Millions of years ago – long before even the strike of the dinosaur-killing asteroid – a Protoceratops laid a dozen eggs in an area that would later be the Gobi Desert of Mongolia. Yet those eggs never hatched and instead became frozen in the mists of time. And eventually, against all the odds, they were discovered by scientists and made their way to the vaults of the American Museum of Natural History in New York. Then, in 2017, experts used a new approach to take a closer look at the fossilized eggs. And what they found could change what we thought we knew about the dinosaurs.
Up until then, you see, there had been a distinct lack of scientific understanding of one particular area of dinosaur life. In fact, Gregory Erickson, a biology professor from Florida State University (F.S.U.), said in 2017 that “virtually nothing is known” about “some of the greatest riddles about dinosaurs.” So he led a new research team to attempt to solve some of these mysteries.
In order to do this, then, Erickson and his group of experts examined embryos belonging to a pair of different species of dinosaurs. And by establishing the age of the embryos, he and his team reached some fascinating conclusions about how dinosaurs lived and reproduced. What’s more, their discoveries could even shed light on the mass extinction event that wiped these creatures from the Earth.
Throughout history, of course, dinosaur fossils have been a source of intense fascination for mankind. And with research and technology being more sophisticated now than when these remains were first discovered, we’re constantly learning new things. But it’s by no means just fully formed dinosaur specimens that have revealed incredible secrets to us.
The science of paleontology began in the mid-19th century, in fact, when researchers in Britain noted dinosaur bones for the first time. And before long, these experts theorized that the creatures had reproduced in a manner similar to modern-day reptiles. It wasn’t until later in 1859, though, that the first fossilized eggs were actually discovered.
Unearthed in France, these fossils were initially incorrectly identified as having belonged to a species of bird. They were therefore overlooked for a seriously long time. In fact, it would be another 64 years before experts successfully identified a clutch of dinosaur eggs. That discovery was made by researchers from the American Museum of Natural History working in Mongolia.
From that point on, though, dinosaur eggs started to emerge from every corner of the world. But what of the creatures that had once inhabited these shells? Well, some of the fossils had formed after the creatures inside had successfully hatched – but others told a very different story. And in rare cases, the tiny remains of developing creatures had even been preserved.
So, before the discovery of dinosaur eggs, little had been really known about how the creatures inside had developed. But now that experts had access to fossilized embryos, they were able to begin theorizing about what happened. And over time, many of the scientists concluded that the incubation process was similar to that seen in today’s birds.
But in 2013 Montana State University’s David J. Varricchio published a paper that proposed an alternative theory. According to him, certain dinosaur eggs had been equipped with pores – suggesting that they had been covered up underground. In turn, Varricchio said, this implied that the incubation process had more in common with that of modern-day reptiles.
Without any definite conclusions, however, much surrounding this area of paleontology remained a mystery. In a 2017 statement given to F.S.U., Erickson summarized the outstanding questions: “Did [dinosaur] eggs incubate slowly like their reptilian cousins, crocodilians and lizards? Or rapidly like living dinosaurs, the birds?”
So, hoping to answer this question once and for all, Erickson decided to take an interesting approach. Just like humans, you see, reptiles apparently produce a substance known as dentin on a daily basis. Found in the teeth, this tissue mineralizes into a tough core that builds up in layers over time.
And thanks to this process, researchers are able to determine the age of some organisms by looking at the layers in teeth. As Erickson told The Washington Post in 2017, “You can basically just count those up and figure out how long it took dentition to form.” In fact, he likens the approach to noting the rings of a tree to establish how long it’s been alive.
It seems that this led Erickson to wonder if the embryos of dinosaurs could be studied in the same way. He subsequently reached out to experts at Canada’s University of Calgary and the American Museum of Natural History in New York. Basically, he wanted to see if there was a method to test his theory.
