Scrambled Eggs and the Demise of the Dinosaurs
Did egg-eating lizards and snakes contribute to the dinosaurs’ extinction?
In 1925, when Yale University paleontologist George Wieland published a paper titled “Dinosaur Extinction,” no one knew why the great archosaurs had disappeared. The fact that the extinction of the dinosaurs was even worth explaining was a new idea. From the time dinosaurs were initially described in the early 19th century through the beginning of the 20th, their existence and disappearance simply seemed to be part of a grand progression of life that required no special attention or explanation. Even when paleontologists began to puzzle over why the dinosaurs vanished, many thought that dinosaurs were inevitably doomed by strange, internal growth factors that made them so large, stupid and ornate that they could not possibly adapt to a changing world.
But Wieland took a slightly different view. While his paper was more opinion than science—there was nothing measured, quantified or tested in the article—Wieland believed that he had perhaps identified some of the “invisible influences” that triggered the demise of the dinosaurs. Egg-eaters were of primary concern.
Wieland was not the first to suggest that the destruction of dinosaur eggs led to the group’s extinction. As pointed out by Wieland himself, paleontologists Charles Immanuel Forsyth Major and Edward Drinker Cope had previously speculated that small mammals may have raided dinosaur nests so frequently that Triceratops and its Mesozoic ilk were incapable of reproducing successfully. This hypothesis seemed plausible in general, but Wieland disagreed about mammals being the primary culprits. Small Mesozoic mammals seemed too weak to break open tough dinosaur eggs, and the most voracious modern-day nest thieves seemed to be those reptiles capable of swallowing eggs whole. “The potent feeders on dinosaur eggs and young must be sought for amongst the dinosaurians themselves,” Wieland remarked, “and perchance, amongst the earliest varanids and boids .”
Wieland believed that egg-eating must have been rampant during the age of the dinosaurs. In fact, he thought that a diet of eggs may have even led to the evolution of some of the largest of all predatory dinosaurs. Considering the giant Tyrannosaurus, Wieland wrote, “What more likely than the immediate ancestors of this dinosaur got their first impulse toward gigantism on a diet of sauropod eggs, and that, aside from the varanids, the theropod dinosaurs were the great egg-eaters of all time?” The cruel irony of this idea was that the immense predatory dinosaurs also reproduced by laying eggs, and Wieland considered it “quite inferable” that their nests, in turn, would have been raided by smaller monitor lizards and snakes.
Dinosaurs were not entirely defenseless against such attacks. Though dinosaurs were often thought in the 1920s to be reptiles write large, Wieland speculated that dinosaurs would have provided some parental care, were probably more active than living lizards and crocodiles and, among the egg-eating varieties, may have even sought out unprotected nests in coordinated “droves.” “With such active and powerful beasts at the jungle-edge,” Wieland wrote, “life was varied and sanguinary, be it within scientific dignity to say so.” Unfortunately, an active and varied existence could not save the dinosaurs. Both ecological factors and the supposed inability of dinosaurs to change sealed the fate of the dinosaurs, Wieland concluded; the great loss of eggs and the “racial senility” of dinosaurs ultimately ushered the group into extinction.
When Wieland wrote his paper, he could only speculate about predation on dinosaur eggs and babies. In the decades since, however, paleontologists have turned up rare fossil evidence that small predators truly did snap up young dinosaurs in various stages of development. In 2010, paleontologists announced the discovery of Sanajeh, a late-Cretaceous snake that may have fed on the eggs of sauropod dinosaurs. Several years before that, a different team of paleontologists found several baby Psittacosaurus skeletons in the fossilized stomach contents of the opossum-sized mammal Repenomamus, and in a 1994 paper, paleontologist James Kirkland suggested that small crocodyliforms like the slender Fruitachampsa may have also gobbled up eggs and little dinosaurs since their bones are sometimes found in association with dinosaur nests.
Despite these recent discoveries and hypotheses, however, there is no indication whatsoever that dinosaurs were driven to extinction by egg-eaters, reptilian or otherwise. Perhaps such a view was tenable when only a few dinosaur genera were known and we understood very little about their ecology, but not now. We have a greatly revised understanding of what happened at the end of the Cretaceous—a mass extinction that wiped out not only the dinosaurs, but a vast swath of life forms on land and sea. There is no hint of a run on dinosaur eggs in the fossil record, and the various types of supposed egg predators lived alongside dinosaurs for millions of years without killing off their egg-laying food supply. Dinosaur eggs certainly were a nutritious resource that were undoubtedly exploited by carnivores and omnivores, but such depredations were not the keys to dinosaur extinction.
Wieland, G. 1925. Dinosaur Extinction. American Naturalist. 59 (665): 557-565