On the Origin of Bats

Despite creationist's claims, paleontologists love gaps in the fossil record. To the paleontologist, gaps represent mysteries yet to be solved. And there is no greater gap in the fossil record than the origin of bats. Recently, at the Society of Vertebrate Paleontology's annual meetings in Austin, Drs. Greg Gunnell, Nancy Simmons and Thomas Eiting hosted a symposium on the evolutionary history of bats. The panel of experts presented a series of presentations detailing the amazing history of this very diverse group of mammals. Yet frustratingly little was shred on the origin of bats. The mystery of the origin of bats still remains to be solved. If you are inclined to solve this mystery, then these facts may help you in your quest:

1) The oldest fully formed bats are known from the middle Eocene (50 million years ago) Green River Formation in Wyoming, and the middle Eocene Messel fossil site in Germany, there is also Eocene bat material from Africa. To find the ancestor of bats you need to look in sediments from the Paleocene and earlier, from any of these continents.

2) Based on the most recent molecular phylogenies bats originated from a single ancestor, and is supported by morphological data.

3) The most recent molecular studies indicate that bats belong in the Laurasiatheria clade, with carnivores, ungulates and Eulipotyphla (hedgehogs, shrews, and moles). Previously researchers suggested bats were closely related to primates, tree shrews, and flying foxes (Dermopterans), but most scientists today place bats in the Laurasiatheria clade. North America, South America and Eurasia are all equally likely the continent of origin for this clade, and perhaps bats as well.

4) To clearly solve this mystery, you need to find complete skeletons. Diagnosing the ancestor of bats is difficult using only teeth. Many times fossil teeth from the Paleocene lend experts to incorrectly identify the ancestor of bats, only to have their hopes dashed when more complete material was found or with further scrutinization.

5) The best places to find complete skeletons are in sediments laid down in ponds and lakes. Where sediments gently cover the body before the skeleton has a chance to disarticulate. Look for thinly layered rock of Paleocene age.

6) There are a number of fossil mammals known from only teeth that are likely contenders for the ancestor of bats.

a) Nyctitheriidae
This group is best represent by the genus Leptacodon from the late Paleocene of North America, although there are other genera known from Asia and Europe. The group also contains Wyonycteris, previously thought to be a bat from the Paleocene of Wyoming. Nyctitherians have the advantage of being very primitive in terms of their teeth. The molars are sharply cusped like in bats, and have slightly reduced posterior heels on their molars. However, nyctitheriids have an extra cusp on their upper molars, which bats lack, and the paraconid is slightly reduced. No skeleton or complete skull exists of a nyctiteriid.
b) Early members of Soricidae
The family that contains living shrews, at first appearances, is a good choice for the ancestry of bats, because of their small size and sharp teeth. However, the oldest members of this family (Domnia, Quercysorex, etc..) are from the middle to late Eocene and are too specialized in their dental anatomy to have given rise to bats.
c) Early members of Talpidae
This group contains living moles, and based on teeth they are very similar to bats. However, just like shrews, moles do not appear in the fossil record until the middle to late Eocene. They are likely closely related to bats, but molecular phylogenies support a stronger relationship with shrews, and hedgehogs.
d) Palaeoryctidae
Few people have suggested this group as the ancestor of bats, despite their small size, similar dental features, and reduced anterior dentition. The upper molars are similar to early bats in lacking that extra upper cusp on the molar, but are more slender. Skulls are known of a few genera, which don’t support a strong relationship to bats, but place them low on the placental mammal tree, near xenarthrans.
e) Early members of Leptictidae
Early members of this extinct group reach back into the late Cretaceous of Asia, and Paleocene of North America. Later forms such as Leptictis and Leptictidium are known from skeletal remains, and both lack any advance skeletal or cranial feature of bats. However, early less well-known forms such as Prodiacodon, Myrmecoboides, and even Zhelestes lack complete skeletons and may have given rise to bats.
f) Deccanolestes
A genus composed of only isolated teeth from the late Cretaceous of India shares a number of characters with basal bats. However, Deccanolestes maybe a member of the Palaeoryctidae or an ancestor to bats.
g) Early Primates
Primates and bats are often placed together in a group called Archonta. Based on a number of shared similarities, especially with the gliding flying lemurs (Dermoptera). Extinct members of this group include the Paleocene-Eocene Plagiomenidae and Plesiadapiformes, which may be closely related to bats. Or simply linked together by shared primitive features.

Yes, there really are lots of possible ancestors to bats and only one group gave rise to them. So, a skeleton must do! Good luck in your search!