Pregnant T. rex may contain the holy grail of all dinosaur fossils: DNA
A pregnant Tyrannosaurus rex has been found, shedding light on the evolution of egg-laying as well as on gender differences in the dinosaur.
The remains also could contain the holy grail of all dinosaur fossils: DNA.
"Yes, it's possible," Lindsay Zanno told Discovery News, referring
to genetic material that may be present in this as well as similar
dinosaur finds. "We have some evidence that fragments of DNA may be
preserved in dinosaur fossils, but this remains to be tested further."
What has been confirmed so far is that the T. rex,
which was found in Montana and dates to 68 million years ago, retained
medullary bone that reveals the individual was pregnant. Medullary bone
is only present in female living dinosaurs, i.e. birds, just before and
during egg laying. It's this type of bone that could retain preserved
DNA.
Zanno is an assistant research professor of biological sciences at
North Carolina State University, where she is also head of the North
Carolina Museum of Natural Sciences' Paleontology Research Lab and is
curator of paleontology. She explained that medullary bone lines the
marrow cavity of the long bones of birds.
"It's a special tissue that is built up as easily mobilized calcium
storage just before egg laying," she said. "The outcome is that birds do
not have to pull calcium from the main part of their bones in order to
shell eggs, weakening their bones the way crocodiles do."
Crocodiles, she said, are the closest living relatives of dinosaurs.
"Medullary bone is thus present just before and during egg laying,
but is entirely gone after the female has finished laying eggs," she
said.
Early on, Mary Schweitzer suspected that medullary bone was present
in the tyrannosaur remains, and was able to confirm her suspicions after
she, Zanno and their team conducted a chemical analysis of the T. rex's femur.
The material, found to be consistent with known medullary tissues
from ostriches and chickens, contained karatan sulfate, a substance not
present in any other bone types.
"This analysis allows us to determine the gender of this fossil, and
gives us a window into the evolution of egg laying in modern birds,"
Schweitzer said.
Zanno explains we now know extinct dinosaurs inherited egg laying
from their ancestors, just as birds inherited this reproductive strategy
from their dino ancestors.
"The discovery of medullary bone is just one more piece of evidence
that blurs the line between birds and other theropod (carnivorous
two-legged) dinosaurs like T. rex," she said.
The research is published in Nature Scientific Reports.
In a prior study, Sarah Werning of
the University of California and Berkeley and her colleagues found
medullary bone in the carnivorous dinosaur Allosaurus as well as in the
plant-eating dino Tenontosaurus. The discoveries happened somewhat by
chance, as she and the other researchers were studying dinosaur growth
rates when they realized three of the dinosaurs were pregnant females.
She said, "We were lucky to find these female fossils. Medullary bone
is only around for three to four weeks in females who are
reproductively mature, so you'd have to cut up a lot of dinosaur bones
to have a good chance of finding this."
Schweitzer agrees, and said that the femur her team studied was
already broken when she received it. Echoing Werning, she acknowledged
that most paleontologists would not want to cut open, or demineralize,
their fossils in order to search for the rare medullary bone.
Nevertheless, because much of the pregnant T. rex's skeleton
was found, including her skull, there is a very good chance that the
paleontologists will soon be able to provide a detailed description of
her overall anatomy and general appearance.
They already know that the dinosaur mom-to-be was 16-20 years old when she died of as of yet unknown causes.
News:Pregnant T. rex may contain the holy grail of all dinosaur fossils: DNA
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