The 50-million-year-old bat specimens are already recognizable as bats, so where did they come from? When, where, why and how the first bats become airborne is another mystery buried by Deep Time.
Refining our sense of what an early proto-bat might look like is also essential. The current record doesn’t offer many hints. Consider Onychonycteris, one of the oldest known bats featuring some of the most complete remains. While this mammal has more primitive limb proportions and claws on its fingers, says Royal Ontario Museum paleontologist Kevin Seymour, “it is still a bat.” The closest paleontologists can get to understanding this animal is looking at living mouse-tailed bats, Seymour notes, which use a combination of fluttering and gliding to move through the air.
What came before is only speculative. Bats are mammals, and so the earliest bats were certainly furry. Based on finds such as Onychonycteris, it’s reasonable to propose that bats went through a gliding stage before powered flight, Seymour says, and the first bats probably were insectivores. But that’s about all scientists can say with confidence without a relatively complete fossil to fill in the gap “It will certainly require articulated material,” Seymour says, relatively complete fossils acting as keystones to the tiny fossils of Paleocene and Eocene mammals that may already be resting in museums drawers.Riley Black, “Why Bats Are One of Evolution’s Greatest Puzzles” at Smithsonian Magazine
So we are looking for a bat that isn’t really a bat? Just wondering.