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Dinosaur Dance Floor: Jurassic Oasis on Arizona-Utah Border - UPDATE

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Bianca
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« on: November 13, 2008, 08:35:03 am »











                         Dinosaur Dance Floor: Numerous Tracks at Jurassic Oasis on Arizona-Utah Border






ScienceDaily
(Oct. 20, 2008) —

University of Utah geologists identified an amazing concentration of dinosaur footprints that they
call "a dinosaur dance floor," located in a wilderness on the Arizona-Utah border where there was
a sandy desert oasis 190 million years ago.

The three-quarter-acre site – which includes rare dinosaur tail-drag marks – provides more evidence there were wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with
a field of sand dunes larger than the Sahara Desert.

Located within the Vermilion Cliffs National Monument, the "trample surface" (or "trampled surface")
has more than 1,000 and perhaps thousands of dinosaur tracks, averaging a dozen per square yard
in places. The tracks once were thought to be potholes formed by erosion. The site is so dense with dinosaur tracks that it reminds geologists of a popular arcade game in which participants dance on illuminated, moving footprints.

"Get out there and try stepping in their footsteps, and you feel like you are playing the game 'Dance Dance Revolution' that teenagers dance on," says Marjorie Chan, professor and chair of geology and geophysics at the University of Utah. "This kind of reminded me of that – a dinosaur dance floor – because there are so many tracks and a variety of different tracks."

"There must have been more than one kind of dinosaur there," she adds. "It was a place that attracted a crowd, kind of like a dance floor."

A study identifying the dinosaur track site was published in the October issue of the international paleontology journal Palaios. Chan is senior author of the study, which was conducted for a master's degree thesis by former graduate student Winston Seiler, who now works at Chevron Inc., in Bakersfield, Calif.

Seiler says the range of track shapes and sizes reveals at least four dinosaur species gathered at the watering hole, with the animals ranging from adults to youngsters.

"The different size tracks [1 inch to 20 inches long] may tell us that we are seeing mothers walking around with babies," he says.

The site – a 6-mile roundtrip hike from the nearest road – is in Arizona in the Coyote Buttes North area of the Paria Canyon-Vermilion Cliffs Wilderness, which is part of the U.S. Bureau of Land Management's (BLM) Vermilion Cliffs National Monument. The track site – about halfway between Kanab, Utah, and Page, Ariz. – is near a popular wind-sculpted sandstone attraction known as the Wave. 
« Last Edit: November 13, 2008, 08:42:05 am by Bianca » Report Spam   Logged

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Bianca
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« Reply #1 on: November 13, 2008, 08:36:21 am »





               




Geologist Winston Seiler with some of the dinosaur tracks he identified for his thesis as a University of
Utah master's degree student.

The impressions once were thought to be potholes eroded by water.

But Seiler and Marjorie Chan, chair of geology and geophysics at the University of Utah, published a scientific paper in the October 2008 issue of the journal Palaios identifying the abundant impressions as comprising a large dinosaur "trample surface" in northern Arizona.

There are so many tracks they wryly refer to the site as "a dinosaur dance floor."

(Credit: Nicole Miller)
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« Reply #2 on: November 13, 2008, 08:38:05 am »









A Dense Collection of Dinosaur Footprints – and a Few Tail Drags



Chan says the new study is the first scientific publication to identify the impressions as dinosaur footprints on a trample surface.

As part of the study, Seiler marked off 10 random plots, each of 4 square meters, or roughly 2 yards by 2 yards. He counted 473 tracks within those plots – an average of 12 per square meter. He conservatively estimates the 3,000-square-meter site (about 0.75 acres) has more than 1,000 tracks, but he and Chan believe there perhaps are thousands.

Numerous dinosaur track sites have been found in the western United States, including more than 60 in Navajo Sandstone, where actual dinosaur bones are rare.

"Unlike other trackways that may have several to dozens of footprint impressions, this particular surface has more than 1,000," Seiler and Chan wrote. And they say the density of tracks is much greater than it is at even larger track sites, such as the one at Coral Pink Sand Dunes State Park in Utah.

