June 12, 2019

A recent reexamination of an important fossil discovery shows that Denisovans, a mysterious group of prehistoric people in Asia, lived in the high-altitude environment of the Tibetan Plateau long before the ancestors of modern Tibetans and Nepalese arrived. The fossil, a Denisovan mandible (lower jawbone) fragment, proves that these ancient humans were the first hominids to settle in that harsh environment where altitude sickness is a constant danger. The scientists studying the fossil also believe that modern people living on the Tibetan Plateau owe their survival to these Denisovan ancestors.

This virtual reconstruction shows details of the Denisovan mandible found on the Tibetan Plateau in 1980. It is some 160,000 years old. Credit: © Jean-Jacques Hublin, MPI-EVA, Leipzig

Chinese scientists recently reexamined the mandible fossil, which was excavated in Tibet in 1980. The jawbone fragment containing a few teeth was unremarkable. However, the scientists were hoping to determine the age of the fossil and extract proteins and genetic material using techniques that were not yet invented in the early 1980′s. The scientists were surprised when dating methods showed the fossil was about 160,000 years old. Scientists had previously believed that the early human populations alive at the time could not survive the harsh environment of the Tibetan Plateau.

The Denisovan mandible was found in this Tibetan Plateau cave, a tourist site and Buddhist refuge, in 1980. Credit: © Dongju Zhang, Lanzhou University

Analysis of proteins extracted from the jawbone fossil showed that it belonged to the mysterious Denisovans, a population previously known only from a few skeletal remains found in the Altai Mountains of southern Siberia. Denisovan DNA has similarities to that of the modern indigenous (native) peoples of Australia, New Guinea, the southern Philippines, and other Pacific Islands. Denisovans contributed up to five percent of the genetic material of some people living in these regions today.

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Analysis of the Tibet jawbone shows that the Denisovans were well-suited to a high-altitude environment. They possessed a genetic adaptation that enabled them to withstand the physical effects of hypoxia (insufficient levels of oxygen in the blood) caused by high altitudes. Today, the indigenous people of Nepal and Tibet also possess this genetic adaptation. Scientists now believe that the modern inhabitants of the Tibetan Plateau inherited this adaptation from Denisovan ancestors of the distant past.

December 27, 2016

Lida Xing, a paleontologist (scientist who studies fossils) from the China University of Geosciences in Beijing, made a spectacular find just by going to the market. There, he found part of a tiny dinosaur—complete with feathers—perfectly preserved in amber.

A lump of amber has preserved this feathered dinosaur tail (along with ants, a beetle, and bits of foliage) for 99 million years. Credit: © Ryan C. McKellar, Royal Saskatchewan Museum

Amber is a hard, yellowish-brown fossilized resin. It comes chiefly from the resins of pine trees that grew millions of years ago. These resins were gummy materials mixed with oils in the trees. When the oils oxidized (combined with oxygen), hard resins were left. These pine trees were then buried underground or underwater, and the resins slowly changed into lumps of amber. These lumps often contain insects trapped as the resins flowed from the trees. But finding larger animals such as small vertebrates (animals with backbones) is incredibly rare.

Xing found the remarkable fossil at an amber market in the Southeast Asian nation of Myanmar (also called Burma). The seller thought the bushy object in the amber was part of a plant and had polished the piece to be made into jewelry. But it was in fact part of the feathery tail of a small dinosaur. Xing promptly brought the specimen to fellow paleontologist Ryan McKellar of the Royal Saskatchewan Museum in Regina, Canada, where they studied it with other scientists using computed tomography (CT). Computed tomography involves taking many X-ray images of an object from a number of directions. A computer combines the set of X-ray “slices” of the object to create a three-dimensional image called a volumetric model. The scientists recently wrote about what they found in the journal Current Biology.

Paleontologists have discovered feathered dinosaur fossils in the past, but the heavy weight of the sediments and rocks deposited above them had flattened the carcasses during the fossilization process. Because this tail was trapped in amber, however, it was preserved in three dimensions, allowing scientists to see the exact layout of the feathers. Even traces of the pigments that colored the feathers have been preserved, showing that the animal would have been light brown with a whitish underside.

The tail likely belonged to a juvenile (young) bipedal dinosaur related to Tyrannosaurus rex. Despite the specimen’s prominent plumage, paleontologists know that the tail belonged to a nonbird dinosaur (all birds are technically dinosaurs). The fossil dates back 99 million years, some 50 million years after the appearance of early birds such as Archaeopteryx. A tail from Archaeopteryx would have been short and stiff. The tail from this new fossil, however, is long and flexible. It is bent a great deal in the amber, and scientists estimate that only a third of the tail was preserved. Furthermore, the beautifully preserved feathers trapped in amber would have been useless for flight. The feathers possess simple barbs and barbules that would hold strands of the feathers together, but they have much thinner central shafts than modern flight-worthy feathers. These ancient feathers would have been soft and downy, and they probably kept the young animal warm.

