Trigonotarbus johnsoni, Pocock, 1911

Jones, Fiona M., Dunlop, Jason A., Friedman, Matt & Garwood, Russell J., 2014, Trigonotarbus johnsoni Pocock, 1911, revealed by X-ray computed tomography, with a cladistic analysis of the extinct trigonotarbid arachnids, Zoological Journal of the Linnean Society 172 (1), pp. 49-70 : 53

TRIGONOTARBUS JOHNSONI

Trigonotarbus johnsoni is a key species, being the namegiving taxon for the order Trigonotarbida . Furthermore, it represents a well-preserved species superficially similar in appearance to the earliest known but poorly preserved trigonotarbid Palaeotarbus jerami , and is not an overt member of either the eophrynid assemblage nor the Palaeocharinus /anthracomartid group. Indeed, both of these groupings have been recently restudied with the aid of X-ray microtomography (micro-CT; Garwood, Dunlop & Sutton, 2009; Garwood & Dunlop, 2011; Dunlop & Garwood, 2014). For this reason we included a redescription of Tr. johnsoni based on restudy of the original material and a micro-CT scan in the present study.

Trigonotarbus johnsoni was erected by Pocock (1911) based on a series of fossils from the famous Coal Measures site of Coseley near Dudley in the English West Midlands (see Material and methods). These specimens originated from the Egginton, Johnson, and Madeley collections. Henry Johnson (1823–1885), after whom the species is named, was a civil and mining engineer and a Fellow of the Geological Society who lived in Dudley and was noted as an avid fossil collector (Jones 1885). Trigonotarbus johnsoni is one of the smaller Coal Measures trigonotarbids, typically about 5–6 mm in body length, and has a rather simple body plan without strong ornamentation of the body. The carapace is notably triangular and is presumably the source of the genus name: a combination of the ancient Greek trigono (τρίγωνo = triangle) and the suffix tarbos (τάρβoς = terror). The carapace has a raised central ridge bearing a pair of median eyes. The legs are fairly short and stubby. As noted above, Pocock (1911) originally allied this species with Anthracosiro in Anthracosironidae , before Petrunkevitch (1949) placed it as the type and only genus of a new family Trigonotarbidae .