May 30, 2013

A newly described 160 million-year-old fossil from China is now the leading contender for the title of the world’s earliest bird. The fossil, given the scientific name Aurornis xui (meaning dawn bird), was described in the online edition of the journal Nature by a team led by paleontologist Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels, Belgium. The scientists claim not only that Aurornis is the world’s oldest bird, but also that their discovery ends the debate about whether another famous fossil, the feathered Archaeopteryx, shared a perch on the bird family tree.

The remains of feathers and birdlike wings are clearly visible in the fossil of Archaeopteryx. This animal had a crow-sized body and lived about 150 million years ago, near the end of the Jurassic Period. (© Sally A. Morgan, Ecoscene/Corbis)

The nearly complete Aurornis fossil, encased in sedimentary (layered) rock, was unearthed by a farmer in the Liaoning Province of northeastern China some time ago. A local fossil dealer sold the specimen to the nearby Yizhou Fossil and Geology Park museum, where it was stored. In 2012, Godefroit and his team examine the specimen. They were able to confirm that the fossil came from the Tiaojishan Formation, a region famous for having produced many fossils of feathered dinosaurs and early birds. They dated the sedimentary rock that encased the fossil to about 160 million years ago. Clear impressions of downy feathers along the tail, arms, legs, neck, and chest of Aurornis suggested the creature was capable of gliding but lacked larger feathers necessary for true flight.

During the Jurassic Period, from about 200 million to 145 million years ago, some meat-eating dinosaurs began evolving birdlike skeletons and sprouting feathers on their bodies. One group of these creatures eventually split off to become birds, although researchers have long debated which one it was and when it actually happened.

Godefroit and his team compared almost 1,000 anatomical features of Aurornis with those of about 100 other dinosaurs and birds. These comparisons allowed them to construct a computer-generated cladogram, a kind of family tree illustrating how the species are related to one another. The resulting cladogram placed Aurornis at the very base of the family tree of modern birds. Combined with the early date for this fossil, the analysis makes Aurornis the oldest known bird by a margin of about 10 million years.

Scientists have long regarded Archaeopteryx, a feathered animal that lived about 150 million years ago near the end of the Jurassic Period, as the oldest example of a bird in the fossil record. First discovered in the Solnhofen limestone beds in Bavaria, Germany, in 1861, this crow-sized creature had a skeleton closely resembling that of a small dinosaur. However, it also had fully developed feathers and birdlike wings. As a result, Archaeopteryx has traditionally been classified as a bird. However, some paleontologists disagree with that conclusion. They argue that Archaeopteryx and similar fossils belonged to a side branch of feathered dinosaurs that separated from the main line leading to birds. However, this new analysis of Aurornis places Archaeopteryx firmly back on the bird line.

Additional World Book articles:

• Prehistoric animal
• Paleontology 2011 (a Back in Time article)

June 21, 2012

A federal judge ordered authorities from the United States Department of Homeland Security to immediately take custody of a fossil dinosaur skeleton held in a New York City storage facility. The fossil, a nearly complete skeleton of Tarbosaurus bataar, is to be returned to its rightful owner, the government of Mongolia. Tarbosaurus bataar was a slightly smaller Asian relative of the giant North American meat-eating dinosaur Tyrannosaurus rex. The skeleton was sold to an unidentified private party on May 20 by Heritage Auctions, a Dallas-based firm, for $1.05 million. However, the federal judge ruled that because the fossil had entered the United States illegally, it could be seized and repatriated (restored to the country or people of origin).

The fossil is about 24 feet (7.3 meters) long and 8 feet (2.4 meters) tall. It is one of the most complete fossils of a tyrannosaur known. Even most of the daggerlike teeth and claws are intact, which is highly unusual.

Early in 2012, paleontologist Mark Norell of the American Museum of Natural History in New York City noticed the listing of a nearly complete fossil tyrannosaur for sale in an auction catalogue and became suspicious about its origin. Such fossils are extremely rare and could only have come from a few locations. He alerted federal officials in Manhattan who asked Norell and four other paleontologists to examine the fossil in question. The experts agreed that the fossil skeleton was Tarbosaurus bataar, a dinosaur that lived 70 million years ago. They believe the specimen was originally discovered in 1946 during a joint Soviet-Mongolian expedition to the Nemegt Basin of the Gobi Desert. Although that fossil was described, it was not collected at that time. Norell and others believe it must have been excavated by illegal fossil hunters some time between 1995 and 2005 and smuggled out of the country. Mongolian law declares all dinosaur fossils to be government property and, therefore, unavailable for export or sale.

