Hand-digging
| Hand-digging | ||||||||||||
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Five-fingered handwheels ( Bipes biporus ) |
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Bipedidae | ||||||||||||
| Taylor , 1951 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Bipes | ||||||||||||
| Lacepède , 1788 |
The hand diggers are small, strange looking reptiles from the genus Bipes . Bipes is the only genus in the family of the two-footed twin snakes (Bipedidae). The hand-diggers are reminiscent of a large earthworm with two mole-like hands, have no other limbs and crawl or dig through the sandy soil of their semi-desert-like Mexican habitats.
The part of the name "-wühlen", the appearance and the way of life can lead to confusion with the not closely related amphibians from the order of the sneak amphibian (Gymnophiona), which are also referred to in German as Wühlen ( Blindwühlen ).
features
Hand-digging are around 20 centimeters (approx. 17–24 cm) long, have a “worm-like” body with regular transverse rings and scaling of the head made of small, smooth horny shields. While their hind legs have receded, they have a stubby pair of arms in front with well-developed, longer-clawed hands. This distinguishes them from double-creeps of other genera that are completely limbless. The eyes sit quite far forward on the bluntly rounded head and are very small; the sense of sight is reduced. There are no ear openings. The tongue is two-pointed and can be stuck out. Like all double snakes, they crawl in a straight line forwards (and backwards!) Without snaking their bodies sideways like other legless lizards. Another special feature is that they only use their left lung for breathing.
Way of life
The hand digging is adapted to a digging way of life. This is indicated by their smooth scales on their head, their receding extremities, their reduced sense of sight and their grave hands. Sparsely overgrown, sandy dry biotopes serve as habitats. Hand-rooting feed on insects and other invertebrates , especially ants and termites . To do this, they also penetrate the structures of these insects.
The males have two hemipenes as mating organs . Like most reptiles, hand-rooting eggs lay eggs. They do this inside termite burrows.
distribution
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The occurrence of the genus is limited to three now disjoint areas in western Mexico, on the one hand to the southwest of the Baja California peninsula ( Bipes biporus ), and on the other to two small areas on the west coast of Mexico, i.e. on the other side of the Gulf of California ( Bipes canaliculatus , Bipes tridactylus ). The spatial separation of the sub-areas on the two sides of the Gulf of California can be traced back to the plate tectonic development of the region: Today's Baja California peninsula was completely connected to the mainland of Mexico until the late Miocene around 6 million years ago, before the East Pacific Ridge swung in North American continent the narrow landmass gradually drifted northwest and as a result the Gulf of California opened up.
Systematics
The genealogical classification of the double creeps within the scale creepers is still controversial, but they are probably close relatives of the real lizards .
According to molecular biological studies, the family Bipedidae was considered to be the sister taxon of the real double snakes (Amphisbaenidae) plus the pointed-toothed double snakes (Trogonophidae). In the meantime, also on a molecular genetic basis, two more double-creeping families are endured, the Blanidae and Cadeidae, and the Bipedidae are considered to be sister taxons of these two groups (see following cladogram):
| Double creeping (Amphisbaenia) |
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According to this hypothesis, the Bipedidae, which are the only double crawls with forelegs and a skull that is not particularly strongly transformed into a burrow, belong to the more derived taxa of the inner group. This implies that if the hypothesis is correct, the development of the head ditch and the reduction of the forelegs must have taken place at least three times independently of each other within the double crawl.
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Within the genus Bipes , the only genus in the family Bipedidae, three species are distinguished:
- Five-fingered handwheels - Bipes biporus ( Cope , 1894)
- Four-fingered handwheels - Bipes canaliculatus Latreille , 1801
- Three-fingered handwheels - Bipes tridactylus ( Dugès , 1894)
Web links
- Bipes in The Reptile Database
- Great photo from the front view of a hand mill
- Film on UTA Diversity Research Center
Individual evidence
- ^ Peter Lonsdale: Geology and tectonic history of the Gulf of California. Pp. 499-521 in: EL Winterer, Donald M. Hussong, Robert W. Decker (Eds.): The Geology of North America, Vol N: The Eastern Pacific Ocean and Hawaii. Geological Society of America, Boulder (CO) 1989, ISBN 0-8137-5208-6 , pp. 516 ff.
- ↑ J. Robert Maceya, Theodore J. Papenfuss, Jennifer V. Kuehla, H. Mathew Fourcadea, Jeffrey L. Boore: Phylogenetic relationships among amphisbaenian reptiles based on complete mitochondrial genomic sequences. Molecular Phylogenetics and Evolution. Vol. 33, No. 1, 2004, pp. 22–31, doi : 10.1016 / j.ympev.2004.05.003 (alternative full text access : Center for North American Herpetology ( Memento of the original from July 29, 2014 in the Internet Archive ) Info : The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this note. )
- ↑ Nicolas Vidal, Anna Azvolinsky, Corinne Cruaud, S. Blair Hedges: Origin of tropical American burrowing reptiles by transatlantic rafting. Biology Letters, Vol. 4, No. 1, 2008, pp. 115-118, doi : 10.1098 / rsbl.2007.0531 .
- ↑ Maureen Kearney, Bryan L. Stuart: Repeated evolution of limblessness and digging heads in worm lizards revealed by DNA from old bones. Proceedings of the Royal Society B. Vol. 271, 2004, pp. 1677-1683, doi : 10.1098 / rspb.2004.2771 , PMC 1691774 (free full text).
