Big Bodies Unbalance Modern Theories

Big bodies fascinate James Farlow. As a child, he watched the dinosaur segment of Walt Disney's movie Fantasia, and a curtain opened on what he wanted to do for the rest of his life. Now an Indiana University-Purdue University Fort Wayne (IPFW) professor of geology, Farlow attempts to unlock mysteries written in rock-- mysteries of bodies that died 65 million or more years ago. Farlow researches dinosaurs: the bigger and nastier, the better. The star of his big-screen dream is Tyrannosaurus rex. Farlow has studied extensively how fast T. rex ran, how deep it dug its teeth into its prey, and how it scavenged for meals. He has developed theories on how a meat eater the size of a large African elephant could survive in the Mesozoic era, and he sees lessons in extinct animal bones that can be applied today.

For a quick explanation of how scientists' current view of dinosaurs evolved, let us revisit the movie theater. The original King Kong portrayed dinosaurs as slow-moving behemoths who postured and roared. Recently Jurassic Park showed scientists' mouths drop open at a T. rex that could run 32 miles per hour. Farlow endorses, with some important reservations, Steven Spielberg's portrayal. Along with IPFW Professor of Physics John Robinson, and Matt Smith, a scientific artist from Bozeman, Montana, Farlow tried to determine how fast tyrannosaurs could have run. Using a 1/20-scale model of the dinosaur, sculpted by Smith, the team first calculated the body's volume. The scientists measured the difference between the weight of the the model in air and when submerged in water. To check the accuracy of this method, the team estimated volume again by collecting water displaced from a container when the model was completely submerged. The scientists then calculated the volume of a full-size creature by multiplying the model's volume by the cube of the inverse of the model's scale (twenty to the third power).

Assuming that the living T. rex would have had a specific gravity (density as compared to water) between 8.5 and 1.00, the scientists arrived at an estimated mass of 6,000 kg. for the animal represented by the model. Plugging the mass estimate into a mathematical equation, the team calculated the animal's "strength indicator," a measurement of how well a skeleton handles the stress of physical activity. They found the T. rex femur claimed a strength indicator of 7.5 to 9 m2/giganewton. (A giganewton is the force needed to move 112,000 tons--roughly the weight of two steam locomotives--one meter.) By comparison, a runner like an ostrich boasts a femur with a strength indicator of 44 m2/giganewton, a muscle-bound mammalian femur like that of a white rhinoceros measures 26 m2/giganewton, and a human femur boasts a strength indicator of 15 m2/giganewton.

The team also calculated how speed would put T. rex at risk should the big hunter fall. Considering the vertical impact that the torso and head would suffer, the horizontal force of impact, and the skid distance, the team created several scenarios set at varying speeds. At 20 meters/second (approximately 44 miles per hour), the body of a fallen T. rex would slide faster than its head. In other words, a skidding stop alone might break the animal's neck. Farlow and his collaborators concluded that T. rex could not afford to run at such speed. Most likely, the feet of the big carnivore never left the ground simultaneously. However, with its long limbs and tail held out behind for balance, T. rex could probably walk or trot up to 10 meters/second (22 miles per hour), with short surges that might reach 15 meters/second (33 miles per hour).

In a research paper that appeared in a book appropriately titled, Dino Fest, Farlow and Yale University student Daniel L. Brinkman discussed their research on the teeth of carniverous dinosaurs. On examination of 279 teeth from close relatives of T. rex, Farlow and Brinkman discovered that prehistoric predator chompers compare favorably with the teeth of two later hunters: the ora, or modern Komodo dragon, and the smilodon, an extinct sabertooth cat (the animal popularly, but not accurately, called "sabertooth tiger"). Because tooth structure and wear were the same, Farlow and Brinkman decided that the three animals probably used their teeth in similar ways. The scientists speculated that tyrannosaurs dug their teeth deeply into victims, through both soft tissues and bone. Upper teeth probably passed on the outside of the lower teeth as the jaw closed. Saw-like serrations on the teeth bound the meat securely as a tyrannosaur jerked its head to rip free bits of its meal. With its relative speed and toothy grin, T. rex looked the part of a dashing hunter. But, Farlow noted in another study, the big carnivore also appeared in a less glamorous role. Like many modern meat-eaters, T. rex probably stooped to scavenging meals of carrion, or animals already dead, when the opportunity presented itself. In this type of food gathering, a big body is a bonus. Farlow observed that a decaying dinosaur carcass would generate large amounts of ammonia, carbon dioxide, amines, volatile fatty acids, and sulfur dioxide. Heat, a by-product of decomposition, would hasten evaporation of the carrion's volatile parts. Wind speeds at 5 to 6 meters above ground--about nostril level for T. rex--could be 1 to 2 meters/second faster than wind speeds just 1 meter up. So if smell were a dinner bell, tyrannosaurs would be among the first invited to a carrion feast. Height similarly helped sight. Farlow used the formula for area of a circle (A=[pi]r2) and figured the circle's radius as a function of an animal's height. Thus armed, he showed that T. rex, who stood up to 6 meters (20 feet) tall, could spot carrion within an area 36 times larger than the view available to a four-legged scavenger 1 meter tall--say for example, a hyena.

