Ancient phylogenetic divergence of the enigmatic African rodentZenkerellaand the origin of anomalurid gliding

Abstract

The “scaly-tailed squirrels” of the rodent family Anomaluridae have a long evolutionary history in Africa, and are now represented by two gliding genera (AnomalurusandIdiurus) and a rare and obscure genus (Zenkerella) that has never been observed alive by mammalogists.Zenkerellashows no anatomical adaptations for gliding, but has traditionally been grouped with the gliderIdiuruson the basis of craniodental similarities, implying that either theZenkerellalineage lost its gliding adaptations, or thatAnomalurusandIdiurusevolved theirs independently. Here we present the first nuclear and mitochondrial DNA sequences ofZenkerella, based on recently recovered whole-body specimens from Bioko Island (Equatorial Guinea), which show unambiguously thatZenkerellais the sister taxon ofAnomalurusandIdiurus. These data indicate that gliding likely evolved only once within Anomaluridae, and that there were no subsequent evolutionary reversals. We combine this new molecular evidence with morphological data from living and extinct anomaluromorph rodents and estimate that the lineage leading toZenkerellahas been evolving independently in Africa since the early Eocene, approximately 49 million years ago. Recently discovered fossils further attest to the antiquity of the lineage leading toZenkerella, which can now be recognized as a classic example of a “living fossil,” about which we know remarkably little. The osteological markers of gliding are estimated to have evolved along the stem lineage of theAnomalurus–Idiurusclade by the early Oligocene, potentially indicating that this adaptation evolved in response to climatic perturbations at the Eocene–Oligocene boundary (∼34 million years ago).