A hodgepodge of current ideas concerning dinosaurs.

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New Scientist
Copyright 1998 New Scientist IPC Magazines Ltd

April 18, 1998

SECTION: Features, Pg. 24

The dinosaur detectives

by Kate Douglas and Stephen Young

WITH a crack of his bullwhip and a touch of computer wizardry, Nathan Myhrvold conjures up a prehistoric sonic boom. It is an echo from more than 100 million years ago when plant-eating giants called apatosaurs were alive and generating 200 decibels with each swipe of their tails. A tonne and a half of flesh and bone moving from side to side must have created quite a spectacle, but what use was it ? Myhrvold particularly likes the idea that it might have been some form of mating display. Of course, there's no knowing for sure. "Behaviours don't fossilise all that well," he admits.

This lack of evidence has put the study of dinosaur behaviour beyond the pale for some palaeontologists. But Myhrvold, who holds down a day job as chief technology officer at Microsoft in Redmond, Washington, relishes a challenge. In fact, his ambitious goal of recreating the lives of long-dead animals is shared by a growing number of researchers. Ingenuity, lateral thinking and a forensic scientist's eye for detail are the tools of their trade as they search for clues among the scant remains of another age.

Take "Tyrannosaurus rex", "king of the tyrant lizards". Dinosaur detectives who want to get under this monster's skin have meagre evidence to work with. The first specimen was found in 1900, and since then excavations have turned up only three animals that are more than half complete. The same sites in America's Midwest have yielded another 20 or so skeletons that are at least 15 per cent intact. Even so, clever dino-sleuths have turned up plenty of clues upon which to work their magic. "Jurassic Park" it isn't, but this work paints a pretty good picture of what a day in the life of a "T. rex" might have been like.

Rise and shine

Were tyrannosaurs and their ilk cold-blooded, relying on outside heat to warm their bodies and get them going ? Or could they remain active whatever the temperature of their surroundings, by burning metabolic fuel to generate their own body heat ? The long-running controversy over whether dinosaurs were ectothermic, like modern lizards, or endothermic, like birds and mammals, is central to our understanding of their lifestyles.

In one strand of research, John Ruben and his colleagues at Oregon State University in Corvallis have been using CAT scanning to probe the secret recesses of dinosaurs' noses. The team found that an assortment of dinosaurs - including a member of the tyrannosaur family - had relatively narrow nasal passages which would have had little space for special scroll-shaped structures called respiratory turbinates. Existing endotherms use these as air conditioners to moisten and warm incoming air and recover some heat and moisture from outgoing air - essential processes when breathing rates are high, as they are in endotherms. The implication is that the dinosaurs had low breathing rates and so wouldn't have inhaled enough oxygen to fuel the high metabolic rate needed for life as an endotherm.

In another study, the Oregon team focused on the lung structure of the famous Chinese feathered dinosaur, Sinosauropteryx (This Week, 19 April 1997, p 6). A distant relative of tyrannosaurs and a fellow member of the Theropoda group, this fossil comes from the Yixian formation in northeast China, where a treasure trove of exquisitely preserved prehistoric remains is being unearthed. Astonishingly, signs of soft tissues are visible in the fossil, and these have helped the team to conclude that "Sinosauropteryx" had relatively simple, crocodile-like lungs that would be incapable of achieving the rates of gas exchange most endotherms need.

What does this all mean for dinosaurs ? According to Ruben they didn't necessarily have the same rate of oxygen consumption or activity as living lizards. "They could have had something intermediate," he says. "But the evidence from this seems to preclude the possibility that they would have been warm-blooded in the sense that we'd ordinarily think of warm-blooded animals."

Ruben points out that this doesn't necessarily mean that dinosaurs were sluggish and dozy. After all, they lived at a time when the world was warm, and their large bulk would have helped them to keep a steady body temperature. Today's Komodo dragon offers a clue to what they might have been like. "If we were to reconstruct theropod dinosaurs with the same sort of metabolic physiology we see in some of these very active lizards we would come up with a very active, dangerous animal that would have been very mammal-like in its behaviour," says Ruben.

First brush your teeth

One palaeontologist memorably described the huge, curved teeth of "T. rex" as "lethal bananas". Their serrated edges and the slots between the serrations were extremely good at trapping meat fibres, according to Chicago-based researcher William Abler. As a result, "T. rex" almost certainly had terrible breath and its mouth would have been a dental hygienist's nightmare. Abler believes its bite may have caused serious infections in any prey that survived an attack.

