Systematic revision of Late Triassic marine gastropods from
Central Perú: considerations on the Late Triassic/Early Jurassic
faunal turnover

S. Mariel Ferrari1, 2

1 Museo Paleontológico Egidio Feruglio, Av. Fontana 140, U9100GYO, Trelew, Chubut, Argentina.
mferrari@mef.org.ar

2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Rivadavia 1917, C1033AAJ, Ciudad Autónoma de Buenos Aires Argentina.

Fig. 1. A-E: Chartronella pacifica (Jaworski, 1923); A-C: AMNH No. 35552; A-B: lateral and apertural views; C: apical view;      D-E: AMNH No. 26530; D: lateral view; E: columellar view; F-G: Chartronella wortheniaeformis (Cox, 1949), AMNH No. 26531; F: lateral and apertural view; G: apical view; H-J: Chartronella gradata Ferrari (2014a and b), MCF-PIPH 552; H-I: lateral and apertural views; J: apical view; K-L: Chartronella atuelensis Ferrari, 2014b MLP (8); K: lateral view; L: basal and apertural view; M-O: Chartronella paganiae Ferrari, 2011, MPEF-PI 4022; M: lateral view; N-O: apical views.

 

The specimens assigned to Chartronella pacifica (Jaworski, 1923) com. nov. (Haas, 1953, p. 81, pl. 5, figs. 31-41, 45-47, 54) are very similar in general shell morphology and size to Chartronella gradata Ferrari (2014a, p. 6, fig. 3i-s) (Fig. 1H-J), from the Early Jurassic (late Pliensbachian-early Toarcian) of Patagonia (Argentina); however, the Peruvian form has more developed and acute nodes on adult whorls. New material tentatively assigned to Chartronella atuelensis Ferrari, 2014b (Fig. 1K-L) has been recently reported form the Early Jurassic (Pliensbachian) of the Neuquén Basin (Argentina). The Argentinean form, however, is slightly smaller, has a lower spire and a more convex sutural ramp. Chartronella paganiae Ferrari (2011, p. 69, fig. 7.1-10) (Fig. 1M-O) from the Early Jurassic (late Pliensbachian-early Toarcian) of Patagonia, is another species comparable to C. pacifica. C. paganiae, however, is much smaller, has a lower spire, and lack strongly prosocline collabral ribs on the shell surface. Chartronella spiralis Ferrari (2011, p. 71, fig. 9.1-6) (Fig. 2A-C) from the late Pliensbachian-early Toarcian of Patagonia has strongly developed spiral cords on the outer face of last whorl and on base, lower spire and a less conical shell.

 

Fig. 2. A-C: Chartronella spiralis Ferrari, 2011, MPEF-PI 3590; A, C: lateral and apertural views; B: basal view; D-F: Eucycloscala pascoensis Haas, 1953; D: AMNH No. 26510A, holotype, lateral view; E-F: AMNH No. 26510B, paratype; E: lateral view; F: lateral and apertural views; G-H: Calliotropis (Riselloidea) keideli Ferrari et al., 2014; G: MPEF-PI 1160, holotype, lateral view; H: MPEF-PI 4132, lateral view; I: Ambercyclus? isabelensis Ferrari et al., 2014, MLP 18822, holotype, lateral view; J-M: Colpomphalus Peruvianus (Haas, 1953), AMNH No. 27543, holotype; J-K: lateral views; L: apical view; M: basal view; N-O: Colpomphalus musacchioi Ferrari, 2014a; N: MPEF-PI 4041, holotype, lateral view; O: MPEF-PI 4018, paratype, basal view.

 

Chartronella wortheniaeformis (Cox, 1949) comb. nov.
Fig. 1F-G

1949 Chartroniella wortheniaeformis Cox: p. 36, pl. 2, figs. 13-15; Haas, 1953: p. 83, pl. 5, figs. 42-44, 48, 55.

Material examined: AMNH No. 26531; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 21 km E, 3.5 km SSE of Huanco Jenks Lot 26, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, conical, gradate, trochiform and slightly low- spired shell, with a height of 17.1 mm and a width of 20.81 mm. The protoconch is not clearly visible; the teleoconch consist of five whorls. The sutural ramp is narrowly horizontal and more developed toward mature growth stages. The flank of whorls is slightly convex to flat; the outer face is vertical, and straight to slightly concave. Last teleoconch whorl is more expanded than spire whorls. The angulation is delimited by a strong spiral keel which is stronger on last whorl. The peripheral spiral keel bears weakly elongated nodes. A second abapical spiral cord is visible on last whorl and covered by subsequent whorls on the spire. The shell surface is covered by fine crowded prosocline growth lines. The base is flattened without ornamentation and bordered by an abapical spiral keel. The aperture is subcircular with the outer lip indented by the peripheral spiral keel; the inner lip is crescent- shaped.
Affinities: Chartronella wortheniaeformis com. nov. is very similar to C. pacifica; however, it has a lower spire, the peripheral keel is more acute and stronger, and the nodes on the peripheral keel are less elongated and weaker. C. wortheniaeformis resembles also C. gradata (see above); even though the Argentinean form has a higher spire, the peripheral keel is weaker and lacks the elongated nodes.

Family Eucycloscalidae Gründel, 2007
Genus Eucycloscala Cossmann, 1885

Type species: Trochus binodosus Münster, 1844 from the Late Triassic of St. Cassian Formation.
Occurrence: Late Triassic-Late Cretaceous; Europe and South America.
Remarks: Bandel (2010, p. 437) proposed an updated diagnosis of Eucycloscala consisting on a ‘slender conical shells; axis of coiling of the planispiral protoconch may deviate from the axis of coiling of teleoconch; first teleoconch whorl ornamented by simple axial costae; later teleoconch whorls are ornamented with strong axial ribs, which are crossed by spiral ribs forming sharp nodes; ornament of base is spiral and sometimes with umbilicus; and the aperture simple, circular and with a continuous peristome’. The material described by Haas (1953) from the Late Triassic of Perú, fits in the diagnosis of Bandel (2010). Morever, Haas (1953) included Eucycloscala in the family Turbinidae Rafinisque and Bandel (2010) in Eucycloscalidae. Here, the classification of Bandel (2010) is followed, considering that the genus diagnosis fits with the updated characterization of the family Eucycloscalidae proposed by Gründel (2007).

Eucycloscala pascoensis Haas, 1953
Fig. 2D-F

Material examined: Holotype, No. 26510A AMNH; well preserved teleoconch. Paratype, No. 26510B AMNH; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 21 km E, 3.5 km SSE of Huanco Jenks Lot 26, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, conical to slightly cyrtoconical, trochiform, very small- sized and relatively high- spired shell, with a mean height of 3.66 mm and a mean width of 2.8 mm. The protoconch consists of one convex, dome shaped and smooth whorl that slightly deviates from the coiling axis of the teleoconch. The first teleoconch whorl is strongly convex and smooth; the ornament becomes more visible from second teleoconch whorl toward the mature whorls. On mature growth stages axial and spiral elements are present; prosocline to prosocyrt axial ribs are intercepted by three to four regularly spaced spiral cords, forming acute nodes at the crossing points. The ramp of whorls is widely flattened and horizontal to slightly sloped; the outer face becomes strongly convex. Suture is visible in a concave furrow. The aperture is holostomatous and circular; basal details are not preserved.
Affinities: Regarding related eucyclid- like forms from South America, Eucycloscala pascoensis Haas (1953, p. 102, pl. 6, figs. 61, 69, 72-76) slightly resembles Calliotropis (Riselloidea) n. sp. Ferrari et al. (2014) (Fig. 2G-H) from the Early Jurassic (late Pliensbachian-early Toarcian) of Chubut and Neuquén provinces; the Argentinean form, however, differs from the Peruvian species in being larger, having more distinct axial ribs on the shell surface, and a more circular aperture. Moreover, E. pascoensis possesses a characteristic reticulate pattern which is not presente in Calliotropis (R.) n. sp. Other comparable species to E. pascoensis is Ambercyclus? n. gen. et n. sp. Ferrari et al. (2014) (Fig. 2I), also from the Early Jurassic of Argentina; however, Ambercyclus? n. gen. et n. sp. has strongly acute and spinose nodes, a larger shell and more distinct prosocline and opisthocyrt axial riblets. Eucyclus subtiliscostatus Gründel (2001a, p. 49 pl. 2, figs. 8-10) from the Early Jurassic of Chile, also resembles E. pascoensis; however, Gründel’s species has a more gradate outline, two strong spiral ribs delimiting the angulation of whorls forming a concave area in between; and strongly opisthocyrt collabral ribs on the shell surface. Eucycloscala tortulosa Bandel et al. (2000, p. 79, pl. 2, figs. 11-13) from the Early/Middle Jurassic of New Zealand is very similar to the Peruvian species; but, E. tortulosa has a less convex and more angulated outline toward mature whorls, and has a more developed spiral striation.

