As mais antigas pegadas conhecidas no Grand Canyon foram deixadas por um réptil misterioso

By Laura Geggel, Senior Writer | November 15, 2018 08:02am ET

This set of 28 footprints, made by an early reptile-like creature about 315 million years ago, are the oldest vertebrate track marks ever to be found in Grand Canyon National Park.

Credit: Courtesy of Stephen Rowland

About 315 million years ago — long before dinosaurs roamed the Earth — an early reptile scuttled along in a strangely sideways jaunt, leaving its tiny footprints embedded in the landscape, new research finds.

It's anyone's guess why this ancient, clawed critter walked sideways (although experts have several ideas), but one thing is certain: The animal's prints represent the oldest-known vertebrate track marks ever discovered in Grand Canyon National Park, said Stephen Rowland, a professor of geology at the University of Nevada, Las Vegas, who is studying the fossilized trackway.

The trackway is so old, that it was made a mere 5 million years after the first known reptiles emerged on Earth, just as the ancient supercontinent Pangaea was forming. "This is right in that little window of the very first reptiles," Rowland told Live Science. "We don't know much about that real early history." [Photos: Dinosaur Tracks Reveal Australia's 'Jurassic Park']

The research, which has yet to be published in a peer-reviewed journal, was presented at the annual Society of Vertebrate Paleontology meeting in Albuquerque, New Mexico, on Oct. 17.

The trackway — preserved on a slab of sandstone measuring about 3.2 feet long and 18 inches wide (1 meter by 45 centimeters) — contains 28 prints from the mystery animal's front and back feet. A friend of Rowland's first noticed the fossilized tracks in 2016 while hiking along the Grand Canyon's Bright Angel Trail, located on the Manakacha formation in northern Arizona.

When Rowland visited the site in May 2017, the 2-inch-long (5 cm) prints befuddled him. At first glance, the track marks looked as if they were left by two animals walking side by side, "which is very bizarre for an early reptile," he said. After lying awake at night, turning the images over in his mind, Rowland had an epiphany: The animal that left the tracks was moving sideways.

The mystery reptile-like creature walked sideways as it made these track marks. It's unclear why the animal did this, but perhaps it was blown by the wind, doing a mating dance or even facing an aggressor.

Credit: Illustration by Stephen Rowland

Normally, four-legged animals walking forward obscure some of their footprints, with the rear foot stepping on top of the front footprint. "In this case, that didn't happen," Rowland said.

He noticed that while the animal's tiny claws were pointing forward, the animal was moving sideways, about 40 degrees toward to the right (each row is offset to the right by about 8 inches (20 cm) compared with the previous row, Rowland said.) Perhaps, a strong wind from the left was blowing against the creature, pushing it sideways. Or, maybe the creature was trying to climb a steep incline and was walking up the slope diagonally. It's even possible that the reptile was walking sideways because it was injured, circling an aggressor or doing a mating dance, Rowland said.

"I don't think we'll know with any confidence," Rowland said.

When the prints were made, during the Carboniferous period (about 359 million to 299 million years ago), Arizona lay close to the equator. At that time, the mysterious reptile walked over a coastal sand dune near a shallow sea to the west, according to co-researcher Mario Caputo, a retired adjunct professor of sedimentology at San Diego State University.

The next-oldest fossilized vertebrate track marks in the Grand Canyon are about 20 million years younger, from the Coconino Sandstone formation, Rowland noted. These date to the Permian period, (about 299 million to 251 million years ago). Because the different trackways look so similar, it's likely that they will be given the same scientific name of Chelichnus, Rowland said. (Like species, fossilized prints are given scientific names.)

"That doesn't mean it was the same animal living in different places," Rowland said. Rather, because the prints look so similar, they're given the same name, even if a different animal made them, he said.

Originally published on Live Science.

Mistério marciano é resolvido

27/5/2010

Agência FAPESP – Um mistério de quase 40 anos em Marte acaba de ser resolvido. Cientistas conseguiram reconstruir a formação de duas características inusitadas no polo norte do planeta: uma série de espirais e um abismo maior do que o Grand Canyon.




Em dois artigos publicados na edição desta quinta-feira (27/5) da revista Nature, John Holt, da Universidade do Texas, e colegas descrevem como usaram dados obtidos pela sonda Mars Reconnaissance Orbiter, da Nasa, a agência espacial norte-americana, para desvendar a composição da camada de gelo no norte marciano.

Na Terra, os mantos são formados principalmente pelo fluxo de gelo, mas em Marte, segundo a nova pesquisa, outras forças têm moldado as calotas. A calota ao norte é uma pilha de gelo e camadas de poeira com até 3 quilômetros de profundidade, que cobre uma área maior do que a do Estado de Minas Gerais.

Ao analisar em computador os dados de radar colhidos pela sonda, os pesquisadores puderam, como se estivessem retirando as camadas de uma cebola, verificar como a cobertura de gelo evoluiu com o tempo.

Uma das partes mais notáveis no polo norte marciano é a Chasma Boreale, uma depressão tão extensa como o Grand Canyon norte-americano, mas mais profundo.

Desde que foi descoberta, em 1972, cientistas estimavam que a depressão teria sido formada a partir do derretimento do fundo do manto de gelo pelo calor vulcânico. Mas o novo estudo indica que tanto a Chasma Boreale como as espirais foram criadas principalmente pela ação de fortes ventos, durante milhões de anos.

A nova pesquisa aponta também que a calota de gelo no norte marciano não é composta por muitas camadas relativamente planas, mas que conta com características mais complexas, entre as quais camadas com espessura e orientação diferentes ou camadas que simplesmente desaparecem em alguns pontos.

“Não se sabia da existência de uma estrutura de camadas tão complexa, que registram a história de acúmulo de gelo, erosão e ação do vento. A partir de agora, poderemos recuperar uma história detalhada do clima em Marte”, disse Holt.

Em 1982, Alan Howard, da Universidade da Virgínia, propôs em um artigo que as misteriosas espirais teriam sido formadas pela ação do vento, mas o trabalho foi ignorado pela comunidade científica, que bancava a hipótese da origem vulcânica. O novo estudo mostra que Howard estava certo.

Segundo Holt e colegas, a formação em espiral deriva dos ventos existentes na região, formados por ar denso e relativamente frio que circula a partir dos polos e por sobre as calotas.

A ação do vento é afetada pela força de Coriolis, perpendicular ao sentido do movimento do planeta. Na Terra, isso leva à formação de furacões, que giram em direções opostas nos hemisférios. Em Marte, essa força influencia nos ventos e nas depressões criadas, que assumem a forma de espirais.

Os artigos Onset and migration of spiral troughs on Mars revealed by orbital radar (vol 465 | doi:10.1038/nature09049) e The construction of Chasma Boreale on Mars (doi:10.1038/nature09050), de John Holt e outros, podem ser lidos por assinantes da Nature em www.nature.com.