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.
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.”
A vertebrate paleontologist studies the fossilized remains of animals with bones. Robert Carroll says, “Paleontology is a very visual science. Even young children can understand that well-preserved fossils represent once-living plants and animals.” Fossils provide the basic evidence for understanding the history of life on Earth. They show that in the past, animals and plants were very different from those living today. And the older the fossils are, the more different they are from modern plants and animals. This gives the investigator an appreciation for both the evolution of life and the overall unity of all living organisms.
The study of paleontology is not just about creatures that died millions of years ago. To understand the nature of fossils one must learn about the anatomy, physiology and genetics of current plants and animals. “To me, this makes paleontology a very unifying profession,” says Carroll. Paleontology also requires knowledge of rocks and geology to work out the age of fossils and the nature of the environment in which they lived. This includes knowledge of major changes in Earth’s climate and the shifting positions of the continents and the oceans. Ultimately, paleontology provides evidence of our own human ancestry prior to the emergence of written history, and it shows the factors that may explain our evolution from primitive, ape-like animals.
Sometimes Carroll gets very excited when he is chipping away the matrix of a fossil, uncovering something never seen before. Preparation may seem a mechanical chore, but it’s the way paleontologists scientifically test their hypotheses. Exposing fossilized bones may help determine the mechanics of a joint, or relationships the animal had with other living things in its environment. It shows the ways of life of extinct animals. Other scientists use telescopes, gene sequencing or rockets to Mars, all of which involve mechanical contrivances. Paleontologists use sharp needles.
An understanding of paleontology cannot come without an appreciation for the scale of geological time compared with historical or human time. Compare these approximate times:
----------------- Historical Time -----------------
----------------- Geological Time -----------------
To put this into perspective, the entire extent of all recorded human history (6,000 years) is little more than one one-thousandth of one percent of the time since the first creatures with backbones crawled out of the sea (365 million years ago).
Click on the graphic to enlarge.
Key to numbers on graphic:
1. People have been around for a very brief time. This chart, with temperature on the vertical, shows that for most of Earth’s history the planet has been more like a tropical greenhouse than an ”icehouse.“ Scientists don’t know if we are now in a short period of warming that might end in another ice age in 10,000 years, or if the Earth will gradually warm up to a temperature like that in the age of dinosaurs.
2. Around 300 million years ago many animals lived on Earth, and countless fossils exist from that period. Hylonomus lyelli, shown here, is the oldest known reptile (315 million years).
3. A mysterious gap in the fossil record of approximately 100 million years exists between any archaic amphibians and the first appearance of fossils of advanced frogs, salamanders and caecilians.
4. Robert Carroll and his colleagues found the key to the ancestry of frogs and salamanders in fossils of the larval stages of two related families of archaic amphibians with external gills like salamanders, but skulls with very large openings, like those of both frogs and salamanders. Caecilians may have arisen from very elongated microsaurs.
5. Fossil of a larva of a 300-million-year-old amphibian close to the ancestry of salamanders. Note the external gills labeled “ex-gills” in the drawing of the same creature (above). Also shown: a pin vise used by paleontologists to expose fossilized bones from rock.
6. A paleontologist must be a good draftsperson. When a fossil is found, the bones are usually crushed or disturbed, as shown in the photo of the skull of a Permian microsaur.
The first step is to draw all the bones as they appear in the rock, then label them. After this, a new drawing is done to reconstruct the skeleton of the original creature based on what we know of the anatomy and physiology of present-day animals. Afterwards, paleontologists can infer details about the animal. This microsaur may have looked like a lizard, but it lived part of its life in the water.
The standard theory of evolution does not explain some things: how generic change occurs, or how specific genetic changes result in specific differences in structure or function. For instance, we still don’t know general things such as how life began or how animals and plants originated. We don’t know where feathers on birds came from, nor how hair originated on mammals. Only in the last 10 or 20 years, with advances in molecular genetics, have we begun to understand how genes themselves have evolved. Carroll hopes a new generation of molecular developmental paleontologists will answer questions about the origins of feathers and hair. They may also find a molecular genetic basis for why we have five digits on our hands and feet. Another paleontological mystery: where did turtles come from? Nobody knows.
Robert Carroll, Vertebrate Paleontology and Evolution, W. H. Freeman & Co., 1987.
Robert Carroll, Patterns and Processes of Vertebrate Evolution, Cambridge University Press, 1997.
“Palaeontology, The Evolutionary History of Amphibians,” Amphibian Biology, vol. 4, Surrey Beatty & Sons, 2000.
Canadian Journal of Earth Sciences, vol. 40, April 2003.
So You Want to Be a Paleontologist
Besides chipping away at fossils and identifying them, paleontologists must spend a fair bit of time in the field, looking for fossils. Once found, they must be carefully removed from the site, transported and then prepared. This may require a great deal of research into the biology of the creature and the time period when it lived. Carroll says, “What I like best about vertebrate paleontology is that it provides an excuse for research in almost any aspect of biology.” During his four-decade career he has come to know something about every group of vertebrates, and he is now becoming interested in the nature of micro-organisms and how they originated.
"I sometimes think of paleontology as being an extension of history, just going on for much longer periods of time and involving a diversity of other organisms besides humans,” he says. However, paleontology is really a science because it investigates the natural world, a world that would be out there whether or not there were humans. Science is based on observations, followed by hypotheses to explain those observations. Scientific data may be the positions of stars, or the sequence of the genetic code. For paleontologists, data come in the form of fossils that record changes in the structure of bones and the natural history of life on Earth.
“What sometimes disappoints me, as a career scientist, is that many scientists become so committed to a particular area of research, or a particular way of doing science — either their techniques or their concepts — that they become isolated from other related problems, other periods of time, or other ways of learning about the world around us,” says Carroll. As a result, he feels, some scientists are unable to advance either knowledge or understanding as much as they could. Science simply becomes another job, rather than a continuing quest.
Careers in paleontology include being a government paleontologist, a university professor, laboratory scientist, chemical, petrochemical, pharmaceutical or pulp and paper industry staff scientist, petroleum/mining consultant, or a private consulting scientist.