Rugged as they look, fossilized dinosaur skulls are frustratingly hard to find; exposure, scavengers, and flash floods ensured that few of the information-laden artifacts survived their day. But in the 28 September issue of Science , researchers report the miraculous discovery of some of the most delicate dino skulls of all--those of fossilized embryos. The tiny skulls belong to the titanosaurs, a group of sauropods known only from incomplete skeletons. "This is a really exciting find," says Jeffrey Wilson of the University of Michigan's Museum of Paleontology in Ann Arbor.
Paleontologists have only been able to identify the embryonic remains of a handful of dinosaurs, and knew of only one skull. Intact embryos of the long-necked, lumbering sauropods remained unknown. The newly found embryos come from a site in Patagonia, called Auca Mahuevo, whose rocks are packed with thousands of dinosaur eggs between 79 million and 83 million years old. In 1998, Luis Chiappe of the Natural History Museum of Los Angeles County, Rodolfo Coria of the Carmen Funes Museum in Plaza Huincul, Argentina, and others described cantaloupe-sized eggs containing fragmentary bones--and the chisellike teeth of titanosaurs. Now, they have found two embryos with intact, 4-centimeter-long skulls.
The find may help show which skeletal features of titanosaurs developed in tandem and which are independent. That's important, because scientists determine evolutionary relationships by comparing such features, or characters, and spurious connections can lead them astray. The embryonic titanosaur skulls confirm earlier suspicions that two key sauropod traits--the orientation of the braincase and the position of the nostrils--are independent, Chiappe and his colleagues say. Further study could tease apart even more characters to help paleontologists sort out the sauropod family tree.
The embryos may also shed light on early sauropod evolution, about which relatively little is known. Although development doesn't necessarily replay evolutionary history, says paleontologist Eric Buffetaut of the basic research agency CNRS in Paris, embryonic features may be reminiscent of more primitive sauropods. "If you can use embryos as proxy to reconstruct this early evolution, that's really original," he says.