(including spiders, scorpions, pseudoscorpions)
should not surprise that Arachnids have enjoyed phenomenal survival
success. The most diverse of land-based predators that appeared
in Silurian time (Jeran, 1990) owe much
of their success to co-evolution with their primary prey, Class
Insecta. However, scorpion
fossils have been found from the Silurian and acarid fossils
from the Devonian. The oldest known spider, Attercopus, was
found in Middle Devonian strata in New York (Selden
et al. 1991). Early spiders from the Carboniferous period
have segmented abdomens not present in their ancestors. Thus,
early in the time that life was movingfrom
marine to terrestrial environments, the Arachnids were evolving
to fill their predatory niches.
not surprising is that where insects are found as fossils, so
are spiders. However, like insects their thin exoskeltons are
not readily fossilized. Fossil arachnids are, however, widespread
in fossil amber, sometimes
caught in the act of predation when caught in the sticky resin.
Other Arachnid behaviors can sometimes be caught in amber, such
as cannibalism during mating shown in the picture to the right
(click picture for more and larger pictures).
with no tail
scorpions, vinegaroons, uropygids
tickspider - very small order
and extinct progenitors
scorpions, camel spiders, sun spiders, solugids
A.J., Selden, P.A., Edwards, D. (1990) Land Animals in the
SIlurian: Arachnids and Myriapods from Shropshire, England.
Science, v. 250, pp. 658-661.
P. A., Anderson, H. M., Anderson, J. M. & Fraser, N. C.
1999. The oldest araneomorph spiders, from the Triassic of
South Africa and Virginia. Journal of Arachnology, 27, 401-414.