How did marine reptiles such as ichthyosaurs breathe?
Mike Benton
Professor of vertebrate palaeontology at the University of Bristol, UK
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Like modern whales, the Mesozoic marine reptiles like ichthyosaurs and plesiosaurs had land-living ancestors. In the case of ichthyosaurs and plesiosaurs, these land-dwelling ancestors were probably something like lizards.
We know that the various ancient marine reptiles produced their young live at sea, as whales and dolphins do today. The fetuses developed fully inside the mother and were born straight into the water, where they rushed to the surface to take their first gulp of air.
The evidence that these reptiles produced live young at sea (rather than coming onshore to lay eggs, as turtles and crocodiles do) comes from dozens of fossils showing well-developed fetuses inside the mother鈥檚 ribcage. Some even show something close to the moment of birth.
Although the ichthyosaur fossils don鈥檛 show internal organs, such as lungs, we know, like all animals, they needed oxygen to survive. And in all other cases where land animals evolved to go back into the water (e.g. modern whales, crocodiles, marine snakes, penguins, seals etc.), they always breathe with lungs and don鈥檛 evolve some form of gills as in a fish. They can all hold their breath 鈥� sometimes for significant lengths of time 鈥� but have to keep coming to the surface to breathe.
We assume that it was the same for the ichthyosaurs and plesiosaurs too.
Jonathan Wallace
Newcastle upon Tyne, UK
Ichthyosaurs and other extinct marine reptiles would have been obliged to resort to the same solution as modern day marine reptiles such as turtles and marine mammals like whales, dolphins and manatees: they would have had to come to the surface to breathe air via their nostrils.
Sea snakes have the ability to absorb oxygen across their skin and this may help to extend the period they can spend underwater. But they are unable to obtain all the oxygen they need in this way and are obliged to surface periodically to breathe.
Alex McDowell
London, UK
Marine mammals, including whales, dolphins and porpoises, surface to breathe air 鈥� just like ichthyosaurs did.
When most dolphins sleep, only one cerebral hemisphere 鈥減owers down鈥� and the other one remains active, thus they have sufficient consciousness to surface to breathe. Maybe prehistoric marine reptiles had similar mechanisms.
Patrick McDonald
Via email
Since they were reptiles and had lungs rather than gills, they would have had to surface, much as dolphins do today. Exceptional preservation would be needed to determine if they had evolved blowholes as well.
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