Tanidromites nightwishorum, 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 : 34-36

Tanidromites nightwishorum sp. nov.

Figure 19

zoobank.org/ E467C990-505E-4047-9DFA-1EF726781C6D

Diagnosis. Carapace rectangular, length-width ratio> 1.4, widest at very swollen epibranchial region. Rostrum with wide base, slightly downturned. Augenrest moderately concave, semicircular, taller than wide, with short groove isolating outer orbital angle; lower orbital margin extending beyond upper orbital margin, which contains some tubercles or spines. Lateral margin rounded; flanks with depression posterior to orbital rim. Cuticle and internal mold bear limited ornamentation as preserved, some small tubercles on hepatic region.

Etymology. Named in honor of the members of the symphonic metal band Nightwish (Troy Donockley, Kai Haito, Marco Hietala, Tuomas Holopainen, Floor Jansen, and Emppu Vuorinen), in particular for their 2015 album “Endless Forms Most Beautiful” about the evolution of life.

Material studied. Holotype and sole specimen: NHMW 1990 /0041/3327.

Occurrence. 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).

Dimensions. (In mm) NHMW 1990/0041/3327: max. length excl. rostrum (L)=>21.6, max. width (W)=15.5.

Description. Carapace rectangular, length-width ratio> 1.4, holotype large for genus, widest at epibranchial region, moderately convex longitudinally and transversely. Rostrum with wide base, with axial groove, slightly downturned. Orbital structure anterolaterally oriented, augenrest moderately concave, semicircular, taller than wide, with short groove isolating outer orbital angle; lower orbital margin extending beyond upper orbital margin, which contains some tubercles or spines. Epigastric regions distinctly swollen. Protogastric and hepatic regions confluent but with shallow groove arising from upper orbital margin to hepatic pit; with circular group of hepatic pits on internal mold (antennar extensor muscle scars), anterior to hepatic pit. Mesogastric region pyriform, with pair of semicircular muscle scars (posterior gastric muscles) at base on internal mold. Uro-metabranchial region short, confluent laterally with epibranchial regions, which are long and swollen laterally. Cardiac region subpentagonal, fairly large, poorly delimited anteriorly. Meso-metabranchial region not divided, depressed, incompletely preserved. Intestinal region not well-visible. Lateral margin rounded, not rimmed; flanks steep, with depression posterior to orbital rim. Mesogastric groove weaker in middle part, with tubercle in posterior part. Cervical groove strong, widely U-shaped in center, then curving more laterally at intersection with mesogastric groove, then bending forward again on flank, with gastric pits just adjacent to longitudinal axis. Postcervical grooves shallow, consisting of two short grooves, not expressed at axial region. Branchiocardiac groove strong laterally, less pronounced at axial region, bending forward on flank. Cuticle and internal mold bear limited ornamentation as preserved, some small tubercles on hepatic region. Posterior margin, appendages, venter, and abdomen not preserved.

Remarks. Superficially, this specimen most resembles Tanidromites insignis , T. aequilatus , and T. alexandrae . Though reminiscent of T. insignis in overall shape, size, groove structure, and convexity, the lower orbital margin is protruding much more than in T. insignis , and the course of the cervical groove appears more forwardly oriented on the flank than in T. insignis (Wehner, 1988, plate 5.2b; Schweitzer and Feldmann, 2008a, figure 6D; Schweigert and Koppka, 2011, figure 6C; Starzyk, 2013, figure 4E, G; herein). Additionally, this specimen contains a number of pits arranged in a circle just anterolaterally to the hepatic pit on the internal mold, not seen in a well-preserved, studied specimen of T. insignis from the Oxfordian of Poland (IF/MP/6253/1588/11) or any other figured specimens of T. insignis , although the quality of the figures is often insufficient to be sure, so more specimens are needed to confirm this difference. This circle is equivalent to the “hepatic pits”, representing antennar extensor muscle attachment scars (Klompmaker et al., 2019), also seen in Eodromites spp. (Starzyk, 2015b). The grooves of the Polish specimen of T. insignis mentioned above are shallower.

Multiple differences exist compared to T. aequilatus . The meso-metabranchial regions of the new species appear much more depressed, and the epibranchial regions are more swollen than in T. aequilatus (Wehner, 1988, plate 5.4, 5.5; Schweitzer and Feldmann, 2008a, plate 3E; Starzyk, 2015b, figure 5). Furthermore, the rostrum may be more downturned in T. aequilatus , the orbital structure is oriented more anterolaterally in dorsal view, and the augenrest seems rimmed more strongly.

