Bats, belonging to the order Chiroptera, stand out as the only mammals capable of sustained, powered flight. Their unique adaptations, such as the elongated finger bones supporting a thin wing membrane and the use of echolocation for navigation and hunting, make them a fascinating group within the animal kingdom. The evolutionary history of bats was long shrouded in mystery, with scientists struggling to place them definitively within the larger mammalian family tree based solely on their specialized body plan. Understanding their true evolutionary relationship requires looking beyond their remarkable features to the underlying genetic code.
The Current Scientific Consensus
Modern genetic analysis has resolved the long-standing question of bat ancestry, placing them within the superorder Laurasiatheria. This large group of placental mammals is named for the ancient supercontinent Laurasia and includes a wide array of animals, such as carnivores, pangolins, and all hoofed mammals, including whales and dolphins.
Bats are considered members of the clade Scrotifera, which also contains carnivorans, pangolins, and ungulates. While the exact sister group for bats remains a topic of ongoing research, they are frequently placed near the Eulipotyphla (shrews and moles) or as a sister group to the Fereuungulata, a clade encompassing carnivores and ungulates. This placement firmly links bats to these groups despite the stark difference in appearance.
Why Bats Were Difficult to Place
For centuries, naturalists relied on morphology, or physical structure, to classify organisms, which complicated the bat’s lineage. Early hypotheses grouped bats with Primates based on superficial similarities, while others suggested a close relationship with rodents due to their small size and insectivorous diet.
The most misleading factor was the evolution of flight, a trait not shared by any other mammal. Flight in bats is a classic example of convergent evolution, meaning a similar trait arose independently in unrelated species. Scientists who focused heavily on this adaptation mistakenly attempted to link bats to other fliers or gliders like the colugos, or “flying lemurs.” These morphological comparisons, which failed to account for the independent development of flight, prevented a correct classification.
The Molecular Proof of Lineage
The use of molecular data provided evidence that overturned morphology-based classification. Scientists used genomic sequencing, analyzing mitochondrial and nuclear DNA, to trace the bat’s ancestry. This genetic evidence overwhelmingly supported the inclusion of bats in Laurasiatheria and refuted previous hypotheses linking them closely to Primates or Dermoptera.
Advanced techniques like molecular clock dating were employed to estimate the time when the order Chiroptera diverged from its closest relatives. This method, which uses the rate of genetic mutation as a timeline, suggests that the common ancestor of modern bats lived approximately 52 to 54 million years ago. The rapid diversification of the bat order occurred over a relatively short period, which explains why morphological studies struggled to resolve their relationships.
The Major Branches of the Bat Family
The internal classification of bats has been revised based on genetic findings, replacing the traditional division into megabats and microbats. The order Chiroptera is now recognized as having two suborders: Yinpterochiroptera and Yangochiroptera.
The Yinpterochiroptera suborder includes the large fruit bats (flying foxes), traditionally known as megabats, but also contains several families of microbats, such as the horseshoe bats. In contrast, the Yangochiroptera suborder contains the vast majority of the world’s microbat species, including the free-tailed bats and the common evening bats. This group is characterized by the use of laryngeal echolocation, a feature that evolved very early in the bat lineage. This reorganization shows that echolocation was lost in some fruit bats, rather than evolving separately in all microbats.