Image 1 - Dinosaurs May Have Doomed Their Species By Laying Eggs
April 18, 2012

Dinosaurs May Have Doomed Their Species By Laying Eggs

New research suggests that the way dinosaurs reproduced could have led to their demise. According to research from the Zoological Society of London, dinosaurs became at risk when they began to lay eggs. Working together with colleagues, Daryl Codron and Marcus Clauss from the University of Zurich conducted this research into the possible beginning stages of the dinosaurs extinction. Their work has been published in the journal Biology Letters.

The trouble could have been the sheer size of the dinosaur and her child. The typical mother dino weighed an average of a hefty 4 tons, making it nearly 2,500 times heavier than her freshly hatched baby. Just as heavy, a mother elephant weighs a lesser 22 times more than her child. Newborn mammals are able to emerge from their mother at a larger size than those who are hatched from eggs. The larger the animal inside the egg, the thicker the shell needs to be. As the animal grows, more oxygen needs to enter the shell, placing a limit on how large the shell can be. This also limits the size of the animal, therefore causing baby dinos to be so much smaller than their mothers.

According to the new research, the baby dinos also had to occupy many different ecological niches in their lifetime, changing constantly as they grew larger, thereby placing them in constant competition with other animals. Mammals, by comparison, occupy only one niche as babies, and as they are fed with their mother´s milk, they do not have to compete for food at such an early age.

In a statement, Daryl Codron explains these niches this way: “The consensus among researchers is that animals of particular body sizes occupy particular niches. In the case of the dinosaurs, this would mean that a single species occupied the majority of the ecological niches while mammals occupied these through numerous species of different sizes.”

Their research also suggests the niches of smaller and medium dinosaurs were more often occupied by older, younger animals. This wasn´t the case with mammals.

“An overview of the body sizes of all dinosaur species – including those of birds, which are also dinosaurs after all – reveals that few species existed with adults weighing between two and sixty kilograms,” says Codron.

Codron and Clauss used computer simulations of these niches in order to conduct their research. Clauss explains their findings, saying, “Firstly, this absence of small and medium-sized species was due to the competition among the dinosaurs; in mammals, there was no such gap. Secondly, in the presence of large dinosaurs and the ubiquitous competition from their young, mammals did not develop large species themselves.”

The third insight gained from the computer simulations concerns the smaller dinosaurs. Codron and Clauss  say their research shows these small animals not only faced competition from larger species and mammals, but also from within their own class. This fierce competition either brought these small dinosaurs either to the brink of extinction or caused them to move into new niches, becoming airborne.

This meant the smaller dinosaurs became birds as the larger dinosaurs started to die out.

Then, as the mass extinction at the Cretaceous-Tertiary boundary occurred, the dinosaurs were unable to rebuild and occupy the empty niches.

According to Codron and Clauss, it all could have begun with a single egg.


Image 1: Mother Diplodocus dinosaur walks along with her brood of youngsters. Credit: Catmando / Shutterstock

Image 2: Why there were no small dinosaurs: While mammals occupied the various ecological niches with different species (left), the egg-laying dinosaurs occupied the same niches with few large species — in their respective different growth stages (right). Consequently, there was no room in the niche for smaller and medium-sized species (far right). The absence of species in the smaller and medium size range proved disastrous for them during the mass extinction as it obliterated all the large species and there were not enough small species of dinosaur that could have reoccupied the vacant niches. Credit: Universität Zürich; Jeanne Peter