Draconisella mortoni, Granier, BRC & Lethiers, A, 2017

Granier, BRC & Lethiers, A, 2017, Draconisella mortoni sp. nov., a Mizzia-like Dasycladalean alga from the Lower Cretaceous of Oman, Palaeontologia Electronica 20 (1), pp. 1-14 : 7-10

Draconisella mortoni sp. nov. Granier

Figure 3

? 1987 Cylindroporella sp. cf. C. arabica . Simmons and Hart, pl. 10.5, fig. 3

1990 Cylindroporella arabica . Simmons, p. 179- 181, pl. 3.130, 3.132,? 3.133 (= Simmons and Hart 1987, pl. 10.5, fig. 3), 3.134

1994 Cylindroporella? arabica . Simmons, pl. 9.5, fig. 3 (= Simmons 1990, pl. 3.130)

Derivatio nominis. This species is dedicated to Douglas Michael Morton (1924-2003), a pioneer exploration geologist in Oman (see Morton, M.Q., 2006) and the author of a seminal paper on the country’s geology (Morton, D.M., 1959).

Holotype. subaxial section of an article, illustrated herein as Figure 3.4 , from sample no. 31, Wadi Al Fayn section.

Type-locality ( Figure 1.1 ). Wadi Al Fayn ( Dujoncquoy, 2011), 23°04'39.63"N 57°47'12.55"E, 5 km N of Imti, 30 km NE of Nizwa, Oman .

Type-level ( Figure 1.2 ). Lekhwairian regional stage, Hauterivian or (?) Lower Barremian.

Depository. This material is deposited with LPB (" Laboratoire de Paléontologie de Brest ") numbers in the collections of the "Département des Sciences de la Terre et de l'Univers, Université de Bretagne Occidentale, Brest" ( France) .

Diagnosis. This Dasycladalean alga exhibits a moniliform thallus with rather short articles on a rather thin and roughly tubular main axis. The calcareous coating dismantled into discrete articles slightly lenticular (thinner than wider) with 4 (or even? 5) whorls of 6–7 (or even? 8) densely arranged phloiophorous to vesicular primary pores. The axial cavity of an article is slightly inflated in its median part from where all the laterals are inserted. The connection of the pores with the axial cavity is rather narrow. The pores widen rapidly in their proximal part to become roughly tubular, and they widen again in their distal part to form a cortex. It is assumed the species is cladosporate. Besides, its gross shape measurements (see Table 1) differentiate it from the other representatives of the genus.

Additional comparison. It has been suggested that the new species should be compared to species with a sphaerical morphology, amongst which Rajkaella iailaensis Maslov ex Dragastan and Bucur, 1988 , non 1965 ( Figure 8 ). However, we note that:

1. in the entire history of the Dasycladales there is only one species, i.e., Bornetella sphaerica ( Zanardini, 1878) , which exhibits such an unusual morphology ( Figure 9.5 );

2. the aforementioned Rajkaella species has a cylindrical thallus. As already documented by Granier (1990), the remaining that Maslov (1965) interpreted as a complete algal specimen ( Figure 10.1 ) turned to be a lateral of a much larger alga ( Figure 10.3 );

3. amongst the five known types (without considering the subtypes) of Dasycladalean thalli ( Figure 9 ), the new Omani species is by far closer to a Cymopolia – type ( Figure 9.3-4 ).

Figures

FIGURE 3. Draconisella mortoni sp. nov.: 1-3, Wadi Mu Aydin, sample “base”; 4, holotype, Wadi Al Fayn, sample no. 31; 5-13, Wadi Kamah; 5-6, sample no. 13; 7-9, sample no. 14; 10, sample 31; 11-12, sample no. 32. 1, 4, 9 and 11 are subaxial sections (the main axis is the open pore on the lower side); 7 and 10 are tangential sections (they do not reach the main axis); 2-3, 5-6, 8 and 12 are oblique sections. Scale bar (for all photos) equals 100 µm.

FIGURE 8. Rajkaella iailaensis Maslov ex Dragastan and Bucur, 1988, non 1965. 1-2 and 4-6, various oblique to tangential oblique sections through a verticil; 5, tangential section of a lateral at its distal end, through the secondary laterals. 1-3, Berriasian, Corbières (France), Collection Jaffrezo; 4-6, Berriasian, French Jura (France). R1: primary lateral; R2: secondary laterals. Scale bar (for all photos) equals 250 µm.

FIGURE 9. The five morphotypes of living Dasycladalean thalli. 1, cylindrical thallus (Batophora oerstedi Agardh, 1854, excerpt from Berger, 2006, Fig. 15); 2, claviform, club-shaped thallus (Bornetella oligospora Solms-Laubach, 1893, excerpt from Berger, 2006, Fig. 33); 3-4, articulated, moniliform thalli, branched (Cymopolia barbata Lamouroux, 1816, excerpt from Berger, 2006, Fig. 64) and not (Cymopolia vanbosseae Solms-Laubach, 1893, excerpt from Berger, 2006, Fig. 72); 5, sphaerical, ball-shaped thallus (Bornetella sphaerica (Zanardini, 1878), excerpt from Berger, 2006, Fig. 43); 6-7, umbelliform thalli (6: Acetabularia kilneri Agardh, 1886, excerpt from Berger, 2006, Fig. 166; 7: Acetabularia schenckii Möbius, 1899, excerpt from Berger, 2006, Fig. 107). Scale bars 1-2 equals 2.5 mm, 3 equals 10 mm, 4-5 equals 1 mm, 6-7 equals 5 mm.

FIGURE 1. 1, Location map and 2, log of the Wadi Al Fayn section (by courtesy of Dujoncquoy, 2011). Star: Type-level of Draconisella mortoni sp. nov., 1) Wadi Nakhr (23°10'26.7"N 57°12'00.4"E), 2) Wadi Kamah (23°06'55.7"N 57°33'07.3"E), 3) Wadi Mu Aydin (23°04'40.1"N 57°29'39.3"E), 4) Wadi Tanuf (22°58'35.3"N 57°40'05.0"E), and 5) Wadi Al Fayn (23°04'39.63"N 57°47'12.55"E). Color code for the main facies: marls and mudstones in blue, bioclastic wackestones in green, oolitic grainstones in yellow, bioclastic and oolitic grainstones in orange, rudist or oncoid floatstones in pink or red.

FIGURE 10. 1, the original interpretation of Koptedagaria iailaensis Maslov, 1965, nom. nud., which has proved to be wrong (Granier, 1990); 2, the inarticulate-sphaerical hypothetical reconstruction of the new Omani alga, which is not sustainable; 3, the revised interpretation of Rajkaella iailaensis Maslov ex Dragastan and Bucur, 1988, non 1965, with a large cylindrical thallus bearing verticils of rather large laterals (as documented in Figure 8); 4, the articulate-moniliform reconstruction of Draconisella mortoni sp. nov., which is finally adopted in this study.