And despite the fact that fossilized dinosaur embryos are extremely uncommon, both institutions were able to assist Erickson in his research. At the American Museum of Natural History, for instance, researchers unearthed a dozen eggs that’d been discovered in the Gobi Desert in Mongolia. According to experts, too, these had belonged to the species Protoceratops andrewsi – a creature related to the Triceratops.
At not quite seven ounces, these eggs were relatively small – roughly the same proportions as a potato. But the other specimens that Erickson was able to get hold of were in a totally different league. Discovered in the Canadian province of Alberta, these fossils had once belonged to a dinosaur known as Hypacrosaurus stebingeri.
Capable of growing up to 30 feet in length, the duck-billed Hypacrosaurus laid eggs that weighed almost nine pounds. Visually, the eggs could be described as having proportions roughly the same as a volleyball. Yet even though these specimens were very different to the ones found in Mongolia, they yielded similarly exciting material for Erickson.
Within both sets of eggs, you see, researchers had discovered the fossilized embryos of dinosaurs. But could Erickson use dentin analysis to learn about their ages – and thus the amount of time that they might’ve taken to hatch? Well, working as the head of a team of researchers, the professor set out to find the answer.
First, Erickson and his team used a CT scanner to look at the dentition present in the embryos’ jaws. Then the group removed a number of teeth from the fossilized remains. Using microscopes, they were subsequently able to zoom in on the ancient specimens to find exactly what they’d been searching for.
According to Erickson, in fact, the lines of dentin in the teeth became clear. As the lead researcher told The Washington Post, “I knew we were in business.” Yes, it was now possible for the team to determine how long the embryos had been alive. “We could literally count them to see how long each dinosaur had been developing,” Erickson explained in his F.S.U. statement.
For the researchers involved, then, it was an understandably exciting development. In the same statement, Erickson’s co-author, Darla Zelenitsky, explained, “Time within the egg is a crucial part of development. But this earliest growth stage is so poorly understood because dinosaur embryos are rare. Embryos can potentially tell us how dinosaurs developed and grew very early on in life and if they are more similar to birds or reptiles in these respects.”
So, as a result of the study, Erickson and his team were able to acquire solid evidence to suggest how long dinosaurs such as Hypacrosaurus and Protoceratops took to hatch. And according to Erickson himself, it’s the first time that such conclusions have been reached. What exactly did they learn from these ancient remains, then?
Well, the team were able to calculate that somewhere close to 40 percent of the embryos’ incubation periods would have been spent developing teeth. The experts also estimated that these dinosaurs took a long time to hatch. Perhaps double the amount of time compared to avian eggs of much the same size, in fact.
Specifically, the team discovered that the smaller Hypacrosaurus would have taken approximately three months to hatch. The larger Protoceratops, meanwhile, may have spent as many as six months developing inside the egg. This is, apparently, the first time that researchers have been able to pinpoint specific incubation times for non-avian dinosaurs.
But that’s not all. For while Hypacrosaurus had been an undeniably sizable dinosaur, it’d been far from the biggest. And because modern reptiles and birds indicate that larger eggs take more time to hatch, it’s likely that some creatures had had much longer incubation periods. In fact, Erickson believes that these could have stretched to almost 12 months.
“It’s really surprising,” Erickson told The Washington Post. “I don’t think that people would have entertained the idea that they would have incubated over the better part of a year.” However, for Varricchio – who’d long believed that dinosaur reproduction had been more similar to that of reptiles than birds – the news was less of a shock. After all, according to Varrichio, present-day reptiles will spend many months incubating as well.
In modern science, though, it’s generally been believed that birds are the closest living things to dinosaurs. It’s not surprising, therefore, that many experts had deduced that dinosaurs might have had similar reproductive processes to birds. Yet thanks to Erickson and his team, it can now be theorized that the creatures of the Mesozoic Era actually had more in common with reptiles.
Typically, then, bird eggs have relatively short incubation periods, with embryos usually taking between ten and 30 days to emerge from their shells. Even emperor penguins – whose young take the longest to hatch out of any avian species – spend just two months developing. Modern reptiles are a different story, however.