Family Discohelicidae Schöder, 1995
Genus Colpomphalus Cossmann, 1906

Type species: Straparollus altus D’Orbigny, 1853, from the Middle Jurassic of France.
Occurrence: Late Triassic-Middle Jurassic; Europe and South America.
Remarks: The genus Colpomphalus Cossmann is common in Early and Middle Jurassic marine deposits of the Tethyan region. According to Gründel (2005), members of Colpomphalus share a discoidal, small- to medium- sized shell, with few whorls rapidly increasing in width, lateral side high and oblique, umbilicus relatively narrow, abapical keel with less and more acute nodes than the sutural keel, and growth lines on the lateral side of last whorl. Gründel (2001a) and Ferrari (2009, 2014a) reported representantives of the genus in the Early Jurassic of South America. Gründel (2001a) described Colpomphalus toarciensis Gründel from the Toarcian of Chile, and later Ferrari (2014a) reported Colpomphalus musacchio Ferrari from coeval deposits of Patagonia. Haas (1953) described a very small Colpomphalus- like species from the Late Triassic of Perú and included it into Phymatifer de Koninck (family Euomphalidae de Koninck). Haas’s species, however, shows the typical characters of Colpomphalus; thus, here it is reassigned to this genus and included in the family Discohelicidae.

Colpomphalus Peruvianus (Haas, 1953) comb. nov.
Fig. 2J-M

1953 Phymatifer Peruvianus Haas: p. 32, pl. 2, figs. 5, 6, 12, 13.

Material examined: Holotype, AMNH No. 27543; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 7.5 km SSE Jenks Lot 31, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, discoidal, auriform, very small- sized and low- spired shell, with a height of 1.48 mm and a width of 2.45 mm. The protoconch is not clearly visible. The teleoconch consists of three whorls slightly gradate in outline; last whorl is more expanded than spire whorls. The sutural ramp of last whorl is widely horizontal, and flattened to slightly concave, and its periphery is delimited by a row of acute and slightly elongated nodes. The peripheral nodes coincide with the angulation of last whorl; the outer face is markedly convex to angular, ornamented by very fine and almost imperceptible spiral lines which are intercepted by fine growth lines. The base is flat to concave and bordered by a row of about 14 acute and pointed nodes. The umbilical area is widely opened and funnel- shaped, with a narrow umbilicus. The aperture is holostomatous, and the peristome oblique with a quadrangular outline.
Affinities: Colpomphalus Peruvianus com. nov. shows striking resemblance to Colpomphalus musacchio Ferrari (2014a, p. 11, fig. 5a-j) (Fig. 2N-O), from the Early Jurassic (late Pliensbachian-early Toarcian) of Patagonia; the Argentinean form, however, has a larger shell, less elongated and more rounded nodes on the angulation of last whorl, six to seven relularly spaced spiral threads and sigmoidal growth lines on the outer face, and a high number of nodes (24) on base. Another South American species comparable to C. Peruvianus is Colpomphalus toarciensis Gründel (2001a, p. 46, pl. 1, figs. 9-13), from the Early Jurassic (Toarcian) of Chile; both are similar in shell shape and ornamentation; however, Gründel’s species is bigger, has high and pointed nodes on the angulation of last whorl, and a third row of nodes sorrounds the umbilicus.

Family Ptychomphalidae Wenz, 1938
Genus Ptychomphalus Agassiz, 1837

Type species: Helicina compressa Sowerby, 1813 from Early Jurassic of France.
Occurrence: Late Triassic-Lower Jurassic; Europe, northern Africa, South America.
Remarks: Bandel (2009) included representatives of Ptychomphalus in the Jurassic family Ptychomphalidae, suggesting that its placement in the family Eotomariidae (proposed by Bouchet and Rocroi, 2005) is erroneous; even though the Ordovician Eotomaria somewhat resembles members of Ptychomphalus. This genus is also represented in the St. Cassian Formation (Bandel, 2009) and Ptychomphalina Fischer, 1885, is a closely related Peruvian Triassic form described by Haas (1953) and assigned by that author to the family Pleurotomariidae. In the present paper, I propose considering the genus Ptychomphalus as an anterior synonymous of the Peruvian Ptychomphalina following the updated classification of the genus proposed by Bandel (2009). The genus was recently revised by Gründel (2011).

Ptychomphalus? discoidea (Haas, 1953) comb. nov.
Fig. 3A-C

1953 Ptychomphalina? discoidea Haas: p. 27, pl. 1, figs. 46, 47, 54-58.

Material examined: Holotype, AMNH No. 27693; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 24.5 km SSE, 0.5 km W of Ninacaca Jenks Lot 86, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, sublenticular, biconical, widely phaneromphalous, lens- like, very small- sized and low- spired shell, with a height of 1.69 mm and a width of 2.15 mm. The protoconch is fragmentary and consists of one convex and smooth whorl. The teleoconch comprises three to four convex whorls; ramp of whorls is convex becoming slightly concave toward the outer face of last whorl. Last teleoconch whorl is markedly more expanded than the spire. Ornament is not present on the shell surface and the selenizone is not completely visible either. Suture is clearly impressed in a weakly deep spiral furrow. The base is strongly convex and smooth, with a widely opened and funnel- shaped umbilicus. The aperture is holostomatous and circular, and the peristome continuous.
Affinities: The species described by Haas (1953) as Ptychomphalina? discoidea, shows the typical diagnostic features of Ptychomphalus, including a sublenticular shell, with low spire, convex base and smooth surface. However, other diagnostic features of the genus, such as, a peripheral selenizone and an umbilicus covered by a callus are absent in the Peruvian form; thus, the open nomenclature is also kept in the updated description of the species. It also shows the diagnostic characters of Cryptaenia Eudes-Deslongchamps, 1864 (see diagnosis in Gründel, 2011); however, an opened umbilicus is not a typical character of the former genus.

Ptychomphalus? discoidea com. nov. resembles Cryptaenia sudamericana Ferrari, 2014b (Fig. 3D-E), from the Early Jurassic (late Pliensbachian-early Toarcian) of Argentina; however, the Argentinean material is bigger that the Peruvian species, the selenizone is narrow, concave and peripheral on last whorl, two weak spiral cords are present at the angulation of whorls, the aperture is subquadrate and the umbilicus completely covered by a callus. Cryptaenia globosa Ferrari, 2014b (Fig. 3F-H), also from the Early Jurassic (Pliensbachian) of Argentina, differs from P.? discoidea in being much bigger, strongly globose, with the periphery forming a rounded angulation.

 

Fig. 3. A-C: Ptychomphalus? discoidea (Haas, 1953), AMNH No. 27693, holotype; A: lateral view; B-C: apertural and basal views; D-E: Cryptaenia sudamericana Ferrari, 2014b, MCF-PIPH 698, lateral and apertural views; F-H: Cryptaenia globosa Ferrari, 2014b, MLP (13a); F: lateral view; G: basal view; H: apical view; I-O: Guidonia Peruviana Haas, 1953; I-K: AMNH No. 26500A, syntype; I: lateral view; J: lateral and apertural views; K: basal view; L-O: AMNH No. 35535A, paratype; L: lateral view; M: lateral and apertural view; N: apical view; O: basal view; P-S: Guidonia bifasciata Haas, 1953, AMNH No. 26502S, paratype; P: lateral view; Q: lateral and apertural views; R: apical view; S: basal view. T-V, Guidonia planetecta Haas, 1953, AMNH No. 35538G, paratype; T-U: lateral and apertural views; V: apical view; W-Y: Guidonia disciformis Ferrari, 2014b, MCF-PIPH 703; W-X: apical views; Y: lateral views.

