Where did bats come from? New research points to Europe

For decades scientists have argued about where bats originated. A recently published study in the journal Nature offers new evidence to address that question. This new international study combining DNA and fossils supports Europe as bats’ likely birthplace.

The problem thus far has been that, unlike birds, which have a superb fossil record showing the transition from dinosaur to “chicken”, when we find bat fossils, they are exquisitely near-fully formed “bats”.

What we knew about early bats

Bats are the only mammals capable of powered flight. Earlier reconstructions suggested the US, Africa or Asia as bats’ birthplace, with different datasets and models producing different answers. The oldest known bat skeletons, discovered in Wyoming in the US, date to the early Eocene geological epoch, about 52 million years ago. Their elongated wing fingers show that bats could already fly.

However, the location of the oldest known fossils does not necessarily reveal where a group first evolved. These fossils nevertheless provide important clues about early bat anatomy, relationships and distributions. What is missing is a fossil sequence documenting the transition from non-flying ancestors to the earliest flying bats.

Most bats use echolocation, a form of sonar in which they produce sounds and use the returning echoes to navigate and find food. Alongside the question of where bats originated, scientists have debated how flight and echolocation evolved. Did flight or echolocation evolve first, or did they evolve together?

A 2008 study of the fossil bat species Onychonycteris supported a flight-first interpretation. Its wings indicated that it could fly, while its ear anatomy suggested that it could not echolocate. However, a 2010 study comparing the anatomy of Onychonycteris with that of living bats challenged that interpretation.

Flight allowed bats to reach new regions, while echolocation provided a way to navigate and find food in darkness. A fossil interpreted as a flying bat without echolocation could support different histories. Its lineage might have branched off before echolocation evolved, or its ancestors might have had echolocation and later lost it.

Combining fossil anatomy with DNA evidence from living bats helps researchers place that animal among its relatives and assess these possibilities. Even a fossil with evidence of both abilities would not, by itself, establish which evolved first or whether they evolved together.

That ability to disperse also complicates the search for bats’ birthplace. The oldest known fossils may belong to populations that had already spread elsewhere. Scientists must combine the bat family tree with evidence of when and where its different branches lived.

What the new study changes

The recent study marks a milestone for Bat1K, an international project aiming to produce high-quality genomes for all living bat species. A genome is an organism’s complete set of genetic instructions. Comparing genomes, anchored to the fossil data, gives researchers many more clues about shared ancestry than analyses based on only a few genes, as it has been done in previous research.

For this study, researchers analysed genomes from 103 bat species representing all 21 living families. The study also assembled anatomical information for 65 species, including 44 extinct ones. Scientists had combined molecular and fossil evidence before. What sets this study apart is the breadth of the evidence, the quality of its genomes, and its investigation of why different stretches of DNA sometimes suggest different relationships between bat groups.

The new analysis places the origin of bats in Europe during the late Palaeocene geological epoch, more than 56 million years ago. In this reconstruction, descendants spread into Africa, followed by further movements into other continents as the major bat groups diversified. This conclusion comes from reconstructing ancestral distributions using the evolutionary tree, fossils and models that account for continental movement and dispersal. Europe received strong support within that analysis.

This study also adds new findings on the origin of echolocation by connecting living bats to vielasia, an extinct bat from France. A 50-million-year-old fossil skull described in 2023 had inner-ear features indicating that it could use a form of sonar similar to that of modern echolocating bats. The new study places vielasia as one of the first groups branching off the evolutionary tree from a common bat ancestor, strengthening evidence that echolocation using the voice box existed before living bat groups diversified. This adds support for an ancient origin of sonar, while leaving the precise sequence of flight and echolocation unresolved.

Today, bat diversity is greatest in the tropics, but their proposed European birthplace was very different from the continent we know. Parts of late Palaeocene Europe supported warm, subtropical forests. At times, land connections through Greenland linked Europe with North America, allowing mammals to move between regions now separated by ocean. To picture the beginnings of bats, we must imagine those ancient forests on a map whose routes and barriers were very different from today’s.