Numerous tracks of therizinosaurs were found over the summer.
Published: August 21st, 2012
Therizinosaurs weighed
six tons, had a giraffe-length neck, claws like scimitars -- and
feathers. Alaska once had a lot of them, said paleontologist Anthony
Fiorillo.
Fiorillo, curator of earth sciences at the Perot Museum of
Nature and Science in Dallas, and his colleague Thomas Adams published a
paper in the June online edition of the scholarly journal Palaios
identifying a single track found in Denali National Park as belonging to
the odd plant-eating dinosaur related to Tyrannosaurus rex and the
modern chickadee.
In an interview last week,
Fiorillo said several more therizinosaur tracks were found in the park
over the course of this summer.
Scientists have been baffled by
this family of dinosaurs, originally thinking they were something like
turtles. The first incomplete specimens came from Mongolia. More fossils
were then found in China and North America. The Denali tracks are the
first evidence that they were among the ancient reptiles that lived in
high latitudes, sometimes called "polar dinosaurs."
The biggest Therizinosaurus is
estimated to have stretched 40 feet. Even the smallest member of the
family was 7 feet from the tip of its tail to its tiny head. They walked
on their hind legs -- very well, as it turns out. Despite those
ferocious front-limb talons, which could be a yard long, they seem to
have come from a meat-eating species that turned vegetarian.
The purpose of the Edward
Scissorhands-like claws is something of a mystery. They could have been
used to scythe leaves or stalks, Fiorillo said. Therizinosaur is Greek
for "reaping lizard."
Likewise, "The feathers are the
source of a lot of speculation," Fiorillo said. Perhaps they were for
display. Perhaps they helped the animal control its body temperature.
In their paper, Fiorillo and
Adams document the configuration of the original Denali track, saying,
"Four-toed theropod tracks are decidedly uncommon." Theropods are the
suborder of dinosaurs to which therizinosaurs belonged. Only two groups
have all four toes facing forward, the researchers note as they
meticulously eliminate other possibilities.
In the case of therizinosaurs,
all four toes bear some weight. It's a design not unlike the human foot,
built for walking rather then springing, perching, swimming or other
things feet do.
And walk they did. The Palaios
article includes a map showing a possible therizinosaur highway from
Lake Baikal in Central Asia to central Canada by way of the Bering Land
Bridge. It likely took generations for the clan to travel that far.
The Denali region, on the other
hand, may have been a major seasonal migration corridor, similar to
those used by the birds and fish that swarm into Alaska during the
summer nowadays. It was a place where different species fed and mingled;
the therizinosaur tracks were found in the same layer of "bedding
plains" as a number of duck-billed dinosaur tracks. It was a family
place; different-size prints show adults and juveniles traveling
together.
The abundant signs of various
dinosaurs and prehistoric birds in Denali suggest to Fiorillo a scene
not unlike the African savannah, with the Cretaceous versions of
wildebeest and zebra herds eying each other across the plain.
"Alaska is the best place on the
planet to study a high latitude ecosystem in deeper geologic time," he
said. "We have something we can contribute to the discussion of what a
warming Arctic might look like."
"There's so much (paleontological) potential in this state," Fiorillo said. "You never know what's around the corner."
The Denali footprints supply
something like a photograph of what was happening in the far North 70
million years ago or more, he said. "We don't have bones. But the tracks
give us a component to the biodiversity of the area that we didn't have
before."
The therizinosaur isn't the first
feathered dinosaur found in Alaska. That honor probably belongs to the
small, wide-eyed, big-brained carnivore Troodon, fossils of which were
previously found on the North Slope.
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