Ordovician Bivalvia and Rostroconchia of Argentina: An Updated Synthesis

Teresa M. SÁNCHEZ1

Abstract: ORDOVICIAN BIVALVIA AND ROSTROCONCHIA OF ARGENTINA: AN UPDATED SYNTHESIS. Knowledge of Ordovician Argentine bivalves and rostroconchs substantially increased in the past ten years. Temporal distribution of bivalves embraces the entire Ordovician, from the Tremadocian to the late Asghill (Hirnantian), while rostroconchs are restricted to the Tremadocian-early Llanvirn interval. Of 27 bivalve genera so far recognized in the Argentine basins, 16 are endemics. Such unusually high endemism is particularly evident in the Arenig volvaniclastic succession of the Famatina basin and in the early Caradoc of the Precordillera, which confirms the importance of Gondwanan shelves and peri-Gondwanan arc-related volcanic islands in the early bivalve diversification.

Resumen: BIVALVIA Y ROSTROCONCHIA ORDOVÍCICOS DE ARGENTINA: UNA SÍNTESIS ACTUALIZADA. Recientes hallazgos en rocas Ordovícicas del oeste de Argentina han incrementado el número de bivalvos y rostroconchos conocidos. La distribución temporal de los bivalvos abarca desde el Tremadociano hasta el Ashgiliano tardío (Hirnantiano), mientras que los rostroconchos están limitados al intervalo Tremadociano-Llanvirniano temprano. De los 27 géneros de bivalvos reconocidos, 16 están restringidos a cuencas argentinas, lo que representa un elevado porcentaje de endemismo. Este fenómeno es particularmente notorio en la sucesión del Arenigiano medio de la cuenca de Famatina y en los niveles de edad Caradociana temprana de la Precordillera, lo que corrobora la importancia de las plataformas Gondwánicas y arcos de islas volcánicas peri-Gondwánicas en la diversificación temprana de los bivalvos.

Key words: Bivalvia. Rostroconchia. Ordovician. Argentina

Palabras clave: Bivalvia. Rostroconchia. Ordovicico. Argentina.

Introduction

Although bivalves are relatively unfrequent in the Ordovician rocks of western Argentina, most typical Ordovician orders are represented. The richest and most abundant bivalve faunas come from the siliciclastic rocks exposed in the Cordillera Oriental, the southern part of the larger Central Andean basin, and from the volcanosedimentary successions of the Sierra de Famatina. Conversely, the early Ordovician carbonate rocks of the Precordillera basin, rich in brachiopods, trilobites and sponges, have yielded up to now only isolated specimens of bivalves and rostroconchs. In view that in limestones other molluscs having aragonitic shells, namely gastropods, are locally very abundant, it is reasonable to assume that the bivalve paucity in carbonate rocks is linked to biotic limiting factors rather than tafonomic conditions, like decalcification processes. As Babin (1993) stated, the Ordovician radiation of bivalves mainly occurs around the siliciclastic peri-Gondwanan shelves.

However, it should be noted that volcanic phenomena may also have enhanced bivalve diversification, as occurs in the Famatina Range, where bivalves constitute a significant part of the nearshore biota (Waisfeld et al., 2001).

The well-documented radiation underwent by most invertebrate clades during the Ordovician is also verified among bivalves. In Argentina, several early groups of bivalves, such as the Palaeotaxodonta (malletids, tironuculids, praenuculids), Heteroconchia (cycloconchids, redonids), and Pteriomorphia (colpomyids, mytiloids, ambonychiids, arcoidan) are well represented since the Tremadocian and Arenig.

Although rostroconchs have been documented in the three main basins of Argentina, they never attain the diversity of other regions (e.g. Australia). So far, a total of four genera and six species have been described. The record of Argentine rostroconchs ranges from the late Cambrian (Ribeiria francae Sánchez, 2000) to the early Llanvirn (Sánchez, 1998). No younger species are yet known. In spite of their scarcity, the four known genera represent the two orders of the class recognized by Pojeta (1978), Ribeiroida and Conocardioida. The former includes the genera Ribeiria Sharpe and Tolmachovia Howell and Kobayashi, and the latter Eopteria Billings and Talacastella Sánchez.

