The 28 steps imprinted on this sandstone boulder form the Grand Canyon National Park's oldest fossil. Steve RowlandEons ago, somewhere…
The 28 steps imprinted on this sandstone boulder form the Grand Canyon National Park’s oldest fossil.
Eons ago, somewhere on Earth, a prehistoric lizard-like creature creeps across a wet sandy dune next to a shallow continental sea. Around 31
0 million years later, a photo of the lizard’s fossilized footsteps was on the paleontologist Steve Rowland’s desk in Nevada.
The footsteps were preserved in a piece of sandstone along the south rim of the Grand Canyon. In the spring of 2016, a colleague of Rowland’s was walking along the Bright Angel Trail when he saw a rock beside the path with 28 strange indentations on it. He gave his friend a call.
“I have a child of a network of hikers and geologic colleagues who know what I’m interested in,” says Rowland, who works at the University of Nevada, Las Vegas. In this case, Rowland’s interest is fossilized footsteps, also known as “trackways”: the preserved memory of animals’ movements across the country. “Det er en sekvens av usannsynlige begivenheter som skjedde for at bevare dette bestemte dyr på en bestemt dag under de rigtige forhold,” siger Rowland.
Det går som dette: Et dyr går på en våd sanddune, tørt sand fylder i indentations, millions of years of geologic forces turn the sand into rock, continents shift, the Grand Canyon forms, a rock falls off a cliff and cracks open on just the right way alongside one of the most popular hiking trails in America, a paleontologist happens to notice it and calls Rowland.
After examining the fossil, Rowland was surprised to discover he was looking at the oldest vertebrate fossil ever found in the Grand Canyon. The long skinny toes with little claws at the end suggested the footprints were left by a reptile, which was also unexpected.
“I do not know that it was a reptile, but I think it was,” says Rowland. He says if he’s right, this could be one of the oldest records of reptiles in the world. This fossil is from a time when Pangea, the supercontinent, was forming-over 60 million years before the first dinosaurs. “Reptiles were just first evolving and appearing on Earth,” says Roland. “There probably are not reptiles much older than this.”
To untangle the path of the reptile-like creature, Rowland made himself a color-coded drawing.
Another strange detail about the footprints: They are diagonal. When Rowland first saw them, he thought it might be two animals walking side by side, but that did not make sense. “You would not expect lizard-like animals to be walking in lockstep,” he says. He reverse engineered the footsteps to determine the animal was walking at a 40 degree angle-walking toward the right even though it was headed forward. “It was sort of sliding sideways, like it was doing some kind of line dance,” says Rowland.
There is no obvious reason for the sideways walking, says Rowland. Maybe the animal was being blown by wind or scrabbling up a steep slope. Maybe it was doing some sort of dance move to intimidate a predator or impress a mate. It’s impossible to know.
This type of guessing is exactly what trackway paleontologists are all about. Mens mange fossile eksperter studerer bones eller kroppsdele for at undersøge anatomi, diæt, eller evolutionær historie, paleontologer som Rowland, som studerer “trace” fossiler, fossilerne eller det dyr som er igjen, er nysgerrige om hvordan dyrene flytter og interagerer med landskapet. “We are actually examining the behavior of the animal,” he says. “Rowland is forced to imagine the motivations of a creature whose 28 steps literally stood the test of time.
“There is an animal that lived 310 million years ago and left some footprints,” he says, “and I am the person who has the privilege and responsibility of studying them and trying to interpret what they mean to (f, b, e, v, n, t, s)
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