The Last of the Dinosaurs

What makes the mystery even greater is that it was not just the dinosaurs which died out. So did the plesiosaurs, the ichthyosaurs, the mosasaurs, and the flying reptiles, the pterosaurs, which we shall meet on the following pages. In fact, over half of all living species became extinct 65 million years ago.

The pteradactyl, which like all the dinosaurs became extinct
around 65 million years ago.

Disease or starvation

Disease has been suggested as a possible cause, but it is difficult to believe a disease could be so effective all over the whole world and affect so many different species.

Some palaeontologists have suggested that the appearance on the earth of butterflies and moths, with their hungry plant-eating caterpillars, destroyed the plants on which the herbivorous dinosaurs fed. This does not explain why the sea-living reptiles died out.

A butterfly feeding.

Thin egg-shells

A palaeontologist studying fossil dinosaur eggs from the south of France has found that at the time the dinosaurs were becoming extinct their egg-shells had become so thin that the embryos could not have developed properly, and the eggs would not have hatched. It is well known that birds' egg-shells become thinner when the birds are under stress and there is reason to believe that the dinosaurs were also under some kind of stress. This might have been because the climate was becoming colder. If dinosaurs were cold-blooded, which is not known for certain, then they would have been more susceptible to cold than the warm-blooded birds and mammals. However, the reptiles living in the sea would have been little affected.

Turtles have survived from pre-historic times

Poisonous plants

A botanist working at Kew Gardens in London has recently suggested that the dinosaurs were affected by the flowering plants. He thinks that these contained unpalatable chemical substances, as some present-day plants do. The grazing dinosaurs would have had to range farther for food as the new plants began to spread across the world, and therefore many dinosaurs would have died of starvation, causing the subsequent death of the carnivores.

Meteor Strike

In 1980 Walter and Luis Alvarez discovered that rock formed at the time of the extinction of the dinosaurs contained high levels of the element iridium. Iridium is in general rare on the earth but is common in meteorites. They calculated that a meteor large enough to produce that much iridium must have been ten kilometres across. The impact on the earth of a meteor of that size would have thrown a huge amount of dust and debris into the atmosphere. That much dust would have blocked out the light of the sun, killing plants and cooling the planet. These changes might account for the mass extinction of the time.

This theory was not accepted by many people. They pointed out that such an impact would have formed a crater more than 150 kilometres across. Where was the crater?

A team of oil exploration scientists found a crater, buried one kilometre beneath the ground's surface, in Mexico's Yucatan peninsula at about the same time that Walter and Luis Alvarez were explaining their idea. Not many people heard of their discovery and it was not for another ten years that it was realised that this crater could be the result of a meteor strike which would explain the extinction of the dinosaurs.

We are not absolutely certain that this theory explains the disappearance of the dinosaurs 65 million years ago. Scientists continue to gather evidence however, and so far all the pieces of the puzzle seem to fit together to suggest that the mystery of the end of the dinosaurs has been solved.