Earths First Steps: Tracking Life Before the Dinosaurs

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Why did a theropod run instead of walk?

Earth's First Steps: Tracking Life Before the Dinosaurs

Was it chasing, or being chased? In the Dinosaur Diamond region, some of the most important and most recent trackway finds have been around Moab and have been dated to between million and million years ago, spanning from the Late Triassic to the Early and Middle Jurassic. During the Late Triassic, the area was covered with lush subtropical habitats, giant horsetails, fish- and amphibian-filled lakes, and turkey- sized carnivorous dinosaurs like Coelophysis , the New Mexico state fossil.

This animal and its anatomically similar relatives left an abundance of small, birdlike three-toed tracks first reported in New England in the mids and called Grallator. The earliest Grallator tracks were all small. Thus track specialists recognized a zone of strata, found over much of the world, packed with small footprints from the dawn of the age of dinosaurs. We can follow the evolution of such early theropod dinosaurs through various family tree branches into the Jurassic formations represented in the Moab area.

It represents a prosauropod, an ancestral relative of giant sauropods like Apatosaurus and Brachiosaurus , which themselves did not debut until the Late Jurassic. Transitioning from the Late Triassic to the Early Jurassic, the rock record indicates that the region was covered in huge, Sahara-like deserts with endless tracts of scorching, barren sands. The famous Navajo Sandstone, seen at the entrance to Arches and along the Colorado River south of Moab, is the classic example of fossilized dunes. Thus, it was a surprise to learn in the s that, in many areas, tracks of desert dwellers were quite abundant at hundreds of sites around Moab and all across southern Utah.

Previously, paleontologists thought desert environments would have been too harsh to sustain trackmaking animals. Their tracks also almost always point uphill, heading nose into the wind. No one really knows why this is. However, it is only in the western U. Desert habitats again prevailed during the Middle Jurassic when the Entrada Sandstone was deposited. The Entrada remains today as the main arch-forming rock formation in Arches National Park.

Protomammals evidently disappeared throughout much of the world by this time, but we still find the small, three-toed tracks of crow-sized theropods.

Earths First Steps Tracking Life Before The Dinosaurs

A very well-preserved three-toed ornithopod hind footprint and small front footprint from the Cretaceous-aged Dakota Sandstone near Delta, Colo. As the Middle Jurassic drew to a close, the region remained a desert. However, a tongue of ocean, known as the Sundance Sea, flooded into the Moab area, creating a sandy shoreline on which we find millions of large theropod tracks. The area is puzzling from an ecological standpoint, because the footprint assemblage is completely dominated by tracks of predators, but none from potential prey.

Perhaps this was a theropod-patrolled zone that prey species avoided. Counterintuitively, rising sea level does not wash away tracks. Instead, the sea acts as a dam allowing river and other shoreline sediment to accumulate along the coast creating coastal plain deposits — a process known as aggradation. As the sea transgressed farther over formerly dry land, dinosaurs tramped up and down the shifting coastlines, leaving behind millions of footprints.

During this period, we also see evidence in preserved tracks for an influx of pterosaurs, which fed in the shallow waters and left their footprints on the ripple-marked shoreline sands. In the Late Jurassic, the marine incursion began to regress, and the Western Slope of the Rockies became less arid. During this time, the Morrison Formation — comprising sandstones interbedded with soft mudstones — was deposited in a region extending from New Mexico to the Canadian border.

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To this list of iconic creatures, all found abundantly in the Dinosaur Diamond area, we can add many other denizens of Morrison time, including the crocodilian Fruitachampsa and the digging mammal Fruitafossor , both named for Fruita, where they were found. This was 18 years before the discovery of dinosaur bones at Morrison, Colo. Late Jurassic-aged Morrison paleoenvironments were not just dinosaur habitats, they were also home to a diverse fauna of small mammals and a flora often described as a fern- and cycad-dominated savanna.

Unlike the theropod-dominated assemblages from the older Entrada Sandstone, the collection of tracks in the Morrison Formation make ecological sense. They include those of large and small theropods, sauropods and a few ornithischian dinosaurs, crocodiles and turtles, thus generally reflecting the presumed composition of the fauna, based on excavated bones.

As we step into the Cretaceous, we find ourselves in the million- to million-year-old Cedar Mountain Formation, which has proved highly productive for dinosaur remains in the Moab area. We also find tracks that match the skeletal record quite well. Theropod footprints include the first two-toed dromaeosaur tracks found in North America, quite possibly belonging to Utahraptor , now an iconic Dinosaur Diamond discovery, for its large size.

Sauropod and Iguanodon -like tracks also match the skeletal record, but a dense assemblage of shorebird-like tracks is significant, because, as yet, the deposit has yielded no bird bones. Well-preserved four-toed hind footprint cast of an armored dinosaur ankylosaur from the Cretaceous-aged Dakota Sandstone near Delta, Colo. As we cross the boundary into the Late Cretaceous about million years ago, we witness a major change in the paleoenvironment. Trending north-south from the Gulf of Mexico to the Arctic, this shallow seaway helped create extensive coastal plain deposits on both its eastern and western shores.


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Rising sea levels again led to the accumulation and preservation of coastal plain deposits, which typically represent a mosaic of low-gradient wetlands, lakes, lagoons, floodplains and vegetation-rich coal swamps. The real questions is, how much money was wasted on this study, when resources could've been put to much better use studying I wonder if humans were wiped out, whether they would come back millions of year later, or something else?

The great dying did FAR more than decimate life in the oceans. Decimate literally means "to reduce by ten percent" but the great dying killed about 96 percent of all ocean life, and vast percentanges of everything else. In every possible way, it was substantially worse than a mere ten percent. Nearly nothing survived. We humans might never have existed, had it gone just a bit further. And that was hardly the only time our ancestors managed to survive truly terrible events. We've been incredibly fortunate. We are what didn't die. And it's something we take for granted and miss just how rare surviving has actually been.

Do we think we are the 'be all and end all' aim of life on earth? The 5 extinction events we see in the development of life on earth have certainly been transformational but life continued and the development of life seems to be a process of constant experimentation adapting to conditions. The last event has led to a world dominating super species that, in all probability, is responsible for the 6th, and largest, extinction event we find ourselves in the middle of. The development of life on earth is, yet again, under threat of radical transformation.

A distinct lack of 'be all and end all' going on there. Whether we successfully negotiate this transition to a sustainable future we're experiencing and avert this threat will determine whether or not our world dominating super species survives but, if not, life will probably continue with the next experiment. If we succeed that too will be a radical transformation for life on earth.

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It will be a successful adaptation that enables, encourages and nurtures more life, the more the merrier. That is the 'be all and end all' aim of life on earth, more life. Instead of examining how long it will take to rebuild a car after a serious car crash, we should focus on slowing down and driving safer Latest Stories.

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