HONR 259C "Fearfully Great Lizards": Topics in Dinosaur Research

Fall Semester 2020
"Fearfully Great Lizards": A History of Dinosaur Research

The "Hall of Extinct Monsters" at the Smithsonian Institution's National Museum of Natural History, c. 1917

Key Points:
•The word "dinosaur" (and its technical equivalent, "Dinosauria") were introduced in 1842.
•"Dinosaur" is not simply a term for any vanished giant reptilian creature. It refers specifically to "any member of Dinosauria"; rather, Dinosauria is a particular branch of the "reptile" (sauropsid) family tree. Not all dinosaurs were large, scaly, or even extinct!
•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.
•In the early 19th Century fossils of giant land reptiles--carnivorous Megalosaurus, herbivorous Iguanodon, and armored Hylaeosaurus--were discovered in southern England. In 1842 Sir Richard Owen recognized these as form distinct group of reptile, which he termed "Dinosauria" (Latinized Greek for "fearfully great lizards").
•The initial dinosaur fossils were very fragmentary. Subsequent discoveries (in England, on the European mainland, and most especially in the United States) revealed better, more complete skeletons, documenting that dinosaurs were a diverse group with very distinctive anatomy.
•In the later 19th and early 20th Centuries expeditions around the world greatly increased our knowledge of dinosaurs.
•After a great slowdown of research in the middle of the 20th Century, the work of John Ostrom sparked a "Dinosaur Renaissance", in which dinosaur evolution, biology, physiology, growth, behavior, and extinction became major fields of study.

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?

"Fearfully Great Lizards
The first major dinosaur discoveries--documenting the large-bodied creatures of the "Age of Reptiles"--were made in Great Britain. The first of these was made by Oxford geologist Reverend William Buckland. Only a few parts were discovered: jaw bones with blade-like teeth as well as some backbones, hip bones, and limb bones. This animal was formally named Megalosaurus ("big lizard") in 1824, and thought to be a giant version of modern monitor lizards.

The next major discovery were made in the in the Weald region of southern England, by husband and wife team Dr. Gideon and Mary Ann Mantell. These included teeth were leaf-shaped, reminiscent of the modern Iguana, a primarily herbivorous reptile, as well as limb bones, vertebrae, and so forth. When Gideon Mantell formally described the animal he called it Iguanodon ("iguana tooth"), and imagined it to be an immense version of the iguana.

The third major discovery, also in the Weald region and also by the Mantells, was a partial skeleton with very large spikes were found arranged along the skeleton: the first evidence of giant armored reptiles. Mantell called it Hylaeosaurus ("lizard of the Weald") in 1833.

Other discoveries were made on the European continents in the 1830s and 1840s.

In 1841, Sir Richard Owen gave public talks about the fossil reptiles of Britain. He concluded that Megalosaurus, Iguanodon, and Hylaeosaurus formed their own distinct group, for which proposed the name Dinosauria ("fearfully great lizards") when he wrote up talk (in 1842):

Other Dinosaurs Hidden in Owen (1842): Although Owen recognized that Megalosaurus, Iguanodon, and Hylaeosaurus belonged in in his new group "Dinosauria", he actually missed that two other fossil reptiles he discussed fit in this group as well. One was little Thecodontosaurus, known at the time from partial lower jaw. This was considered by him as a more typical (i.e., not particularly "fearfully great"). Another was gigantic Cetiosaurus (probably the largest animal described in his British fossil reptile paper), which he considered a giant sea reptile. Subsequent discoveries showed that these were representatives of the long-necked plant-eating dinosaur group Sauropodomorpha, but given the very limited material Owen had access to, it makes sense that he was not able to recognize this.

In the 1850s as part of the Great Exposition (one of the first World's Fairs), natural history artist Benjamin Waterhouse Hawkins sculpted life-sized reconstructions of Megalosaurus, Iguanodon, and Hylaeosaurus (and other non-dinosaurs) under Owen's guidance. (Here is a recent photo of those models.) Because of this (and popular writings) dinosaurs became parts of the general public discourse: in popular science books, in political cartoons, in science fiction writing, etc.

But up until this point, there were still no complete dinosaur skeletons.

Dinosaurs in America and the Great Dinosaur Rush
There were North American discoveries that were contemporary to the early English discoveries. For instance, three-toed tracks in rocks of the Connecticut River Valley, and were thought to be giant bird tracks. In the same rocks, a fragmentary skeleton was found, but interpreted as an "Indian skeleton" (it would later turn out to be a close relative of British Thecodontosaurus).

