Trigonotarbida Petrunkevitch, 1949

Dunlop, Jason A. & Garwood, Russell J., 2014, Tomographic reconstruction of the exceptionally preserved trigonotarbid arachnid Eophrynus prestvicii, Acta Palaeontologica Polonica 59 (2), pp. 443-454 : 446-447

Order Trigonotarbida Petrunkevitch, 1949

Remarks. ―As noted above, Trigonotarbida was split by Petrunkevitch (1949) into two, supposedly unrelated, groups. This scheme was subsequently questioned (e.g., Shear et al. 1987) and the two names (Anthracomartida and Trigonotarbida ) were reunited by Dunlop (1996). A formal synonymy list of trigonotarbid ordinal names can be found in Garwood and Dunlop (2011).

Family Eophrynidae Karsch, 1882

1882 Eophrynoidae fam. nov.; Karsch 1882: 560.

1890 Eophrynidae Karsch, 1882 ; Haase 1890: 651–652.

Type genus.― Eophrynus Woodward, 1871 ; see below.

Included genera.― Nyranytarbus Harvey and Selden, 1995 ; Petrovicia Frič, 1904 ; Planomartus Petrunkevitch, 1953 ; Pleophrynus Petrunkevitch, 1945 ; Pocononia Petrunkevitch, 1953 ; Somaspidion Jux, 1982 ; Stenotrogulus Frič, 1904 .

Emended diagnosis. ―Large, long-limbed and heavily ornamented trigonotarbids with nine opisthosomal tergites. Tergite 1 highly reduced, forming a locking ridge, tergites 2 and 3 unfused. Tergite 9 divided into medial and lateral plates. Opisthosoma bears two pairs of terminal spines originating from the lateral plates of tergites 8 and 9, and upward facing spines originating from the sternite on all opisthosomal segments anterior to this, except tergite 1. Anterior margin of the carapace drawn out into a long spine. Dorsal surface densely tuberculated, ventral surface sparsely tuberculated (emended from Dunlop 1994).

Remarks. ― Petrunkevitch (1955) recognised two eophrynid subfamilies: Eophryninae, characterised by conspicuous large opisthosomal tubercles, and Areomartinae, characterised by a more granular dorsal opisthosoma. These subfamilies were adopted to a certain degree by subsequent authors, although the resurrection of Haase’s (1890) family Kreischeriiidae by Rössler and Dunlop (1997) to accommodate the more “granular” eophrynids has rendered Areomartinae largely superfluous. We do not recognise subfamilies here. Some of the genera traditionally assigned to Eophrynidae (cf. Petrunkevitch 1953, 1955) are problematic, being based on incomplete and/or poorly described specimens. Dunlop (2010) excluded two problematic taxa. Areomartus ovatus Petrunkevitch, 1913 from West Virginia, USA —which also represents the type genus of Areomartinae—was treated as Trigonotarbida incertae sedis. Vratislavia silesica ( Römer, 1878) from Poland was transferred to Anthracosironidae . Figures of the (probably lost) type imply eophrynid-like terminal spines, but the rest of the elongate opisthosoma has proportions much more consistent with anthracosironids.

With respect to the remaining genera, Garwood and Dunlop (2011) proposed using XMT-based reconstructions of well-preserved anthracomartids as baseline models for the typical life appearance of members of this family. As noted in the introduction, a general problem with trigonotarbids is that some taxa are based on characters prone to being influenced by taphonomic processes—particularly in specimens hosted in shales—e.g., length/width ratios, absence of eyes, truncated carapaces, etc. We propose that our model here represents a “typical” and almost complete eophryind, and that deviations from this, which may be due to preservational factors represent poor grounds for maintaining separate taxa. Only a few eophrynid genera have been revised in detail, but provisional comments on differences between them and Eophrynus can still be made.

Pleophrynus Petrunkevitch, 1945 contains a single species, Pleophrynus verrucosus ( Pocock, 1911) . It is known from the Coal Measures of the UK and North America and was redescribed by Dunlop (1994). It differs from Eophrynus in having (i) somewhat isolated rows of large tubercles set against a background of smaller tubercles, and (ii) a distinct pattern of elongate ridges on the sternites close to the ventral midline ( Dunlop 1994: figs. 1b, 2c). Eophyrnus, by contrast, has tubercles formed on the midline in particular into complexes of four larger tubercles, and has as noted above more widely spaced ventral tubercles on the sternites rather than midline ridges. Stenotrogulus Frič, 1904 also contains a single species, Stenotrogulus salmii ( Stur, 1877) . It is known from the Coal Measures of the Czech Republic and was redescribed by Dunlop (1995a). It differs from Eophrynus (and Pleophrynus ) in having rather weakly expressed tubercles on the midline of the tergites, such that each tergite primarily reveals four distinct, large tubercles rather than six. The ventral surface of S. salmi is not known in detail.

Genus Eophrynus Woodward, 1871

1871 Eophrynus gen nov.; Woodward 1871: 386.

Type species.― Curculoides prestvicii Buckland, 1837 ; by monotypy; see below.

Included species.― Eophrynus udus Brauckmann, Koch, and Kemper, 1985 .

Remarks.―A number of trigonotarbid fossils were originally assigned to Eophrynus (cf. Stur 1877; Gill 1924; Dix and Pringle 1930; Guthörl 1938; Petrunkevitch 1949; Ambrose and Romano 1972). With the exception of E. prestvicii and E. udus , all have since been either synonymised or transferred to other genera/families; see e.g., Dunlop (1994, 1995 a, 1998) and discussions of the genera above. “ Eophrynus ” scharfi Scharf, 1924, from the early Permian Rotliegend of the Ilfeld region of Germany is an incomplete specimen in ventral view. It yields no unequivocal characters of Eophrynidae —or any other trigonotarbid family—and was treated by Rössler et al. (2003) as Trigonotarbida incertae sedis. An Eophrynus sp. was described from the Coal Measures of Ohio by McComas and Mapes (1988), but is incomplete and mostly preserved in ventral view.