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| Family: | Eocarcinidae Withers, 1932
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| Genus: | Eocarcinus Withers, 1932
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| Species: | E. praecursor
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| Binomial name | |
| Eocarcinus praecursor Withers, 1932
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Eocarcinus praecursor is a Jurassic species of decapod crustacean, sufficiently distinct from its relatives to be placed in its own family (Eocarcinidae).[1] Often considered the oldest true crab, it was considered by a 2010 study to be an early member of the Anomura. However, a reanalysis in 2020 again found it to be the earliest known stem-group crab.[2]
It lived during the early Pliensbachian age (Lower Jurassic),[3] and has been found in rocks at two sites in the United Kingdom – Mickelton Tunnel (near Aston Magna), Gloucestershire and Runswick Bay, Yorkshire.[4]
In many of its characters, it represents a transitional stage between the Glypheoidea and the Middle Jurassic crabs in the Prosopidae.[3] Since its ancestors were long-tailed decapods, and its successors were short-tailed crabs, Eocarcinus has been described as "the lobster who decided to become a crab".[5] Previously considered to be the oldest known true crab, a 2010 revision concluded that Eocarcinus could not be accommodated among the Brachyura, and was instead transferred to the Anomura.[6] However, a 2020 reanalysis found that it was again the earliest known stem-group crab, but that it had not undergone the process of carcinisation.[2]