Did stress destroy the dinosaur?
HOW 70 MILLION-YEAR-OLD EGGS COULD EXPLAIN A MYSTERIOUS DISAPPEARING ACT
Sunday 28 February 1999
Analysis of 70 million-year-old dinosaur egg shells now suggests prehistoric creatures could, in fact, have done with hugs of reassurance and that they were just as stressed out as any modern-day commuter.
The research is based on the fact that some dinosaur eggs are "double- shelled", a recognised sign of stress in the eggs of modern animals, such as turtles, crocodiles and chickens. Scientists are now speculating that stress was a factor in the death of the dinosaurs - or that it was symptomatic of the apocalyptic event which wiped them out 65 million years ago.
Scientists in Glasgow and Montana in the US have carried out research showing that the eggs of a small dinosaur called Troodon formosus, which lived around 76 million years ago, displayed similar signs of stress to those exhibited by turtles which have been subjected to human interference and pollution.
"The phenomenon of double egg shells is not restricted to modern-day birds. It also existed in dinosaurs," says Professor Sally Solomon, of the poultry research unit of Glasgow University's Veterinary School, which carried out the research.
The findings have been backed by Dr Angela Milner, head of fossils and vertebrates at the Natural History Museum in London. "It's fair to say that if you see abnormalities in the eggs of modern birds like chickens you can expect the abnormalities to arise for the same reasons in dinosaurs," she says.
Scientists liken egg shells to fingerprints because of the detail they can provide about the environment in which they were laid. They have learned that chickens and turtles delay laying their eggs in times of danger, allowing an extra layer of calcium - or a double shell - to be formed.
"We know dinosaurs held on to their eggs for longer than they should have. So we can wonder at what the environmental factors were that caused them to do that," says Prof Solomon. "And what contribution that fact made to the end of a species."
Double-shelled eggs are widely known to be formed by turtles as a result of stress and pollution, says Prof Solomon. "Marine turtles come ashore during the hours of darkness to lay their eggs but in some parts of the world this magnificent act of mother nature has become something of a tourist attraction.
"Turtles are not used to an audience. I've seen many occasions when the mother has simply returned to the water and not laid her egg." Pollution has also been found in Mediterranean turtles that retain their eggs, suggesting mothers sense the conditions are not right to lay them.
Double-shell eggs have also been seen in chickens, though surprisingly they are common among free range poultry, which are more likely to encounter foxes and barking dogs, than battery farm hens, whose monotonous routine is less likely to produce the factors which would cause them to retain their eggs.
"These creatures seem to be saying `I'm not going to lay my egg because it is vulnerable,' and they decide to hold on to it for a while," says Prof Solomon.
A number of environmental factors could have been stressful to dinosaurs, including climate change, crashing meteor- ites and rising sea levels, according to Dr Milner. All such events could cause stress in any dinosaur, regardless of size or its place in the food chain, she said.
"These eggs were laid well before the Earth was hit by a meteorite, so they provide interest to those who believe dinosaurs died out because of longer- term reasons, such as climate change," says Dr Milner. "We know that at the time the Troodon lived major changes in sea levels were taking place."
If dinosaurs were regularly laying double-shelled eggs they could have contributed to their own demise. "Holding on to the eggs is actually a retrograde step," says Prof Solomon, one that makes it harder for offspring to survive. "If laying is delayed it can lead to the formation of a heavily calcified egg shell, which is too much for the hatchling to break through and affects the amount of oxygen the embryo can get."
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