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)

Nov. 4, 2011

Weakened muscles and certain other signs of aging could be reversed or even prevented if a technique used in mice can be applied to humans, says a team of researchers at the Mayo Clinic in Rochester, Minnesota. The technique involves targeting worn-out cells, called senescent cells, for destruction. Senescence is the process of growing old.

Scientists have long known that all cells in the body divide during growth and development. But cells can divide only a limited number of times. Aging cells often die. Only about 5 to 15 percent of the cells in the body of a typical elderly adult become senescent. But these few cells have a dramatic effect on the body.  In people, age-related changes include graying or loss of hair, weakened muscles, wrinkled skin, and hearing and vision problems. One way senescent cells produce such changes is by secreting a variety of harmful compounds that cause inflammation. In healthy individuals, inflammation is the body’s normal response to injury or infection. However, inappropriate or uncontrolled inflammation can damage healthy tissue. Scientists believe inflammation is an underlying cause of many age-related diseases in people, including arthritis, cataracts, and dementia.

Exercise can help elderly people maintain or improve physical fitness. © Chuck Savage, Corbis.

The Mayo scientists experimented with a strain of mice that were genetically engineered so their cells produced a molecule called caspase 8 as they aged. They then injected the mice with a drug that specifically targets the molecule and causes those cells that contain it to commit suicide. The drug has no effect on normal cells, so healthy tissues were spared and there were no side effects. The drug did not affect the life expectancy of the mice. This kind of genetic engineering cannot be used in people, but researchers hope to develop other ways of targeting human senescent to produce the same beneficial effects. However, such techniques are probably years away.

Additional World Book articles:

• Antioxidant
• Death
• Telomere