Figure 1. Spatial and temporal distribution of bivalve and rostroconch genera of Argentine Ordovician. Single asteriscs mark endemic genera, double asterisc indicates endemic genus of the Central Andean Basin (Argentina and Bolivia).

The geographic distribution and stratigraphic ranges of Argentine bivalves and rostroconchs are shown in the figure 1. Both groups have been documented in the three Ordovician basins of Argentina, the Precordillera terrane (Mendoza, San Juan and La Rioja provinces), the arc-related Famatina basin (La Rioja and Catamarca provinces) and the Central Andean Basin (Salta and Jujuy provinces) (Figs. 2, 3). In the Precordillera basin, rostroconchs are confined to the Arenig and early Llanvirn carbonate platform deposits, while bivalves, even though sporadically present in these rocks, become relatively abundant in the overlying Caradoc and Ashgill siliciclastic units in both deep and shallow water facies (Fig.2, C). In the Central Andean basin (Cordillera Oriental and Sierras Subandinas) rostroconchs range from the latest Cambrian/earliest Tremadocian to the mid-Arenig.

It is interesting to note that the earliest known bivalves of Argentina, of mid-Tremadocian age have been discovered in this basin. In general, bivalves are a subordinate component of the Late Tremadoc and especially of the Arenig communities of the Central Andean basin. Caradoc bivalves are locally abundant in the Santa Gertrudis and Capillas formations which are exposed in the Sierra de Mojotoro (Cordillera Oriental) and the Sierra de Zapla (Sierras Subandinas), respectively (Fig.3). Finally, in the Sierra de Famatina, both bivalves and rostroconchs are restricted to the Middle Arenig volcanosedimentary deposits (Suri and Molles formations) cropping out in the Chaschuil area (Fig. 2 A) and in the central region of the mountain belt, along the Cachiyuyo, Saladillo Grande and Los Molles rivers) (Fig. 2 B).

A list of bivalves and rostroconchs illustrated and described until now is given in the figure 1. Bivalves which generic identification is in need of revision include Ctenodonta laevigata Harrington, Ctenodonta minuscularia Harrington, Ctenodonta famatinensis Harrington, Modiolopsis sanbernardica Harrington (Harrington, 1938) from the Cerro San Bernardo (Acoite Formation), and Ctenodonta bonetensis Aceñolaza, from Jagüé, La Rioja province (Aceñolaza, 1970). From a biogeographical viewpoint, it is interesting to note that of these 27 bivalve genera, 16 are restricted to the Argentine basins, pointing out that an important bivalve diversification occurred in the western Gondwana clastic shelves, especially in the Famatina basin during the Arenig and in the Precordillera basin during the early Caradoc.

There are no bivalve genera in common among the three basins except Goniophorina, which has been recorded from Famatina and the Cordillera Oriental. The remainder genera are confined to a single basin. Goniophorina probably was an opportunistic form capable to inhabit in both clastic shelves and volcanic settings. With respect to the rostroconchs, Ribeiria has been documented in the three basins in nearly contemporaneous horizons (middle Arenig), represented by R.. spinosa in Famatina and Cordillera Oriental and by a R. cf. compressa in the Precordillera. Tolmachovia, on the other hand, appears in the Middle Arenig clastic successions of the Cordillera Oriental and in slightly younger (early Llanvirn) carbonate rocks of the Precordillera basin.

Stratigraphic distribution of taxa

Tremadocian

Harrington (1938) first noticed Tremadocian bivalves from the Cordillera Oriental (Iruya, Jujuy Province) and from the Sierra de Famatina (Volcancito River, Catamarca Province). From the former locality he reported Goniophorina (Cosmogoniophorina) tenuicostata Harrington and Palaeoneilo iruyensis Harrington, whereas from the ‘black shales of the Volcancito river’ (presently Volcancito Formation) the only species recorded is Ctenodonta famatinensis Harrington. Both the Iruya and Volcancito samples are early Tremadocian in age according to the associated trilobites mentioned by Harrington (1938), the latter being slightly older (Parabolina frequens argentina Zone). Because this material represents the earliest known palaeotaxodonts it might play a significant role in the debate about the origin of hinge types in bivalves. Clearly, if these specimens are palaeotaxodonts, this strongly supports the hypothesis that the taxodont pattern is ancestral to the actinodont dentition. Unfortunatelly, hinges are not preserved neither in the specimens of ‘Palaeoneilo’ nor in those referred to ‘Ctenodonta’, so that in the available matrial there is no evidence supporting its palaeotaxodont condition (for a discussion on the hinge origin see Sánchez and Babin, 1998, and references therein).

