Posts Tagged 'bone'

Guest Post: Dysalotosaurus histology

Today Tom Hübner takes us through his recent paper on the bone histology of Dysalotosaurs. This little ornithopod is a close relative of Dryosaurus (pictured here) but unlike the US Dryosaurus, comes from the famous Tendaguru beds of Tanzania. This is a great piece of work to see for me as Tom started this work for this PhD thesis in Munich while I was there and so I know the long hours and hard work Tom put into this and it’s great to see it come to fruition.

Many of you might know it already that I finally got a rather long paper on the bone histology of a small ornithopod dinosaur (Dysalotosaurus) published in PLoS ONE. 29 pages sounds like a lot but I wanted to break with tradition a bit to publish only as brief a paper as possible. This had something to do with the beginnings of my studies on bone histology because most papers at that time restricted the information to the most necessary facts which was quite difficult to follow and reconstruct. Without the personal help of ‘experts’ I never would have understood all that. Another reason for the length of the paper is the enormous variation in the microstructure of the bone. Many times I was struck by a completely different type of tissue and it needed some time to identify them and sort them out. That’s because ‘variation’ is also one of the three main topics of the paper.

Anyway, for everyone interested in bone histology, I think it is worth reading [seconded, it’s a great review as well as providing new information and analyses]. The most important aspect is the usage of a new type of growth cycles for life history reconstructions which might be applicable for other vertebrates as well, especially when they lack lines of arrested growth (LAGs).

From Hubner, 2012. Thin sections of Dysolotosaurs bone in normal and polarised light

Some might wonder why such a small animal delayed sexual maturity until about its 10th year of life because it should suffer many losses by all types of predators. Well, that’s a good question and difficult to answer. One strategy is definitely the precocial breeding strategy, but the predators could also be the reason for delayed sexual maturity. The animals would not start breeding until they were large and strong enough to withstand the additional stress of mating and breeding, and they still had at least 5 years for reproduction because, according to the size-frequency distribution, only after about 15 years of age decreased their abundance within the herd significantly. Large ornithopods, on the other hand, had the opposite strategy (see Cooper et al. 2008) by outgrowing predators in a short time. Most of them also had altricial breeding behavior. This, and other arguments presented in the paper, could be a good non-phylogenetic difference between small and large ornithopods in general, but there is still much do to before this can be a strongly supported theory. As always: “More fossils and more studies …”.

From Hubner, 2012: Comparative growth rates of Dysolotosaurs with other dinosaurs and mammals

Constructive criticism is always welcome, so don’t hesitate to post them. I’m still not at all too old to change my mind. Well, this is science – nobody can learn something new without knowing where the mistakes are.

As this is in PLoS ONE, the paper is freely available here.

Hübner TR (2012) Bone Histology in Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia) – Variation, Growth, and Implications. PLoS ONE 7(1): e29958. doi:10.1371/journal.pone.0029958

Pachycephalosaur heads

And so ends Carnegie marginocephalic week with the last of their pachycephalosaur material. For once though, this is something I really haven’t had before. While long ago I did feature a cast of a Pachycepahlosaurus skull (that looks suspsiciously identical to the various mounted skeletons I’ve show) here at least is something a bit different. First off, there’s a skull of Stegoceras (above, and the small one below) which even to my inexpert eye is clearly rather different to that of Pachy. Moreover, the ‘shelf’ at the back of the head – the key character that unites the pachycephalosaurs with the ceratopsians, is clearly visible and more dramatic that the usual fine bosses and spines that are generally available.

The second piece is also a Pachycepahlosaurus skull-cap though in rather less good condition, though I’m not sure if the lack of spikes and so on at the back of the head is due to wear / damage, or a lack of development. I suspect the former, since this was rather larger than the cast on display.

Pathologies

Animals, somewhat inevitably, get ill. (As a minor aside, this is one of the great fallacies about life in the wild that animals live in some kind of paradise where everything lives free and happy and never gets eaten alive by a predator, or starves to death, or gets and infected wound and disintegrates from gangrene for example. Anyway, while of course most illnesses only affect soft tissues, some diseases and infections will leave a mark on the bones themselves and obviously as a palaeontologist these do turn up in the fossil record.

There are all kinds out there (I’ve mentioned one on a Mamenchisaurus before) but of course it is useful to see these things in modern animals to see what effects cause which pathologies and then try to track them on the fossils. There are fossils (including dinosaurs) diagnosed with arthritis, cancers and pathologies resulting from infected injuries. In this case, this is the jaw of a hippo which has clearly had something go quite wrong (though what I’m not sure, though my guess is a nasty infection). The bone is swollen and pitted at the base of the tooth is actually visible – this is clearly not natural and looks very different to the other side of the jaw. These kinds of thing at least can give you an idea if the feature you are looking at is a weird bit of anatomy or the result of a pathology – it’s not always easy to tell.

Box heads

Have an ankylosaur skull. Euoplocephalus apparently (I would not claim to know much about ankylosaurs so I’m going with what it said on the sign).

You want *more* than this? OK, well ankylosaurs are actually quite interesting but in their own way they rather suffer from the same problem as pterosaurs. That is that their taxonomy is rather problematic since a lot of the characters you might expect to find to help sort them out are concealed. In pterosaurs its due to the way the bones are sutured in the head and because they have a very conservative bauplan, in ankylosaurs it’s the armour getting in the way. As you can see here, the cranium is essentially a box with holes for the eyes and nostrils and so you can see how it might be tricky to find out how all the underlying bones are moving around and changing shape (evolutionarily) and thus work out which features various taxa have in common or were they differ (or even if two animals are the same species or not).

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