|Artist's reconstruction of Palaeochiropteryx in life.|
|Fossils of Palaeochiropteryx are only known from Messel Pit, Germany.|
Palaeochiropteryx (// 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. The name Palaeochiropteryx means "Ancient hand-wing", from Greek παλαιός (palaios, "old"), χείρ (kheir, "hand"), and πτέρυξ (pteruks, "wing").
The two species have only been found at Messel. They are quite common and account for three quarters of all bat fossils found there, with Archaeonycteris, Hassianycteris, and Tachypteron making up the rest. 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. 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. Authorities specializing in bat fossils, however, maintain the distinction between the two families.
Along with Onychonycteris, Icaronycteris, Hassianycteris, and Archaeonycteris; members of Palaeochiropteryx are among the oldest known bats. 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.
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.
Both P. tupaiodon and P. spiegeli were small bats. P. speigeli is slightly larger than P. tupaiodon. 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). They had wingspans between 25 to 30 cm (9.8 to 11.8 in) in length.
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.
Paleobiology and paleoecology
Messel Pit (known in German as Grube Messel) is one of the most famous and richest fossil sites of the world. The site is renowned for the quality of preservation in the fossils found. Preserved in very fragile bituminous shale, they often retain exquisite details of the soft parts of animals and plants. As its name suggests, the pit is a dry depression about 60 m (200 ft) deep; the surface is around 200 m (660 ft) above sea level. It covers an area approximately 1,000 m (3,300 ft) by 700 m (2,300 ft).
48 million years ago, the pit was a small but very deep lake, originally at least 190 m (620 ft) deep. It was located around 10° south of its current location in a tropical and subtropical Eocene Europe. Messel Pit was volcanic in origin, probably a caldera created by a massive volcanic eruption. It remained geologically and tectonically active during the Eocene, intermittently releasing puffs of poisonous volcanic gases. A virtually stagnant lake, its low oxygen levels enabled the types of preservation found in its fossils.
Messel pit was surrounded by a lush tropical jungle ecosystem teeming with wildlife. Among these were several bat species, including Palaeochiropteryx. Fossils of Palaeochiropteryx (particularly Palaeochiropteryx tupaiodon) occur in great abundance in the pit. They account for three-fourths of all recovered bat fossils in the area.
The fossils recovered are usually of healthy adults with full stomachs, making the reasons why they ended up at the bottom of a lake a bit of a mystery. They may have been snagged or poisoned by thick algal mats on the surface of the lake as they swooped down to drink. Or they may have been knocked out midair by poisonous fumes rising from the lake and subsequently drowned.
The small bodies of Palaeochiropteryx coupled with their relatively broad wingspan indicate that they may have been low level flyers, much like some modern bats with the same body structure. They specialized in hunting close to the ground, beneath the jungle canopy and among vegetation unlike other bats found in Messel Pit which flew at higher altitudes (an early evidence of niche partitioning). They had low wing loading and low aspect ratios, suggesting that they were relatively slow flyers but were able to maneuver midair quickly – essential for avoiding collisions with the numerous obstacles near the forest floor. This fact may have made them especially vulnerable to the poisonous gases of the former Messel lake, explaining the abundance of their fossils.
The shape of their teeth and the stomach contents of the numerous extremely well preserved fossils of the Messel Pit indicate that Palaeochiropteryx were insectivorous. P. tupaiodon fed almost exclusively on (presumably slow-moving) moths of the primitive Microlepidoptera family. P. spiegeli, on the other hand, also consumed caddisflies (Trichoptera) in addition to moths. Most members of those insect families are active at night, giving a strong indication that Palaeochiropteryx were also nocturnal, or at best, active during twilight (crepuscular).
From the results of radiographic analysis, Palaeochiropteryx (as well as Archaeonycteris and Icaronycteris) all have enlarged cochleae relative to the size of their skulls. They are still smaller than that of modern echolocating insectivorous bats (Microchiroptera) but they are already larger than that of modern non-echolocating fruit-eating bats (Megachiroptera). Along with their known diets and habits, this is a clear evidence that Palaeochiropteryx was very much capable of echolocation like modern microchiropterans.
Taxonomy and phylogeny
The fossil record of bats extends back at least to the early Eocene, and chiropteran fossils are known from all continents except Antarctica. Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx, unlike most other fossil bats, have not been referred to any extant family or superfamily. These Eocene taxa are known from exceptionally well-preserved fossils, and they have long formed a basis for reconstructing the early evolutionary history of Chiroptera.
Smith (1977) suggested that these taxa represent an extinct clade of early microchiropterans which he dubbed Palaeochiropterygoidea. In contrast, Van Valen (1979) argued that these fossil forms are representatives of Eochiroptera, a primitive grade ancestral to both Megachiroptera and Microchiroptera. Novacek (1987) reanalyzed morphology of Icaronycteris and Palaeochiropteryx and concluded that they are more closely related to Microchroptera than to Megachiroptera. Most recently, Simmons and Geisler (1998) found that Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx represent a series of consecutive sister-taxa to extant microchiropteran bats.
