Living Dinosaurs: Fossil Eggs Reveal Evolutionary Link Between Birds and Dinosaurs

Birds may have more in common with dinosaurs than we once thought. Paleontologists have discovered a small North American dinosaur that incubated its eggs in a similar way to brooding birds. The finding could point to a strong, evolutionary link between the two.

How dinosaurs cared for and hatched their young has baffled paleontologists for years. It's possible that they buried their eggs in nest materials like crocodiles, or placed them in open nests like brooding birds. Until now, though, researchers weren't sure which theory was most likely.

Using clutches found in Alberta and Montana, researchers closely examined the shells of the fossil eggs found within them. The eggs themselves were laid by a small, meat-eating dinosaur called Troodon. Existing around the Late Cretaceous period, this creature ranged widely; its fossils can be found all the way from Texas to Alaska. Possessing one of the largest known brains of any dinosaur group relative to its body mass, this creature also possessed large eyes that were slightly forward facing, which probably aided in hunting.

After examining the eggs, the researchers found that only the bottoms of them would have been buried in mud while the tops would have stuck out vertically. It turned out that, like brooding birds, this particular dinosaur did not bury its eggs.

"Both the eggs and the surrounding sediments indicate only partial burial," said Darla Zelenitsky, co-author of the paper recording the study, in a press release. "Thus an adult would have directly contacted the exposed parts of the eggs during incubation."

Although this particular nesting style is unusual among birds, it does have certain similarities with one particular species: the Egyptian Plover. This bird broods its eggs while they're partially buried in the sandy substrate of its nest, rather like the Troodon partially burying its eggs in mud.

"For now, this particular study helps substantiate some bird-like nesting behaviors evolved in meat-eating dinosaurs prior to the origin of birds," said Zelenitsky in a press release. "It also adds to the growing body of evidence that shows a close evolutionary relationship between birds and dinosaurs."

That body of evidence has grown by leaps and bounds as paleontologists continue to unearth more clues about the behaviors of dinosaurs. One of the first comparisons between birds and dinosaurs occurred in 1969 when J.H. Ostrom described Deinonychus antirrhopus and its similarities to Archaeopteryx. Since then, researchers have continually noted the similarities between theropod dinosaurs and birds, according to the University of California Berkeley. Whether a specific species of dinosaur actually gave rise to birds, though, remains to be seen.

The new study is published in the journal Paleobiology.