Toothy feller, isn’t he? |

Toothy feller, isn’t he?

John Colson
Photo courtesy Denver Museum of Nature and Science

About 100 million years ago, the land now occupied by Aspen and the Roaring Fork Valley was entirely covered by a vast, if shallow, inland sea.In that early epoch, according to paleontologists, geologists and others, the land we now inhabit probably was not where it is now in relation to such global place markers as the Equator or either of the polar regions.

In fact, the land that currently sits under Aspen is believed to have been much nearer the Equator in the late Triassic and early Jurassic Periods, somewhere around 210 million to perhaps 290 million years ago.Back then, according to various reports, the continents of the northern hemisphere were bunched up in a mass known as Pangea but were slowly breaking apart. America drifted to the north and east, away from Africa, and the motion of huge plates riding beneath the earth’s crust formed a range of mountains along the Pacific shoreline, while the area that would become the Southwestern United States already was a desert populated by the precursors of dinosaurs.But by the early Cretaceous period, roughly 100 million years ago, scientists believe, a combination of geologic and oceanographic factors caused an arm of the Arctic Ocean to extend southward over the central portion of western North America.Meeting up with waters from the Atlantic that were flooding northward from the area that would become the Gulf of Mexico, this vacillating inland sea once stretched from eastern Utah to the southern Appalachian Mountains, roughly 1,600 miles at its widest. It is estimated to have been only about 1,500 feet deep, and was filled repeatedly by erosion from the Appalachians in the east and the infant Rockies in the west, shrinking and growing in several different stages over the course of the Cretaceous period.The uplift that would form the Colorado Rockies was still in its infancy, and the ocean waves rode softly above what would someday be the Roaring Fork Valley.This inland ocean was called the Mowry Sea, named for a characteristic rock formation rich in an organic substance called kerogen, itself known by another name now – oil shale, which some believe holds enough energy reserves to save the United States from its dependence on foreign oil.It was during this time, the early Cretaceous period, that a certain marine reptile known to researchers as a plesiosaur died and was buried deep in the ocean bed in what would ultimately become the Roaring Fork River drainage.

It would take about 90 million years before a young local hunter, Mike Gordon, would stumble on that plesiosaur’s fossilized bones and start a process that Gordon hopes will lead to a full-blown excavation (see related story).Paleontologist Brent Breithaupt of the University of Wyoming checked out the bones Gordon brought to him at the University of Northern Colorado, where Breithaupt lectures. Breithaupt tentatively identified the bones as those of a marine reptile, and sent Gordon to another expert, Kenneth Carpenter, curator of vertebraic paleontology at the Denver Museum of Nature and Science. Carpenter said the bones appear to be those of a plesiosaur.Breithaupt said this week that earlier published estimates of the creature’s age – possibly as high as 200 million years – were incorrect.”Two hundred million years is way too old,” he said. “It’s more like 90 million.”That, he said, would put it in the Cretaceous Period, when there was an ocean covering Colorado, which would be necessary for a plesiosaur’s existence. Breithaupt believes the plesiosaur might have lived during what is called the Turonian stage of the Cretaceous Period, which fell between 93.5 million and 89.3 million years ago.Carpenter, who is known on the Internet as The Dinosaur Detective for his work in educating the young about paleontology, said finds such as Gordon’s are rare because the uplift of the Rocky Mountains, which began about 68 million years ago, coupled with eons of erosion, has obliterated many fossils.Its significance, Carpenter said, depends on its location in geologic time.”If it occurs very low in the mancos shale, it could be much older than the other example we have here,” referring to a plesiosaur on display at the museum.