Tyrannosaurus rex was a slightly larger North American relative of the Asian meat-eating dinosaur Tarbosaurus bataar. (Museum of Science in Boston)

Executives at Heritage Auctions claimed that they purchased the fossil in good faith and without the knowledge that it had been obtained illegally. However, U.S. officials cited false claims on customs documents made by Heritage Auctions when the fossil was imported into the United States from the United Kingdom in 2010. The documents described the fossil as a collection of broken and assorted unidentified fossil bones worth only $15,000. The false claim makes any sale of the fossil illegal under U.S. law.

U.S. Attorney Preet Bharara emphasized the importance of returning the fossil when he stated, “The skeletal remains of this dinosaur are of tremendous cultural and historic significance to the people of Mongolia, and provide a connection to the country’s prehistoric past. When the skeleton was allegedly looted, a piece of the country’s natural history was stolen with it, and we look forward to returning it to its rightful place.”

Additional World Book articles:

• Cretaceous Period
• Could Dinosaur’s Live in a Zoo (a special report)
• Tyrannosaurus rex: The Tyrant Still Reigns (a special report)

May 15, 2012

Scientists studying the fossil of a monstrous ocean-dwelling reptile that lived about 150 million years ago found evidence that the fearsome carnivore was even tougher than they had imagined. The reptile, a female pliosaur, had apparently survived into old age even though its massive jaw had been seriously weakened by a condition similar to arthritis. Until this finding by researchers at the University of Bristol in the United Kingdom, scientists had not known that pliosaurs could develop a degenerative disease that is often linked to the aging process.

Pliosaurs were a type of plesiosaur, a now-extinct marine reptile that lived in the Mesozoic Era, from about 200 million to 65 million years ago. Pliosaurs, which were not dinosaurs, had large crocodile-like heads, short necks, and stiff whale-like bodies. The Bristol pliosaur was 26 feet (8 meters) long, with a 10-foot- (3-meter-) long head containing 8-inch- (20-centimeter-) long teeth. Paleontologist Michael Benton noted that a person could have lain down in the reptile’s huge mouth. Equipped with two pairs of flippers, pliosaurs were fast, powerful swimmers. Pliosaurs, which probably fed on large fish and other ocean reptiles, were the top predators (highest predators on the food chain) in the ocean for millions of years. Plesiosaurs evolved (developed gradually) from reptile ancestors that lived on land. Like modern whales, plesiosaurs had to surface to breathe air, and they likely gave birth to live young.

Pliosaurs were a kind of plesiosaur (above), a large ocean reptile that lived from about 200 million to 65 million years ago, during the time of the dinosaurs. Like plesiosaurs, pliosaurs had a round, stiff trunk and a tail. They had two pairs of flippers instead of arms and legs. (World Book illustration by Jay Bensen, Studio 3 Creative Associates)

The arthritis-like disease, which was likely painful, had caused the pliosaur’s left jaw to shift to one side. Tooth marks from the upper jaw in the bone of the lower jaw indicated that the pliosaur had survived for a numer of years even with a crooked jaw. The scientists also found that a tooth from the lower jaw had apparently caused an infection in a tooth socket of the upper jaw. At some point, the jaw had become so weak that it broke and the animal was unable to hunt. The pliosaur’s large size and fused skull bones suggested that it was old when it died.

Additional World Book articles:

• Prehistoric animal
• Reptile (The evolution of reptiles)

March 30, 2012

Fossilized foot bones discovered in Ethiopia show that an unknown early human relative from East Africa had apelike feet more suited for life in the trees than for walking. Anthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History in Ohio described 3.4 million-year-old fossils in the March 28, 2012, issue of the journal Nature. The scientists concluded that the fossils are from an early hominid. (Also called hominins, hominids are the scientific family that includes human beings and early humanlike ancestors.) However, the fossils are from a foot with long digits and an opposable big toe much like those in modern apes. (An opposable digit can be placed opposite another digit, such as the human thumb to the fingers.) These feature are useful for grasping tree limbs, but they make walking upright on the ground difficult. The fossils also indicate the creature’s foot lacked a distinctive arch, a necessary feature for efficient upright walking.

