Europrosopon aculeatum (von Meyer, 1857) 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 : 21-24

Europrosopon aculeatum (von Meyer, 1857) comb. nov.

Figures 11 , 12

zoobank.org/ 19380D4D-A956-4270-A9EA-B0BBB5CF7255

1857 Prosopon aculeatum von Meyer , p. 556.

1858 Prosopon verrucosum Reuss , p. 11.

1858 Prosopon marginatum von Meyer, 1842 ; Quenstedt, p. 779, pl. 95.34.

1859 Prosopon verrucosum Reuss ; Reuss, p. 70, pl.

24.1.

1860 Prosopon aculeatum von Meyer ; von Meyer, p.

211, pl. 23.24.

1867 Prosopon marginatum von Meyer ; Quenstedt, p. 315, pl. 26.9.

1964 Prosopon verrucosum Reuss ; Bachmayer, fig.

130.

1966 Prosopon verrucosum Reuss ; Patrulius, fig. 1B.

1988 Prosopon aculeatum von Meyer ; Wehner, p. 17, fig. 6, pl. 1.1-1.2.

2000 Prosopon aculeatum von Meyer ; Müller et al., fig. 17A.

2009d Prosopon verrucosum Reuss ; Schweitzer and Feldmann, p. 71-73, fig. 2.7, 2.8, 2.11, 2.12.

2009d Prosopon aculeatum von Meyer ; Schweitzer and Feldmann, p. 74-75, fig. 2.10.

2012b Prosopon verrucosum Reuss ; Schweitzer et al., fig. 10.1c.

2013b Prosopon verrucosum Reuss ; Klompmaker, fig. 1A.

2016 Prosopon verrucosum Reuss ; Hyžný and Zorn, p. 130, pl. 2.7a-b.

2016 Prosopon verrucosum Reuss ; Klompmaker, fig. 2 (left).

2018 Prosopon barbulescuae Schweitzer, Feldmann, Lazăr, Schweigert, and Franţescu , p. 327-328, fig. 13.

2018 Prosopon verrucosum Reuss ; Schweitzer et al., fig. 18.8.

Diagnosis. Carapace (excluding rostrum) longer than wide (l/w ratio ~1.1-1.3), ovoid, proportionally wider in larger individuals; usually widest at epibranchial regions in small specimens, widest at meso-/metabranchial regions in large specimens;

strongly convex transversely, moderately longitudinally. Entire carapace covered with small tubercles on internal mold, slightly larger tubercles on cuticle.

Material studied. NHMW 1990/0041/0033, 1990/

0041/0034, 1990/0041/1690, 1990/0041/2110,

1990/0041/2516, 1990/0041/2520, 1990/0041/

3071, 1990/0041/3205, 1990/0041/3756, 1990/

0041/3961, 1990/0041/4059, 1990/0041/4908, 2007z0149/0003, 2007z0149/0004, 2007z0149/ 0005: coral reef Ernstbrunn Limestone of the Ernstbrunn quarries (Google Earth coordinates: 48.54, 16.35), Austria, Late Jurassic (Tithonian) (Schweitzer and Feldmann, 2009d; Schneider et al., 2013); UF 288714 , 288756 : coral reef Štramberk Limestone of locality 3 at level 6 of the Kotouč quarry (Google Earth coordinates: 49.583, 18.116), Czech Republic, Late Jurassic (late early Tithonian) (Vašíček and Skupien, 2016; Vašíček et al., 2018) .

Occurrence. Late Jurassic of Central Europe. Tithonian of Austria, Czech Republic, and Romania; Kimmeridgian of Germany.

Dimensions. (In mm) NHMW 1990/0041/0033: max. length excl. rostrum (L)=~5.5, max. width excl. projections (W)=~4.8; 1990/0041/0034: L=~7.4, W=5.8; 1990/0041/1690: L=~7.0, W=-; 1990/0041/2110: L=7.3, W=6.2; 1990/0041/2516: L=5.7, W=4.7; 1990/0041/2520: L=8.2, W=7.3; 1990/0041/3071: L=~4.4, W=~3.6; 1990/0041/ 3205: L=-, W=~4.1; 1990/0041/3756: L=4.5, W=3.5; 1990/0041/3961: L=9.6, W=8.2; 1990/ 0041/4059: L=7.9, W=6.4; 1990/0041/4908: L=~2.1, W=~1.8; 2007z0149/0003: L=~14.6, W=13.7; 2007z0149/0004: L=~14.4, W=12.7; 2007z0149/0005: L=6.5, W=5.8; UF 288714: L=~4.0, W=~3.5; 288756: L=~4.4, W=~3.6.

Maximum length excluding rostrum (mm)

Description. Carapace (excluding rostrum) longer than wide (l/w ratio ~1.1-1.3), ovoid, proportionally wider in larger individuals; usually widest at epibranchial regions in small specimens, widest at meso-/metabranchial regions in large specimens; strongly convex transversely, moderately longitudinally. Rostrum downturned, with axial groove, triangular in frontal view, with fairly wide base. Orbital cavity shallow, anterolaterally oriented, with vertical ridge within with augenrest lateral to it; orbital rim with laterally oriented spine at outer orbital angle, modest triangular projection at lower orbital margin, one large node marked by groove posteriorly at upper orbital margin. Epigastric regions marked by subcircular swellings. Protogastric and hepatic regions confluent, protogastric regions may contain weak tubercle adjacent to mesogastric region. Subhepatic regions slightly swollen. Mesogastric region pyriform, well-delineated, may contain short axial groove at base. Metagastric region wide, curving around post-cervical groove, weakly separated from epibranchial regions. Urogastric region as wide as maximum width cardiac region, short but wide, best delineated posteriorly and laterally. Cardiac region triangular to pentagonal, with three small tubercles on internal mold. Meso-/metabranchial regions confluent, with rounded lateral margins. Small intestinal region defined anteriorly. Posterior margin with wide rim and two concavities. Grooves well-developed. Cervical groove sinuous, with two pits near axis. Post-cervical groove best defined in lateral portion, straight to slightly curving forward laterally. Branchiocardiac groove nearly parallel to cervical groove in lateral portion, where it curves forward to merge with cervical groove. Entire carapace covered with small tubercles on internal mold, slightly larger tubercles on cuticle. Weak posterior gastric muscle scars may be present at base mesogastric region on internal mold. Ventral surface, abdomen, and appendages unknown.