Even so, until recently some experts believed that this impressive oral weaponry was rather fragile. Then, a few years ago, Gregory Erickson was studying for his master's degree at the Museum of the Rockies in Montana when Ken Olson, a fossil collector, appeared with a "Triceratops" pelvis. The pelvis bore some extraordinary bite marks that looked like the work of "T. rex". "If you took your thumb and pushed it down into clay - that was the depth of the holes," says Erickson.

Erickson and Olson's studies on the pelvis suggested that "T. rex" fed by "puncture-and-pull" biting. "They'd bite very deeply into flesh and bone and once they stopped they'd pull straight back," says Erickson, "and that would rip out a big chunk of flesh." With a group of colleagues at Stanford University, Erickson staged further tests to try to measure the bite force of a "T. rex". The team simulated bites on a cow's pelvis using a life-size replica tooth and a hydraulic press, and measured the force needed to produce holes like the ones on the "Triceratops" specimen. The results showed that "T. rex" would have chomped like a champion, producing a force of at least 13.4 kilonewtons - outperforming wolves and lions, and biting in the same league as alligators.

Off to work

In Hollywood, "T. Rex" runs races with Jeeps, but some researchers doubt it was so fleet. McNeill Alexander of Leeds University has looked for clues about the running speeds of various dinosaurs by studying the structure of their leg bones. He calculates a "strength indicator" which represents the strength of the bones in relation to the animal's weight. "If you do that for "Tyrannosaurus" you find that the leg bones were relatively weak for an animal that was that heavy," he says. Faster animals need stronger leg bones and his approach suggests that "T. rex", which could have weighed 6 tonnes or more, moved more like an elephant than a rhino or a gazelle. "We're not talking about the sort of speeds that are good if you're going to chase jeeps," says Alexander. He offers a tentative figure of about 25 kilometres an hour. That's less than half the speed of one modern top predator, the lion.

However, Theagarten Lingham-Soliar of the Russian Academy of Sciences in Moscow argues that tyrannosaurs might have been faster than their bone structure alone implies, because of other factors such as the presence of large, shock-absorbing chunks of cartilage in their legs and their highly flexed knees.

With a little lateral thinking, James Farlow and his colleagues at Indiana-Purdue University at Fort Wayne have come up with another ingenious way to deduce tyrannosaurs' top speed. They asked themselves: what damage might a fully grown "T. rex" do to itself if it came a cropper at speed ? A fall at 72 kilometres an hour, they calculated, could have been fatal. They came up with a top speed of about 36 kilometres an hour. "For an animal its size, I think it was pretty fast," says Farlow. "I suspect it could have caught any other large dinosaur in its environment."

In theory, fossil footprints could provide decisive evidence, but there are very few known tyrannosaur tracks, says Martin Lockley of the University of Colorado, Denver. The best, in New Mexico, shows just one footprint with about 3 metres of untrampled surface in front of it. It's difficult to draw conclusions from a single footprint, says Lockley, but if this distance is taken as the distance between steps, then the calculations show that the animal was travelling at around 11 or 12 kilometres an hour. Of course, this need not represent its top speed. It may well have put on a spurt when in pursuit of its dinner.

Dinner time

The idea that "T. rex" was a mighty hunter looks like an open-and-shut case. But is it ? According to some researchers, including palaeontologist Jack Horner of Montana's Museum of the Rockies, there is evidence that this terrifying beast lived by scavenging. Horner points out that "T. rex"'s femur was longer than its tibia, whereas bipedal animals that run fast have the opposite arrangement. "T. rex" appears to be adapted for long-distance walking, he says. Its brain had a huge olfactory lobe - like that of a turkey vulture, which depends on smelling carrion from a long way off. And those extraordinarily small arms look hopeless for grappling with prey. What's more, its physique would have been ideal for scaring hunters away from a fresh carcass.

Most researchers still see "T. rex" as the most ferocious predator of its day, although it might have scavenged when it got the chance, just as modern hunters do. "I would be astonished if tyrannosaurs had not been hunters as well as scavengers," says Farlow. Hunting was their main method of procuring food, according to Lingham-Soliar. He bases his conclusion on studies of tyrannosaur anatomy and comparisons with modern animals. In particular, he points to the huge skulls of tyrannosaurs, which were immensely strong in critical areas and clearly designed to resist large stresses such as those that might be encountered in hunting and dismembering large prey.

