Bats make up more than one fifth of all living mammal species, yet where and when they first took to the air has been debated for decades. New work points to Europe.
An analysis of 103 bat genomes identifies the European continent as the birthplace of the only mammals capable of powered flight, overturning earlier theories that favoured Africa, Asia or North America. The findings, published in Nature, come from the Bat1K consortium, an international effort to sequence the genomes of all living bat species.
In the first phase of the project, researchers analysed high-quality, chromosome-level genome assemblies from 103 species, 42 of them newly produced, representing at least one species from each of the 21 currently recognised bat families.
They combined that genetic data with 699 anatomical characters drawn from 65 species, including 44 fossil species that predate the Quaternary period. Using statistical models that account for the ages of the fossils, they concluded that the ancestor of all bats lived in Europe in the Late Paleocene.
"Bats have ruled the night skies for about 65 million years, but working out where they first took flight has been more difficult to resolve," said Professor Suzanne Hand of the University of New South Wales. "Advances in genome sequencing and computing have now allowed us to compare and combine data from the DNA of living bats with the fossil record in a way that wasn't previously possible."
The analysis assigned a 99.2% probability to a European origin. The major bat lineages appear to have diversified within a narrow window in the Early Eocene, around 56 million years ago, coinciding with the Paleocene-Eocene Thermal Maximum, a sharp episode of global warming.
The team also addressed one of the field's most persistent questions: whether laryngeal echolocation evolved before or after bats diversified. Placing the fossil species Vielasia in the oldest branch of the tree indicates that it came first.
"Our analysis shows that the oldest branch of bats already had species that unambiguously echolocated," said Professor Liliana Dávalos of Stony Brook University. "Therefore, based on the tree with these fossils bat echolocation evolved shortly after mammalian flight did."
The genomic data also reorganised the family tree, placing Myzopodidae, found on Madagascar, at the earliest branch within the superfamily Vespertilionoidea, and identifying Emballonuroidea and Vespertilionoidea as sister groups.
"Bats constantly surprise us," said Professor Sonja Vernes, the Bat1K director, at the University of St Andrews. "They are one of evolution's greatest experiments. This extraordinary genomic resource is finally allowing us to understand how their remarkable biology evolved."
The figure that will travel furthest, however, is 99.2%, and this newspaper wishes to be the first to take it at its word.
If the order is 99.2% European, then 0.8% of it is not. Bats number more than 1,500 species. Eight tenths of one per cent of 1,500 is twelve. Somewhere in the night sky there are twelve species of bat from somewhere else, and the study does not name them.
The Department of Unnecessary Research regards this as the most significant open question in mammalian biogeography, and notes that the usual methods of resolving it are unavailable. The fossil record has been searched. The genomes have been sequenced. Forty-four extinct species were consulted and none of them volunteered.
Our analysts have accordingly proposed the only remaining approach, which is to ask. The obstacle is not access. Bats are distributed across every continent except Antarctica, they emerge nightly, and they are not difficult to find.
The obstacle is that the twelve have had sixty-five million years to declare an alternative origin and have used none of it. Laryngeal echolocation, the study confirms, was in place at the oldest branch of the tree, before the modern families separated.
Every bat alive has therefore been broadcasting its position, continuously, since the Paleocene. Not one has ever given a different address.