With the wealth of information fossils have to offer, it's no surprise that some people devote years to hunting for them. Fossils — the preserved remains of animals, trees, and other organisms — provide insights into the evolution of and relationships between extinct species and those around today. They also indicate when and how continents were once connected and offer details about the environmental conditions of different eras.
Yet fossils are very rare — paleontologists refer to a figurative "one in a million" chance for an animal to become a fossil. Other estimates suggest that less than .001% of all the animal species to ever exist will end up as fossils. This is because fossilization requires that an organism be covered by tar, ash, or another kind of sediment before it decomposes. A fossil must be buried deep enough to avoid scavengers and lucky enough not to be torn apart by shifting rocks and land, or to sink so deep that it's destroyed by heat and pressure. Then, ultimately, the layers that cover a fossil must wear away so that it can be discovered.
In other words, the circumstances have to be just right — so when a fossil is found, it's something to celebrate. Here are the stories of six fascinating fossil finds.
Sue the Tyrannosaurus Rex
On August 12, 1990, paleontologist Susan Hendrickson was looking for fossils on a South Dakota cattle ranch when she caught sight of several large vertebrae sticking out of a cliff. The find turned out to be a 65-million-year-old Tyrannosaurus rex skeleton. The skeleton was around 90% complete, making it the most complete T. rex fossil to be discovered. At 13 feet high and more than 40 feet long, it's also the largest T. rex ever found. Sue was named in Hendrickson's honor, though the dinosaur's sex isn't known.
In 1992, while parts of Sue were still being excavated, the fossil was seized by federal agents. Because the ranch where the T. rex came from was on the Cheyenne River Sioux reservation and under federal jurisdiction, the government hadn't given its permission for the team to excavate the fossil. Essentially, the government viewed the fossil as being “stolen.” A court ruling ultimately handed Sue over to the ranch owner and the Bureau of Indian Affairs.
Sue's skeleton went up for auction in 1997. The fossil was purchased by Chicago's Field Museum for more than $8 million and went on display in May 2000. Sue, who has an active Twitter account, is still at the museum and continues to be studied by scientists.
Lucy, an Early Human Ancestor
In 1974, paleoanthropologist Donald C. Johanson was looking for fossils in Ethiopia's Afar region. By chance, he noticed a forearm bone in a stream bed. It was from a 3.2-million-year-old female hominid, a distant relative to humans. Johanson's team named the fossil “Lucy” because the Beatles' song "Lucy in the Sky With Diamonds" was playing in camp on the night of the discovery.
Lucy's species was called Australopithecus afarensis to acknowledge where the fossilized skeleton was discovered. The skeleton was 40% complete when found. Scientists were surprised to learn the 3.5-foot-tall hominid had walked upright even though her brain was much smaller than that of a modern person.
The Devil Toad
Some fossil discoveries require more time than others. Paleontologist David Krause first uncovered large frog bone fossils in Madagascar in 1993, but it wasn't until 2008 that he and his team assembled enough fossil fragments to be able to share what this frog, which lived about 70 million years ago, had been like.
These fossilized remains may be from the largest frog ever to exist. It weighed 10 pounds and was around 16 inches long. Thick skull bones offered protection, and its teeth indicate that the frog could consume lizards, small vertebrates, and possibly even hatchling dinosaurs. This enormous frog was named Beelzebufo, which translates to devil toad, or devil frog.
Though Beelzebufo was found in Madagascar, analysis revealed it was more closely related to modern horned frogs from South America than to present-day African frogs. Beelzebufo's discovery provides additional evidence for the theory that South America, Antarctica, and Madagascar were physically connected around 65 to 70 million years ago.
La Brea Tar Pits
The La Brea Tar Pits in Los Angeles, California, are bubbling pools of asphalt. Their existence was common knowledge for centuries; Indigenous inhabitants such as the Chumash and Gabrielino tribes used the asphalt to waterproof items. Yet, until the 1870s, it was assumed that bones found in the pits were from present-day animals.
In the early 20th century, after people realized the pits held fossils, efforts to find and study them took off. Scientists learned that the asphalt had trapped and preserved flora and fauna from the tail end of the last ice age, around 10,000 to 40,000 years earlier. Some fossils were from species that are still alive, like fish and insects, but others were from vanished animals such as mammoths, American camels, saber-toothed tigers, and American lions. The finds have raised questions about what drove certain species to extinction.
Plants and animals are not the only organisms that can become fossils — microbes can fossilize as well. The oldest microbial fossils offer insights into when life began.
In 2012, a group of scientists headed to Greenland, where Earth's oldest known rocks are located, to look for ancient microscopic fossils. Four years later, they announced they had discovered microbe fossils in 3.7-billion-year-old rocks known as stromatolites. An earlier find of stromatolites from Australia was dated at 3.4 billion years old, so this placed the beginning of life more than 200 million years earlier than previously thought.
However, in 2018, another paper posited that the layered structures in Greenland had not been biologically created by microbes, but instead mimicked the appearance of stromatolites because the rocks had been compressed. The debate still continues about the validity of the stromatolites.
In 2008, a man looking for lost sheep in Argentina’s Patagonia region discovered much more than a fluffy animal: an extremely large femur. Excavation began and uncovered partial skeletons, including 100-million-year-old dinosaur fossils, from seven individuals.
In 2017, that species was named Patagotitan mayorum in honor of the region where it was found and the family, Mayo, whose ranch it was on. Scientists believe that Patagotitan mayorum is a species of titanosaurs, the largest terrestrial animal ever to walk the Earth.
Patagotitan mayorum is estimated to have weighed 77 tons. It may have been 130 feet long and 65 feet tall. However, these figures may be overestimated, and without a complete skeleton, definitive answers are elusive.
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