Tetranota Ulrich & Scofield, 1897

Genus Tetranota Ulrich & Scofield, 1897 View in CoL

Type species: Bucania bidorsata Hall, 1847 , by original designation; from the Watertown Formation (Trenton Group) of the Turinian, Upper Ordovician, North America.

Remarks.— Wahlman (1992: 144) proposed the diagnosis of the genus Tetratona to include “shells with selenizone lying on broad, elevated dorsomedian band and usually bordered by a pair of revolving threads, with one or two pairs of dorsolateral revolving angular ridges; the apertural lip chiefly expanded laterally”. According to Wahlman (1992), species of Tetranota also have shells variable in size with the umbilicus more or less large and deep. The whorls are broad and depressed and the aperture wider than long throughout growth stages. The selenizone is located on a broad, elevated, gently convex to nearly flat topped dorsomedian band, which generally has revolving threads along its edges; lunulae faint in most cases. Outward from the dorsal band, the shell is briefly concave and has a dorsolateral pair of angular revolving ridges. The growth lines are fine and closely spaced.

The present research records the first occurrence of Tetranota in the lower Palaeozoic (Upper Ordovician) of Argentina and South America.

Stratigraphic and geographic range.—Ordovician; North America, England, and South America ( Argentina).

Tetranota argentina sp. nov.

Fig. 2D View Fig .

2020 Tetranota bidorsata ( Hall, 1847) View in CoL ; Bertero 2020: 42, pl. 1: 12, 13, pl. 2: 1–3.

ZooBank LSID: urn:lsid:zoobank.org:act: 06C088B3-73F8-4451-9C49

-E1A04F4AEA24.

Etymology: Referred to the first occurrence of the genus in the lower

Palaeozoic (Upper Ordovician) of Argentina.

Type material: Holotype CEGH-UNC 24713 ( Fig. 2D View Fig ), partially preserved teleoconch without protoconch and aperture . Paratypes: CE-

GH-UNC 24714, 24715, 24716, from the type horizon and locality.

Type locality: Sierra de Villicum locality, San Juan Province, Argentina . Type horizon: La Pola Formation, Sandbian, Upper Ordovician .

Material.— Type material and 38 specimens composed of internal moulds with patches of external shell with fragmentary ornamentation ( CEGH-UNC 24700–24712 , 24717–24732 , and 24774–24782) from the type locality and horizon .

Diagnosis.—Shell involute and subreiniform with a moderately wide umbilicus (umbilical angle of 70º). A dorsal and broad median band carries a concave selenizone. Two acute revolving threads border the selenizone, and two central-lateral grooves are present outward the dorsomedian band. The strong reticulate ornament pattern consists of distinct and fine growth lines which are intercepted by spiral ribs.

Description.—Involute, depressed, whorl profile subreiniform, small to medium-sized shell with a width of 15 mm and a length of 13 mm. Umbilicus deep and moderately wide with an angle of 70º, ( Fig. 2D View Fig 1 View Fig , D 2 View Fig ). In cross section the whorls are lenticular, with well rounded periphery and without thickening of the shell ( Fig. 2D View Fig 4 View Fig ). Dorsum with prominently elevated, broad median band of 2.3 mm (6 times the width of the shell) that carries a slightly concave selenizone ( Fig. 2D View Fig 1 View Fig , D 5 View Fig , D 6). The selenizone is bordered by two angular and acute revolving threads. Outward from the dorsomedian band, a pair of central-lateral concave grooves are visible. Dorsal slopes are also visible near the umbilical shoulder. Ornament consists of raised and distinct, regularly and densly spaced fine growth lines which are intercepted by spiral lirae forming a reticulate pattern. Spiral lirae run into an anteroposterior direction.

