Ferroranina tamilnadu, Van Bakel & Guinot & Artal & Fraaije & Jagt, 2012

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 32-33

Ferroranina tamilnadu n. sp.

( Fig. 9A–J )

Cretacoranina cf. dichrous ( Stenzel, 1945) ; Guinot et al. 2008: 705, 712, fig. 9C.

Diagnosis. Carapace large, elongated, greatest width anterior of mid-line, weakly convex longitudinally, more so transversely; front produced; medial keel over nearly entire length of carapace, fronto-orbital margin wide, thin; supraorbital margin with 2 fissures; anterolateral margin convex, with 5 short spines directed anteriorly, including epibranchial, even smaller mesobranchial teeth; posterolateral margin nearly straight, narrowly rimmed; short, concave posterior margin; dorsal surface with conspicuous division of anterior carapace portion along jagged line; small tubercles on hepatic region; carapace regions poorly defined; cardiac grooves short, curved; coxa of mxp3 large, placed between thoracic sternum, pterygostome; sternite 2 short, crown shaped, sternite 3 individualised, diamond shaped; sternite 4 large, clearly wider than sternite 3, with lateral expansions; episternite 4 wide, clearly separated from sternite 4; chelipeds robust, tuberculate, of comparable size.

Derivation of name. After the type locality, the Cauvery Basin in Tamil Nadu, southeastern India; noun used in apposition .

Material examined. Holotype, and only specimen so far known ( OUM KY.2861; leg. A.S. Gale, 1999) from between the villages of Kunnam and Odiyam, 60 km northeast of Tiruchirapalli , section G–H (A.S. Gale 1999, field notes), Cauvery Basin (Tamil Nadu, southeastern India), Uttatur Group, Karai Formation, 209 m level, middle Cenomanian, Acanthoceras rhotomagense Zone ( Gale et al. 2002) .

Description. Carapace large (total length, exclusive of broken-off rostrum, 59 mm), elongated, width c. 80 % total length; greatest width anterior of mid-line, at level of epibranchial teeth (about one-third of carapace length); carapace weakly convex longitudinally, more so transversely, medial keel highest point; front produced, rostrum apparently extended well beyond orbits, but broken off, only thin central ridge, curved grooves on either side remaining; medial keel over nearly entire length of carapace, widest antero-centrally, effacing before reaching posterior margin; fronto-orbital margin wide, 32.5 mm (c. 69 % carapace width; c. 55 % carapace length), thin; supraorbital margin with 2 fissures, only one of which partially preserved on either side, slightly curved, widest posteriorly, slightly constricted medially; element adjoining rostrum not preserved, but assumed to have been broadly concave in dorsal view; spine at inner fissure not preserved; second element wide, quadrate but only fragmentarily preserved, lacking anterior margin; third element comparable to second, wide, with convex outer margin, no spine preserved; orbits slanting, but details not observable. Anterolateral margin convex, with 5 short, anteriorly directed spines, including epibranchial spines, even smaller mesobranchial teeth; posterolateral margin nearly straight, narrowly rimmed, tapering rather abruptly to short, concave posterior margin, 19 mm (c. 40 % carapace width), narrowly rimmed. Dorsal surface with conspicuous division of anterior carapace portion along jagged line, delineating a lower-lying anterior portion, extending from root of rostrum to close to epibranchial tooth; anteriorly carapace with larger, well-spaced granules of variable sizes; otherwise decorticated carapace surface apparently smooth with close-set granules; jagged line comprising 4 anteriorly directed, narrowly rounded lobes on each side, 3 posteriorly directed, pointed recesses; small tubercle on hepatic region; cervical groove only partially visible; carapace regions poorly defined; cardiac grooves short, curved. Ventral surface with subhepatic lobe divided by longitudinal furrow into 2 tuberculate crests; mxp3 endopodite ischium long, flat, grooved centrally, mxp3 exopodite thin, flat; mxp3 coxa large, placed between thoracic sternum, pterygostome; sternite 2 short, crown shaped, sternite 3 individualised, diamond shaped; sternite 4 large, clearly wider than sternite 3, with lateral expansions; central portion of sternite 4 flat, sides tilted; episternite 4 wide, clearly separated from sternite 4; suture 4/5 deep; sternite 5 partially preserved as is part of abdominal somite 6; P1 coxa flat; P2, P3 block like, sturdy; P1‒P3 coxae well developed.

Chelipeds robust, tuberculate, of comparable size; propodus compressed, outer surface nearly flat, with rows of small tubercles, lower edge tuberculate, rounded at proximal end, fixed finger only partially preserved; carpus short, curved, with scattered tubercles of variable sizes, narrow ridge parallel to propodus/carpus joint; merus rounded rectangular, except for flat inner surface, covered in tubercles, with sharp, oblique ridge near proximal end; ischium short, triangular, with stout spine near merus/ischium joint.

