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| September 2004 |
Feature |
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Bigger, earlier - and hungry. Meet t-rex the teenager.Christina Scott
Using a technique pioneered by a South African palaeo-biologist, researchers in North America have announced that they have solved the puzzle of how the notorious meat-eating dinosaur known as Tyranosaurus rex got to be so darn big. "The study provides fascinating insight into the growth dynamics of Tyranosaurus rex and highlights the importance of bone microstructure in assessing the biology of extinct animals," says Pretoria-born Professor Anusuya Chinsamy-Turan from the University of Cape Town zoology department, who received special mention for her dinosaur detective work in the Women in Science awards in Johannesburg in August. Her work in dinosaur bone microstructure, using a polarizing microscope, is cited in the latest research, which formed the cover story in a recent issue of the journal Nature. It now appears that 65 million years ago, the teenage T. rex put on a massive growth spurt, piling on a weight gain of two kilograms a day, every day for four years, before eventually reaching its adult weight of some 5000 kilograms. But there may have been a down side to being the biggest on the carnivore block: some scientists suspect that the dinosaur got too big to move quickly and may have had to scare away more effective predators in order to steal their meals. In other words, the king of the dinosaurs may have been rifling through the Cretaceous era's equivalent of a garbage bin: he was a scavenger. Our only evidence is in the bones. Microscopic clues such as growth rings - similar to the rings used to date trees - provided the information - but only after the scientists were able to take small samples from a handful of the precious fossils, carving the small chunks of bone off with a diamond-edged cutting blade, and then shaving it down until the samples are see-through. They then used a special microscope to view the traces of long-gone blood vessels, cartilage, and other clues to a dinosaur life. "It is very exciting to have the growth series for the T. rex," said Professor Anusuya Chinsamy-Turan, who earlier this year won a new award as the country's top senior black researcher in South Africa's first decade of democracy from the National Science and Technology Forum. "I have done growth series studies for three other species of dinosaurs. The most difficult thing is to obtain different sized specimens to work with, because ideally you need material from hatchling to subadult to adult." Over four years, the team of American and Canadian scientists also compared the bones with growth patterns of modern reptiles, such as alligators and lizards of known ages, in order to test their theories as to the relation between bone size and animal size, and accurately predict lifespan. They used a group of about twenty fossil skeletons from four close relatives of T. rex but as fossils are not exactly a renewable resource, they were only able to work on seven actual bones from a T. rex itself, using rare specimens ranging in age from 2 to 28. "This is really the first look at how dinosaur giantism was achieved,'' was how Dr. Peter J. Makovicky of the Field Museum of Chicago explained the research at a press conference attended by the New York Times and many others. "We can stop guessing.'' Dr. Makovicky and the team of palaeontologists used the technique of estimating ages by counting growth rings in the bones - dense mineral deposits laid down in the bones on a yearly basis as the animal grows - as well as by calculating the corresponding body size from circumference measurements of leg bones. Although many large dinosaur bones displayed growth rings, much like tree rings, they are incomplete and hard to read. An additional problem is posed by the fact that this technique is generally used on large, weight-bearing bones such as the thigh. In therapods such as the T. rex, the huge thigh bones are hollow, so many of the early growth rings are missing. The study relied instead on smaller solid bones, including ribs and shin bones. These do not develop hollow cavities or remodel (in which primary bone is replaced by secondary bone), which can pose particular problems as the dinosaurs age. It is assumed that these bones retain a good record of the animal's growth. However, Professor Chinsamy-Turan, who completed her Phd at Wits University in Johannesburg, points out that there are still many unanswered questions regarding the research, as numerous environmental and genetic factors can affect bone development, and different species respond in different ways. The newest research also suggests that the dinosaurs lived fast and died young. Sue, the largest of the T. rex skeletons used, has just had 70 years lopped over her presumed age, which had been calculated by scientists struck by the general wear-and-tear of her bones. It now seems that she died at the age of about 28, already showing signs of old age, rather than on the edge of her centenary. "It seems a waste to get that big and then go away so soon," said a wistful-sounding Dr. Paul Sereno of the University of Chicago, a paleontologist not involved in the research. In fact, the scientists in the latest research project say no T. rex got beyond the age of 30, unlike a number of large mammals currently alive, such as elephants and whales. But Professor Chinsamy-Turan isn't so sure: " I doubt this is true. The dinosaurs reached skeletal maturity by about twenty, as humans do, and could have lived for longer as adults - like we do!" Palaeontologists have long puzzled over how dinosaurs such as T. rex got so big. Some experts once believed they grew slowly throughout their lives, like modern-day reptiles. Others will be delighted with the apparent confirmation in Nature that they had an initial growth spurt that later subsided. But the debate is not over yet. There will be efforts to see if the same growth curve holds true for female as well as male dinosaurs. And the next step is to see if really big plant-eating dinosaurs underwent a massive weight gain in adolescence. It seems possible that massive, four-footed, vegetarian dinosaurs who resided in the swamps that once covered the Karoo took a less hasty approach, putting on their weight over decades. "Very large dinosaurs like the diplodocus found in the Algoa Basin took about three decades to reach adulthood," says Professor Chinsamy-Turan. There are still many T. rex mysteries to be solved. If it got too big to run, how did it hunt? "As it got bigger, T. rex probably suffered from a progressive decline in its running ability," says dinosaur expert John Hutchinson from the Royal Veterinary College in London in the UK. Younger, smaller versions of T. rex could have reached speeds of up to 40 kilometres per hour. But as their weight passed 1,000 kilograms, still just a fifth of their eventual adult size, this would have become biomechanically impossible, says Hutchinson. The same dilemna troubled the designers of the T. rex dinosaur in the movie Jurassic Park, who said their eyes refused to believe it when their computer-manipulated huge dinosaur was sprinting after humans in a jeep. The editors solved that particular problem by focusing on the scared faces of fleeing humans whenever the dinosaur was lumbering towards its prospective lunch, and simply cutting to it when it was sniffing out prey or roaring. It's not as easy for scientists. For those who believe T. rex was a hunter rather than a scavenger, it
is a mystery how the animals managed to eat enough to maintain their growth
spurt, given that their ability to chase prey would have been seriously
impaired. Perhaps the next question to be asked will be: did the mighty T.
Rex waddle? Or sit on its victims? Was he in fact, the hyena of the dinosaur
world? More information: * Anusuya Chinsamy-Turan has just been selected to give the keynote lecture at Africa's largest science festival, the Sasol Scifest in Grahamstown, South Africa, on 18 March 2005. The Festival itself is due to run from 16 to 22 March 2005 and attract close to 50,000 people. For more information phone 27 (0)46 603 1106 or fax 27 (0)46 603 1143 or visit their website is http://www.scifest.org.za
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