Egg Size Fatal for Dinosaurs
Thursday, April 19, 2012 7:27:08 AM
The reason is simple. Dinosaurs were egg laying, and there are physiological limits to egg size. The embryo inside the egg needs air to breathe, so the egg shell must be sufficiently thin to allow gaseous exchange. Larger eggs need thicker shells, but the need of air imposes a maximal eggshell thickness.
Elephants nurse their youngs with milk, so that the young ones reach a certain size before they compete on resources in their ecological niche, while the tiny dinosaur babies begin to eat the same sort of food as their parents the day they leave their egg.
According to a new study published in Biology Letters limited egg size made dinosaurs more vulnerable to the intense pressures of the end-Cretaceous extinction about 65 million years ago.
Competition at smaller size classes, the authors suggest, drove dinosaurs to become bigger and bigger, and this created a lack of species that were small at maturity. Mammals and avian dinosaurs occupied those niches. If the catastrophe targeted large animals, but was less severe among small animals, then non-avian dinosaurs would have been doomed. The big dinosaurs disappeared, and there were no small non-avian dinosaurs left to quickly proliferate in the aftermath.
Ontogenetic niche shifts in dinosaurs influenced size, diversity and extinction in terrestrial vertebrates
By Codron et al.