Tired! Not so long as there is an undescribed intestinal worm, or the riddle of a fossil bone, or a rhizopod new to me.
—JOSEPH LEIDY, ANSWERING A QUESTION ABOUT WHETHER HE WAS TIRED OF LIFE
THE LAST MAN WHO KNEW EVERYTHING
The study of dinosaurs emerged in England in the 1830s through 1850s, but comparable discoveries of dinosaurs were not yet found across The Pond. American engineering and science was still in its infancy, focused mainly on practical topics such as agriculture and canal building. Fossils of the first mastodonts had been found in the mid-1700s, and they puzzled scholars from America to France. So had the giant claws studied by Thomas Jefferson, who thought they belonged to a giant lion and instructed Lewis and Clark to look for such a feline on their trip across the continent. (The claws came not from a cat but from a giant ground sloth, now named Megalonyx jeffersoni in his honor.) Aside from these rare Ice Age mammals, few fossil bones had yet been found in North America. There were no American vertebrate paleontologists yet, so doctors and other scholars who had some biological training occasionally had a fossil bone sent to them for identification. John James Audubon and many other naturalists were focused on discovering, collecting, and describing the living species of North American animals for the first time—not looking for fossils.
Into this void stepped America’s first great naturalist, Joseph Leidy (figure 4.1). His work spanned many different fields of natural science, from paleontology to geology to parasitology to embryology to forensic medicine. In an obituary for Leidy, Henry Fairfield Osborn wrote:
Among zoologists he was the last to treat of the whole animal world from the protozoa to man, rendering in every branch contributions of permanent value. From his researches among the minerals, plants, infusorians, entozoa, and mollusks, he ranged into comparative anatomy as well as into his greatest field of research, vertebrate palaeontology. In the year 1852 we find him writing upon fossils from the West, the geology of the Badlands, the life history of bees, their anatomy and the physiology of their reproductive organs, as well as entering the discussion of some new fungi with an English microscopist, the specific determination of various parasites, as well as numerous plants, the investigation of some new points in comparative anatomy, the observation of the movements of some new Rhizopods. His encyclopaedic knowledge, broad grasp of the whole field of natural history, precision and originality of observation in every field, present a combination of endowments which will never reappear in a single individual.
Figure 4.1
Joseph Leidy in mid-career at the time he began his work on dinosaurs, about 1865. (Courtesy of Wikimedia Commons)
No wonder Leonard Warren’s excellent 1998 biography of Leidy is subtitled “The Last Man Who Knew Everything.” By the time Leidy died in 1891, the amount of science information (to which Leidy was a key contributor) had exploded, and no later natural historian could claim equal expertise in so many different fields. Since then, scientists have become specialists with limited knowledge of other fields of science due to the huge amount of information that science has accumulated.
Born September 9, 1823, in Philadelphia, Joseph Mellick Leidy’s father, Philip Leidy, was a hatmaker of German ancestry. His mother, Catharine Mellick Leidy, died giving birth to his younger brother Thomas. Joseph’s father soon remarried, choosing his former wife’s first cousin, Christiana Mellick, to help him raise the young boys. His father wanted young Joseph to become a sign painter, but his stepmother supported him in more ambitious career goals, so he went to the University of Pennsylvania to study medicine. He was trained by the noted anatomist Dr. James McClintock and the pioneering microscopist Paul B. Goddard. Once he earned his medical degree in 1844 at age 21, his father expected him to set up a lucrative medical practice and earn his keep. Instead, he stayed around Penn medical school, helping the others teach medicine and microscopy and beginning a research career. In 1845, he was commissioned to do dissections and illustrations for Amos Binney’s book on American snails. The publication of this book brought Leidy many accolades, and he was soon elected to the scholarly societies of Philadelphia and Boston. By the end of his life, Leidy was a member of more than 50 scientific societies. He finally received a permanent post in 1846 as a curator at Philadelphia’s Academy of Natural Sciences.
Leidy rose quickly through the scholarly ranks as he began his research career, publishing more than 553 scientific papers in his lifetime. Leidy’s skill in dissection and microscopy and brilliance in anatomy soon elevated him to a post in the University of Pennsylvania medical school where he taught anatomy in 1853. Later he also occupied posts at Swarthmore College and Wagner Free Institute, where he taught many subjects. His textbook on medical anatomy became the standard that instructed almost all American medical students for more than 40 years. During the Civil War, Leidy served as an Army surgeon, pioneering many innovative practices in surgery that improved the outcomes for wounded soldiers.
