News Services, 919/515-3470
Fossil Bone Leads to Gender, Age Determinations
of medullary bone from T.Rex (D), emu (E)
and ostrich (F).
It’s a girl … and she’s
Paleontologists at North Carolina State University
have determined that a 68 million year-old Tyrannosaurus
Rex fossil from Montana is that of a young female,
and that she was producing eggs when she died.
The proof, they say, is in the bones.
In a case
of a literal “lucky break,” the
scientists discovered unusual bone tissue lining the
hollow cavity of the T. rex’s broken leg bone.
In a paper published in the June 3 issue of the journal Science,
Dr. Mary Schweitzer, assistant professor of paleontology
with a joint appointment at the N.C. Museum
of Natural Sciences, and her technician, Jennifer Wittmeyer,
along with colleagues at Montana State University,
share their findings and say that the presence of this
particular tissue provides evidence of the dinosaur’s
gender and a connection between the extinct giants
and living birds, specifically ostriches and emus.
Schweitzer believes that the unusual tissue inside
the T. rex bone is actually medullary bone:
a thin layer of highly vascular bone that is found
female birds only during ovulation. This estrogen-linked
reproductive bone tissue is laid down inside the hollow
leg bones of the birds and persists until the last
egg is laid, at which time it is completely resorbed
into the bird’s body. Its formation is triggered
by an increase in estrogen levels, and the temporary
tissue provides the calcium necessary to form eggshells.
Medullary bone is only found in present-day female
birds; no other egg-laying species – including
crocodiles, the other living dinosaur relative – produces
this tissue naturally.
the dinosaur tissues didn’t look exactly like pictures published
of medullary bone in living birds like chicken and quail, Schweitzer’s
team compared the tissue from the femur of the T. rex to that taken from leg
bones of more primitive ratites, or flightless birds, such as ostriches and
emus. These birds share more features with dinosaurs than other present-day
birds. They selected an ostrich and an emu in different stages of their laying
cycles, when medullary bone is present.
viewed the tissues under both a light and an electron
microscope, and found that the dinosaur
tissues were virtually identical to those of the modern
birds in form, location and distribution. Demineralization – the
chemical removal of a bone’s minerals in order
to obtain organic material that is much easier to work
with in a lab environment – of the samples revealed
that the medullary bone from the ostrich and emu was
virtually identical in structure, orientation and even
color, with that seen in the T. rex.
Since only females produce medullary bone, its presence
in the T. rex femur indicates that this fossil was
a female, and probably one who died toward the end
of her laying cycle. From a biological perspective,
the tissue is another link between dinosaurs and living
discovery of medullary bone in the T.
rex is important because it allows us to objectively
sex a dinosaur,” says Schweitzer. “It also
adds to the robust support linking birds and dinosaurs
and shows that their reproductive physiologies may
have been similar. Hopefully we’ll be able to
identify features within dinosaurs that will help us
determine the gender of our other fossils, and lead
to more information about their herd structure or family
N.C. Museum of Natural Sciences will soon become
home of the cast of the thigh bone. “We’re
pleased to be able to provide a way for the public
to see for themselves evidence that after millions
of years, soft tissue can actually be preserved in
dinosaur bone,” said Dr. Betsy M. Bennett, museum
director. The cast will be placed in the museum’s
Paleo Lab along with the complete story of where it
was found, how it was excavated and how Schweitzer
discovered the unique tissue cells in the hollow.
The research was funded by NC State,
the N.C. Museum of Natural Sciences and the National
- peake -
Note to editors:
An abstract of the paper follows.
Tissue in Ratites and Tyrannosaurus Rex”
Authors: Mary H. Schweitzer and Jennifer L. Wittmeyer,
North Carolina State University; John R. Horner, Montana
Published: June 2, 2005, in Science
Abstract: Unambiguous indicators of gender in dinosaurs
are usually lost during fossilization along with other
aspects of soft tissue anatomy. We report the presence
of endosteally derived bone tissues lining the interior
marrow cavities of portions of Tyrannosaurus rex (MOR
hindlimb elements, and hypothesize that these tissues
are homologous to specialized avian tissues known as
medullary bone. Because medullary bone is unique to
female birds, its discovery in extinct dinosaurs solidifies
the link between dinosaurs and birds, suggests similar
reproductive strategies, and provides an objective
means of gender differentiation in dinosaurs.