Siberian dinosaur spreads feathers around the dinosaur tree
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Version 0 of 1. For the last 20 years, huge numbers of fossils from China have dramatically demonstrated that large numbers of dinosaur species that were closely related to the birds had all manner of feathers on their bodies. However, a new find named Kulindadromeus from eastern Russia published today in Science, suggests that in fact feathers, or at least very feather-like structures may have been present in huge numbers of other species of dinosaur, including those which are from totally different branches of the dinosaurian family tree to the birds. The dinosaurs are essentially split into three great evolutionary lineages. The theropods were primarily bipedal carnivores and ultimately gave rise to the birds, and all dinosaurs known with feathers are theropods of some description. The various groups that are evolutionarily closest to the birds are those on which feathers are normally found. Then there are the sauropodomorphs, mostly giant quadrupeds and herbivores with long necks (Diplodocus being the quintessential example) and while they may not look it, are the nearest relatives of the theropods within the dinosaurs. Finally there are the herbivorous ornithischians, which include everything else and home to a bewildering array of different body shapes, including armoured forms, those with horns and spikes and all manner of odd headgear, and both bipeds and quadrupeds. Although soft tissues like scales and feather are rarely preserved (there’s a reason most dinosaur exhibits in museums focus on bones) we do have quite a bit of information on the body cover of many dinosaurs. Now we can be quite confident that a variety of dinosaurs did have scales since we have various bits of fossil skin or skin impressions in rocks, but just because we have say some skin from the legs, doesn’t mean there were not feathers elsewhere on the body. In particular, feathers are rarely preserved as the local conditions have to be just right, so finds are currently largely limited to a few sites globally with some additional. Thus the possibility remains that many species had feathers but that evidence is just lacking at the moment. In some cases this is a reasonable inference since, for example, several tyrannosaurs are known with feathers, strongly implying that even Tyrannosaurus had them, but what about more distant relatives? In the case of the ornithischians, there are two dinosaurs that already preserve some covering that is at least non-scaly. One comes from a lineage of early ornithischians and another from the much later group of horned dinosaurs. Both have long and thin filaments on their bodies that are rather similar to the feathers seen in various fossil theropods and indeed some modern birds. While we are most used to thinking of the kind of feather than comes from the tip of a birds’ wing (the classic quill-pen type), birds have a wide variety of feathers including the simply fluffy down of chicks and the stiff bristles on penguins and the non-avian theropod dinosaurs were the same. Many have filaments that are rather like very long and quite thick strands of hair (stiffened, but rather flexible too), so did these ornithischians perhaps inherit their filaments from some earlier dinosaur before the split into the big three groups, or were these a couple of unusual one-offs representing a bit of evolutionary convergence. In short, how many times did these things evolve? If it was only once, then maybe many other dinosaurs had filaments or feathers too, including earlier theropods, and maybe even some of the sauropodomorphs. The problem is, even some other fossil reptiles have evolved some filaments too (including the flying pterosaurs), so a kind of simple filament might easily have evolved multiple times. What we don’t tend to see are more complex structures of filaments with multiple strands that are in part characteristic of later feathers and the relationships between scales and feathers or other filaments is also not clear. Into this problem steps the newly named dinosaur Kulindadromeus zabaikalicus described by an international team of researchers. Although its exact age is not clear, this new dinosaur it is from an evolutionary lineage of ornithischians that comes between the currently known filament-bearing ornithischians, and came at least 50 million years after the split from the theropods. These were small herbivorous dinosaurs, only around 50 cm or so from the snout to the base of the tail and would have been bipedal with long legs, but only small arms. Hundreds of bones and several skulls have been collected from sites in eastern Siberia but critically a number of them are preserved a variety of both scales and feather-like filaments. First off then, this extends again the number of fossil deposits from the age of the dinosaurs that are capable of preserving feathers. This adds to the growing list of sites in Germany, Canada, Brazil and two that extend across China and North Korea, and that alone presents the potential of many new finds of dinosaurs and other animals with soft tissues. We can expect Siberia to be a hot topic in future years of dinosaur research. Secondly there is the variety of different bits of covering preserved on different body parts. There are overlapping scales (rather like those seen on the feet of modern birds) on the legs and a second kind on the tail, but there are also small and near circular scales on the feet, though they are more similar to those seen on many lizards. This alone is rather interesting since overlapping scales are rare in dinosaurs, and mutiple scale-types in single animals are also unusual, but it is the filaments that are naturally getting the most attention. Again there are multiple types preserved across several specimens of Kulindadromeus with very simple filaments on the head, neck and body that are similar to those seen in various theropods but also like those of the other ornithischians, though rather shorter. Then there is an apparently new form of cover, little ribbon-like strips that are composed of multiple filaments. Finally, and wonderfully, on the upper arms and upper legs are preserved multiple filaments all coming out of a single central point. This apparently small distinction (between a single filament and multiple filaments) is actually important since multiple filaments of this kinds are very much seen in various ancient theropods as well as modern birds and to date had not been seen in the ornithischians (or indeed pterosaurs). In other words, we now have something that is much more like a more derived feather than ever seen before and in a lineage very well separated from the theropods. Not only that, but these seem to arise form something rather like a scale. Previously it has been suggested that scales were modified into feathers in some way, (evolutionarily, a large raised scale could easily get very long and thin over time to form something like a filament and then later split into multiple fibers) but it is also possible that they are something like more derived feathers that have a base (the shaft) and the filaments protrude from the top or side. It cannot be said right now that any of the various filaments seen in Kulindadromeus are genuinely feathers in the sense that they share a single evolutionary origin back at the very origin of the dinosaurs and before the ornithischians split from the theropods and sauropodomorphs. However, at least to a degree that is not actually such a big deal. While the previous filamented ornithischians could at least potentially be written off as oddities, or as ‘only’ having simple filaments, the fact that multiple filament types are turning up in a single species, and that this includes multiple filaments from a single point of origin really make it clear that more structurally complex coverings close to feathers are not exclusive to theropods. Moreover, the evolutionary placement of Kulindadromeus so far from the origin of theropods and between the other covered ornithischians means these things either turned up again and again, or kept coming and going at various times. In either case, it does open up the potential that many more dinosaurs had filaments of some description. Not just among the ornithischians, but if it can be shown that these new structures are genuinely shared with the theropods (and maybe even beyond the dinosaurs) then this raises the possibility of sauropodomorphs, basal theropods and perhaps other reptilian lineages with filamented coverings. This in the short term is likely to lead to suggestions that all dinosaurs were covered in fuzz, feathers, fluff, filaments and other analogous structures and while I’m personally confident that plenty were still scaly (or at least mostly scaly), it is tempting to imagine the plates of a Stegosaurus poking up between a fine coat of ‘fur’ or a giant Brachiosaurus with a little Mohawk of fuzz along the top of its head. Such suggestions are perhaps rather too fanciful based on the data available right now, but are much more plausible now than even last year and that’s a marked step towards understanding their real distribution. Feathers and their like are so important because they help address all manner of questions about the origins of birds and powered flight, evolutionary drivers such as display and other behaviours, internal temperatures and levels of activity, how animals use or react to their changing environments and more. The origins of feathers, and by extension anything that is feather-like in these groups is thus core to the understanding of the rise of, duration, and extinction of the non-avian dinosaurs, and for that matter, the survival of the dinosaurs that remain with us, the birds. Godefroit, P. et al. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science, 435: 451-455. |