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 27, 2014

To scientists’ surprise, 70-million-year-old dinosaur fossils found some years ago in Alaska actually belonged to a previously unknown miniature cousin of Tyrannosaurus rex. This new species of pygmy dinosaur, Nanuqsaurus hoglundi, had a skull that was only 23 to 27 inches (60 to 70 centimeters) as an adult. The skull of an adult T. rex could be up to 60 inches (150 cm) long. (Note: The words pint-sized and pygmy here are relative. N. hoglundi was about the length of a polar bear, compared to which, students are pint-sized.)

The fossils—fragments of the top of the skull and jaw—were found in 2006 on Alaska’s North Slope, inland from Prudhoe Bay. The discoverers, who were involved in analyzing other fossils, shelved the fragments in a museum. When they recently examined the find, they discovered that the bones represented a new species of tyrannosaur. The tyrannosaurs, which lived during the late rank part of the Cretaceous Period, rank among the most frightening meat-eaters of their time. Tyrannosaurus rex, whose name means king of the tyrant lizards, is the most famous—but not the only—member of the genus.

Tyrannosaurs were fast, active carnivores. They roamed what are now western North America and east-central Asia. (c) Jan Sovak

A study of T. rex‘s mini cousin revealed that the part of N. hoglundi‘s brain devoted to smell was particularly enlarged. This suggests, the scientists said, that the dinosaur stalked its prey mainly by smell. A keen sense of smell would have been important in N. hoglundi‘s challenging environment. Although temperatures in what is now Alaska were much warmer 70 million years ago, the area still experienced long periods of darkness and challenging seasonal changes in the amount of available food. Scientists think the small size of this dinosaur predator was an adaption to its harsh environment. A smaller body is favored by natural selection because of the limited food sources available.

Additional articles in World Book:

• Tyrannosaurs rex: The Tyrant Still Reigns (a Special Report)
• What Has Caused Mass Extinctions? (a Special Report)

July 17, 2013

A fossilized tooth from Tyrannosaurus rex found in the tailbone of a plant-eating dinosaur has provided convincing evidence that the “tyrant lizard king” was, in fact, a fearsome predator–not a scavenger, as some scientists had speculated. Scientists from the University of Kansas discovered the broken tooth and tailbone at a famous fossil site called the Hell Creek Formation in Montana. The scientists concluded that the duckbilled dinosaur had survived its encounter with the T. rex because the area around the tooth had healed. Thus, the plant eater was not a dead animal that the T. rex had scavenged.

A Tyrannosaurus attacks two small plant-eating dinosaurs in an illustration showing the meat eater as a fast, active creature. Tyrannosaurus's skin is tight and scaly, making its body look athletic and limber. (c) Jan Sovak

Tyrannosaurus rex lived during the Cretaceous Period, which lasted from about 145 million to 65 million years ago. The dinosaur has often been portrayed as a deadly predator, but the case for this view was not conclusive. Most scientists believed that T. rex was an active hunter that could run for short distances and may have waited in hiding for its prey to come closer. The dinosaur would then have made a fast dash, attacking the prey with its sharp teeth and strong jaws.

The remains found in the stomach of other T. rex fossils as well as the dinosaur’s fearsome bite and body plan all suggested the beast attacked and ate prey. But some scientists had a different view. They felt that T. rex’s body plan suggested the creature may have been too slow or too clumsy to hunt effectively. Instead, they speculated that the dinosaur may have been a scavenger that feed on dead animals.

Additional World Book articles:

• Prehistoric animal
• Tyrannosaurus rex: The Tyrant Still Reigns (a special report)

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)