Scorpion Species Typhochactas mitchelli
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Scorpion Species Typhochactas mitchelli

December 8, 2010
Scorpion species Typhochactas mitchelli is among the smallest known scorpions and is part of the Typhlochactidae family of cave scorpions, endemic to Mexico. Like all scorpions, it fluoresces in long-wave ultraviolet light as this image of its ventral side highlights. [See related image Here.]

More about this Image In the course of evolution, researchers have assumed that specialized adaptations were irreversible. But research by Lorenzo Prendini, associate curator in the division of invertebrate zoology at the American Museum of Natural History, shows that the evolution of troglobites, or animals adapted for life in caves, is reversible. A new phylogenetic analysis of the family Typhlochactidae found that scorpions currently living closer to the surface (under stones and in leaf litter) evolved independently on more than one occasion from ancestors adapted to life further below the surface (in caves).

The family Typhlochactidae, which includes nine species of scorpions endemic to the karstic regions of eastern Mexico, have adapted to the dark with features such as loss of eyes and reduced pigmentation. Included in the family are one of the world's smallest scorpions, Typhlochactas mitchelli, and the scorpion found at the greatest depth (nearly 1 kilometer below the surface), Alacran tartarus.

For the study, data for 195 morphological characteristics among the species of Typhlochactidae was gathered, and included a detailed mapping of the positions of all trichobothria (sensory setae) on the pedipalps (the second pair of appendages on the first (anterior) major body section). The resulting phylogenetic tree shows that adaptation to life in caves has reversed among this group of scorpions: Two of the less specialized, surface-living species, T. mitchelli and T. sylvestris, share a common ancestor with a much more cave-adapted species, and a similar pattern was found for the third less specialized, surface-living species, T. sissomi.

Prendini says, "This unique group of eyeless Mexican scorpions may have started re-colonizing niches closer to the surface from the deep caves of Mexico after their surface-living ancestors were wiped out by the nearby Chicxuluxb impact along with non-avian dinosaurs, ammonites, and other species." [This research was supported in part by National Science Foundation grants EAR 02-28699 and DEB 04-13453.] (Date of Image: 2007-2009)

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