Dinosaur dads used to guard the nest and look after the kids, researchers have concluded, after comparing the sizes of dinosaur clutches with those of modern-day reptiles and birds.

While studying Troodon formosus, Oviraptor philoceratops and Citipati osmolskae — three species of bird-like dinosaurs — David Varricchio, a paleontologist at Montana State University in Bozeman, and his colleagues made a curious observation. “By volume, these dinosaurs were laying clutches that were two to three times larger than what would be expected for their adult body size,” Varricchio told National Geographic.

They examined the sizes of clutches from 400 species of reptiles and birds. Clutches that were cared for by dads were the largest, followed by clutches that were cared for by mothers. Clutches that were cared for by mother–father pairs were the smallest. These findings, they report in Science, suggest that because Oviraptor, Citipati and Troodon clutches were so large, males may have been the primary care providers.

While journalists delight in the “softer side” of dinosaur culture (Reuters, Globe and Mail), these findings have implications for today’s bird watchers — they suggest that the primary paternal care system of some modern-day birds might be an evolutionary relic from ancestral dinosaurs.

Top image: Bill Parsons.