March 23, 2016

A recreation of a horse-sized tyrannosaur, Timurlengia euotica, stalks through its natural environment of 90 million years ago. Two other reptiles (Azhdarcho longicollis) fly nearby. The newly-discovered fossilized remains of a Timurlengia euotica reveal how Tyrannosaurus rex and its close relatives became top predators. Credit: © Todd Marshall (Smithsonian)

Rex means king, and, sure enough, Tyrannosaurus rex was the king. As top predator at the end of the age of dinosaurs, T. rex hunted down prey with its heightened senses and tore them apart with its powerful jaws. It wasn’t always like that, however. Tens of millions of years earlier, the smaller ancestors of T. rex cowered from other predators called allosaurs (like the well-known Allosaurus). Little is known about how ancestors of T. rex evolved (changed over time) from small, nimble hunters into the huge predators of the Late Cretaceous (80-66 million years ago). Last week, a team of paleontologists, led by Stephen Brusatte of Scotland’s University of Edinburgh, announced a discovery, Timurlengia euotica, that helps fill in this gap in the Tyrant Lizard King’s family tree. The paleontologists announced their findings in the journal Proceedings of the National Academy of Sciences. 

Tyrannosaurus rex was a large, meat-eating dinosaur that lived about 68 to 65 million years ago in what is now western North America. It was one of the largest meat-eating dinosaurs, measuring about 40 feet (12 meters) long and about 12 feet (3.7 meters) high at the hip, and weighing about 7 short tons (6.3 metric tons). Similar animals roamed Asia and Europe. These monsters were the last of a group of meat-eating dinosaurs called tyrannosaurs, which came into existence some 150 million years ago.

Unlike the giant T. rex, most early tyrannosaurs were modestly sized hunters. They probably had hairlike feathers for warmth, camouflage, and display. Timurlengia reveals tyrannosaurs’ humble origins, but it also hints at their future dominance. It was a horse-sized tyrannosaur that lived in what is now Uzbekistan some 90 million years ago. The dinosaur is named for Timur (sometimes called Tamerlane, as in a poem by Edgar Allan Poe), a conqueror who ruled that region with an iron fist from the late 1300’s through the early 1400’s. Its specific name, euotica, references its keen sense of hearing. While Brusatte’s team only found a little over a dozen fragments of Timurlengia’s skeleton, some of these pieces contained a large inner ear, similar to later giant tyrannosaurs like T. rex. The fragments revealed that the dinosaur had a relatively large brain, also like its later cousins. Apparently, tyrannosaurs had all the smarts and sensory equipment to become top predators 90 million years ago, but they still lived in the shadow of the more primitive allosaurs.

At some point 80 to 90 million years ago, the allosaurs were replaced as apex predators by the tyrannosaurs, which eventually reached the giant proportions of T. rex. Although Stephen Brusatte and the team’s findings reveal that tyrannosaurs were already smart hunters with keen senses, it still isn’t known why exactly this change in dominant dinosaur occurred. Tyrannosaurs could have slowly replaced allosaurs because of their superior intelligence and senses. Or, an environmental disaster could have caused the allosaurs to go extinct, making room for the tyrannosaurs to thrive. More finds like Timurlengia will help scientists determine how tyrannosaurs emerged from the shadows to become the kings of the dinosaurs.

March 9, 2016

Next month, in April, a deep-ocean drilling project will begin off the Yucatán coast in the Gulf of Mexico. Most such oceanic drill projects are concerned with oil exploration. This isn’t your usual drill team, however. The drillers in this case come from the International Ocean Discovery Program, the National University of Mexico, and the University of Texas. And they will be drilling into Chicxulub Crater, an impact crater formed by a giant asteroid that helped kill the dinosaurs some 65 million years ago. They won’t be looking for oil; they’ll be looking for answers.

