News flash: not all dinosaurs were terrible parents
The history of paleontology has not been kind to dinosaurs. For the most part, they’ve been portrayed as vicious, cold-blooded killers with nothing but a capacity for carnivorous destruction. Fortunately, we think to ourselves, they were wiped from the face of the Earth with the bolide-driven extinction event that struck the Yucatan 65-million-years ago.
A new finding, however, has shown us that these dinosaurs may have had a greater potential for love and kindness than previously imagined. Instead of the horrible killers we’ve learned them to be (thanks, Jurassic Park), they actually showed a few measures of sociality. While exceptionally rare among reptiles — and doubly rare among non-avian reptiles — this new finding has shown that among certain species of dinosaur there was parental care. The ostensibly irredeemable theropod dinosaurs might have had a warm, gooey center after all.
The recent finding was published in the journal Geology early last month. An excavation site in Mongolia’s Gobi Desert showed that 15 egg clutches (with a total of 50 eggs) were laid closely together and at the same time. From this, paleontologists could infer many things about the dinosaurs’ parental and group behavior. Among these were that the eggs were laid, monitored, and guarded communally in an effort to combat the vicissitudes of predation.
Similar sites have been unearthed in the past, yet none have been able to provide clear evidence of having existed at the same time. In other words, while we’ve found dozens of eggs located in the same geographic areas, these sites were not enough to establish that the eggs were laid at the same time and during the same year by a group of dinosaurs roaming together. Because these data were lacking, the eggs could have been laid successively, one after the other, and not in groups like the scientists were thinking.
Egg Mountain, for instance, was the first site — discovered in 1977 — thought to have shown dinosaurs nesting together. Located in Choteau, Montana, it showed 14 dinosaur nests confined to one localized area. While the site helped prime paleontologists to expect a certain degree of parental care in some species of dinosaur, it wasn’t enough to establish the connection completely. Because there were no geologic markers to unify the eggs into one particular strata, it was possible that the eggs were laid during distinct geologic time periods.
What made this site in Mongolia different from Egg Mountain was that a small series of floods would unite the egg clutches. During the Late Cretaceous (100 to 66 million years ago) in which the eggs were laid, the site was eventually overtaken by two floods — the first diminutive and the second large. The latter flood was so large, in fact, that it would fully encase the eggs in silty waters that would eventually harden to preserve them. This flood shows itself in a red band of lithified mud that filled each of the eggs and surrounding rock.
Luckily for the dinosaur parents, 60 percent of the eggs managed to hatch prior to the muddy entombment. This is evidenced by the little windows that adorn the top of the majority of these eggs. (And, in case you were wondering, 60 percent as a rate of survival is not unique to these ancient beasts. We find the same ratio in crocodiles, another reptilian species that shows parental care, and extant birds. When laying batches of eggs, not all are expected to survive and thrive.)
The scientists suspect that the eggs belonged to a species of therizinosaurs (therizo in Greek means “to reap”). Therizinosaurs are known as some of the largest species of terrestrial dinosaurs to have ever existed. They measured around 10 meters (33 feet) tall and weighed up to five tons. Amazingly, these dinosaurs worked in teams to protect their babies.
On the hands of these therizinosaurs were razor-sharp talons that were used, scientists think, to grip and tear down branches. The largest of these razors we’ve found measured about one meter (3.3 feet) in length. Fortunately, scientists hypothesize that the thing was herbivorous, implying that it didn’t have too strong a penchant for slicing up its dino compatriots.
Ultimately, the fact that these eggs were laid in groups suggests that the therizinosaurus exhibited a certain type of parental behavior. Its strategy was to work with others to minimize the possibility of baby-eating. For what other reason would animals group together to raise their young? It’s not like they were trying to preserve a friend group and late-night cocktail hour. Anyways, the finding helps add to a growing consensus that not all dinosaurs were murderous monsters. Some of them, as shown here, liked to care. Whether we acknowledge that fact is up to us.