Diplodocus was one of the largest dinosaurs to ever walk the earth, yet the females produced some of the smallest eggs. Now, scientists say they’ve cracked the mystery: The substantial incubation time required for sauropod embryos to develop may have constrained egg sizes. ​

Sauropods, including diplodocus, apatosaurs, and other friendly giants, had very long necks and tails, measuring up 33 meters in length and 16,000 kilograms in weight. Their had small clutch sizes compared to modern egg-laying animals; and their individual eggs, which are incubated in underground nests, weighed about 1.5 kilograms. That’s just a little more than an ostrich egg, despite how the dinosaur is about 50 times heavier than the bird. 

To investigate factors affecting sauropod clutch size, a team led by Graeme Ruxton from the University of St. Andrews in the U.K. analyzed data from modern birds and crocodiles. The living bird with the largest eggs, the ostrich, incubates its eggs for 42 days; and during this time, many eggs are lost to predators.  

The duo estimated that the time between egg laying and dino hatching was between 65 and 82 days. This long incubation period increases the risk of predation -- which, coupled with the relatively low temperatures expected in the nest, may have limited the sizes of the eggs and clutches.

Having larger eggs would have meant larger hatchling size, which could have been advantageous; but the benefits may have been outweighed by the increased risk of egg predation. By laying their eggs in small clutches, and in different nesting sites, female dinosaurs had a better chance of protecting their offspring from predation. 

“Some people might find it a bit disappointing that giant dinosaurs didn't lay equally giant eggs,” Ruxton says in a news release, “but it’s very satisfying to think that we might finally understand why."

The work was published in Paleobiology this week. 

[Via University of Lincoln]

Image: Katja Xenikis / Fotolia via ScienceDaily