In Argentina, the oldest known preserved dentitions are of actinodont type. Specimens with this kind of dentition appear in the Floresta Formation exposures near the Dique La Ciénaga (Sierra de Mojotoro, Jujuy Province) (Sánchez and Vaccari, in press). According to the faunal content in other localities (Moya et al., 1994; Moya, 1998) this unit has been referred to the Bienvillia tegragonalis- Conophrys minutula Zone of Harrington and Leanza (1957). Calibration of the trilobite zones with conodont and graptolite data (Aceñolaza and Albanesi, 1997; Albanesi and Moya, 2000; Albanesi et al., 2001; Moya et al., 1994; Ortega et al., 1997; Tortello and Rao, 2000) indicates that fossiliferous strata are late Tremadoc in age (P. deltifer Zone). The bivalve assemblage from the Floresta Formation includes the actinodont Intihuarella Sánchez, characterized by a very simple actinodont type of hinge with a single posterior pseudolateral tooth. Another associated actinodont-like form is Redonia? jujuyensis Sánchez, in which the dentition is also reduced. The other two forms, Goniophorina (Cosmogoniophorina) tenuicostata Harrington, and Ucumaris Sánchez, are edentulous (Sánchez and Vaccari, in press).

Early Tremadocian rostroconchs are represented by Eopteria agustini Sánchez (Sánchez, 2000) (Pl. 1, fig. 16), which comes from the Cardonal Formation exposed on the eastern flank of the Sierra de Cajas, Jujuy province (Aceñolaza, 1968).

Arenig

Only two bivalve species are presently known from the Precordillera, both from the early Arenig Archaeorthis Zone (Herrera and Benedetto, 1991) of the San Juan Formation: Modiolopsis? sp. and an undetermined ambonychiid (Sánchez, 2001a). Although this material is represented by a few specimens, its mention is important as these species represent the oldest records of their respective groups. The Middle Arenig beds of the same formation have yielded a single species of rostroconch, Ribeiria cf. compressa Withfield (Sánchez, 1998).

In the Cordillera Oriental the following early Arenig bivalves have been reported by Harrington (1938) from the lower part of the Acoite Formation (San Bernardo Formation sensu Moya, 1998):

Ctenodonta laevigata Harrington, Ctenodonta minuscularia Harrington, and Modiolopsis sanbernardica Harrington. Due to the absence of diagnostic features (hinge, muscle scars) in the type material there is little or no evidence to support these generic assignements. These species are in need of revision.

Some specimens from the Cerro San Bernardo assigned by Harrington (1938) to the inarticulate brachiopod Obolus andinus Harrington correspond to the rostroconch Tolmachovia, as was demonstrated by Gutierrez-Marco and Aceñolaza (1991), who also reported Ribeiria spinosa Babin and Branisa from slightly younger beds (Middle Arenig) cropping out at the Espinazo del Diablo, east of Mina Aguilar, Jujuy province.

The Acoite Formation contains shelly faunas dated as early to Middle Arenig on the basis of graptolite content (Toro, 1994, 1997). It contains two bivalve species (Sánchez, 1995b, 1997a, 1997b), Natasia boliviensis (Babin and Branisa) (Pl.1, fig.1), and Goniophorina (Cosmogoniophorina) tenuicostata Harrington (Pl. 1, fig. 2). The species boliviensis was first described from the Arenig Sella Formation of Bolivia by Babin and Branisa (1987) and assigned to the genus Ekaterodonta Babin. Additional information obtained from better preserved and abundant specimens than those available at the time the Sella species was described, including specimens of different size showing different growth stages, revealed important differences with Ekaterodonta and provided the basis for the erection of the genus Natasia Sánchez (Sánchez, 1995b) (Pl.1, fig. 1). The genera Natasia, Tironucula Morris and Fortey, and Ekaterodonta all belong to the Family Tironuculidae Babin, but there are important differences between them, especially in the growth stages of dentition, justifying the recognition of two subfamilies, the Tironuculinae, including Tironucula and Ekaterodonta, and Natasiinae, including Natasia (Sánchez, 1997b).

