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

. The Late Triassic/Early Jurassic boundary is marked by a mass extinction event which had an important effect on the marine benthic communities on a global scale. In the Andean region of South America, however, the impact of this phenomenon on the earliest Mesozoic marine invertebrate associations has not been evaluated thus far. The pres-ent contribution is a systematic revision of the Late Triassic marine benthic gastropod faunas from the Pucará Group of Central Perú, giving a detailed characterization of 18 species and an updated systematic assigment of representatives of the genera Chartroniella , Phymatifer , Ptychomphalina , Paracerithium , Rhabdocolpus and Omphaloptycha . This research includes a comparison of the Peruvian fauna with their related counterparts from the Early Jurassic of Argentina and the Early/Middle Jurassic of New Zealand. This approach attempts to interpret the Late Triassic/Early Jurassic faunal turnover after the end Triassic crisis and establishes a palaeobiogeographical scheme for the gastropod faunal exchange in the Southern Hemisphere across the palaeo-Pacific seaway during the Late Triassic/Early Jurassic.


Introduction
The Late Triassic marine gastropods from the Pucará Group (Central Perú) were studied by Haas (1953), who described 181 gastropod species which many are represented by only few and/or fragmentary specimens.Most of the species defined by Haas (1953) were subsequently compared with coeval and better preserved gastropod assemblages from the St. Cassian Formation (in northern Italy) (Bandel, 1994).Bandel (1994) related many genera (and families) of five major gastropod taxa (Vetigastropoda, Decoglossa, Neritimorpha, Caenogastropoda and Heterobranchia) from the St. Cassian Formation with those marine gastropods from the Pucará Group and noted several similarities in their taxonomic composition.Later, Bandel et al. (2000) compared some gastropod species from the Early/Middle Jurassic of New Zealand with representatives of the Peruvian association and also found resemblance between these associations.However, a detailed comparison of the Late Triassic fauna from Perú with other South American Mesozoic gastropods has not been assessed so far.
The Late Triassic/Early Jurassic boundary is marked by a mass extinction event which had an important effect on the marine benthic communities at world wide scale.In recent years, several studies greatly improved the knowledge on the systematics and phylogeny of the extant and fossils gastropods, suggesting that generic and higer level assignments of the older literature need systematic revision (Monari et al., 2011).Thus, an updated systematic knowledge of marine benthic faunas would certaintly facilitate palaeobiogeographical and diversity comparisons across the Late Triassic/Early Jurassic boundary.
The present paper aims at a systematic revision of the Late Triassic Peruvian gastropods originally described by Haas (1953), including a detailed characterization and an updated systematic assignment of 18 taxa, and the comparison with their related counterparts from the Early Jurassic of Argentina.An updated systematic assignment of the genera Chartroniella, Phymatifer, Ptychomphalina, Paracerithium, Rhabdocolpus and Omphaloptycha is also provided.The selection of the 18 Peruvian gastropod species relies on their striking resemblance and their close systematic affinities with the Early Jurassic fauna from Argentina, and with the Early/Middle Jurassic gastropod association from New Zealand.This approach attempts to interpret the Late Triassic/ Early Jurassic faunal turnover after the Late Triassic marine mass extinction in South America, and establishes a palaeobiogeographical scheme for the gastropod faunas across the palaeo-Pacific sea way during the Late Triassic/Early Jurassic boundary.The Peruvian seaway is considered the most plausible mechanism for biotic exchange from Perú to the Andean region of Argentina.

