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."


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.

Time Scales

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 -----------------

  • Grade school: 12 years
  • A human lifetime: 80 years
  • A country’s existence (U.S.A.): 200 years
  • A religion (Christianity): 2,000 years
  • All recorded human history: 6,000 years
  • ----------------- Geological Time -----------------

  • Existence of humans like us (using tools, art): 50,000 years
  • Humans diverge from apes: 6,000,000 years ago
  • Disappearance of dinosaurs: 65,000,000 years ago
  • Vertebrates crawl onto the land: 365,000,000 years ago
  • Multicellular animals appear: 530,000,000 years ago
  • Origin of life on Earth: 3,500,000,000 years ago
  • Formation of Earth: 4,600,000,000 years ago
  • Origin of the universe: 13,000,000,000 years ago
  • 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).


    Geological time line, a paleontological problem and how paleontology is done. Click to enlarge.

    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.


    ACTIVITY

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    MYSTERY

    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.

    Explore Further

    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.

    Read Robert L. Carroll's answers to questions...The StoryCareer Advice