Long before Sherlock Holmes or real forensic detective work existed, Leidy’s skills as a microscopist made him one of the first scientists involved in detective work and forensic medicine. In 1846, the police brought him a case of a man accused of murdering a Philadelphia farmer. The suspect claimed that the blood on his clothes and hatchet was chicken blood that had spattered on him when he had killed some birds earlier. Leidy used his microscope to determine that the red blood cells had no nuclei, a characteristic of human blood and not animal blood. He further ruled out chickens by leaving samples of their blood out to dry, and they never lost their nuclei. This evidence forced the suspect to confess.
In addition to being the founder of American vertebrate paleontology, Leidy was one of the founders of parasitology and protozoology. His 1879 monograph on protozoans was the beginning of that field of research. Using his microscope, he was able to identify many of the human parasites for the first time. His most famous find was discovering the worm that infects pigs and causes trichinosis in people who eat undercooked pork.
As one of the few people at that time with any knowledge of comparative vertebrate anatomy, fossils also came to Leidy. His many responsibilities in Philadelphia left him little time or resources to mount his own expeditions. Instead the specimens were sent to him; they were mostly fragmentary fossils picked up by the early explorers of the American West. Beginning in 1847, he received a steady stream of fossils from what is now Badlands National Park in South Dakota, including the first American camel Poebrotherium, the first American rhinoceros Subhyracodon, and the first horse found in North America, Mesohippus, plus many other extinct archaic mammals such as oreodonts, entelodonts, and brontotheres that have no living descendants. He also was sent Ice Age horse teeth, which confirmed that horses had been present in North America and then vanished long before Columbus reintroduced them in 1493. Leidy received numerous other Ice Age fossils, so he was the first to name and describe the dire wolf, the giant American lion, the short-faced bear, the Ice Age camel, bison, and horse, and many others. For many American paleontologists, a trip to the Academy of Natural Sciences is essential because it is necessary to see Leidy’s original fossils to understand whether a particular genus or species is valid or not.
In the 1860s and early 1870s, Leidy embarked on a few collecting trips to the Rocky Mountains to obtain his own fossils. However, by 1871, vertebrate paleontology became a crowded and contentious field as the warfare between Edward Drinker Cope and Othniel Charles Marsh (see chapter 7) soon escalated to outright stealing of fossils, bribery, and fraud. Leidy was too much of a gentleman to get into this nasty feud, so he gave up fieldwork and most of his research in fossil vertebrates rather than get between Cope and Marsh and their self-destructive war on each other. He did publish on some fossils from Florida (including the hippo-like rhino Teleoceras) later in life, but he did not try to compete with Cope or Marsh, who had much more free time and more resources to obtain all the good fossils from the emerging fossil beds out west.
THE NEW JERSEY MARL PIT
Long before the Cope-Marsh wars ended opportunities for collecting fossils in the field, Leidy got some specimens from just down the road in a marl pit near Haddonfield, New Jersey. Marl is a mixture of lime and clay or muddy limestone that is commercially mined to add lime to soil and make it less acid. John Estaugh Hopkins was digging in a marl pit on a tributary of the Cooper River in 1838 and hit some large fossilized bones, which he brought home and put on display. Many locals picked up bones as well.
Twenty years later, a prominent lawyer and abolitionist, William Parker Foulke, was visiting Hopkins’s home and saw the huge fossil bones. Since Foulke was also an avid amateur naturalist and geologist, he got the directions to the marl pit where Hopkins had gotten the bones decades earlier. He began digging and found many more bones there. Soon he contacted the eminent Dr. Leidy and convinced him to join the excavation. Together they recovered many more bones until they had an almost complete set of limbs, a partial pelvis, parts of the feet, and 28 vertebrae (including 18 from the tail), but there was almost no skull—only eight teeth and part of the jaw. (The complete skull is still unknown.)
By the end of 1858, Leidy had finished his study and a short description of the bones and formally named it Hadrosaurus foulkii, in honor of the man who brought it to him. Hadros means “heavy” in Greek (as in the heavy nuclear particle known as “hadrons”), so its name means “heavy lizard.” The giant size and the robust shafts of the limb bones unquestionably indicated a very heavy reptile of some sort.
Leidy kept up with the latest scientific papers imported from England, and he had been following the discovery and description of Iguanodon for some time. He knew that Hadrosaurus must be another member of Owen’s Dinosauria, the first to be found in North America. The parts he had, however, were more complete than anything Mantell had found for Iguanodon. His specimen definitely had strong robust hind limbs and relatively delicate forelimbs, so it was primarily bipedal. Finally, he wrote up all the detailed descriptions and had detailed illustrations of the bones prepared for his monograph on Cretaceous Reptiles of the United States. It was due to be published in 1860, but the Civil War delayed its publication until 1865.