Remarks.—According to the characterization of Wahlman (1992) the new species here described represents a true member of Tetranota . Shells identified here as Tetranota argentina sp. nov. were originally ascribed by Bertero (2020) to the type species Tetranota bidorsata ( Hall, 1847) (in Wahlman 1992: 145, pl. 21: 1–14, pl. 22: 1–10), from the Katian, Upper Ordovician of North America, considering that both are very similar in shell shape ornamentation. However, the type species is slightly larger, has a more elevated dorsal median band and a more concave selenizone bordered by more sharper revolving threads, has stronger growth lines and weaker spiral lirae, and thus, shows a weaker reticulate ornament pattern than T. argentina sp. nov. Wahlman (1992) also described other species of Tetranota from the Katian, Upper Ordovician of North America. One of these Laurentian species, Tetranota obsoleta Ulrich in Ulrich & Scofield, 1897 (in Wahlman 1992: 146, pl. 20: 13– 15, pl. 22: 16–21), differs, however, from Tetranota argentina sp. nov. in having a smaller shell, with a narrower and deeper umbilicus, a dorsomedian band slightly elevated and concave, and lunulae and growth lines poorly preserved. Tetranota sexcarinata Ulrich & Scofield, 1897 (in Wahlman 1992: 147, pl. 22: 11–15; in Bertero 2020: 44, pl. 2: 4–8), from the Sandbian–Katian, Upper Ordovician of Argentina and North America, differs from T. argentina sp. nov. in having two pairs of acute dorsolateral ridges on both sides of the elevated dorsomedian selenizone, more widely spaced growth lines, and lacks spiral lirae and a reticulate ornament pattern. Tetranota wisconsinensis ( Whitfield, 1878) (in Wahlman 1992: 148, pl. 38: 13–16), from Sandbian– Katian, Upper Ordovician of North America, has a larger and more tightly coiled shell than the new species, with the dorsolateral ridges gradually disappearing during ontogeny. Tetranota scanica Ebbestad et al., 2013 (fig. 8L–N), from the Katian, Upper Ordovician of Sweden, differs from T. argentina sp. nov. in having finer and sharper growth lines and denser and more irregularly spaced lunulae.

The genus Tetranota (with the species Tetranota sexcarinata Ulrich & Scofield, 1897 ), has been previously reported in the Middle Ordovician of Argentina by Bertero (2020: 44, see above); thus, T. argentina sp. nov. is the first report of the genus in the Sandbian, Upper Ordovician, marine deposit of the Precordillera Argentina, which extends the palaeobigeographical distribution of the genus to South America during the early Palaeozoic.

Stratigraphic and geographic range.—Sandbian, Upper Ordovician, La Pola Formation, Sierra de Villicum, San Juan Province, Argentina.

Family Sinuitidae Dall, 1913 View in CoL

Subfamily Sinuitinae Dall, 1913

Genus Sinuites Koken, 1896 View in CoL

Type species: Bellerophon bilobatus Sowerby, 1839 , by subsequent designation of Bassler (1915); from the Soudleyan–Longvillian, Upper Ordovician of England.

Remarks.— Wahlman (1992: 110) characterized representatives of Sinuites as having tightly coiled and convolute shells, with a closed or very small umbilicus. The dorsum is generally rounded, somewhat flattened with a dorsomedian ridge. The aperture is large and narrow, with a deep, rounded, median sinus and lateral margins projecting downward as rounded or subangular lobes. Parietal deposits are thin. Shell generally ornamented with closely spaced and fine growth lines which may be intersected by faint revolving lines. Following the characterization of Wahlman (1992), the specimens here analyzed are assigned to Sinuites .

Ebbestad and Yochelson (2000) highlighted that there have been much controversy related to this genus and regarded the discussion on preserved muscle scars of torted versus untorted molluscs. Horný (1996) also addressed a number of the problems related to morphology, systematic delimitation and ecology of Sinuites , proposing a semiinfaunal, predatory mode of life for this genus.

Here we supply the first occurrence of Sinuites in the Upper Ordovician, lower Palaeozoic of Argentina and South America.

Stratigraphic and geographic range.—Ordovician; North America, South America, Europe, Baltic region, and North Africa.

Sinuites View in CoL aff. S. reticulatus Perner, 1903 View in CoL

Fig. 2E–H View Fig .

2020 Sinuites View in CoL aff. S. reticulatus Perner, 1903 View in CoL ; Bertero 2020: 45, pl. 1: 7, 8; pl. 2: 9–12; pl. 3: 1.

Material.— CEGH-UNC 24694–24699 , six incomplete teleoconchs preserved with fragmentary ornament pattern; from the Sandbian, Upper Ordovician , La Pola Formation, Sierra de Villicum, San Juan Province, Argentina

Description.—Involute, rounded and elongated to subglobose, small to medium-sized shell with 16 mm large and 9 mm width, with closed umbilicus (or cryptomphalous). The teleoconch is slightly compressed laterally. The aperture is oval, and the lateral and anterior-dorsal margins of the shell are covered by parietal inductura visible in specimen CEGH-UNC 24696 ( Fig. 2F View Fig ). The sinus is moderately shallow. The sculpture consists of a reticulate pattern of spiral almost concentric irregular wavy revolving lirae near the labro-umbilical depression ( Fig. 2G View Fig ).

