Dinosaurs roamed for thousands of years on Earth. They thrived in various environments, so they must have had some pretty good strategies for keeping offspring alive and ensuring the species' survival.
Learning about what these techniques might be hasn't been easy for paleontologists, who've primarily worked with scarce, fragmented fossil evidence.
The main theory is that just like living animals exhibit a variety of behaviors from species to species, it's likely that dinosaurs also were variable in their parenting. Some were neglectful and buried their eggs, while others caringly tended to their nest. And some lived alongside each other while others parted way soon after birth.
The Challenges of Learning About Dino-Parenting
While paleontologists know more about dinosaurs and their lifestyles than you'd expect, it's been hard to collect solid evidence on the different parenting skills these ancient creatures could have had.
Much of what we know today relies on experts meticulously piecing together knowledge based on exceptional specimens of fossilized eggs, remains from nesting grounds and trackways and solidified footprints.
According to Paul Barrett, a paleontology researcher at the Natural History Museum in the U.K., researchers have no evidence of nesting and parenting behavior of armored dinosaurs — such as Stegosaurs and Ankylosaurus — as well as many horned dinosaurs. What experts know tends to be reconstructed from the knowledge of living dinosaur relatives: birds and crocodiles.
"We don't have very much obvious direct evidence of parenting behavior in dinosaurs; there's still quite a lot of speculation," says Barrett. "Really, what we need are just more lucky discoveries of those critical specimens caught in the act of doing something that looks like parenting. Not just for dinosaurs but for any extinct animal. This type of evidence is really rare."
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The Oviraptor Is Caught In The Act — Sitting On Its Eggs Like A Hen
One of the most striking examples of good parenting among dinosaurs is that of Oviraptor. When scientists in the 1920s found a fossilized Oviraptor next to a nest, they thought the dinosaur was trying to steal somebody else's eggs — hence the name in Latin means egg-snatcher.
Fifty years later, and thanks to additional discoveries, they regard Oviraptor fossils as some of the most compelling visual examples suggesting that some dinosaurs hunched over their nests to protect their babies. Researchers found a 75-million-year-old Mongolian dinosaur that was fossilized sitting right on top of a nest. They dubbed it "Big Mama."
"They sit on those nests in a very bird-like way with their bodies positioned in the center of the nest, and their arms held over the eggs to help protect them," says Barrett. Their bodies would have been covered in large, down-like feathers that would have helped conceal and insulate the eggs. "I think that's the most visually striking example of an obvious parental care behavior from a dinosaur."
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How Did Large Dinos Lay Eggs?
That Oviraptor fossil was relatively small — like a modern-day ostrich — but for other larger Oviraptorosaurs dinosaurs like Gigantoraptor who got as big as rhinos, sitting on their eggs could have been a risk. So, fossils suggest they laid their elongated oval eggs in a near perfect ring-shape, with two or three rings stacked on top of one another, leaving a spot in the middle for them to set their weight. The ring size ranges from less than 40 centimeters (about 15 inches) to well over 2 meters (over 6 feet) in diameter, and the dinosaur's body may still have had contact with the eggs.
"The similarities in the eggs and nest shape across oviraptorosaur species indicate that broodlike behavior was practiced by all species, small to giant," says Darla Zelenitsky, a paleontologist at the University of Calgary. "They were obsessed with their eggs, no doubt."
"Oviraptorosaurs seem to be the first dinosaurs, evolutionarily speaking, to figure out how to incubate and hatch their eggs without completely burying them," says Zelenitsky.
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Maybe Dad Does The Denning?
Fossilized clutches from these oviraptorosaurs examples and other dinosaurs like Troodon housed 22 to 30 eggs each. This is a lot of eggs for an animal that size, especially compared to clutch sizes of living birds and crocodilians — or animals that tend to have both the mother and father nurture the children. The eggs found were also larger than they should have been for animals their size, suggesting that it took females a lot of energy to produce them.
