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Study suggests egg-laying process wiped out dinosaurs

You may think that making babies increases population numbers, but this is not the case for the mighty dinosaur. A new study from Switzerland and the United Kingdom has discovered that by laying their eggs, dinosaurs only helped bring about their extinction. The findings are p...

You may think that making babies increases population numbers, but this is not the case for the mighty dinosaur. A new study from Switzerland and the United Kingdom has discovered that by laying their eggs, dinosaurs only helped bring about their extinction. The findings are presented in the journal Biology Letters. Daryl Codron and Marcus Clauss from the University of Zurich in Switzerland, in cooperation with colleagues from the Zoological Society of London in the United Kingdom, researched what triggered the extinction of the dinosaurs - the largest land animals for 150 million years. The mass extinction at the Cretaceous-Tertiary boundary generated a species gap in the medium-size range. Researchers have long postulated that all the larger animals weighing between 10 and 25 kilograms were wiped out. Many different mammals had a body weight below this threshold, and larger species emerged after the huge wipe-out, successfully occupying the empty niches again. The problem with the dinosaurs, however, was that they did not have the species needed to fill these empty niches. This, in turn, led to their demise. A female elephant is about 22 times heavier than her calf. So baby mammals are already large in size. A mother dinosaur, meanwhile, could be around 2 500 times heavier than her newly hatched baby. The researchers say the huge difference in size between newly hatched dinosaurs and their parents was because of the eggs' limitations on size. The larger an egg, the thicker its shell. The embryo needed oxygen to grow, and the thickness of the shell only restricted its growth. So newly hatched dinosaur babies were not larger in the same way the larger species of mammal are. It should be noted that baby mammals occupy the same ecological niche as their mothers and fathers. But dinosaurs occupied their parents' niche as well as many of their own; they had to pass through a range of niches: for small-, medium- and large-sized animals. 'The consensus among researchers is that animals of particular body sizes occupy particular niches,' explains Dr Daryl Codron. '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.' The data show that small and medium-sized dinosaurs lacked the number of different species to fill the size range of niches while mammals did not. '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 2 and 60 kilograms,' Dr Codron explains. For his part, Dr Marcus Clauss says: '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.' Another factor was that small dinosaurs competed against each other and other small mammals. This essentially compelled them to either find new niches or die.For more information, please visit: Biology Letters:http://rsbl.royalsocietypublishing.org/University of Zurich:http://www.uzh.ch/index_en.html

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Switzerland, United Kingdom

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