity, unossified parts can also make themselves scarce. However, not all parts of the skeleton always even ossify – the skeleton is not synonymous with bones. Chickens have a mostly cartilaginous sternum for example.

So while a fossil might preserve all of the bones, it won’t necessarily preserve all of the skeleton. Add to the fact that as noted with ossified tendons, not all things that can ossify always do (and of course with tendons, most of them do not) making things harder. Coupled to this is the fact that, as with ossified tendons, there is likely to variation if how such a feature is expressed. You might have half a dozen good specimens with only one preserving a given feature. That might not be missing in the others, it simply ossified in one of them and not the rest. Part of this variation also comes from age, with typically older animals having more bones or parts of bones that are ossified than juveniles (or even other adults if it’s a particularly old individual) so this has to be factored in too.

This is an especially important consideration why trying to track evolutionary changes in groups where certain characters or bones seem to come and go regularly. An example are the clavicles / furcula that I touched on recently. If you match a phylogeny to the specimens we have with furculae / clavicles the picture is a little confusing with the elements apparently disappearing and reappearing multiple times. Part of this will be down to the incompleteness of some fossils, but it’s also likely to be in part due to how these bones ossify. Based on their inconsistent appearance and incomplete preservation in at least some taxa, it’s likely that they were largely present in most, if not all, theropods and merely remained as cartilaginous elements and did not ossify, hence their apparent (but not genuine) absence.

Characters can of course be lost, and reappear (we’ll be dealing with this issue next up) but caution should be taken in assuming that this is the norm. Obviously knowledge of the vertebrate skeleton really helps as some elements are more prone to this pattern of only occasionally being ossified, or ossification patterns changing during ontogeny etc. but the first assumption should not be that an element is genuinely absent, even when there is an apparently complete set of bones present. There’s more to the skeleton than just those lumps of calcium and phosphate based crystals.

More on ossified tendons

When covering ornithischian ossified tendons, I really only just mentioned their existence rather than what they were or what they meant, and the post rather implied that this was a unique situation. Far from it, they turn up quite often as you might have noticed if you ever took apart a turkey and looked at the legs and wings.

Tendons are of course those bits of tissue that connects muscles to bones. However, while this typically requires at least a small degree of elasticity, it is the muscles that really have to deal with that. If therefore you want those tendons to be especially strong and resistant (because they are taking some high loads) then they can be firmed up with a bit of bone. Quite literally part of the tendon ossifies and becomes bony tissue which of course massively increases its strength at the expense of elasticity.

While the ornithischians are of course a good example of this phenomenon, it turns up in other clades too like the nyctosaurian pterosaurs which have lots. Pterosaurs have interesting problems when it comes to attaching muscles on those massive arms and fingers and with the high stresses encountered through flight, it’s more of a surprise that more pterosaurs don’t have lots of ossified tendons than that a few do.

Ossified tendons (red arrows) on the arm of the nyctosaurian pterosaur Muzquizopteryx. From Frey et al., 2006.

While certain clades or genera are pretty consistent in the way in which tends ossify it can happen in most animals after an injury or a result of unusual stresses on certain muscles groups. This means that the pattern of expression is complex, and while the presence or absence of such tendons can be a useful diagnostic character, they are not necessarily the best ones to adopt. Some specimens of Pteranodon for example preserve ossified tendons, but they are very much in the minority, though of course owing to their overlap in the fossil record and their great similarity, it would be easy to misidentify a couple of wing bones with an ossified tendon as belonging to Nyctosaurus. They also have a role to play in revealing the presence of certain muscle groups since you can’t really get an ossified part of a tendon where there were no tendons to ossify so their presence can be useful when trying to reconstruct the soft anatomy of the animals in question too.

Diplodocus skull

This time out, it’s a rather nice cast of a Diplodocus skull at the IVPP. However, it’s mounted on the end of a Mamenchisaurus skeleton which rather reduced the impact.

Still, that’s not as bad as it sounds, for a very long time there was confusion and disagreement about what sort of sauropods were and although there were quite a few specimens known, no Mamenchisaurus had been recovered with anything like a decent skull. Thus not only did we not know what kind of skull they had, it was hard to guess what kind of skull they might have had since their immediate relatives were not known. As a result, you can see a Diplodocus, Shunosaurus or even Apatosaurus skull attached onto a Mamenchisaurus skeleton in various Chinese museums. Since they don’t always have the money to replace them, these things tend to hang around (and replacing a skull on the end of a 10+ m neck is no mean feat either) it’s perhaps no surprise, though can look a bit odd to those who know better.

Those who aren’t in the know will be pleased to find out that in 2002 a very complete and well preserved Mamenchisaurus was described complete with an intact skull. This looks, superficially at least, like those of brachiosaurs with a nice big internarial bar that arches off the top of the skull.

