On Deep Sea Grazers

This may not be a particularly interesting post for the vast majority of people but it’s one that I care about, it’s going to give the background to a dissertation I’m writing to hand in in the next two weeks (I handed it in on April the 27th). Everybody in the house interested in paleoethology, ichnology, evolution or deep sea worms that evolved around 542mya and have continued up to the present developing more and more complex grazing behaviour give me a hell yeah?! Ahem, yes well that’s what this post is all about so read on if you’re curious.

So how do we know that such behaviours actually exist? Well Ichnology, specifically paleoichnology is the study of trace fossils, fossils which record the tracks and trails of extinct animals, for instance Dinosaur footprints are on type of ichnofossil (Another name for trace fossils). Ichnology is the study of all tracks and trails and neoichnology is the branch of ichnology which focuses on extant (living today) animal tracks. There are fossils which record the movements of animals and they can be grouped by what sort of behaviours produced them. The particular group I am interested in are the group ostentatiously called Pascichnia (Pass-ik-nee-ah, I think). It literally means grazing tracks (Latin Pascos lit. Grazing Ichnos lit. Track) how inventive of them. If you want to know more about the inventive naming system, google the name Adolf Seilacher, he came up with the original categorisation system.

Pascichnia have been discovered from some of the earliest periods in history, the first fossils were simple and looked much like childrens’ scribbles, think what you did as a kid in MS paint scribbling randomly then colouring in the gaps between the lines. They look much like that but in rock and less colourful.

The next stage along was a couple of hundred million years later when the animals had learned to loop back and forth (This is but one example) but the loops were quite loose and there were often large gaps before the animal moved back to follow alongside it’s path. The final part of this example I will describe is those trace fossils which have been found from the Cretaceous, again, a few hundred million years after the previous ones. These showed a very tight strafing pattern back and forth minimising the area left unused by the animal.

So the patterns have gotten more complex, but why? There has to have been some sort of pressure to force the worms to develop more complex behaviours. It is possible that the behaviours developed by chance, that is, genetic drift in the development of their neurons would develop such behaviours, however there are a couple of reasons why this is unlikely.

First, neurons are expensive, unless the worms had another reason for the development of the neuronal capacity to develop these complex patterns then they wouldn’t have the neuronal capacity in the first place and no amount of genetic drift could generate these behaviours.

Second, the behaviours are temporally distinct, that is, each level of complexity is isolated from the others in time, only simple behaviours at the start, semi-complex behaviours in the middle and complex behaviours at the end (Or at least at the present, who knows what will happen in the future of such animals). This would suggest a directionality to the behaviour, if it were mere chance that developed these patterns then it would be a reasonable assumption that all behaviours would be represented at almost the entire length of their history. The fact that this is not the case would suggest that the complex behaviours are more selective.

So to conclude, these behaviours have gotten more complex over time, and it is highly likely that this is not the result of genetic drift, rather an evolutionary response to an environmental or ecological pressure which forced the development of such behaviours.

Comments and criticisms welcome.