Eocarcinus Explained

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]

Distribution

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]

Description

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.

Notes and References

1. . 2009 . Suppl. 21 . 1–109 . A classification of living and fossil genera of decapod crustaceans . Sammy De Grave . N. Dean Pentcheff . Shane T. Ahyong . etal . dead . https://web.archive.org/web/20110606064728/http://rmbr.nus.edu.sg/rbz/biblio/s21/s21rbz1-109.pdf . 2011-06-06 .
2. Scholtz. Gerhard. November 2020. Eocarcinus praecursor Withers, 1932 (Malacostraca, Decapoda, Meiura) is a stem group brachyuran. Arthropod Structure & Development. en. 59. 100991. 10.1016/j.asd.2020.100991. 32891896. free.
3. M. Krobicki . M. Zaton . 2008 . Middle and Late Jurassic roots of brachyuran crabs: Palaeoenvironmental distribution during their early evolution . . 263 . 1–2 . 30–43 . 10.1016/j.palaeo.2008.01.025. 2008PPP...263...30K .
4. Une nouvelle famille de Crabes du Crétacé, et la notion de Podotremata Guinot, 1977 (Crustacea, Decapoda, Brachyura) . Danièle Guinot . Marcos Tavares . . 2001 . 23 . 3 . 507–546 .
5. Anonymous . . The Royal Society Conversazione . 1 . 3724 . 1932 . 946–947. 10.1136/bmj.1.3724.944 . 220003084 . JSTOR: 1st page, 2nd page
6. Rodney M. Feldmann . Carrie E. Schweitzer . 2010 . Is Eocarcinus Withers, 1932, a basal brachyuran? . . 30 . 2 . 241–250 . 10.1651/09-3230.1. free .