Scientists Discover Why Female Dinosaurs Laid Smaller EggsReuters

A team of researchers have discovered that though dinosaurs were the largest creatures to have ever walked on Earth, they did not lay the world's largest eggs. Both individual egg size and clutch size of sauropods, one of the largest group of dinosaurs, were found to be a lot smaller than previously thought.

Sauropods, including diplodocus, apatosaurs and other such giants, had long necks, with smaller heads and measured up to 33 meters in length and 16,000 kilograms in weight. These creatures roamed the Earth billions of years ago. Yet, they laid relatively smaller eggs like those of modern egg-laying animals.

The team including biologists from the University of Lincoln, UK and George Mason University, Virginia, US, along with Graeme Ruxton, the lead researcher from University of St Andrews, used data from modern reptiles and birds and compared the factors responsible for the smaller clutch size in sauropods.

Ostrich, the living bird with the largest eggs, incubates its eggs for 42 days. It is during this time that the bird loses many of its eggs to predators. 

"The living bird with the largest eggs, the ostrich, has to incubate its eggs for 42 days; during which time many eggs are lost to predators. An ostrich weighs about 100 kg and lays a 1.5 kg egg; a sauropod dinosaur might be 50 times heavier than an adult ostrich but its eggs were only a little heavier than an ostrich egg. Some people might find it a bit disappointing that giant dinosaurs didn't lay equally giant eggs-but it's very satisfying to think that we might finally understand why." said Ruxton in a news release.

Keeping this in mind, the researchers examined time duration of sauropod eggs from laying to hatching of eggs using previous data. These huge creatures incubated their eggs in underground nests and it took around 65 to 82 days for their eggs to hatch. Scientists believe that this long incubation time increased the predation risk along with some low level temperatures inside the nest, which may be the factors responsible in limiting the size of the eggs.

"We think that a long incubation period of sauropods is likely to have led to very high mortality through predation. We suggest that the females laid their eggs in small clutches, possibly in different nesting sites, as an adaptive strategy to mitigate the high predation risk associated with long time of exposure in the egg stage." said Charles Deeming, one of the researchers.

Larger eggs would have larger hatchling size, which could have been an advantage; but the benefits may also increased risk of egg predation. But female dinosaurs having laid their eggs in different nesting sites and in small clutches, had better opportunity of protecting their offspring from predation.

The findings are published in the summer 2014 issue of the Paleontological Society's journal, Paleobiology.