Frozen in time: Scientists find rare fossil of dinosaur sitting on eggs with embryos inside

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Beneath the weight of 70 million-year-old rocks in Ganzhou City, China, lies the skeleton of a dinosaur nurturing its eggs. 

This is the first fossil of its kind, as it shows an oviraptorosaur sitting upon a nest with ready-to-hatch embryos inside. 

Matt Lamanna is a paleontologist and dinosaur researcher from the Carnegie Museum of Natural History. He is part of an international team of researchers who studied the remains and published their findings in the Science Bulletin journal in December.

He spoke with As It Happens host Carol Off about the significance of this discovery. Here is part of their conversation.

Matt, how rare is a find like this one?

Oh, this is as rare as they come.

People have found a few dinosaurs sitting on nests with their own eggs before, and they've found plenty of nests that contain embryos. But this is the first time the two have been combined in one single, spectacular fossil.

So because the animal was fossilized in this position, atop a nest of eggs that contain oviraptorosaur embryos — presumably its own — we think that this animal perished in the act of incubating its nest.

What would it have looked like?

Imagine a big ground bird, like an ostrich. Or ... if you're familiar with something like a cassowary ... an ostrich relative that lives in Australia and New Guinea that has a crest on its skull. 

This animal would look something like a cassowary or an ostrich, except with long, well-developed four limbs that were tipped with three big claws.

Wow. And so it had feathers, but it didn't fly, right?

Absolutely.

Now, what is the oviraptorosaur actually doing at the moment that it's fossilized?

It was fossilized in what we think is an incubating position.... We think this is probably just due to erosion.

The head and neck were lost, as was part of the back and the end of the tail. But the rest of the animal is there ... the forelimbs, the high limbs, part of the torso, part of the tail, part of the neck. And what's there is crouched in the middle of a nest with its arms wrapped around the outer edge of the nest ... a position very, very similar to what you see many modern birds do when they're sitting on their nests. 

We presume it was female, right?

We actually tried to test this in our study, but the results were inconclusive. 

The reason why I say it's uncertain is that some modern birds, such as ostriches, take turns with the male and female incubating the eggs. 

Although it's quite possible that this was a female, it's also possible that this was the dad. And we don't know for sure.

If the embryos are fairly well-developed, how close were they to actually hatching?

[We observed] seven of the embryos ... out of the 24 eggs. There may be more embryos inside some of those eggs — or maybe all of them. All of those embryos are at relatively advanced developmental stages, but they're slightly apart from one another.

That suggests that maybe the eggs in the top layer of the nest — the layer that was closest to the adult — hatched a little bit before the eggs in the next layer, and so on and so forth. So we think that they were close to hatching, but they might not have all hatched at the same time.

And this oviraptorosaur had 24 eggs?

Yeah.

We don't really go into the reasons for this on the paper, but I sometimes wonder whether these animals may have nested communally, like the way ostriches do, for instance. 

[With] ostriches, multiple females can contribute to the nest and then, a single pair — a male and female — take turns incubating that nest.

If some of these embryos are pretty close to hatching and it appears that this dinosaur, male or female, is incubating them, does it change any assumptions or theories about oviraptorosaurs and their young?

I would say it doesn't change all that much, but it provides some of the best evidence yet that oviraptorosaurs, and presumably many what we call non-avian dinosaurs, did probably nurture their young. 

For instance, a few oviraptorosaurs have been found sitting on nests before. But some people have claimed that in those cases, the animal perished while it was in the act of laying its eggs, or maybe the animal was guarding its nest in the fashion that, say, alligators and crocodiles do today. In other words, hanging around and protecting the eggs, but not incubating them. 

The combination of circumstances preserved here ... provide some of the best evidence yet that oviraptorosaurs and potentially other dinosaurs incubated their nests.

To find this creature frozen in this moment with his or her young, what's your theories as to how he or she died?

I'll confess we didn't really explore this question all that much in our study. But the rocks in which this fossil is preserved are mudstone. So in other words, it's rock that's formed from ancient mud, and seemingly quite a significant quantity of mud at that.

I sometimes wonder [if] something like a flash flood potentially [killed them].... If that's the case, if this animal hung around on top of its nest trying to protect its eggs to the very last as this flood was bearing down on it, starting to bury it in mud — I mean, that, to me, is devotion. That's a devoted parent that's doing everything it can to protect its offspring, even to the very end.

Written by Mehek Mazhar. Interview produced by Katie Geleff. Q&A edited for length and clarity.