For the blind bat, it is assumed that it evolved from an insectivorous (insectivores include creatures such as moles, shrews, and hedgehogs), non-flying mammal. The fossilized blind bat has a very specific structure. In fact, a revolution in structure would be necessary for an animal like a mole, shrew, or hedgehog to turn into a bat. In the blind bat, 4 out of 5 fingers are extremely long compared to a normal hand and support the wing membrane. In this case, following the evolutionary scenario, a series of genetic errors caused the four fingers of the ancestral mammal to increase in length, while other random mutations created the wing membrane, flight muscles, etc. Oh yes, we must not forget the sonar system that allows bats to fly flawlessly even in total darkness, also produced by a series of genetic errors, of course.
If bats evolved from an insectivore or some other creature, transitional forms should be found that would document the origin of this and other structures unique to bats.
As already stated, such transitional forms have not been found anywhere in the fossil record. The oldest known bat was found in a rock believed to be 50 million years old. The authors claim that a fossil of a bat older than this has never been found.
So, we have the oldest known bat. And what is it? A 100% bat. The complete absence of any transitional forms between the bat and its alleged ancestor does not provide an answer, based on the evolutionary hypothesis, to questions such as: when, from what, where, and how did bats originate?