| Geograpsus severnsi Temporal range: Holocene |
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|---|---|
| Type specimen | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Crustacea |
| Class: | Malacostraca |
| Order: | Decapoda |
| Infraorder: | Brachyura |
| Family: | Grapsidae |
| Genus: | Geograpsus |
| Species: | G. severnsi |
| Binomial name | |
| Geograpsus severnsi Paulay & Starmer, 2011 |
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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.
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Specimens of G. severnsi have been recovered from several of the Hawaiian high islands, including Hawaiʻi, Maui, Oʻahu and Kauaʻi. They have been found up to 2 km (1.2 mi) inland, and at altitudes of up to 950 m (3,120 ft).[1] Its range appears to have overlapped with that of the more coastal G. crinipes, a species which is widespread across the Indo-Pacific.[1]
Geograpsus severnsi was probably the largest species in the genus. Based on the size of sternites, its carapace width may have been up to 66 mm (2.6 in).[1] Its claws were 20–49 mm (0.79–1.9 in) long, and in all the specimens with both claws preserved, the right claw was larger than the left.[1] 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.[1] 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.[1] It would have been an omnivore and a predator, possibly feeding on insects, land snails and bird's eggs.[2] 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 (160 ft) inland, at elevations up to 10 m (33 ft).[1]
G. severnsi is one of five species in the genus Geograpsus. Its closest relative appears to be G. grayi, a species found from the western Indian Ocean to the Line Islands and Marshall Islands.[1] It has been known to Hawaiian zoologists since the mid 1970s, but was only formally described in 2011.[1] The specific epithet severnsi commemorates Mike Severns, the discoverer of the cave which housed most of the remains.[1]