The takahe of New Zealand had not been seen since 1898 when it was 'rediscovered' in 1948.
In paleontology, a Lazarus taxon (plural taxa) is a taxon that disappears for one or more periods from the fossil record, only to appear again later. Likewise in conservation biology and ecology, it can refer to species or populations that were thought to be extinct, and are rediscovered. The term Lazarus taxon was coined by Karl W. Flessa & David Jablonski in 1983 and was then expanded by Jablonski in 1986. Wignall and Benton defined Lazarus taxon as, ‘At times of biotic crisis many taxa go extinct, but others only temporarily disappeared from the fossil record, often for intervals measured in millions of years, before reappearing unchanged’. Earlier work also supports the concept though without using the name Lazarus taxon, like work by Christopher R. C. Paul.
Lazarus taxa are observational artifacts that appear to occur either because of (local) extinction, later resupplied, or as a sampling artifact. The fossil record is inherently sporadic (only a very small fraction of organisms become fossilized, and an even smaller fraction are discovered before destruction) and contains gaps not necessarily caused by extinction, particularly when the number of individuals in a taxon is very low.
After mass extinctions, such as the Permian–Triassic extinction event, the Lazarus effect occurred for many taxa. However, there appears to be no link with the abundance of fossiliferous sites and the proportion of Lazarus taxa, and no missing taxa have been found in potential refuges. Therefore, reappearance of Lazarus taxa probably reflects the rebound after a period of extreme rarity during the aftermath of such extinctions.
A zombie taxon is a taxon that contains specimens that have been collected from strata younger than the extinction of the taxon. Later such fossils turn out to be freed from the original seam and refossilized in a younger sediment. For example, a trilobite that gets eroded out of its Cambrian-aged limestone matrix, and reworked into Miocene-aged siltstone.
A living fossil is an extant taxon that appears to have changed so little compared with fossil remains, that it is considered identical. Living fossils may occur regularly in the fossil record, such as the lampshell Lingula, though the living species in this genus are not identical to fossil brachiopods.
Other living fossils however are also Lazarus taxa if these have been missing from the fossil record for substantial periods of time, such as applies for coelacanths.
Finally, the term "Lazarus species" is applied to organisms that have been rediscovered as being still alive after having been widely considered extinct for years, without ever having appeared in the fossil record. In this last case, the term Lazarus taxon is applied in neontology.
Bush dog (Speothos venaticus), last surviving species of the genus Speothos; first described as an extinct taxon in 1842 by Peter Wilhelm Lund, based on fossils uncovered from Brazilian caves; Lund found and described living specimens in 1843 without realizing they were of the same species as the fossils, dubbing the living bush dogs as members of the genus "Icticyon"; this was not corrected until some time in the 20th century.
Chacoan peccary (Catagonus wagneri), last surviving species of the genus Catagonus; believed to be the closest living relative to the extinct genus Platygonus. First described as extinct in 1930 as fossils; live specimens found in 1974.
Coelacanth (Latimeria), a member of a subclass (Actinistia) thought to have gone extinct 66 million years ago; live specimens found in 1938.
Majorcan midwife toad (Alytes muletensis), in the family Alytidae, described from fossil remains in 1977, discovered alive in 1979.
Dawn redwood (Metasequoia), a genus of conifer, described as a fossil in 1941, rediscovered alive in 1944.
Monito del monte (Dromiciops), sole surviving member of the order Microbiotheria; first described in 1894, thought to have gone extinct 11 million years ago.
Bulmer's fruit bat (Aproteles bulmerae), originally described from a Pleistocene garbage pile, it was subsequently discovered alive elsewhere in its native New Guinea.
Lazarus taxa reflect the sporadic nature of the fossil record
Monoplacophora, a class of molluscs believed to have gone extinct in the middle Devonian Period (c. 380 million years ago) until living members were discovered in deep water off Costa Rica in 1952.
Mountain pygmy possum (Burramys parvus), first discovered in the fossil record in 1895; rediscovered alive in 1966.
Megachile pluto, the world's largest bee. Not seen after 1858, when it was first collected, until it was rediscovered in 1981.
Dinosaur ant (Nothomyrmecia macrops), a rare genus of ants consisting of a single species, discovered in 1931, not seen again until 1977.
Petasida ephippigera, a species of grasshopper in the family Pyrgomorphidae; thought to be extinct from 1900 until 1971, when a single male specimen was spotted, followed by a breeding pair shortly afterwards.
Bone skipper fly (Thyreophora cynophila), in the family Piophilidae; first described (1794) and last seen in Central Europe (1850), before being photographed in Spain in 2009.
Black kokanee (Oncorhynchus nerka kawamurae), a Japanese species of salmon in the family Salmonidae; believed extinct in 1940 after attempts at conservation seemingly failed. The species was rediscovered in Lake Saiko in 2010.
Philautus chalazodes (chalazodes bubble-nest frog, white-spotted bush frog or Günther's bush frog), a species of frog in the family Rhacophoridae; no verifiable reports of this species, until its rediscovery in 2011.
Sumatra toad (Bufo sumatranus), a species of toad in the family Bufonidae.
Bavarian pine vole (Microtus bavaricus), is a vole in the family Cricetidae; believed extinct in the 1960s, until it was rediscovered in 2000.
