Dinosaurs Dug Dens

["Richard W. Travsky" <rtravsky@uwyo.edu>]

with diagram

http://www.sciencenews.org/articles/20071027/fob1.asp

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.