Fossil Record

The fossil record of the Crustacea is exceptionally good, stretching back to the Cambrian. However, they don't appear in any abundance until the Carboniferous.

The first undisputed crustaceans are Canadaspis and Perspicaris which belong to the Subclass Phyllocarida and were found in the Middle Cambrian Burgess Shale.

By the Carboniferous, all the other major groups of crustaceans are present except for the Eucarida. Most of these fossils are found within shallow marine sediments because these offered good potential for preservation. The Eucarida appeared in the Mesozoic, but they had their origins in the Devonian/Carboniferous. The Eucarida, especially the Decapoda, underwent an adaptive radiation during the Jurassic, with the appearence of crabs and modern shrimps.

Canadapsis perfecta is one of the earliest crustaceans from the Middle Cambrian of the Burgess Shale. Copyright Smithsonian Institution.
A= Shrimp Aeger tipularis from Solnhofen (Late Jurassic, Germany).
B= Lobster from Solnhofen.

The crabs and lobsters carried on diversifing to become one of the major groups of marine organisms. Hermit crabs are an unusual group that seek protection inside discarded mollusc shells. Hermit crabs are known at least from the Cretaceous Speeton Clay where hermit crabs inhabited empty ammonite shells.

Cretaceous hermit crab within an ammonite shell. A-B left and right side of the inhabited ammonite. C-E different apertural views with the hermit crab Palaeopagurus vandenegeli within it. Image taken from Palaeontology vol 46 part 1, 2003.

Artist's reconstruction of P. vandenegeli living within the ammonite shell. Taken from Palaeontology vol 46 part 1, 2003.
The ostracods, which have a fossil record going back to the Cambrian, are commonly found in sediments of all ages. They are so abundant that they can be used in biostratigraphy and show such a range of environmentally-dependent morphologies that past ocean temperatures can be calulated from them. On the right is a picture of a marine ostracod.
In Tertiary sediments the barnacles started to appear in abundance. This was the group that Charles Darwin studied in great taxonomic detail before embarking upon the Origin of Species. On the left is a picture of some fossil barnacles.