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Fossils trace

Trace fossils, the most inconspicuous bite-sized window into ancient worlds

Itching for ichnofossils — “One animal could have made thousands of traces during its lifetime, but only left one skeleton.” Jeanne Timmons – Jun 11, 2021 11:30 am UTC Enlarge / It may not look like much, but you can actually learn a lot from a fossilized leaf that preserves insect damage.He knew what it…

Itching for ichnofossils —

“One animal could have made thousands of traces during its lifetime, but only left one skeleton.”


Image of a rock with oval outlines embedded in it.

Enlarge / It might not seem like much, but you may actually learn a lot from a fossilized foliage that prevents insect harm.

He understood what it was as soon as he saw it: the signature hint of a bird landing. He’d seen hundreds of such tracks along the Georgia coast. He’d photographed them, measured themand attracted them. The distinction ? This landing track was roughly 105 million years old.

Dr. Anthony Martin, a favorite professor at Emory University, recognized that landing track in Australia in the first 2000s when he passed with a fossil slab in a museum. “Because my eyes had been trained for so long from the Georgia coast seeing those kinds of patterns, that’s how I noticed them,” he said. “Because it literally was out of the corner of my eye. I was walking by the slab, I glanced at it, and then these three-toed impressions popped out at me.”

Impressions of feet may seem to be pretty dull compared to some fully reconstructed skeleton. But a lot people yearn for a window into historical worlds, to really see how long-extinct animals looked, lived, and behaved. Paleontology enables us crack open the window; using fossilized remains, scientists glean information about growth rates, diet, diseases, and where species roamed. But there is a lesser-known branch of paleontology that completely opens the window by researching what the extinct creatures actually did.

‘Fossil’ may conjure a mental image of a million-year-old bone, but it could also mean traces of behavior that survived the fossilization process: whatever in the swipe of a tail because it circulates round the floor and bite marks to fossil poop and vomit. ‘Ichnology’ is the title of that particular branch of study, and’ichnofossils’ are the traces left from the fossil record, such as the bird tracks Martin recognized.

When you think of how frequently and how many ways anything can leave its mark in an environment, and then consider how many of those traces might have survived after countless years, the chance of locating a vast assortment of ichnofossils throughout the world seems a distinct possibility.

To put it yet another way, Martin wrote:”One animal could have made thousands of traces during its lifetime, but only left one skeleton, parts of which may or may not be preserved.” The odds of finding ichnofossils are significantly greater.

So why does this matter?

Trace fossils offer clues to what ancient species might have been doing, in what situation, and also, in some instances, how they interacted with different species. A pair of footprints, as an instance, can tell us whether a creature was walking, jogging, or swimming, as well as something about the surroundings that captured those footprints. Bite marks may offer clues into historical diets. And a few traces show previously unknown connections involving multiple species.

Tracks in the sand

These kinds of interactions have been discovered repeatedly in White Sands National Park in New Mexico. The website may be known more for its stunning white gypsum dunes, but to those interested in paleontology, White Sands is a ichnofossil treasure trove. Countless fossil footprints have been found here, a lot of them in prolonged tracks that cross great distances. As a result of the record these footprints maintain, paleontologists know that an early lake was visited by Columbian mammoths, Harlan ground sloths, saber-toothed cats, dire wolves, bison, camels, and historical humans.

David Bustos, resource application manager at White Sands who has been working for 15 years, explained that they frequently find sloth and mammoth paths near human tracks. But whereas the mammoths appear to walk on without stopping, the giant ground sloth tracks show signs of reacting: this enormous beast, estimated to weigh up to a ton, consistently turns around and then walks into another direction by the individual footprints. Remarkable, but what exactly does this mean? What was it on a human existence that appeared to affect giant ground sloths although maybe not mammoths?

A clue can be found in a specific set of paths in another place from the park. In these paths, we could see ancient humans following from the footprints of a giant ground sloth, culminating in a place where the human monitors surround the sloth, which divides on two legs.

Fossilized human footprints at White Sands.

Enlarge / Fossilized human footprints at White Sands.

One special set of human monitors tells an fascinating narrative, with more unanswered questions. Dependent on the magnitude of the footprints, the space between them, and also how the footprints were formed, scientists can gauge how fast that human may happen to be traveling. Along with the tracks revealed something bones couldn’t: the human was carrying another, smaller humananatomy. At some point in the trip, the footprints stopped–a smaller pair of prints found facing them, just as a young human carrying its sibling could do if that intruder were becoming a little too heavy or when alterations were needed to clothes. Those small footprints vanished soon after, the only set of monitors continue, their formation like those created when a human is carrying extra weight. The journey was in haste, the footprints slipping in ancient mud.

A set of only human tracks on the return journey no more signify some excess weight. The smaller human was not carried on back, and there certainly are no longer any smaller footprints.

Perhaps even more intriguing: this individual trackway intersects with two types of Pleistocene megafauna–a giant ground sloth and three mammoths. Because the human footprints step into mammoth paths in their journey north, then a massive measures onto the human tracks after that human returns walking south, scientists know that these monitors were contemporaneous. In other words, they had been made hours, maybe days after each other. And that’s astounding.

Bustos and an international team of investigators continue to research the approximately 80,000 acres of the park. The size of the playground, the relatively recent intense analysis of the fossils, and the increasing amount of revelations in ensuing papers hint that there is much yet to be discovered.

Migration, by the intestine

Even without footprints, however, ichnofossils can offer clues to the paths traveled by ancient animals. Scientists used a specific kind of rock to follow the possible path of sauropods–gigantic long-necked dinosaurs–in Wyoming. These weren’t just any rocks; they have been smooth, polished, round, and of a distinctly different kind of mineral compared to anything else from the region. All those features indicated that these rocks were gastroliths: stones ingested to assist with the animal’s digestion.

Stones that once resided in the digestive tract of giant sauropods.

Enlarge / Stones that formerly lived in the gastrointestinal tract of giant sauropods.

Joshua Malone

There were no fossils found in association with at least one of these gastroliths. So how can we determine which species ingested them, let alone discover the 1,000 kilometer path traveled by this species?

The relatively large size of those gastroliths signaled they could only have been swallowed by big animals. Of the fossils discovered to date in the same geological formation, a small percentage have been found with gastroliths, all either long-necked sauropods or the bipedal carnivore Allosaurus. Of both, sauropod fossils are more abundant and are more inclined to have them.

The smooth, curved rocks, located by Joshua Malone, (a PhD student in the University of Texas at Austin), his daddy, along with his additional co-authors, were reddish quartzite–a kind of rock not seen in the region rather than known from this layer of sediment. They utilized detrital zircon geochronology, an innovative but destructive analysis which helped them determine the source of these gastroliths and discovered that one chance was in southern Wisconsin–right at the bottom of an ancient stream that directed back to Wyoming during the Jurassic.

Bighorn Basin, part of the geologic formation where the gastroliths were found.

Enlarge / Bighorn Basin, a portion of the geologic formation where the gastroliths were found.

Joshua Malone

Building upon other research, including potential sauropod migration, the authors suggest that these enormous animals ingested the reddish quartzite in Wisconsin as part of a possible seasonal migration path across the river. The gastroliths are found without fossils indicates the bones didn’t survive fossilization when these animals finally died.

Mass death

Lack of fossils wasn’t an issue facing the researchers o

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