n 1858, 
a collection of large bones was found in a field in southeastern New Jersey. Today the site is lost within the unremarkable sprawl of suburban residences, and there is an easy-to-miss plaque that commemorates a 78-million-year-old Cretaceous herbivore called the Hadrosaurus foulkii. Unless you’re a hardcore dinosaur aficionado or a paleontologist by profession, most likely you have never heard of the Hadrosaurus, but this dinosaur is more significant to science than the immediately recognizable Tyrannosaurus rex.

The way we imagine dinosaurs has evolved over the three centuries since their discovery. It’s an evolution characterized by the forces of fame, for the animals that rivet the public’s imagination are not the ones that yield the most interesting information about ancient biology. Stars such as T. rex, Stegosaurus, and the Triceratops bask in the glory of public attention while little known dinosaurs such as Hadrosaurus, Deinonychus, Maiasaurua and other unsung species do the heavy lifting of scientific revelation.

The injustice of fame is a common trope in science, but the history of paleontology provides a particularly vivid example, for it is an unusually harsh jury that decides which dinosaurs get memorialized in popular culture. Fond memories of museum trips and sandbox battles between plastic effigies of dinosaurian champions linger long past the “dinosaur phase” of many children. Even as scientists try to retire the “Brontosaurus” from the canon—because 19th-century confusion resulted in too many dinosaurs named from too few bones—it is still beloved by many, a sign of how hard it is to shake the public’s devotion to these creatures.

That devotion stretches back to the 18th century, when European naturalists recognized the curious bones found in mining pits and countryside rock outcrops as the clues to a past that predated humans. The first guesses as to the size and shape of the owners of these bones conjured up visions of creatures both stupendous and preposterous.

Dinosaurs were first imagined as relatives of fire-breathing dragons, then as the ancestors of lizards who swept their gigantic tails as they slithered along the ground. They were also portrayed as slothful crocodiles that spent the days in the sun trying to move the needle on their naturally cold-blooded body temperature. As more fossils were discovered over the course of next two centuries, new light was shed on the dimensions of these creatures, as well as the texture of their outer coat (scaly, armored, or even fuzzy), whether they were meat-eaters or plant-munchers, their reproductive habits, whether they lived in packs or alone, and why some went extinct and others evolved into birds.

In the late 19th and early 20th centuries, several dinosaurs, including T. rex, Triceratops, Stegosaurus, and a handful of others, emerged as the celebrity faces of all the species. And while these stars are fixed in the public eye, they are not immutable. How we imagine them is periodically updated and revised thanks to the ongoing paleontological finds that continue to reveal new species. They are paraded around at conferences, receive long Latinate names, and even get their 15 minutes of fame in media headlines. But many dinosaur species fail to exert any real staying power on the public imagination and pass into obscurity while the valuable information they provide serves to refine and deepen our knowledge of all dinosaur species. We take information gleaned from newly discovered species and slap it back on dinosaurs we know and cherish. It’s a boon to the brand name dinosaurs that receive regular makeovers that help them stay relevant.

Stars such as T. rex, Stegosaurus, and the Triceratops bask in the glory of public attention while little known dinosaurs do the heavy lifting of scientific revelation.

Such is the trajectory of Tyrannosaurus rex, literally the “King of the Tyrant Lizards,” which was first described on the basis of an incomplete specimen found in Montana in the early 20th century. Henry Fairfield Osborn, a curator at the American Museum of Natural History (AMNH), named the massive carnivore in 1905. The following year, the museum began to construct the mounted skeleton that still draws visitors to the fourth floor exhibits. When only the legs of the enormous theropod were erected, The New York Times proclaimed T. rex the “prize-fighter of antiquity,” and wrote that the hundreds of thousands of schoolchildren who poured into the museum would now have “a larger outlook into the future of a world that has such a past.” T. rex became a bridge to the past.

