Background

Bats (Chiroptera), the only mammals to have acquired sustainable flight capabilities, exhibit rich ecological diversity, accounting for over 20% of all mammalian species. The unique traits that these animals have acquired during their evolutionary process include the ultrasonic echolocation sense, an unusually long lifespan relative to their body size, and immune tolerance that allows them to carry viruses without experiencing cytokine storms. However, for a long time, it remained a challenging problem in evolutionary biology to determine when, where, and in what order their ancestors acquired these distinctive traits. This is because their bones are thin and fragile, resulting in a significant gap in the paleontological fossil record.

Previously, researchers estimated phylogenetic trees based on fragmentary mitochondrial DNA sequences. Confusion in the academic community increased as the order of divergence at the family level shifted depending on analysis techniques and samples. There was also competition among Asia, Africa, and North America over the original source. This was due to the lack of whole-genome data capable of determining whether flight capability or ultrasonic sensing emerged first.

Key Discoveries

The Bat1K consortium, an international bat genomics research alliance, is a large-scale collaborative research network involving 137 researchers from 64 countries. The researchers newly completed chromosome-level genome assemblies for 103 species, covering all 21 extant bat families. This result, integrating morphological data from 44 ancient fossil taxa, is considered the largest-scale molecular phylogeny to date.

According to molecular clock analysis, the common ancestor of all extant bats emerged in Europe approximately 65 million years ago. This implies that they occupied the ecological niche left vacant by the disappearance of dinosaurs immediately following the Cretaceous-Paleogene (K-Pg) mass extinction in Europe. This discovery overturns existing theories that bats originated in Asia on the North American continent. Subsequently, during the early Paleogene warming period approximately 56 million years ago, major families diverged explosively and spread across the globe.

The timing of the formation of flight capabilities and specialized sensory organs is also clearly defined. The researchers chose to precisely compare the auditory skeletons of the early fossil species Vielasia with those of extant species. Powered flight and ultrasonic echolocation were already established as a single package in the very early stages of evolution, before the divergence of modern bat families. Contrary to the existing hypothesis that flight capability appeared first and echolocation followed much later, this indicates that these two complex functions were completed as an integrated system early in the ancestral stage.

Significance and Outlook

The completed phylogeny and genomic map have put an end to the debate over bat evolution that has lasted for over half a century. High-quality genomic information representing all 21 orders will serve as an unparalleled standard reference framework for future mammalian comparative genomics research. A solid foundation has been laid to trace the evolutionary history of energy metabolism mechanisms that withstand extreme oxidative stress, defense mechanisms that immediately repair damaged genes, and immune regulatory factors that suppress inflammatory responses even upon exposure to lethal pathogens.

Clear limitations also remain. Because soft tissue data cannot be extracted from fossil specimens, the error margin of dating models could not be completely eliminated. To identify the genetic regulatory networks coordinating flight and echolocation, large-scale functional experimental verification of non-coding regulatory elements must follow. In the future, integration with single-cell transcriptome analysis and genome editing technologies is expected to further widen the pathway for expanding research on bats' unique adaptive traits into biomedical science.