Dinosaur egg ID

Dinosaur eggs are, sadly, very often for sale as they don’t seem to attract the attention of the law in the way in which bones do (that and the fact that they are obviously easier to fake). But what fascinates me about them is the monotonous regularity with which they are identified as belonging to specific taxa. Quite a few people seem to be under the bizarre impression that you can diagnose the family or even genus of dinosaur that laid an egg based on, well, I’m not sure what, but I’d guess the size and shape.

The truth is of course that to look at, most dinosaur eggs are not really any more diagnostic than those of living birds. Some do have distinctive proportions or textures, but mostly they are much of a muchness, and there seems to be quite a lot of variation present, even within single species. Unless you find an embryo inside (or even the egg inside an adult), a brooding parent on top, or can get a sample under the microscope (and match it up to those for which embryos are known) it’s really quite hard, if not impossible, to tell what might have come out of any given egg. Thus, while we do have vast collections of dinosaur eggs, what actually laid them is, in most cases, a mystery for now at least.

These could be from anything really.

I had the fortune to spend some time with an expert on dinosaur eggs when out in Henan a few years back. After some scrabbling in a very productive egg locality I had fished out something like ten very different looking pieces with a variety of curvatures, thicknesses, and ornamentation on both the inner and outer surfaces. On asking I was told that none of them were diagnostic beyond one that ‘might belong to a theropod’.

More and more work is revealing which eggs likely below with which clades or more specific taxa, but the number of times I have seen a random egg or nest listed as belonging to a ‘sauropod’ or ‘hadrosaur’ or still more unrealistically ‘Tyrannosaurus’, is really quite unnecessary. In the case of people selling eggs it’s obvious that they want to increase the value of the material by putting a familiar name to the specimen, but the implied accuracy is nonsense. A little more depressing, I’ve seen a few museums try to pull off the same thing on eggs they can’t possibly have identified.

While it’s nice to poke fun and incompetent fossil dealers who are passing off illegally acquired material, there is a more general lesson here. For all that we do know about dinosaurs, there is, naturally, quite a bit we still don’t know. There are also areas that are often overlooked or neglected and personally I’d put dinosaur eggs into that category. There is a lot more information that can be gained from these once we can match more of them to their ‘owners’ and this and certainly will reveal more secrets in the future.

More for the journos

Having tried to help out with my last post in this area (hopefully without being too patronising) I thought I’d be a bit less helpful and a little more confrontational / exasperated in this one with some of the more obvious and constantly repeated errors that seem to crop up in dinosaur-related reporting. Rather like my good old ‘top 10’ for pterosaurs but a bit more generalised and directed more at reporting than general ignorance / inaccuracy.

As noted before on here, science progresses and while facts do not change, our interpretation of them does. Things go out of date, new ideas are added and new fossils are found or new hypotheses applied to old ideas. Still, some things are very basic or so outdated that it’s hard to imagine while they persist, yet they do. Ignorance can always be excused – not everyone knows everything and journalists are often asked to write things they know little about. Not doing basic research if however quite a sin, especially in these days of instant information access and when something like Wikipedia (for all it’s faults) can present you with at least a good starting point for further reading.

Bearing that in mind, here are a few of my biggest (and generally most unbelievable) bugbears in writing about palaeontology. Continue reading ‘More for the journos’

Bonus micro post – go read this blog

I really should have mentioned this before, but those on the lookout for a new blog to read that zoology / palaeo related should go and read Zygoma. It’s written my my old buddy Paolo Viscardi, museum curator and one of my chief lieutenants on Ask A Biologist (whose next iteration is about to take wing incidentally). Take a gander and enjoy a mix of  ‘what’s this specimen?’ fun, bad science reporting and general biological musings.

Melanistic dinosaurs

On a trip to the Natural history Museum in London aged about 10 my parents bought me a poster of various dinosaurs to colour in. I remember quite vividly tackling it with my felt-tipped pens and deciding that one thing I really needed to include was a black dinosaur. The Iguanodon I selected of course was a grave disappointment since I obliterated all of the black lines that delineated it’s arms and legs and scales (and of course the eye and nostril) so that I basically was left with a black blob filling (as I recall) the lower right portion of my poster.

I have on occasion nudged palaeoartists with a few suggestions in the past (like here and here) and this is another for the list – let’s have some more black dinosaurs. After all, not only is black quite a common colour in some animals (at the least there are plenty of black, or at least grey, birds) but dinosaurs would have suffered from the same mutations as other animals and the possibility of a melanistic Tyrannosaurs or Velociraptor to go with things like melanistic penguins or zebras would make a nice image as well as of course more common melanisitc animals like black leopards. So let’s see some black dinosaurs, or albinos or amelanisitc ones, the odd one must have existed from time to time.