Paleobiogeographically, the record of Natasia boliviensis in the Sella and Acoite formations constitute an additional evidence supporting the strong faunal links between the Argentine and Bolivian parts of the Central Andean basin.

By the Middle Arenig, an important diversification of bivalve faunas occurs in the volcanic arcrelated Famatina basin. The Chaschuil river outcrops, in the northern part of the basin, yielded excelently preserved bivalves (Aceñolaza and Toselli, 1977; Sánchez and Babin, 1993, 1994), whereas the more continuous successions exposed along the Cachiyuyo and Saladillo rivers (central Famatina) have fournished both bivalves and rostroconchs (Sánchez and Babin, 1993, 1994; Sánchez, 1997a).

In the Chaschuil river area, the Loma del Kilómetro Member of the Suri Formation (sensu Mángano and Buatois, 1996) contains the following species: Goniophorina (Cosmogoniophorina) tenuicostata Harrington, Catamarcaia chaschuilensis (Aceñolaza and Toselli) (Pl. 1, figs. 4 and 5), Suria ovalis Sánchez (Pl. 1, fig. 6), and Redonia suriensis Sánchez and Babin (Pl. 1, fig.7). Morphology of Catamarcaia Sánchez and Babin is now known in considerable detail and supports that this genus was the ancestor of the arcoidean clade (Sánchez, 1995a), which is in agreement with the phylogenetic ordering recently proposed by Carter et al. (2000).

The overlying Molles Formation, well exposed in the stratotype of the ‘Arroyo Los Molles’ and partially in the Saladillo Grande river, has yielded the bivalves Redonia riojana Sánchez, Notonychia emmae Sánchez, Famatinadonta gonzaloi Sánchez (Pl. 1, fig.3), Colpomya elongata Sánchez (Pl. 1, fig. 8), and Suria ovalis Sánchez (Sánchez, 2001b). The only rostroconch recorded from this unit is Ribeiria spinosa Babin and Branisa. In the Famatina volcanic-arc related basin bivalve diversification mostly occurred in nearshore settings, the infaunal suspensivorous guild occupied by Redonia, Famatinadonta, Catamarcaia and Colpomya is dominant. Other guilds were occupied by single taxa: the epifaunal suspensivorous by Notonychia and the infaunal detritivorous by Suria. The guild occupation in the Central Andean basin differs in that the infaunal suspensivorous guild was occupied by a single genus, Goniophorina (Waisfeld et al., 2001).

Llanvirn-Caradoc

Sedimentary rocks of Llanvirn age have only been documented in the Precordillera basin.

Abundant external molds from the Cerro Condor Formation of Jagüé, La Rioja province, (Aceñolaza and Bernasconi, 1969) were assigned to Ctenodonta bonetensis by Aceñolaza (1970). However, the absence of preserved dentition in the available material makes doubtful its assignement to the palaeotaxodonts. On the basis of associated graptolites, the levels bearing C. bonetensis were referred to the Llandeilo (Aceñolaza, 1970), and more recently Astini et al. (2000) placed this unit within the Caradoc.

Talacastella herrerai Sánchez (1986) (Pl. 1, fig. 15) and Tolmachovia sp. (Sánchez, 1998) are the two known Llanvirn rostroconchs of Argentina. Both come from the uppermost part of the San Juan Formation (early Llanvirn, Ahtiella Zone, Herrera and Benedetto, 1991) of the Precordillera of San Juan.

Caradoc

By the Caradoc, the total number of bivalve genera increased considerably in the Precordillera basin (Sánchez, 1999a). At this time the bivalve diversification reaches a peak, probably related to a

global increase of water temperature, also verified in other regions during the Caradoc (Sánchez, 1999b).