The same imposing anatomy has prompted David Norman of the University of Cambridge to suggest that "T. rex" might have charged at its victims with mouth agape. Lingham-Soliar, on the other hand, believes that this would have been highly damaging to their teeth: "Like running at a brick wall with one's mouth open." He offers a different rationale for the stoutly built skull, which also explains how tyrannosaurs managed to break up their prey despite their lack of effective grasping forelimbs. He believes they tore their victims apart by seizing them in the mouth and shaking them violently - rather like many of today's marine predators that also feed without the help of limbs, such as sharks and killer whales. Enormous forces would have acted upon the skull and neck, putting a premium on size and strength. Larger prey wouldn't have been shaken, but chunks of flesh would have been gouged out with the teeth, he says.

Family life

Female tyrannosaurs were larger than males. That's the conclusion of Peter Larson from the Black Hills Institute of Geological Research in South Dakota, following his discovery of two distinct body types in "T. rex". "The pelvis in the robust form is wider inside, which might be an indication that this form is female," says Larson. Further evidence comes from a living descendent of dinosaurs. Male crocodiles have an extra bone known as a chevron at the base of their tail where the muscle that retracts the penis is attached. The same is true of saurornithoides, a group of dinosaurs from China that are closely related to tyrannosaurs. Larson is looking for a similar pattern. "I haven't got absolute proof on "T. rex" yet," he admits. The clincher will come later this year when the robust skeleton of Sue, the most complete "T. rex" ever found, goes on display at Denver Museum of Natural History. "I believe we're going to find that Sue has one less chevron than the males," says Larson.

Finding that female tyrannosaurs were more stoutly built than males is not as surprising as it sounds. Larson points out that, contrary to most people's expectations, throughout the animal kingdom females tend to be larger than males, because of the obvious advantages for laying eggs or carrying young. "The only time you see males larger is where they have a harem and have to compete for females," he says. ""T. rex" was not a herding animal in that sense." He goes even further, pointing out that in birds of prey - which are probably among dinosaurs' closest living relatives - outsized females and monogamy go hand in hand. "Tyrannosaurs may have pair-bonded," concludes Larson.

Another palaeontologist who wants to dispel the image of "T. rex" as a loner is Tom Holtz from the University of Maryland, College Park. He points out that Sue was found in what looks like a family group, with a male and two juveniles. And this is not an isolated example. "There are multiple occurrences of multiple rexes," says Holtz. "Whether or not they hunted together or had division of labour within the group is difficult to tell." Pact hunting in " T. rex" society is Myhrvold's current area of interest, but he is yet to publish his results.

""T. rex" probably organised into highly social, protective and cooperative family groups," concludes Larson. Even if this harmonious picture is correct, other clues suggest that there were outbreaks of violence between individuals. For example, tyrannosaur teeth sometimes bear telltale marks made by the teeth of their fellows. These could have been made during feeding, fighting or courtship, according to Abler. Then there are the numerous broken bones found in fossilised specimens. Many of these were healed by the time of the animal's death, suggesting that struggles with prey and competitors were common. Bite marks on Sue's skull show that she died after the left side of her face was almost torn off by another "T. rex". Even before this brutal attack Sue's life must have been agony. Research last year at the Denver Museum of Natural History revealed that Sue suffered from gout.

Music of the crests

THE SKULL of a so-called trombone duckbill discovered in New Mexico in 1995 was as impressive as the beast's name implies. In life, this hadrosaur, formally known as "Parasaurolophus", was a ten metre giant and its crowning glory was an enormous, hollow crest on top of its head. Long, looped tubes led from the nostrils up to the top of the crest and then back down towards the throat.

Some people think the crest acted as a resonator, and in 1981 David Weishampel of Johns Hopkins University in Baltimore, Maryland, worked out how it might have sounded. But the New Mexico discovery presented researchers with an opportunity to find out more about the musical properties of this bizarre structure.

With the help of a hospital in Albuquerque, Tom Williamson of the New Mexico Museum of Natural History and Science and Carl Diegert of Sandia National Laboratories took a CAT scan of the skull, which is 1.5 metres long. The internal arrangement of tubes and chambers in the specimen turned out to be very different from what they had expected.

To work out how the crest may have sounded, Williamson and Diegert modelled it on high performance computers. No one knows whether dinosaurs had vocal organs, but either way "Parasaurolophus" would have put on an impressive performance. Without vocal organs, it could have got sounds to resonate in the crest just as you can produce noises by blowing across the top of a bottle. The result would have been a very low note (similar in pitch to the lowest note on a piano). With vocal organs, it would have been rather more musical, producing a wider repertoire of frequencies. The sound has been compared to that of a didgeridoo.

Williamson believes that the crest would have been used for both visual and vocal displays, maybe to attract mates. The low-frequencies would have travelled well through the dense vegetation in which "Parasaurolophus" lived. They could have been used to coordinate the movements of a group or even as alarm calls.

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