Reading Triassic Life on Land
As the great 20th century paleontologist William Diller Matthew once wrote, "The story of life on Earth is a splendid drama, as interesting as we watch its action and study the interplay of causes and motives that lie behind its movement as any great historic play." Within this great play, the Triassic—the time period spanning approximately 250 to 200 million years ago—was one of the most stunning acts, yet it is often cast as simply being the "beginning of the Age of Dinosaurs" for the first appearance of the famous group about 230 million years ago. This habit obscures the grander story of Triassic life, one of catastrophic extinctions and evolutionary innovation involving a weird cast of unfamiliar creatures. Now paleontologists Hans-Dieter Sues (a paleontologist with the National Museum of Natural History) and Nicholas Fraser have outlined this fantastic story in their new reference book Triassic Life on Land: The Great Transition.
The first thing that should be noted about Triassic Life on Land is that it is primarily aimed at specialists. While Fraser wrote a glossy, popular-audience book filled with wonderful pieces of paleo-art by Douglas Henderson several years ago, called Dawn of the Dinosaurs, the new volume is more of a directory of Triassic life. For example, here is a passages about the relationships of several Triassic creatures more closely related to early mammals than to reptiles:
Cynognathus, Diademodon, and Trirachodon belong to the Eucynodontia, which are distinguished by a greatly enlarged dentary with a tall coronoid process and distinct articular process and reduction of the postdentary elements to a bony rod lodged in a medial recess on the dentary.
(In other words, this particular group of mammal-like creatures can be identified by a large lower jaw in which 1) the parts of the jaw that connect to the skull are tall and distinctive, and 2) the bones behind the dentary bone—the bone that makes up the majority of the lower jaw in these animals—have been compressed into a small rod connected to the inside of the lower jaw.)
The authors provide a glossary of terms in the back of the book, but Triassic Life on Land will be a difficult read for anyone without a firm background in anatomy and paleontology.
That point aside, during a time when our understanding of life during the Triassic is rapidly changing, this new book is a very useful resource for tracking down what kinds of organisms (primarily vertebrates, but also plants and insects) lived where and when. For the bulk of the book, Sues and Fraser trace fossils from the earliest parts of the Triassic preserved among the southern continents through the Late Triassic of what is now the American West, noting interesting tidbits about the biology of certain critters along the way. (Of special interest to this reader was the discussion of Triassic sites along the east coast of North America. These sites are not as well-known as others, and—if paleontologists can get to them before they become victims to suburban sprawl—may yield important insights into life towards the end of the Triassic.) This orderly progression then leads to a chapter focused on two particular Triassic sites—the Solite Quarry in Virginia and the Madygen Formation of eastern Europe—followed by two chapters on changes among organisms during the Triassic and the mass extinction event that marked the end of the period. These last two chapters summarize some of the great mysteries that remain about that period in life's history, from why dinosaurs eventually became the dominant vertebrates on land to what could have caused the mass extinction at the end of the period.
While I would have preferred a few more details about interactions between organisms, paleoecology, and evolutionary patterns in the book—especially since the Triassic was a time when there were major changes going on among vertebrates on land—Triassic Life on Land remains an excellent repository of information. It is like a giant-sized review article about this peculiar act in earth's history. Its format and extensive references make it easy for interested readers to track down original source materials, and, even though we are learning more about the Triassic every day, I think it will remain an extremely useful volume for many years to come.