Brazilian arboreal mouse (Rhagomys rufescens), a South American rodent species of the family Cricetidae; first described in 1886, was believed to be extinct for over one hundred years.
Onychogalea fraenata (Bridled nail-tail wallaby, bridled nail-tailed wallaby, bridled nailtail wallaby, bridled wallaby, merrin or flashjack), a vulnerable species of macropod; thought to be extinct since the last confirmed sighting in 1937, but rediscovered in 1973.
Caspian horse (Khazar horse), thought to be descended from Mesopotamian horses; remains dating back to 3400 B.C.E, but it was rediscovered in the 1960s.
Zyzomys pedunculatus (central rock rat, central thick-tailed rock-rat, Macdonnell Range rock-rat, Australian native mouse, rat à grosse queue or rata coligorda), a species of rodent in the family Muridae; thought to be extinct in 1990 and 1994, until a reappearance in 2001 and in 2002, then the species went unrecorded until 2013.
Cuban solenodon (Atopogale cubanus), thought to have been extinct until a live specimen was found in 2003.
Gilbert's potoroo (Potorous gilbertii), extremely rare Australian mammal presumed extinct from the 19th century until 1994.
Humboldt marten (Martes caurina humboldtensis), subspecies of the Pacific marten thought to be extinct until rediscovered in 1996 on remote camera traps in the Six Rivers National Forest in northern California.
New Guinea big-eared bat (Pharotis imogene), previously, the species was believed to have been extinct since 1890, when it was last spotted. In 2012, researchers realised that a female bat collected near Kamali was a member of this species.
Vietnam mouse-deer (Tragulus versicolor), last known from a specimen acquired from hunters in 1990, not seen again for nearly 30 years until multiple individuals were sighted with camera-trap photographs in a 2019 survey of prospective habitat.
Woolly flying squirrel (Eupetaurus cinereus), known only from pelts collected in Pakistan in the late 19th century, until live specimens were collected in the 1990s.
Terror skink (Phoboscincus bocourti), a 50-cm-long lizard, was previously known from a single specimen captured around 1870 and was long presumed extinct. In 2003, on a tiny islet, it was rediscovered.
Fernandina Island Galápagos tortoise (Chelonoidis phantasticus), only known from a single male specimen in 1906 and putative droppings and bite marks throughout the 20th century up to the 2010s. A female individual was rediscovered on the island on an expedition in 2019.
Bermuda petrel or "cahow" (Pterodroma cahow), thought extinct since 1620 until 18 nesting pairs were found in 1951 on an uninhabited rock outcropping in Bermuda. Bermudian David B. Wingate has devoted his life to bringing the birds back, and in the 2011-12 breeding season they passed 100-pairs.
Discus guerinianus, a Madeiran land snail thought extinct in 1996 but found again in 1999.
Greater Bermuda land snail (Poecilozonites bermudensis), last recorded sighting made in the early 1970s, survey in 1988 and studies in 2000, 2002, and 2004 seemed to confirm extinction, rediscovered in City of Hamilton alleyway in 2014.
Because the definition of a Lazarus taxon is ambiguous, some like R. B. Rickards, do not agree with the existence of a Lazarus taxon.
R. B. Rickards and A. J. Wright
Rickards and Wright questioned the usefulness of the concept of a Lazarus taxon. They wrote in "Lazarus taxa, refugia and relict faunas: evidence from graptolites" that anyone could argue that any gap in the fossil record could potentially be considered a Lazarus effect because the duration required for the Lazarus effect is not deﬁned. They believed accurate plotting of biodiversity changes and species abundance through time, coupled with an appraisal of their palaeobiogeography was more important than using this title to categorize species.
Communication and education
The lack of public engagement around environmental issue has led conservationists to attempt newer communication strategies. One of them is the focus on positive messages, of which Lazarus species are an important part  One conservation outreach project that has focused exclusively on species rediscoveries is the Lost & Found project which aims to tell the stories of species once thought extinct but that were subsequently rediscovered.
^Ryan, Gerard; Baker, Christopher (November 2016). "A general method for assessing the risks and benefits of secrecy in conserving 'Lazarus species'". Biological Conservation. 203: 186–187. doi:10.1016/j.biocon.2016.09.022.
^Freiwald, André; Lavaleye, Marc; Heugten, Bart Van; Beuck, Lydia; Hoffman, Leon (4 June 2019). "Last snails standing since the Early Pleistocene, a tale of Calliostomatidae (Gastropoda) living in deep-water coral habitats in the north-eastern Atlantic". Zootaxa. 4613 (1): 93–110. doi:10.11646/zootaxa.4613.1.4. ISSN1175-5334.
^"APNewsBreak: Idaho Scientists Find Fabled Worm," The New York Times, April 27, 2010.
^Messer, A. C. (1984). "Chalicodoma pluto: The World's Largest Bee Rediscovered Living Communally in Termite Nests (Hymenoptera: Megachilidae)". Journal of the Kansas Entomological Society. 57 (1): 165–168. JSTOR25084498.
^Miguel Carles-Tolrá, Pablo C. Rodríguez & Julio Verdú (2010). "Thyreophora cynophila (Panzer, 1794): collected in Spain 160 years after it was thought to be extinct (Diptera: Piophilidae: Thyreophorini)". Boletín de la Sociedad Entomológica Aragonesa (S.E.A.) 46: 1–7.