How Many Dinosaurs Remain Undiscovered?

Paleontologists are uncovering new dinosaurs at an astonishing rate. On average, a new species of “terrible lizard” is named about every two weeks from fossil sites all over the world. And as experts announce each astonishing species, the nature of the dinosaur family tree shifts. Fossil hunters are not just uncovering new dinosaur species—they’re revealing entirely new dinosaur groups that were unknown even ten years ago.

“One of my go-to lines whenever I’m giving a public talk or writing a pop science article or book,” says University of Edinburgh paleontologist Stephen Brusatte, “is that we’re in the golden age of paleontology.”

While the 19th-century “Bone Wars” are widely known as when many dinosaurs were discovered and named, the early 21st century is seeing the greatest dinosaur bone rush of all time. Paleontologists are rapidly documenting various non-avian dinosaurs that roamed our planet between 66 million and 235 million years ago—a span of time more than two and a half times as long as the post-Cretaceous history of our planet. And experts hypothesize that more dinosaurs remain unknown than have been uncovered.

“Not all of these new dinosaurs are just another flavor of sauropod or stegosaur, not just another type of tyrannosaur that differs from other tyrannosaurs by a tiny bump on its snout or an extra tooth,” Brusatte says. Some represent entire groups of dinosaurs paleontologists didn’t know about and can alter the big picture of how dinosaur evolution unfolded through the Triassic, Jurassic and Cretaceous Periods.

Earlier this month, paleontologists named Iani, a new dinosaur from Utah, which belonged to a group called rhabdodontomorphs that was only recognized in 2016. The following week, a different group of experts named another beaked dinosaur called Gonkoken from Chile that represents a previously unknown offshoot of dinosaurs that convergently evolved some of the same features as the famous duck-billed dinosaurs. And just last year, experts announced a dinosaur named Jakapil from Argentina that could either be a form of early armored dinosaur or be from a new group entirely.

“Of course there are more groups out there,” says New York Institute of Technology paleontologist Karen Poole.

Paleontologists often stress the incompleteness of the fossil record. Geologists have known since the late 19th century that the world’s fossil-bearing rocks represent a discontinuous fraction of the various environments that have come and gone through time. Places like dune-filled deserts, floodplains and sea bottoms where sediment accumulated are preserved, but mountains and other environments have eroded away and been erased from the record.

And even within those ancient environments, most life-forms never made it into the fossil record. They were either consumed, decayed or otherwise broken down. The vast majority of organisms that have lived on the planet didn’t stand a chance of becoming fossils.

Yet paleontologists make new discoveries every year. Even against the geological odds, in many places dinosaurs were covered over quickly enough to be tucked into the rock. Every geological formation of the right age and type has the potential to contain an entire menagerie of unseen dinosaurs, from small to large to enormous. A 2006 study estimated that paleontologists had found less than 30 percent of all non-avian dinosaurs and that bumping the count up to 90 percent would take over a century of exploration.

“I like to wonder about dinosaurs that lived in mountains or uplands,” Poole says. The dinosaurs that lived in those habitats probably didn’t make it into the fossil record unless they traveled to a different habitat or, for example, were washed down a mountain stream to a lowland environment like a floodplain where preservation was more likely. But the elevated environments probably required different adaptations and behaviors, just as today you’ll find different species of deer or elk depending on elevation and what plants grow where. “While animals in these areas may have had lowland relatives, it’s quite possible there were small clades specialized to environments where they were unlikely to become fossils,” Poole says.

Future finds are likely to be of small dinosaurs. Big dinosaurs were often found first because their remains were more resilient to scavenging, weathering and destruction than those of smaller animals, and museums liked having large, impressive dinosaurs to reconstruct for patrons. Small species were harder to find and often overlooked when they were uncovered. Now that paleontologists are making a concentrated effort to fill in entire ecosystems, however, they’re discovering some of those smaller dinosaurs and filling in parts of the dinosaur story that were previously missed—even in formations that have been explored for more than a century. In 2019, paleontologists named a new, raptor-like dinosaur called Hesperornithoides from the Jurassic Morrison Formation, a group of rocks in the western United States that paleontologists have been picking over since the 1800s.

The new discoveries don’t always fit neatly into our existing picture of dinosaur relationships. Paleontologists have reshuffled and refined the dinosaur family tree multiple times, sometimes finding that what looked like a familiar animal actually represents an entirely new group with its own evolutionary history. In 1970, paleontologists named the giant dinosaur Deinocheirus from a set of massive arms. The rest of the body was missing, leading to broad speculation on the animal’s appearance and relationships. Only in 2014 did paleontologists reveal the rest of the animal—it had a shovel-beak and sail-back and belonged to its own evolutionary group called the Deinocheiridae.

Searching the rocks is only part of the required effort. Sometimes paleontologists know they’ve uncovered something new right away, but just as often discoveries are made in museum collections or through examining previously known fossils. “There are bound to be dinosaurs we don’t know about,” Poole says, “and some we may still find, either through new fossils or new analyses of what we already know.”

The numbers may be even greater than what paleontologists previously expected. “Today, about 14,000 dinosaur species live on as birds,” Brusatte says. “Do the math and we’re probably talking about millions of dinosaur species that once lived, maybe tens of millions.”

“So head out to the rocks, wherever they are,” he says, for “dragons be there.”

Image Credits:  Connor Ashbridge via Wikipedia under CC By-SA 4.0 / FunkMonk (Michael B.H.) via Wikipedia under CC By-SA 3.0 / Arsdraco via Wikipedia under CC By-SA 4.0 / Jorge Gonzalez