The specimen sat in alcohol at the bottom of an opaque plastic container. Its luxuriant black fur was dark and matted, its characteristic tail curled. David Fernandez peered at the odd-looking critter, which he’d spent the better part of the past year trying to track down, and hoped it was the real thing.
Fernandez had worked on Bioko Island in Equatorial Guinea for 14 years, but he’d never seen one of these animals in its entirety before. No scientist ever had.
He lifted the specimen out of its container and snapped a photo with his phone. Then he texted the image to his colleague Erik Seiffert, one of the few people in the world who would recognise the creature.
“I think he was even more excited than I was,” Fernandez recalls. “It was amazing, the first entire specimen available for us, and for science basically.”
Zenkerella insignis, the critter caught on Bioko, is one of the world’s most ancient and mysterious mammals. Until now, it was known only by its fossils and 11 scattered specimens, many of which had been languishing in natural history collections for more than 100 years. Researchers who were interested in the species (and there aren’t many) had little to go on aside from a hind limb here, a few teeth there. No scientist in history has seen it alive.
But, in a study published last week in the journal PeerJ, Fernandez, Seiffert and their colleagues describe the capture of three freshly killed Z. insignis specimens. The discovery means that, for the first time, scientists were able to examine the genome of one of the bizarre mammals, and finally figure out where Zenkerella fits in our evolutionary family tree.
Members of the Zenkerella genus are creatures of another world, “living fossils” that have evolved very little over the past 49 million years. For context, they’re only about 15 million years younger than the dinosaurs, and some 35 million years older than the oldest great apes. When they first arose, Australia was still connected to Antarctica, and the Himalayas didn’t even exist.
“It’s a long lineage that stretches all the way back 50 million years, and we only have one species left that we don’t know anything about,” Seiffert said. “We don’t know when it is active, or what it eats, or if it spends all of its time in the trees or on the ground.”
That’s pretty much unprecedented for mammals, which are among the best-researched taxonomic classes of creatures.
Much of what is known about the Zenkerella genus comes from the fossil record, which is how Seiffert, a palaeontologist at University of Southern California, became one of the world’s only specialists on the creatures. Fifteen years ago, while working on a dig in Egypt, he and his colleagues uncovered the fossilised remains of a now extinct Zenkerella cousin. Examining the arm and leg bones of the 37-million-year old creature, he realised, “we know more about this species than we know about something that is alive today running around in the forest”.
Seiffert was certain that the living Zenkerellas could tell scientists a great deal about rodent evolution, not to mention the changes that have taken place in Africa in the past 50 million years. But first, he would have to find one.
So he reached out to Fernandez, who was then the director of a wildlife centre run by the Bioko Biodiversity Protection Program. Fernandez is a conservation biologist and lecturer at the University of the West of England, but he’d never even heard of Zenkerella before. When he spoke to friends and colleagues in the community, most of them hadn’t heard of it either.
But Seiffert told him that Zenkerella specimens had been spotted on Bioko before, so Fernandez showed his neighbours a picture of the funny little creature and asked them to keep an eye out for it. Most of the island’s residents are subsistence hunters, and it seemed likely that, eventually, someone would catch a Zenkerella in one of their traps.
Weeks passed. Then months. Finally, almost a year after he made his initial request, Fernandez got a call from a colleague. “They said, ‘We got one of your guys,'” he recalled. “I took a look, and it was one of them.”
The living Zenkerella looks almost like the reconstructions of its long-dead ancestors envisioned by palaeontologists. It is a squirrel-y creature with fluffy black fur, including a fluffy tail. But beneath all that hair, the base of the tail is covered in scales.
It lacks the parachute-like membrane found in its close cousins, the “gliders” Anomalure (also known as scaly tailed squirrels) andIdiurus, leading scientists to wonder whether Zenkerella had somehow lost its ability to fly during its evolution.
“Which would be strange because it would be the loss of a complex anatomical adaptation,” Seiffert says.
But he and his colleagues determined that Zenkerella is actually a member of a separate taxonomic family, indicating that the flight membrane evolved after the group branched off into its own lineage. The finding supports a growing consensus that advanced adaptations such as flying, swimming and gliding, once acquired, are unlikely to be reversed over the course of evolution.
Indeed, Zenkerella is the ultimate survivor. Of the 5400 mammal species known to science, only it and five others are the sole surviving members of ancient lineages. Even among that select group, Zenkerella’s living fossil status makes it almost unique. But it is the least studied of all these ancient creatures.
That’s bad news for Zenkerella, whose habitat in Central Africa is under threat from deforestation and development. Since scientists have never seen the animal alive in the wild, they’re not entirely sure where they live, or how many of them there are left. The utter lack of information has led the International Union for Conservation of Nature to designate Z. insignis a “species of least concern”.
“These small obscure animals, they’re not getting the attention they would actually need to confirm their distribution,” Seiffert said. We don’t know for certain that Zenkerella is threatened, but we don’t know that it isn’t, either. “When more work is done, we could easily find that is the case.”
For now, Seiffert, Fernandez and their colleagues are hoping to sequence the genome of their three specimens to understand the genetic roots of their strange and ancient traits. They’re analysing the animals’ gut contents, which will help researchers understand what they eat and hopefully track down where they live. After all those years looking at fossils, Seiffert holds out hope that he might yet see a Zenkerella in action, a living ghost of the ancient world.
“It really is one of those pretty incredible examples of discovery,” Seiffert says, “and a sign of the kinds of discoveries that can still be made.”