Tanidromites alexandrae is similar in many aspects, including the extended lower orbital margin and the shape of this margin, the presence of mesogastric groove tubercles, the single hepatic pit, a posterior groove originating from the upper orbital margin (sensu Starzyk, 2015a), and the overall pattern and strength of the grooves. As in T. alexandrae , there also appear to be small spines/ tubercles on the upper orbital margin. However, the augenrests appear wider relative to the height in T. alexandrae (Starzyk, 2015a, figure 2F, 2G; Figure 19 ). Another difference is the presence of a groove within the lateralmost part of the augenrest intersecting with the upper orbital margin but not with the lower orbital margin, a feature not present in T. alexandrae (e.g., Starzyk, 2015a, figure 2; UF 272110; UF 272116). Furthermore, the ratio of the length from the outer orbital angle to the cervical groove at the lateral margin divided by the estimated length from the tip of the rostrum to the cervical groove on the axis is ~0.33 for the new species, whereas this ratio ranges from 0.21-0.26 for T. alexandrae (Starzyk, 2015a) . It may be possible that this ratio increases as the animal grows because a single relatively large specimen of the type series of T. wysokaensis (=junior synonym of T. scheffnerae ) has the highest ratio (0.41), but a larger specimen of T. scheffnerae from the same region and stratigraphic level (I-F/MP/6261/1588/ 11) has a ratio of only 0.34. Another possible difference is the maximum size: out of 211 specimens, the maximum length of T. alexandrae is only 9.6 mm, whereas the single specimen under study is> 21.6 mm long excluding the rostrum. Finally, the cervical groove is directed more forward in this specimen compared to T. alexandrae (Starzyk, 2015a, figure 2B).

Nearly all other congenerics bear less swollen epibranchial regions, except perhaps for Tanidromites lithuanicus and T. schweitzerae . Furthermore, T. etalloni , a species with a smaller maximum size, shows a cervical groove that is more vertically oriented on the flank in lateral view (pers. obs. AAK of I-F/MP/6254/1588/11 and I-F/MP/1740/1517/08), and the lower orbital margin seems less prominent. The small specimens of T. hyznyi have a proportionally shorter distance of the lateral margin anterior to the intersection of the cervical groove, and they possess proportionally wider augenrests. Tanidromites lithuanicus has a more downturned rostrum, more ornamentation on the cuticle, and a more swollen cardiac region. The orbital margins of T. longinosa are less prominent so that the augenrests appear shallower. Unlike the new species, T. maerteni bears two strong tubercles/spines on the lateral margin. The meso-metabranchial region of T. montreuilense seems proportionally larger, and its rostrum is more downturned. Tanidromites pustulosa (Schweitzer and Feldmann, 2010c, figure 1.13-1.14; Hyžný and Zorn, 2016, plate 2.4) bears many tubercles across the carapace (rare in the new species as preserved) and has a narrower base of the rostrum. Tanidromites raboeufi and T. scheffnerae bear less concave augenrests. Tanidromites richardsoni exhibits larger outer orbital projections. Specimens of T. sculpta , much smaller in maximum size in the same Ernstbrunn assemblage based on 12 specimens, have a proportionally shorter distance of the lateral margin anterior to the intersection of the cervical groove, which applies too to T. muelleri and T. weinschenki sp. nov. The latter two species are also more tubercular. The comparably-sized holotype of T. schweitzerae (~ 14.8 mm wide) has no tubercles/spines on the upper orbital margin, bears lower orbital margins that are projected more forwardly, and the rostrum’s base is narrower. The small specimen of Tanidromites starzykae contains grooves that are oriented more transversely than in the new species.

Superfamily KONIDROMITOIDEA Schweitzer and Feldmann, 2010a

Family KONIDROMITIDAE Schweitzer and Feldmann, 2010a

Genus KONIDROMITES Schweitzer and Feldmann, 2010a

Type species. Oxythyreus gibbus Reuss, 1858 , by original designation.

Included species. Konidromites gibbus (Reuss, 1858) ;? K. schneideri (Stolley, 1924) .

Figures

FIGURE 19. Holotype and sole specimen of the crab Tanidromites nightwishorum sp. nov. (NHMW 1990/0041/3327) from the Late Jurassic (Tithonian) of Ernstbrunn, eastern Austria. A, dorsal view of carapace. B, frontal view. C, orbital view (straight on). D, left-lateral view. E, orbital view (laterally). Scale bar width is 5.0 mm, except for C and E (1.0 mm).