"I'd say that those theropod dinosaurs close to birds certainly cared for their young and for their eggs," says David Varricchio, a paleobiology researcher from Montana State University. But these clues all point towards an arrangement by which father Oviraptors were charged with looking over large, mega-clutch nesting sites while collecting eggs from various different females, according to a study Varricchio penned.
"You see that in birds like emus and rheas, where one male will mate with several females and he does that, he has all the responsibility of tending the nest, routing the eggs and then taking care of the young once they hatch," says Varricchio. "And usually, those females will also mate with other males later in the season."
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The Maiasaura from Montana
In the 1970s, paleontologist Jack Horner discovered what was later dubbed "Egg Mountain" in Montana: a gigantic, fossilized nesting site of hundreds of specimens of duck-billed Maiasaura dinosaurs from up to 80 million years ago. This was one of the first findings that helped researchers learn more about how much some dinosaurs parented, even after their babies hatched.
At Egg Mountain, evidence of trampled eggshells suggests that the hatchlings were in the nest for a while. Along with the shells, there was plant matter in the nests, suggesting parents may have fed the young before they ventured out into the world. Researchers also found evidence that these dinosaurs may have used those nesting sites year after year.
Experts also found a group of one-foot-sized individuals and then a second group of three-foot-long individuals (the duck-billed dinosaur grows to 25 to 30 feet long) together in one nest. This suggests that they hatched out at one foot and then grew to three feet while still in the nest and under the care of the adults, says Varricchio.
Since the Maiasaura finding, researchers have suggested that the Psittacosaurus and Massospondylus also probably had similar parenting behaviors.
Read More: The Daunting Task of Measuring Dinosaur Intelligence
How Did Sauropods Lay Eggs?
Except for the dinosaurs closely related to birds, most dinosaurs fully buried their eggs in vegetation, sand or soil for the incubation and hatching process, not unlike many reptiles today.
Sauropods, such as the giant, heavy long-necked Brachiosaurus and Mussaurus, would have crushed their eggs if they were brooding on them, though — and they would have also risked crushing their babies if they were hanging out together a lot.
They were more likely to lay their eggs and then let them hatch on their own without any parental care. Researchers have come to these conclusions because, for example, their fossilized eggs were soft-shelled and leathery, like those of modern reptiles. Porous eggs are better at taking in the heat from their surroundings, even without somebody sitting on or next to them.
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Did Sauropods Guard Their Eggs?
What happens afterward is a little bit murkier. However — while there are certainly lots of dinosaur eggs that were made to be buried underground, Varricchio says, we really don't know if the parents then just left them or if they may have guarded their eggs from close by like crocodilians do.
They weren't just burying their eggs underground like modern turtles do: they were also getting crafty. For instance, an ancient nesting ground uncovered in Argentina was very close to volcanic activity and geothermal heat sources, suggesting that dinosaurs might have been leaving their eggs there to warm themselves while roaming to forage.
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Herds, Families, And Leaving Young Ones to Fend For Themselves
Laying eggs tied dinosaurs to one fixed location, but since some species took several years to reach maturity, that would mean that any hands-on parenting couldn't have lasted too long without food sources dwindling in the area.
Researchers have found some groups of young dinosaurs fossilized while bunched together, like these three Triceratops from Montana. As recently as 2021, a new study on the finding of an exceptional nesting site in Patagonia — over 100 eggs and more than 80 skeletal specimens of individuals of the Mussaurus patagonicus — serves as the most recent, convincing evidence that some dinosaurs traveled in age-segregated herds.
"The juvenile groups, I think, are important," says Varricchio, because they suggest the young ones might have been taking care of each other rather than having a parenting figure. Maybe, Varricchio says, dinos like Mussaurus would lay eggs, have parental care of those hatchlings but, by the next reproductive season, have left them on their own to come back to nest and reproduce again.
"I'm kind of doubtful that parental care extended for most dinosaurs beyond six, seven, eight or nine months[…] but not to second reproductive season," says Varricchio. "The evidence suggests that dinosaurs were good parents, but I don't think we had family groups."
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