This traditional view has been opposed in recent years by practitioners of a new field called Science and Technology Studies (STS), who claim that scientists are mistaken in thinking that their views are shaped mainly by objective evidence. They regard a notion such as "objectivity" as passé. Instead, they see nonscientific factors such as personal ambition, vested social interests, ideology, racism and sexism playing a major—or exclusive—role in molding scientific opinion. One branch of the STS movement aims to debunk the notion of a scientific "fact" altogether, claiming that these so-called "facts" are merely "constructs," and that they are not "discovered" but are "created" or constructed from what scientists agree upon as factual.

Now lest the reader too hastily dismiss this "constructivist" claim, let me point out that some scientific episodes do raise doubts about scientific objectivity and rationality. One major incident occurred at Carnegie Museum of Natural History.

From 1934 to 1979, the museum displayed one of its prize dinosaur specimens with the wrong head, an incident as potentially shocking as if a horse skeleton were to be topped with a giraffe’s skull. During those 45 years the museum’s great Apatosaurus louisae was displayed with a head that is now regarded as belonging to Camarasaurus—a very different sort of dinosaur. This error supports the constructivist view. For 45 years Carnegie Museum of Natural History, and the world, believed in a creature that never existed. Of course, we now know that the Apatosaurus that was accepted for 45 years was a construct, a figment of scientific imagination. But if this could happen at one of the world’s great natural history museums, and, even worse, be accepted by the whole paleontological community, who is to say that the world’s museums are not still full of such chimeras? Let’s look more closely at just how Apatosaurus got the wrong head.

The late 19th and early 20th centuries are appropriately called the "heroic age" of vertebrate paleontology. Great discoveries were announced regularly, and vertebrate paleontology was an exciting adventure. In the American West, range wars threatened to erupt as heavily armed fossil hunters staked out their prize fossil beds. This spirit of fierce competition was reflected by the museums that sponsored the fossil hunts and by the wealthy patrons who funded the museums.

In November of 1898 Andrew Carnegie was interested to read that the fossil remains of a dinosaur regarded as the "world’s most colossal animal" had been discovered by a collector for the University of Wyoming at Laramie. Carnegie sent a note and the newspaper clipping to W.H. Holland, director of Carnegie Museum of Natural History, instructing Holland to buy the dinosaur for his museum. But no such specimen existed; the University of Wyoming’s collector had concealed the fact that he had found only a single leg bone. In 1899 Carnegie therefore commissioned an expedition to find an appropriately massive dinosaur.

Amazingly, on July 4 of that same year the expedition discovered the rarest of paleontological finds—an almost complete skeleton of an enormous sauropod dinosaur, which the curator, J.B. Hatcher, named Diplodocus carnegii after their benefactor. Carnegie was so delighted at the discovery that he funded further expeditions, and within a few years a rich fossil site had been located near Vernal, Utah. Named Carnegie Quarry, it was excavated for many years by the museum’s fine field paleontologist Earl Douglass. The quarry soon yielded a dinosaur even more massive than Diplodocus—the huge Apatosaurus louisae, named for Carnegie’s wife, Louise. These two magnificent specimens now dominate the Dinosaur Hall in Carnegie Museum of Natural History.

The problem with Apatosaurus was that no skull was found connected to the end of the neck. A Diplodocus-like skull, however, was found nearby. Might this skull, catalogued as CM 11162, be the skull of Apatosaurus? Both Holland and Douglass suspected that it might be. But the weight of scientific opinion was against them.

CM 11162 was small, not much larger than a horse’s head, and it had feeble, peg-like teeth. How could such a structure suffice to feed a giant like Apatosaurus? It was not known until much later that these sauropods ground their food in a gizzard, like birds do today. The weak teeth only had to rake in the food, not chew it. More importantly, paleontologists came to regard Apatosaurus as closer in overall structure to the larger-headed Camarasaurus than to Diplodocus. The skull found close to the Carnegie’s Apatosaurus looked decidedly like a Diplodocus skull.

Nevertheless, Holland insisted that CM 11162 was the skull of Apatosaurus. He defended his view in an address to the Paleontological Society of America in December 1914, but he left the mounted skeleton of Apatosaurus headless. Why didn’t Holland attach a cast of CM 11162 if he thought it was the right one? Some have suggested that Holland wanted to avoid conflict with Henry Fairfield Osborn, head of the American Museum of Natural History, who had dared Holland to mount the Diplodocus-like skull. Holland, though, was not afraid of controversy. On the contrary, he was a skilled polemicist who could devastate opponents with a combination of biting sarcasm and airtight logic.

