MALE NARRATOR: In the 1920s, American paleontologist Roy Chapman Andrews led an expedition to the Gobi Desert of Mongolia in search of human origins.

That particular quest would end up going unfulfilled.

But Andrews and his team did find something pretty spectacular.

Instead of early humans, the rocks of the Gobi yielded a trove of dinosaur fossils that were completely new to science, including the world's first recognized dinosaur eggs.

The fossils confirmed that dinosaurs, like birds and reptiles, laid eggs.

But one of the more interesting specimens was a small, bird-like theropod dinosaur whose skull was found right on top of a nest of eggs that are believed to belong to a plant-eating dinosaur.

It appeared to be a thief, caught in the act of taking the eggs of another dinosaur.

When these fossils were sent back to the American Museum of Natural History in 1924, another paleontologist, Henry Fairfield Osborn, described the dinosaur and gave it the name oviraptor, or egg thief.

But Osborn had doubts about oviraptors' alleged behavior.

In the very paper where he named it "egg thief," he actually questioned whether oviraptor really did feast on other dinosaurs' eggs.

It would be decades before the case of the dinosaur egg thief was reopened.

But when it was, those new investigations would help reinvent how we thought about dinosaurs.

It would show that they weren't cold, unfeeling reptiles.

At least some of them were social, bird-like animals.

And instead of being the nightmarish nest robbers that they were thought to be, dinosaurs like oviraptor would reveal themselves to be caring parents, so dedicated to their offspring that they sometimes tried to protect their young to the very end.

In the early days of paleontology, we didn't know much about the parenting habits, if any, of non-avian dinosaurs.

That's mainly because there weren't any recognized dinosaur eggs in the fossil record, or even fossils of baby dinosaurs in a nest.

Some researchers like Osborn suspected that dinosaurs probably cared for their young a lot like birds do.

And species that do this use a strategy called K-selection.

This is where a parent uses its energy to ensure that its few offspring survive the early stages of development.

But many other paleontologists thought dinosaurs were more like some modern reptiles like turtles, which just lay their eggs and then leave, giving their offspring very little direct attention.

This strategy is known as R-selection.

Instead of using a lot of energy to make sure that one or just a few offspring survive, a parent uses that energy to produce many more offspring at once to increase the likelihood that at least one will make it.

And the expeditions to Mongolia in early 20th century provided more insights into which strategy dinosaurs might have used.

At the flaming cliffs of the Gobi Desert the first recognized dinosaur eggs were found.

But none of those eggs contained identifiable bones of the young inside.

But there were abundant remains of one species of dinosaur from the same fossil formation-- protoceratops, a small, hornless ceratopsian.

Because those dinosaurs were so abundant, the eggs were first thought to have belonged to protoceratops, which led Osborn to describe the skull found on top of the eggs to have belonged to the egg thief, oviraptor.

It would take about five decades before new discoveries would make experts rethink what actually happened at that site in the Gobi Desert.

In 1978, just outside of Choteau, Montana, not far from where I am now, a series of small dinosaur bones were found.

And they weren't just any little bones.

They were the first-ever fossils of baby dinosaurs found in a nest.

There were more than 10 of them, just over a half meter long.

And they were all in a big, oval-shaped nest.

The teeth of these baby dinosaurs showed a considerable amount of wear, which suggests that they were already eating.

And the bones, while still unfused, were sturdy enough to have allowed them to go outside the nest.

So those clues suggested that these baby dinosaurs weren't newborns.

They'd actually been in the nest for some time after hatching.

And if they stayed in the nest after they hatched, that would mean that something had to have been taking care of them-- parents.

So this new dinosaur was given the name maiasaura, or the "good mother lizard."

Now paleontologist had direct evidence of dinosaur parental care, caring for their offspring after they hatched, much like birds do today.

This discovery was part of the dinosaur renaissance that started in the late 1960s, which we've talked about before.

