The Cloudinids lived during the late Ediacaran, and became extinct
at the base of the Cambrian. They are one of the earliest of
what is termed the Small Shelly Fauna (SSF) to emerge in the
They consisted of nested calcareous cones that were thought to
have been a defense measure against predation.
Indeed some have been found with holes drilled in the shelss,
the result of some unknown predator.
classification of these enigmatic animals is uncertain.; they
have been variously looked
upon as polychaete worms and as cnidarians. Their lifestyle is
equally mysterious. They have been thought to have shared a
home with the stromatolites,
adding additional shells as the microbial mat grew. Since none
have been found embedded in a mat, this
interpretation is open to question. One specimen has been etched
with acid to show the shell detail while the other has been
polished to show the shells in a more natural state.
fossils often have show borings that are thought to have
been made by predators.
the distribution of borings in Cloudina suggests selection for
size – the largest holes appear in the largest shells. This
evidence of selective attacks by predators suggests that new species
may have arisen in response to predation, which is often presented
as a one potential cause among many of the rapid diversification
of animals in the Cambrian
Hahn, G., and H. D. Pflug (1985). "Die Cloudinidae n. fam.,
aus dem Vendium und Unter-Kambrium". Senckenbergiana lethaea