And the reign of T. rex has continued unabated. In 1937, the doors of the Dinosaur Park in Rapid City, South Dakota were opened as part of a New Deal initiative. An 80-foot plastic model that took 14 men 15 months to construct looked down on tens of thousands of visitors just in the first year. Today the park sees upwards of 120,000 per year. In an article about the park’s opening, The New York Times ran pictures of the star dinosaurs that were on display, showing a striking difference to how we see them today and underscoring how much our image of the dinosaur evolved in the past seven decades.

But even with two relatively complete skeletons collected for the AMNH by professional fossil hunter Barnum Brown, the details of what T. rex was truly like eluded experts. Contributions from the British anatomist Richard Owen (who coined the term “dinosaur” in 1842) established a set of characteristics that differed drastically from those that had come before. Naturalists had previously compared the bits of broken jaw or teeth and noted their close match to those of crocodiles. A 1 to 1 proportion ratio from the teeth to the body projected an impressively large lizard of more than 100 feet who dragged its enormous torso along the ground. Owen revised the image of the giant lizard and cut the size of dinosaur down to about 40 feet long. He envisioned a creature that had the hide of scaly reptiles but an upright posture like that of a rhinoceros or an elephant. But even Owen’s conception of dinosaurian nature was not to last.

It was displaced by the discovery of Hadrosaurus, that little-feted New Jersey native. This creature was significant because, unlike dinosaur specimens found in Europe, the recovered bits of backbone, limbs, hip, and skull came from a single individual. With the full skeleton, experts were able to see that the forelimbs of the dinosaur were significantly shorter than the hind limbs. So instead of resembling a giant crocodile, scientists understood that dinosaurs must have stood up, balancing on their hind limbs.

Owen revised the image of the giant lizard and cut the size of dinosaur down to about 40 feet long.

The Philadelphia naturalist and polymath Joseph Leidy, who named the Hadrosaurus, noted that, “this great herbivorous Lizard sustained itself in a semi-erect position… while it browsed on plants.” To Leidy, Hadrosaurus was less a reptilian rhino and more like a kangaroo., The image of the dinosaur became that of an active creature who stood upright instead of slithering on the ground. The skeleton of the Hadrosaurus helped to create a more up-to-date model of the dinosaurs. The English artist and sculptor Benjamin Waterhouse Hawkins constructed a version for Philadelphia’s Academy of Natural Sciences that stood about 30 feet in length.

Just as the Hadrosaurus helped establish a dinosaur posture different from what naturalists had previously suspected, another little-known species helped scientists determine whether dinosaurs were warm- or cold-blooded.  The 19th-century comparison of dinosaurs to iguanas and crocodiles led naturalists to assume that they were cold-blooded creatures. However, in the late 19th century, the discovery of an agile raptor, Laelaps anquilunguis, later renamed the Dryptosaurus, showed a dinosaur that was a ripping, tearing predator who moved about swiftly on two legs. The agility of this carnivore strengthened the argument for warm-blooded dinosaurs. It also planted the idea that not all dinosaurs went extinct and that some may have evolved into birds. 

The discovery of another fossil—a whole a century later—sparked the idea that dinosaurs were warm-blooded. The 11-foot long, switchblade-clawed Deinonychus antirrhopus, named in 1969, was pieced together from the bones of multiple individuals found in a Montana quarry along with a beaked herbivore that seemed to have been slaughtered. Based on their being found together, Yale paleontologist John Ostrom speculated that Deinonychus was a pack hunter that slashed at victims with swift motions of a frightening foot claw. Disemboweling looked to be his preferred mode of dispatch. In his description of Deinonychus, Ostrom emphasized the animal’s fierceness. “When all these features are considered together,” Ostrom wrote, “we have a rather convincing picture, I think, of Deinonychus as an active and very agile predator.” There was little doubt at that point that the dinosaur’s rate of metabolism was high. And as Ostrom continued his investigations, he realized that the formidable Deinonychus resembled a larger version of another animal—the first bird, Archaeopteryx. Dinosaurs, Ostrom proposed, did not go totally extinct. If birds evolved from dinosaurs like Deinonychus, then dinosaurs survived.

