Palaeochiropteryx

Palaeochiropteryx (/ˌpæliːoʊkaɪˈrɒptərɨks/ PAL-ee-oh-ky-ROP-tər-iks) is an extinct genus of bat from the Middle Eocene of Europe. It contains two very similar species – Palaeochiropteryx tupaiodon and Palaeochiropteryx spiegeli, both from the famous Messel Pit of Germany. They are usually found complete and exceptionally preserved, even retaining the outlines of their fur, ears, and wing membranes.

They are one of the oldest bats known, existing around 48 million years ago. Despite this, they were already quite advanced, showing evidence of the ability to hunt by echolocation like modern insect-eating bats.

Palaeochiropteryx were small bats, with a wingspan between 25 to 30 cm (9.8 to 11.8 in). Their wings were short but broad, indicating an adaptation for slow but highly maneuverable flight beneath forest canopies and among dense vegetation. They preyed mostly on moths and caddisflies and were probably nocturnal.

Discovery and classification
Fossils of both species of Palaeochiropteryx were first recovered from the Messel Pit, near the village of Messel, Germany in 1917. They were described and named by the Swiss naturalist Pierre Revilliod. He placed them under their own family – Palaeochiropterygidae.[2] The name Palaeochiropteryx means "Ancient hand-wing", from Greek παλαιός (palaios, "old"), χείρ (kheir, "hand"), and πτέρυξ (pteruks, "wing").[3]

The two species have only been found at Messel.[4] They are quite common and account for three quarters of all bat fossils found there,[2][5] with Archaeonycteris, Hassianycteris, and Tachypteron making up the rest.[4] Like other fossils from the locality, they are often found in remarkable states of preservation, retaining traces of fur, stomach contents, wing membranes, and even ears.[6] The two species belonging to the genus are the following:
 * †Palaeochiropteryx tupaiodon Revilliod, 1917
 * †Palaeochiropteryx spiegeli Revilliod, 1917

In 1980, their parent taxon, Palaeochiropterygidae, was merged with Archaeonycteridae by the paleontologists Björn Kurtén and Elaine Anderson.[2][7][8] Authorities specializing in bat fossils, however, maintain the distinction between the two families.[9]

The Messel Pit formation dates from the Lutetian age of the Middle Eocene. Between 48.6 ± 0.2 and 40.4 ± 0.2 million years ago.[6]

Along with Onychonycteris, Icaronycteris, Hassianycteris, and Archaeonycteris; members of Palaeochiropteryx are among the oldest known bats.[10] All are identifiable by more or less complete skeletons. While there are fossils of other older bats such as Australonycteris, these are only recognisable from fragmented examples. Close relatives of Palaeochiropteryx include the Middle Eocene Cecilionycteris, Lapichiropteryx and Microchiropteryx, all recovered from partial remains from Germany, China, and India, respectively.

Description
Palaeochiropteryx differed little from modern bats, a surprising fact given their relative age. Palaeochiropteryx had wings formed from enlarged hands, even though their wings were less advanced than the modern bats. For example, they still possessed a claw in the index finger.[12]

Both P. tupaiodon and P. spiegeli were small bats. P. speigeli is slightly larger than P. tupaiodon.[3] P. tupaiodon had an estimated body mass of 7 to 10 g (0.015 to 0.022 lb) and a forearm length of 39 to 46 mm (1.5 to 1.8 in). P. spiegeli was slightly larger and heavier, with an estimated body mass of 10 to 13 g (0.022 to 0.029 lb) and a forearm length of 43 to 49 mm (1.7 to 1.9 in).[10] They had wingspans between 25 to 30 cm (9.8 to 11.8 in) in length.[13]

The complete dentition of Palaeochiropteryx is known. They had 38 teeth, composed of four upper and six lower incisors, four canine teeth, twelve premolars, and twelve molars. Their dental formula is the same as at least three living families of bats, such as bats from the genus Myotis.