 |
 |
 |
 Rockwatch Science Editor, Peter Doyle (pictured left), delves into the murky remains of ancient fossilised meals.
The seas of the Jurassic period teamed with life. It was the 'golden
age' of the ammonites, animals so common that their beautiful coiled
shells are found across the world. So many tiny shells of planktonic
plants and animals gathered on the seabed that they formed whole rocks.
Many other animals flourished in those rich seas - fish and molluscs
(sea-shells), crinoids (sea-lillies) and belemnites (squid-like creatures).
The most exciting of these were the large marine reptiles: the plesiosaurs
with their long necks and tails; the pliosaurs with their fearsome
jaws; and the long-snouted ichthyosaurs.
Pecking order
There were many different animals around in the Jurassic period. But, what did they all eat? The simple answer to this question is each other! In 1830, Henry De la Beche drew a picture of 'Ancient Dorset' (below) which showed all the large animals eating the smaller ones in a kind of pecking order, with the ichthyosaurs eating plesiosaurs, plesiosaurs eating turtles, fish eating lobsters and so on. But how did he know this, and was he right?
 
'Ancient Dorset' by Henry De la Beche
Well-preserved
In some parts of the world, rocks have preserved the whole bodies of large animals, almost perfect in every detail. This happens when there is so little oxygen in the water at the bottom of a sea that it stops scavengers and decay from eating away at dead bodies. Rocks like these are found across the world, and some Jurassic ones are known from Dorset and Yorkshire in England. They preserve reptile skeletons whole and intact. Henry De la Beche was using intelligent guess work when he drew his picture, but what he didn't know was that museum curators were unknowingly making his job more difficult!
Full stomachs
If you look at the skeletons of ichthyosaurs and plesiosaurs on the wall of the Natural History Museum in London you can see plenty of bones. But you might not see many fossils like the shark pictured below, showing a stomach full of belemnites or hooks. These were often cleaned off by curators in the early days of museums, so that Henry De la Beche didn't get to see them. Fortunately these hooks are now left in specimens, so that scientists can study them. So what does this tell us about a Jurassic take-away?
This fossilised shark from Germany was found with 250 belemnite guards in its stomach
Hard to swallow
 The hooks belong to belemnites, (right) and their close relatives. Belemnites are relatives of the squid and the octopus, but instead of having suckers on their arms, they had strong, horny, hooks. The presence of these hooks in the stomachs of large animals shows that they were more likely to have eaten belemnites than each other! Belemnites were common in the Jurassic, and can be found almost anywhere in the world, just like their relatives, the ammonites. Belemnites not only had hooks on their arms, they also had stony 'guards' inside their body. These tough shells were designed to help the animal swim straight, but would have been a rather unpleasant part of any meal. Interestingly, no belemnite guards have been found in the stomach of any ichthyosaur, and yet up to 250 have been found together with hooks on the stomach of a Jurassic shark from Germany. So what happened to the guards in an ichthyosaur's belemnite dinner?
Jurassic fur-balls
The answer is that they either didn't eat them at all, or got rid of them later. Ichthyosaurs could have just eaten belemnite heads, but this seems unlikely. It's more probable that they swallowed the belemnite whole, just like an owl does when it eats mice. Just like owls, ichthyosaurs probably regurgitated (sicked-up) the unwanted guards in a kind of pellet, so that they didn't gather and cause the animal stomach-ache! Sperm whales do this kind of thing today with the tough beaks of the squids they eat, so the idea is not far-fetched.
Unfortunately, the hooks were more difficult to shift, and these may have stayed locked together in the stomach for longer. They may have been regurgitated later in a kink of Jurassic 'fur-ball', just like cats do today after washing their fur.
Fossilised sick
 If you go to the Yorkshire coast on holiday, you may be lucky enough to find some 'Jurassic sick', the unwanted part of an ichthyosaur's dinner. It would be in the form of a patch of belemnites surrounded by small shiny hooks (see right). Don't worry, it's not squidgy any more, but remember it was an ichthyosaur's meal 180 million years ago!
This report was first published in the Summer 1999 issue of Rockwatch magazine
ROCK INFO:
 |
As well as being a Rockwatch Science Editor, Professor Peter Doyle is one of two scientists who discovered the world's oldest fossilised dinosaur sick!
|
|
|
|
 |
|
Rockwatch