 

Family Nododelphinulidae Cox, 1960
Genus Guidonia De Stefani, 1880

Type species: Trochus rotulus Stoliczka, 1861, subsequent designation by Haas (1953, p. 56). Hierlatz Alpe (Northern Calcareous Alps, Austria), Early Jurassic (Late Sinemurian).
Occurrence: Upper Triassic (Norian)-Early Jurassic (Sinemurian-Pliensbachian); Europe, New Zealand and South America.
Remarks: Haas (1953) described many species of this genus from the Late Triassic of Perú and defined Trochus retulus Stoliczka, 1861 as its genotype, including the most representative forms into the family Trochonematidae Zittel. Gründel (2004) assigned Guidonia to the family Liotiidae H. Adams and A. Adams. In contrast, Szabó (2009), on the basis of the bicarinate whorls and the gradate shell outline, included the genus into the family Nododelphinulidae Cox. Szabó (2009) pointed out that the shell shape of Guidonia resembles also the typical Chartronella, and suggested accommodation in another family. The similarities between Guidonia and Chartronella were also stated out by Ferrari (2011). The classification of Guidonia in Nododelphinulidae was subsequently followed by Gatto and Monari (2010). Here, I adopt the proposal of Szabó (2009) and Gatto and Monari (2010) based on the similarities in shell shape of Guidonia with the representatives of the family Nododelphinulidae.

Guidonia Peruviana Haas, 1953
Fig. 3I-O

Material examined: Paratype No. 35535A AMNH; ‘well preserved’ and replaced teleoconch. Syntype, No. 26500A AMNH; ‘well preserved’ and replaced teleoconch.
Occurrence: Cerro de Pasco locality, 24.5 km SSE, 0.5 km W of Ninacaca Jenks Lot 86 and 18.75 km S, 7.75 km W of Ninacaca Jenks Lot 70, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, trochiform, gradate to step- like, moderately low- spired and small- sized shell. The protoconch is not preserved; the teleoconch comprises about five strongly gradate whorls, with a mean height of 7.48 mm and a mean width of 7.98 mm. Earliest teleoconch whorls are slightly convex and become straight and angular to mature growth stages. The sutural ramp on adult whorls is slightly flat to concave; the outer face is straight, vertical and concave. The periphery of last whorl is delimited by a strong spiral keel which forms an angulation; a second weak and abapical spiral cord is visible on last whorl but covered by subsequent whorls on the spire. Collabral ornament appears on the outer face of last whorl; it consists of fine and crowded prosocline growth lines. The base is slightly convex, narrowly phaneromphalous, with a deep and funnel- shaped umbilicus. The aperture is holostomatous and circular; the outer lip is indented by external angulation; the basal lip is flat and slightly expanded abapically, and the columellar lip is thickened forming a crescent- shaped callus. Fine and spaced collabral ribs are also visible on base.
Affinities: According to the diagnosis of Bandel et al. (2000), the species described by Haas certainly shows the typical characters of Guidonia. Guidonia Peruviana Haas (1953; p. 65, pl. 4, figs. 1-3, 5-9, 11-18, 20. 32, 42), however, is very similar in general shell morphology to Chartronella paganiae Ferrari (2011; p. 69, fig. 7.1-10) (Fig. 1M-O), from the Early Jurassic of Patagonia; but, the Argentinean form has a less gradate outline, a more convex sutural ramp, and lacks umbilicus. The absence of umbilicus is the reason for keeping C. paganiae separately from Guidonia. A new specimen tentatively assigned to Guidonia disciformis Ferrari, 2014b (Fig. 3W-Y) has been recently reported form the Early Jurassic (Pliensbachian) of the Neuquén Basin (Argentina) (Ferrari, 2014b), however, has a smaller size, a lower spire and a less gradate outline, very weak and prosocline growth lines on the ramp of last whorl, base flatter with three to four spiral keels, and the umbilical area flat with the umbilicus not deeply developed.

Bandel et al. (2000) pointed out the difference between Guidonia riedeli Bandel et al. (2000; p. 82, pl. 4, figs. 1-3, 5), from the Early Jurassic of Kaiwara Valley (New Zealand), and G. Peruviana, showing that the latter has a less developed spiral and axial ornament in comparison to the New Zealand form. Moreover, G. riedeli differs also from the Peruvian form in having a less gradate and lower spire, with a strongly horizontal sutural ramp, a larger and wider funnel- shaped umbilicus, and a subcircular aperture. Guidonia pseudorotula Gatto and Monari (2010; p. 786, text-figure 6H-N), from the late Sinemurian of Austria, has a ramp moderately oblique, less concave outer face, a wider umbilicus, and growth lines prosocline and straight on the ramp and outer face, slightly prosocyrt on the abaxial region of the base and opisthocyrt on the umbilical region.

Guidonia bifasciata Haas, 1953
Fig. 3P-S

Material examined: Paratypes, AMNH No. 26502D, No. 26502S; ‘well preserved’ and silicified teleoconchs. Syntype, AMNH No. 26502H; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 24.5 km SSE, 0.5 km W of Ninacaca Jenks Lot 86, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, trochiform, slightly gradate, small- sized and moderately low- spired shell. The protoconch is not preserved; the teleoconch consists of about four whorls, with a mean height of 5.18 mm and a mean width of 5.83 mm. Earliest whorls are convex and become angular and gradate in mature growth stages. Suture is impressed. From third to mature whorls, two acute spiral keels become visible; the weaker adapical one borders the suture, and the stronger is peripheral and delimits the angulation. Fine and regularly spaced spiral keels are present on the ramp of last whorl, between the adapical and peripheral spiral keels; the specimen 26502H has four well preserved and regularly spaced spiral ribs on the outer face of last whorl. The third and fourth whorls have very weak axial ribs intercepting the spiral elements and forming weak nodes at the intersection points. Base is slightly convex ornamented by five regularly spaced spiral keels. The umbilical area is bordered by the inner spiral keel; the umbilicus is deep and narrow. The aperture is holostomatous and circular; the outer lip indented by peripheral spiral keel and the columellar lip crescent- shaped.
Affinities: G. bifasciata Haas (1953; p. 74, pl. 4, figs. 76-78, 81-85, pl. 5, figs. 1-3) is very similar in general shell morphology to G. Peruviana; however, G. bifasciata has a slightly more conical and less gradate shell, five regularly spaced spiral keels on base, and its columellar lip is slightly thickenned in comparison to G. Peruviana. The present species also resembles Chartronella spiralis Ferrari (2011, p. 71, fig. 9.1-6) (Fig. 2A-C), from the Early Jurassic of the Chubut Province, in ornament pattern, having well developed spiral keels on base; however, the Argentinean form has also strong spiral keels on the shell surface crossed by fine prosocline collabral lines, and a more expanded and subcircular aperture.

Guidonia planetecta Haas, 1953
Fig. 3T-V

Material examined: Paratype, AMNH No. 35538G; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 18.75 km S, 7.75 km W of Ninacaca Jenks Lot 70, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, gradate, step- like, low- spired and very small- sized shell, with a height of 4.24 mm and a width of 6.66 mm. The protoconch is not preserved; the teleoconch consists of three gradate whorls. The sutural ramp on adult whorls is flattened and horizontal; the outer face is sharp straight and strongly concave, bordered by two acute spiral keels. The two acute spiral keels are equally developed, completely visible on last whorl, and coincide with the angulation; they appear to have small and very weak nodes. No collabral ornament is observed on the shell surface. The base is flat to slightly convex, smooth, and widely phaneromphalous, with a deep and funnel- shaped umbilicus. The umbilical area lacks the typical bordering spiral keel. The aperture is holostomatous and circular; the outer lip indented by the external angulation. Basal lip slightly expanded abapically, and columellar lip crescent- shaped.
Affinities: The species here described is very similar in shell shape and ornamentation to Chartronella paganiae (Fig. 1M-O) and Guidonia disciformis Ferrari, 2014b. (Fig. 3W-Y), both from the Early Jurassic of Argentina (see above). G. planetecta, however, is smaller than C. paganiae, has a more step-like shell and an open umbilicus; and Guidonia disciformis has a more depresed shell.