Regularly referred to as cousins of the dinosaurs, today’s reptiles have average incubation periods of between one and two months. But it’s not just the time that it takes for their eggs to hatch that’s different to their prehistoric relatives. Apparently, you see, the way in which reptiles interact with their developing young is also at odds with the dinosaurs.
For one thing, today’s reptiles bury their fertilized eggs underground. And while some species will remain with their young in order to protect them, the vast majority abandon them to fate. So if dinosaur eggs took a similar time to incubate, did prehistoric moms-to-be also engage in such a detached approach to parenthood?
Amazingly, there’s evidence to suggest that dinosaurs – unlike modern-day reptiles – actually remained with their young throughout the incubation period. According to Varricchio, you see, previous research has indicated that parental care existed within some species. This typically related to those creatures whose eggs had been limited in size and likely took less time to hatch.
The dino-parents’ constant presence would have protected their young and prevented them from being eaten by predators, too. Yet if some dinosaur eggs took the best part of a year to hatch, that would’ve been a long time for the moms and dads to have remained in the same locations. On the balance of things, then, might this lengthy incubation period have actually contributed to the dinosaurs’ ultimate extinction?
Interestingly, the discoveries made by Erickson and his team have called many pre-existing theories into question. For example, it’s long been suspected that some dinosaurs spent the warmer summer months in the Arctic. This line of thinking also states that the creatures would have migrated south to Canada for the colder part of each year. But now such a journey seems improbable.
In fact, given the time that it would’ve taken some dinosaur embryos to develop, it seems unlikely that the creatures could have migrated at all. It wouldn’t have been easy for the adults to choose sites for their nests, either. Because if the eggs took so long to hatch, it likely would’ve been necessary to find spots that could be looked after for long periods.
But those aren’t the only difficulties associated with tending to nests of eggs for extended times. By staying in one place for months, you see, dinosaurs may have made themselves more vulnerable to starvation, natural calamities and predators. In short, they could already have been at a disadvantage when disaster eventually struck.
Yes, scientists believe that somewhere close to 66 million years ago, an asteroid dramatically collided with our planet. Afterwards, it’s thought that debris from the impact filled the atmosphere too. This would have prevented light from the sun reaching Earth. And in the ensuing darkness, temperatures plummeted – and ecosystems were thrown into disarray.
In the end, scientists say, this event led to the extinction of 75 percent of living things on the planet. The creatures that did survive likely did so by being adaptable and fast to reproduce. For example, the progenitors of contemporary birds are thought to have had short incubation periods. And this would have allowed them to quickly repopulate the stricken planet.
But with their slow incubation times, creatures such as Hypacrosaurus and Protoceratops wouldn’t have found it so easy to reproduce. In the statement from F.S.U., Erickson explained, “We suspect our findings have implications for understanding why dinosaurs went extinct at the end of the Cretaceous period. Whereas amphibians, birds, mammals and other reptiles made it through and prospered.”
Yet although Erickson and his team believe the dinosaurs’ slow incubation periods may have stood in the way of their survival, it wasn’t the only factor. Apparently, these lumbering creatures were also disadvantaged in some other ways. As large, warm-blooded animals, for instance, dinosaurs were terrible at conserving energy.
Aside from that, Erickson claims, the dinosaurs also took a long time to mature – even after they’d finally hatched. From an evolutionary point of view, then, these creatures were not particularly well-equipped to handle change. And when their habitat drastically altered, dinosaurs seemingly had little to help them adapt to their new world.
“The dinosaurs found themselves holding some bad cards,” Erickson told The New York Times in 2017. “They had a dead man’s hand.” Millions of years after the mass extinction, then, creatures such as Hypacrosaurus and Protoceratops have naturally long since vanished from the Earth. But thanks to researchers such as the team at F.S.U., we’re still learning more about them every day.