Geograpsus severnsi
Encyclopedia
Geograpsus severnsi is an extinct
species of land crab
from Hawaii
. It died out shortly after humans colonized the Hawaiian Islands
, and is the first documented example of a crab becoming extinct in historical times.
s, including Hawaii
, Maui
, Oahu
and Kauai
. They have been found up to 2 km (1.2 mi) inland, and at altitude
s of up to 950 m (3,116.8 ft). Its range
appears to have overlapped with that of the more coastal G. crinipes, a species which is widespread across the Indo-Pacific
.
width may have been up to 66 mm (2.6 in). Its claws were 20 millimetre 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
in the population. This is also seen in the Ascension Island
species Johngarthia lagostoma
, where females are likely to die on their reproductive migration. It is therefore likely that G. severnsi had a similar ecology
to other land crabs. It would have been an omnivore
and a predator, possibly feeding on insect
s, land snail
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 50 m (164 ft) inland, at elevations up to 10 m (32.8 ft).
. Its closest relative appears to be G. grayi, a species found from the western Indian Ocean
to the Line Islands
and Marshall Islands
. It has been known to Hawaiian zoologists since the mid 1970s, but was only formally described in 2011. The specific epithet severnsi commemorates Mike Severns, the discoverer of the cave which housed most of the remains.
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally 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 recover may have been lost before this point...
species of land crab
Land crab
Gecarcinidae is a family of true crabs that are adapted for terrestrial existence, commonly known as land crabs. Similar to all other crabs, land crabs possess a series of gills. In addition, the part of the carapace covering the gills is inflated and equipped with blood vessels. These organs...
from Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. It died out shortly after humans colonized the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, and is the first documented example of a crab becoming extinct in historical times.
Distribution
Specimens of G. severnsi have been recovered from several of the Hawaiian high islandHigh island
In geology , a high island is an island of volcanic origin. The term can be used to distinguish such islands from low islands, whose origin is due to sedimentation or uplifting of coral reefs.-Definition and origin:...
s, including Hawaii
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
, Maui
Maui
The island of Maui is the second-largest of the Hawaiian Islands at and is the 17th largest island in the United States. Maui is part of the state of Hawaii and is the largest of Maui County's four islands, bigger than Lānai, Kahoolawe, and Molokai. In 2010, Maui had a population of 144,444,...
, Oahu
Oahu
Oahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the U.S. state of Hawaii. The state capital Honolulu is located on the southeast coast...
and Kauai
Kauai
Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...
. They have been found up to 2 km (1.2 mi) inland, and at altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
s of up to 950 m (3,116.8 ft). Its range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
appears to have overlapped with that of the more coastal G. crinipes, a species which is widespread across the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
.
Description
Geograpsus severnsi was probably the largest species in the genus. Based on the size of sternites, its carapaceCarapace
A carapace is a dorsal 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 underside is called the plastron.-Crustaceans:In crustaceans, the...
width may have been up to 66 mm (2.6 in). Its claws were 20 millimetre 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
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
in the population. This is also seen in the Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
species Johngarthia lagostoma
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 exists in two distinct colour morphs, one yellow and one purple,...
, where females are likely to die on their reproductive migration. It is therefore likely that G. severnsi had a similar ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
to other land crabs. It would have been an omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
and a predator, possibly feeding on insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, land snail
Land snail
A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod mollusks that have shells, It is not always an easy matter to say which species are terrestrial, because some are more or less...
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 50 m (164 ft) inland, at elevations up to 10 m (32.8 ft).
Systematics
G. severnsi is one of five species in the genus GeograpsusGeograpsus
Geograpsus is a genus of crabs in the family Grapsidae, containing five species:*Geograpsus crinipes *Geograpsus grayi *Geograpsus lividus *Geograpsus stormi De Man, 1895...
. Its closest relative appears to be G. grayi, a species found from the western Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
to the Line Islands
Line Islands
The Line Islands, Teraina Islands or Equatorial Islands, is a chain of eleven atolls and low coral islands in the central Pacific Ocean, south of the Hawaiian Islands, that stretches for 2,350 km in a northwest-southeast direction, making it one of the longest islands chains of the world...
and Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
. It has been known to Hawaiian zoologists since the mid 1970s, but was only formally described in 2011. The specific epithet severnsi commemorates Mike Severns, the discoverer of the cave which housed most of the remains.