AT THE SMITHSONIAN

A History of Life In 10 Fossils

From their new book A History of Life in 100 Fossils, Paul Taylor and Aaron O’Dea share the story of 10 incredible fossils

Natasha Geiling

October 15, 2014

In 1970, scientists aboard the deep-sea drilling ship *Glomar Challenger* set out to document the types of rocks on the seabed of the Mediterranean. They were surprised to find fossilized stromatolites, which grow mostly in shallow water, as well asCyprideis, microscopic shelled crustaceans that live only in shallow, salty pools. The scientists concluded that millions of years ago the Mediterranean—which today is far from shallow—must have all but dried out. Smithsonian Books

Though massive creatures may look like a dinosaur, the *Dimetrodon* lived 50 million years before the first dinosaurs appeared. The function of the spines on its vertebrae is still unknown. Was it for camouflage in long reeds? Did it strengthen the backbone? Did it function as a “sail” to help the *Dimetrodon*navigate in water? Was it for body temperature regulation? Did it signal readiness for mating? We may never know for sure. Smithsonian Books

*Foraminifera*, still abundant in today's oceans, are a group of single-celled organisms that are members of the floating plankton in oceans around the world. After death they create chalky skeletons that fall to the sea floor and create sediments known as oozes. These oozes are slowly laid down one on top of the other so that a physical record builds up over time. By drilling through layers of oozes, paleontologists can observe the *foraminifera* that lived both before and after the mass extinction that occurred 65 million years ago. Smithsonian Books

*Homo heidelbergensis*, found in Africa in 1921, is estimated to be between 200,000 and 300,000 years old. Although undeniably human in general appearance, the skull has a huge face and eyebrow ridges, as well as a low forehead. Scientists estimate that *Homo heidelbergensis* would have had a stature close to that of modern humans, with a skull capacity allowing for a brain only about 14 percent lighter than that of the average modern human. This find has particular importance in human evolution, as many scientists interpret it as the common ancestor of modern humans. Smithsonian Books

This cousin of the armadillo reached the size of a Volkswagen Beetle. Glyptodonts initially survived in abundance, perhaps because of their colossal protective shells. Yet what might have safeguarded them for millions of years may also have ultimately led to their demise: Glyptodonts went extinct around 10,000 years ago, coinciding with the arrival of the earliest humans to the Americas, and there is evidence that these early Americans used their enormous shells as shelters or dwellings. Smithsonian Books

Finding a fully intact dinosaur egg is quite rare, so this complete nest of unhatched *Troodon* eggs is a remarkable find. The embryos inside the eggs are fully preserved to this day, and give us insight into the parenting behaviors of one of the last dinosaurs to evolve. Reptiles don’t spend too much time caring for their offspring, but lay many eggs in the hopes that some will survive. Birds, on the other hand, lay only a few eggs but care for them greatly, ensuring a higher rate of survival. *Troodon*, as we can see from the embryos in this egg nest, fall somewhere in between. Smithsonian Books

It took scientists 150 years to finally complete the fossil of *Basilosaurus*, an early whale. But even then, no one could agree on a name: it was first called *Basilosaurus*, or "king lizard," then later *Hydrarchos*, or "giant sea serpent." Its bones were seen as having been part of a long-extinct flightless giant bird. Today the complete fossil that we know to be the intermediary between older land mammals and modern limbless whales is hanging in the Ocean Hall in the Smithsonian National Museum of Natural History. Smithsonian Books

The move from water onto land by our early, marine-based ancestors must have been driven by the search for new habitats, sources of food, mates and protection from increasingly efficient aquatic predators. Once on land, however, life became equally competitive, and it wasn’t long before heading back into the water became a more favorable option. *Rodhocetus* fossils show that it has a short, thick neck, paddle-like feet to efficiently move through water and a large tail to act as a rudder. Yet it retained small hooves at the end of its toes. Smithsonian Books

*Helicoprion* is a unique marine fossil that perplexed paleontologists for more than a century: was it the remains of a toothed snout, tail or tongue? In fact, *Helicoprion* is a set of teeth from a distant relative of a modern shark. The tooth whorl sat within the lower jaw and grew, tooth by tooth, with the largest, more recent ones exposed at the front. As larger teeth were added, the smaller ones were pushed back inside the jaw, where they coiled up and were kept for life. Smithsonian Books

*Rhamphorhynchus* is a long-tailed pterosaur, the first true flying vertebrate. This particular fossil was the first one discovered with a well-preserved wing membrane. The teeth of the upper and lower jaw show an intermeshing configuration, which is suitable for capturing slippery prey like fish. Pterosaurs appeared over 220 million years ago and survived until the end of the Cretaceous period 65 million years ago. Smithsonian Books

When the history of Earth is read, it won't be in words on paper—it will be the fossil record that most clearly tells the story of life, migration, evolution and death on this planet. At least that's the feeling one gets from A History of Life in 100 Fossils, a new book by paleontologists Paul Taylor and Aaron O'Dea. The authors strive to "highlight milestones in the history of life, from its origin to the emergence of modern humans" through 100 fossils. The fossils, taken from both the Smithsonian's National Museum of Natural History and the Natural History Museum, London, range from a 3,465 million-year-old filament to 200,000 to 300,000 year-old skull—potentially that of our last ancestor.

But Taylor and O'Dea aren't the only ones spreading the incredible story of fossils. For five years, the National Parks Service has organized National Fossil Day, a celebration meant to shed light on the important story that fossils can tell. In conjunction with National Fossil Day, the Smithsonian Museum of National History will host a celebration today, including a recitation of the "Junior Paleontologist Pledge" in the museum's Rotunda by more than 400 elementary school students. Part of Fossil Day's mission is to inspire the next generation of fossil enthusiasts and paleontologists. "The Smithsonian and the National Park Service are critical stewards of our nation's natural history heritage," says the museum's director Kirk Johnson. "For the first time, we have the privilege of hosting National Fossil Day entirely at the Museum of Natural History, and we look forward to sharing our excitement and knowledge about fossils with visitors here in the nation's capital."

A History of Life in 100 Fossils