concept

Signor-Lipps effect

Philip Signor and Jere Lipps pointed out in 1982 that because every species' fossil record is incomplete, a taxon's *observed* last appearance is almost never when it actually went extinct. The consequence is uncomfortable: take several species that died out at the same instant, and the common one's last fossil sits just below the true horizon while the rare one's sits far below it - so when plotted, an abrupt event looks like a long staggered decline with rare species apparently dying first. None of that sequence is real.