Excerpt: 'The Link: Uncovering Our Earliest Ancestor'

Colin Tudge's book tells the story of the 47-million-year-old fossil.

ByABC News via logo
May 20, 2009, 2:38 PM

May 20, 2009 — -- Scientists say a 47-million-year-old fossil found in Germany may be a key link to explaining the evolution of early primates and, perhaps, telling them about developments that led to modern human beings.

The fossil, of a young female that probably resembled a modern-day lemur, is described as "the most complete primate fossil ever found." Read about the history of "Ida" herself and the story of her discovery in Colin Tudge's new book, "The Link: Uncovering Our Earliest Ancestor."

Read an excerpt from the book below and then head to the "GMA" Library for some more good reads.

In the glow of a gibbous moon, a petite being moves through the palm trees surrounding a lake that seems almost impossibly pristine. The small creature living in this lush tropical forest has a light coat of fur, and she's less than two feet (half a meter) tall. With forward-facing eyes, her elongated head is slightly overproportioned to her body, suggesting intelligence. Her legs are a bit longer than her arms, allowing her to climb trees and move between them to avoid dangers on the ground below.

This is Ida, less than a year old and just weaned from her mother. She now has the freedom to roam, climb, and fend for herself. Moving as though she's chasing down the wind, she pushes off one branch with her feet, using her tail like a rudder to guide her, and then grasps the next branch with her long fingers. She secures her position with her toes, all of which are of nearly equal length and used for nothing except movement. Her opposable thumbs enable her to gracefully grab and go.

As she searches for her next meal, Ida ignores the varieties of insects, easy targets all, and settles on a piece of fruit. She wraps her hands around the fruit, pulls it from its branch, and pops it into her oblong mouth. Moving her jaw rhythmically, she chews the fruit with her rounded teeth. For a living being, searching for food in any forest would usually be a rather straightforward process — were it not happening 47 million years ago in this particular forest, by this particular lake.

The rain forest where Ida lives would be recognizable to us but not identical to any we have seen. It is a sight to behold, and though its features are relatively common for its time, it's a place that could only have been made by a special confluence of events. It has a warm and equitable climate that stimulates the growth of its plants and trees, making life comfortable for its inhabitants. Palm trees with large root masses shoot into the air, as do cycads, which have a stout trunk at their base and large, tightly wound bundles of leaves at the top. Pygmy horses prance the verdant land. Opossums and armadillos share space with giant mice and salamanders. Birds with woodpecker- like beaks and short wings fill the air, but there are also powerful flightless ground-dwelling birds six feet (almost 2 meters) tall that are feasting on mammals. Large insects protect themselves by imitating tree leaves. Rat-size "longfingers" with tails twice the length of their bodies rip bark from the trees with their two clawlike fingers in hopes of finding insect larvae. Anteaters seethe as they eye giant ants an inch (2.5 centimeters) long, but these ants often make last-second getaways by spanning their wings a full six inches (15 centimeters) and beating a retreat.

In the center of the forest sits the lake, which is an endless source of fascination for the creatures living around it.

The crater it fills was formed by a volcanic eruption thousands of years before Ida was born. Deep underground, the earth's crust split, sending boiling-hot molten magma rushing toward the surface. Just before the magma broke through the surface, it collided with a layer of groundwater and instantly turned into steam, a process that eliminated all the lava. This reaction caused an explosion that blew out a large chunk of earth and left behind a vast crater a mile (1.6 kilometers) wide and more than eight hundred feet (250 meters) deep known as a maar lake.

Over time, the hole filled with a combination of groundwater seeping from below and rainwater trickling down from the heavens, and a lake was created. Though there are a few streams, no rivers flow in and out, so the water in the lake remains relatively still. Because of the lack of currents, the water at the bottom is cut off from the upper layers and unable to draw down oxygen from the atmosphere above. All the fish live near the top, and there are no scavengers prowling the lake floor.

The lake is so rich in algae that from above, it resembles a green eye in the middle of the rain forest. As the surface algae die, they sink to the bottom and turn to slime. Eventually the slime turns to mud. The combination of this heavy mud and an almost total lack of oxygen kills nearly all the bacteria, allowing any creature that perishes and sinks to the bottom to rest virtually undisturbed for eternity.

The lake is the heart of this forest ecosystem, and it sustains a diverse array of life. At the water's edge, enormous crocodiles patrol their territory, and frogs make a tock sound as they search for insects. The land frogs have short hind legs and dig for food, while the water frogs have long, thin legs. In the water, turtles with paddle-like feet push their way across the surface of the slimy water. Shells are attached to sunken rocks lining the sides of the lake. Repelled by the lack of oxygen at the deeper levels of the lake, the bowfin, perch, gar, and eels swim near the surface. Many of the fish eat hard-shelled prey such as snails.

As Ida moves through this vast array of wildlife, dodging bats and staying out of reach of the saw-toothed crocodile's snapping jaws, it's clear that she is different from the others resembling her. She's much lower in the trees than they are, and at first she appears to be playing with the other wildlife. But as she moves, it's apparent that she's tentative with her right wrist and her left arm.