Saetograptus cf. varians ( Wood, 1900 )

Saetograptus cf. varians ( Wood, 1900)

Fig. 7C View Fig , 8C, D View Fig .

Material.— Two immature specimens with sicula and firsts 7–8 thecae (INGEO-PI-2187, 2198A, B) well preserved in relief filled by carbonate siltstone from 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 tubarium of a maximum recorded length of 7.67 mm (INGEO-PI-2198A), with a gently ventrally curved proximal end. The dorso-ventral width is 0.65– 0.89 mm at Th1, 0.78–0.93 mm at Th2, 0.92–0.93 mm at Th3, 0.83–1.05 mm at Th4, 0.89–1.13 mm at Th5, and 0.99 mm at Th8. The sicula is slightly ventrally curved, 1.55 mm long. Sicular aperture is 0.25–0.34 mm wide. The sicular apex reaches up to the level of Th2 aperture. A 0.38 mm long virgella and 0.09–0.15 mm long antivirgellar spine are present. Thecae are biform, with Th1 to Th6–7 displaying spine-like lateral apertural lappets. Subsequent thecae gained simple pristiograptid appearance. Thecae incline at 37–39° to the tubarium axis. 2TRD values range from 1.39 mm at Th2 to 1.55 mm at Th5. Thecae number 6.5–7 in 5 mm, and overlap for three-fifths to ¾ their length.

Remarks.—The studied specimens from the Los Espejos Formation are similar to S. varians in its proximal width, 2TRD, thecal spacing, etc.( Hutt1969; Lenz and Kozłowska-Dawidziuk 2004; Wilkinson 2021). On the other hand, the presence of spine-like thecal lappets in theca Th4–7, of antivirgellar spine, and lower dorso-ventral width (cf. Wilkinson 2021), suggest that the Argentinian material belongs to a different taxon, for which a reliable specific determination requires a further material.

Specimens of S. cf. S. varians and S. varians were mentioned by Branisa (1969) and Suarez-Soruco (1975) in Bolivian outcrops in association with S. argentinus . The material of the Los Espejos Formation means the first mention and description of this species in Argentina.

Genus Uncinatograptus Tsegelnyuk, 1976

Type species: Monograptus uncinatus Tullberg, 1883 ; 12a, lectotype, selected by Přibyl 1948: 35 ( Tullberg 1883: pl. 1: 25;? LO collection, specimen not identified); 12b–c, proximal end in lateral (3b) and ventral (3c) views; from the Ludlow of Bohemia ( Czech Republic).

Uncinatograptus elsae sp. nov.

Figs. 4D–F View Fig , 5F–J View Fig , 6C View Fig .

Zoobank LSID: urn:lsid:zoobank.org:act:B90B4DF2-6ECB-4D16-8B64-0ED5DBC1FF78

Etymology: In honour of Elsa Nelly Borcia (1957–2020), mother of FEL, a woman with an exceptional affection and patience, who instilled to FEL the love for the knowledge, and to whom is greatly thankful.

Type material: Holotype: INGEO-PI-2115, almost mature relief preserved tubarium. Paratypes: INGEO-PI-1870, well preserved fragmented tubarium; INGEO-PI-2042, moderate preserved specimen; INGEO-PI-2035, proximal specimen; INGEO-PI-2137A and B, specimen with preserved hoods. All from the type locality and horizon.

Type locality: Poblete Norte Creek , Talacasto, 77 km NNW from San Juan city. Central Precordillera , San Juan, Argentina .

Type horizon: PNN-02N, North detailed section, Middle Member of the Los Espejos Formation, Poblete Norte section, Talacasto, lower Gorstian, lower Ludlow, Silurian.

Material.—13 proximal ends or complete specimens in relief (INGEO-PI-2023, 2035, 2042, 2048A, B, 2066A, B, 2069, 2082, 2087, 2088, 2091, 2111A, B, 2115, 2132A, B, 2137A, B, 2162) filled by carbonate or oxidized pyrite from levels PNN-02N and 02S, all from the type locality and horizon.