Material and methods
The Late Triassic marine gastropod species described by Haas (1953) from the Pucará Group are currently stored in the American Museum of Natural History (AMNH) invertebrate collection.The material examined in the AMNH collection includes 18 gastropod species, represented by 5 holotypes, 9 paratypes and 9 syntypes.During the present research, the specimens were reinvestigated and redescribed, and new photos have been taken by the technnical staff of the AMNH and by the author.The quality of the new photos relies on the relatively bad preserved conditions of the specimens.Most of the AMNH gastropod material is coarsely silicified and generally poorly preserved, showing broken, frgamentary and desarticulated early whorls.The AMNH gastropod material was compared with Early Jurassic faunas from Argentina which are currently stored in the MLP, MCF-PIPH and MPEF-PI collections.Comparisons were also made with the New Zealand gastropods described by Bandel et al. (2000) and with Antarctic gastropods described by Edwards (1980) and Thompson and Turner (1986).For the updated systematic assignment the recent classifications of Bandel (1993Bandel ( , 2006Bandel ( , 2009Bandel ( , 2010)), Bandel et al. (2000), Gründel (1999Gründel ( , 2001bGründel ( , 2005Gründel ( , 2008)), Gründel and Nützel (2012), Kaim (2004), Kaim et al. (2009), Nützel and Erwin (2004), Szabó (2009), Gatto andMonari (2010), andFerrari (2014a).
A biodiversity analysis and rarefaction curves have been calculated for each accesible sample of marine gastropod taxa recovered thus far from Perú and Argentina using a statistical software PAST (Hammer et al., 2001).The samples conteined a total of 248 species representing 34 families.Institutional abbreviations: AMNH: American Museum of Natural History, New York, USA; MLP: Museo de Ciencias Naturales de La Plata, Buenos Aires, Argentina; MPEF: Museo Paleontológico Egidio Feruglio, Trelew, Chubut, Argentina; MCF-PIPH: Museo Paleontológico Carmen Funes, Plaza Huincul, Neuquén, Argentina.Chartron and Cossmann, 1902, from the Early Jurassic of France.Ocurrence: Triassic-Jurassic; Europe, Asia, Africa, Perú and Argentina.Remarks: Haas (1953) described two species of Chartroniella and included representatives of the genus in the family Paraturbinidae Cossmann. Gründel (2008) proposed an updated diagnosis of Chartronella and moved it to the tribe Costataphrini Gründel. Ferrari (2011) however, suggested that representatives of Chartronella should be assigned the tribe Collonini Cossmann, based on their resemblance with the extant Cantrainea Jefreys (see laso Kaim et al., 2009).In the present study, the proposal on Ferrari ( 2011) is followed and the genus name Chartronella is retained instead of Chatroniella.
Fig. 1A-E 1923 Chartroniella pacifica (Jaworski); Haas, 1953: p. 81, pl. 5, figs. 31-41, 45-47, 54.Affinities: According to the characterization of Gründel (2008), the specimens here analyzed fit in definition of Chartronella, with an angular shell, two strong peripheral keels (the abapical keel is covered by subsequent whorls on the spire and is visible only on mature whorls), and a crescent shaped-columeallar lip as the most diagnostic features of the genus (see also Ferrari, 2011) 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.(Cox, 1949)     (2010) is followed, considering that the genus diagnosis fits with the updated characterization of the family Eucycloscalidae proposed by Gründel (2007).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 (2009Ferrari ( , 2014a) ) reported representantives of the genus in the Early Jurassic of South America.Gründel (2001a)  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 Pliensbachianearly 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)  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.
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.(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 Remarks: Haas (1953) proposed the subfamily Hesperocirrinae to include the genera Hespero-cirrus 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.Description: Sinistral, conical, trochiform, smallsized 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; 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.

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 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.
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.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.

Paracerithium? vixstriatum
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.

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.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.
Order Ptenoglossa Gray, 1853 Family Ampullinidae Cossmann, 1919 Genus Oonia Gemmellaro, 1878 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   Jaworski (1926) and Weaver (1931).The species Oonia euspiroides (Gemmellaro) (Jaworski, 1926, p. 200;Weaver, 1931, p. 371 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) 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   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).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 Juras-sic 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 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.

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.

Family Eucycloscalidae Gründel, 2007 Genus Eucycloscala Cossmann, 1885 Type species: Trochus
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.binodosus Münster, 1844 from the Late Triassic of St. Cassian Formation.
Haas (1953)0)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.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 The material described byHaas (1953)from the Late Triassic of Perú, fits in the diagnosis ofBandel (2010).Morever,Haas (1953)included Eucycloscala in the family Turbinidae Rafinisque and Bandel (2010) in Eucycloscalidae.Here, the classification of Bandel

Cirridae Cossmann, 1916 Subfamily Hesperocirrinae Haas, 1953 Genus Hesperocirrus Haas, 1953 Type species:
(Cox, 1949)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.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 spiralisFerrari (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 disciformisFerrari, 2014b.(Fig.3W-Y),bothfrom 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.Hesperocirrus triasicus(Cox, 1949), from the Upper Triassic of Perú.
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.Affinities: The species here described is very similar in shell shape and ornamentation to Chartronella paganiae (Fig.1M-O) and Occurrence: Late Triassic; Perú.
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.
species in Cryptaulax.
Gründel (2001b)aworskii 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 ofGründel (2001b), extending also the chronostratrigraphic distribution of the genus into the Late Triassic.

Opisthobranchia Milne-Edwards, 1848 Family Cylindrobullinidae Wenz, 1947 Genus Cylindrobullina Von Ammon, 1878 Type species:
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.Actaeonina fragilis Dunker, 1846, from the Early Jurassic of Europe.
is followed and the Late Triassic Cylindrobullina are accomoded into Cylindrobullinidae.

TABLE 1 . DIVERSITY OF LATE TRIASSIC AND EARLY JURASSIC GASTROPOD FAUNAS IN COMPARISON: SPECIES RICHNESS, FAMILIES, SIMPSON, SHANNON AND MARGALEF DIVERSITY INDICES.
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. gastropod