Remarks. The closest relative of Ferroranina tamilnadu n. sp. is F. dichrous from the upper Cenomanian of Texas ( Figs. 7A–F ; 8A–D ). Stenzel (1945: 408, 440) indicated the locality and stratigraphic level of F. dichrous to be California Crossing, about 10 miles northwest of Dallas, in Dallas County (Texas, U.S.A.), from the Britton Formation (Eagle Ford Group, Gulf Series) or ‘lower Turonian’. However, his list of associated macrofaunal taxa, in particular ammonites, and recent papers by Kennedy (1988; see also Bishop et al. 1992; Jacobs et al. 2005) document a late Cenomanian age for the Britton Fomation, equivalent to the European Metoicoceras geslinianum Zone. Ferroranina dichrous is a smaller-sized species than F. tamilnadu n. sp.; Stenzel (1945: 440) noted lengths and widths of 34.3 and 27 mm, respectively. In addition, F. dichrous is less elongated, with a flatter carapace, has longer and more laterally directed spines on the anterolateral margin, typically shows two small, subrounded pits just behind the grooves of the rostrum (not seen in F. tamilnadu n. sp.), a less clearly separated episternite 4 and sternite 4 and a less-developed medial keel. In other features (carapace ornament, structure and ornament of chelipeds), both species appear closely related, F. tamilnadu n. sp. predating the Texas species by about two ammonite zones ( Gale et al. 2002).

Ferroranina australis ( Secretan 1964: 158, text-figs. 90, 91, 92 (right), 97 (left), pl. 18, figs. 1–3, as Notopocorystes ; Fig. 10G, H herein), from the upper Santonian–lower Campanian of Madagascar, is close to F. dichrous in size (the holotype measuring 32 and 24 mm in length and width, respectively), proportions, carapace ornament and structure of fronto-orbital margin. However, there are subtle differences in rostrum structure ( Secretan 1964: textfig. 92) and in the number of spines on the anterolateral margin. None of the specimens available to Secretan (1964) preserves the abdomen. In comparison to F. tamilnadu n. sp., F. australis is smaller, has a less well-developed medial keel, a different course of the jagged line that delineates the anterior, deeper-lying carapace portion ( Secretan 1964, text-fig. 97 left) and much more intricate fronto-orbital and anterolateral margins, with betterdeveloped spines and deep recesses separating these ( Secretan 1964: text-fig. 91).

Cretacoranina sp. cf. C. dichrous of Vega et al. (2007a: 418, figs. 9.6–9.8), from the lower-middle Turonian (Eagle Ford Group) of Coahuila, northeastern Mexico, appears close to F. dichrous , but preservation is such that a definitive assignment cannot be made, although carapace ornament is similar in consisting of fine granules (see also Haj & Feldmann 2002: fig. 10.4).

Figures

FIGURE 7. Ferroranina dichrous (Stenzel, 1945) n. comb. (Palaeocorystidae), Cenomanian, Dallas County, Texas (U.S.A); A, E, MGSB unregistered (indeterminate sex), frontal view showing chelipeds, and ventral view showing propodus and dactylus of right P2; B, MAB k. 2983 (indeterminate sex), dorsal view of carapace; C, F, MAB k. 2984 (indeterminate sex), dorsal view of anterior portion of carapace, and detail of orbitofrontal margin; D, MAB k. 2877 (male), left lateral view showing merus of cheliped, arrow indicating a distal crest. Scale bars: A-E: 5mm; F: 2mm.

FIGURE 8. Ferroranina dichrous (Stenzel, 1945) n. comb. (Palaeocorystidae), Cenomanian-Turonian, Little Elm, Dallas County, Texas (U.S.A); A, B, MAB k. 2876 (female), dorsal view of carapace, and ventral view showing abdomen, anterior portion of thoracic sternum and appendages; C, D, MAB k. 2878 (female), frontal view, and detail of right frontal region showing orbit and antenna. 3, 4, thoracic sternites 3, 4; a5, a6, abdominal somites 5, 6; ant3, article 3 of antenna; cmxp3, coxa of mxp3; cx1, cx2, cx3, P1, P2, P3 coxae; e4, episternite 4; f, front; mxp3, third maxillipeds; o, orbit; pt, pterygostome; t, telson. Scale bars: 5mm.

FIGURE 9. Ferroranina tamilnadu n. gen., n. sp. (Palaeocorystidae), OUM KY.2861 (holotype), middle Cenomanian, Tamil Nadu (southeastern India); A, right lateral view of carapace, showing displaced pterygostome; B, carpus of left cheliped; C, merus of left cheliped; D, detail of thoracic sternum with appendages; E, frontal view of carapace; F, dorsal view of left cheliped; G, propodus of left cheliped; H, ventral view of left cheliped; I, dorsal view of carapace; J, ventral view showing thoracic sternum and appendages. 2, 3, 4, 5, thoracic sternites 2, 3, 4, 5; a6, abdominal somite 6; cx1, cx2, cx3, P1, P2, P3 coxae; e4, episternite 4. Scale bars: 10mm.

FIGURE 10. Palaeocorystids from Madagascar; A, B, Cretacoranina denisae (Secretan, 1964), lower Campanian, Ampolipoly-Antsirasira region; (A; paratype, labelled Notopocorystes australis Secretan, 1964; MNHN R03878) and MNHN R03875 (B; holotype); C, F, Notopocorystes bituberculatus Secretan, 1964, MNHN R03951 (holotype), Albian, Malandriandro, dorsal view of carapace, and ventral view showing thoracic sternum; D, E, Joeranina sp., MNHN R03930 (indeterminate sex), Cenomanian, Antsirane, dorsal view of fragmentary carapace and ventral view; G, H, Ferroranina australis (Secretan, 1964) n. comb., MNHN R03874 (G; holotype), lower Campanian, Berere, dorsal view of carapace, and MNHN R03903 (H; paratype), lower Campanian, Ampolipoly-Antsirasira, dorsal view of carapace. Scale bars: 5mm.