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Dinosaurs Dug Dens
Paleontologists have unearthed an ancient, sediment-filled burrow that
holds remains of the creatures that dug it. The find is the first
indisputable evidence that some dinosaurs maintained an underground
lifestyle for at least part of their lives.
While scouring 95-million-year-old strata in southwestern Montana,
paleontologist David J. Varricchio of Montana State University in Bozeman
and his colleagues stumbled upon an unusual patch of sandstone protruding
from the rock that surrounded it. Soon after they began to excavate the
sandstone, they found a compact mass of small bones. After teasing apart
the tangle, they discovered that the remains represented an adult and two
juvenile dinosaurs of a completely new species.
Further excavation revealed that the sandstone mass was S-shaped and about
2.1 meters long. For most of its length, the sinuous feature had an oval
cross section about 30 centimeters wide and about 40 cm tall. However, at
its lower endwhere the dinosaur bones were foundit broadened to a width of
45 cm. The elongated sandstone mass cut through three distinct layers of
stone derived from mud and clay, a sign that those strata were in place
before the material that formed the sandstone arrived, says Varricchio.
Individual bones in the fossils were unbroken and showed no signs of
having been weathered before they were buried. Varricchio and his
colleagues propose that the anomalous mass of sandstone represents a
sudden influx of material that filled in a burrow, trapping its occupants.
The dinosaur skeletons found in the burrow were essentially complete.
That, plus a lack of bite marks on the bones, suggests that the creatures
hadn't been dragged into the burrow by a predator, says Varricchio.
Varricchio and his colleagues dubbed the new species Oryctodromeus
cubicularis, which, in Greek, means "digging runner of the lair."
"All the pieces are there" to support the burrowing interpretation, says
Paul Sereno, a paleontologist at the University of Chicago.
The foremost bones in its skull were fused, a characteristic that could
have enabled the creature to dig more effectively.
Scientists have noted similar skeletal features on several close relatives
of Oryctodromeus, says Thomas R. Holtz Jr., a paleontologist at the
University of Maryland at College Park. Burrowing dinosaurs may have been
more common than paleontologists previously suspected, he suggests.