In 1868, the British sculptor Benjamin Waterhouse Hawkins, who had built the famous Crystal Palace models of British prehistoric animals, came to the United States with the intent of restoring Hadrosaurus. At that time, most museums kept their specimens in the storage area for research and rarely displayed them to the public. Hadrosaurus was the most complete dinosaur yet found, and Hawkins was prepared to produce the first-ever mounted skeleton that could be used for display purposes so the general public could see the skeletons of dinosaurs for the first time. Hawkins had to cast additional bones to replace the missing limbs, ribs, vertebrae, tail bones, and especially the head and neck. He had to guess at what the plaster reconstruction of the skull would look like. Naturally, he made it similar to what was known of Iguanodon (figure 4.2A) rather than giving it the more duck-like bill that was later found on other duck-billed dinosaurs related to Hadrosaurus. There are many pictures of the Hadrosaurus mount in a scaffold of wood and rope, holding the bones in place. Once the mount was open to the public, it was a sensation, and long lines of people came to the academy to marvel at the gigantic extinct reptile. America had its first taste of dinomania, although the modest mount did not match the elaborate giant skeletons and models that would become popular at the beginning of the twentieth century. With the exception of the skull model, all of Hawkins’s reconstructions of Hadrosaurus have disappeared.
Figure 4.2
Hadrosaurus foulkii: (A) as originally mounted by Benjamin Waterhouse Hawkins; (B) current display in the Academy of Natural Sciences in Philadelphia. (Courtesy of Wikimedia Commons)
Hadrosaurus became iconic as America’s first dinosaur. The marl pit is now a state monument, and there is a statue of the dinosaur in the center of Haddonfield. In 1994, it was formally named as New Jersey’s state fossil. In other respects, however, Hadrosaurus fell into the shadows. Within 50 years after its discovery, dozens of additional duck-billed dinosaurs were discovered in North America. Leidy himself named some duck-billed dinosaur teeth Trachodon, a name applied to many duck-billed dinosaurs until scientists determined that the specimens were not complete enough to assign to any known dinosaur; the name is now invalid. Cretaceous beds in Wyoming, Montana, and especially the Red Deer River badlands of Alberta soon yielded many complete articulated skeletons of duck-billed dinosaurs, and most of them came with skulls attached. The skull turned out to be the most diagnostic feature because some duckbills (the Lambeosaurinae) such as Lambeosaurus, Corythosaurus, and Parasaurolophus, have spectacular crests on the top of their head. Others, such as Gryposaurus, Brachylophosaurus, and Edmontosaurus (the Hadrosaurinae), apparently had no crest. The known skeletal features of Hadrosaurus usually place it among these noncrested duckbills, so it is assumed that its unknown skull had no crest.
The lack of a skull presents problems as well. Because it is missing the most important features that paleontologists use to analyze the relationships and family tree of duckbills, Hadrosaurus was often ignored or left out of the analysis. Some even suggested that the name was invalid because it is not diagnostic enough to determine where it belongs among duckbills. But a 2011 study focusing just on the limbs and other parts of Leidy’s and Foulke’s skeleton has shown that Hadrosaurus can be placed among the family tree of duckbills, even without a skull, so now most dinosaur paleontologists regard it as a valid genus.
Even today, many people use the term “hadrosaur” or “Hadrosauridae” to refer to the complete gamut of duck-billed dinosaurs, although a more careful analysis suggests that the name only applies to part of the duckbill family tree. Nevertheless, this informal use of the word “hadrosaur” is still widespread among paleontologists.
THE WORLD OF HADROSAURS
Hadrosaurus opened up the world to the existence not just of American dinosaurs but especially to the panoply of different kinds of duck-billed dinosaurs. They first appeared, along with their close relatives the iguanodontids, in the Early Cretaceous, and then began a huge evolutionary radiation of more than two dozen genera. They were among the most common dinosaur fossils found in the Cretaceous, suggesting that they were the most common herbivores during that time and may have even roamed in herds. If you collect in certain Cretaceous beds in the Rocky Mountains, such as the Fox Hills or Lance formations, you invariably find that the most common fossils are little cylinders and rods of bone about as thick as your finger. These are the ossified tendons of hadrosaurs, which once formed an elaborate trusswork of crisscrossing tendons that helped these dinosaurs hold their back and tail out in a rigid straight line. Leidy was clearly correct: like many other dinosaurs, hadrosaurs were primarily bipedal with the back and tail held straight and parallel to the ground, balanced on their hips and hind legs. Yet many hadrosaurs had relatively robust arms, so they could drop down and walk in a quadrupedal posture, and some were primarily quadrupeds that rarely walked on two legs.
