Signor–Lipps effect

[1] The Signor–Lipps effect is often applied specifically to cases of the youngest-known fossils of a taxon failing to represent the last appearance of an organism.

[2] One famous example is the coelacanth, which was thought to have become extinct in the very late Cretaceous—until a live specimen was caught in 1938.

[3] The animals known as "Burgess Shale-type fauna" are best known from rocks of the Early and Middle Cambrian periods.

Since 2006, though, a few fossils of similar animals have been found in rocks from the Ordovician, Silurian, and Early Devonian periods, in other words up to 100 million years after the Burgess Shale.

[4][5] The particular way in which such animals have been fossilized may depend on types of ocean chemistry that were present for limited periods of time.