Most taxa were recorded in fossiliferous pebbles contained in the glacigenic diamictite of the Don Braulio Formation (late Ashgill). Associated shelly fauna, mainly brachiopods, indicate an early Caradoc age for these assemblages (Benedetto, 1998). A striking feature is that such a diversification mostly occurs within a single family, the praenuculids. It should also be noted that of nine genera identified, seven are confined to the Precordillera, reflecting a local radiation-extinction event (Sánchez, 1999b). A variable level of endemism, though less marked than in bivalves, has also been verified in other groups such as brachiopods, ostracods and trilobites (Benedetto et al., 1999).

The following praenuculids have been identified (Sánchez, 1999a): Praenucula sp., Cuyopsis symmetricus Sánchez (Pl. 1, fig. 12), Trigonoconcha acuta Sánchez (Pl. 1, fig.10), Villicumia canteraensis Sánchez (Pl. 1, fig. 11), Concavodonta ovalis Sánchez (Pl. 1, fig. 9), Hemiconcavodonta minuta Sánchez, and Emiliania cuerdai Sánchez. Differences in orientation of the chevroned teeth led to separate these forms into two subfamilies: Prenuculinae, including Praenucula Pfab, Cuyopsis Sánchez, Trigonoconcha Sánchez, Villicumia Sánchez, and Concavodontinae, including Concavodonta Babin and Melou, Hemiconcavodonta Sánchez, and Emiliania Sánchez (Sánchez, 1999a). As Sánchez (1999b) suggested, the widespread Praenucula Pfab and the perigondwanan Concavodonta Babin could be at the origin of the subfamilies Praenuculinae and Concavodontinae, respectively.

Other endemic taxa reported from this assemblage are Concavoleda braulense Sánchez (Sánchez, 1999a) and the cycloconchid Poladonta sanjuanina Sánchez (Sánchez et al., in press). An oustanding feature is that diversification occurs almost entirely within the family Praenuculidae, which means that species origination took place within a limited range of adaptive posibilities. Analysis of modes of life of the seven endemic species of praenuculids indicates infaunal, shallow burrowing habits, with similar degree of rocking movements. Additionally, it is important to mention that apart from the cycloconchid Poladonta, all the species of the association were detritus feeders, suggesting a muddy, probably low-oxigenated bottom (Sánchez, 1999b).

Plate 1. Some Ordovician Bivalvia and Rostroconchia from Argentina. 1, Natasia bolviensis fragilis Sánchez, left valve, intermediate stage of dental development, early-Middle Arenig, Acoite Formation, Cordillera Oriental, CEGH-UNC 15082 (x 6). 2, Goniophorina (Cosmogoniophorina) tenuicostata Harrington, dorsolateral view, articulated specimen, early-Middle Arenig, Acoite Formation, Los Colorados locality, CEGH-UNC 15026, (x 2). 3, Famatinadonta gonzaloi Sánchez, right valve, Middle Arenig, Molles Formation, central Famatina, CEGH-UNC 18585 (x 3,7). 4, 5, Catamarcaia chaschuilensis (Aceñolaza and Toselli). 4, right valve, Middle Arenig, Suri Formation, Chaschuil river, CEGH-UNC 10530 (x 2,7). 5, latex replica of the same specimen, (x 3). 6, Suria ovalis Sánchez, laterodorsal view of left valve, umbo crushed to show dentition, Middle Ordovician, Suri Formation, Chaschuil and Cachiyuyo rivers, Famatina Range, CEGH- UNC 15016 (x 5,5). 7, Redonia suriensis Sánchez and Babin, right valve, Middle Ordovician, Suri Formation, Chaschuil river, holotype, CEGH-UNC 10474 (x 4). 8, Colpomya elongata Sánchez, right valve, Middle Arenig, Molles Formation, central Famatina, CEGH-UNC 18694 (x 3). 9, Concavodonta ovalis Sánchez, right valve, early Caradoc, basal diamictite of the Don Braulio Formation, Precordillera, CEGH-UNC 16169 (x 6). 10, Trigonoconcha acuta Sánchez, right valve, early Caradoc, basal diamictite of the Don Braulio Formation, Precordillera, CEGH-UNC 16167b (x 6). 11, Villicumia canteraensis Sánchez, incomplete left valve, early Caradoc, basal diamictite of the Don Braulio Formation, Precordillera, CEGH-UNC 17361 (x 6,5). 12, Cuyopsis symmetricus Sánchez, left valve, early Caradoc, basal diamictite of the Don Braulio Formation, Precordillera, holotype, CEGH-UNC 16719 (x 3,7). 13, Costaledopsis fuertensis Sánchez, articulated specimen, Ashgillian, N. persculptus Zone, unnamed unit, Cerro del Fuerte, Precordillera, holotype, CEGH-UNC 039 (x 2). 14, Modiolopsis cuyana Sánchez, left valve, articulated specimen, Ashgill, N. persculptus Zone, Don Braulio Formation, Villicum Range, Precordillera, holotype, CEGH-UNC 055 (x 2,7). 15, Talacastella herrerai Sánchez, right lateral view, early Llanvirn, San Juan Formation, Precordillera, CEGHUNC 17368 (x 4). 16, Eopteria agustini Sánchez, left lateral view, early Tremadocian, Cardonal Formation, Sierra de Cajas, holotype, CEGH-UNC 18465 (x 5). (Note: Fossils are housed in the Catedra de Estratigrafía y Geología Histórica, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, prefix CEGH-UNC).