Family Cirridae Cossmann, 1916
Subfamily Hesperocirrinae Haas, 1953
Genus Hesperocirrus Haas, 1953

Type species: Hesperocirrus triasicus (Cox, 1949), from the Upper Triassic of Perú.
Occurrence: Late Triassic; Perú.
Remarks: Haas (1953) proposed the subfamily Hesperocirrinae to include the genera Hesperocirrus and Sororcula, both form the Late Triassic of the Pucará Group. The author considered Hesperocirrus as one of the less diversified genera within the Peruvian fauna, which is represented only by five species. Bandel (1993) pointed out the differences between Hesperocirrus with the coeval Cassianocirrus Bandel and Zardinicirrus Bandel from the St. Cassian Formation, differing from the Peruvian form in shell profile and sculpture. The author also compared the Jurassic Hamusina Gemmellaro with Hesperocirrus and emended the subfamily diagnosis to include the genera Heperocirrus, Sorocula Haas, Hamusina and Sensuitrochus Quintero and Revilla. The classification of Bandel was subsequently followed by Ferrari (2014a) and also adopted here.

Hesperocirrus robusteornatus Haas, 1953
Fig. 4A-B

Material examined: Syntype, AMNH No. 34406; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 18.75 km S, 7.75 km W of Ninacaca, Jenks Lot 69, Central Perú; Late Triassic, Pucará Group.
Description: Sinistral, trochiform, conical to slightly gradate, medium- sized and relatively high- spired shell. The protoconch is not preserved. The teleoconch consists of six whorls, with a height of 23.28 mm and a width of 18.52 mm. Earliest teleoconch whorls are fragmentary and last whorl slightly more expanded than the spire. Suture is impressed in a deep spiral furrow. The ramp of whorls is narrowly horizontal; the outer face is strongly convex and ornamented by two acute nodose rows; the adapical is stronger and has more acute nodes than the abapical. The outer face is strongly concave between the spiral rows. Weak opisthocline collabral ribs are present on the shell surface; they are opisthocline on the upper portion of the outer face and become prosocyrt toward the lower portion. The base is angular and flattened, with a relatively wide umbilicus. The aperture is strongly circular and the peristome continuous.
Affinities: The resemblance between Hesperocirrus robusteornatus Haas (1953, p. 42, pl. 2, figs. 35-37, 41, 43, 44, 47-49, 51-53, 58) and Hamusina? wahnishae Ferrari (2014a, p. 10, fig. 4n-u) (Fig. 4L-P), from the Early Jurassic of Patagonia, was discussed by Ferrari (2014a) who stated that Hesperocirrus robusteornatus differs from the Argentinean species in having axial and nodular elements, more conspicuous spiral threads, and a wide umbilicus. Another similar form to H. robusteornatus is Hamusina maxwelli Bandel (1993, p. 58, pl. 4, figs 9, 10; pls 5, 1-5; Bandel et al., 2000, p. 77; pl. 2, figs. 1-6) from the Early Jurassic of New Zealand; however, H. maxwelli is much smaller, has stronger axial riblets which are inclined toward the base and lacks nodose rows on the outer face.

 

Fig. 4. A-B: Hesperocirrus robusteornatus Haas, 1953, AMNH No. 34406, syntype; A: apertural view; B: lateral view; C-G: Hesperocirrus striatus Haas, 1953; C-D: AMNH No. 34427, paratype; C: lateral and apertural view; D: apical view; E-H: AMNH No. 34428, syntype; E-F: lateral views; G: apical view; H: basal view; I-K: Sororcula gracilis Haas, 1953, AMNH No. 35517, syntype; I: lateral view; J: basal view; K: apical view; L-P: Hamusina? wahnishae Ferrari, 2014a, MPEF-PI 3592, holotype; L-N: lateral views; O: apertural view; P: basal view.

 

Hesperocirrus striatus Haas, 1953
Fig. 4C-G

Material examined: Paratype, AMNH No. 34427; ‘well preserved’ teleoconch. Syntype, No. 34428; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 24.5 km SSE, 0.5 km W of Ninacaca, Jenks Lot 86, Central Perú; Late Triassic, Pucará Group.
Description: Sinistral, trochiform, gradate, small- to medium- sized and relatively low- spired shell, with a mean height of 6.77 mm and a mean width of 6.26 mm. The protoconch is typical of vetigastropods, consisting of one convex and smooth whorl; the teleoconch consists of five gradate whorls. First teleoconch whorl strongly convex, ornamented by regularly spaced axial ribs; mature whorls become angular. The ramp of whorl is flat to slightly concave; the outer face become straight, vertical and concave. Suture is impressed in a weak spiral furrow. The angulation of whorls is bordered by a row of pointed and separate nodes; nodes are more acute and stronger on the peripheral spiral keel. A weaker adapical spiral cord with less conspicuous nodes borders the suture. Thin axial ribs connect the nodes of adapical and peripheral spiral keels. The base is angular and flattened, and ornamented by irregularly spaced spiral threads. The aperture is holostomatous and circular, with a thin outer lip; the basal lip is flattened and the columellar lip thickened. The umbilicus is very narrow and deep, partialy covered by a thin columellar callus and ornamented by fine and weak collabral ribs.
Affinities: Hesperocirrus striatus Haas (1953, p. 48, pl. 2, figs. 42, 46, 54, 56, 57, 60) resembles H. robusteornatus (see above). The present form, however, is smaller, has a more gradate outline shell, less rounded and more acute nodes at the periphery of the shell, less developed collabral ribs, a lower spire and a narrower umbilicus, which is covered by a thin columellar callus. Hamusina? wahnishae (see above; Fig. 4L-P), is slightly larger, has a more conical outline shell, stronger spiral cords on the flanks of whorls, sutures feebly impressed, lack axial and collabral elements, lacks of umbilicus, and the aperture is quadrangular instead of circular. H. maxwelli (see above), is also very similar to H. striatus in shell shape and ornamentation; however, the species from New Zealand lacks pointed nodes and has a subangular aperture.

Genus Sororcula Haas, 1953

Type species: Sororcula gracilis Haas, 1953, by original designation, Upper Triassic of Perú.
Occurrence: Late Triassic; Perú.
Remarks: This genus was proposed by Haas (1953) to include sinistral, slender and small shells, with flank of whorls flattened to slightly concave, ornamented by distinct transverse ribs, sutures incised in a spiral furrow, base nearly flat with a narrow umbilicus or at least with an umbilical notch. According to Haas (1953) Sororcula differs from Hesperocirrus in ‘being smaller, having a more slender shell, flat or even slightly convace whorl faces, shallower sutures, lower pleural angle, almost flat base, narrower umbilicus, and a more delicated ornamentation’. Haas (1953) designated Sororcula gracilis as the type species of the genus and considered Sororcula less common than Hesperocirrus, represented only by two species and 27 specimens.

Sororcula gracilis Haas, 1953
Fig. 4H-K

Material examined: Syntype, AMNH No. 35517; ‘moderately well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 9.5 km SSE, 2.72 km N of Pasco, Jenks Lot 67, Central Perú; Late Triassic, Pucará Group.
Description: Sinistral, conical, trochiform, small- sized and slightly high- spire shell, with a height of 6.16 mm and a width of 4.6 mm. The protoconch is not preserved; the teleoconch consists of five whorls; earliest whorls slightly convex, becoming flattened toward mature whorls stages. Sutures are weakly incised in a spiral furrow. The ornament is clearly visible on the flanks of mature whorls. It consists of five to six fine, regularly spaced and crowded spiral cords; two stronger nodular spiral elements, developed as keels, are located adapically and abapically on whorls; the abapical is stronger with more pointed nodes. The base is flattened, angular and smooth. The aperture is quadrangular; with the columellar lip thickened. The umbilicus is absent or with a umbilical notch.
Affinities: Sororcula gracilis Haas (1953, p. 52, pl. 3, figs. 28, 30, 31, 35, 36, 42-46) is very similar in shell shape and ornament to Hamusina? wahnishae (see above; Fig. 4L-P), from the Early Jurassic of Patagonia. Both have a conical shell, with flattened flanks ornamented by five regularly spaced spiral cords on mature whorls, and lacks an umbilicus. However, the Peruvian form is slightly smaller and has two nodular spiral keels bordering the suture; nodes on H.? wahnishae are absent. Probably, Hamusina? wahnishae belong indeed to Sororcula. Hamusina maxwelli (see above) has more developed axial and nodular elements, and lacks spiral cords on the shell surface. The affinities between S. graciclis and Hesperocirrus were also noted by Haas (1953, p. 53). Sororcula differs from Hesperocirrus in being smaller, with a lower pleural angle, slender shell shape and not gradate in outline (see above).