Pterosaur tail vanes – a very rough diamond

Having briefly covered the presence of a tail vane (or otherwise) in various pterosaurs and glossed over their structure, it’s time to deal with a trickier subject – their shape.

Most palaeoart illustrations of tail vanes show a diamond or kite-like outline for a tail vane, but this shape is not actually seen in any adult rhamphorhynchoids. A long, narrow and paddle-shaped vane is seen in Sordes and Pterorhynchus and thus is likely the norm for the scaphognathines (the group to which both probably belong) at least. The biggest adult specimens of Rhamphorhynchus have a vane that is roughly in the shape of an equilateral triangle with one side at the tip of the tail and the correspondingly opposite apex lying anteriorly (like an arrow pointing forwards). So where does the diamond tail concept come from?

Dimorphodon with a diamond tail vane. Image courtesy of Luis Rey.

The key above is the word ‘adult’ – while previously specimens of Rhamphorhynchus were split into quite a number of species, more recently these were brought together as a single species by Chris Bennett, but one represented by numerous juvenile animals. Specimens of Rhamphorhynchus do have a diamond or kite tail vane, but none of them are adults (though they may be close to adult size), and indeed the presence of different vane shapes does correlate with the apparent age of the animals, thus these shapes do seem to be part of an ontogenetic sequence leading up to the adult shape of a triangle. The youngest specimens have a rather thing leaf shape or spear-head shaped tail, mid-sized specimens have the diamond or kite and one especially large and adult animal has the triangle.

Tail vanes from various Rhamphorhynchus specimens. From Wellnhofer, 1978.

The diamond has persisted in palaeoart for a number of reasons. First of all it’s already the most commonly illustrated tail van both in the literature and in reconstructions and thus will inevitable serve as a model for those following. It’s also present in probably the most specimens, and is present in the specimens that were referred to the type species of Rhamphorhycnhus. However, the application of this tail vane to pretty much every rhamphorhynchoid is clearly incorrect. Not only do we know that there is variation in the tail vane shape in rhamphorhynchoids (meaning that it’s not really more right or wrong to use a paddle vane or a triangular vane for anything outside of the scaphognathines or rhamphorhynchines) but adult Rhamphorhynchus probably don’t have a diamond tail.

It’s really time to ditch the diamond and I’d love to see some more illustrations of rhamphs without them. Sure, some Rhamphorhynchus had them, but probably not the adults that are most often illustrated and outside of that it’s hard to justify the use of the diamond all the time. Variety is, so we are oft told, the spice of life, so let’s see a bit of spice in those rhamphorhynchoid illustrations.

Pterosaur tail vanes – presence and structure

Time for some more pterosaurs since we’ve been rather short of them on the Musings for a while. It seems pretty well know than the rhamphorhynchoids are blessed with a long tail, but also a vane of soft tissue at the end of this. However, beyond this, things get a bit murky and quite a lot is often illustrated with little reference to the actual fossils. This is a bit of a surprise as there is really very little known about them since so few are preserved so it shouldn’t be too hard to check up.

First off, what does have a tail vane? Quite a number are known for Rhamphorhynchus itself, and one specimen of Sordes has one as does Pterorhynchus, and, errr, that’s about it. Aside from the taxa listed above, it’s probably fairly safe to assume that most, if not all rhamphorhycnhoids had a tail vane. Pterosaurs are generally fairly conservative in their anatomy, and of course when it comes to soft tissues, these are rarely preserved and so have to be inferred from the few that do have them. Anuroganthids near certainly don’t have one however – not only does the short tail of this clade argue against this mechanically (since the vane is thought to have  role in steering or steadying during flight) but we do have several specimens of anurognathids that preserve soft tissues in excellent condition with no sign of a vane.

Secondly, what lacks a vane? Anuroganthids aside, it’s generally considered that no pterodactyloids have one. Again the mechanics argument comes into play, but also again we do have a number (while admittedly very few) of pterodactyloid specimens with good soft tissues preserved and no trace of a tail vane. Given the huge change in character evolution from the rhamphorhynchoid to the pterodactyloid bodyplan (change in wing proportions, shape of the fifth toes and foot, tail length, skull elongation, neck elongation etc. etc.), this is pretty reasonable.

Tail vanes do turn up quite often in Rhamphorhynchus at least, and appear in cases where the wings are not preserved or not so well preserved which rather implies that they were fairly tough structures. Certainly they are more common and by inference, more robust than wing membranes or foot webbing at any rate (this also feeds back to the point about their absence in pterodactyloids – these should preserve if present). Structurally, all vanes have transverse banding across them which is presumably some form of reinforcement, though where the vanes are composed entirely of skin and interstitial tissues or have perhaps cartilage or anything else involved in their composition is not known.

But what shape were these vanes? If I had more time, that information would be appearing here, but I don’t so it won’t – more tomorrow.

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