The question at the heart of a long-standing paleontological mystery solved Wednesday reads like the premise of a Dan Brown novel: How could a 1800s hermit, fossilized footprints collected in the 1950s, and a modern-day North Carolina museum curator change what we know about the ancient world? In a paper in Palaeontologica Africana, researchers who solved the mystery say it all hinges on the existence of a group of early mammal relatives called dicynodonts.

Dicynodonts were assumed to be extinct by the Late Triassic Period, the time when dinosaurs proliferated throuhgout Earth. But Christian Kammerer, Ph.D., paleontology curator at the North Carolina Museum of Natural Sciences, explained in his article that in the 1950s, the discovery of short-toed, five-fingered footprints alongside dinosaur tracks in southern Africa suggested that there was at least one late-surviving, vegetarian “phantom” dicynodont that lived during the Late Triassic. He has solved the mystery of that phantom, using data from a new analysis of old fossils.

“For several years now, there has been increasing evidence that the ‘traditional’ timescale for Triassic animals was wrong,” Kammerer tells Inverse. “New discoveries of synapsids, like my new paper, have been found in younger-than-expected strata, pulling them well into the Late Triassic.”

A skeleton of the dicynodont Placerias, a close relative of the newly-discovered Pentasaurus. Christian Kammerer

Old assumptions about when the dicynodonts lived were thrown out the window when Kammerer examined fossils collected by a reclusive, amateur paleontologist named Alfred Brown who lived in the late 1800s. His analysis revealed that dicynodonts actually did live alongside dinosaurs in southern Africa at least 200 million years ago.

When the phantom footprints were first found 50 years ago, scientists hesitated to confirm that they were truly made by dicynodonts until fossils of the animals that made the footprints were found. What they didn’t realize was that Brown had already sent dicynodont fossils to the Natural History Museum in Vienna in 1876, which had archived the fossils away without much thought.

Decades later, when Kammerer examined Brown’s collections in Vienna, he immediately noticed dicynodont jaw and arm bones among the box of ‘dinosaur’ fossils. Moving through the bones, he discovered parts of a skull, limbs, and a spinal column — the first skeletal evidence of a dicynodont found from the Late Triassic in South Africa. These fossils made up a new taxon of dicynodonts, newly named Pentasurus goggai.

Dicynodont mandibles in anteroventral view. Christian Kammerer

Dicynodonts appeared 260 million years ago, roaming Earth before the dinosaurs. The protomammals were more closely related to mammals than they were reptiles, but they were not true mammals. With tusks and turtle-like beaks, the abundant vertebrates are part of a group of animals called synapsids that include mammals and creatures with mammalian characteristics. Today, terrestrial vertebrates that produce eggs that contain an embryo surrounded by extra-embryonic membranes are descended either from the lines Synapsida or Reptilia, lineages that both descend from a common ancestor.

“This work is part of the broader question of the changing fortunes of the mammal and reptile lineages in the Triassic,” explains Kammerer. “The mammal lineage [synapsids] were the dominant land animals in the Permian Period, prior to the Triassic. In the Jurassic and Cretaceous, later in the Mesozoic, the reptile lineage was dominant, most notably in the form of dinosaurs.”

It’s been thought that the transition between these fauna occurred during the Triassic, with plant-eating dinosaurs taking over for large-bodied herbivores like the dicynodonts. Now, there is direct evidence that these two groups of Triassic herbivores coexisted, with long-necked sauropods competing for the same ecological niche as the Bulbasuar-looking protomammals.