These new fossils were discovered at a site called Burtele in the Afar region of northeastern Ethiopia. The site is about the same age and only a few miles from Hadar, where fossils of Australopithecus afarensis were first discovered by anthropologist Donald C. Johanson in 1974.  A. afarensis was an early humanlike creature known in part from a fossil skeleton nicknamed “Lucy.” The anatomy of Lucy and other A. afarensis fossils reveals that the creatures were small but walked upright on the ground like modern humans. Lucy’s foot anatomy shows a distinct arch and her big toe was aligned with the other four digits of the foot, the way it is in modern humans. These anatomical features allow for efficient walking on two legs on the ground. Preserved footprints at Laetoli, a site in northern Tanzania that also preserves fossil remains of A. afarensis prove that these creatures walked much the same way as modern humans do as long as 3.7 million years ago.

The skeleton of "Lucy," a prehuman ancestor that lived about 3.2 million years ago, has revealed that this australopithecine walked in much the same way as modern humans do. Lucy lived at about the same time as a newly discovered prehuman species that lived mostly in the trees. (Institute of Human Origins)

Scientists cannot assign a species name to the Burtele fossil without finding additional parts of the skeleton, such as the skull or teeth. But the fossils demonstrate that Lucy and her kind were only one of perhaps several hominid species that inhabited the forests and grasslands of East Africa more than 3 million years ago. Each species was adapted to a different habitat and likely had different anatomy and behavior, including how they moved around. As Lucy and her kind strolled along the plains, their distant cousins may have watched them pass from a perch in the trees.

Additional World Book articles:

• Evolution
• Prehistoric people
• Rethinking the Human Family Tree (a special report of historic interest)
• Anthropology 1974 (Back in Time article)
• Anthropology 1983 (Back in Time article)

Dec. 27, 2011

The discovery of the first sauropod fossil ever found in Antarctica has been announced by a team of scientists from Argentina. Sauropods, a common kind of planet-eating dinosaur, hold the record as the largest land animals to inhabit Earth. The fossil, which has been dated to about 70 million years old, is only a single vertebra–too small for scientists to determine the exact species. (Vertebrae are the bones that make up the spine.) But the scientists determined that the bone belonged to a sauropod. Scientists have found only a few dinosaur fossils in Antarctica because of the continent’s harsh conditions making searching difficult, though they believe many kinds of dinosaurs lived there.

Some sauropods may have grown as long as 130 feet (40 meters) and weighed as much as 85 tons (77 metric tons). They are among the most familiar dinosaurs, with long necks and tails. There were many kinds of sauropods, including such well-known species as Brachiosaurus and Apatosaurus. Sauropods fossils had previously been discovered on all other continents.

Supersaurus was one of the largest dinosaurs that ever lived. It measured from 100 to 130 feet (30 to 40 meters) long, stood about 27 feet (8.2 meters) tall at the hips, and may have weighed more than 40 tons (36 metric tons). The animal's slender neck may have stretched as long as 40 feet (12 meters). Its huge, whiplike tail probably extended about 50 feet (15 meters). World Book illustration by John Francis, Bernard Thornton Artists

The newly discovered dinosaur lived during the Cretaceous Period, which lasted from about 145 million to 65 million years ago. During this time, Antarctica was not covered by a thick ice sheet, as it is now. Earth’s climate was much warmer in the Cretaceous Period than it is today. As a result, Antarctica was able to support plant life, which provided food for large dinosaurs. Also, Antarctica was still connected to what are now Australia and South America in a supercontinent called Pangaea. The fossil was discovered on Ross Island, in West Antarctica.

Additional World Book articles:

• Diplodocus
• Plants (Early plants)
• Prehistoric animal
• Seismosaurus
• Supersaurus

October 26, 2011

A spear point embedded in a fossilized mastodon rib discovered near Seattle is the latest archaeological finding to challenge a long-held theory that humans did not arrive in the Americas until about 13,000 years ago. Mastodons were elephant-like animals that lived across North America until they became extinct about 10,000 years ago.

