Star

The San Juan Daily Star
Monday, March 21, 2015 26
SCI & TECH
Fossil Hints T. Rex Got Smart Before It Got Big
An artist’s conception of Timurlengia euotica, a smaller and earlier cousin
of Tyrannosaurus rex.
By KENNETH CHANG
At the end of the dinosaur age,
Tyrannosaurus rex was a behemoth
killer animal, up to 40
feet long and weighing several tons —
the top carnivore in the food chain.
The very first tyrannosaurs, which
arose about 100 million years earlier,
were small, about the size of a person.
The evolutionary jump of tyrannosaurs
from people- and horse-size to
behemoths has remained a mystery.
A recent fossil finding in Uzbekistan
is providing paleontologists with a
missing link in the lineage: They have
discovered a tyrannosaur with many
of the giant’s characteristics — but not
its stature or heft.
“It has long been thought that
tyrannosaurs were such successful
predators, in part, because of their
large brains and ears well-attuned to
low-frequency sound,” said Stephen
L. Brusatte, a paleontologist at the
University of Edinburgh in Scotland
and lead author of a paper published
Monday in Proceedings of the National
Academy of Sciences, describing
the new dinosaur. “The new Uzbek
tyrannosaur has basically the same
brain as T. rex — same shape, proportions,
etc. — just smaller.”
The finding, he said, is a new indication
that tyrannosaurs got smart
before they got big.
“It is one of the closest cousins of
T. rex and tells us that tyrannosaurs
evolved sophisticated brains and senses
before they became colossal apex
predators,” Dr. Brusatte said.
When the first tyrannosaurs evolved,
about 170 million years ago, they
lived in the shadows of larger meateaters
like Allosaurus. For tens of millions
of years, tyrannosaurs remained
small.
And because few rocks of the age
100 million years to 80 million years
old are now lying exposed or at the
surface anywhere in the world, few
clues exist to explain how the early
tyrannosaurs evolved into large animals
like T. rex.
“The fossil record just stops,” Dr.
Brusatte said. “We don’t know what
goes on in that time.”
Before the gap, all tyrannosaurs
were small. After the gap, none were.
Tyrannosaurus rex and its relatives
weighed one ton or more.
A CT scan of the Timurlengia fossil
showed details about the brain and
inner ear.
Uzbekistan is one of the few places
with geological formations that fall in
that 20-million-year gap. Beginning
in 1997, Hans-Dieter Sues, chairman
of the paleobiology department at
the Smithsonian’s National Museum
of Natural History, and Alexander
O. Averianov, a senior scientist at the
Russian Academy of Sciences, organized
fossil-collecting expeditions to
the Kyzylkum Desert in northern Uzbekistan.
The paleontologists uncovered
some scattered bones of what appeared
to be tyrannosaurs, but the key
finding came in 2004 when they found
the part of the skull surrounding the
brain.
“The braincase proved to be the
Rosetta stone for the whole thing,” Dr.
Sues said.
Dr. Brusatte, an expert on tyrannosaurs,
was visiting Dr. Averianov
a couple of years ago to study some
other fossils. “He pulled open a box
and pulled out this object about the
size of a grapefruit,” Dr. Brusatte recalled.
“And he handed it to me and
said, ‘You know, what do you make of
this?’ ”
Dr. Brusatte joined an international
team of researchers, including Dr.
Sues and Dr. Averianov, in the analysis
of the new tyrannosaur. Named Timurlengia
euotica, the dinosaur lived
about 90 million years ago, right in the
middle of the fossil gap. (Timurlengia
was named after a Central Asian warlord,
Timur; euotica roughly means
“well eared.”)
Based on a few scattered bones, the
scientists estimated that Timurlengia
was about the size of a horse, like
earlier tyrannosaurs, weighing about
600 pounds, with long legs and bladelike
teeth. Lithe and fast, it probably
chased down plant eaters like early
duck-billed dinosaurs also found in
the region.
But a CT scan of the braincase
showed that the shape of the brain
was similar to that of the later tyrannosaurs,
and that the inner ear structure
was tuned to low frequencies.
“We were very surprised it already
had this sensory organization associated
with T. rex and related animals,”
Dr. Sues said.
Timurlengia does not explain why
tyrannosaurs got big, but Dr. Sues
said he suspected that an unusually
warm climate, one of the warmest in
Earth’s history, had played an important
role. Allosaurus and its relatives
did not adapt and died out, and then
tyrannosaurs grew in size to replace
them.
So far, Timurlengia is just one clue.
It is possible, for instance, that larger
tyrannosaurs had already evolved elsewhere.
“Like at a murder scene,” Dr.
Brusatte said, “one clue is better than
none.”
A tyrannosaur from China named
Xiongguanlong, imprecisely dated to
100 million to 120 million years ago, is
another important clue.
“At a glance, Xiangguanlong looks
to my eye like an advanced tyrannosaur,”
said Thomas Carr, a paleontologist
at Carthage College in Kenosha,
Wis., who has examined the braincase
fossil.
“This is what this work is all about,
completing that evolutionary narrative,”
Dr. Carr said. “At the end of the
day, there’s much more to discover.
It’s still a great leap from Timurlengia
to T. rex.”