Remarks.—The material here described strongly resembles Sinuites reticulatus Perner, 1903 ( Horný 1996: 94), from the Darriwilian, Middle Ordovician of Czech Republic in shell shape and ornamentation; however, in S. reticulatus two visible layers of inductural deposits are distinguished, the lower, carrying lirae and corrugation which is located directly over the uppermost shell layer. Another similar species to Sinuites aff. S. reticulatus is Sinuites sowerbyi Perner, 1903 (in Horný 1997: 48, pl. 5: 1–2), from the Darriwilian, Middle Ordovician of Morocco, but it has a more featherlike ornament pattern covering the ribs within the dorsal sinus, and 5–6 regularly spaced collabral lines per mm. Sinuites destombesi Horný, 1997 (48, pl. 5: 3–10, pl. 6: 1–11, pl. 7: 1–3), from the Katian–Hirnantian, Upper Ordovician of Morocco, is slightly smaller than the Argentinean species, has a well-developed subinductura around the umbilicus and dense network of collabral and spiral elements. Sinuites cancellatus Hall, 1847 ( Wahlman 1992: 111, pl. 11: 6–12), from the Katian, Upper Ordovician of North America, is very similar to S. aff. S. reticulatus ; although, S. cancellatus has a moderately shallow and V-shaped sinus, an inductura ornamented by fine and wavy spiral lines, and fine growth lines and even finer spiral elements on the shell surface. Another species comparable to S. aff. S. reticulatus is Sinuites globularis ( Miller & Faber, 1894) ( Wahlman 1992: 114, pl. 10: 1–13), also from the Katian, Upper Ordovician of North America; but the Laurentian form has broader and more inflated whorls, a dorsum with distinct and round dorsomedian ridges bounded by a shallow and deep sinus, and fine and closely spaced growth lines. Sinuites granistriatus Ulrich in Ulrich and Scofield, 1897) ( Wahlman 1992: 113, pl. 11: 1–5, pl. 21: 1; pl. 45: 1–9), also from the Katian, Upper Ordovician of North America, resembles Sinuites aff. S. reticulatus , even though the Laurentian species has a clearly visible dorsomedian ridge in juvenile growth stages which tends to disappear toward mature whorls. Sinuites cf. niger Koken, 1897 (in Ebbestad et al. 2013: 317, fig. 9D–J), from the Sandbian–Katian, Upper Ordovician of Sweden, has the subinductura in the near part of the last whorl consisting of irregular wrinkled wavy lines that may bifurcate. Sinuites usitatus Isakar, 1991 (49, pl. 4–5; in Ebbestad and Yochelson 2000: 192, fig. 5A–I), from the Katian–Hirnantian, Upper Ordovician of the Baltic region, is slightly larger than the Argentinean form, has a wider and open umbilicus, strong wrinkles on dorsal part of the shell, and a post-apertural constriction on the last whorl. Finally, Sinuites sp. (in Ebbestad 2016: 89, fig. 3A–D), from the Floian, Lower Ordovician of Morocco, is less globose and more compressed laterally than Sinuites aff. S. reticulatus , has a weakly open umbilicus, and lacks the wavy revolving lirae near the periumbilical area.

Family Tropidodiscidae Knight, 1956 View in CoL

[= Temnodiscinae Horný, 1963]

Genus Tropidodiscus Meek & Worthen, 1866 View in CoL

Type species: Bellerophon curvilineatus Conrad, 1842 , by original designation of Meek and Worthen (1866); from the Eifelian, Middle Devonian of North America.

Remarks.—Members of this genus have a laterally compressed and lenticular shell, consisting on several whorls, whorls expanding gradually, with a large open umbilicus and deep sutures. Tropidodiscus also is characterized by the presence of a V-shaped sinus that leads into deep slit, a very narrow selenizone on a narrow keel, with or without lunulae, and ornament consisting on prosocyrt growth lines curving backward ( Wahlman 1992: 118; Ebbestad and Yochelson 2000: 194). The species of Tropidodiscus have also small to large sized-shells which may run from few to more than 30 mm, the slender shell with the elongated aperture has been interpreted as well suited for high mobility ( Linsley 1978; Wahlman 1992; Ebbestad and Yochelson 2000) but small members of the genus could have fed on algal fronds ( Ebbestad and Yochelson 2000).

Ebbestad and Yochelson (2000) addressed that Tropidodiscus has a wide palaeobiogeographical distribution and occurs in Early Ordovician to Devonian in Laurentia, Baltica, Siberia, Kazakhstan and Gondwana including more than 50 species, but Ebbestad et al. (2008) suggested that the genus is most widely distributed along the western Tethyan sea (Avalonia).

Here we supply the first occurrence of Tropidodiscus in the Upper Ordovician of Argentina and South America.

Stratigraphic and geographic range.—Lower Ordovician (Canadian) to Upper Devonian; North and South America, Europe, North Africa and Asia.