Retodus tuberculatus ( Tabaste, 1963 ) Churcher & Iuliis & Kleindienst, 2006

Churcher, Charles S., Iuliis, Gerardo De & Kleindienst, Maxine R., 2006, A new genus for the Dipnoan species Ceratodus tuberculatus Tabaste, 1963, Geodiversitas 28 (4), pp. 635-647 : 637-638

Retodus tuberculatus ( Tabaste, 1963) n. comb.

Ceratodus tuberculatus Tabaste, 1963: 444 , 445, fig. 3, 448, pl. 2, figs 3, 4, pl. 3, figs 1-6, pl. 4, figs 1-3. — Cappetta 1972: 185. — Kemp 1997a: 729; 2001: 430, 434, fig. 16. — Lehman 1966: 271, fig. 27B, 291. — Martin 1984b: 233. — Schultze 1992: 192.

Neoceratodus tuberculatus – Martin 1982a: 612; 1982b: 56, 60, 61; 1984b: 225, 226, 243, fig. 44 non 46, 244, 245, fig. 49, 246, fig. 50, 248, 251-253, fig. 53, 257, 258. — Schaal 1984: 44-46. — Churcher & De Iuliis 2001: 305.

“ Neoceratodus ” tuberculatus – Churcher 1999: 64, table 2.2.

LECTOTYPE. — Mandibular tooth plate HGO 49 (Ct 2) ( Tabaste 1963: pl. II, fig. 3a, b), designated by Martin (1984a: 244). (See also Fig. 4B ).

REFERRED SPECIMENS. — Ct1, Ct3-Ct6 ( Tabaste 1963: pl. II, fig. 3a), Albian-Early Cretaceous age.

ROM 44609 ( Churcher 1995: figs 2, 3), Campanian- Late Cretaceous age.

ROM 47638, probably Campanian-Late Cretaceous age. (See also Fig. 4D ).

TYPE LOCALITY. — Rouaix ( Algeria). Albian-Lower Cretaceous.

TYPE STRATA. — Erg Iller ( Algeria) and Mt. Igdaman ( Niger): Albian-Lower Cretaceous.

DIAGNOSIS. — Same for genus and species. Four ridges oriented almost transversely across the plate, concave distally (not straight) when unworn, and cross-linked by smaller lunate secondary ridges into a network of crests and hollows, best seen in the Egyptian Campanian form. Tooth plate size is considerably larger than those of coeval Ceratodus or Neoceratodus . Length 76-100 × breadth 32.0-48.5 mm.

REFERRED STRATA. — Baris and Ain Umm Dabadib, Kharga Oasis, Egypt : Baris (= Qusseir) Formation shale, Campanian-Upper Cretaceous. Dakhleh Oasis, eastern area, Egypt : Mut (= Qusseir) Formation shale, Campanian-Upper Cretaceous. Bahariya Oasis, Egypt : Bahariya Formation shale, Albian-Lower Cretaceous (probable occurrence).

DESCRIPTION AND COMPARISONS

Upper right tooth plate ( Figs 1 ; 4 )

When compared to other species placed within the genus Neoceratodus , the Ain Umm Dabadib fragment, representing the unworn condition of tooth plates of its taxon, does not fit easily within the previously observed tooth plate morphotypes. Compared with other dipnoan tooth plates from Saharan Africa, those of Ceratodus africanus ( Haug, 1905) most closely resemble those of R. tuberculatus n. comb. in that their six or seven ridges are arranged in a poorly radiating pattern, and the central ones, i.e. nos 2 and 3, are concave distally, and are oriented approximately across the axis of the plate fide Tabaste (1963: pl. I, figs 2-7) and Martin (1981: pl. 1, figs 6, 12, 17, 18; 1982a: fig. 1.10), contra Martin (1984a: 273, figs 24 [HGN 28], 26 [HGO 7?]); 275, fig. 30 [HGN 30]) who assigns specimens from north and west of the Ahoggar Massif (Hoggar Mountains) with only four crests to N. africanus . (N.B. HGS 114, from In Abangarit, south of the Ahoggar [“Hoggar Sud”] is given as HGN 114 in text [ Martin 1984a: 238, 241, fig. 38]). These plates fit best within Ceratodus humei ( Priem, 1914) on the basis of size, crest orientation, and in possessing only four crests.

As R. tuberculatus n. comb. tooth plates have only four ridges which run almost transversely across the plate, are bowed rather than straight, may be cross linked by smaller cross ridges into a network of crests and hollows, at least in the Egyptian Campanian form, and are considerably larger than tooth plates of all African species of Ceratodus or Neoceratodus , these plates differ strongly from Ceratodus and Neoceratodus . Unobservable diagnostic characters considered by Martin (1982b) are the position of the palatine process relative to the ridges (currently unknown) and resorption at the internal angle during growth (not deducible on isolated specimens or from the material illustrated by Tabaste 1963).