The almost coeval Las Plantas Formation exposed in the northern Precordillera contains a single bivalve species, Modiolopsis inflata Sánchez (Sánchez, 1990).

The Caradocian bivalves of the Central Andean basin are by far less diverse than in the Precordillera.

The Capillas Formation, cropping out in the Sierra de Zapla, and the Santa Gertrudis Formation (Quebrada del Gallinato, Sierra de Mojotoro) have yielded Cadomia typa De Tromelin and a cycloconchid previously assigned to Cycloconcha cf. C. oblonga Foerste (Sanchez, 1986) but now assigned to Zaplaella capillaensis Sánchez (Sánchez et al., in press). Cadomia typa is a typical form of the Armoricain Massif and Iberia, and its record in the Central Andean basin indicates a clear faunal link between northwestern Argentina and these peri-Gondwanan areas. The age of this units has been matter of debate.

Harrington and Leanza (1957) referred this unit to the early Llanvirn, but Monaldi and Monaldi (1978), also based on the trilobite content, suggested a younger early Caradoc age. On the basis of the bivalve fauna Sánchez (1986) also supported a Llandeilo age for the Santa Gertrudis Formation.

According to Albanesi and Rao (1996), the conodont assemblage from the beds containing the shelly fauna indicates the early Caradoc. The Capillas Formation, bearing a similar bivalve and trilobite fauna, can be confidently correlated with the Santa Gertrudis Formation (Waisfeld, 1996).

Ashgill

Ashgill bivalves are presently known only from the Precordillera basin. The uppermost part of the Trapiche Formation exposed at the Gualcamayo river section has yielded a poorly preserved ambonychiid (Cleionychia? sp., Sánchez, 1990) and other undeterminable forms. These levels have been considered as late Ashgill on the basis of the brachiopod Trucizetina Benedetto (1999), even though no typical elements of the Hirnantia Fauna have been discovered. The Late Ashgill (Hirnantian) Don Braulio Formation contains Modiolopsis cuyana Sánchez (Pl. 1, fig. 14) and Paleoneilo sp. (Sánchez, 1990). Calcareous lenses developed at the first stages of the latest Ashgill transgression yielded abundant specimens of Modiolopsis cuyana associated with the brachiopods Hirnantia sagittifera (McCoy), Dalmanella testudinaria (Dalman), and Paromalomena polonica (Temple) (Benedetto, 1986), the trilobite Dalmanitina sudamericana Baldis and Blasco (1975), and encrusting bryozoa, all of which integrate the shallow-water Modiolopsis-Hirnantia community. This relatively low diverse community probably reflects a fluctuating resource supply in a cold-water shallow environment (Sánchez et al., 1991).

The unnamed latest Ashgill (N. persculptus Zone) mudstone succession exposed in the Cerro del Fuerte area (Benedetto et al., 1986) has provided specimens of Costaledopsis fuertensis Sánchez (Pl. 1, fig. 13) and Whiteavesia sp. (Sánchez, 1990). This unit probably represents a deep-water equivalent of the late Ashgill succession of the Sierra de Villicum.