A more likely explanation is that Earl Douglass continued to make spectacular discoveries at Carnegie Quarry, and as long as Douglass’ excavations continued, there was a chance that he would find an Apatosaurus neck with the skull attached. Such a find, of course, would settle the dispute once and for all. But a skeleton of Apatosaurus with the skull in place was never found. In 1934, after Holland’s death, the cast of a skull was placed on the headless Apatosaurus—not CM 11162, but the skull that is now regarded as that of a Camarasaurus.

Why was the cast of the Camarasaurus skull attached and who was responsible for the decision? My research has failed to disclose an answer to the latter question. Andrey Avinoff, director of Carnegie Museum in 1934, says in his monthly report for May of that year only that the cast of the skull "was mounted." Records do not show who made the decision. However, it is possible to speculate on what motivated the decision. In 1934, noted paleontologist C.W. Gilmore came to the Carnegie to study the skeleton of Apatosaurus. Gilmore did not endorse the Camarasaurus head, but he did assert that Holland had been wrong in regarding CM 11162 as the correct skull. Further, the bulk of paleontological opinion still favored an affinity between Apatosaurus and Camarasaurus.

Probably, though, the strongest motivation for the decision to mount the Camarasaurus head was not strictly scientific. The display of a headless Apatosaurus no doubt had been a perennial source of embarrassment to the museum. Unlike the Venus de Milo, Apatosaurus did not gain charm by being displayed with parts missing. The Camarasaurus skull, meanwhile, was most impressive. It was massive with big, strong teeth, an appropriate skull for a monster like Apatosaurus. Thus, the decision was likely motivated by a desire to impress the public.

So the Camarasaurus skull remained on Apatosaurus louisae until the 1970s, when Apatosaurus attracted the attention of J.S. McIntosh, the world’s leading expert on sauropod dinosaurs. He reexamined all the evidence, including the letters written by Earl Douglass describing his discoveries at the Carnegie Quarry. McIntosh came to the conclusion that CM 11162, the Diplodocus-like skull favored by Holland, was in fact the correct skull of Apatosaurus.

In 1978 McIntosh and Carnegie Museum paleontologist David Berman co-authored the definitive monograph establishing that Apatosaurus did indeed have a Diplodocus-like skull. By thoroughly examining the postcranial anatomy of Apatosaurus and Diplodocus, Berman and McIntosh showed that Apatosaurus bore a much greater anatomical affinity to Diplodocus than to Camarasaurus. They also argued that CM 11162 had just the sort of modifications of the Diplodocus skull design that one would expect to find in a more massive creature such as Apatosaurus. Further, they included a detailed historical account of the Apatosaurus discoveries, showing that various mistakes and confusions had led to the incorrect belief that Apatosaurus was similar to Camarasaurus. Their argument quickly convinced the paleontological community.

Carnegie Museum of Natural History agreed, and on October 20, 1979, a ceremony was held in which the wrong skull was removed and a cast of CM 11162 was attached. CM 11162 itself, the most complete Apatosaurus skull ever found, was too precious to be mounted and rests in a display case in Dinosaur Hall. That is how Apatosaurus finally got the right head, or perhaps we should say it finally got the head we now think is right.

When Carnegie Museum changed the head on its type specimen, which is the scientific example against which all other members of the species must be compared, other natural history museums were forced to change the heads on their own displays of Apatosaurus.

What lessons can we draw about the nature of science from the infamous Wrongheaded Dinosaur Incident? It is clear that science does not always proceed in a completely rational manner. Social influences certainly play a role, maybe even a larger role than most rationalists would like to admit. Nevertheless, reason and evidence, the traditional "scientific" factors, also molded and shaped every step of our story. The desire to impress the public and end the embarrassment of a headless Apatosaurus may have motivated the decision in 1934 to mount the Camarasaurus head. However, at the time the weight of scientific opinion, including that of leading authorities, did not oppose such a mounting. Further, just as rationalists expect, over the long run (45 years in this case) the evidence did win out. Berman and McIntosh’s study finally produced the conclusive evidence and argument that, for the paleontological community, placed the issue beyond controversy.

Science is complex and multifaceted, a process not reducible to any stereotype. Like all human endeavors, science is subject to social influences at every level.But to a greater degree than the vast majority of human enterprises, science uses objective methods and standards that limit the effects of bias and elevate scientific hypotheses to a high level of reliability. The best established scientific claims—that blood circulates, that germs cause disease, that evolution has occurred, that atoms can be split, that DNA is the genetic material and that the universe is expanding—should not be called "constructs." To attempt to debunk these great discoveries, among the crowning glories of human achievement, is to demean reason and ultimately humanity itself.

Keith M. Parsons investigated the wrongheaded dinosaur incident while completing a Ph.D. in the Department of History and Philosophy of Science at the University of Pittsburgh. Parsons is a Carnegie Museum of Natural History research associate.