The Chicxulub Crater along the northern coast of Mexico’s Yucatán Peninsula formed when an asteroid hit the earth about 65 million years ago. Debris from the impact may have led to the extinction of the dinosaurs.
Credit: WORLD BOOK map

At the end of the Cretaceous Period, dinosaurs were the dominant land animals on the planet. Other reptiles filled the seas, and birds—descendants of dinosaurs—roamed the skies. Mammals existed, but they were far smaller and less common than today. Then, an asteroid at least 6 miles (10 kilometers) wide slammed into the Yucatán Peninsula, in present-day Mexico. The impact threw up large amounts of gas and dust into the atmosphere. This material would have blotted out the sun for many years. Plants that use sunlight to make their food would have died out, followed by the animals that ate them. With no more prey animals, large carnivores starved as well.

When the dust settled, about half of all species on Earth had gone extinct. All the dinosaurs—except birds—were dead. Only a few kinds of other reptiles survived. Mammals survived too and over time evolved to become the dominant large-bodied animals on land and in the sea.

The Yucatán asteroid formed a large impact crater, which is now partly on the peninsula and partly in the Gulf of Mexico. Tens of millions of years of plate tectonics and erosion have taken their toll on the crater, and it is barely visible in satellite images today. But the mark that it left in the rocks should still be clear.

The team plans to use a drilling ship to sample rock deep beneath the ocean floor. In drilling into the crater, scientists hope the presence (or lack) of microfossils (tiny preserved remains of ancient organisms) will teach them more about the nature of the asteroid impact and how quickly life returned to the area afterwards.

The drilling evidence may also better explain how responsible the impact was for the mass extinction at the end of the Cretaceous Period. Most scientists agree that the asteroid did most of the damage, but others argue that other causes, such as massive volcanic activity in present-day India, were more to blame. Such extinction hypotheses are not mutually exclusive, however: it may have taken more than one disaster to knock out the dinosaurs. In fact, they may even be linked. Recent studies have suggested that the Yucatán impact caused the spike in volcanism on the other side of the globe in India. Whatever the case, the drilling team will help get to the bottom of this and other stories, as well as to the bottom of the impact crater itself!

June 10, 2015

Fossilized jaws and teeth discovered in northern Ethiopia belong to a previously unknown ancient human ancestor that lived 3.3 million years ago, according to scientists who announced the discovery in late May 2015 in the journal Nature. The new species, named Australopithecus deyiremeda by the scientists who described the fossil remains, lived at the same time and in the same region as another early human ancestor.

Yohannes Haile-Selassie, a paleoanthropologist at the Cleveland Museum of Natural History, holds casts of the jaws of Australopithecus deyiremeda, a new human ancestor species from Ethiopia. (Credit: Laura Dempsey, Cleveland Museum of Natural History)

The Ethiopian anthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History in Ohio described the fossils, which were found at a site in the Afar region of northeastern Ethiopia. The scientists concluded that the fossils are from an early hominin. Hominins, also called hominids, are the scientific family that includes human beings and early humanlike ancestors. The site is about the same age and only a few miles from Hadar, where fossils of Australopithecus afarensis were first discovered by the anthropologist Donald C. Johanson in 1974.  A. afarensis was an early humanlike creature known in part from a famous fossil skeleton nicknamed “Lucy.” The two species are similar in their anatomy, but they can be distinguished by different shaped jaws. Haile-Selassie believes the fossil jaws and teeth belong to the same species as several fossil foot bones that were discovered at a nearby site in Ethiopia and described in 2012.

The scientists believe the fossils demonstrate that Lucy and her kind were only one of perhaps several hominin 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 it moved around. However, scientists are not certain if any of these species are direct ancestors to modern humans.

Paleoanthropologists speculate that the distinct jaw shapes of A. deyiremeda and A. afarensis could mean that they used their teeth on different kinds of food. This means that the two species could have lived side-by-side, because they would not have directly competed for food, shelter, and territory. However, not all scientists agree that these new fossils represent a new species of hominin. Some scientists think that the fossils simply demonstrate that physical variation was great among A. afarenis.

