Dinosaur Size Result Of Egg-Laying?

The largest animal on the planet happens to be a mammal; the blue whale. Of course, on land the largest animal is significantly smaller; a the African elephant. For anyone that has grown up with a keen interest in the wild kingdom, there’s always been a mystery surrounding big animals. For instance, how is it that our largest animal today is still only a hundredth the size of some of the largest animals several hundred million years ago? To be sure, it adds to the allure of dinosaurs that nature no longer seems to suffer anything so grand in size. To explain why that may be, University of Zurich zoologist Daryl Codron studies the dinosaur’s egg.

Egg-laying creatures have some of the largest size discrepancies in nature, the difference between a new-born specimen and a fully-grown adult. According to Codron’s article, published in Nature, dinosaur eggs would produce very small young, some being only 2,500^th the size they will be when fully grown. By comparison, the largest discrepancy among mammals today is 1 to 25, about a thousandth that of a large dinosaur. Dinosaur eggs could get large, some being as big as small refrigerator, but it’s still much smaller than their fully grown adult size. The problem lies within an egg’s structure. After a certain point the egg is so big, and the shell is so thick, that it cannot absorb the necessary oxygen and other gasses to sustain the embryo inside. As a result, dinosaur young were comparatively very small….at first.

As Codron explains in Nature, “When the young of large animals start out small, they must grow through a large size range before reaching adulthood, and compete with species of many different sizes as they do so.” As a result, dinosaurs were likely to have evolved in a way that would allow them to grow quickly. With so much competition among smaller and mid-sized dinosaurs, it was evolutionarily advantageous to grow bigger than the competition. Thus, dinosaurs would start small, and grow to be bigger than those competing dinosaurs around them. Other species, then, would grow even bigger to compete. Think of it like a game of hand-over, which each species growing larger to out-pace and out-compete the others. Inevitably the world ended up with a lot of very large animals roaming its surface.

The problem came with the Cretaceous-Tertiary Boundary and the famous “asteroid collision”, which is still the dominant theory of the dinosaur extinction. Such large creatures were unable to adapt to such dramatic changes in climate brought on by the impact, and so died off about 65 million years ago. However, in 65 million years one would think we might see the pattern repeating. The difference? Mammals don’t lay eggs.