Family uncertain
Genus Jurassiphorus Cossmann, 1915

Type species: Jurassiphorus cailliaudanus (D’Orbigny, 1853), Middle Jurassic (Callovian), France.
Occurrence: Late Triassic-Middle Jurassic (Callovian); North America, South America and France.
Remarks: Jurassiphorus was reported by Haas (1953) from the Late Triassic of the Pucará Group and included it in the caenogastropod family Xenophoridae Cossmann. Bandel (1994) listed this genus under the trochomorph vetigastropods and compared it with the similar coeval Rolandomphalus armatus (Zardini) from the St. Cassian Formation. Gründel (1997) described the protoconch of the type species Jurassiphorus cailliaudanus (D’Orbigny), and also included the genus in the trochomorph taxa. Nützel and Erwin (2004) classified species of Jurassiphorus in an uncertain family within vetigastropods, classification followed subsequently by Ferrari (2014a). Here, the classification proposed by Nützel and Erwin (2004) is adopted.

Jurassiphorus triadicus Haas, 1953
Fig. 5A-D

Material examined: Holotype, AMNH No. 26514A; ‘well preserved’ specimen.
Occurrence: Cerro de Pasco locality, 21 km E, 3.5 km SSE of Huanco Jenks Lot 26, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, discoidal, gradate, low- spired and small- sized shell, with a height of 3.97 mm and a width of 9.04 mm. The protoconch is not preserved; the teleoconch consists of four trochospiral whorls, with last whorl markedly expanded. The sutural ramp is flattened and horizontal; the outer face becomes vertical and straight to slightly convex, and ornamented by strong elongated nodes at the angulations. Spiral elements are not observed. A big flattened and horizontal crest is developed on last teleoconch whorl. The base is flat to slightly convex and ornamented by two spiral nodose keels. The aperture is circular and holostomatous, with the outer lip indented by external crest.
Affinities: Ferrari (2014a) described a congeneric species, Jurassiphorus? cf. triadicus Haas (Ferrari, 2014a, p. 13, fig. 5k-p) (Fig. 5E-J), from the Early Jurassic of Patagonia; the Argentinean form, however, lacks an external crest on the last teleoconch whorl. Another related form to the Peruvian species is the type Jurassiphorus cailliaudanus (D’Orbigny) from the Callovian of France; but the European form has one nodose spiral keel on the base instead of two (Gründel, 1997; p. 87, pl. 4, fig. 9-11).

 

Fig. 5. A-D: Jurassiphorus triadicus Haas, 1953, AMNH No. 26514A, holotype; A-B: apical view; C-D: apertural and basal views; E-J: Jurassiphorus? cf. triadicus Haas, 1953 (Ferrari, 2014a); E-H: MPEF-PI 4023-1; E-F: apical views; G-H: lateral and apertural views; I-J: MPEF-PI 4023-2, apical views; K-N: Paracerithium tambosolense Haas, 1953; K-L: AMNH No. 35710B, syntype, apertural and lateral views; M-N: AMNH No. 26576C, paratype, lateral and apertural views; O-R: Procerithium (Rhabdocolpus) patagoniensis Ferrari (2012); O-P: MPEF-PI 3517, holotype, lateral and apertural views; Q-R: MPEF-PI 3518, lateral views.

 

Order Caenogastropoda Cox, 1959
Family Procerithiidae Cossmann, 1905
Genus Paracerithium Cossmann, 1902

Type species: Paracerithium acanthocolpum Cossmann, 1902, from the Early Jurassic (Hettangian) of France.
Occurrence: Late Triassic-Late Jurassic; Perú, Europe and New Zealand.
Remarks: Haas (1953) reported the first Triassic occurrence of the genus Paraceithium Cossmann in the Peruvian Andes. The author corroborated the occurrence of this genus in the Late Triassic by comparing the type speceis, P. acanthocolpum, with the similar counterpart ‘Kotosira’ seelandica Kittl from the St. Cassian Formation, suggesting that both resemble in shell shape, apertural details and ornamentation. Haas, thus, included ‘K.’ seelandica into Paracerithium and pointed out that the coeval forms fom the Pucará Group certaintly belong to Paracerithium. Bandel et al. (2000) described two new species of this genus from the Early/Middle Jurassic of New Zealand and considered as its most diagnostic features the presence of wide conical shell, an aperture oval with a well developed siphonal notch, whorls with strong spiral keels, and widely spaced axial ribs intercepting spiral elements and forming nodes at crossing points.

Paracerithium tambosolense Haas, 1953
Fig. 5K-N

Material examined: Paratype, AMNH No. 26576C; ‘well preserved’ teleoconch. Syntype, AMNH No. 35710B.
Occurrence: Cerro de Pasco locality, 22 km SSE, 4.5 km W of Pasco, Jenks Lot 78 and 80 km SE, 4 km E of Tilarnioc Jenks, Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, turriculate, conical, small- sized and high- spired shell, with a mean height of 5.58 mm and a mean width of 2.85 mm. The protoconch is not preserved; the teleoconch consists of about six to seven whorls. The sutural ramp is narrowly horizontal and the outer face becomes strongly convex in shape. The ornament consists of spiral and axial elements; five regularly spaced and rather weak spiral cords appear on the outer face of mature whorls. The spiral elements are intercepted by seven to eight strong and orthocline to slightly opisthocyrt axial ribs. The base is convex and ornamented by two to three regularly spaced spiral cords. The aperture is holostomatous and oval, with a strongly convex and thickened outer lip and the columellar lip straight and parallel to the coiling axis. The basal lip is expanded as a siphonal notch.
Affinities: Paracerithium tambosolense Haas (1953, p. 225, pl. 15, figs. 25, 33-39) show close resemblance to Procerithium (Rhabdocolpus) patagoniensis Ferrari (2012, p. 329, figs. 4G-P, 5A-K) (Fig. 5O-R) from the Early Jurassic of Patagonia; however, the Argentinean form is slightly larger than P. tambosolense, has up to eight spiral cords on mature whorls, a high number of axial ribs which are stronger opishtocyrt, less developed sutural ramp and lacks the siphonal notch on base.

Other two related species to the one here described are those described by Bandel et al. (2000) from the Early/Middle Jurassic of New Zealand. Paracerithium spinosum Bandel et al. (2000, p. 87, pl. 5, fig. 5, pl. 7, figs. 1-2, 4) has 10-12 teleoconch whorls, a more step- like outline shell with a higher number (10-11) of axial ribs which are less opisthocyrt; the peripheral edge of the sutural ramp forms small nodes, and the base has an oblique and twisted anterior channel. Paracerithium pacificum Bandel et al. (2000, p. 87, pl. 6, figs. 1-3, 7) has a widely conical shell with a more convex appearence and two spiral keels located in a central position of the flanks with acute nodes at the crossing points with axial ribs.

Paracerithium? vixstriatum Haas, 1953
Fig. 6A-D

1953 Paracerithium vixstriatum Haas: p. 230, pl. 15, figs. 57-64, 69, 70, 73-75.

Material examined: Syntype, AMNH No. 26580A; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 80 km SE, 4 km E of Tiliarnioc, Jenks Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, turriculate, slender to strongly convex, very small- sized and high- spired shell, with a height of 4.93 mm and a width of 2.41 mm. The protoconch is not clearly visible, probably consisting of one convex and smooth whorl. The teleoconch comprises seven strongly convex whorls. The sutural ramp is narrowly developed and horizontal, more clearly visible on mature whorls. Axial ribs are predominant and they appear in numbers of 11 toward mature growth stages. The axial ribs are acute and strongly developed giving the shell outline a strongly convex appearence; they are prosocline to strongly opisthocyrt. Spiral elements are absent on the shell surface. The base is flattened to angular and smooth, although delimited by a weak spiral cord. The aperture is holostomatous and oval, with the basal lip expanded abapically forming a weak siphonal notch. The outer lip is slightly reflected into the aperture, forming a weak adapical channel.
Affinities: According to the characterization of Bandel et al. (2000), the species described by Haas (1953) seems to be a representative of Paracerithium, considering a wide to conical shell, convex in outline, aperture oval with a siphonal notch, and widely spaced axial ribs as its typical characters. However, other diagnostic features such as strong spiral keels intercepting the axial elements and forming nodes at intersection points, are not visible in Paracerithium? vixstriatum Haas (1953, p. 230, pl. 15, figs. 57-64, 69, 70, 73-75). The Peruvian form also resembles members of Zygopleura Koken. Mesozoic zygopleurids are generally characterized by a high spired teleoconch ornamented with wavy axial ribs and without any spiral ornament. However, zygopleurid teleoconch can not be assigned to Zygopleura without knowledge of the protoconch, and the recognition of such chacaters relies on good preservation (Nützel and Erwin, 2004). In the single specimen here analyzed, the protoconch is not clearly visible. Here, I propose to keep the species in Paracerithium but I added question marks to express the uncertainty.

