Thursday, May 10, 2007

Love was a dangerous game for these animals

18rex190_1Most dinosaur hatchlings never made it through the early-life hoops of predation, cannibalism and starvation. But the reward for surviving the first two years was a childhood of sunny prospect, a new study suggests, with the best years of a dinosaur’s life usually lasting up to the age of sexual maturity at about 14.

Puberty for dinosaurs held mortal risks, not just adolescent angst. The females probably suffered from the stresses and physiological demands of egg production and periods of fasting while nesting. The males often died in lusty combat with rivals for mates.

At the crest of desire and its fulfillment, death rates of maturing dinosaurs shot up to more than 23 percent a year. Only the rare tyrannosaur reached old age — about 28.

“Love was a dangerous game for these animals,” said Gregory M. Erickson of Florida State University, the leader of the research team that just completed a study of the life histories of the well-known predatory tyrannosaurs.

In the first detailed research of mortality rates of these dinosaurs, the paleontologists found that 70 percent of the dinosaurs that survived the first two dismal years were still alive at 13. But few of them would enjoy long reproductive life spans; their average life expectancy was estimated to be 16.6 years.

This was new evidence, the scientists concluded, that the tyrannosaurs as a group had life patterns closer to that of wild populations of long-lived birds and large mammals than their fellow reptiles. But the exceptionally low mortality of juveniles appeared to be unmatched by that of many modern vertebrates, humans excepted.

“By age 2, most tyrannosaurs were as large or larger than all other predators in their realm,” Dr. Erickson said. The juveniles started at lengths of 6 feet and reached 20 feet by maturity.

The research into the lives and deaths of four tyrannosaur species was reported in the current issue of the journal Science by two dinosaur paleontologists, Dr. Erickson and Philip J. Currie of the University of Alberta, and two population biologists at Florida State, Brian D. Inouye and Alice A. Winn.

Richard Lane, director of earth science programs at the National Science Foundation, which supported the research, called the findings “a breakthrough in unraveling these dinosaurs’ life cycles.”

Other paleontologists not involved in the work said the results laid the foundation for understanding the vicissitudes of dinosaurian life. The species studied lived 70 million years ago, in the closing era of dinosaur dominance on earth.

In their investigation, the scientists examined 22 individual fossils of Albertosaurus from a site near the Red Deer River 120 miles northeast of Calgary. Nine of the skeletons were collected a century ago by the famous fossil hunter Barnum Brown of the American Museum of Natural History. Starting in 1997, Dr. Currie and teams from the Royal Tyrrell Museum of Paleontology, in Alberta, re-excavated the site for the rest of the specimens.

The researchers counted growth lines in the limb and foot bones to determine ages at death. Then they drew a “survivorship curve” based on the proportions of individuals that died during each life stage.

“Ideally, you would like to have a larger sample,” Dr. Erickson said in a telephone interview. “But if you randomly selected 22 out of 10,000 animals, that would be a large enough sample to have a 90 percent confidence that the pattern you’re getting is significant.”To test their interpretation, the scientists examined the age at death of 70 more tyrannosaur skeletons at museums in Canada and the United States. The specimens included Gorgosaurus, Daspletosaurus and the mighty Tyrannosaurus rex.

It was no surprise that hatchlings were absent in the primary study sample. Their fragile bones were not likely to survive to fossilization. In preparing the survival curve, scientists assumed the mortality rate of the very young to be similar to that of modern vertebrates like birds and crocodiles — up to 80 percent.

At the other end of the life spectrum, the Red Deer deposit contained only one Albertosaurus that attained the probable maximum size and age for the species, 30 feet and 28 years. The oldest known T-rex died at 28, a giant apparently enfeebled by arthritis, fungal infections and other afflictions of aging.

The few juveniles in the sample may have cleared up a mystery: why are they so scarce in the fossil record? Some paleontologists speculated that tyrannosaurs grew to adult size in such a brief time that they left no detectable fossil traces of their juvenile period of transition.

“However, this notion is inconsistent with our growth curve,” Dr. Erickson and colleagues wrote in Science. “Instead, we suggest that these young animals simply had low mortality, just like older juveniles and subadults of most large terrestrial mammals today.”


For Tyrannosaurs, Puberty Meant the End of the Good Life
NYTimes,  July 18, 2006

Posted at 06:49 AM in Science | Permalink


TrackBack URL for this entry:

Listed below are links to weblogs that reference Love was a dangerous game for these animals:


The comments to this entry are closed.