Eodromites cristinarobinsae, 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 : 7-9

Eodromites cristinarobinsae sp. nov.

Figures 3 , 4

zoobank.org/ 0C2666F1-87E8-45CF-A13F-454831236171

2012 Eodromites grandis (von Meyer) ; Klompmaker et al., p. 790, fig. 5.

Diagnosis. Carapace ovoid to rectangular, narrowing posteriorly. Lateral margins distinctly rimmed anteriorly, rounded posteriorly. Rostrum triangular with axial concavity. Orbits deep and wide. Deep fissure in the lower orbital margin. Sinuous cervical groove in large specimens (see Klompmaker et al., 2012, figure 5).

Etymology. Named after Cristina M. Robins , expert on fossil galatheoid decapods.

Material studied. Holotype: MGSB78750 [previously MAB k2951 as in Klompmaker et al. (2012)]; paratypes: MAB k2952 (Klompmaker et al., 2012, figure 5C), 3592; UF 271883 ; other material: MAB k2475, 2513, 2626, 2638, 2950, 2953, 2954, 3089,

Maximum width (mm)

3589, 3596; UF 271792, UF 271793, UF 271794, UF 271835.

Occurrence. Koskobilo quarry, northern Spain (coordinates in Google Earth: 42.88, -2.20), reef limestones of the lower upper Albian Albeniz Unit of the Eguino Formation (Klompmaker, 2013a; López-Horgue and Bodego, 2017).

Dimensions. (In mm) MAB k3592: max. length excl. rostrum but incl. epigastric swellings (L)=5.2, max. width (W)=5.0; UF 271883: L=4.8, W=4.7; see Klompmaker et al. (2012, table 2) for more measurements.

Description. Carapace longer than wide in small specimens, about as long as wide in large specimens; oval to rectangular in shape; strongly vaulted in both directions in small specimens, moderately so for large specimens; widest at hepatic or epibranchial region. Fronto-orbital margin slightly smaller than maximum width. Lateral margins distinctly rimmed anteriorly, less so at epibranchial regions, not at meso-metabranchial regions. Posterior margin straight to slightly concave. Rostrum with wide base, triangular, downturned, with blunt tip, with axial concavity in dorsal view. Orbits deep, wider than tall, somewhat anterolaterally oriented, with vertical rim within orbit. Upper orbital margin with protrusion at outer orbital angle in larger specimens; deep fissure in orbital margin at lateralmost part of lower orbital margin; lower orbital margin rectangular, straight to weakly concave in dorsal view, not extending beyond upper orbital margin. Epigastric regions weak, transversely oriented. Protogastric and hepatic regions confluent, may show circular region with pits representing antennar extensor muscle scars ( Figure 4A ). Subhepatic region bulbous. Mesogastric region triangular to pyriform, with pair of scabrous posterior gastric muscle scars at base and weak axial groove in between, best defined anteriorly and posteriorly, weakly so in middle part. Uro-metagastric region indistinct, wide, confluent with epibranchial regions. Large epibranchial regions somewhat swollen laterally. Cardiac region pentagonal, weakly delimited, usually with three tubercles in triangle pointing posteriorly. Meso-metabranchial regions confluent, depressed laterally. Intestinal region not visible. Cervical groove moderately strong, with gastric pits on both sides of axis, strongest axially, widely V-shaped axially, then sinuous or at lower angle to longitudinal axis, with short transverse middle segment in large specimens, curving around subhepatic region on lateral side. Postcervical groove weak, absent axially. Branchiocardiac groove strongest away from longitudinal axis, nearly transverse on dorsal side, bending forward on lateroventral side to join cervical groove below subhepatic region. Posterior margin with groove. Epibranchial pits and pit on upper orbital margin sensu Starzyk (2015b) variably present. Weak tubercles laterally and anteriorly in some large specimens. Cuticle, appendages, majority of ventral side, and abdomen unknown.

Remarks. Specimens of this taxon were studied previously and referred to Eodromites grandis (Klompmaker et al., 2012) . The differences they noted were ascribed to intraspecific variation, including a larger maximum size for Late Jurassic specimens, possibly a somewhat more concave posterior margin, and a deeper fissure in the lower orbital margin. As a result of the collection of new specimens from Koskobilo (e.g., MAB k3592, 3589, 3596) and a non-cast specimen of E. grandis from the late Kimmeridgian of Germany (SNSB-BSPG 2016 XXI 404) for comparison, our restudy has led to the erection of the new species.

The new species is different from Eodromites grandis ( Figure 2 ) in multiple aspects. The fissure in the lower orbital margin near the lateralmost part of the margin in E. cristinarobinsae sp. nov. (MAB k2950, 2626, 3589; UF 271883) is indeed narrower and more prominent than in the Kimmeridgian specimen from Germany (SNSB-BSPG 2016 XXI 404) and using existing images in the literature (Wehner, 1988, plate 7.2B; Schweitzer and Feldmann, 2008a, plate 4C, D; Schweitzer and Feldmann, 2010a, figure 5.1; Hyžný et al., 2015, figure 6A). The more concave posterior margin for the Late Jurassic specimens of E. grandis is also confirmed. Maximum size is difficult to use as a convincing difference because size may be (micro)habitat-dependent (e.g., Klompmaker et al., 2013a, 2015a). Finally, the length-width ratios of E. cristinarobinsae sp. nov. are smaller than those of E. grandis for similar-sized specimens ( Figure 3 ). Moreover, using all data yields a statistical difference in length-width ratios (Mann-Whitney p=0.004).