Paracerithium? vixstriatum resembles also members of Protofusus Bonarelli, 1921. Bonarelli (1921) proposed Protofusus for three species from Carabajal (Salta Province, Argentina).

 

Fig. 6. A-D: Paracerithium? vixstriatum Haas, 1953, AMNH No. 26580A, syntype; A-B: apertural and lateral views; C-D: basal views; E-F: Rhabdocolpus (Rhabdocolpus) praeco Haas, 1953, AMNH No. 26594, paratype, lateral views; G-I: Cryptaulax tilarniocensis Haas, 1953, AMNH 26593F, paratype; G-H: apertural and lateral views; I: basal view; J-N: Cryptaulax damboreneae Ferrari (2009); J-K: MPEF-PI 1878b, holotype, lateral views; L: MPEF-PI 4036, four associated specimens in lateral and basal views; M: MPEF-PI 1877, apertural view; N: MPEF-PI 4013, lateral view; O-P: Cryptaulax redelii Ferrari (2012), MPEF-PI 3508, holotype, lateral views.

 

Genus Rhabdocolpus Cossmann, 1906

Type species: Melania scalariformis Deshayes, 1830-1932, from the Middle Jurassic of France.
Occurrence: Late Triassic-Late? Jurassic; Europe, New Zealand, Antarctica and South America.
Remarks: The diagnosis of Rhabdocolpus Cossmann was emended by Gründel (1999) and Bandel et al. (2000). The authors included in this procerithiid genus forms with a high- spired and flattened to slightly convex outline shell, with an horizontal to strong sloping subsutural ramp, opisthocyrt axial ribs on the teleoconch, forming nodes at the crossing point with spiral elements, and base with an adapical channel and lacking abapical notch. The genus is well known from the Jurassic of Europe, and Haas (1953) reported the first occurrence of Rhabdocolpus from the Late Triassic of South America.

Subgenus Rhabdocolpus (Rhabdocolpus)
Cossmann, 1906

Remarks: Gründel (1999) retained the subgenus Rhabdocolpus (Rhabdocolpus) to include shells with a narrow and nearly horizontal subsutural ramp, whorls delimited against each other in a step- like appearence, and the outer face of whorls nearly straight. Here, the classification of Gründel (1999) is followed considering that Haas’s material belongs to the present subgenus.

Rhabdocolpus (Rhabdocolpus) praeco Haas, 1953
Fig. 6E-F

1953 Rhabdocolpus praeco Haas: p. 237, pl. 16, figs. 1-11, 13, 14, 27

Material examined: Paratype, AMNH No. 26594; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 80 km SE, 4 km E of Tilarnioc Jenks, Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, turriculate, slender, very small- sized and high- spired shell, with a mean height of 6.3 mm and a mean width of 2.5 mm. The protoconch is not preserved; the teleoconch consists of about nine flattened to slightly convex whorls. Sutural ramp is narrowly horizontal and whorls have a step- like appearence. Suture is impressed in a weak spiral furrow. The ornament consists of spiral and axial elements. Regularly spaced spiral keels are present in numbers of six on each whorl; the spiral keels are intercepted by strong orthocline axial ribs which run from suture to suture. Acute nodes appear at the crossing points of axial and spiral elements; nodes are stronger at the intersection of the adapical spiral keel. The base is convex and smooth, delimited by two strong spiral keels. The aperture is holostomatous and oval, with the columellar lip thickened and the basal lip expanded abapically forming a siphonal notch.
Affinities: According to the characterization of Gründel (1999), the species described by Haas (1953) certainly belongs to the subgenus Rhabdocolpus (Rhabdocolpus), based on the presence of an horizontal subsutural ramp and a step- like appearence as the most diagnostic features. Rhabdocolpus (Rhabdocolpus) praeco Haas (1953, p. 237, pl. 16, figs. 1-11, 13, 14, 27) is more similar to Procerithium (Rhabdocolpus) patagoniensis Ferrari (see above; Fig. 5O-R) than to Paracerithium tambosolense Haas (see above; Fig. 5K-N). The Argentinean form, however, has a higher spire with a mean height of 12.42 mm, the teleoconch whorls are slightly more convex, have less developed subsutural ramp, the axial ribs are opisthocyrt and the base is ornamented by 10 regularly spaced spiral keels which are intercepted by prosocline growth lines, and the basal lip is flattened without an abapical notch. Rhabdocolpus? kowalkei Bandel et al. (2000, p. 88, pl. 6, figs. 4-6, 8, 10), from the Early/Middle Jurassic of New Zealand, differs from the Peruvian species in being smaller with six teleoconch whorls, the axial ribs are stronger forming concave interspaces between each other, nodes at the crossing points of spiral and axial elements are stronger, and sutures are slightly more impressed. Rhabdocolpus sp. Edwards (1980, p. 38, fig. 2b; Thompson and Turner, 1986, p. 26, tb. 1) from the Early Jurassic (Sinemurian) of Antarctica, resembles also R. (R.) praeco; however, the Antarctic form is more similar to the representatives of Rhabdocolpus (Infacerithium) (see diagnosis in Gründel, 1999, p. 11), differing from R. (R.) praeco in having sloping subsutural ramps which are not delimited against each other as a step- like appearance, and has more spaced and orthocline axial ribs.

Genus Cryptaulax Tate, 1869

Type species: Procerithium (Xystrella) protortile Cox, 1965, pro Cerithium tortile Hébert and Eudes-Deslongchamps, 1860, from the Middle Jurassic (Callovian) of France.
Occurrence: Late Triassic-Lower Cretaceous; Cosmopolitan.
Remarks: The species of Cryptaulax are cosmopolitan and common in the Jurassic. Haas (1953) reported the first certain representatives of Cryptaulax from the Late Triassic of Perú, though the same taxa were previously recorded by Jaworski (1923) but classified as Promathildia Andreae, 1887. Haas (1953) described two Cryptaulax species from the Late Triassic of Perú. In the present research, the genus concept expressed by Gründel (1999), Kaim (2004) and Bandel (2006) are followed to retain Haas’s (1953) species in Cryptaulax.

Cryptaulax tilarniocensis Haas, 1953
Fig. 6G-I

Material examined: Paratype, AMNH No. 26593F; ‘well preserved’ teleoconch. Syntype, AMNH No. 26593C; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 80 km SE, 4 km E of Tilarnioc Jenks, Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, turriculate, slender, very small- sized and high- spired shell, with a mean height of 3.06 mm and a mean width of 1.4 mm. The protoconch is fragmentary and convex, consisting of one smooth whorl; first teleoconch whorl angular, ornamented by one weak peripheral spiral keel. From second teleoconch whorl to mature whorls, orthocline axial ribs appear from suture to suture. Spiral ornament is weakly developed; strong adapical and abapical spiral keels appear on whorls and are intercepted by the strong axial ribs, forming rounded nodes at the crossing points. Secondary spiral ribs are almost imperceptible. The base is flattened to slightly angular and delimited by two acute spiral keels. The aperture is holostomatous and circular, without an abapical notch.
Affinities: Cryptaulax tilarniocensis Haas (1953, p. 250, pl. 16, figs. 60-71) shows close resemblance to Cryptaulax damboreneae Ferrari (2009, p. 452, fig. 3B-D; Ferrari, 2012, p. 325, fig. 2A-H) (Fig. 6J-N) and to Cryptaulax redelii Ferrari (2012, p. 327, fig. 2I-K) (Fig. 6O-P), both from the Early Jurassic (late Pliensbachian-early Toarcian) of Patagonia. Cryptaulax damboreneae, however, is slightly larger than the Peruvian form, has a more gradate shell, and two well developed secondary spiral ribs on mature whorls. Cryptaulax redelii differs from Cryptaulax tilarniocensis in being larger, having stronger axial ribs and more conspicuous nodes at the crossing points with spiral elements, and four (or probably more) secondary spiral ribs on mature whorls. Cryptaulax cf. protortile (Cox, 1969), from the Early/Middle Jurassic of New Zealand, is also comparable to Haas’s species; but, Cox’s form has more convex whorls, more developed axial and spiral elements, and a slightly more gradate shell (Bandel et al., 2000, p. 89, pl. 6, figs. 9, 11-13).

