When, and where, did bats first take to the sky?

Flora introduces bats as a Halloween creature whose form has been developing for roughly 60–65 million years, then asks Dr. Emma Teeling what the Bat1K consortium discovered about their origins. Teeling explains that the consortium aims to sequence the genome of every living bat species. For this study, the team produced reference-quality genomes for 103 bat species and combined them with information from 65 fossil bats. By integrating genetic and fossil evidence into evolutionary trees, they concluded that bats originated in Europe about 60–65 million years ago. This result rejects earlier hypotheses that bats first evolved in North America, Africa, or Asia. The researchers also reconstructed how bats moved across the world and inferred the ancestral genome of the first flying mammal, which was a bat. Teeling says the result was surprising because she had worked on bat evolution since 1997 and the new analysis confirmed some conclusions that had seemed “crazy,” including the grouping of some highly advanced echolocating bats with bats that do not echolocate. She also describes the bat genome as highly “mosaic”: different parts can produce different evolutionary histories, probably because bats have hybridized frequently. The team therefore had to revise earlier evolutionary papers, including some of Teeling’s own work.

When Flora asks what was happening among other mammals when bats appeared, Teeling places their emergence just after the extinction of the dinosaurs, when a meteorite impact may have opened ecological niches. She says modern-looking ancestral bats arose around 65 million years ago but had been evolving for about 20 million years from earlier mammalian ancestors. The exact ancestor remains an open question in biology. Teeling places bats in the mammalian group Laurasiatheria. In the evolutionary arrangement she describes, true shrews branch off first, bats branch next, and a much larger group includes carnivores such as lions, tigers, and bears, along with horses, whales, and deer. This means bats are not especially close relatives of mice, as scientists once thought; their closer relatives are among those Laurasiatherian mammals. The study, led in this part by Liliana Dávalos and her team, used genome alignments to compare matching DNA regions across species and infer relationships. But the researchers also wanted to use the fossil record. Fossil bats from 50–55 million years ago are unusually complete “Lagerstätten” fossils: their long fingers reveal wings, while their skulls and highly coiled cochleae preserve evidence of echolocation. The new analytical tools allowed the team to combine these anatomical data with genomic data and place fossil bats into the evolutionary tree.

Flora asks how researchers decide whether a fragmentary fossil should count as a bat, especially while searching for the animal that came before bats. Teeling says the paleontologists on the team rely on diagnostic characteristics, including wings, the shape of the wing bones, tooth form, and other anatomical features. However, the “proto-bat” has not yet been identified. Several possible transitional fossils exist, and researchers are still trying to understand their anatomy well enough to determine where they belong. The fossil record already shows that bats were not primitive, barely functional fliers when they first appear in the record. The 50–55-million-year-old fossils have elongated fingers supporting wings, and features of the inner ear and jaw indicate that they could echolocate as well as fly. Flora repeats the conclusion for emphasis—“Echolocation is old”—and Teeling agrees. Because DNA cannot be recovered from fossils tens of millions of years old, their anatomical traits are essential for connecting ancient bats to the genome-based tree. Teeling describes the new study as a major step forward, but not the final answer. Scientists may now have a stronger framework for locating the earliest bats and studying their transition into flight, yet the precise ancestry and appearance of the pre-bat remain unresolved.

Flora asks whether Teeling feels she is at a watershed moment after pursuing bat evolution for decades. Teeling says she would like to think so, but cautions that scientific discoveries often create more questions: the more researchers learn, the more they realize they do not know. She compares the current study with her group’s 15–20 years of work on aging in long-lived bats. Even when a result seems close, it still requires repeated refinement. The Bat1K framework is intended to support research beyond ancestry. About 1,500 bat species are currently recognized, making up roughly one in five living mammal species, and they are divided among about 21 families. Teeling says that diversity makes the project harder because the team must keep sequencing newly identified species, but it also makes the project powerful. Evolution has already run many natural experiments: some bats live unusually long lives, some feed on blood, some eat insects, and others feed on nectar. Comparing their genomes can reveal how those traits evolved over 15–55 million years. Researchers are using the genomes to investigate conservation and possible genomic decline, sensory changes associated with echolocation and vision, differences between nectar-feeding and insect-eating bats, immune systems that tolerate viruses without causing illness, and the ability to control tumors. Teeling stresses that this work must be global because bats are found around the world, including vampire bats in South America.

Teeling says the consortium’s global scale is both its central advantage and its main challenge. To understand why a vampire bat evolved its unusual biology, or how bats acquired different diets and immune responses, researchers need genomes from related species across the world. The team therefore depends on scientists working in many countries, and Teeling says continued progress will require more people and more funding. The conversation ends with Teeling characterizing the European origin result as a strong step in the right direction rather than a complete solution. The researchers now have a combined genomic-and-fossil evolutionary network on which they can “hang” the unique traits of bats and ask what DNA changes underlie them. But the exact pre-bat ancestor, the mechanisms behind traits such as echolocation and longevity, and the conservation consequences of genomic decline remain active questions. After thanking Teeling, Flora promotes the Science Friday Halloween costume contest. Listeners are invited to submit a photo of a spooky, science-themed costume at ScienceFriday.com/Halloween by Sunday for a chance to win prizes. The episode is credited to producer Charles Berquist and hosted by Flora Lichtman.