Robert L. Carroll

Paleontology, paleobiology

Vertebrate palaeontologist who recognized and described the oldest known ancestor of all reptiles birds and mammals; the origins of terrestrial vertebrates, the origin of various amphibians such as frogs and salamanders.

"Any high-school kid can go out and make fossil discoveries."

Robert Carroll was relaxing. To an observer it might have appeared that he was working: he was bent over a microscope, pecking away at a fist-sized rock with a tiny pick called a pin vise — a pen-sized tool with a needle-sharp pin clamped into one end. As a graduate student at Harvard in 1961, Carroll’s day had been filled with meetings, lectures and seminars and there was nothing he liked more than the exacting yet peaceful chore of exposing fossilized bones. He worked on it for several hours at the end of every day at a desk in the paleontology lab, in a pool of light from the microscope. The room was warm and smelled of old stone and varnish. For Carroll, these hours alone with a rock and a pin vise were a kind of meditation.

Sometimes he would listen to music while preparing fossils, but he couldn’t have distracting daydreams. The work was mentally demanding. Imagine a dentist cleaning teeth: A brief loss of attention could result in a sharp tool slipping and chipping a tooth or cutting a gum. For a paleontologist, such a slip could damage the specimen.

While he worked, Carroll was thinking how each fossil is a unique and highly informative treasure — if it weren’t, it wouldn’t be worth preparing. He was trying to picture the anatomy of the animal he was holding. What was it like when it was alive millions of years ago? He had to imagine how that related to the broken state of the fossil in his hands. He asked himself, “Where is the surface of the bone likely to continue beneath the surrounding rock? At what angle should I direct the needle so as not to damage the bone I see, or other areas of bone that are still covered?”

The rock he was working on came from Texas. Embedded in the hard, dark shale was a lighter-coloured pattern, a skeleton of a microsaur (one of a group called dissorophoid amphibians). Carroll was meticulously chipping away the surrounding stone — the matrix — to better identify the bones of the creature. He was trying to figure out whether it was related to the origin of reptiles or of amphibians, the main difference being that amphibians have an early stage during which they live in water. He knew the rock was at least 300 million years old, so this animal had walked the earth 100 million years before dinosaurs appeared. After about a week of chipping and pecking, Carroll was able to see and recognize a number of anatomical features that very clearly distinguished this animal from a reptile.

He was working on this fossil in preparation for a trip to McGill University in Montreal, where he would spend two years studying a collection of fossils discovered in the mid-1800s at Joggins, Nova Scotia, by Sir William Dawson, the first Canadian-born scientist of worldwide reputation. The Joggins find included many groups of primitive amphibians and Dawson believed them to contain the oldest known reptiles, 315 million years old. Carroll wanted to find out whether Dawson’s ideas were right.

“With the information I had from the Texas fossil, I was able to recognize the true reptiles of the time, which are actually very similar to some living lizards,” says Carroll. He examined the Joggins fossils and picked out reptiles from the numerous animals that lived at that time. This was very important, because the reptiles from Joggins closely match the ancestry of all land animals, including modern lizards, turtles, crocodiles, mammals and birds, as well as the extinct dinosaurs. He eventually discovered that microsaurs, whose name literally means “little lizards,” were not lizards or even closely related to reptiles. They were primitive amphibians, but very different from present-day amphibians. As always, Carroll was trying to answer the questions: Where did we come from? How did life evolve?

He studies the anatomy and relationships of Paleozoic and Mesozoic amphibians and reptiles, creatures that lived between 65 and 500 million years ago. He discovered and described the crucial life forms that led to the emergence of vertebrates — animals with backbones — onto land. Recently, he has been integrating paleontology with modern genetics and molecular developmental biology to learn more about how this could have happened.

After graduate school, Carroll began researching fossils of the oldest vertebrates that spent most or all of their life on dry land, in contrast to the earliest amphibians that lived in or very close to the water. Such fossils were part of the Joggins discovery. The fossilized bones of these early terrestrial vertebrates were found inside the stumps of giant lycopods — fernlike trees — rather than in rocks formed in streams, ponds or lakes, where most fossils are found. Carroll showed that the skulls, vertebrae and limbs of these animals were very similar to those of living lizards and that they probably laid their eggs on land. They are the oldest known relatives of all modern reptiles, birds and mammals.

Carroll, with other biologists, also investigated why fish that eventually gave rise to all terrestrial vertebrates originally came onto land. Researchers recognized that the large size (more than a metre long) of early amphibians and their fish ancestor would have enabled them to use the heat of the sun to warm up and stay warm by sunbathing on the shores of ancient oceans. Being warmer, they could be more active, and like modern crocodiles this would make them better at catching fish. To get onto land and back into the water they evolved larger fins, which, over millions of years, gradually evolved into “hands” and feet, very much like those of all later land vertebrates.

Carroll now studies the early history of frogs and salamanders and how they evolved from large, clumsy ancient amphibians. One of the most important features of amphibians is the great difference between their aquatic larvae — babies that hatch and live in water — and the adults that live on land. He has been examining the fossilized larvae of ancient amphibians and has shown how one group evolved toward salamanders by specializing their way of feeding in the water and delaying their emergence onto land. A second group had a very different pattern of development: It evolved the capacity to mature very quickly and metamorphose to terrestrial adults, as occurs in frogs.

Carroll is writing a book for general audiences that describes the changes in the anatomy and way of life of these animals over the past 365 million years, explaining how the forces of evolution led to the development of all land animals, including amphibians, reptiles, birds, mammals — and ourselves.

As a young scientist ...

Like many kids,when Robert Carroll was eight years old, he asked his parents for his very own real dinosaur bone. He was perhaps a bit more serious than most children his age. “I remember saying I wanted either that, or a million dollars to go on an expedition to find one.” His father wrote to the chief vertebrate paleontologist at the American Museum of Natural History in New York to explain his son’s passion and to ask if there were any spare dinosaur bones not required for research or exhibit. Both father and son were surprised when the left femur (the thigh bone) of an Allosaurus arrived by mail a few weeks later. Allosaurus is a large carnivorous dinosaur and the specimen was from the Morrison formation in Moab, Utah. Years later it would be incorporated into a display in a museum at Michigan State University, but for the young Carroll the fossil bone was a treasure that began a lifelong search for the origins of life on Earth.

Carroll was an only child and he grew up on a farm outside Lansing, Michigan. When Robert was five years old, his father brought home a box of fossils from the school where he taught. “I was instantly excited,” says Carroll, and he immediately wanted to collect some for himself. He began looking for fossils on the farm by following the horse as it worked the fields. There were not many fossils, but the boy found some. His mom used to take him to gravel pits and there he found more fossils, of plants and marine invertebrates. These he displayed in the family’s barn, which he designated the “Mason Museum of Natural History.” In his teen years his parents took him on trips to Wyoming and South Dakota, always on fossil-hunting expeditions. After high school, Carroll went to Michigan State University and earned his bachelor of science (BSc) degree in geology. From there he went to Harvard, where he studied biology and paleontology. After a brief stint in London at the British Museum, he moved to Montreal in 1964 and never returned to live in the United States. He has been the curator of vertebrate paleontology at the Redpath Museum since 1965. One of Canada’s oldest museums, the Redpath opened in 1882 to display Sir William Dawson’s fossil collections.

Robert Carroll has produced a tremendous amount of work in his lifetime. When asked how he does it, he says, “I never watch TV. I’m reading books and papers all the time — even in bank teller lineups and university meetings.” His wife confirms, “His nose is always in a book.”

Read Robert L. Carroll's answers to questions...The Science