Many geologists believe that a series of smooth, red quartzite cobbles discovered in Wyoming's Morrison Formation were deposited there by dinosaurs traveling from Wisconsin.
The research, which was published in the journal Terra Nova, is the first of its kind to use stomach stones as a proxy for dinosaur migration.
Sauropods, which grew to be over 100 feet long and 40 tons in weight, swallowed stones called gastroliths daily, possibly to aid in plant digestion.
DORCHESTER, DORSET - FEBRUARY 09: Dippy the dinosaur, a diplodocus skeleton on loan from the Natural History Museum is unveiled at Dorset County Museum on the first stage of an eight-stop tour of the UK on February 9, 2018, in Dorchester, Dorset. Some 5 million people are expected to see Dippy over the next two years at venues ranging from the Welsh assembly to Norwich Cathedral.
New York Times said the Wisconsin-Wyoming connection suggests a journey hundreds of miles longer than previous sauropod migration estimates. Seasonal changes can trigger animal migrations as they look for food and water.
These factors will clarify how the rocks' smooth and rounded textures developed. However, there are still doubts about whether they made the whole journey in the bellies of these massive beasts.
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The team determined that the gastroliths evolved 1.8 billion years ago, matching those from Wisconsin, by analyzing zircons' minerals, which function as little clocks.
"We believe [the stones] were transported from southern Wisconsin to north-central Wyoming in the belly of a dinosaur," paper author and geoscientist Josh Malone of the University of Texas at Austin told Live Science.
Forbes said the Morrison Formation is a 650-foot-thick (200-meter) sequence of mudstone, sandstone, siltstone, and limestone layers formed by rivers in the Bighorn Basin. Paleogeographic reconstructions and paleocurrent data in the rocks show that Morrison sediments were transported from the north and west.
However, the Baraboo quartzite is located east of the Bighorn Basin. There were no major rivers linking Wisconsin and Wyoming at the time. The researchers argue that natural forces such as water or wind are unlikely to have deposited the quartzite rocks here.
Researchers claimed all of the recovered quartzite cobbles are small enough to fit into a large animal's stomach, such as a dinosaur. Unfortunately, no quartzite rock was discovered to be connected to any particular dinosaur fossil.
The study suggests a sauropod genus, such as Barosaurus, Diplodocus, and probably Camarasaurus, as the gastroliths' possible origin, based on known species that once roamed the interior of North America. Sauropod dinosaurs that ate plants seem to have used stomach stones to grind tough plant matter or swallowed them by mistake while feeding.
After migrating westward more than 600 miles (1,000 kilometers), the dinosaurs possibly consumed fragments of the Baraboo quartzite (or eventually the somewhat similar Jacobsville quartzite) and expelled them naturally or died there, leaving the now rounded and polished cobbles in a new area, where they were buried in the fluvial sediments of the Morrison Formation.
Recent discoveries have shown that dinosaurs moved hundreds of miles, possibly searching for new food sources or responding to the yearly cycle of weather and temperature changes. The results of the study more than double the longest journeys previously attributed to sauropods.
There is still no clear evidence linking the quartzite cobbles found in the Morrison Formation to dinosaurs, confirming for sure that they are indeed gastroliths, according to some researchers. However, they concede that the possibility of reconstructing migration routes using genuine gastroliths is fascinating.
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