During the time I've been the Dinosaurs guide at About.com, I've received about two dozen emails from readers claiming to have discovered fossilized dinosaur eggs. Usually, the person has been doing construction work in his or her backyard (laying a new sewer pipe, fixing a foundation) and the "eggs" have been dislodged from their nesting place a foot or two underground. Most of these individuals are simply curious, but a few have dollar signs flashing in their eyes, imagining that the world's leading natural history museums will soon be bidding the price of their fossilized eggs into the million-dollar range.
Take this to the Bank: Dinosaur Eggs Are Phenomenally Rare
The average person might be forgiven for believing that he's accidentally unearthed a cache of fossilized dinosaur eggs. Paleontologists dig up the bones of adult dinosaurs all the time; since the average female dinosaur probably laid hundreds of eggs in her lifetime, shouldn't fossilized dinosaur eggs be hundreds as time as common as fossilized dinosaurs?
Well, no. The surprising fact is that dinosaur eggs are only rarely preserved in the fossil record. The reason for this is simple: an abandoned clutch of eggs would inevitably attract the attention of predators, who would crack them open, feast on their contents, and scatter the fragile eggshells to the wind. Barring predation, the vast majority of eggs would probably have hatched normally, as nature intended, and the result would be (once again) an indistinguishable pile of fractured eggshells.
Of course, paleontologists do, every now and then, make spectacular discoveries of fossilized dinosaur eggs. "Egg Mountain," in Nebraska, has yielded numerous clutches of Maiasaura eggs, and elsewhere in the American west researchers have identified Troodon and Hypacrosaurus eggs. One of the most famous clutches belongs to a fossilized Velociraptor mother, buried (probably by a sudden sandstorm) in the act of brooding her eggs. Questions?
Q: If these aren't dinosaur eggs, what the heck are they?
A. The most likely answer is that you've found a collection of smooth, rounded rocks, which have been eroded over millions of years into vaguely ovoid shapes. You may also (don't laugh) have found the remains of chicken eggs that, say, were buried 200 years ago in a flood.
Q. These are much stranger-looking than chicken eggs. How do you explain that?
A. There were a lot more birds around 200 years ago than there are today! The eggs may have belonged to a turkey, an owl, or even (if you happen to live in Australia or New Zealand) an ostrich or emu. The point is that they were almost certainly laid by a bird, not by a dinosaur.
Q. I'm still not convinced. They look an awful lot like those Velociraptor eggs I saw a picture of in National Geographic.
A. Let's sit back and think this out for a moment. Velociraptors were native to Inner Mongolia. What makes you think they lived in the suburbs of New Jersey 75 million years ago?
Q. So you're saying that there's no chance these are real dinosaur eggs?
A. Well, never say never. The first thing you need is to figure out whether any of the geologic sediments in your state (or country) date back to the Mesozoic Era, from about 250 to 65 million years ago. Many regions of the world yield fossils older than 250 million years (before dinosaurs had even evolved) or less than a few million years (long after dinosaurs had gone extinct). That would reduce the odds of your being in possession of genuine dinosaur eggs to almost exactly zero.
Q. I don't believe you. Where can I get a second opinion?
A. If you have a university or natural history museum in your area, a curator or paleontologist may be willing to take a look at your discovery (or she may not, depending how many people have queried her about dinosaur eggs that week.) Just be nice, and be patient--it may take a busy professional weeks, or months, to get around to looking at your pictures, and then breaking the bad news.