This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Ichthyosaurs ruled the oceans for 150 million years during the Mesozoic Era. Their fish-shaped bodies were built for high speeds.
In that context, it is normally an advantage to be as light as possible. "Ichthyosaur skeletons are in general quite light, but the ribs are not," says Jørgen Krøglid. The results from his master's thesis were recently published in a paper in the journal PeerJ.
"This was a bit surprising to us. Compact bones are typically found in animals that move slowly, such as manatees," says postdoctoral researcher Lene Liebe Delsett at the Natural History Museum at the University of Oslo. Delsett has taken part in excavating the ichthyosaur fossils on Svalbard and leads the project "ECHO—Evolutionary Convergence in Historical Oceans: The case of whales and ichthyosaurs." The question the researchers are asking is whether there are multiple pathways to a fish-shaped body.
The answer they are getting when they compare ichthyosaurs with living toothed whales is a clear yes. Both ichthyosaurs and whales appear to be perfectly adapted to life in water. It's easy to imagine that they have always lived there, but this is not the case.
Both descend from four-legged land animals that returned to the sea: whales from mammals, more specifically artiodactyls, and ichthyosaurs from some yet-unknown reptiles. This difference in origin, combined with their similarity in appearance and way of life, makes them ideal for comparison to understand the phenomenon and look for signs of what is called convergent evolution: when different groups of species independently evolve similar traits. "Both went from being land animals to becoming fully aquatic.
They feed in the water and they reproduce in the water, and they have evolved a very hydrodynamic body," says Krøglid. Since ichthyosaurs are extinct, we can't see them in action. Other methods have to be used.
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