Nodoprosopon, Beurlen, 1928 b

Klompmaker, Adiël A., Starzyk, Natalia, Fraaije, René H. B. & Schweigert, Günter, 2020, Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura), Palaeontologia Electronica (a 32) 23 (2), pp. 1-54 : 12-13

Genus NODOPROSOPON Beurlen, 1928b

Type species. Prosopon ornatum von Meyer, 1857 , by original designation and monotypy.

Included species.? Nodoprosopon echinorum Collins in Collins and Wierzbowski, 1985; N. ornatum (von Meyer, 1857) , as Prosopon .

Remarks. Nodoprosopon was originally placed in Prosopinidae (= Prosopidae ) by Beurlen (1928b) and Prosopidae was still its placement in 2007 (Schweitzer et al., 2007a). Subsequently, Schweitzer and Feldmann (2009d) placed this genus in a new family, Nodoprosopidae , because they found the shape of the carapace and rostrum to be unique among Jurassic brachyurans and the genus differed from members of Prosopidae and Longodromitidae . They recognized that placement of Nodoprosopidae within Glaessneropsoidea may be an issue because the orbital structure was unknown. Despite attempts to reveal the orbits, we did not find a single orbital cavity in 28 specimens of Nodoprosopon ornatum , from which we conclude that this cavity is likely to have been poorly developed and/or lightly calcified. Guinot (2019) opined that Nodoprosopon may be close to Bucculentidae . There are multiple similarities including the overall regional definition, but differences also exist such as the orbits and the hepatic region of Bucculentum Schweitzer and Feldmann, 2009d , which is much more swollen, so that the carapace of bucculentids is more rectangular in shape than in Nodoprosopon ( Guinot, 2019; pers. obs. AAK). The trifid rostrum combined with the outer orbital spines are not known among Glaessneropsoidea, but they are characteristic of Homolodromiidae (Homolodromioidae). This still extant family is represented by Homolus auduini Eudes-Deslongchamps, 1835 , in the Jurassic (Schweitzer and Feldmann, 2010d). Nodoprosopon fits Homolodromiidae well in many aspects (Schweitzer et al., 2004, 2012b): overall outline of dorsal carapace with diverging lateral margins posteriorly, presence of outer orbital and rostral spines (one central spine at a lower level and two diverging spines), lacking well-defined orbits, a somewhat inflated subhepatic region, well-defined cervical and branchiocardiac grooves paralleling each other, and a spinose character on anterior carapace as in a number of fossil members ( H. auduini and Antarctidromia inflata Förster, Gaździcki, and Wrona, 1985 ). Thus, we propose that the trifid rostrum and outer orbital spines in Nodoprosopon are not an example of convergent evolution toward members of Homolodromiidae . Instead, we place Nodoprosopon in Homolodromiidae .

Rostral spines on their own do represent an example of convergent evolution, however. Diverging rostral spines in combination with a posteriorly widening carapace also occur in the mid-Cretaceous majoids, Priscinachidae Breton, 2009 (Breton, 2009; Klompmaker, 2013a). However, Nodoprosopon bears a third, central rostral spine and appears to exhibit less developed orbits not visible adjacent to the rostral structure and without notches. Another Mesozoic crab, the homolid Doerflesia ornata Feldmann and Schweitzer, 2009 , characterized by a linea homolica not observed in Nodoprosopon , also bears two diverging rostral spines. Other non-homolodromiids with at least two rostral spines include, for example, Poupiniidae Guinot, 1991 (Guinot, 1991; Feldmann et al., 1993), some Raninoida (Van Bakel et al., 2012), some Prosopidae ( Laeviprosopon laeve ) (Schweitzer and Feldmann, 2008b), and Bucculentidae Schweitzer and Feldmann, 2009d (Starzyk et al., 2011).

Nodoprosopon echinorum was placed in the homolid genus Tithonohomola Glaessner, 1933 by Wehner (1988) based on the presumed possession of a linea homolica. Subsequently, Schweitzer et al. (2007a) placed N. echinorum in Nodoprosopon after comparison to N. ornatum , and Feldmann and Schweitzer (2009) added that no linea homolica could be found in the holotype. However, the taxon has not been mentioned in the literature about Nodoprosopon since (see Schweitzer and Feldmann, 2009d; Schweitzer et al., 2010). The species resembles Vectis Withers, 1945 , and Verrucarcinus Schweitzer and Feldmann, 2009d , in overall shape, delineation of regions, and overall ornamentation. Unfortunately, the frontal region of N. echinorum is not preserved. For now, we questionably retain that species in Nodoprosopon , but further study of the holotype and new specimens when available would be welcome to reevaluate its generic placement.