An artist’s recreation shows (top to bottom) the skeleton, muscles, and living appearance of Deinosuchus.
Credit: © Tyler Stone

Paleontologists (scientists who study prehistoric life) learned more about a terrible crocodile this summer. A study by Adam Cossette of the New York Institute of Technology and Chris Brochu of the University of Iowa examined newly discovered fossil remains of the extinct crocodilian Deinosuchus. Crocodilians are group of reptiles that includes crocodiles, alligators, gavials, and caimans. The scientists published a revised description of the animal in the Journal of Vertebrate Paleontology.

Deinosuchus lived from about 82 million to 75 million years ago, during the late Cretaceous Period. Its closest living relatives are alligators. In most ways, it looked much like a modern alligator, except that it was enormous. Deinosuchus grew to a length of 33 feet (10 meters) or more and weighed about 8,000 pounds (3,600 kilograms). In comparison, the largest crocodilian alive today, the saltwater crocodile, reaches lengths of about 23 feet (7 meters) and weighs 2,200 pounds (1,000 kilograms).

Deinosuchus also lived like modern crocodilians. During the late Cretaceous, much of central North America was covered by a shallow sea. Deinosuchus lived in the vast wetlands on the edges of this sea. Like large crocodilians today, Deinosuchus was an ambush predator. It would swim over to an animal at the water’s edge, lunge out of the water to grab it with its powerful jaws, drag its prey into the water, and drown it. What was on the menu? Just about anything—including dinosaurs.

Numerous fossils of contemporary dinosaurs show bite marks from an animal that could only have been Deinosuchus. It even attacked large, meat-eating theropods (dinosaurs like Tyrannosaurus Rex) on occasion. But for the most part, these predators stayed out of each other’s way, much as lions and Nile crocodiles do in modern Africa.

Deinosuchus was not identical to modern crocodilians, however. it had a greatly thickened skull relative to its size. The thickness likely strengthened it for struggle against dinosaurs and other large prey. Deinosuchus also had a bulbous (rounded) snout, with two small openings at its tip. Paleontologists do not yet know what purpose these features served.

Deinosuchus wasn’t the only giant crocodilian. Sarcosuchus, which lived about 110 million years ago, may have reached 40 feet (12 meters) long, about the length of a bus. Another titan was Purussasaurus, which attained similar proportions during the Miocene Epoch, long after the dinosaurs went extinct.

Discovering a new kind of prehistoric animal is great, but learning more about one that has already been discovered is great, too! Deinosuchus is not a recent discovery. In fact, it was first described in 1909. But many of the fossils were incomplete. With the new material, Cossette and Brochu were able to uncover more about the animal’s lifestyle and better differentiate between the small handful of Deinosuchus species. In doing so, they paint a more complete picture of what the world was like tens of millions of years ago—and what a terrifying place it was!

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)

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)

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)