North American dinosaur discoveries from Leidy to Sue

North America became one of the world’s richest sources of dinosaur fossils through a sequence of local finds, museum expeditions and increasingly systematic fieldwork. The familiar story of famous rivals Edward Drinker Cope and Othniel Charles Marsh is only one part of it. Quarrymen, ranchers, Indigenous guides, preparators, students and regional institutions also shaped what was collected and what survived in museum drawers.

An early landmark came from Haddonfield, New Jersey. In 1858, William Parker Foulke investigated reports of large bones in a marl pit and helped recover a partial skeleton. Joseph Leidy studied and named it Hadrosaurus foulkii. The skeleton was incomplete, but it was among the first relatively substantial dinosaur skeletons recovered in North America. In 1868, a reconstruction of Hadrosaurus was mounted at Philadelphia’s Academy of Natural Sciences, giving the public a three-dimensional image of a dinosaur based on fossil evidence. The mount necessarily included inference because much of the animal was missing.

That distinction between a fossil and its reconstruction became central to public understanding. A mounted skeleton communicates scale and posture, but missing elements may be copied from related animals or sculpted from comparative anatomy. The surviving bones remain the primary evidence. This was already apparent in the nineteenth century, when artists and scientists had to decide how an incomplete animal might have looked.

The western surveys and the Bone Wars

After the American Civil War, geological surveys and railway expansion opened fossil-bearing lands in the West to scientific collecting. Cope and Marsh began as correspondents and colleagues, but their relationship turned bitter. From the late 1870s, they competed over new species, fossil localities, collectors and scientific priority. Their rivalry helped popularise dinosaurs and produced many descriptions, but it also encouraged haste, public attacks and destructive collecting practices.

The rivalry did not create North American palaeontology by itself. Field collectors such as Benjamin Mudge, William Harlow Reed and many others located and excavated fossils, often working under difficult conditions. Their letters and shipments show how much a named scientist depended on people who knew the terrain and could recognise promising rock. Fossils travelled east to universities and museums, where they were prepared and described. In some cases, competition led to quarry damage or deliberate removal of material before a rival could study it. The costs were real: damaged sites and poorly recorded context can never be fully restored.

Cope and Marsh’s expeditions were especially productive in formations such as the Jurassic Morrison Formation and Cretaceous deposits of the Great Plains. Their work brought animals such as Stegosaurus, Diplodocus and Allosaurus into scientific debate. The often repeated claim that one man “won” the Bone Wars oversimplifies a complicated record. Both made errors, both contributed important descriptions, and many specimens still require careful reassessment.

From spectacular quarries to broader evidence

Later field programmes widened the map and changed the pace of research. Large bonebeds, trackways and isolated specimens can each answer different questions. Dinosaur National Monument on the Utah–Colorado border preserves a quarry face crowded with fossil bones, while sites in Montana, Alberta and the Dakotas preserve rich Cretaceous faunas. A bonebed is not automatically a herd buried at one moment: sedimentology and the orientation, abrasion and condition of bones help determine how an accumulation formed.

Footprints contribute evidence where skeletons are rare. Trackways from the western United States and Canada record foot shape, stride and movement across ancient surfaces. They do not usually identify a species exactly, and a trackmaker’s speed estimate depends on assumptions about limb length and substrate. The preserved track is a direct trace; the animal’s name and behaviour are inferred.

In 1990, rancher and amateur fossil hunter Susan Hendrickson found the specimen known as Sue at a site near Faith, South Dakota. The nearly complete Tyrannosaurus rex skeleton became the subject of a legal dispute over land ownership and was eventually acquired for the Field Museum in Chicago. The case made clear that a scientific discovery also has a chain of custody: permission, land rights, documentation, preparation and public access all affect what happens next. Sue’s skeleton was prepared and studied for years before its public display in 2000.

Why collections are re-examined

North American museums contain fossils gathered over more than a century. New preparation, imaging and anatomical comparisons can revise old identifications or reveal details hidden by matrix. A specimen’s label may record a state or formation but omit the exact quarry, collector or circumstances of discovery. Researchers compare field notebooks, accession records and original publications to restore that context where possible.

Reassessment matters because early naming rules and comparative samples were limited. A dinosaur once described from a few bones may later be shown to overlap with another species, or a new skeleton may reveal that the group was more varied than scientists thought. These changes do not make early work useless. They show how hypotheses are tested against specimens that can be examined again.

Modern dinosaur fieldwork is more collaborative and more explicit about data management than many nineteenth-century expeditions. Teams record coordinates, stratigraphic position and three-dimensional relationships, and they deposit specimens in public research collections. The steps outlined in our fossil-study guide help explain why a careful field record can be as important as the bones themselves.

The history from Hadrosaurus to Sue is therefore not a straight march toward bigger skeletons. It is a story of changing methods, contested collecting, new institutions and corrections. The strongest account gives credit to the people who found and prepared fossils, distinguishes preserved anatomy from display reconstruction, and keeps each specimen tied to its geological and legal history.