Re: Theories on the extinction of dinosaurs

Tony Hedges writes:

1. Impact.
It is accepted that an extraterrestrial body struck the earth in Mexico at
the right time. It is accepted that this alone is not enough to fully
account for the complete extinction of all the life that was extinguished at
the end of the Cretacious.

2. Volcanism.
Volcano's errupting at or near to the end of the Cretacious, in the Indian
sub continent, formed the Deecan Traps. It was a massive erruption, nothing
on the same scale has been seen since. This would have had a massive effect
on the atmosphere.

3. Atmosphere.
Studies of the atmospheric content contained within amber dated to the end
of the Cretacious period has shown that towards the end of the last period
of the dinosaurs reign contained a smaller ammount of Oxygen in the mix, and
towards the end of the Cretacious the Oxygen content shot up by some 20 -
23%. This is a significant increase.<<

4. Stress.

Heinrich Erben of Bonn university's institute of Palaeontology did some research in the early 70's into thousands of eggshell fragments from the upper maastrichtian of the french pyrenees. His studies showed that eggshells in the older layers had eggshells around 2.5mm thick. The younger, more recent layers produced shell fragments a mere 1mm thick - too thin to provide enough calcium to the bones of the developing embryo within. The thinning of the eggshell is a sure-fire sign of stress. Seagulls in crowded colonies lay thinner eggshells than ones not subject to mass territoriality and food supply issues. The previous 3 events, especially the top two, are known to have occured and all the animals at that time would have been subjected to the same conditions. Perhaps it was their way of dealing with those conditions that decided who would survive and who wouldn't.

References:

Erben, H. K., 1972. Ultrastrukturen und Dicke der Wand pathologischer Eischalen. Abh. Akad. Wiss. Lit, math-nat. Kl., 6, pp. 191-216. See also Tafel I, Figs. 5 and 6.