Order Ptenoglossa Gray, 1853
Family Ampullinidae Cossmann, 1919
Genus Oonia Gemmellaro, 1878

Type species: Melania abbreviata Cossmann Terquem 1855=Pseudomelania hettangiensis Cossmann, 1909, from the Early Jurassic of France.
Occurrence: Late Triassic-Middle Jurassic; Europe, South America.
Remarks: According to the characterization of Gründel (2001b), members of Oonia have an oval shell with pointed apex, the teleoconch lack of sculpture, subsutural ramp is absent, and growth lines, when present, are distinctly sinuous and prosocline. Haas (1953) reported Omphaloptycha jaworskii Haas, from the Late Triassic of Perú and included it into the family Coelostylinidae Cossmann. Haas’s species is very similar to the Jurassic Oonia. Here, I propose accommodation of Omphaloptycha jaworskii in the genus Oonia following the classification of Gründel (2001b), extending also the chronostratrigraphic distribution of the genus into the Late Triassic.

Oonia jaworskii (Haas, 1953) comb. nov.
Fig. 7A-E

1953 Omphaloptycha jaworskii Haas; p. 137, pl. 8, figs. 1-28, 31.

Material examined: Holotype, AMNH No. 26522D; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 24.5 km SSE, 0.5 km W of Ninacaca, Jenks, Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, globose to strongly turbiniform, small- sized and moderately high- spired shell, with a height of 10.2 mm and a width of 6.68 mm. The protoconch is fragmentary and consists of one convex and smooth whorl and is slightly deviated from the coiling axis. The teleoconch comprises five strongly convex whorls. Suture is deeply impressed in a spiral furrow. The sutural ramp is slightly developed on earliest whorls; on mature whorls the ramp is very weak, narrowly horizontal and slightly concave. The outer face becomes strongly convex. The shell surface is smooth and lacks spiral ornament. On last whorl, sigmoidal collabral threads appear; on the upper portion of the outer face they are orthocline to slightly opisthocyrt, becoming strongly prosocline in the lower portion. The base is convex and expanded abapically, with a very narrowly opened umbilicus. The aperture is holostomatous and oval, with the basal lip flattened to concave; the columellar lip is thickened forming a callus which partially covers the umbilicus. A weak adapical channel is also developed.
Affinities: Oonia jaworskii com. nov. shows close resemblance with Early Jurassic species from Chile and Argentina. For instance, cf. Oonia Gründel (2001a, p. 59, pl. 4. figs. 1-4), from the Early Jurassic (Hettangian-Pliensbachian) of Chile, differs from the Peruvian form in being bigger and in having less convex teleoconch whorls. The genus Oonia was also reported in the Early Jurassic of Argentina by Jaworski (1926) and Weaver (1931). The species Oonia euspiroides (Gemmellaro) (Jaworski, 1926, p. 200; Weaver, 1931, p. 371 as O. cf. euspiroides), however, has well developed growth lines on the shell surface. Oonia? sp. (Fig. 7F-H) was recently reported in the Early Jurassic (Pliensbachian) of Argentina and is also comparable to Haas’s species; Oonia? sp., however, has a more acute shell shape and the last whorl is more expanded and elongated.

 

Fig. 7. A-E: Oonia jaworskii (Haas, 1953), AMNH No. 26522, holotype; A-C: lateral views; D-E: apertural and basal views; F-H: Oonia? sp., MLP 12159; F-G: lateral views; H: apertural view; I-N: Cylindrobullina (Cylindrobullina) avenoides Haas, 1953; I-K: AMNH No. 27634B, syntype; I-J: apertural and lateral views; K: basal view; L-N: AMNH No. 27634K, paratype; L-M: lateral and aprtural views; N: basal view; O-Q: Striactaeonina transatlantica (Behrendsen, 1891), MLP 25094, lateral views; R-T: Actaeonina ovata Behrendsen (1891), MCF-PIPH 546; R: lateral view; S: apical view; T: lateral and apertural views.

 

Order Opisthobranchia Milne-Edwards, 1848
Family Cylindrobullinidae Wenz, 1947
Genus Cylindrobullina Von Ammon, 1878

Type species: Actaeonina fragilis Dunker, 1846, from the Early Jurassic of Europe.
Occurrence: Late Triassic-Late Jurassic; Europe and South America.
Remarks: Bandel et al. (2000) defined representatives of Cylindrobullina by having egg- shaped, conical to step- like shells, with growth lines as the major sculptural elements, aperture elongated, oval, and lacks columellar folds, larval shell sinistral and twists into the teleoconch. Later, Gründel and Nützel (2012) emended the genus’s diagnosis as ‘the shell has cylindrical shape; the whorls embrace just below the subsutural ramp; the aperture is high and narrow; the spire is low; the whorls have a subsutural ramp with a rounded edge as transition to the almost straight flanks; the base is convex and has an evenly rounded transition to the whorl flanks; the whorls are smooth or weakly ornamented...there are no columellar folds; the protoconch is heterostrophic’. Haas’s (1953) material fits with the characterization of Bandel et al. (2000) and Gründel and Nützel (2012); however, Haas (1953) included the Late Triassic species in the family Acteonidae D’Orbigny, while Bandel et al. (2000) and Gründel and Nützel (2012) considered members of Cylindrobullina to belong to the family Cylindrobullinidae. Here, the classification of Bandel et al. (2000) and Gründel and Nützel (2012) is followed and the Late Triassic Cylindrobullina are accomoded into Cylindrobullinidae.

Cylindrobullina (Cylindrobullina) avenoides Haas, 1953
Fig. 7I-N

Material examined: Paratype, AMNH No. 27634K; ‘well preserved’ teleoconch. Syntype, AMNH No. 27634B; ‘well preserved’ teleoconch.
Occurrence: Cerro de Pasco locality, 80 km SE, 4 km E of Tilarnioc, Jenks, Lot 48, Central Perú; Late Triassic, Pucará Group.
Description: Dextral, oval, cylindrical, egg- shaped, step- like, small- sized and slightly high- spired shell, with a mean height of 4.3 mm and a width of 2 mm. The protoconch is fragmentary; the teleoconch consists of five whorls, with the last whorls markedly more expanded than the spire. Sutural ramp is widely horizontal forming an angular to slightly convex demarcation with the outer face. The outer face becomes straight to slightly convex. Suture is weakly impressed in a spiral furrow. The shell surface shows fine, regularly spaced spiral furrow, more visible toward the outer face of last whorl; collabral ornament is not developed. The base is slighlty convex to angular and strongly expanded abapically; the aperture is elongated and oval, and lacks columellar folds. A weak adapical channel is also visible.
Affinities: Cylindrobullina (Cylindrobullina) avenoides Haas (1953, p. 261, pl. 17, figs. 35, 36, 39-42, 46, 49-51, 58, 59) is comparable to Cylindrobullina fragilis Dunker (Jaworski, 1926, p. 205; Weaver, 1931, p. 389) from the Early Jurassic of Argentina; however, the last form is slightly bigger, has a more ovoid shell, and lacks spiral furrows. Striactaeonina transatlantica (Behrendsen, 1891) (Behrendsen, 1922; Möricke, 1894; Jaworski, 1926; Weaver, 1931; Gründel, 2001a), also from the Early Jurassic (Pliensbachian) of Argentina, resembles Cylindrobullina (Cylindrobullina) avenoides; however, the Argentinean species is bigger, has strongly developed spiral furrow on the shell surface, and has a more step- like shell (Fig. 7O-Q). Striactaeonina atuelensis Gründel (2001a; p. 66, pl. 4, figs. 7-8) from the early Pliensbachian of Río Atuel (Mendoza) is also similar to the Peruvian species; but, Striactaeonina atuelensis has a sutural ramp nearly horizontal to sloped, and the shell outline is rather broader. Actaeonina ovata Behrendsen (1891, p. 383, pl. 22, fig. 7) (Fig. 7R-T), from the Early Jurassic of Argentina, is similar to Cylindrobullina (C.) avenoides; however, A. ovata has an ovoid shape and has smooth shell surface.

