Lobograptus sp.

Lopez, Fernando E., Conde, Osvaldo A., Braeckman, Alejandro R., Segura, Diego G., Drovandi, Juan M., Bueno, Andrea J. & Abarca, Ulises, 2024, New Ludlovian, upper Silurian, graptolite faunas from the Los Espejos Formation, Central Precordillera, San Juan Province, Argentina: correlations and biostratigraphic remarks, Acta Palaeontologica Polonica 69 (3), pp. 351-370 : 359

Lobograptus sp.

Fig. 7D , 8F .

Material.— One specimen with mould and countermould (INGEO-PI-53A and B) well preserved in relief filled by carbonate siltstone. Level PNN-04S, middle to upper Los Espejos Formation , lower Gorstian , lower Ludlow , upper Silurian. Poblete Norte section, Talacasto area, San Juan Province, Argentina .

Description.—Straight 9.82 mm long fragment, with proximal end not recovered. The dorso-ventral width increases from 0.60 mm to 0.71 mm. Thecae inclined 10–18° to the tubarium axis. Thecae show ventral bends in its ventral wall or are slightly geniculate, giving a weakly monoclimacid-shape in profile. The thecal aperture shape is straight to sigmoidal, with orthogonal to obtuse angles to the tubarium axis. Thecal spacing counts 4 in 5 mm, the 2TRD varies 2.70–3.06 mm, and the thecal overlap is ¼ to two-fifths.

Remarks.—Very rare component of the Los Espejos Formation graptolite fauna. The specimen exhibits morphological similarities with the material described and illustrated by Palmer (1971), Lenz (1990), Zhang and Lenz (1997), Koren’ and Sujarkova (2004), Lenz and Kozłowska-Dawidziuk (2004), Pashko (2020), and Wilkinson (2021) as Lobograptus sp. In particular, the studied specimen shares features with L. progenitor in thecal shape, middle to distal dorso-ventral width, thecal inclination, shape, spacing, and overlap. On the other hand, the absence of essential diagnostic characteristics (proximal end and tubarium curvature shown by Palmer 1971), does not allow for a specific determination.

The specimen of Lobograptus described herein represents the first record of this genus in South America.

Genus Saetograptus Přibyl, 1942

Type species: Graptolithus chimaera Barrande, 1850 ; original description Přibyl 1942; Neodiversograptus nilssoni Zone, Gorstian, Ludlow of Bohemia ( Czech Republic).

Figures

Fig. 7. Ludlow (Silurian) graptolite fauna of the Los Espejos Formation, Talacasto Range, San Juan Province, Argentinian Precordillera: early Gorstian to early Ludfordian Saetograptus argentinus argentinus (Cuerda, 1969) (A, B), the early Gorstian Saetograptus cf. S. varians (Bouček, 1936) (C), and Lobograptus sp. (D). A. INGEO-PI-2195, level PNN-04S. B. INGEO-PI-2196A, level PNN-04S. C. INGEO-PI-2198A, level PNN- 04S. D. INGEO-PI-2199A, level PNN-04S. Scale bars 1 mm.

Fig. 8. Line drawings of the Ludlow (Silurian) graptolite fauna of the Los Espejos Formation, Talacasto Range, San Juan Province, Argentinian Precordillera: early Gorstian Bohemograptus bohemicus (Barrande, 1850) (A, B), Saetograptus cf. S. varians (Bouček, 1936) (C, D), and Lobograptus sp. (E), the early Gorstian to early Ludfordian Saetograptus argentinus argentinus (Cuerda, 1969) (F–I). A. INGEO-PI-1865, level PNN-02N. B. INGEO-PI-1879 B, level PNN-08S. C. INGEO-PI-2187, level PNN- 04S. D. INGEO-PI-2198A, level PNN-04S. E. INGEO-PI-2144A, level PNN-05N. F. INGEO-PI-2199A, level PNN-04S. G. INGEO-PI-2195, level PNN-04S. H. INGEO-PI-2195, level PNN-04S. I. INGEO-PI-2200A, level PNN-04S.