Archaeodictyomitra massarii Dumitrică, 2022

Dumitrica, Paulian, Dieni, Iginio & Massari, Francesco, 2022, Valanginian Radiolarians Of Ne Sardinia (Italy) In The Frame Of The Weissert Event, Acta Palaeontologica Romaniae 18 (2), pp. 97-159 : 136-138

Archaeodictyomitra massarii Dumitrică nov. sp.

Figs. 13 g-k,?14l

1982 Archaeodictyomitra sp. – Okamura & Uto, pl. 1, figs. 16-19; pl. 5, fig.7; pl. 6, fig. 2.

1989 Mita sp. A – Tumanda, p. 8, pl. 3, fig. 13.

Description. Shell long ovoid with usually 6-8 segments and about the two apical thirds conical with slightly convex sides, and the distal third narrowing. Surface with 9 to 11 continuous and deep costae from top to distal end on half the perimeter. Wall thick, of commonly cavernous structure, with rather deep intercostal areas, each one with a row of dense circular pores on the inner side of wall, and oval or transversally elongated and usually very complicated sculpture on the outer surface. Sculptures resulted from the cavernous structure of wall. Distal part without a neck.

Studied material. Six illustrated specimens.

Holotype. Figure 13i , coll. MGP-PD, stub PD120 - OZ839- R02-12 .

Dimensions. Length of shell 140-200 µm, maximum diameter 86-96 µm.

Etymology. The species is dedicated to Prof. Francesco Massari for his contribution to the knowledge of the geology of eastern Sardinia.

Remarks. What is interesting in the population of this new species is that most pores of some specimens are slitshaped and transversally positioned on the surface of shell, and the surface is sculptured ( Figs. 13g 1 , k 2 ) whereas on the inner side of the wall the pores are circular ( Fig. 13k ). This difference is the result of the cavernous structure of wall ( Figs. 13k, k 1 ), which seems to be original, not secondary, resulted from a differential dissolution of the shell. The same kind of superficial sculpture and transversally or obliquely directed slit-like pores are present in some specimens of Archaeodictyomitra mitra Dumitrică 1997 , a species quite close morphologically to this new species, from which it differs by having a slightly spindle-shaped shell and the distal end without a neck, and also in the specimens of Eucyrtidium brouweri illustrated by Tan (1927) in pl. 11, figs. 90 and 91. The cavernous structure of shell, that was never mentioned in Radiolaria, seems to be characteristic of several Lower Cretaceous archaeodictyomitrid species or only specimens illustrated by Thurow (1988, pl. 6, figs. 18-22; pl. 7, figs. 7), O’Dogherty ( 1994) on his pl. 5, figs. 4-6, 12, 23, 25-27, 31-33; pl. 6, figs. 1-4, 10, 15, Jud ( 1994) on Thanarla guta Jud (1994, pl. 23, figs. 4, 5, Thanarla pulchra , pl. 23, figs. 6, 7) or other authors. Some specimens of these species in his pl. 5, figs. 4, 23, 26), to cite only the most visible, have also pores on the top of costae. We do not know whether this cavernous structure has a taxonomic meaning or a palaeobiological one. All these specimens are archaeodictyomitrids. Anyway, it is interesting to mention it, radiolarian skeleton being known to be compact, by comparison with that of Phaeodaria, that has an alveolar or porous structure (Takahashi & Hurd, 2007; Dumitrică, 2016).

Range and occurrence. Berriasian to Barremian of Masirah Island, Oman, and upper Valanginian of Sardinia.

Figures

Fig. 13 a, b - Apiaromitra apiarium (Rüst): a - OZ836, b - OZ839, a1 - detail of ornamentation of last segment, b1 - detail of ornamentation of penultimate segment. c - Archaeodictyomitra robustovum Dumitrică n. sp., OZ837. d - Archaeodictyomitra sp., OZ839. e, f - Archaeodictyomitra mitra Dumitrică: e - OZ838, f - OZ824. g-k - Archaeodictyomitra massarii Dumitrică n. sp.: g - OZ834, g1 - detail of surface x1000. h - OZ834, i - OZ839, j - OZ834, k - OZ839; k1 - detail of wall showing the cavernous structure, k2 - detail of surface. l, p - Archaeodictyomitra longipora Dumitrică n. sp., OZ836; l - portion of surface of p much magnified showing the elevated intercostal area. m - Apiaromitra tyaughtonensis (Cordey), OZ837. n, t - Archaeodictyomitra dienii Dumitrică n. sp.: n - OZ836, t - OZ837. o - Thanarla cf. pulchra (Squinabol), OZ824. r - Archaeodictyomitra judae Dumitrica n. sp., OZ839. s - Archaeodictyomitra humerosa Dumitrică n. sp., OZ839. Figs. a, b x250, k1 and k2 x450, all the others x300.

Fig. 1 Geologic map of the Siniscola area, NE Sardinia (from Dieni & Massari, 1971, updated in 1986). Legend: a - Recent and present alluvial deposits (Holocene). b - Scree deposits (Würm-Holocene). c - Detrital cones mostly composed of gelifraction limestone clasts (“éboulis ordonnés”) (Würm-Holocene). d - Uncemented alluvial cones mostly consisting of limestone clasts (Würm-Holocene). e - Terraced alluvial deposits composed of clasts of basement rocks (Riss?). f - Tightly cemented and dismembered alluvial cones mostly made up of gelifraction limestone clasts (Riss?). g - Cuccuru ’e Flores Conglomerate: polymict, chaotic and thick-bedded breccia and stratified sandstone (middle Eocene). h - Siniscola Marl: grey and grey-yellow marl and, in the upper part, alternating marl/marly limestone with ammonites and very abundant radiolarians and sponge spicules (late Valanginian). i - Schiriddè Limestone: light-brown cherty limestone and limestone with marly interbeds, containing ammonites, radiolarians, sponge spicules and calpionellids (early Valanginian). j - Monte Bardia Limestone: thick-bedded to massive white limestone in places bioconstructed, with corals, nerineids, etc. (early Tithonian - late Berriasian). k - S’Adde Limestone: light-brown to grey fine-grained, well-bedded limestone, condensed with hardgrounds near the base, cherty in the upper part, with ammonites and belemnites in the uppermost part (latest Bathonian - earliest Tithonian). l - Dorgali Formation: well bedded quartz-arenitic and locally ooidal brown dolostone (middle-late Bathonian). m - Crystalline basement (phyllite, micaschist, paragneiss, quartzite, etc.) (Palaeozoic). n - Fault. o - Attitude of beds and schistosity planes. p - Limits of slumped masses of Jurassic formations (Quaternary). q - Concave-upward slip surfaces delimiting rotational slumps (Quaternary). r - Edge of fluvial terrace. s - Quarry. A-A’ Trace of the geological section of Fig. 2. (extracted from Bottini et al., 2018).

Fig. 2 Geological section across the S’Ozzastru area (trace A-A’ in the geological map of Fig. 1). Legend: a - Recent and present alluvial deposits (Holocene). b - Cuccuru ’e Flores Conglomerate: sandstone and breccia (middle Eocene). c - Siniscola Marl: marl (1) and marly limestone (2) (late Valanginian). d - Schiriddè Limestone: cherty limestone (early Valanginian). e - Monte Bardia Limestone: limestone (early Tithonian - late Berriasian). f - S’Adde Limestone: limestone and cherty limestone (latest Bathonian - earliest Tithonian). g - Dorgali Formation: dolostone (middle-late Bathonian). h - Metamorphic basement (Palaeozoic). i - Fault (modified from Bottini et al., 2018).