- Donald E. Russell & Philip D. Gingerich (1981). "Liptophyla, Proteutheria(?), and Chiroptera (Mammalia) from the Early-Middle Eocene Kuldana Formation of Kohat, (Pakistan)" (PDF). Contributions from the Museum of Paleontology (University of Michigan) 25 (14): 277–287. Retrieved May 16, 2011.
- "Palaeochiropteryx". Paleobiology Database. Retrieved May 16, 2011.
- Glover Morrill Allen (2004). Bats: Biology, Behavior and Folklore. Courier Dover Publications. p. 177. ISBN 978-0-486-43383-7.
- Michael Morlo, Stephan Schall, Gerald Mayr, & Christina Seiffert (2004). "An annotated taxonomic list of the Middle Eocene (MP 11) Vertebrata of Messel" (PDF). Courier Forschungsinstitut Senckenberg (E. Schweizerbart Science Publishers) 252: 95–108. ISSN 0341-4116. Retrieved May 17, 2011.
- Kenneth David Rose (2006). The Beginning of the Age of Mammals. JHU Press. pp. 160–162. ISBN 978-0-8018-8472-6.
- Hillel J. Hoffmann & Jonathan Blair (2000). "Messel, Window on an Ancient World". National Geographic (National Geographic Society) 197 (2): 48. ISSN 0027-9358.
- Nancy B. Simmons & Tenley Conway (1998). "Higher-level Classification of Bats". Tree of Life web project. Retrieved May 17, 2011.
- Björn Kurtén & Elaine Anderson (1980). Pleistocene mammals of North America. Columbia University Press. ISBN 978-0-231-03733-4.
- "Palaeochiropterygidae". Paleobiology Database. Retrieved May 19, 2011.
- J. Rydell & J. R. Speakman (1995). "Evolution of nocturnality in bats: Potential competitors and predators during their early history" (PDF). Biological Journal of the Linnean Society (The Linnean Society of London) (54): 183–191. doi:10.1111/j.1095-8312.1995.tb01031.x. ISSN 0024-4066. Retrieved May 17, 2011.
- Thierry Smith, Rajendra S. Rana, Pieter Missiaen, Kenneth D. Rose, Ashok Sahni, Hukam Singh, & Lachham Singh (2007). "High bat (Chiroptera) diversity in the Early Eocene of India". Naturwissenschaften (Springer-Verlag) 94: 1003–1009. doi:10.1007/s00114-007-0280-9. PMID 17671774. Retrieved May 19, 2011.
- "Bat ears go way back". New Scientist (Reed Business Information) 106 (1456): 19. 1980. ISSN 0262-4079. Retrieved May 16, 2011.
- Jordi Agustí, Mauricio Antón (2002). Mammoths, sabertooths, and hominids: 65 million years of mammalian evolution in Europe. Columbia University Press. p. 32. ISBN 978-0-231-11641-1.
- "Messel Pit Fossil Site, Hesse, Germany" (PDF). World Heritage Sites (United Nations Environment Program, World Conservation Monitoring Centre). 2007. Retrieved May 19, 2011.
- Evelies Mayer (2007). "Messel Pit Fossil site" (PDF). WHC Nomination Documentation (World Heritage Committee). Retrieved May 19, 2011.
- Tom Woolrych (June 4, 2009). "Time Tunnel". Cosmos: The Science of Everything. Retrieved May 19, 2011.
- Patrick Barkham (June 4, 2009). "The treasures of Messel". The Guardian. Retrieved May 19, 2011.
- Gregg F. Gunnell (2001). Eocene biodiversity: unusual occurrences and rarely sampled habitats. Springer. pp. 224–225. ISBN 978-0-306-46528-4.
- Conrad C. Labandeira (2002). "Paleobiology of Predators, Parasitoids, and Parasites: Death and Accommodation in the Fossil Record of Continental Invertebrates" (PDF). Paleontological Society Papers (The Paleontological Society) 8: 211–250. ISSN 1089-3326. Retrieved May 19, 2011.
- Michael J. Novacek (1987). "Auditory Features and Affinities of the Eocene Bats Icaronycteris and Palaeochiropteryx (Microchiroptera, incertae sedis)" (PDF). Novitates (American Museum of Natural History) (2977): 1–18. ISSN 0003-0082. Retrieved May 16, 2011.
- John R. Speakman (1999). "The evolution of flight and echolocation in pre-bats: an evaluation of the energetics of reach hunting" (PDF). Acta Chiropterologica (Museum and Institute of Zoology, Polish Academy of Sciences) 1 (1): 3–15. ISSN 1508-1109. Retrieved May 17, 2011.
- Nancy B. Simmons & Tenley Conway (1997). "Chiroptera. Bats. Version 01". The Tree of Life Web Project. Retrieved May 17, 2011.