by Whit Gibbons

January 13, 2008

Paleoecology is a field of science that relies primarily on the use of fossils to study relationships among organisms and environments of the past. Paleontologists interpret clues to reconstruct not only what extinct animals and plants looked like but also when and where they lived and under what environmental conditions. But how do we know that our impression of geological times millions to hundreds of millions of years ago is realistic and not just random guesswork?

The answer comes from a paleontologist, Jim Farlow of Indiana-Purdue University, who works with dinosaurs. Jim is the lead editor (with coeditor M. K. Brett-Surman,) of the 1997 book The Complete Dinosaur. I first knew Jim when he was in the undergraduate research program at the Savannah River Ecology Laboratory many years ago. We worked on a turtle project together. Although turtles live a long time, they apparently were not ancient enough to suit him, so he went on to Yale University to get his doctorate and become a paleontologist. In one of his scientific papers he stated that "most aspects of dinosaur biology cannot be observed directly but must be reconstructed by a variety of often speculative approaches."

He recently sent me a book chapter he wrote about the paleoecology of dinosaurs from Late Jurassic sediments in Wyoming and adjacent states. The creatures lived more than 145 million years ago, and more of these Late Jurassic dinosaur fossils have come from this rock formation than all the rest of North America. His chapter was on "a speculative look at the paleoecology" of Camarasaurus and Allosaurus, two of the giant dinosaurs from the era.

Camarasaurus, which superficially resembled the brontosaurs most people are familiar with, was a plant-eating monster as big as a house. In fact, Jim reports that large individuals would have weighed more than "six big elephants," or about 100,000 pounds. Allosaurus, which to most of us would look like the familiar T. rex, was smaller, but also enormous by modern standards for a strict carnivore, weighing a little over a ton, about three times as large as the biggest tigers of today.

Determining the size, the shape, and even the general diet of extinct creatures like these is usually straightforward because bones and teeth can provide clear clues to what the animal looked like, how it moved about, and whether it ate plants, animals, or both. Projecting this initial information into understanding the general ecology of a species, however, enters the realm of speculation. This next step for paleodetectives becomes more difficult; they must understand the ecology of animals today and use educated guesses about what happened in the past.

One example from the chapter is an estimate of how much rangeland would have been necessary to accommodate a grazing Camarasaurus. In fact, Jim gives two very different estimates because of major uncertainty and disagreement among paleontologists about whether dinosaurs were "cold-blooded" like today's reptiles or "warm-blooded" like today's mammals. Using a basic formula that a typical cow would require 10 to 20 acres of rangeland, a 50-ton herbivore (or "cowzilla," as Jim Farlow calls it) would require at least 180 to 360 acres. Even if Camarasaurus was reptile-like in its eating habits it would need 60 to 120 acres. In either case, as Jim notes at the end of the section, "dinosaur ranching would require a substantial investment in real estate."

Meanwhile, the paleoecology of Allosaurus is even more speculative because of mysteries about how often and in what manner these smaller carnivores actually attacked the gigantic plant eaters. Some authorities suggest that Allosaurus used its powerful jaws to crush the skulls of bigger prey. Others speculate that a fast-moving, big-jawed Allosaurus could take a meal-sized bite out of a slow-moving Camarasaurus and make a speedy escape. And whether Allosaurus hunted in packs like lions and wolves or as a solitary stalker like tigers and foxes remains part of the speculation.

We will never know for certain about many of the relationships between Late Jurassic dinosaurs and their environments. But logical, knowledge-based paleosleuthing can lead to fascinating reconstructions of the past that give us a better understanding of the world we live in today.

If you have an environmental question or comment, email

(Back to Ecoviews)