4. Palaeobiogeography and Diversity

The distribution patterns of Mesozoic benthic marine gastropods in South America may be interpreted following the idea of a shallow marine connection along the eastern Paleo-Pacific sea way between Perú and the Andean region of Argentina during the Late Triassic (Norian-Rhetian)/Early Jurassic (Toarcian) boundary (Fig. 8). Vicente (2005) pointed out the evolution of the Jurassic Andean retroarc basin at a global scale for the Central Andes. The author systematically checked the time of the marine transgressions along the Andean region of South America and distinguished two main gulfs of passage through the arc from which waters have progressed at the same time northward and southward in a narrow retroarc furrow. One of these gulfs is located at 25ºS and known as the Taltal; the Curepto Pacific gulf is found further south at 35ºS. Both Pacific gulfs initiated in the Late Triassic and extended during the Hettangian, and their evolution as separate basins ended in the middle Pliensbachian, giving rise to a continuous elongate basin from Chubut Province (Argentina) to northern Perú (Vicente, 2005) (Fig. 8).

 

Fig. 8. Map of the Andean region of South America showing the palaeobiogeographical distribution of benthic gastropod faunas across the Late Triassic/Early Jurassic boundary.

 

Some gastropod taxa that are well known from the Late Triassic of the Pucará Group occur in Early Jurassic marine deposits of the Andean region of Argentina. In particular, the genera Chartronella, Guidonia, Cryptaulax, Colpomphalus, Cryptaenia, Jurassiphorus, Oonia and Cylindrobullina are distributed along the South American Andes, from Perú to Chubut Province and also have a chronostrotigraphic range from the Late Triassic (Norian-Rhetian) to the Early Jurassic (Toarcian). These genera are interpreted here to represent a component of survivors of the end Triassic mass extinction in South America. The ancient seaway from Perú to Argentina is considered the most plausible explanation for biotic exchange of these faunas across the Late Triassic/Early Jurassic boundary. On the other hand, the Peruvian genera Hesperocirrus, Sororcula, Paracerithium, Rhabdocolpus, Eucycloscala are not represented in the Early Jurassic of Argentina but seem to have related counterparts. For instance, Hesperocirrus and Sororcula show close resemblance to Hamusina (see above); Paracerithium and Rhabdocolpus are also comparable to the genus Procerithium (see above); and Eucycloscala is related to the eucyclid genera Calliotropis and Ambercyclus, which are also reported in the Andean region of Argentina (see above). Figure 9 shows the taxonomic composition of the Peruvian and Argentinean Mesozoic marine gastropods across the Late Triassic/Early Jurassic boundary. Note that several families are well represented in the Late Triassic of the Pucará Group (Perú) but are absent in the Early Jurassic marine deposits of Argentina; these are Vermetidae, Mathildidae, Lacunidae, Neritidae, Naritopsidae, Spirostylidae, Coelostylinidae, Loxonematidae, Eucycloscalidae, Anomphalidae, Platyacridae, Euomphalidae and Murchisoniidae. On the other hand, families such as Trochotomidae, Carinariidae, Nerineidae, Protorculidae, Pseudomelaniidae and Proconulidae seem to be characteristic in the Early Jurassic of Argentina but are not represented in the Peruvian Triassic. There are, however, several taxa that occur in both regions: Zygopleuridae, Acmaeidae, Cylindrobullinidae, Ampullinidae, Purpurinidae, Procerithiidae, Ptychomphalidae, Nododelphinulidae, Trochidae, Discohelicidae, Cirridae, Pleurotomariidae, Ataphridae and Eucyclidae. Regarding the latter families, only four (Eucyclidae, Ataphridae, Discohelicidae and Ampullinidae) are better represented in Argentina with a higher number of species (Fig. 9A, C). This suggests that some Late Triassic Peruvian gastropod taxa were probably more susceptible than others to the end Triassic extinction. The appearence of new gastropod genera and families in the Early Jurassic of Argentina, which are not represented in the faunal assemblages of the Pucará Group, also show a relatively rapid faunal recovery after the crisis. However, the Peruvian gastropod fauna is slightly more diverse and abundant than the Argentinean (Fig. 9).

 

Fig. 9. A. Bar Graph showing the taxonomic composition (families) of the Peruvian and Argentinean Mesozoic marine gastropods across the Late Triassic/Early Jurassic boundary; B. Pie chart of families composition (%) from the Late Triassic of Perú; C. Pie chart of families composition (%) from the Early Jurassic of Argentina. Note that only the families Eucyclidae, Ampullinidae, Ataphridae and Discohelicidae are far more diverse in the Argentinean Jurassic.

 

In order to assess the gastropod diversity across the Late Triassic/Early Jurassic boundary, a biodiversity analysis was performed integrating all accessible data of marine gastropod faunas recovered thus far from the Late Triassic of Perú and from the Early Jurassic of Argentina. The analysis was based on PAST statistical software (Hammer et al., 2001) which calculated Simpson, Shannon and Margalef indices for the included samples. The Simpson and Shannon diversity indices provide an estimate of the variation in abundance among species within an assemblage (Table 1); the Margalef indice estimate the biodiversity of a community based on the numerical distribution of individuals of different species. Margalef values above 5.0 are considered to be indicative of high diversity. The primary results of the analysis show that the gastropod faunal association from the Pucará Group displays the highest diversity during the Late Triassic (Table 1, Fig. 9). In contrast, the Early Jurassic marine gastropods from Argentina indicate a lower diversification during the Hettangian /Toarcian times, showing a smaller number of species and families at that time (Table 1, Fig. 9). It is indeed clear, that the Late Triassic mass extinction had an impact on the South American marine benthic gastropod faunal turnover.

Rarefaction analysis (PAST) have also been calculated for each accesible sample of marine gastropod taxa recovered thus far from Perú and Argentina in order to assess species richness in a function of the collection effort. The samples conteined a total of 248 species representing 34 families. For the Peruvian association, a curve was calculated for the entire Haas’s (1953) gastropod collection. The Argentinean curve displayed less diversity than the Haas’s (1953) collection, although it represents a sample of widely distributed gastropod species which covers similar span of time. It is not surprising considering that the end Triassic crisis could have had a major incidence on the South American Early Jurassic faunal recovery. However, a more detailed research of Early Jurassic gastropod faunas in Argentina, including the investigation of new fossiliferous localities and the collection of new gastropod material with accurate geographical and stratigraphical data is currently in progress.

Regarding other Mesozoic gastropod assemblages from the Southern Hemisphere, the Peruvian fauna shows also close resemblance to the Early/Middle Jurassic New Zealand gastropod associations and with Early Jurassic Antarctic species. Bandel et al. (2000) described many species from the Kaiwara Valley (New Zealand) which are treated here to be nearly coeval and related counterparts to the Peruvian and Argentinean forms. At least representatives of the genera Guidonia, Hamusina, Eucycloscala, Paracerithium, Rhabdocolpus, Cryptaulax and the families Mathildidae and Cylindrobullinidae show affinities with the South American taxa, and suggest palaeobiogeographical connections along the southern Paleo-Pacific ocean. The Early Jurassic Antarctic Procerithiidae show also close systematic affinities to the South American taxa.

 

Agradecimientos
This work was supported by the Collection Study Grant Program awarded by the American Museum of Natural History, New York (AMNH). I thank the AMNH for this financial support. I also extend my gratitude to Ms. B. Hussaini (American Museum of Natural History, New York) and to Dr. N. Landman (American Museum of Natural History, New York) who allowed me access to the AMNH invertebrate collection. I specially thank B. Hussaini (Americam Museum of Natural History, New York) for taking the gastropod photographs. Critical reviews by H. Campbell (GNS Sciences, New Zealand), A. Kaim (Instytut Paleobiologii PAN, Warszawa, Poland) and A. Nützel (Bayerische Staatssammlung für Paläontologie und Geologie, München, Germany) of an earlier version of this manuscript contributed to improve it and are gratefully acknowledged.

 

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