Remarks. Wehner (1988) was aware of the close similarity between Europrosopon aculeatum and E. verrucosum , but she decided not to synonymize the two taxa because of lack of comparative material of E. verrucosum . Wehner (1988, p. 19) mentioned that the anterior part of E. verrucosum seems to be shorter, and that “the two small, oblique elevations between the cardiac and urogastrical regions” of E. aculeatum would be different. Furthermore, Schweitzer and Feldmann (2009d) mentioned that E. verrucosum would have a much longer metagastric region and that E. aculeatum had nodes on the protogastric regions, which would be absent in E. verrucosum . The arguments that the anterior part of E. verrucosum would be shorter and that its metagastric region would be proportionally longer is not supported by the data we gathered (see Appendix 3). The oblique elevations on the urogastric region as drawn by von Meyer (1860, plate 23.24) and Wehner (1988, figure 6) are more horizontally oriented in the actual specimens (Wehner, 1988, plate 1.1- 1.2). Similar elevations can also be seen in some specimens ascribed to E. verrucosum (Schweitzer and Feldmann, 2009d, figure 2.8; Klompmaker, 2013b, figure 1A). Finally, fairly similar nodes on the protogastric regions can also be seen in some specimens of E. verrucosum (Bachmayer, 1964, figure 130; Schweitzer and Feldmann, 2009d, figure 2.8; Klompmaker, 2013b, figure 1A). Stratigraphically, the taxa are not separated by much (upper Kimmeridgian for E. aculeatum versus Tithonian for E. verrucosum ) and both taxa are found in Central Europe. Thus, we consider E. verrucosum to represent a junior synonym of E. aculeatum .

Recently, Schweitzer et al. (2018) erected Prosopon barbulescuae based on two specimens from the Tithonian of Romania, mentioned to differ mainly from congenerics by having its widest point at the epibranchial regions rather than at the confluent meso-/metabranchial regions, which was also noted by Guinot (2019). However, the specimens of this taxon are smaller compared to figured coeval specimens of E. aculeatum (= E. verrucosum ) (e.g., Schweitzer and Feldmann, 2009d, figure 2; Hyžný and Zorn, 2016, plate 2.7a-b). Given that many brachyurans, including goniodromitids, become proportionally wider as the animal grows, in particular by allometric growth of the meso-/metabranchial region (e.g., Klompmaker et al., 2012), this raises the question as to whether P. barbulescuae is juvenile of E. aculeatum . We reexamined the material ascribed to E. verrucosum by Schweitzer and Feldmann (2009d) plus some additional specimens. We find that the length-width ratios of P. barbulescuae fall within the range of E. aculeatum ( E. verrucosum ), and that width increases faster than length as the crab grows (allometric growth) ( Figure 12 , Appendix 4). Moreover, small specimens identified as E. verrucosum are usually widest at the epibranchial regions ( Figure 11A, B , NHMW 1990/0041/3071), whereas larger specimens are consistently wider at the meso-/metabranchial regions ( Figure 11F ). Schweitzer et al. (2018, p. 328) mentioned other differences between E. verrucosum and P. barbulescuae : stronger spines on the upper margin of the augenrest for P. barbulescuae , the epigastric region of E. verrucosum would be square instead of ovoid, the postcervical groove would bend concave forwardly in the lateralmost portion in E. verrucosum rather than being straight, and the cardiac region of E. verrucosum would be longer. These minor, possible differences are absent to inconsistent across all studied specimens previously ascribed to E. verrucosum . Thus, we consider P. barbulescuae to represent a junior synonym of E. aculeatum (= E. verrucosum ).

Figures

FIGURE 11. Specimens of the crab Europrosopon aculeatum (von Meyer, 1857) comb. nov. from the Late Jurassic (Tithonian) of Central Europe, all dorsal views. A, C, F, Specimens from Ernstbrunn, Austria (NHMW 1990/0041/3756, 2007z0149/0005, and 1990/0041/2520, resp., previously identified as Prosopon verrucosum by Schweitzer and Feldmann (2009d). B, Specimen (UF 288714) from the Kotouc quarry (locality 3 of level 6), Czech Republic. D, E, Specimens (LPBIII art 279 and LPBIII art 278, resp.) from Waypoint 162, Romania, previously identified as Prosopon barbulescuae (modified from Schweitzer et al., 2018, figure 13, reproduced with permission). Those images are not published under the terms of the CC-BY license of this article. For permission to reuse, please see Schweitzer et al. (2018). Note that the specimen in D is oriented toward the anterior portion of the carapace. Scale bar width equals 2.0 mm.

FIGURE 12. Comparison of length-width ratios relative to specimen size for carapaces of three previously recognized brachyuran species that are synonymized herein: Europrosopon aculeatum (=E. verrucosum and E. barbulescuae). Specimens grew proportionally wider (allometric growth). Data: Appendix 4.