Still, a nagging question remained: whatever the source, how could a meat eater the weight of a mid-size truck find enough food to survive? Farlow cooked up theories that called for two main ingredients: the availability of large prey, and the correct ratio of prey to predators within a region the carnivore inhabited. To satisfy the need for large prey populations, Farlow pointed out that in the late Cretaceous, congregations of leaf-eating dinosaurs thundered across the land in herds larger than any seen by man. The fact that dinosaurs laid eggs gave them a numerical advantage over mammals. Egg layers do not need to carry their young for long periods of gestation, which frees them to reproduce more often. Vegetarian dinosaur's own food supply--plants--grew to great size and in prolific numbers, aided by a carbon dioxide-rich environment.

With the prey accounted for, Farlow added T. rex to the equation. In weighing his theories, Farlow had to balance numbers so that he did not create a theoretical population of tyrannosaurs too large for its food supply, nor so small and thinly stretched that it would disappear altogether. Borrowing a mathematical formula from previous studies, Farlow calculated that for a warm-blooded predator to grow to the same size as its prey, it would need to live in an environment where the prey-to-predator ratio was at least 50:1. To produce herds of plant-eating dinosaurs the same size as T. rex would require vast plains of vegetation for food. But in hunting prey its size over such distances, tyrannosaurs would seriously jeopardize opportunities to mate, said Farlow. Accounting for chance factors of disease and accident, as well as competition with other predators, Farlow concluded that a warm-blooded T. rex was theoretically possible, but not likely. Because cold-blooded animals do not create their own body heat, they need much less energy and, therefore, less food. Cold-blooded tyrannosaurs could survive on prey their size even if the prey-to-predator ratio was as low as 13:1, Farlow calculated. His research leads him to speculate that T. rex and other dinosaurs were either cold-blooded or had metabolic rates somewhere between those of typical modern warm-blooded and cold-blooded animals.

Currently the classroom anchors Farlow to less exotic aspects of his quest for knowledge of big bodies. But he sees a connection between teaching and field work. "In trying to explain to people who are not professionals in the field, you have to think about a subject more clearly," he says. "So I would say that teaching and research interact nicely." In addition, Farlow says, a teacher's enthusiasm grows through research, and that excitement spills over into the classroom. Even so, finding other practical applications in the study of animals that died 65 million years ago can be tough. When asked how his research applies to humanity's condition today, Farlow deadpans: "I have always prided myself on being in a field that has no practical application." Yet ideas, like life, don't survive in a vacuum. Ecologists-- scientists who study how species interact--have recently shown interest in paleontological studies, Farlow says.

When conducting a census of animal groups, ecologists found that the number of species of small-bodied animals are greater than the number of species of big-bodied animals. That fact may not surprise the scientific community. But ecologists also discovered that the ratio of the number of small animal species to big animal species varies with the size of the animals' home continent: Africa, for example, has more species of larger animals than Australia. Why? The answers reside on the outskirts of theory. Yet, Farlow warns, a look at the modern world would give ecologists a limited view of animal life--and, perhaps, a skewed view. Farlow grabs a sheet of paper and draws a bell curve leaning toward the left. This represents living animals, he says: lots of small- and medium-size species, very few large species. Then he draws a mirror image of the first curve, leaning to the right. This represents the dinosaurs, he says: very few small species, lots of big ones. "If you try to come up with a theory on body sizes of living animals, and then I show you the dinosaurs, the theory won't work," Farlow says. "The dinosaur world is different from the modern world. Dinosaurs are so much bigger than other living land animals, they kind of push the envelope."

Time will not erase the dinosaurs' legacy. Farlow points out that the earth's largest land inhabitants lived from 225 years ago until 65 million years ago--160 million years altogether. For humans, a species that arrived on the scene less than a million years ago and that prides itself on intellect, the lesson is clear: dinosaurs should not be ignored. "As a group of animals living on the earth," Farlow says, "they were quite successful."

--Lee P. Sauer