Biology and anatomy

Were they warm-blooded?

Question

I am doing an essay which involves plesiosaurs, and I was wondering were they warm blooded. I know the great white, and one of the large tunas , and I think, one of of the sea turtles is.

Answer

I wish I knew the answer to this question!

You're right about tunas and sea turtles, though I believe that their homothermy is not as stable as that of mammals and birds. Chris McGowan wrote about it is one of his books - "Dinosaurs, Spitfires, and Sea Dragons" (I think). The difficulty is that there is little evidence in the skeleton to resolve the argument one way or another. In modern animals such as turtles, morphologially similar animals can have very different temperature control mechanisms. Tuna and Marlin are a good example of animals of a similar size, with similar lifestyles, one of which is endothermic the other homothermic.

I am hoping at some stage to be able to look at the varaition in isotope ratios along the spinal column of a specimen of Muraenosaurus we have in Leicester Museum, but this will depend on being able to raise the funds to do so. Such ratios can tell us about the temperature gradient along the body. If it is relatively uniform, the likelihood is that the animal was warm-blooded.

Similar work was done on a skeleton of Tyranosaurus about five years ago, and concluded that it was warm-blooded. I haven't been able to track down the reference.

What colour were they?

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Question

hello we need some info on Pleisosaurs and we need it A.S.A.P and it is for a grade two class project. and do u know what color they were? and how did they protect them selves?

Answer

We don't know for sure the colour if any extinct animal - colour is never preserved in fossils. However, it would be a good guess that plesiosaurs coloration was similar to that of modern marine creatures. It is normal for marine animals to be countershaded - dark on top, grading to light underneath. This makes them less visible in water, which is always lit from above. Colours again are usually blues and greys, to match the colour of the sea. There is nothing to hide behind in the open sea, so in order for animals to hide themselves either to escape from predators, or to get close to prey, they need to match the colour of their surroundings.

One special thing about plesiosaurs is their long neck, and we don't know why they had it, or why it was so long. No modern animals have a long neck like that. One idea we have is that they had heads coloured and marked to look like fish. The plesiosaur could them sneak its head into shoal of fish without scaring them off, and start snapping them up from the middle of the shoal.

Plesiosaurs were pretty big animals, and didn't need to protect themselves except against other bigger and fiercer plesiosaurs, crocodile and mosasaurs. The biggest plesiosaurs, which we call pliosaurs, were some of the biggest meat-eating animals ever to have lived. They didn't need to protect themselves against anything! The smaller ones were probably more manoeuvrable than the big ones, and could dodge out of the way, but were often prey for the pliosaurs. The plesiosaurs I study are about 160 million years old, and come from the Lower Jurassic of England. They were often prey to larger ones, and more than half the bones we find have bite marks on them.

I hope this helps. Please let me know how well you do with your project.

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How much did they weigh?

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Question

Hi. I am doing a report on the plesiosaurus. I need to know how much they weighed.

Answer

Obviously, in deaing with an extinct animal we know only from the bones, estimates of weight can only be approximate. Plesiosaurs varied widely in size, the smallest being about a metre long, probably weighing around 30 kilos. The largest, the pliosaurs reached lengths of about 15 metres. I have made a rough estimate of the weight of such an animal as around 25 tonnes. The large, long-necked elasmosaurs were longer than this - up to 18 metres - but less heavily built, and probably weighed around 8 tonnes.

How did plesiosaurs breathe?

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Total Layman here, but it occured to me, how did plesiosaurs, especialy elasmosaurs and kin, breathe? The head just seems to small to admit enough air for an animal that spend smost of its time underwater

Answer

The simple answer is that they must have had big lungs!
It's certainly a problem in imagining how an elasmosaur with a 7 meter long neck could breathe. The volume of air needed to fill a trachea over 7 meters long must be considerable, and one can imagine a situation in which the process of breathing was simply shunting the same air up and down the neck. Of course, reducing the diameter of the trachea reduces this problem - but then we have the problem of fitting enough air through a narrow tube.

My best guess is that they had, as I said, big lungs. There are other possibilities such as a system of air sacs as are found in modern birds which allow air to be circulated rather than simply shifted back and forth, or that the skin had some respiratory function. There is however no fossil evidence to support either of these hypotheses.

Why are there no intermediate necked plesiosaurs?

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There appear to be short necked and long necked plesiosaurs, but why are there no intermediate necked plesiosaurs? Did they diverge somehow, and rather than one type being more fit for the environment than the other, and the less fit type dying out, they both lived?

Answer

In a sense, there are intermediate necked plesiosaurs. The early species of the genus Rhomaleosaurus, found in the lower Jurassic of Britain have relatively long necks and relatively large heads, although they are assigned to the pliosauridae - the large-headed, short-necked type. These animals came early in plesiosaur evolution, and although there were longer-necked and smaller-headed types around at the time, they did not reach the extremes found much later in the Cretaceous, where we find animals with extremely long necks (as in Elasmosaurus, with 72 neck vertebrae), and animals with very large heads (Kronosaurus was pretty well a giant head with a relatively small body attached to move it around).

One of the big questions in plesiosaur taxonomy (the study of their evolutionary relationships) is this: are the two body types separate clades (i.e. are all long-necked plesiosaurs more closely related to other long-necked plesiosaurs than they are to the large-headed types) or are they morphotypes (i.e. do evolutionary pressures produce the two types independently from basic plesiosaur stock). There is some evidence (though it is a matter of heated dispute) that the two body plans are morphotypes.

One of the main problems in studying plesiosaur evolution is that the fossil record is patchy. Most of the specimens we have come from a few places, so that although we know a lot about the plesiosaur fauna of the Oxford Clay, in the middle/upper Jurassic, and a fair bit about the middle Cretaceous fauna from North America, we know very little about what happened in between - a gap of 40 million years. A new location with good plesiosaur material from this gap could throw a lot of light onto their evolutionary relationships.