The dinosaur tracks and tail marks near the Wave were preserved in the vast Navajo Sandstone Formation. But unlike the dunes that make up much of the Navajo Sandstone, the tracks are within what was a wet, low watering hole between the dunes.

"We're looking at an area much like the Sahara Desert with blowing sand dunes," Seiler says. "Areas between these sand dunes could have had ponds – oases."

The 2.4-inch-wide tail-drag marks – which are up to 24 feet long – are a special discovery because there are fewer than a dozen dinosaur tail-drag sites worldwide, Seiler says. Four tail drags were within the 10 plots he surveyed, and there are others nearby.

"Dinosaurs usually weren't walking around with their tails dragging," he says.   
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« Reply #3 on: November 13, 2008, 08:39:55 am »










Potholes – or Prints from Four Kinds of Dinosaurs?



Chan first visited the site of the dinosaur tracks in 2005 with a BLM ranger who was puzzled by them. Chan initially called them potholes, which are erosion features common in desert sandstone, "but I knew that wasn't the whole story because of the high concentration and because they weren't anywhere else nearby but along that one surface."

Seiler first saw the site in 2006. "At first glance, they look like weathering pits – a field of odd potholes," he says. "But within about five minutes of wandering around, I realized these were dinosaur footprints."

One anonymous reviewer of the Palaios study still believes the holes are erosion features. The study argues the impressions are from dinosaurs because:

They are the correct size for tracks made by big animals, and are limited to a single rock bed.

Four different kinds of footprint shapes are seen repeatedly in 14 percent of the impressions, and they include obvious claw, toe and heel marks. The other impressions "are clearly similar."

One-third of the prints are surrounded by small ridges or mounds. Such features would be expected when animals stepped in wet sand.

The tracks "are rarely flat and are typically oriented at an angle into the sediment … and indicate a clear direction of travel" to the west-southwest. Seiler says the direction the dinosaurs walked "either was dictated by the large dunes that bounded this wet area, or it could be communal behavior, like walking together as a pack."

About one-eighth of the tracks show "overprinting," in which a dinosaur stepped in the footprint of another or even in its own prints.

"While these impressions may be mistaken for potholes caused by weathering, close examination reveals many footprint features," Seiler says.

Dinosaur footprints are named by their shape because the animals that made them haven't been identified. Four kinds of footprints were found on the trample surface:

Eubrontes footprints measure 10 inches to 16 inches long and have three toes and a heel. Eubrontes tracks are believed to have been made by upright-walking dinosaurs 16 to 20 feet long, or smaller than Tyrannosaurus rex.

Grallator tracks are about 4 inches to 7 inches long, are three-toed and were left by small dinosaurs only a few feet tall.

Sauropodomorph dinosaur tracks, which are more circular than the other types, were left by creatures that walked on four legs and were the largest dinosaurs at the site. Their tracks range from 6 inches to 11 inches long. Seiler says the tail-drag marks are associated with these circular footprints, so they likely were made by sauropods.

Anchisauripus tracks measure 7 inches to 10 inches long and were made by dinosaurs that ranged from 6 feet to 13 feet in length.
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« Reply #4 on: November 13, 2008, 08:42:39 am »










An Oasis for Dinosaurs in a Vast Desert of Dunes

When the footprints were made 190 million years ago, "the continents were arranged so this area was in the tropics" and was part of the supercontinent named Pangaea, says Seiler. "It was a desert, like the Sahara but much larger than the Sahara is today," covering much of Utah, Wyoming, Colorado, New Mexico, Arizona and Nevada.

"Some studies indicate winds probably were much stronger than normal because all the continents were together," says Chan. "That's why you had monster dunes."

"To support large dinosaurs, there probably wasn't just one watering hole for them to go to, but many," Seiler says. "They wandered between a network of watering holes for food and water."

