Geoscience Reference
In-Depth Information
cleaning away the surrounding rock, most fossils still require some
manual preparation before they can be studied. Usually the sur-
rounding rock must be removed by hand with small tools, such as den-
tal picks, needles, miniature sandblasters, and miniature vibrating
tools, although sometimes the rock surrounding a fossil can be etched
away in a bath of dilute acid. Preparing delicate fossils such as our
embryos requires enormous skill and patience. Under a microscope,
the fossil preparator must slowly and carefully pick away the rock sur-
rounding the fragile bones with the mechanical tools of the trade, then
protect the bones by applying thin coats of transparent glue. To pre-
pare just one tiny fossil embryo can take days or even weeks of
painstaking work, but this had to be done to reveal the clues to iden-
tify the kind of dinosaur that had laid the eggs.
In late December 1997 and early January 1998, Marilyn Fox, our
preparator at Yale University, made an important discovery. Inside one
of the eggs, she uncovered some minute skull bones and miniature
teeth. We hoped that the shape of the skull bones and the teeth would
give us clues to identify the victims in the eggs, but this is never easy.
Because the animals were so young, the bony tissue in their delicate
bones was not well developed, thus obscuring comparisons with
adult sauropods, whose bones are fully formed. Furthermore, the
embryonic bones were crushed against the lower eggshell as the fluid
in the egg leaked out and the bones became fossilized. Unfortu-
nately, this would make identifying these small fossils difficult.
Luis took the train up to Yale to examine what Marilyn had uncov-
ered. He brought several specimens back to New York just before
Rodolfo came up from Argentina in the spring to see the fossils and
help us write the scientific paper to announce our discoveries. One of
our eggs contained a nearly complete skull, an important clue for iden-
tifying the kind of dinosaur that had laid the eggs because the skull
bones of different kinds of dinosaurs are usually quite distinctive. The
skull bones in our embryo were similar in shape to those of sauropod
dinosaurs, the long-necked giants that include diplodocids,
dicraeosaurids, barchiosaurids, and titanosaurs. This tiny skull was also
remarkable because few adult skulls of sauropods have been discov-
ered, let alone skulls of embryos. In fact, only a handful of adult sauro-
pod skulls had been found in South America. Several bones in the
skull of our embryo were not preserved well enough to be identified,
