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A walk back 360 million years
Paleontologist confident impressions in rock along Hay River are tracks of prehistoric fish

Paul Bickford
Northern News Services
Published Friday, June 15, 2012

A paleontologist is 90 per cent sure that impressions in rock along the Hay River just south of Enterprise are tracks created 360-380 million years ago by a large walking fish.

NNSL photo/graphic

Donald Henderson, curator of dinosaurs at the Royal Tyrrell Museum of Paleontology in Drumheller, Alta., gets an up-close look on June 11 at impressions in rock along the Hay River south of Enterprise. Henderson is confident they are tracks laid down 360-380 million years ago by a large fish. - Paul Bickford/NNSL photo

Donald Henderson, curator of dinosaurs at the Royal Tyrrell Museum of Paleontology in Drumheller, Alta., made that assessment after examining the tracks on June 11.

Henderson believes that, based on the age of the limestone rock, the impressions were likely made by a large lobe-finned fish called sauripterus, which was up to six metres long. Those animals lived long before dinosaurs even existed.

"I'm convinced it is a track way," he said of the impressions in the rock above Alexandra Falls at a public presentation at NWT Centennial Library in Hay River on June 11. "They're not random erosional features."

Henderson said the tracks are an interesting and important find.

"It's not unique in the world. We've got other Devonian tracks," he said, referring to the geologic period. "It's probably a first for North America. Unfortunately, the quality is kind of rough."

The world's only other example of such tracks by large lobe-finned fishes from the Devonian Period is in Poland.

Henderson visited the Hay River site accompanied by two representatives of the Department of Industry, Tourism and Investment (ITI), since the tracks are in Twin Falls Gorge Territorial Park.

The expert looked for a pattern in the impressions and measured their size and distance apart.

About 10 circular/oval impressions can be seen in the rock. They are about a foot in diameter one way and eight inches in diameter the other way. They are spaced about four feet apart, plus they are in a pairs.

"It's the regularity. They're in a straight line. They're all the same shape," Henderson said.

However, he added they are also heavily eroded and no detail can be seen , noting that, if they had been spotted 10 years sooner, there might have been signs of fin rays the equivalent of digits.

When they were created, he believes the rock was underwater near the shore of a shallow tropical sea and the impressions were made by a sauripterus pushing itself along in shallow water by using its large fins.

"This was clearly a tidal flat," Henderson said.

At that time, the land was near the equator, but over the last few hundred million years has moved north with the tectonic motions of the continents.

Henderson expressed concern about the future of the tracks, noting they have almost been erased by erosion.

"They're probably not going to last another year," he said.

Since the tracks were spotted in 2009 by a visitor to the park their condition has noticeably deteriorated. In fact, some tracks can no longer be seen, but it is unclear if they have eroded, been scrapped away by spring breakup ice, or been covered by mud and rock.

Near the tracks, there is a rocky shelf, and Henderson thinks there might be more tracks underneath that. While he would like to excavate to find those tracks, he said there would probably be too many regulatory hoops to jump through.

As for what happens to the tracks now, Henderson said they could be cut out of the rock for preservation and possibly displayed in the same pattern in which they were found.

However, he said the rock is so crumbly it may be destroyed by any attempt to rock saw or jackhammer it out.

Plus, he explained storage would require a proper constant temperature and a dry environment to preserve the rock and the tracks.

If that is not available, there would be no point in just putting them in some kind of shed, he said, "You're just going to end up with a bag of crumbs."

Henderson said taking latex peels would probably be the best idea logistically, and that would mean the tracks could stay where they are.

"You don't want to take people's fossils away from them. Let them come and see them the way they really are and, unfortunately, you have to let nature take its course," he said.

Tom Colosimo, manager of tourism and parks for the South Slave region with ITI, said it is good to finally get some answers about the impressions in the rock, noting it is phenomenal for them to be tracks dating back 360 million years.

"This is certainly a new and exciting discovery for this region," he said.

Colosimo noted it is too early to provide details on what ITI will do now, although he did say it will mean getting more expert advice to determine the next steps. Peter Osted, co-chair of the Hay River Museum Society, said he would like to see the Prince of Wales Heritage Centre in Yellowknife somehow become involved in preserving the tracks.

"Our museum just doesn't have the facilities to do that," Osted said referring the Hay River Heritage Centre. "It's climate control and that's expensive."

Henderson is unsure if he will write a scientific report about his findings, since the quality of the tracks is not good.

Three years ago when he originally saw only photos of the tracks, he initially believed they might be dinosaur footprints because, based on the geology map to which he referred, he thought the rock was not as old as it turns out to be.

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