Other World Book articles:

• Anthropology (1973-a Back in time article)
• Anthropology (1983-a Back in time article)
• Anthropology (2012-a Back in time article)

June 1, 2015

Genetic clues from a 35,000-year-old fossil provide evidence that the dog became our best friend thousands of years earlier than most archaeologists had previously thought. Until recently, scientists believed that dogs—as we know them today—and people had lived with each other for at least 14,000 years. That date made the dog the oldest known domesticated animal. However, this latest research pushes that date back even further. The findings suggest that dogs may have been first domesticated as long as 40,000 years ago.

Scientists know that modern domestic dogs are descended from wolves. Earlier genetic studies of wolves and ancient and modern dogs placed the dog’s domestication in Europe, China, or the Middle East. The oldest archaeological sites where human and dog remains occur together are dated from 11,000 to 12,000 years old. However, archaeologists now suspect that dogs may have been domesticated much earlier.

Geneticist Pontus Skoglund of the Harvard Medical School in Boston, Massachusetts, analyzed DNA obtained from the fossilized rib of a Siberian wolf discovered in 2010. The fossil was part of a collection recovered by a joint Swedish and Russian team on the Taymyr Peninsula in Russian Siberia in 2010. The frozen permafrost of this region preserves the remains of long-extinct prehistoric animals in such good condition that scientists can extract DNA from the fossilized bones.

Skoglund’s team compared the DNA they obtained from the 35,000-year-old rib bone of an ancient wolf, labeled Taimyr 1, to DNA sequences from ancient and living wolves and dogs. They found that the Taimyr 1 wolf belonged to a lineage that diverged from the ancestors of dogs and existing wolves at roughly the same time that dog and wolf lineages split from each other. From this, they used various techniques to calculate when the earliest dogs split from the ancestors of modern wolves. The results suggests that the two groups split some time between about 40,000 and 27,000 years ago.

Some dogs, including huskies, preserve DNA from a line of wolves that lived 35,000 years ago in the area that is now Siberia. (copyright melis/ShutterStock)

Some dogs today, including Siberian huskies and Greenland sled dogs, still preserve some DNA inherited from the wolf lineage that included Taimyr 1. The researchers involved believe that the first domestic dogs might have been hunting companions for people who settled Europe and Asia during the last Ice Age.

Other World Book articles:

• DNA

• Genetics

• Prehistoric people

March 25, 2015

A 3-D representation of Metoposaurus algarvensis, a monster salamander from the Triassic. (Credit: Marc Boulay, Cossima Productions)

Paleontologists have discovered a collection of fossilized, car-sized giant salamanders that once terrorized early dinosaurs in a prehistoric lake bed in southern Portugal. Scientists from the University of Edinburgh published a description this week of the fossils of Metoposaurus algarvensis, a 6-foot (2-meter) amphibian distantly related to the modern frogs, salamanders, and newts that occupy many gardens and ponds. One scientist claimed “Most modern amphibians are pretty tiny and harmless. But back in the Triassic these giant predators would have made lakes and rivers pretty scary places to be.”

Metoposaurus algarvensis was part of a wider group of primitive amphibians that were widespread in what is now Europe and North America between 220 million and 230 million years ago. With massive jaws full of sharp teeth, Metoposaurus algarvensis likely squatted at the very top of the food chain. The fossils were discovered in a huge collection in an ancient dry lakebed. Like all amphibians, they mostly lived in water and had to lay their eggs there. The creatures might have died after they were trapped when the lake they inhabited dried up.

Modern amphibians, including the earliest frogs and salamanders, first appeared in the early part of the Mesozoic Era, about 250 million years ago. Many of the larger early amphibians had died out by the end of the Triassic Period, some 200 million years ago, as dinosaurs came to rule the land. But a few, like Metoposaurus algarvensis, persisted well into later times.

Like some other early giant amphibians, Metoposaurus algarvensis lived much as crocodiles do today, feeding mostly on fish and occasionally snatching larger animals from the shores. Their prey likely included some of the earliest dinosaurs that also appeared by about 220 million years ago.

Other World Book articles:

• Amphibian

• Paleontology

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