GEOL 104 Dinosaurs: A Natural History

Fall Semester 2019
The Science of Uncovering the Past & The Meaning of Fossils

Paleontologist Dan Chure studying the Late Jurassic dinosaur fossils at Douglass Quarry exposure at Dinosaur National Monument

Key Points:
•"Science" is more than a body of knowledge. It is a way of approaching questions about the natural world.
•Observations (data) about nature are used to develop hypotheses: questions you can test
•Science progresses by the subjecting of hypotheses to tests (experiments) to see if you can reject them; those you cannot reject are provisionally accepted until new information is available.
•Scientific studies are presented as papers: publications where scientists state their observations, methods, analytical results, and conclusions. Other researchers can build upon this information; sometimes supporting it, sometimes rejecting it.
•Fossils as the remains of extinct species were only fully recognized as such in the late 1700s.
•In the last years of the 18th Century fossil marine reptiles (mosasaurs, ichthyosaurs, plesiosaurs) and flying reptiles (pterodactyls) had been recognized, but no fully terrestrial forms.

What is Science?

The following (from Thomas Kida's Don't Believe Everything You Think) are a useful set of characteristics of thinking like a scientist:

Some Relevant Videos
Below are a seriesVERY short videos by TechNYou, called "This Thing Called Science""
"Part 1: Call me skeptical" (2:02):

"Part 2: Testing, testing 1-2-3" (2:30):

"Part 3: Blinded by Science" (2:45):

"Part 4: Confidently Uncertain" (3:01):

"Part 5: Do the right thing" (2:38):

"Part 6: Citizen Science" (3:34):

The Meaning of Fossils
Fossils (remains of once-living things and traces of their behavior preserved in the rock record) have been known since before humans had evolved into modern humans, but their origins were obscure. Some considered them what they really are--fossil shells were once shells, fossil leaves were once leaves, fossil bones were once bones--but others considered various other alternatives. Perhaps they were unusual crystals, or traces of an incomplete creation, or made by the Devil to confuse us.

A key hindrance to understanding fossils is that you first have to understand rocks and how they form. Although some earlier thinkers' speculations came close to the truth, it wasn't until the 17th and 18th Centuries that a combination of field observations and laboratory work found the answer: rocks were recycled bits of previously existing rocks, and that different pathways (melting and cooling; recrystallization; or fragmentation and reassembly) produced different types of rocks. It was in this last pathway (what would be called sedimentary rocks) that fossils would be found.

17th Century naturalists such as Nicolas Steno, Robert Hooke, and John Ray discovered that fossils had once been parts of living things that had died. Their remains were buried in sand, silt, or mud, and that this sediment later was transformed into rock.

18th-early 19th Century naturalists such as Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, Georges-Louis Leclerc, Comte de Buffon and (most especially) Jean Léopold Nicolas Frédéeric Cuvier established the science of comparative anatomy. With access to the large and growing collections of modern and fossil specimens of animals and plants, they were able to describe the particular features of each species. Given this database, Cuvier was able to establish that at least some of the fossils being discovered were not any known living species, but instead must be extinct.

Cuvier and colleagues also established that there was not a single "prehistoric age", but that instead different assemblages of fossils were earlier or later than others. For instance, mammoths and mastodons were among the youngest (closest to us in time) of fossils, and that different mammals (more different than any living ones) were found in earlier times.

Among the major sets of discoveries in the late 1700s and early 1800s were a series of giant reptile fossils older than the mammal fossils. These were among the specimens that first helped demonstrate that fossils were in fact remains of extinct creatures, and not simply to bodies of still-extant species. These included the "Great Animal of Maastricht", a giant marine reptile eventually recognized by Cuvier and others as a huge sea lizard, and now named Mosasaurus: the first giant fossil reptile known to Science! Others include the discoveries of fossil collector Mary Anning: fish-like Ichthyosaurus and long-necked Plesiosaurus. In addition to these sea reptiles, flying reptiles such as Pterodactylus and Dimorphodon. So it became apparent that before the age in which mammals were the dominant animals, there was an "Age of Reptiles". But so far these discoveries were swimmers and fliers: what lived on land during this age?

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Last modified: 11 June 2019

Ken Carpenter's (2013 doi: 10.2992/007.081.0301) map of the Dinosaur National Monument Carnegie Quarry.