The first fossils recognized as being from dinosaurs were teeth and bones found by explorers in western territories (now Montana). These were described in 1856 by first American vertebrate paleontologist Joseph Leidy. Some were recognized to be similar to Iguanodon, others to be similar to Megalosaurus, still others to be some sort of lizard

In 1858, the first major, relatively complete North American dinosaur fossil: was described. It had been discovered near Haddonfield, New Jersey. Leidy named it Hadrosaurus ("heavy lizard"). Its teeth and bones were similar to Iguanodon, but fossil was more complete. In particular, the front leg was smaller and more slender than hindlimb, indicating it was bipedal (two-legged). This suggested that Iguanodon was bipedal, too.

In 1866, another New Jersey discovery (this time partial skeletal material similar to that of Megalosaurus. The difference between the very small forelimbs and the long hindlimbs showed that it, too, was bipedal). Leidy's younger colleague Edward Drinker Cope of Philadelphia described it, using the name "Laelaps". (It turned out that the name "Laelaps" was already used for a mite, and so Cope's rival Othniel Charles Marsh of Yale University re-named Dryptosaurus ("wounding reptile").)

Cope and Marsh had a long professional rivalry, which led to a conflict (primarily over fossils of dinosaurs and mammals from American West) during the 1870s and 1880s nicknamed "The Bone War". Among the dinosaur discoveries that came our of this rivalry were some of the first relatively complete dinosaur fossils, revealing body shapes unlike previously known animals, living or extinct! The vast numbers of fossils discovered formed the central collections of major museums and greatly increased the knowledge of extinct life (including some of the first complete dinosaur fossils).

(The Bone Wars has been featured in various stories, including an episode of American Experience on PBS and a segment on Drunk History!)

In Europe, new discoveries were also being made during this same interval. For instance, many nearly-complete specimens of Iguanodon (confirming a Hadrosaurus-like body), and the first small dinosaurs (Compsognathus, Hypsilophodon)

The Bone Wars were the start of the great "dinosaur rush" (comparable to the Gold Rush), where rival teams traveled out to collect dinosaur (and other fossil) skeletons. By the beginning of 20th Century, new, wealthy museums sponsored major expeditions to American and Canadian West: the Royal Ontario Museum (Toronto), the National Museum of Canada (now the Canadian Museum of Nature, Ottawa), the Carnegie Museum of Natural History (Pittsburgh), the United States National Museum (aka the Smithsonian Institution) (Washington), the Field Columbian Museum (now the Field Museum of Natural History, Chicago), and most especially, the American Museum of Natural History (AMNH) (New York) under the leadership of vertebrate paleontologist Henry Fairfield Osborn.

Also, the AMNH and various European museums began the era of imperial paleontology (major expeditions to foreign lands, to bring fossils back to the home institution)

The Dinosaur Renaissance
The Great Depression of the 1930s and World War II led to a slowdown in research in dinosaurs (and, to be fair, much non-essential scientific research in general). Furthermore, dinosaur science itself had been tarnished in the eyes of some during the early and mid-20th Century as not serious science. Dinosaur fossils might be good to bring people to museums, but "serious" paleontology focused on other groups of organisms.

There were a few paleontologists actively researching dinosaurs in the mid-20th Century. One was John Ostrom of Yale University. As a graduate student he had examined feeding in duckbilled dinosaurs, showing that they were limited to feeding on soft aquatic vegetation but instead had some of the most complex chewing adaptations among the vertebrates. Afterwards he would show that horned dinosaurs were comparably good at slicing up plants. Most famously was his discovery in 1964: the first raptor dinosaur know from good material, which he named Deinonychus ("terrible claws") in 1969. The sickle-like claw on foot indicated it was an active leaping predator, and later comparisons between Deinonychus and the primitive bird Archaeopteryx caused Ostrom to revive idea that dinosaurs were bird ancestors.

This research, and those of his colleagues and students, became known as the Dinosaur Renaissance. The number of dinosaur researchers (and topics of research) soared. Among other questions, the following became important areas of study:

New expeditions around the globe greatly increased the number of dinosaurs known: at present, about one new species of Mesozoic dinosaur is named per week and half. As opposed to the old days of Imperial paleontology, most of these expeditions are organized by local researchers (although sometimes in collaboration with outside teams). Entire new methods of examining fossils have been developed: CT scans, molecular studies, and computer modeling, for instance.

The discoveries of the Dinosaur Renaissance are the subject of the rest of this course.

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Last modified: 30 July 2020

Detail from Robert T. Bakker's 1969 reconstruction of the dromaeosaurid Deinonychus