Diagnosis.—Straight, robust, and rapidly widening Uncinatograptus reaching a dorso-ventral width of more than 1 mm (without hood) at Th3–4, decreasing to 0.8 mm at Th10 and then continuously increasing distally, giving a half spindle-shape to the tubarium. Hoods rarely preserved. Thecal number 5.5–7 in 5 mm, the 2TRD is 1.45 mm proximally and 1.86 mm distally, and interthecal septum inclination is 48–56° proximally and 40–33° distally.

Description.—Straight tubarium of a maximum length of 9.21 mm (INGEO-PI-2115), with slightly to moderately ventrally curved proximal end. The dorso-ventral width varies 0.64–0.80 mm (0.70 mm mean value) at Th1, 0.72–0.89 mm (0.79 mm) at Th2, 0.83–1.05 mm (0.91 mm) at Th3, 0.89– 1.21 mm (1.05 mm) at Th5, 0.82–1.18 mm (1.03 mm) at Th7, 0.74–0.90 mm (0.80 mm) at Th10, and 0.97–1.06 mm (0.98 mm) distally. Sicula is moderate to strongly ventrally curved, with 1.91–2.44 mm long, with 0.25–0.39 mm wide aperture, and the apex generally attaining the level of the Th2 aperture. Ventrally-directed, up to 0.68 mm long virgella and 0.05–0.16 mm long dorsal apertural process are usually seen. The distance between the sicular and Th1 apertures ranges 1.12–1.65 mm (1.32 mm in average). Thecae are of Uncinatograptus­ type, with dorsal hoods and ventrally facing apertures. Due to taphonomy these hoods are usually not visible, giving the aspect of a pseudomonoclimacid-like thecae or apertural spines. The supragenicular ventral walls are slightly oblique proximally, to parallel medially and distally to the tubarium axis. The interthecal septum inclines 48–56° proximally, to 40–33° distally. 2TRD values range from 1.45 mm proximally to 1.86 mm distally, and the thecal spacing counts 5.5–7 in 5 mm. Thecal overlap for about half their length.

Remarks.—Common species of the lower graptolitic levels of the Los Espejos Formation (PNN-02N and 02S) preserved in different astogenetic stages. Specimens of Uncinatograptus elsae sp. nov. can be differentiated from other Uncinatograptus species by its dorso-ventral width, which initiates in near values (0.64–0.80 mm) and rapidly increases and exceeds 1 mm from Th3 (1.05 mm maximum) to Th7 (1.18 mm maximum); subsequent dorso-ventral width values decrease to less than 1 mm, to finally stabilize in values similar to those in Uncinatograptus uncinatus notouncinatus distally (0.97–1.06 mm). The increase-decrease width results in a half spindle-shape of mature tubaria (from Th1–10) or a conic-shape in juvenile specimens, that helps to distinguish this species from the parallel-shaped Uncinatograptus lisandroi sp. nov., and the steadily widening of U. u. uncinatus and U. u. notouncinatus (with maximum distal values of 1.56 mm and 1.02 mm, respectively). In addition, proximal interthecal septum tilting can be helpful to differentiate the respective species, where U. elsae sp. nov. shows higher values (48–56°) than U. u. notouncinatus (40°) and U. lisandroi sp. nov. (32–40°), and distal values, with U. elsae sp. nov. showing slightly higher angles than U. u. uncinatus (25–20°). Moreover, sicula length is similar in all the species, showing only slightly higher values in sicular aperture width in U. elsae sp. nov. than U. u. uncinatus (0.22–0.26 mm; Urbanek 1958). These differences are summarized in Fig. 6 View Fig . On the other hand, if the specimen shows only the firsts pair of thecae, its features will be similar between species denying a reliable taxonomic determination. It is important to mention that similar tubaria shape and sizes to U. elsae sp. nov. are illustrated by Garrat (1978: figs. 6A, B), classified as Monograptus aff. uncinatus .

Stratigraphic and geographic range.—Levels PNN-02N and 02S, middle to upper Los Espejos Formation, lower Gorstian, lower Ludlow, upper Silurian. Poblete Norte section, Talacasto area, San Juan Province, Argentina.