Hadrosaurs are unusually well known among dinosaurs because many have been found as complete articulated skeletons, often in death poses. Even more impressive, 10 different hadrosaur species have impressions of their skin preserved as well, and some appear to have dried out and mummified in a death pose before they fossilized. Most of these fossils show a skin with a pebbly texture of rounded scales and other dermal bone, with no indication so far that their preserved skin was feathered. One specimen found in 1999 in the Hell Creek Formation of North Dakota is so completely preserved as a mummy that it has been CT scanned to image all its muscles, ligaments, tendons, cartilage between the vertebrae, and internal organs as well. Using this extraordinarily well-preserved specimen in dynamic computer animation models, it was suggested that they were much more muscular than previously thought, and probably could outrun a predator like Tyrannosaurus rex.
Another commonly found duckbill fossil is their teeth. Instead of rows of individual teeth separated from one another (like most animals), most duckbill teeth are shaped like long prisms and were packed together tightly into a giant grinding plate known as a dental battery (figure 4.3). You may have read that some duckbills had almost 1,000 teeth. How is this possible? Their teeth were tiny prisms packed closely together, and each battery might contain 250 teeth all tightly fused. With a 250-tooth battery on the right and left side of both upper and lower jaws, there would literally be 1,000 teeth. The jaws were built so the upper grinding plate of the dental battery scraped down against the grinding surface of the lower battery, giving duckbills an incredible ability to chew up any tough vegetation. A 2009 study showed how these dental batteries worked. The lower jaw is relatively rigid, but still has some movement in the front where the jaws meet. However, both sets of upper jaws are hinged against the skull, so when the lower jaw is brought upward in a chewing motion, the upper jaws flex outward and maximize the amount of grinding between the teeth in each chewing stroke.
Figure 4.3
Jaw of a hadrosaur, showing the hundreds of small prism-shaped teeth packed together into a dental battery. Together they formed a single hard mass of enamel ridges and dentin that would wear down into a flat grinding surface and occlude with the dental battery on the upper part of the mouth. (Courtesy of Wikimedia Commons)
In fact, many paleontologists think that the explosive radiation of duck-billed dinosaurs in the Cretaceous (along with some other herbivores) might have co-evolved with the evolution of flowering plants, which also exploded in diversity in the Early Cretaceous. Flowering plants have evolved several mechanisms to regrow quickly after dino damage, including vegetative reproduction (sprouting new plants without forming seeds). If a big radiation of herbivorous dinosaurs occurred in the Early Cretaceous, then fast-growing flowering plants would be favored over more primitive plants. These in turn would provide more food sources for herbivores, and thus the co-evolutionary “arms race” ratchets up the specializations of both the herbivores and their plant food.
Studies of the wear patterns in their teeth and the content of their fossilized feces, or coprolites, confirm that hadrosaurs ate a diet of leaves and low-growing plants, and even some rotting wood and occasionally shelled invertebrates. They probably used their broad bills to graze on low plants close to the ground (although not grass because broad grasslands had not yet evolved). This contrasts with notions from the early twentieth century that the duck-like bill was needed for feeding in the water like a duck and eating soft water plants. Hadrosaurs also could rise up and reach the leaves of tall shrubs and low-growing trees, food that was unavailable to low-slung four-legged herbivores such as ceratopsians and ankylosaurs.
As mentioned previously, one branch of hadrosaurs (the lambeosaurs) bore remarkable crests on top of their skulls, from the tall compressed crest of Tsintaosaurus to the helmet-like crest of Corythosaurus to the long curved tubes of Parasaurolophus (chapter 22). The function of this crest remains controversial. Many of them were hollow and are thought to have served as a resonating chamber for making sounds.
Much more is known about duck-billed dinosaurs than just about any other group because there are so many of them. Many are known from complete articulated skeletons with skin, and they underwent a huge diversification in Asia and North America. By contrast, they arrived in South America only in the latest Cretaceous, were rare in Europe, and we don’t have enough Upper Cretaceous rocks in Africa to know whether they lived on that continent or not. And it all started with Foulke and Leidy and Hadrosaurus, America’s first dinosaur.
FOR FURTHER READING
Colbert, Edwin. Men and Dinosaurs: The Search in the Field and in the Laboratory. New York: Dutton, 1968.
Howard, Robert West. The Dawnseekers: The First History of American Paleontology. New York: Harcourt Brace Jovanovich, 1975.
Lanham, Url. The Bone Hunters. New York: Columbia University Press, 1973.
Naish, Darren. The Great Dinosaur Discoveries. Berkeley: University of California Press, 2009.
Spaulding, David A. E. Dinosaur Hunters: Eccentric Amateurs and Obsessed Professionals. Rocklin, Calif.: Prima, 1993.
Thomson, Keith. The Legacy of the Mastodon: The Golden Age of Fossils in America. New Haven, Conn.: Yale University Press, 2005.
Warren, Leonard. Joseph Leidy: The Last Man Who Knew Everything. New Haven, Conn.: Yale University Press, 1998.