Say aaah analyses of modern-day species suggest a correlation between the number of neurovascular foramina in facial bones and the type of soft
tissue around the mouth. with few of these holes for blood vessels and nerves, Herrerasaurus may have had lizard- or snakelike lips. Camarasaurus had
more foramina, suggesting fleshy, mammal-like cheeks. turtles and birds had even more foramina, and alligators, with bare-toothed grins, had the most.
Aardonyx, a recently described ancestor of sauropods, he and his colleagues
inferred that the creature had lips but
didn’t have fleshy cheeks. Without that
constraint on its gape, the dino could
have opened wide to gather large mouthfuls of browse — an ability that may have
set the evolutionary stage for subsequent sauropod species to grow exceptionally large (SN Online: 11/10/09), the
team reported online November 10 in
Proceedings of the Royal Society B.
Such insights aren’t limited to faces,
Bonnan notes. The surface texture of
well-preserved limb bones holds information about where muscles attached
and how big — and powerful — those
muscles might have been.
Know what’s missing
Though most of an animal’s soft tissues
decompose after death, some partially
mineralized bits have a head start on fossilization and become preserved. These
remnants may provide hints about tissue
that’s missing, Bonnan says.
While it’s easy to measure the cartilage
in a fossil, for example, it’s often difficult
to estimate how much uncalcified — and
now missing — cartilage was present to
begin with. That, in turn, makes it difficult to ascertain the spacing and positioning of limb bones and, from that, the
efficiency of a creature’s movement.
Previously, scientists looked to general similarities among modern creatures and employed a lot of informed
guesswork and trial and error to fit
bones together. Now, Bonnan and his
colleagues have come up with detailed
methods to better estimate how much
cartilage may have been present in a
dinosaur’s joints. Once again, the team
reported at the paleontology meeting in
Bristol, the technique stems from analyses of modern-day dino relatives.
For their study, the researchers
looked at joints from the front and
hind limbs of alligators, as well as those
in the wings and legs of ostriches and
helmeted guinea fowl. First, the team
measured the total amount of cartilage
present in recently dissected joints.
Simmering the bones at 60° Celsius for
24 hours removed the uncalcified cartilage but left calcified tissue intact. “The
lab smelled like bad chicken soup for
quite a while,” Bonnan admits.
Removing the uncalcified cartilage
from the joints of alligators shortened
the humerus, the bone analogous to the
one in the human upper arm, by about
5 percent, the team found. In the hel-
meted guinea fowl, removing that tissue shortened the limb bones by around
8 percent, and in juvenile ostriches, it
trimmed the bones’ length about 15 percent. With this information, the team
suggests, scientists can estimate the
amount of uncalcified cartilage missing
from a fossil limb bone and reconstruct
the creature accordingly.
“If you want to be accurate, you need
to account for these things,” says Tyler
Keillor, a paleoartist at the University
of Chicago. “What is the missing joint
surface? How much space is there going
to be? How would that have affected the
range of motion?” Answering such questions helps scientists get a well-developed idea of how a dinosaur functioned
as a living creature, he notes.
Scientists have been attempting to
reconstruct ancient creatures by studying
top, from left: ekratzig/istockphoto; oariff/istockphoto; wrangel/istockphoto; awc007/istockphoto; triceratops: t. keillor