If you want to spoil budding paleontologists, says Alexander Kellner, co-curator of the new Pterosaurs exhibition, send them on their first dig to the Romualdo Formation in the Araripe Basin, in northeastern Brazil.
In the Romualdo (like all of the Araripe Basin), says Kellner, “You always find fossils! It’s amazing.”
Many are beautifully preserved, immediately recognizable as the animals they once were. The fossils are also of particular geological interest because they date from a time—110 million years ago—when the continents weren’t in the same positions as they are today. South America was only starting to split off from Africa, and a north-south seaway may have run down through today’s Brazil, including through the Romualdo. So the fossils form a snapshot of a vanished assemblage of animals in an ever-changing world.
A diorama in the Pterosaurs exhibition brings to life a scene from the Romualdo Formation from that time—a time when pterosaurs ruled the skies and hunted for fish along an ancient coast.
Life-size models of large, crested pterosaurs, Thalassodromeus sethi, swoop over a lagoon, hunting schools of the unsuspecting fishes in the water below. Underwater, schools of Rhacolepsis fish are being chased by a predatory 3-foot-long Cladocyclus. In the background, spinosaurid dinosaurs walk amid trees called Brachyphyllum, which paleontologists know were part of the ecosystem at the time.
This early Cretaceous scene is “definitely a plausible scenario,” says John Maisey, curator in the Division of Paleontology, who studied the fossil fishes of the Araripe for decades.
“These fossils are world-famous,” he says, because they are often so well-preserved, sometimes including soft tissue, muscles, and blood vessels. Why? For one thing, says Maisey, the animals may have fossilized very quickly. Instead of being scavenged, perhaps they sank quickly to the bottom of the water, getting stuck in what Maisey calls, evocatively, a low-oxygen “algal goo.” There, bacteria may have eaten through the tissue, afterward excreting phosphates that, in effect, created a 3D model of what was there before—hence the beautiful preservation. “It’s like a 3D printer, using bacteria,” says Maisey.
The Pterosaurs exhibition includes a remarkably well-preserved fish fossil that visitors can touch: Vinctifer comptoni, a filter-feeding fish from about 110 million years ago that was one of the most common fossil fishes in the Romualdo Formation. Find it on the right side of the Romualdo Formation diorama—you can even feel its scales!
Visit the Pterosaurs exhibition, then see more fish fossils from the Santana Formation (also known as the Araripe Basin) on display in the Museum’s Hall of Vertebrate Origins.
A version of this story appears in the Spring 2014 issue of Rotunda, the Member magazine.