Page 26 - The Restless Earth Fossils

the tortuous road to Fossilhood 25

both humans and other animals. Three species of giant ground
sloth, for example, lived in North America 13,000 years ago. The
largest species, Paramylodon, could rear up 6 feet (1.82 meters)
and weighed 3,500 pounds (1,590 kilograms). This veggie eater
spent time in caves—perhaps seeking sheltered space when giving
birth. Individual sloths also died in caves. Scientists have found
complete sloth skeletons with hair, skin, nails, and soft tissues
like muscles and tendons dried but still intact. Some sloth skin
still contains small nodules of bone called ossicles, which are
common in reptiles, but only found in armadillos among today’s
living mammals.
Insects, lizards, small mammals, and various plants and plant
parts sometimes blunder into and get stuck in the gooey resin of
certain trees. The resin, over long stretches of time, heat, and pres-
sure, becomes amber. As fans of Jurassic Park movies know, amber
can preserve DNA (deoxyribonucleic acid) and other complex
organic molecules for millions of years. While reconstructing indi-
vidual animals (like dinosaurs) from fragmentary bits of DNA is
currently impossible, creatures trapped in amber provide a wealth
of detail about the world in which they lived. For example, the
husband and wife scientific team of George Poinar Jr. and Roberta
Poinar have looked at a stingless bee trapped in amber with “gos-
samer wings outstretched and perfectly preserved down to the
last hair” and contemplated what its eyes saw in a Dominican
Republic rainforest 40 million years ago. By observing and record-
ing hundreds of amber “sapsicles,” they have convincingly recre-
ated this animal’s lost world in their book The Amber Forest.
A young Columbian mammoth searching for food 20,000
years ago steps on what he thinks is solid ground only to sink
into the black goo of a tar pit—a natural pool of asphalt formed
when organic material slowly decays as it heats up underground.
He struggles, but only gets stuck more deeply. His cries attract
dire wolves, perhaps an old saber-toothed cat, and giant birds
of prey, called teratorns. Some of them get stuck in the tar as
well, and what looked like a “free lunch” becomes their last
meal. Scientists have “read” this and many similar stories while

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