In that sense, the trample surface is not "just a wet pond," but "it's possibly a record of global climate change" – a shift from drier to wetter conditions, Chan says.

She says the traditional view is that the Navajo Sandstone represents "a vast, dry uninhabitable desert. But now we are seeing there are a lot of variations, and there were periods when dinosaurs were living there."

Seiler envisions the dinosaurs were "happy to be at this place, having wandered up and down many a sand dune, exhausted from the heat and the blowing sand, relieved and happy to come to a place where there was water."

The trample surface "helps paint a picture of what it was like to live back then," he says. "Tracks tell us what the dinosaurs were doing, what their behavior was, what life was like for them, what they did on a day-to-day basis."

After the dinosaurs left their prints, the trample surface was covered by shifting dunes, which eventually became Navajo Sandstone. Then, the rock slowly eroded away, exposing the tracks. The tracks eventually will erode too, Seiler says.


--------------------------------------------------------------------------------

Adapted from materials provided by University of Utah.
Need to cite this story in your essay, paper, or report? Use one of the following formats:
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 MLA University of Utah (2008, October 20).

Dinosaur Dance Floor: Numerous Tracks at Jurassic Oasis on Arizona-Utah Border.

ScienceDaily. Retrieved October 20, 2008, from

http://www.sciencedaily.com­ /releases/2008/10/081020093414.htm 
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« Reply #5 on: November 13, 2008, 08:47:36 am »










                                        Dinosaur "Dance Floor" Found in Arizona






Rebecca Carroll
for National Geographic News
October 21, 2008

At least four types of Jurassic dinosaurs left more than a thousand footprints and tail-drag marks at
a remote site in northern Arizona, according to a new study.

About 190 million years ago, during the Jurassic period, the area was likely an oasis surrounded by a vast desert, researchers said.

"All these footprints at a watering hole might tell us something about the social life of the dinosaurs," said Marjorie Chan of the University of Utah.

Chan wonders which species might have mingled at this "dinosaur dance floor."

She co-authored the study with University of Utah graduate student Winston Seiler, who found the site in 2006.

(Related: "First Dinosaur Tracks Found on Arabian Peninsula" [May 20, 2008].)

But the research has received mixed reactions from area paleontologists, with some doubting the tracks' authenticity.

Their work appears this month in the journal Palaios.
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« Reply #6 on: November 13, 2008, 08:49:32 am »










Crossing Dino Paths



Chan noted that the prints appear in what was once very wet, soft sand, which allowed for deep impressions.

"You can see the mounds of the sand going around their toes," she said.

Dinosaur footprints are named according to their shape and can't be linked conclusively to an exact species and genus without other evidence, such as bones. But some of a creature's habits can be guessed from its tracks.

The site's 16-inch (40-centimeter), three-toed Eubrontes tracks, for instance, are believed to come from an upright-walking meat-eater that was smaller than Tyrannosaurus rex, the scientists say.

Smaller tracks could be smaller species or younger dinosaurs. "Sometimes it's really hard to tell," Chan said.

Other large prints may have come from unknown sauropods, Chan said, referring to the long-necked herbivores that eventually evolved into Earth's most gigantic creatures
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« Reply #7 on: November 13, 2008, 08:51:07 am »









Not Convinced


Alan Titus, a paleontologist at Grand Staircase-Escalante National Monument in nearby Kanab, Utah, has not seen the site in person but is not convinced that these are really dinosaur tracks.

"I've observed thousands of [Eubrontes] tracks in early Jurassic rocks of the Colorado Plateau and have never seen one that looked like the one in the news release," he said by 0email, noting that he would need to see the site before drawing a firm conclusion.

Andrew Milner, a paleontologist at St. George Dinosaur Discovery Site at Johnson Farm in Utah, also felt the photos were not enough evidence.

"What they're showing here look nothing like Eubrontes in my opinion," Milner said.

"If they do turn out to be tracks, it's really an interesting site—showing what they're doing behavior-wise would be interesting," he said.

