The Signor–Lipps effect is a

paleontological Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

principle proposed in 1982 by Philip W. Signor and

Jere H. Lipps Jere Henry Lipps (August 28, 1939) is Professor of the Graduate School, University of California, Berkeley, and Curator of Paleontology at the University of California Museum of Paleontology. Lipps was the ninth Director of the museum (1989–1 ...

which states that, since the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

record of organisms is never complete, neither the first nor the last organism in a given

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

will be recorded as a fossil. 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. The inverse, regarding the oldest-known fossils failing to represent the first appearance of a taxon, is alternatively called the Jaanusson effect after researcher

Valdar Jaanusson Valdar Jaanusson (1923–1999) was an Estonian-Swedish geologist. In 1960 he introduced the concept of topostratigraphy into Swedish stratigraphy. A recognized expert on the geology of the Ordovician period, he was member of the Estonian Academy ...

, or the Sppil–Rongis effect (''Signor–Lipps'' spelled backwards). One famous example is the

coelacanth The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

, which was thought to have become extinct in the very late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

—until a live specimen was caught in 1938. The animals known as " Burgess Shale-type fauna" are best known from rocks of the Early and Middle

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

periods. Since 2006, though, a few fossils of similar animals have been found in rocks from the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

, and Early

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

periods, in other words up to 100 million years after the Burgess Shale. The particular way in which such animals have been fossilized may depend on types of

ocean chemistry Marine chemistry, also known as ocean chemistry or chemical oceanography, is influenced by plate tectonics and seafloor spreading, turbidity currents, sediments, pH levels, atmospheric constituents, metamorphic activity, and ecology. The fie ...

that were present for limited periods of time. But the Signor–Lipps effect is more important for the difficulties it raises in paleontology: *It makes it very difficult to be confident about the timing and speed of

mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It ...

s, and this makes it difficult to test theories about the causes of mass extinctions. For example, the

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s was long thought to be a gradual process, but evidence collected since the late 1980s suggests it was abrupt, which is consistent with the idea that an

asteroid impact An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or me ...

caused it. *The uncertainty about when a taxon first appeared makes it difficult to be confident about the ancestry of specific genera. For example, if the earliest-known fossil of genus X is much earlier than the earliest-known fossil of genus Y and genus Y has all the features of genus X plus a few of its own, it is natural to suppose that X is an ancestor of Y. But this hypothesis could be called into question at any time by the finding of a fossil of Y that is earlier than any known fossil of X—unless an even older fossil of genus X is found, and so on. Signor Lipps.gif, As a result of the Signor-Lipps effect, the last fossil occurrences only approximate the extinction rate. This approximation is better the more fossils per time unit are preserved. Fossil record gaps - delicate and soft-bodied animals.svg, The sporadic nature of the fossil record is reflected in huge gaps spanning a number of epochs.

References

External links

Enchanted Learning glossarySteve C. Wang, Asst. Prof. of Statistics, Swarthmore College
{{DEFAULTSORT:Signor-Lipps effect Extinction Fossil record Paleontological concepts and hypotheses

See also

References

External links