Were Giant Dinosaurs Gregarious? - Walking On Eggs - page 147

of rock containing the trackways of twenty-three sauropods all mov-
ing in the same direction within a narrow corridor about fifteen yards
wide. The overlapping of the trackways, based on the analysis of
Lockley, documents that larger sauropods were leading the way and
younger, smaller individuals followed in line. The herd was moving at
a modest walking pace, veering from right to left. There is no evidence,
though, to suggest that the larger adults had encircled the smaller
juveniles to protect them, as some researchers had speculated earlier.
Even though sauropods had a complex social structure that, at
least at times, involved herding, it is still not known whether they
gave their eggs and hatchlings parental care, that is, whether the
adults fed and protected their young. Parental care has, however,
been documented for other types of dinosaurs, including some meat-
eating theropods and plant-eating ornithischians.
Working with another team of paleontologists from the American
Museum of Natural History in the Gobi Desert of Mongolia, we
were part of the crew that discovered the first fossil dinosaur skele-
ton—the parrot-beaked Oviraptor —actually sitting on its nest. Inter-
estingly, when the first skeleton of Oviraptor was found in 1923, it was
collected from on top of a clutch of eggs. When described in 1924, this
was regarded as evidence for Oviraptor's predatory activities. Paleon-
tologist Henry Fairfield Osborn assumed that the Oviraptor had died
while seizing the eggs of a plant-eating Protoceratops —a primitive
horned dinosaur common in the Gobi deposits. Osborn's assumption
led to Oviraptor's condemning name, which means "egg seizer." But
the eggs underneath that first Oviraptor skeleton did not contain any
embryos, and their identity remained a mystery until seventy years
later, when our crew discovered eggs of an identical shape and appear-
ance that contained an embryo of an oviraptorid inside. Thus, this cru-
cial piece of evidence showed that the skeleton collected in 1923 and
those discovered decades later were actually brooding nests of eggs
that contained their own kin. Subsequent discoveries by the Ameri-
can Museum team and by other paleontological expeditions of other
Gobi skeletons in exactly the same pose provided solid evidence that
certain types of dinosaurs, including Oviraptor, did care for their
voung, and evidence from other nesting grounds in Montana has sug-
gested the same. The meat-eating dinosaur Troodon, one of the clos-
est relatives of birds, has also been found to nest on top of its brood.