Hollywood stars have nothing on the Tyrannosaurus. The dinosaur has been a celebrity for centuries, taking pride in its showcase in museum halls and on the big screen, from the days of stop motion to those of CGI. All that adoration is a little bit strange for a baby-eater.
Let me back up a little bit. Tyrannosaurus was the ultimate dinosaurian carnivore—the last and among the largest of the meat-eating theropods. Velociraptor, Ceratosaurus, Spinosaurus, and so many other Mesozoic celebrities belonged to the same group of flesh-rippers. (And while not all theropods were meat-eaters, all meat-eating dinosaurs were theropods.) Most of the time, we imagine these vicious saurians locked in combat with the giants of their age: Allosaurus versus Stegosaurus, Tyrannosaurus staring down Triceratops, and Giganotosaurus nipping at the flanks of the immense Argentinosaurus. It’s the sort of thing that makes you want to grab your collection of dinosaur models and make them snarl at each other in the nearest sandbox.
But these epic fights were probably rare, if they happened at all. Carnivorous dinosaurs might look monstrous, but the fact of the matter is that they were real animals that carefully selected their menus the same way many modern meat-eaters do. That means targeting the old, the sick, and the very, very young. And the fossil evidence for this isn’t so much in what paleontologists have directly uncovered as what they don’t find.
The next time you stroll around a museum hall, imagining the jaws of T. rex in action, think about the age of the dinosaurs on display. Not in geologic time, but how many candles that Edmontosaurus would have had on its last birthday cake. Most of them are subadults or adults. Geriatric dinosaurs are very rare, mostly because dinosaurs seem to have lived fast and died young, but hatchlings and juveniles are just as elusive. Part of this is the bias of the fossil record. Only a fraction of a fraction of a fraction of all life is preserved in the rock. An even smaller sliver is exposed to where paleontologists can find it, and a tinier slice still is what scientists will eventually discover. But there’s probably something else at play. That is, carnivorous dinosaurs loved eating babies.
Paleontologists David Hone and Oliver Rauhut laid out the case in a 2009 paper. While there have been a few cases of juvenile dinosaur bones found in the gut contents of big carnivores like spinosaurs and tyrannosaurs, it’s more startling that paleontologists don’t find baby dinosaurs more often. All dinosaurs laid clutches of multiple eggs. In some places, herbivores congregated in vast nesting grounds where each mama dino deposited a dozen or so eggs apiece. A wave of hatchling dinosaurs would have flooded the local habitats every season. You’d think we’d find more of these little ones, yet hatchlings and other young dinosaurs are very hard to track down.
The fate of baby sea turtles might be an echo of what might have happened in the Triassic, Jurassic, and Cretaceous. As multiple nature documentaries have taught us, mother sea turtles will periodically lay their eggs beneath the sand of the same beach, and some months later the hatchling sea turtles will emerge around the same time and make a dash for the ocean. Many of them don’t make it. Predators snaffle them up before they reach the waves, and something similar likely happened to many little dinosaurs. As infant dinosaurs hatched and left the nest, either immediately or after some amount of parental care, they ran right into the jaws of predators waiting to pick them off. And if the carnivores didn’t get them, many of those dinosaurs died within their first year from catastrophes like drought. Being a dinosaur sounds fun until you realize that, for some species, nearly 90 percent of baby dinosaurs perished before their first birthday.
This all makes sense from a predator’s perspective. Consider Allosaurus, for example. While the largest Allosaurus could reach about 40 feet in length (about the same size as a T. rex), adult herbivores such as Apatosaurus and Diplodocus were twice as big, if not even larger. And some came armed; Stegosaurus wielded a spiky tail that could be swung with enough speed to pierce bone. Taking on these giants risked dire injuries, some of which are preserved as broken and infected bones on Allosaurus skeletons. So the safer bet was to go after the smaller, naive dinosaurs as they tottered about in the woods.
So yeah, our favorite meat-eating dinosaurs were infant-gobbling jerks. But they were also vital to the Mesozoic world. Without them, the herbivores would have scarfed down every scrap of green food and driven the dinosaurs to an early extinction via starvation. So, if you look at it that way, The Land Before Time‘s Sharptooth is a hero, taking the ecological long view while the wandering dinobabies whine about missing their favorite treestar snack.
IMAGE: Brian Switek