Lazarus taxa and fossil abundance at times of biotic crisis

Mass extinctions are often followed by intervals in which taxa disappear from the fossil record only to reappear again later. This "Lazarus effect" is often attributed to a poor-quality fossil record or migration to refuges. Testing these alternatives, with examples from the end Permian and late Triassic extinctions, reveals that there is no link with the abundance of fossiliferous sites and the proportion of Lazarus taxa nor are missing taxa encountered in potential refuges. Therefore, the abundance of Lazarus taxa in the aftermath of these extinctions is probably a reflection of the extreme rarity of organisms at this time.