Jurassic Park was wrong. Again.
In the second movie, hunters find an infant Tyrannosaurus rex and use it to lure the adults into a trap.
But in reality, that baby would have been much smaller, about the size of a cat. And it probably wouldn’t have been alone – the nest may have been absolutely crawling with dozens of them.
It likely wouldn’t have been very useful as bait either: Its parents probably would have considered losing a baby or two as just part of the process, and wouldn’t have cared enough to push a research trailer off a cliff.
So why are we updating our understanding of T. rex‘s childhood?
In a “vanishingly rare” discovery, paleontologists have found and closely examined fossils of tyrannosaur hatchlings. The remarkable findings are published in the journal Biology – and the implications go way beyond everyone’s favorite dinosaur.
“Going through museum collections, my colleagues and I have discovered the first remains of hatchling tyrannosaurs,” announced Nick Longrich, paleontologist and evolutionary biologist at the University of Bath in the UK.
When people think of dinosaurs, they tend to think of giants with long necks craning into the treetops, huge horned herbivores duking it out, and of course, the biggest land carnivores the planet has ever known.
But we know far less about the smaller species of reptiles, mammals, and other dinosaurs that were running around underfoot. That’s because not only did their remains fossilize less frequently than the behemoth’s, but modern scientists also tend to favor the big, attention-grabbing bones.
“Paleontologists overlook these little remains, which are almost always isolated bones, in favor of larger and more complete skulls and skeletons,” Longrich told ScienceAlert.
“There’s just a bias in what people study. Partly the small isolated stuff is hard to study, and partly people just assume it’s not that important, so it ends up stuck in a museum and neglected.”
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Longrich and his team set out to investigate these fragmented fossils gathering dust in storeroom drawers, expecting to find adult specimens of small dinosaurs. Instead, ironically, the work led the team back to the big guys.
One of the small bones appeared to be a third metatarsal – the middle foot bone – of a theropod dinosaur. But on closer inspection, it didn’t look like it came from a fully grown animal.
“The surface of the bone was incredibly porous,” Longrich says in a video on his YouTube channel.
“And this is the result of all these little microscopic blood vessels creating this dense network of blood vessels. And these nourish the bone as it grows. So they’re providing blood to the bone cells as they deposit bone tissue and remodel the bone. And this is typical of an immature dinosaur.”
When the bone was compared to others of its era, the researchers realized only one species fit the characteristics they were seeing.
“This is the foot bone of a very, very tiny T. rex. This is the smallest T. rex that we’ve ever seen,” said Longrich.
After that find, the team began to look more closely at other small fossils of bones and teeth, and realized that many could also be attributed to tyrannosaur hatchlings.
“I was most surprised by how closely the hatchling Tyrannosaurus fossils resembled those of big adults,” Eric Snively, paleontologist at Oklahoma State University in the US, told ScienceAlert.
“The foot bone had all the traits of a huge adult Tyrannosaurus; it was just narrower compared to its length. The teeth were chunky and worn, so the babies were biting into bone just like a 10-ton adult sundering bones of a big Triceratops.”
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Importantly, these bones were distinct from Nanotyrannus, a pygmy tyrannosaur species that can be mistaken for a juvenile T. rex. Other bone features excluded the possibility that these tiny tyrannosaurs were just embryos.
In the end, the researchers paint a very different picture of T. rex hatchlings, of which we know almost nothing. They estimate the main specimen to have been about 75 centimeters (30 inches) long and to have weighed around 2.5 kilograms (5.5 pounds).
Scaling back, it could have been as light as 1.7 kilograms when it first hatched. That’s much smaller than previous estimates, which suggested tyrannosaurs could have been up to a meter long when they hatched.
From this new size estimate, the team was able to calculate roughly how big an egg these hatchlings emerged from. These were surprisingly small too, given the sheer size of the monster laying them.
That suggests tyrannosaurs laid many eggs: the researchers estimated 20 to 30 per clutch. And that has some fascinating implications for their reproductive strategy.
No complete or certain Tyrannosaurus rex egg has ever been found.
The goal of reproduction is obviously to make more of yourself, and in a general sense, organisms use one of two broad strategies to get there.
They either have lots of offspring, quickly and often, so that it doesn’t really matter if some (or most) of them don’t live very long – there are plenty of backups. Organisms that use this method, such as rodents, are known as r-strategists.
The other method is to have fewer babies, but invest heavily in making sure they survive. These are the K-strategists, and that group includes whales and, of course, us.
It’s a trade-off, for sure: Do you leave dozens of your offspring on a beach to fend for themselves from birth? Or will you still be bringing snacks to their room after two decades? Both strategies seem to work for different species.
Because larger animals and modern dinosaurs (ie, birds) tend to be K-strategists, it was long thought that tyrannosaurs would raise their young with care.
But the new discovery that tyrannosaur young were small and numerous suggests they had more r-strategist tendencies than we thought.
Related: Baby Giants Were The Fast Food of The Jurassic, Study Reveals
That’s not to say T. rex parents were completely (tiny) hands-off, though. They seem to mark a kind of transitional phase that was happening throughout the animal kingdom during the time of the dinosaurs.
“It shows tyrannosaurs are transitional between reptiles like crocodilians and turtles on the one hand, and modern birds on the other,” said Longrich.
“Avian-mammal intensive parental investment and care seems to evolve gradually in the Mesozoic. At the same time tyrannosaurs are evolving larger and fewer young (relative to reptiles), we see mammals and plesiosaurs and even insects making similar shifts. Parental investment strategies change a lot in the Jurassic and Cretaceous.”
The research was published in the journal Biology.
This article was fact-checked by Carly Cassella and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