The discovery of the Deinonychus helped spur the “Dinosaur Renaissance” of the 1970s and ’80s. Dinosaurs suddenly became a subject of respectable scientific interest again and the new facts trickled back to revise the public’s image of the celebrity creatures. In Steven Spielberg’s 1993 blockbuster Jurassic Park, famous dinosaurs vividly flaunt their newly acquired characteristics. The Brachiosaurus stopped sunning in the Jurassic mornings to warm up and became a proud herbivore that strutted over floodplains to show off its elegant neck. Tyrannosauraus became a super-charged predator that terrified audiences. Large, hulking reptiles were replaced by active, bird-like animals that were far more complex than believed earlier.

Dinosaurs, Ostrom proposed, did not go totally extinct. If birds evolved from dinosaurs like Deinonychus, then dinosaurs survived.

Part of the complexity lay in dinosaurs’ family structure. Before the Dinosaur Renaissance researchers believed that dinosaur parents provided almost no care at all to their offspring. Another fossil find in 1979 in Montana challenged that narrative, spurring paleontologists Jack Horner and Robert Makela to discover entire nesting grounds where there were bones of adults as well as hatchlings. They concluded that at least one parent must have been looking after the babies and bringing food for them to eat and that the young were staying within the nest for some time after hatching. Researchers could no longer just assume that dinosaurs laid eggs and walked away from them. This dinosaur, dubbed Maiasaura, was an argument in favor of more intriguing—and caring—animals than had ever been suspected. Horner and Makela named her the “caring mother lizard,” and this raised the possibility that other species, like the Stegosaurus and Triceratops, partook in prolonged parental care.

But the latest, and greatest, alteration to our understanding of what dinosaurs were like came from a critter much smaller than either Deinonychus or Maiasaura. A theropod dinosaur, a distant and smaller cousin of T. rex and Deinonychus, Sinosauropteryx stood barely a foot off the ground. What made this creature fascinating was what covered its tiny frame. Instead of scales, its coat was a mane of filamentous feathers running along its back.

When paleontologists Philip Currie and Chen Peiji showed off a snapshot of Sinosauropteryx at a meeting in 1996 of the Society of Vertebrate Paleontology, their colleagues were astounded. Yale’s Ostrom, who had long argued for bird-like dinosaurs on the basis of his own Deinonychus find as well as other discoveries, told The New York Times that a photo put him “in a state of shock.” At long last, the crucial soft tissue connection between dinosaurs and birds had been discovered. To bastardize an Emily Dickinson quote, researchers had found that dinosaurs are the things with feathers.

What made this creature fascinating was what covered its tiny frame. Instead of scales, its coat was a mane of filamentous feathers running along its back.

The Sinosauropteryx was just the first of dozens of feathery fossils to be found in China. Together, these dinosaurs confirm that birds truly are dinosaurs, and that feathers were a feature shared among many dinosaur lineages. The 2012 announcement of a 30-foot-long tyrannosaur covered in fuzz, named Yutyrannus, has even raised the distinct possibility that our cherished T. rex bore a fuzzy coat. This would mean a heady revision of how dinosaurs looked and what end they may have met.

Imagine the next Jurassic Park with an angry T. rex covered in feathers lunging at the tiny terrified humans. How we see dinosaurs will keep changing for as long as we study them, and lesser-known species will undoubtedly be at the heart of whatever major transmutations to dinosaur imagery come next.

Just how drastically our most favorite dinosaurs will be changed by unsung species is an open-ended question. We haven’t even found most dinosaurs yet. One 2006 estimate proposed that there may have been about 1,850 different types during their Triassic to Cretaceous heyday—a run of about 245 to 66 million years ago. If that’s so, then the 500 or so genera named so far mark the start of our paleontological discoveries and might mean more changes for famous and beloved icons such as the T. rex. Dinosaurs are anything but set in stone.

Brian Switek dressed up as a stegosaurus when he was 5. He is the author of My Beloved Brontosaurus