Ferroranina, 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 : 29-32

Genus Ferroranina n. gen.

Type species. Notopocorystes dichrous Stenzel, 1945 , by present designation.

Diagnosis. Carapace of medium to large size, subhexagonal in outline, widest at epibranchial spine, situated approximately one-third of total carapace length from front; dorsal surface convex in transverse cross section, moderately convex from front to posterior margin; axial carina weak; orbitofrontal margin distinctly wide; orbits large, with 2 closed supramarginal fissures, supramarginal teeth, outer orbital teeth strongly developed, with long, conical spines; front markedly narrow, with lateral margins weakly concave, distally with pair of distal, subdistal divergent spines, axial portion of front with short, narrow ridge, deep furrows, which shortly extend onto dorsal surface; anterolateral margins nearly straight, with strong spiniform teeth; posterolateral margin straight, rimmed, anteriorly with small spine; posterior margin concave; dorsal regions indistinct; cervical groove only medially defined, Vshaped, interrupted between gastric pits; post-frontal terrace created by 3 transversely placed subtriangular lobes; hepatic region depressed, with small tubercle; cardiac region rather narrow, bounded by clear branchiocardiac grooves; dorsal surface covered by fungiform nodes, hepatic, orbital regions granular. Pterygostome large, with blunt crests, buccal margin concave, with broad buccal collar. Thoracic sternum narrow, elongated, no junction with pterygostome; sternites 1, 2 narrow, subglobose, sternite 3 crown shaped, incision separating sternites 3, 4, sternite 4 subtrapezoidal, lateral margins weakly concave, anteriorly much wider than sternite 3, episternite 4 wide; sternite 5 laterally depressed, episternite 5 elongated, directed backwards; abdomen narrow, covering thoracic sternum in width in both sexes, all somites free, somites 1‒6 with medial portion raised; somite 4 with central tubercle; mxp3 elongated, coxae large, flabelliform, basis short, with a clear suture; ischium, merus long, grooved axially; P1 chela homochelous, homodontous, tuberculate, upper, lower margins spinose, merus with distal crest; P2–P4 long, flattened merus, propodus, dactylus; P5 reduced, subdorsal.

Derivation of name. From Latin ferro, meaning ‘iron’, in reference to the rusty colour of numerous specimens of the new species.

Species included. Ferroranina australis ( Secretan, 1964) [as Notopocorystes ], F. dichrous ( Stenzel, 1945) [as Notopocorystes ] and F. tamilnadu n. sp.

Material examined. Ferroranina australis : holotype, MNHN F.R03874, a well-preserved carapace, lower Campanian , Berere, Menabe region, Madagascar ; paratype, MNHN F.R03903, incomplete carapace, lower Campanian , Ampolipoly-Antsirasira, Madagascar (see Fig. 10G, H ; Charbonnier et al. in press) . F. dichrous: MAB k. 2876, large female specimen with mxp3, sternum and abdomen; MGSB unregistered (indeterminate sex), carapace with chelipeds and P2, Britton Formation , Eagle Ford Group , Cenomanian-Turonian, Dallas County, Texas ; MAB k. 2878, female, partial carapace with sternum and well-preserved frontal area, Little Elm , Texas; building site named ‘ Sunset Pointe addition’, just west of FM Road 423 ; MAB k. 2877 (indeterminate sex), carapace with wellpreserved cuticle and chelipeds, MAB k. 2983 and k. 2984 (indeterminate sex), carapaces with extremely well-preserved cuticle, Elm Fork Shale , Eagle Ford Group , Cenomanian-Turonian , California Crossing on Elm Fork of Trinity River , Dallas County, Texas. F. tamilnadu n. sp.: type series, see below .

Remarks. Ferroranina n. gen. contains species that until recently were assigned to Cretacoranina or to Notopocorystes . The new genus exhibits a unique set of characters: front with short, narrow axial ridge, bounded by deep furrows that shortly extend onto the dorsal surface; post-frontal terrace present with three obliquely arranged, subtriangular lobes; cervical groove only medially defined and V-shaped; axial carina weak or obsolete; cuticle microstructure with fungiform nodes; sternite 4 anteriorly much wider than sternite 3.

Ferroranina n. gen. is considered closely related to both Cretacoranina emend. and Joeranina n. gen. Characters that distinguish Ferroranina n. gen. from members of Cretacoranina emend. are: presence of a cervical groove (absent in Cretacoranina emend.), frontal furrows that are longer and extended onto the carapace (short, only on rostrum, in Cretacoranina emend.) and presence of a post-frontal terrace with three lobes (absent in Cretacoranina emend.). The new genus appears closely related to Joeranina n. gen., but substantially differs in that frontal furrows are not as long, the cervical groove is only medially defined (cervical groove complete in Joeranina n. gen.), the medial portion of the cervical groove is V-shaped (U-shaped in Joeranina n. gen.), the axial carina weak or obsolete (well developed in Joeranina n. gen.), the dorsal carapace surface has fungiform nodes (granules and pits in Joeranina n. gen.) and sternite 4 is much wider anteriorly (only slightly wider than sternite 3 in Joeranina n. gen.).

Ferroranina n. gen. is easily differentiated from Notopocorystes by the presence of frontal furrows, the lack of tubercles on regions and an axial tuberculate carina, by the different shape and definition of the cervical groove and a better-developed anterior portion of sternite 4.

The lack of cuticle has usually been taken into account when describing fossil crabs. On some occasions, the internal mould presents features that are indistinct when the cuticle is present and well-preserved. In Ferroranina n. gen. the cuticle tends to efface the cervical groove that normally has a constant appearance in different genera. The cervical groove can be traced in some decorticated specimens of F. dichrous , contrary to specimens that retain the cuticle; it presents a continuous transverse, thin line from side to side of the carapace.

After re-examination of Secretan’s 1964 type material ( Fig. 10A, B ), it has become apparent that one of the paratypes of Notopocorystes australis (MNHN F.R03878; Secretan 1964: pl. 18, fig. 3), should be referred to Cretacoranina denisae on account of the lack of the post-frontal terrace and a different orbitofrontal margin configuration.

The morphology of Raninella (?) armata Rathbun, 1935b, from the upper Albian of Texas ( Rathbun 1935b: 50, pl. 11, figs. 32, 33), is typical of Ferroranina n. gen., and it may well represent the male abdomen of Ferroranina dichrous n. comb. ( Figs. 7A–F ; 8A–D ).

Ferroranina n. gen. ranges from the upper Cenomanian to the upper Campanian, with records from India, Madagascar, Mexico and Texas ( U.S.A.).

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 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.