Snake time

ASK A SCIENTIST
Last updated 11:23 15/12/2009

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Jessica Wratt, of Ngahere School, asks: How long have snakes been on Earth?

Pete Hodgson, a veterinarian and a former Minister of Research, Science and Technology, responds:

About 130 million years. That is during the time that geologists call the cretaceous period. As with many things to do with science though, the answer is really a bit more complicated.

The reason for this is that snake skeletons are very delicate and do not fossilise easily. Scientists have had to use the small pieces of fossilised snake skeleton they have found to try to put together the complicated jigsaw puzzle that explains the evolution of snakes.

Snakes are members of a class of animals called reptiles. Reptiles originally evolved from a large group of ancient amphibians.

The thing that made reptiles different from amphibians was that reptiles laid eggs with a shell. Amphibians, including today's frogs, have eggs covered with a soft membrane. Their eggs have to be laid in water.

The oldest fossil egg found is about 275 million years old. This probably belonged to an ancient group of reptiles which were the ancestors of the reptiles we have on Earth today.

Reptiles today include members of the lizard, snake, crocodile and turtle families. The first snakes probably evolved from a family of lizards during the time of the dinosaurs. Over many millions of years the ancestral snakes lost their legs and external ears, developed a tough clear eye cover in place of eyelids, and developed their distinctive way of moving.

The first modern groups of snakes began to appear in the fossil record about 20-40 million years ago. These were the ancestors of the boas and pythons.

It is only in the past 10-15 million years that groups of snakes have developed fangs that are designed to inject poisonous venom into their prey.

We don't have any native land snakes in New Zealand but we do occasionally find sea snakes washed up on our northern beaches. These are tropical snakes that have ventured far from their normal warm tropical waters.

Although these sea snakes have highly toxic venom, their teeth are tiny and they don't bite people.

Send questions to Ask-A-Scientist, PO Box 31-035, Christchurch 8444, or email questions@ask-a-scientist.net.

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- © Fairfax NZ News

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