SYDNEY: New fossil evidence of male-only parenting by dinosaurs explains the same behaviour in modern birds, researchers have said.
Scientists have long debated whether male-only or bi-parental care first evolved for birds, but “it now appears that male-only care was the ancestral condition,” said David Varricchio, a palaeontologist at Bozeman’s Montana State University in the USA.
Varricchio led the research, published today in the journal Science, that suggests fatherly care in modern birds evolved before the origin of flight.
Eggs and bones
Previous studies have shown that dinosaurs shared several reproductive features with modern birds, including asymmetric eggs, multi-layered eggshells and similar ovulation patterns. Some dinosaurs even had bird-like brooding postures.
The new research shows bird and dino similarities extending even further, into parenthood behaviour.
To make the discovery, Varricchio’s team examined unusually large egg clutches from three species of carnivorous dinosaur, found with fossilised bones atop them – dinosaurs that died brooding the eggs.
Men sitting around
Among living birds, male-only care is found in species that have the largest clutches. With this in mind, the researchers suggested, male-only care best explains the occurrence of the big clutches of up to 30 eggs found.
They also examined the fossilised dinosaur remains, from the species Troodon formosus, Oviraptor philoceratops and Citipati osmolskae. None showed signs of the minerals typically stored by female birds for egg laying, said Varricchio, and this indicates the brooding specimens were indeed male.
The researchers propose the evolution of large egg clutches with male guardians enabled females to conserve energy by focusing strictly on their own feeding and egg-laying duties. “[For modern birds], this suggests that there is a trade-off strategy between clutch size and parental care,” Varricchio said.
Caring dino dads
“[This research] is a very clever piece of forensic palaeontology,” said John Long, head of sciences at Museum Victoria in Melbourne, Australia.
“Such discoveries are real jewels of evolution as they highlight the value of fossils in uncovering not only what the past life of the planet looked like, but how extinct creatures might have behaved,” Long said.
“This presents us with a new picture of dinosaurs as caring animals, even the dads!”
The research also raises further questions of when parental care evolved in dinosaurs and their relatives, and what role male care played in dinosaur ecologies, Verracchio said.