Newly discovered fossil footprints force paleontologists to rethink former desert dwellers

An international team of paleontologists met to study important fossil footprints recently discovered in a remote location in Grand Canyon National Park, Arizona. A large block of sandstone contains several tracks of primitive four-legged tetrapods (exceptionally well-preserved animals) that inhabited an ancient desert environment. The traces of fossils dating back to 280 million years date almost from the beginning of the Permian, before the appearance of the earliest dinosaurs.

The first scientific article reporting the fossil record of the Grand Canyon was published in 1918, just one year before the park was established as a unit of the National Park Service. One hundred years later, at the centennial celebration of Grand Canyon National Park, new research on the park's ancient footprints is presented in a scientific publication published this week. Dr. Heitor Francischini, a Brazilian paleontologist from the Vertebrate Paleontology Laboratory of the Federal University of Rio Grande do Sul, is the principal author of this new publication, which works with German and American scientists.

Francischini and Dr. Spencer Lucas, paleontology curator at the New Mexico Museum of History and Natural Science in Albuquerque, New Mexico, visited the Grand Canyon Fossil Trail for the first time in 2017. Paleontologists immediately recognized that traces of fossils had been lost parent of very young reptiles and resembled the known traces of Europe called Ichniotherium (ICK-nee-oh-thay-ree-um). This new discovery at the Grand Canyon is the first occurrence of Ichniotherium in the sandstone of Coconino and in a desert environment. In addition, these tracks represent the youngest geological record of this type of fossil trail from anywhere in the world.

Ichniotherium is a kind of imprint believed to have been created by an enigmatic group of extinct tetrapods known as diadectomorphs. The diadectomorphs were a primitive group of tetrapods with the characteristics of both amphibians and reptiles. The evolutionary relationships and paleobiology of diadectomorphs have long been important and unresolved issues in the science of vertebrate paleontology.

Although the manufacturer of the tracks for the Grand Canyon footprints may never be known with certainty, the Grand Canyon tracks preserve the displacement of a very ancient terrestrial vertebrate. The measurable characteristics of the tracks and tracks indicate a primitive animal with short legs and a massive body. The creature walked on all four legs and each foot had five fingers without claws.

Another interesting aspect of the new fossil record of the Grand Canyon is the geological formation in which they are preserved. Coconino Sandstone is a wind-shaped rock formation with cross-layers and other sedimentary features indicating a desert / dune deposit environment. Therefore, the presence of Ichniotherium in the sandstone of Coconino is the oldest evidence of diadectomorphs in an arid desert environment.

According to Francischini, "these new traces of fossils discovered in Grand Canyon National Park provide important information on the paleobiology of diadectomorphs.The diadectomorphs should not live in an arid desert environment, as they would not have the conventional adaptations to be completely The group of animals with such adaptations called Amniota (reptiles, birds and existing mammals) and diadectomorphs do not belong to it. "

Lucas also notes that "paleontologists have long thought that only amniotes could live in the hard and hard Permian deserts." This discovery shows that tetrapods other than reptiles lived in these deserts and, surprisingly, were already adapted to life. in a limited environment, water. "

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Provided by
New Mexico Museum of Natural History and Science