Other species of Eodromites differ as well from the new species. Differences between E. bernchrisdomiorum sp. nov. and E. cristinarobinsae sp. nov. have been described above. Eodromites depressus has much more depressed metamesobranchial regions compared to E. cristinarobinsae sp. nov. (von Meyer, 1860, plate 23.18). Eodromites dobrogea is close to the new species, but its upper orbital margin lacks a projection at the outer orbital angle (Feldmann et al., 2006, figure 3.10; Schweitzer et al., 2007a, figure 4.3; Schweitzer and Feldmann, 2010a, figure 5.4-6) as seen in E. cristinarobinsae sp. nov. Moreover, the upper orbital margin of E. dobrogea bears granules or tiny spines (Schweitzer and Feldmann, 2010b), absent in E. cristinarobinsae sp. nov. The pits on the carapace cannot be used to distinguish the two species as they are variably present on the new species (see also above). Assuming that the drawing of E. nitidus is accurate (A. Milne-Edwards, 1865, plate 5.1a), E. nitidus has a lower orbital margin that is protruding much more in dorsal view and the axial part of the rostrum does not show a concavity in dorsal view as in E. cristinarobinsae sp. nov. The course of the cervical groove of E. polyphemi is more continuous and does not contain a short transverse middle segment as in large specimens of E. cristinarobinsae sp. nov. The single specimen of E. polyphemi is larger than any reported specimen of E. cristinarobinsae sp. nov. known thus far (Klompmaker et al., 2012; Appendix 2). Again, if the drawing of E. rostratus (von Meyer, 1860, plate 23.3) is accurate, the cervical groove of E. rostratus is more transversely oriented away from the longitudinal axis in E. rostratus . Finally, Eodromites rotundus has a less downturned rostrum and an orbital margin that appears more open laterally.

Ontogenetic differences were noted previously with smaller specimens being proportionally longer and more vaulted (Klompmaker et al., 2012). Furthermore, the cervical groove is more sinuous in larger specimens. Although the orbital structure has been used previously to distinguish between Eodromites species (Starzyk, 2015b), possible ontogenetic changes were not investigated thus far. The extent of the fissure in the lower orbital margin does not change much if anything as the animal grows, implying that this aspect of the orbital structure can be used to distinguish between species in Eodromites . The protrusion at the outer orbital angle is more pronounced in larger specimens (Klompmaker et al., 2012, figure 5; Figure 4 ).

Figures

FIGURE 2. Specimens of the crab Eodromites spp. from the Late Jurassic of Europe. A, F, G, Eodromites grandis (von Meyer, 1857) from the Upper Jurassic (upper Kimmeridgian) coral limestones of Saal an der Donau in southern Germany in dorsal, frontal, and left-lateral views, resp. (SNSB-BSPG 2016 XXI 404). B-E, Holotype of Eodromites bernchrisdomiorum sp. nov. from the Upper Jurassic (lower-middle Oxfordian) deposits of Ogrodzieniec in southern Poland in dorsal, frontal, right-lateral, and orbital views, resp. (I-F/MP/6259/1588/11). E, an oblique view of right orbital structure, primarily the lateral margin with a wide fissure. H-K, Late Jurassic (Oxfordian) Eodromites bernchrisdomiorum sp. nov. from southern Poland in dorsal view (H, I-F/MP/4874/1534/08, Niegowonice, middle-late Oxfordian; I, I-F/ MP/6255/1588/11, paratype, Niegowonice, middle-late Oxfordian; J, I-F/MP/6258/1588/11, Ogrodzieniec, early-middle Oxfordian, paratype; K, I-F/MP/1369/1508/08, Bzów, middle Oxfordian). L-O, Holotype of Eodromites polyphemi (Gemmellaro, 1869) from the Late Jurassic (Tithonian) of Sicily, Italy, in dorsal, frontal, right-lateral, and left-lateral views, resp. (MGUP-020.18). Scale bar width is 5.0 mm, except for E (1.0 mm).

FIGURE 3. Length-width ratios versus maximum width of carapaces of Eodromites grandis compared to E. cristinarobinsae sp. nov. (previously identified as E. grandis). Data: Appendix 2.

FIGURE 4. Specimens of the crab Eodromites cristinarobinsae sp. nov. from the mid-Cretaceous (lower upper Albian) reef limestones of Koskobilo, northern Spain. A-C, dorsal views (holotype MGSB78750, paratype UF 271883, and paratype MAB k3592, resp.). D-F, frontal views (MGSB78750, UF 271883, and MAB k2638, resp.). G, H, right- and left-lateral views (MAB k2950 and MAB k2953, resp.). I, oblique view of lateral part of orbital structure with fissure (MAB k2626); upper orbital margin incomplete; height figure ~1.0 mm. A, D, G, and H colored dark and subsequently coated with ammonium chloride prior to photography; from Klompmaker et al. (2012, figure 5B, H, J, and K, 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 Klompmaker et al. (2012). Scale bar width equals 1.0 mm.