UWE scientist discovers new specimens of 'living fossil', shedding new insights into evolution of scaly-tailed squirrels

Issue date: 16 August 2016

an image of a skeleton of a scaly-tailed squirrel (Zenkerella insignis)

A conservation biologist from the University of the West of England (UWE Bristol) has secured three specimens of the very rare and elusive flightless scaly-tailed squirrel (Zenkerella insignis), uniquely found in the forests of Cameroon, Gabon, C.A.R and Bioko Island, Equatorial Guinea that has barely evolved for over 30 million years.

The 'find' has enabled an international team of scientists led by Dr Erik Seiffert from the University of Southern California to conduct the first genetic and anatomical study of Zenkerella, giving new insights into the evolution of gliding within Anomaluridae, a group of mammals endemic to Africa and characterised by the presence of a 'patagium', a skin flap that extends from the arms to the legs that allows them to glide among the forest canopy. Zenkerella is the only member of this group of animals that lack this skin flap, and thus is unable to glide.

The flightless scaly-tailed squirrel has been determined by the scientists to be a 'living fossil' based on the fact that it has hardly changed for over 30 million years. Other mammals considered also as living fossils include the pen-tailed tree shrew of Southeast Asia and the marsupial monito del monte of South America. Seiffert noted that, “It is remarkable that there are still mammals out there that scientists have never seen alive, and in the case of Zenkerella this is particularly surprising because it is so unique in terms of its genetics, anatomy, and strange evolutionary history.”

These findings have been published today in PeerJ

Dr David Fernández, lecturer in Conservation Science, from UWE Bristol said, “As a comparison, humans and chimpanzees split between 6 and 8 million years ago, and all anthropoid primates, that is, all monkeys such as baboons and squirrel monkeys; and apes, which includes humans, chimpanzees and gorillas, evolved from a common ancestor that lived between 35 and 45 million years ago.

“For such a little creature to have remained unchanged for such an incredibly long time is quite extraordinary.

“I have spent my academic life studying and monitoring wildlife and identifying conservation threats that may jeopardise the survival of species and their habitats.

"Zenkerella (the flightless scaly-tailed squirrel), had been reported in the village of Ureca, on the southern tip of Bioko Island in 1995. Given the importance that Zenkerella may have on our understanding of the evolution of gliding, and that at the time I was doing research in the area for the Bioko Biodiversity Protection Program, we decided to try to locate it.

“Talking to the villagers from Ureca I found out that they occasionally catch the animal in hunting traps that they used to catch small forest mammals. Given that, as they put it, 'it hardly has any meat', they immediately dispose of it. I asked if the next time one was found it could be preserved in alcohol so that we could study its morphology (shape) and extract DNA to find out more about the evolution of this obscure species. To put this find into perspective Zenkerella has never been seen alive by scientists to date so we are very excited by what the specimens can tell us.”

“The findings are astounding. In the paper we describe the external morphology (the branch of biology that deals with the form and structure of organisms) and phylogeny (the evolutionary relationship between organisms) of this elusive creature.

“We have proposed a new evolutionary scenario for the evolution of gliding in anomalurid mammals, the group in which Zenkerella belongs. The study is based on three specimens villagers of Ureca saved for me.

“There are only three genera within anomalurids: Idiurus and Anomalurus, which have the skin-flap and thus are able to glide, and Zenkerella, which lack this feature and thus do not glide. Traditional phylogenies, which were based on the few Zenkerella skull and tooth remains available until now, suggested that Zenkerella and Idiurus were more closely related to each other than to Anomalurus. In other words, the skull and teeth were more similar to one another than they were to those of Anomalurus. This phylogeny would mean that either the skin-flap, that is, the ability to glide, had evolved twice – once in Idiurus and once in Anomalurus, or that it evolved only once but that it was subsequently lost in Zenkerella.

“DNA extraction and analysis by Steven Heritage at Stony Brook University has enabled us to determine that previous phylogenies were incorrect, that the two gliding anomalurids, Idiurus and Anomalurus, were more closely related to each other than to Zenkerella, and thus that the skin-flap evolved just once.

“The comparison with fossilised remains of Zenkerella's ancestors that are known to be over 30 million years old, combined with the newly available genetic data, indicate that this group has remained virtually unchanged for millions of years, and that Zenkerella is a “living fossil”.

“We do not know how or why this species remained unchanged for such a long time. By studying the anatomy of the new specimens we will be able to reconstruct their living habits: what they eat, whether they are arboreal or terrestrial, nocturnal or diurnal.”

This information will help scientists understand how Zenkerella managed to survive with hardly any change in over 30 million years. The conservation status of these rare animals is unknown, it is also unknown if they are found beyond the village of Ureca, and thus their population size in Bioko Island.

The rapid socioeconomic development that Equatorial Guinea is undergoing is putting a lot of pressure in their forests and the species that live in it. The team is currently conducting the first ever field study on Zenkerella to try to find out more about their population size and their biology.

Dr Fernández continues, “I am currently examining the distribution of Zenkerella across Bioko Island. I also have two UWE Master Students involved in this project. One student is examining their population density and habitat preference. A second student is analysing the gut content of the three specimens we used in this paper to determine their diet. We plan to use this information to assess their conservation status, and whether we need to develop a management plan for this species.”

See also this insightful blog post by Dr Erik Seiffert from the University of Southern California that describes the findings and the chronology of events that collided to enable this discovery.

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