Why did plesiosaurs become extinct
Why and when did plesiosaurs become extinct?
Plesiosaurs became extinct at the end of the Cretaceous period, about 65 million years ago.

This was one of the great extinction events in the history of the Earth, when many different kinds of living things died out at the same time. The most well-known of these are of course the dinosaurs.

There have been many theories about why this event happened. At the moment, there are two main theories being researched by geologists and palaeontologists.

The best-known of these is that the Earth was hit by a giant asteroid. There is a huge crater buried under the Yucatan peninsular in Mexico. There are deposits all around the globe which have a thin layer which contains an unexpectedly high proportion of an element called iridium. Iridium is rare in normal rocks, but much more common in meteorites, and which gives added support for the asteroid impact theory. The devastation caused by this catastrophe wrecked ecological systems all over the earth, including those in the seas.

Another possible cause is massive volcanic activity. In the southern states of India, an area of 500,000 square kilometers is covered in volcanic deposits over 2,000 meters thick. This was deposited in a series of massive eruptions around 60-65 million years ago, and may have contributed to the mass extinction event. Volcanic eruptions produce large amounts of toxic gasses, and these can also have a devastating effect on living organisms.

It is likely that both these event contributed to the wide-scale destruction of habitats both on land and in the water. It might be that there was already much destruction from volcanic fallout when the asteroid hit.

However it happened, the consequences were massive and far-reaching. On the land, only the birds survived from the dinosaur lineages. Some mammals survived to become the ancestors of all modern mammals, including humans. In the sea, ichthyosaurs, mosasaurs, ammmonites and many other organisms including the plesiosaurs became extinct.