It caused paleontologists to rethink how they interpreted dinosaurs' social behavior, not as slow, dimwitted, solitary reptiles, but as smart, active animals.

And it was during this time that scientists started to rethink what we really knew about oviraptor.

They knew it was a theropod, specifically a maniraptoran, which is a group of dinosaurs that includes modern birds.

And since it was part of that branch of the dino family tree, paleontologists began to question how bird-like they really were in terms of behavior.

So in the 1990s, the American Museum of Natural History finally returned to the Gobi Desert.

And they found the evidence that would exonerate the alleged egg thief.

A series of expeditions brought back a variety of new fossils, among them an egg very similar to the ones originally found with oviraptor.

But this egg was really close to hatching, and preserved the bones of the baby inside.

And it turns out the embryo was not a protoceratops, as they expected.

Instead the bones were of a baby oviraptor, meaning that the eggs from their earlier expedition were also from oviraptor.

So the original specimen of oviraptor that was found on that nest-- it wasn't trying to steal the eggs; it was trying to protect them.

Oviraptor wasn't an egg thief.

It was actually a parent that was dedicated enough to die while trying to protect its offspring from a sandstorm, or a flood, or maybe a sand dune collapse.

So Henry Fairfield Osborn was right to doubt the name that he gave oviraptor, which means he was also wrong to have called it that in the first place.

And since then more specimens from the same family as oviraptor have been found.

And they've been key to our understanding of dinosaur parenting.

During that same expedition to the Gobi, another relative oviraptor was found, named citipati.

And it showed just how close dinosaurs were to birds and their parenting behavior.

The specimen was about 70 million years old.

And it was given the nickname Big Mamma because it was found sitting on top of a nest of about 20 eggs.

And we know this was its nest because of how it was positioned on the eggs.

Its body was in the center, with the eggs surrounding it in a circular pattern.

The wider ends of the eggs were all pointed toward the center of the nest, and the dinosaur's forelimbs were spread out, covering the eggs as if to protect them.

And the eggs closest to the body were found touching the dinosaur's gastralia, those bones found along the bellies of some reptiles, suggesting that the dinosaur kept them right next to its abdomen.

This is very similar to a behavior seen in modern birds called brooding, in which birds use their body heat and feathers to incubate and protect the eggs in their nest.

Fossils like the one of Big Mamma that directly depict behavior are really rare.

But since this discovery, other specimens in the same family as oviraptor and citipati have been found to also show signs of brooding behavior.

And while it's still being debated, there's some evidence that suggests to brooders of these eggs may not have been mothers, but fathers.

In 2008, a study collected a bunch of data on dinosaurs' body sizes as well as the number of eggs they typically had in each clutch.

The study then compared that data with the same info from different groups of living archosaurs, the group that includes birds, non-avian dinosaurs, and also all the crocodilians.

And some of the archosaurs they used were maternal, meaning that parenting is done by the females.

And some were paternal, where dads do the work.

The results showed that dinosaurs like oviraptor and citipati lined up closely with birds that display paternal care, like emus and most of their close relatives.

Another part of this study also showed that the fossils of those brooding dinosaurs didn't have medullary bone, a type of bone tissue found in ovulating female birds that remains for a short time after they lay their eggs.

So again, experts are still arguing about this, but there's some evidence that suggests the dinosaurs found in those nests were probably males.

If true, this might mean that oviraptor and its relatives were good father lizards-- dads for the win.

Over the last century or so, while oviraptor has gone from potential egg thief to attentive father, we've also learned more about the origins of parenting behavior.

Some archosaurs like crocodilians have been shown to exhibit general parenting behavior.

But the behavior that we associate with birds, like brooding and long-term care of their young, seems to have originated in non-avian dinosaurs.

So it's time to exonerate oviraptor.

And while we're at it, we should probably change the name too.

Instead of "egg thief," might I suggest whatever the Latin is for dinosaur dad?