DISCUSSION

Distribution and age of Retodus tuberculatus n. comb. and Ceratodus humei in the

Central Sahara

Tabaste’s (1963) species Ceratodus tuberculatus was founded without a designated holotype on a collection of 36 specimens. Tabaste (1963: 444) states: “Presque toutes les pièces (32) rapportées à cette espèce proviennent du gisement Rouaix ( Soudan). trois ont été trouvées à l’Erg Iller et une au Niger (Mt. Igdaman) où elle était accompagnée d’un échantillon de Ceratodus humei ”. This extralimital specimen of C. humei unfortunately is not illustrated as it is possibly its most southerly occurrence in Saharan Africa. Rouaix and Erg Iller (Ilafehr), both in southern Algeria west of Tamanrasset and the Hoggar Mountains, are exposures of Albian-Early Cretaceous age (“Crétacé inférieur continental”, fide Tabaste 1963), and Mt. Igdaman in Niger is of Late Cretaceous (“Maastrichtien”) age.

Martin (1984a: 244) lists numbers for 25 specimens of “ N. ” tuberculatus from Rouaix (22), and Erg Iller (3) and designates as the lectotype a lower plate (HGO 49) recorded by Tabaste (1963: pl. II, fig. 3a, b) as “Ct 2 ” ( Fig. 4B ). This appears not to be the tooth plate discussed as “Ct 1 ” by Tabaste. In effect, Martin designated as the lectotype a specimen that Tabaste did not consider typical (see below).

The 10 entire and six fragmentary tooth plates of C. humei discussed by Tabaste (1963: 443) derive from “trois zones: la dépression du Djoua [ Algeria], le Sud marocain [ Algeria], le Niger ”. All the specimens are not listed but the entire ones comprise five upper and four lower plates from Rouaix, of which a lower (Ch 1) is described and illustrated, and an upper from In Afarag also illustrated ( Tabaste 1963: pl. II, figs 1, 2, respectively). The Djoua Depression lies to the east of Fort Flatters (now Bordj Omar Driss), Algeria ( Fig. 2B ), and contains no C. tuberculatus sites. Its “gisements” are given as Lower Cretaceous by Tabaste (1963: 440). However, the figured plate from Rouaix is of Albian-Early Cretaceous age and that from In Afarag is of Maastrichtian-Late Cretaceous age. Thus the C. humei plate noted as associated with R. tuberculatus n. comb. may be from either the Early or Late Cretaceous! We therefore are concerned with the ages assigned to these materials.

Figures

FIG. 4. — Comparisons of tooth plates of Retodus tuberculatus (Tabaste, 1963) n. comb.: A, left lower plate (ROM 44609) from Baris, Kharga Oasis, Western Desert, Egypt, modified from Churcher (1995: fig. 2), max. length c. 100 mm; B, left upper plate Ct2 = HGO 49, from Rouaix, NW of Tikarkas, Southern Algeria, modified from Tabaste (1963: pl. II, 3a), overall length 83.3 mm; C, right upper plate Ct4, from Rouaix, NW of Tikarkas, Southern Algeria, modified from Tabaste (1963: pl. III, 1), overall length 90 mm; D, partial right upper plate (ROM 47638) from Ain Umm Dabadib, Kharga Oasis,Western Desert,Egypt, estimated overall length 76-100 mm. Diagrams not drawn to same scale but to show ridges to similar sizes.

FIG. 1. — Stereoscopic image of a partial tooth plate of Retodus tuberculatus (Tabaste, 1963) n. comb. (ROM 47638), from the surface of a Pleistocene terrace on the Libyan Escarpment near Ain Umm Dabadib, Kharga Oasis, Wadi el-Gedid, Egypt. It is presumed to derive from the underlying Campanian Baris Formation, of Late Cretaceous (Campanian) age. Compare with those illustrated by Tabaste (1963: fig. 3, pl. II, fig. 3a, b, pl. III, figs 1, 2, 4) and Churcher (1995: fig. 2). Scale bar: 12 mm.

FIG. 2. — Map of North Africa showing sites from which Ceratodus africanus (Haug, 1905), C. humei (Priem, 1914), and Retodus tuberculatus (Tabaste, 1963) n. comb. have been recovered, with inset maps of the oases of Kharga and Dakhleh (A, after Vivian 1990) and the Djoua Depression (B, after Foureau 1904). R. tuberculatus n. comb. was first described from Erg Iller and Rouaix (C), west of the Hoggar Mountains (Ahoggar or Hoggar Massif), and from Mt. Igdaman, south of the Hoggar Mountains in Niger (Tabaste 1963). National borders as dashed lines. Escarpments in A and B hatchured, dune areas in B stippled, Ain Umm Dabadib indicated by ●, Retodus tuberculatus n. comb. recovery sites indicated by □ in A, Ceratodus humei sites by ■ in A, and C. africanus sites by ■ in B, and trig points by ▲ with heights in metres. In A roads and the River Nile are shown as solid lines. In B, Bordj Omar Driss (= Fort Flatters = Timassânine) lies near ▲ 368. Information on Ceratodus sites in A after Churcher & De Iuliis (2001).