Body plan of a typical ichthyosaur



Above: This ichthyosaur in the Bristol City Museum has the remains of an embryo

preserved along side indicated by an arrow (see below).

Above: The ichthyosaur embryo: The vertebrae, ribs, jawbone and an eye socket are clearly visible



Above: The sclerotic ring is found in most vertebrates, except mammals, crocodiles, and some others. In ichthyosaurs they were very well developed, so we can take accuarate measurements and use them as a relaible proxy for eyeball size. Ichthyosaurs had quite flat eyeballs so the sclerotic rings may have been usefull in maintaining their shape. Relative to body size, ichthyosaurs had huge eyes, possibly up to a metre in the largest species.


Above: The vertebrae of fish shaped ichthyosaurs (left) are flattened, resembling hockey pucks. In contrast, those in lizard shaped ichthyosaurs (right) are more elongate, and so resemble camera film cases.



Lizard shaped ichthyosaurs had a slender body, and thin backbone with many vertebrae, which suggests they swam in an eel like motion, as do modern lizards when in water. Fish shaped ichthyosaurs had a thicker body and a thicker backbone so probably swam like tuna or mackerel sharks.





Author: P. T. Hadland
Last updated: Date 21st November 2005
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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2005-6