''Geograpsus severnsi'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

species of

land crab A number of lineages of crabs have evolved to live predominantly on land. Examples of terrestrial crabs are found in the families Gecarcinidae and Gecarcinucidae, as well as in selected genera from other families, such as '' Sesarma'', altho ...

from

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

. It died out shortly after humans colonized the

Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...

. It is the first known documented crab to become extinct after the ice age.

Distribution

Specimens of ''G. severnsi'' have been recovered from several of the Hawaiian

volcanic island Geologically, a volcanic island is an island of volcanic origin. The term high island can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed ...

s, including

Maui Maui (; Hawaiian language, Hawaiian: ) is the second largest island in the Hawaiian archipelago, at 727.2 square miles (1,883 km2). It is the List of islands of the United States by area, 17th-largest in the United States. Maui is one of ...

Oahu Oahu (, , sometimes written Oahu) is the third-largest and most populated island of the Hawaiian Islands and of the U.S. state of Hawaii. The state capital, Honolulu, is on Oahu's southeast coast. The island of Oahu and the uninhabited Northwe ...

and

Kauai Kauai (), anglicized as Kauai ( or ), is one of the main Hawaiian Islands. It has an area of 562.3 square miles (1,456.4 km2), making it the fourth-largest of the islands and the 21st-largest island in the United States. Kauai lies 73 m ...

. They have been found up to inland, and at

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

s of up to . Its

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

appears to have overlapped with that of the more coastal '' G. crinipes'', a species which is widespread across the

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

Description

''Geograpsus severnsi'' was probably the largest species in the genus. Based on the size of

sternite The sternum (: sterna) is the ventral portion of a segment of an arthropod thorax or abdomen. In insects, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the su ...

s, its

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

width may have been up to . Its claws were long, and in all the specimens with both claws preserved, the right claw was larger than the left. Most of the known specimens are males, but this is thought to reflect behavioral differences between the sexes, rather than an extreme

sex ratio A sex ratio is the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. However, many species deviate from an even sex ratio, ei ...

in the population. This is also seen in the

Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the Atlantic Ocean, South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overs ...

species ''

Johngarthia lagostoma ''Johngarthia lagostoma'' is a species of terrestrial crab that lives on Ascension Island and three other islands in the South Atlantic. It grows to a carapace width of on Ascension Island, where it is the largest native land animal. It exist ...

'', where females are likely to die on their

reproductive migration The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...

. It is therefore likely that ''G. severnsi'' had a similar

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

to other land crabs. It would have been an

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

and a

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

, possibly feeding on

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...

s and bird's eggs. Outside the genus ''Geograpsus'', there are no truly terrestrial crabs in Hawaii; the only well documented species is '' Chiromantes obtusifrons'', which may move up to inland, at elevations up to .

Systematics

''Geograpsus severnsi'' is one of five species in the genus ''

Geograpsus ''Geograpsus'' is a genus of crabs in the family Grapsidae, containing four extant taxon, extant species, and one extinct species: *''Geograpsus crinipes'' (Dana, 1851) *''Geograpsus grayi'' (H. Milne-Edwards, 1853) *''Geograpsus lividus'' (H. Mi ...

''. Its closest relative appears to be '' G. grayi'', a species found from the western

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

to the

Line Islands The Line Islands, Teraina Islands or Equatorial Islands () are a chain of 11 atolls (with partly or fully enclosed lagoons, except Vostok and Jarvis) and coral islands (with a surrounding reef) in the central Pacific Ocean, south of the Hawa ...

and

Marshall Islands The Marshall Islands, officially the Republic of the Marshall Islands, is an island country west of the International Date Line and north of the equator in the Micronesia region of the Northwestern Pacific Ocean. The territory consists of 29 c ...

. ''G. severnsi'' has been known to Hawaiian zoologists since the mid-1970s, but was only formally described in 2011. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''severnsi'' commemorates Mike Severns, the discoverer of the cave which housed most of the remains.

References

{{Taxonbar, from=Q4039345 Grapsidae Terrestrial crustaceans Holocene extinctions Endemic fauna of Hawaii Crustaceans described in 2011