Why the Largest Dinosaurs on Earth Laid Smaller Eggs

Dinosaurs may have been the largest creatures to walk the Earth, but they certainly didn't have the biggest eggs--at least comparatively to their size. Scientists have found that both individual egg size and clutch size for sauropods, the dinosaurs that were once the largest on our planet, were a lot smaller than expected.

With their long necks, small heads and massive bodies, sauropods once roamed the Earth millions of years ago. This group of dinosaurs included the famous Diplodocus. Yet it seems as if while the dinosaurs themselves were massive, their eggs were another matter.

Relative to modern egg-laying animals, sauropod eggs are far smaller. That's why scientists decided to investigate a bit further as to why that is. The researchers used data from modern birds and reptiles to examine factors associated with clutch size in sauropods. They estimated the time from laying to hatching of eggs, which were incubated within underground nests.

So what did they find? The scientists believe that it's possible that the substantial incubation time required for sauropod embryos to develop and hatch may have been an important constraint on egg size. In fact, they estimated that it took between 65 and 82 days to incubate the eggs, which increased the risk of predation and may have helped limit clutch and egg size.

"We think that a long incubation period of sauropods is likely to have led to very high mortality through predation," said Charles Deeming, one of the researchers, in a news release. "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."

The findings reveal a bit more about these massive dinosaurs. More specifically, it shows exactly why the clutch and egg sizes are limited.

"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," said Graeme Ruxton, one of the researchers, in a news release. "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."

The findings are published in the journal Paleobiology.