"To be honest, I really want to go have a look."

Utah's state paleontologist Jim Kirkland also has not been to the site personally, but he has seen many of the researchers' photos and agrees with some of their conclusions.

"Some of the [imprints] are definitely tracks," he said. "I'm a little more leery about [the] tail-drags."

Tail-drag marks are rare and can be difficult to verify.

Kirkland said he's not convinced any of the prints are from sauropods, because "there's no fossil record in North America of sauropods that old." But, he added, "it's not impossible."

(Related: "Dinosaur Tracks Shed Light on Sauropod Evolution" [May 29, 2002].)

In any case, he said, the find could reveal a wealth of new information about dinosaur behavior.

"Someone needs to take this to the next level," Kirkland said. "It's an exciting site." 
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« Reply #8 on: November 13, 2008, 08:52:37 am »









Alternative Explanations


The study rejects several alternative explanations for the unusual collection of pothole-like impressions in the rock.

"An initial interpretation of the impressions might be that they are potholes, the product of modern erosion," Seiler said.

"However," Seiler said, "upon close inspection many of the impressions are ringed by mounds of displaced sand that had to be formed when the sand was soft, before it was turned to rock."

The research team also "started seeing repeating patterns … footprints and, in some cases, three clear toes," he said.

Such evidence for dinosaur tracks outweighs evidence for the other possibilities, he said. 
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« Reply #9 on: November 13, 2008, 08:53:57 am »









No Bones?


Chan noted one lingering mystery: "Why aren't there any dinosaurs bones? We still don't really know the answer to that."

Bones were not found at other track sites in the region, the scientists say, so it might just be that the environmental conditions weren't conducive to preserving them.

Until further research is done, what really happened at the dance floor is anyone's guess.

"You can put your feet in their footprints," Chan said. "It's a very odd and kind of thrilling feeling to do that."
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« Reply #10 on: November 13, 2008, 08:55:49 am »











University of Utah geologist Winston Seiler walks among hundreds of what appear to be dinosaur footprints in a "trample surface" that likely was a watering hole amid desert sand dunes during the Jurassic Period 190 million years ago.

The track site, which also appears to include some dinosaur tail-drag marks, is located in Coyote Buttes North area along the Arizona-Utah border.

(Credit: Roger Seiler)
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« Reply #11 on: November 13, 2008, 08:57:34 am »










                                       Paleontologists Doubt 'Dinosaur Dance Floor'






ScienceDaily
(Nov. 8, 2008) — 

A group of paleontologists visited the northern Arizona wilderness site nicknamed a "dinosaur dance floor" and concluded there were no dinosaur tracks there, only a dense collection of unusual potholes eroded in the sandstone.

So the scientist who leads the University of Utah's geology department says she will team up with the skeptics for a follow-up study.

"Science is an evolving process where we seek the truth," says Marjorie Chan, professor and chair of geology and geophysics, and co-author of a recent study that concluded the pockmarked, three-quarter-acre site in Vermilion Cliffs National Monument was a 190-million-year-old dinosaur "trample surface".

"We went through the proper scientific process of careful study, comparisons with other published works and peer review" of the study by independent scientists, Chan adds. "We gave the project considerable critical thought and came up with a different interpretation than the paleontologists, but we are open to dialogue and look forward to collaborating to resolve the controversy."

On Oct. 30 – more than a week after the Utah study was publicized worldwide – four scientists hiked to the remote wilderness-area site: paleontologist Brent Breithaupt, director and curator of the University of Wyoming's Geological Museum; U.S. Bureau of Land Management paleontologist Alan Titus and geologist Rody Cox; and paleontologist Andrew Milner of the St. George (Utah) Dinosaur Discovery Site at Johnson Farm.

They saw dinosaur tracks en route, but none in the pockmarked "dance floor."

"There simply are no tracks or real track-like features at this site," Breithaupt says. "We will be investigating the formation of these features in the upcoming study. Science works best when
scientists work together."
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