Taxonomic ordering of bivalve species

PALAEOTAXODONTA

-Family Praenuculidae McAlester, 1969

Subfamily Praenuculinae Sánchez, 1999a

Praenucula sp.

Costaledopsis fuertensis Sánchez, 1990

Cuyopsis symmetricus Sánchez, 1999a

Trigonoconcha acuta Sánchez, 1999a

Villicumia canteraensis Sánchez, 1999a

Subfamily Concavodontinae Sánchez, 1999a

Concavodonta ovalis Sánchez, 1999a

Hemiconcavodonta minuta Sánchez, 1999a

Emiliania cuerdai Sánchez, 1999a

- Family Malletiidae Adams and Adams, 1858

Paleoneilo sp.

‘Palaeoneilo’ iruyensis Harrington, 1938

Concavoleda braulense Sánchez, 1999a

Cadomia typa De Tromelin, 1877

Suria ovalis Sánchez, 1997a

- Family Tironuculidae Babin, 1982

Subfamily Natasiinae Sánchez, 1997b

Natasia boliviensis (Babin and Branisa, 1978)

- Family Ctenodontidae Wöhrmann, 1893

‘Ctenodonta’ famatinensis Harrington, 1938

‘Ctenodonta’minuscularia Harrington, 1938

‘Ctenodonta’laevigata Harrington, 1938

‘Ctenodonta’ bonetensis Aceñolaza, 1970

HETEROCONCHIA

- Family Cycloconchidae Ulrich, 1884

Famatinadonta gonzaloi Sánchez, 2001b

Zaplaella capillaensis Sánchez (in Sánchez et al., in press)

Poladonta sanjuanina Sánchez (in Sánchez et al., in press)

- Familly Intihuarellidae Sánchez (in Sánchez and Vaccari, in press)

Hintihuarella simplicidentata Sánchez (in Sánchez and Vaccari, in press)

- Family Redoniidae Babin, 1966

Redonia suriensis Sánchez and Babin, 1994

Redonia riojana Sánchez, 1997a

Redonia ? jujuyensis Sánchez (in Sánchez and Vaccari, in press)

PTERIOMORPHIA

- Family Modiolopsidae Fischer, 1887

Modiolopsis cuyana Sánchez, 1990

Modiolopsis inflata Sánchez, 1990

‘Modiolopsis’ sanbernardica Harrington, 1938

Modiolopsis? sp.

Whiteavesia sp.

- Family Colpomyidae Pojeta & Gilbert-Tomlinson, 1977

Colpomya elongata Sánchez, 2001b

- Family Ambonychiidae Miller, 1877

Cleionychia? sp.

Notonychia emmae Sánchez, 2001b

ARCOIDA

- Family Catamarcaiidae Cope, 2000

Catamarcaia chaschuilensis (Aceñolaza and Toselli, 1977)

ANOMALODESMATA

- Family Modiomorphidae Miller, 1877

Goniophorina (Cosmogoniophorina) tenuicostata Harrington, 1938

- Family Ucumariidae Sánchez (in Sánchez and Vaccari, in press)

Ucumaris conradoi Sánchez (in Sánchez and Vaccari, in press)

Taxonomic ordering of rostroconchian species

RIBEIROIDA

- Family Ribeiridae Kobayashi, 1933

Ribeiria spinosa Babin and Branisa, 1987

Ribeiria cf. R. compressa Whitfield, 1886

- Family Technophoridae Miller, 1889

Tolmachovia andina (Harrington, 1938)

Tolmachovia sp.

CONOCARDIOIDA

- Family Eopteriidae Miller, 1889

Eopteria agustini Sánchez, 2000

Talacastella herrerai Sánchez, 1986

Acknowledgements. I thank the volume editor, F. G. Aceñolaza, for the invitation to participate in this volume.

Paleontologic studies carried out in the last years were made possible through support of the Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET (Grant 05/1316), and the Agencia Nacional de Promoción Científica y Tecnológica, ANPCyT (Grant 5387).

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Recibido: 25 de Agosto de 2002

Aceptado: 10 de Octubre de 2002