Dinosaur Stress
Stress on the dinosaurs is a possible solution for their extinction. This theory was first thought up by Heinrch K. Erben when he found that the shell thickness of a certain type of dinosaur species decreased as time went on. It was thought that the warm climate and good habitats in the Cretaceous period could have caused over population of dinosaurs, thus an increase of stress on the dinosaurs would develop. Stress is known to cause hormonal imbalances in modern day birds and lizards, so this could have happened to female dinosaurs. An increase of estrogen in the dinosaurs would have caused the females to lay eggs with shells too thin. If this happened it would greatly reduce the chances of the young to be hatched and live to adult hood.

Ozone Layer Depletion
The destruction of the earth's ozone layer is another proposal for the dinosaurs extinction. Hydrochloric acid from volcanic explosions (which are known to be numerous in the Cretaceous period) could have depleted the earth's ozone layer to a great extent. With the absence of this layer there would be nothing to protect the dinosaurs from the ultra violent rays of the sun. This could also explain why the dinosaurs and not the mammals seemed to die out because dinosaurs had no hair to protect them from the suns rays like the mammals of that time did.

Greenhouse Effect
The "greenhouse effect" is another possible solution to the dinosaurs demise. Massive volcanic eruptions could have released so much carbon dioxide into the atmosphere that it caused a drastic increase in the world wide temperature. Some deep sea drills have shown that the temperature of the ocean increased 65 million years ago so the temperature of the atmosphere also likely increased. The excess carbon dioxide from the eruptions in the atmosphere would have permitted the sun's heat into the earth's atmosphere, but would have blocked most of the heat from exiting the earth's surface back into space. This would have created a "greenhouse effect", the increase in temperature could have killed the tiny plankton responsible for converting most of the earth's carbon dioxide into oxygen which would further compound the problem. Only a few degrees increase in the temperature can affect the fertility of an animal by affecting their ability to produce fertile sperm.

Supernova
Could a supernova have been responsible for the death of the dinosaurs? A supernova is an exploding star. It can blast material huge distances into space. Some scientists think cosmic radiation caused by the explosion would cause extremely high rates of deadly cancer among the dinosaurs. Others believe the radiation reacted with the Earth's atmosphere and destroyed the ozone layer. Without the ozone layer to filter out dangerous radiation, once again high rates of cancer could have occurred within the dinosaurs. Only small animals and plants, whose homes were sheltered from the harmful radiation would have survived.

Caterpillars
Caterpillars which were believed to have evolved late in the Cretaceous period could have stripped plants of their leaves, a valuable food to the plant eating dinosaurs. If the caterpillars were able to strip all of the leaves from trees, then the plant eaters would not have anything to eat and would die. If the plant eaters died then the meat eaters would die from lack of food. Beware, this theory is thought to be extremely unlikely for caterpillars would have to strip all of the trees around the world of their leaves at virtually the same time.

Other Theories

• The climate became too dry, making the environment too arid for the dinosaurs.
• Multi-layer egg shells formed, with two or three shells on individual eggs, suffocating the embryos.
• There is evidence that many of the large dinosaurs, must have had very small brains compared to their body size. With such small brain capacity responses to the surrounding environment would have been so slow that they could not compete with faster thinking animals.
• Mass flooding destroyed important dinosaur habitats.
• Dinosaur overpopulation could have resulted in severe competition and rivalry.
• Mammals ate the dinosaur eggs preventing new generations surviving.
• Carnivores over-killed their prey, and had nothing to eat.
• Uranium leaked from the soil causing poisoning to the dinosaurs.
• High levels of carbon dioxide destroyed the dinosaur embryos

Further Reading

• Fresh Angle on Dead Dinosaurs
• Did Cancer Kill the Dinosaurs