Mastodons, like the two shown in this illustration, had huge tusks and wrinkled gray skin. World Book illustration by Bernard Robinson

Precise radiocarbon tests revealed that the rib dates to about 13,800 years ago. This date is several hundred years earlier than the first appearance of the Clovis culture in North America. (The Clovis culture is named for a site near Clovis, New Mexico, where remains of the culture were first recognized. The culture is identified by distinctive stone spearheads that are often found with the remains of extinct prehistoric animals.) For decades, scientists believed that the Clovis culture people were the first humans to arrive in the Western Hemisphere. The study of the mastodon rib, published in the Oct. 21, 2011, issue of the journal Science, strongly suggests that this long-held “Clovis-first” theory is wrong.

The fossil rib was discovered with other parts of the mastodon skeleton by a farmer in the late 1970′s at Sequim, Washington. Archaeologists found some signs that the mastodon had been butchered. But they did not find any stone tools that could have been used by human hunters to butcher their kill. The bones were kept in storage for nearly 30 years. Recently, scientists at the Center for the Study of the First Americans at Texas A&M University took another look at the bones.

Computed tomography (CT) scans of the rib revealed an embedded spear point, showing that the animal had been killed by human hunters. The scans also showed that the broken tip of the spear point, which was made of bone, had been carefully sharpened to a needle-like point. The scientists believe the original point was about 10 inches (25 centimeters) in length. The age and location of this prehistoric kill site suggests that human beings migrated to the Americas long before the development of the Clovis culture. Most archaeologists believe that the first humans arrived in North America after crossing a shelf of land across the Bering Sea during low sea levels toward the end of the last Ice Age. These prehistoric people followed and hunted mastodons and such other large animals as camels, horses, giant bison, and mammoths that lived in the region.

Additional World Book articles:

• Indians, American
• The First Americans (a special report)

Fossil skeletons of two primates who lived 1.97 million years ago may represent the oldest known direct ancestor of modern human beings, according to a report by scientists from South Africa. The fossils have been given the scientific name Australopithecus sediba.  They were discovered between 2008 and 2010 at Malapa, a cave site in South Africa, by paleoanthropologist Lee Berger from the University of the Witwatersrand in Johannesburg. Australopithecines were a group of early humanlike creatures that lived in Africa from about 4 million to about 1 million years ago.

The fossils include bones from two individuals-an adult female and a juvenile male. They were found close together, suggesting that they may have died together, perhaps by falling into an underground cavern. The fossils include nearly complete skulls, portions of the hipbones, and a rare collection of bones from the hands and feet.  The skulls show A. sediba had a small brain, about the same size as that of a chimpanzee. But a detailed study of the inside of the skull shows that the front of the brain was much more humanlike than apelike.

The hipbones are short and wide, more like those of a modern human. Anklebones and a nearly complete right hand from the adult female are nearly identical to those of a modern person, only smaller. These features show that A. sediba could walk like a modern human and could have made  and used stone tools.

Berger and his colleagues argue that A. sediba was more like a modern person than Homo habilis, another species of early human that originated in Africa around 2 million years ago. They claim that A. sediba represents a direct link between the apelike australopithecines and Homo erectus, a species that appears a bit later. Most scientists think Homo erectus was a direct ancestor to Homo sapiens, the species that includes all people living today.

Additional World Book articles:

• Prehistoric people
• Stone Age
• Homo florensiensis

The fossils of single-celled organisms found in Australia may be the oldest evidence of life on Earth. The fossils are 3.4 billion years old, only about 1 billion years younger than Earth itself, according to a report by a team of scientists from Australia and the United Kingdom. The team was headed by David Wacey of the University of Western Australia and Martin Brasier of the University of Oxford.

Scientists search for fossils. © Ken Abbott, University of Colorado at Boulder

Wacey and Brasier reported finding the microfossils in rock formed from sand that once covered an ancient beach in what is now Western Australia. The beach lay at the edge of what may have been one of the first sections of solid land to form.  At that time, most of Earth was covered by water.

Previously, what were believed to be the oldest known fossils, also found in Western Australia, were dated to 3.465 billion years ago. But a number of scientists have expressed doubts that these structures are fossils from that early in Earth’s history. Similarly, some scientists argued for more research to confirm that the structures presented by Wacey and Brasier actually represent ancient organisms and were not created by nonbiological processes.