Adding to the wealth of information gleaned from the discovery a few years ago of a Late Cretaceous dinosaur nesting ground in Patagonia, researchers have unearthed from the site six fossil eggs complete with fetal titanosaurs. The newly found embryos, described in a report published today in the journal Science, feature beautifully preserved skulls that provide insight into the evolutionary development of these beasts.

Titanosaurs, as their name implies, were enormous creatures, some weighing as much as 90 tons. Members of the long-necked, herbivorous sauropod group, these behemoths have turned up in many parts of the world. Yet titanosaur skulls have proved exceedingly rare. The nearly complete embryonic skulls described by Luis M. Chiappe of the Natural History Museum of Los Angeles County and his colleagues thus go a long way toward filling that gap. (The photograph at the right features one such skull. Here, the snout points toward the lower left corner of the photo, while the eye socket lies at its center.)

These skulls, the authors report, "shed light on the evolution of some of the most notable cranial features of sauropod dinosaurs." Contrary to what some researchers have suggested, the characteristic retraction of sauropod nostrils, for example, appears to have evolved separately from the forward rotation of the braincase. Certain key features of their cheek and eye regions, however, could have evolved in concert. "The discovery of the new embryonic sauropod dinosaur skulls," the team notes, "provides another example of how developmental data inform our understanding of evolutionary events.