Plesiosaurs are described in Wikipedia, the online reference resource, as “carnivorous aquatic (mostly marine) reptiles” that “first appeared at the very start of the Jurassic Period [about 208 million years ago] and thrived until the K-T Extinction at the end of the Cretaceous Period [about 65 million years ago].”The K-T Extinction is named for the Cretaceous-Tertiary Periods, but the initial “K” is used to avoid confusion with the Carboniferous Period.Known also as the K-T Boundary Event, it is believed to have coincided with the impact of a huge meteor in the area of the Yucatan peninsula, which scientists think prompted a mass die-out of the dinosaurs and most animal and plant life across much of the earth. There also is evidence that the dinosaurs already were dying out or gone anyway, so the verdict remains out as to whether the K-T Extinction alone killed off the great reptiles.In any event, Wikipedia says of the plesiosaurs, “While they were Mesozoic reptiles that lived at the same time as dinosaurs, they were not dinosaurs.”They lived primarily on fish, had a broad body with four large flippers and a short tail. Within the species there were two main types that thrived for millennia. One had a long, serpentine neck and a small head, while the other had a medium-long neck and a more stocky build.It is generally believed that, while plesiosaurs might have been the model for the popular image of the Loch Ness Monster, they could not support their heads out of the water and spent most of their time in the depths. And since the western shore of this Cretaceous-era sea is believed to have been in what is now eastern Utah, the presumption is that Gordon’s specimen was swimming in deep water, hunting for fish – not at the ocean’s shore, as Gordon hypothesized.This is not the first indication of what kinds of creatures lived in the Western Slope region of Colorado in the distant past, Gordon noted.

While he was at the Denver museum recently, meeting with Carpenter for the first time, he saw a casting of a skeleton of a fish believed to have lived around 65 million to 100 million years ago, which was found in 1970 not far from where the plesiosaur lies.Gordon said he was told that the skeleton crumbled in the process of excavation, leaving scientists with only the impression the bones made in the rocks.Carpenter said the skeleton impression is about 10 feet long, and that the find provided “a tip that there could be fossils to be found up there.”There also are the remains of five different dinosaurs, from the Upper Jurassic Period, in a fenced-off area on the south side of the Colorado River near New Castle. According to Harley Armstrong, regional paleontologist for the U.S. Bureau of Land Management, the bones were discovered in 1971 but were too “carbonized” by flooding from a nearby mineral hot spring to be excavated.In addition, hikers in the Maroon Bells-Snowmass Wilderness in 2001 found footprints believed to have been left behind from a pig-sized reptile that lived around 290 million years ago, called Diadectes.”The discovery created a stir among paleontologists because no bones had ever been found and tracks were rare in the Maroon formation,” said a story in The Aspen Times in 2006, when the U.S. Forest Service erected informational signs telling about the creatures.

According to Bryan Small of the Denver Museum of Nature and Science, researchers found hundreds of sets of tracks in the Maroon formation left by the Diadectes, along with a few tracks left by other animals. And other Diadectes tracks reportedly have been found in the Maroon layer near Glenwood Springs and State Bridge, providing scientists with a glimpse into life in this area some 70 million years before the first dinosaurs appeared.At that time, according to researchers, this area was still hot and arid, and the Pangea land mass was still located near the equator, alternating between dry and monsoon season, similar to the climates of India or Africa today.Worldwide, as the continents tore and drifted apart during the Jurassic period, vertebrate life began to evolve into the largest and most distinct range of species to date. Over the next 150 million years or so, by the early Cretaceous period, huge plant-eating dinosaurs appeared on land, feeding on lush plant life such as ferns and palm-like cycads and stalked by smaller but very efficient carnivores.In the seas, fish and squid thrived fin-by-tail alongside great ichthyosaurs and plesiosaurs and, by the late Cretaceous, the ferocious Mosasaur. Above the surface, vertebrates first took to the air as pterosaurs and the earliest bird species appeared. Flowering plants appeared, and insects began to diversify into specialized categories.

Toward the end of the Cretaceous Period, the Western Interior Seaway had begun retreating northward and southward, from a dividing line roughly at the latitude of North and South Dakota.And then came the Cretaceous/Tertiary Extinction Event, or K-T Extinction.Among the species that disappeared, possibly even before the K-T Extinction, was the plesiosaur family.And as for our particular plesiosaur, it lay buried on the seabed until, starting around 68 million years ago, tectonic forces started pushing the Rocky Mountains upward. And as the uplift pushed Gordon’s reptile a mile into the air, erosion washed away the ground around it until it lay exposed, a thin line of bluish-looking stones, waiting for Gordon to come along.John Colson’s e-mail address is