Just like the daintiest of birds, rhinoceros-sized dinosaur parents successfully brooded their eggs in open-air nests. But how did they sit on them without crushing them? They didn't have to, thanks to clever organization skills. These findings were presented at the annual Society of Vertebrate Paleontology meeting, Science reports.
Kohei Tanaka from the University of Calgary studied the fossils of oviraptorosaurs, feathered dinosaurs closely related to birds. Recent work showed that these “egg thief lizards” were neither lizards, nor egg thieves: They weren’t eating the eggs they were often found fossilized with, they were nesting. These dinosaurs ranged in weight from that of an ostrich to that of a modern day rhino; the latter had eggs that were up to 40 centimeters in diameter.
There’s been debate about the sorts of nests that the largest oviraptorosaurs built. Some say they were open nests like birds and smaller oviraptorosaurs, others say the nests were buried like crocodiles today. Nests that are exposed to the air suffer from water loss, so these sorts of eggs would have to have been less porous to prevent water from escaping. Based on Tanaka’s calculations of oviraptorosaur egg porosity, even the largest of these dinosaurs built open-air nests.
Then he estimated the amount of weight the eggs could support before cracking open. A dozen snuggly-packed eggs of small and medium-sized oviraptorosaurs could bear the weight of an adult roosting on top. As expected, the eggs of the larger guys would break if a parent sat on top of them.
So Tanaka turned to nest shape. The smaller dinosaurs built nests where the eggs are packed closely together. Eggs in the nests of larger oviraptorosaurs, however, were arranged in a large ring around an empty center. The parent sitting in the open space in the middle could put most of its weight on the ground, while still protecting its hatchlings-to-be.
Image: University of Calgary via Twitter @UofC_Geoscience