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The skull of Oviraptor. This fossil was found with fossil eggs, indicating that this parent was brooding over a nest. From Osborn et al., 1924.

In 1994, paleontologists made a discovery that turned one dinosaur’s name into an irony. That dinosaur was Oviraptor – the so-called “egg thief” discovered several decades before, but that turned out to be a caring mother.

The story starts in 1923. In that year, an expedition from the American Museum of Natural History discovered dinosaur eggs in the Cretaceous rock of Mongolia’s Gobi Desert. At the time, the paleontologists thought that the eggs had been laid by Protoceratops – a small horned dinosaur that commonly found in these deposits – but there was another dinosaur associated with one nest. The AMNH team also discovered the skull of a toothless theropod dinosaur on top of a clutch of eggs. When paleontologist Henry Fairfield Osborn described the dinosaur in 1924, he presumed that the theropod’s jaws were well-suited to crushing eggs, and that this dinosaur was killed in the act of robbing another dinosaur’s nest. Oviraptor seemed like a fitting name for the Cretaceous looter.

Only, that Oviraptor was probably brooding over the nest. In 1993, fieldwork at another Gobi Desert site uncovered similar eggs, and, fortuitously, same of the eggs preserved the delicate skeletons of near-term embryos. The most spectacular baby was the little skeleton of an Oviraptor-like dinosaur, curled up inside its egg. Even better, the shape of this egg matched the supposed Protoceratops eggs discovered years before. Osborn’s Oviraptor wasn’t stealing eggs, but watching over them, and this conclusion was sooner supported by beautiful skeletons of oviraptorosaur skeletons preserved on their nests, their arms spread to encompass the eggs.

But there was something else very curious about the embryo described by Mark Norell and colleagues in 1994. In the same nest, the paleontologists discovered the partial skulls of two little dromaeosaurids – sickle-clawed dinosaurs such as Velociraptor. These two tiny dinosaurs were either embryos or hatchlings, but why should they be preserved in the same nest with a totally different species?

Norell and co-authors suggested several possibilities. The baby dromaeosaurids could have been the prey of adult oviraptorosaurs, might have been trying to prey on oviraptorosaur eggs, or, after death, could have been transported a short distance into in oviraptorosaur nest. The most tantalizing possibility, though, is that one of the two dinosaur taxa was a nest parasite. Perhaps, when no one was looking, a mother Velociraptor – or similar dinosaur – added a few eggs to an oviraptorosaur’s nest, passing off her parenting duties. Then again, the scenario could have played out the other way around (although I would not envy a baby oviraptorosaur born into a family of vicious raptors).

Frustratingly, we may never know why these two species of dinosaurs were preserved together in the same nest. But I have to wonder if some non-avian dinosaurs were brood parasites. After all, some species of birds – the one lineage of living dinosaurs – sneak their eggs into the nests of other birds, so it’s not inconceivable that this behavior has much deeper, Mesozoic roots. Perhaps, as paleontologists continue to collect and study dinosaur eggs, someone will find more direct evidence of sneaky oviraptorosaurs, raptors, or other dinosaurs.

Reference:

Norell MA, Clark JM, Demberelyin D, Rhinchen B, Chiappe LM, Davidson AR, McKenna MC, Altangerel P, & Novacek MJ (1994). A theropod dinosaur embryo and the affinities of the flaming cliffs dinosaur eggs. Science (New York, N.Y.), 266 (5186), 779-82 PMID: 17730398