Welcome to the blog of the Mesozoic vertebrates research group of the Bayerische Staatssammlung für Paläontologie und Geologie

Sunday, 27 January 2013

The tale of a tail...

Recently, Richard Butler and colleagues, including myself, published a short paper describing only a part of a tail of a basal sauropodomorph dinosaur, a "prosauropod", from the Early Jurassic (some 185 million years ago) of South Africa. "So what?", you might think. Well, of course it is not just any random basal sauropodomorph tail, but there is something unusual about it: When we excavated the specimen, probably of the genus Massospondylus, in the Elliot Formation of Eastern Cape Province in 2008, we noted that the tail of the animal ended in a strange mass of bone. After preparation it turned out that the end of the tail had obviously been severed while the animal was still alive, and it survived the injury, at least for some time, as evidenced by reactive bone growth around the point where the tail had been cut off.
The corpus delicti: an injured tail.
Thus, the interesting question of course is: What happened to the animal? And how did it affect it in life?
There are several possibilities how this individual might have lost its tail. One is trampling, that a cogeneric simply stepped on the tail, causing an injury that got infected and finally led to the end of the tail falling off. However, given the type of injury and reactive bone growth, this seems rather unlikely. So, the second possibility is that the injured tail is evidence of an unsuccessful attack by a predatory animal, most probably a predatory dinosaur. This is the scenario that we considered more likely, and it has some interesting implications. First of all it indicates that Early Jurassic predatory dinosaurs were active predators, and not merely scavengers, and that they did target large animals and not only small prey. This is somewhat surprising, given that the largest known predatory dinosaurs from the Elliot Formation are about the same size as the Massospondylus specimen attacked, and they were rather gracile animals. On the other hand, the fact that the attack was unsuccessful indicates that Massospondylus had means to survive an attack by a predatory dinosaur, even after having received a serious wound, such as loosing a third of its tail. Maybe the animal got away, despite the injury, or maybe these basal sauropodomorphs lived in groups and helped each other when attacked. As you can see, such a specimen can lead to interesting thoughts. However, one should keep in mind that the actual FACT that we have is an injured tail - everything else becomes more and more speculative.

This leads me to another topic: If you look into the newspapers (be it on paper or online) to look at science news, you might get the idea that everything reported there is groundbreaking, shaking the foundations of our current knowledge. So, is this the case with our new study as well? Rather not; this observation tells us certainly more about how journalism works than how science works. Now and then there really are new discoveries and new studies that challenge accepted views, but these are rather exceptional events. However, the journalist must sell the story to her/his readers and thus has the tendency to hype the significance of the study reported, and, since we are all under pressure to get public attention in order to be competitive for the limited resources allocated to science, many scientists have learnt to play this game as well. But this is not the nature of science!
The world as seen by science: looking for the next pieces.
Most scientists I know do not start an investigation with the aim to overthrow accepted knowledge, but rather out of curiosity of what they might find. Science is like an enormous puzzle; there sure are some key pieces, but to get the entire picture, you also need the rather insignificantly looking pieces as well, and most of science is working on such pieces. Thus, although there are of course some studies that might be more important than others, there is no scientific investigation that is completely useless - even negative results can tell us something. This is something to keep in mind next time you read about science that might, at first, seem insignificant - such as a description of an injured tail in a basal sauropodomorph: Scientists are looking for another piece of the puzzle to complete our picture of the world. However, the analogy with the puzzle is also only partially correct: What often happens is that the discovery of one piece makes you realize that even more others are still missing...

3 comments:

  1. I could only see the first page of the paper, plus the figures in the supplement, so if I missed something that you have already written, sorry...

    How do you figure that the critter was attacked as a (large) adult? If attacked while small would you have expected a more 'rounded-off', smoother mass of bone?

    Any way to guess the chances of the tail having been whacked by a falling tree or rock, instead of being chomped? (I think I know the answer to that one: No, not really).

    Neat find.

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  2. To the first question: Although the end of the tail shows signs of healing, it was far from vaing healed completely when the animal died. After such an injury, there is usually excessive bone growth, often with infected, pus-filled cavities. Over time, the infections cease and some of the excessive bone is resorbed. In our specimen, reactive bone growth is excessive, and there are cavities that might indicate infections. It seems that the animal survived the attack, but probably not by much - maybe the infection of the wound finally killed it.

    As for the second question - of course, we cannot rule out a freak accident, but an injury by a predator simply seems more likely. But, as I said in the text, the fact is that there is a traumatically amputated tail - all the rest is speculation... ;-)

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