The loss of the dinosaur’s tail in amber probably cost it its life. Dinosaurs could not detach their tails the way some lizards can. A dinosaur could likely survive without the tip of its tail, but this fossil is from the mid-section of a dinosaur’s tail. Once the hapless youngster got stuck in resin, it probably either starved to death or became an easy snack for a predator—except for the part stuck in resin, of course.

Lida Xing has a knack for making spectacular finds of amber-entrapped animals. Earlier this year, he announced the discovery of a pair of 100-million-year-old bird wings. His remarkable discoveries are shining a new light on the evolution of feathers in birds and dinosaurs.

September 16, 2015

Illustration of the fossils, sediments, and flowstones within the Dinaledi Chamber of the Rising Star cave system.
Credit: Paul H. G. M. Dirks et al (licensed under )

Last week, scientists from the University of the Witwatersrand in South Africa reported on a new find. Lee Berger, an American paleoanthropologist (expert on human evolution), and his colleagues unveiled a huge collection of fossils from the Rising Star cave site, about 30 miles (50 kilometers) northwest of Johannesburg. The fossils represent a previously unknown prehistoric human species. The scientists have named this new species Homo naledi. The Latin word Homo means human being, while naledi means star in the Sotho language of South Africa.

The Rising Star fossil site was first discovered in 2013 when spelunkers (people who explore and map caves) noticed an unusual number of fossilized bones in a huge cave complex they were exploring. The spelunkers alerted Berger, who hired a number of them to help recover the fossils from the narrow tunnels of the large underground caverns. Berger hired spelunkers of small stature to recover the fossils because the scientists could not fit through the narrow passage into the cave—only 7.1 inches (18 centimeters) wide. Over the following months, the team collected 1,550 fossils, representing partial remains of at least 15 individuals—the single largest collection of hominins ever found at a site in Africa. (In scientific classification, hominins are the group that includes human beings and early humanlike ancestors.)

Berger and his colleagues classified the fossils as a new hominin species based on the unusual anatomy of the fossils, which show an odd mix of primitive and modern features. The skull of Homo naledi is rounded like a human skull, yet small, with a brain only about one-third the size of a modern human brain. The front teeth are small, like humans, but the molars (back chewing teeth) are quite large. They had a small, thin body, and the bones of the shoulder and hands suggest they were adept at climbing trees. Yet the legs and feet show they were able to walk upright and possibly to make and use stone tools, as could the earliest humans.

The scientists have not been able to determine the precise age of the fossils, so it is difficult to determine exactly where Homo naledi fits on the human family tree. Most paleoanthropologists think that the first people evolved from an Australopithecus ancestor. Homo naledi may be a very close relative to such an ancestor. The scientists are also puzzled by the Rising Star site itself, which preserves almost no fossils of other kinds of animals. This may indicate the hominins at the site became trapped in an unusual event, such as a flood, and died together. However, Berger suggests that Homo naledi may have intentionally buried their dead at the site, a uniquely human behavior. Such behavior is virtually unknown among other species of early human ancestors.

Other World Book article

• Funeral customs

February 4, 2015

A 3-million-year old relative of guinea pigs was as large as a buffalo, had a bite as strong as a tiger, and used its tusklike front teeth as an elephant would, according to a new analysis of fossils published this week by an international team of scientists in the Journal of Anatomy. Scientists from the University of York used computer modeling to reconstruct the skull of Josephoartigasia monesi, a gigantic fossil rodent. In 2007, this fossil was discovered in Uruguay by paleontologists (scientists who study animals, plants, and other living things from prehistoric times [more than 5,500 years ago]). Josephoartigasia is the largest rodent species ever discovered.

An artist’s impression of a giant, prehistoric rodent as big as a buffalo found as a fossil in Uruguay. (Credit: James Gurney/University of York)

Josephoartigasia roamed the grasslands of what is now South America during the Pliocene Epoch (about 5.3 million to 2.6 million years ago), a warm period that occurred before the Ice Age. Huge mammals, such as mammoths and giant sloths, were abundant in North and South America during this period. The Isthmus of Panama also formed around this time as North and South America collided. The isthmus (narrow strip of land connecting larger bodies of land) enabled land animals to pass between North and South America. Josephoartigasia likely became extinct soon after this event, about 2 million years ago.

In addition to its massive size—far larger than any rodent ever seen, living or in the fossil record—Josephoartigasia had large, tusklike incisor teeth at the front of its jaw. The scientists analyzed the skull of Josephoartigasia using a computer-simulation technique that calculates the force and strain acting on a complex geometric object, such as an animal’s jaw. They found that Josephoartigasia had incredibly strong incisor (front) teeth compared with other large rodents and a bite as strong as a modern tiger. Scientists think that Josephoartigasia probably used its giant teeth in the same way an elephant uses its tusks—to dig for food and defend itself from predators.

Other World Book articles:

• Fossil (Research guide)
• Prehistoric animal