Tanidromites scheffnerae Schweigert and Koppka, 2011

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 : 28-30

Tanidromites scheffnerae Schweigert and Koppka, 2011

Figure 16

2011 Tanidromites scheffnerae Schweigert and Koppka , p. 230, fig. 8.

2013 Tanidromites scheffnerae Schweigert and Koppka ; Starzyk, p. 180, figs. 3, 6.

2016 Tanidromites wysokaensis Starzyk , p. 7, figs. 2, 4.

Diagnosis. Species with large maximum size (~27

mm in length), length (without rostrum)-width ratio

~1.5, moderately-strongly convex transversely and longitudinally. Distance from outer orbital angle to cervical groove long (0.3-0.4 x length rostrum to cervical groove). Rostrum with sharp tip. Augenrest rounded, flat, and short (length about 0.6 x width); outer orbital spine absent. Mesogastric groove tubercles present. Lateral margins very rounded, paralleling in dorsal view. Cuticle and internal mold without to very limited ornamentation (modified from Starzyk, 2013, p. 180, after restudy, with major changes in italics).

Material studied. NHMW 1990 /0041/1318, 1990/ 0041/3962, 2014/0194/0312, 2014/0194/0314, 2014/0194/0988: Late Jurassic (Tithonian) specimens from coral reef limestones of the Ernstbrunn Limestone, Ernstbrunn quarries, Austria (Google Earth coordinates: 48.54, 16.35) (Schweitzer and Feldmann, 2009d; Schneider et al., 2013); I-F / MP/ 6261 /1588/11: Late Jurassic (Oxfordian) specimen from sponge-microbial limestones at Wysoka (Google Earth coordinates: 50.25, 19.21); I-F / MP/ 6263 /1588/11 (= paratype T. wysokaensis ): Late Jurassic (Oxfordian) specimen from sponge-microbial limestones at Niegowonice (Google Earth coordinates: 50.23, 19.26) .

Occurrence. Late Jurassic of Central Europe: middle-late Oxfordian of southern Poland (Starzyk, 2013, 2016; herein), late Kimmeridgian of southern Germany (Schweigert and Koppka, 2011), Tithonian of eastern Austria (herein).

Dimensions. (In mm) NHMW 1990/0041/1318: max. length excl. rostrum but incl. epigastric swellings (L)=> 16.5, max. width (W)=12.2; 1990/0041/ 3962: L=~25.0, W=~16.8; 2014/0194/0312: L=> 13.7, W=10.6; 2014/0194/0314: L=> 26.0, W=18.3; 2014/0194/0988: L=~23.7, W=16.0.

Description. See Schweigert and Koppka (2011, p. 230) and Starzyk (2013, p. 180-182). Additionally: hepatic pits arranged in a circle (antennar extensor muscle scars), as in Eodromites (Starzyk, 2015b) , present in this species.

Remarks. The second pair of muscle scars above those at the base of the mesogastric region (posterior gastric muscle scars) are not confirmed based on the Ernstbrunn material. Unlike the species diagnosis in Starzyk (2013, p. 180) suggests, a pit in the hepatic region seems present in two Ernstbrunn specimens (NHMW 1990/0041/1318, 2014/ 0194/0314). The posterior margin is not often preserved, giving this species a proportionally wider appearance than in reality. Limited intraspecific variation is observed. Unlike for some Mesozoic brachyurans (e.g., Klompmaker et al., 2012), the transverse and longitudinal convexity of smaller specimens is not markedly greater in this species. The augenrest shape is not noticeably different for small vs large specimens, except that larger ones may be somewhat wider proportionally ( Figure 16J, 16K ), confirming that overall augenrest shape may be used to distinguish species of different sizes.

Figures

FIGURE 16. Specimens of the crab Tanidromites scheffnerae Schweigert and Koppka, 2011, from the Late Jurassic (Tithonian) of Ernstbrunn, eastern Austria. A-C, G, dorsal views (NHMW 2014/0194/0988, 2014/0194/0314, 2014/ 0194/0312, and 1990/0041/1318, resp.). D-F, two left and one right views of augenrest (NHMW 1990/0041/1318, 2014/0194/0312, and 2014/0194/0314, resp.). H, I, L, two left- and one right-lateral views (NHMW 2014/0194/0314, 2014/0194/0312, and 2014/0194/0988, resp.). J, K, frontal views (NHMW 2014/0194/0312 and 2014/0194/0988, resp.). Scale bar width is 5.0 mm, except for D-F (1.0 mm).