Prosopon josephcollinsi, Klompmaker & Starzyk & Fraaije & Schweigert, 2020

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 : 25-26

Prosopon josephcollinsi sp. nov.

Figure 14

zoobank.org/ 738A9151-07FA-4659-997A-069F5B821578

Diagnosis. Carapace longer than wide (l/w ratio ~1.15), rectangular to trapezoid in dorsal view, widest at branchial region, bulbous appearance anteriorly. Rostrum downturned, with broad base, triangular in frontal view. Mesogastric region pyriform, well-delineated, with two strong nodes posteriorly along axis. Mesobranchial region divided from swollen epibranchial region by strong groove. Tubercles primarily present on anterior carapace and on lateral parts posterior carapace.

Etymology. Named after Joseph S.H. Collins (scientific associate of the Natural History Museum in London until he passed away in 2019), for a lifetime of work on fossil crustaceans, particularly Brachyura .

Material studied. Holotype and sole specimen: NHMW 1990 /0041/0738.

Occurrence. Coral reef Ernstbrunn Limestone of the Ernstbrunn quarry “Werk II” (Google Earth coordinates: ~48.54, ~16.35), Austria, Late Jurassic (Tithonian) (Schweitzer and Feldmann, 2009d; Schneider et al., 2013).

Dimensions. (In mm) NHMW 1990/0041/0738: max. length excl. rostrum (L)=11.4, max. width (W)=9.9.

Description. Carapace longer than wide (l/w ratio ~1.15), rectangular to trapezoid in dorsal view, widest at branchial region, strongly convex transversely, weakly-moderately longitudinally, bulbous appearance anteriorly. Lateral margins rounded, slightly diverging posteriorly. Posterior margin bounded by groove, with two slight concavities. Flanks fairly tall. Rostrum downturned, with broad base, triangular in frontal view. Orbital structure not exposed. Epigastric region consisting of two circular swellings. Protogastric and hepatic regions divided by oblique groove. Mesogastric region pyriform, well-delineated, with two strong nodes posteriorly along axis. Uro-metagastric region fairly narrow, confluent with mesobranchial region that is divided from swollen epibranchial region by strong groove. Cardiac region pentagonal in shape with tip pointing posteriorly, somewhat inflated anteriorly. Metabranchial region largest. Intestinal region not visible. Grooves generally deep, with cervical groove widely U-shaped. Cervical and branchiocardiac grooves paralleling each other in dorsal view except on axial part, merging on flank around epibranchial region. Post-cervical groove marks anterior border of cardiac region, ends in deep pit lateral to cardiac region. Tubercles primarily present on anterior carapace and on lateral parts posterior carapace. No clear muscle scars visible. Cuticle present around tip of mesogastric region, on posterior part right metabranchial region, and partly on left flank. Appendages, ventral surface, and abdomen unknown.

Remarks. For comparison to the type species, Prosopon tuberosum from the “Neocomian” (earliest Cretaceous, Berriasian-Hauterivian) of eastern France, we assumed that the drawing accurately reflects the specimen, which has not been located and is presumed to have been lost (Wehner, 1988; Schweitzer and Feldmann, 2009d). Prosopon josephcollinsi sp. nov. bears more tubercles on the antero-lateral and anterior portion of the carapace on its internal mold, which tends to have fewer tubercles than the cuticle (see Klompmaker et al., 2015c); has somewhat narrower branchial regions for this similar-sized specimen; and the nodes on the posterior part of the mesogastric region are more pronounced. Prosopon jocosum from the Kimmeridgian of Switzerland was described based on two syntypes, figures of which can be found online (science.mnhn.fr/taxon/species/prosopon/ jocosum). One specimen (MNHN.F.A29786) is clearly deformed anteriorly so that length-width ratio is lower than in reality, but its rostrum appears narrower as preserved and with a strong axial groove unlike P. josephcollinsi sp. nov. The other specimen (MNHN.F.A29787), of comparable length to P. josephcollinsi sp. nov., has a much higher length-width ratio than the new species (~1.38 vs ~1.15). Prosopon mammillatum from the Bathonian of England (see also Withers, 1951) does not have a clear groove separating epibranchial region from metagastric region and bears smaller nodes on the posterior part of the mesogastric region.

Figures

FIGURE 14. Specimen of the crab Prosopon josephcollinsi sp. nov. (NHMW 1990/0041/0738) from the Late Jurassic (Tithonian) of Ernstbrunn, eastern Austria. A, dorsal view of carapace. B, left-lateral view. C, frontal view. D, right-lateral view, angled. Scale bar width equals 5.0 mm.