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We describe early Tremadocian (Kainella meridionalis Biozone) cephalopods from the Cordillera Oriental, Jujuy, NW Argentina. They consist of numerous small specimens collected at the Quebrada de Arenal, Trancas section, near the town of Tilcara, in the Alfarcito Member of the Santa Rosita Formation. All but three specimens were assigned to a new species of Ellesmeroceras (Family Ellesmeroceratidae), E. humahuacaensis sp. nov., based on its slightly endogastric curvature, the characteristics of the siphuncle and chambers dimensions. Micro CT scanning of one specimen aided in the description of the apex and facilitated the construction of a 3D model of the species. A single, similar specimen was assigned to Ellesmeroceras sp. pending the availability of additional material. Two specimens differ from the rest, being exogastric with a lower angle of expansion. They are tentatively assigned to Bassleroceras sp. This material indicates that Cambrian and early Tremadocian cephalopods are not as different as previously thought. "Diversification" and "extinction" events during the late Cambrian may be attributed to taxonomic "over-splitting" and taphonomic and/or sampling biases, respectively. These specimens are currently the oldest recorded in the Central Andean Basin and of West Gondwana, and probably represent the first migration of cephalopods into the region, when the water column was still poorly colonized. During the middle Tremadocian, subsequent immigrations and originations of several cephalopod orders accounted for a rise in diversity and expansion into new niches during this interval. Some of these taxa persisted into the middle Floian, at which time, a second increase in diversity is recorded. Ellesmeroceras humahuacaensis sp. nov. is interpreted as a sub-vertical nektobenthic organism. [ABSTRACT FROM AUTHOR]

The following new Toernquistiidae from Whiterockian (Llanvirn to lower Caradoc) strata of the Precordillera, western Argentina, are described: Chomatopyge canasi new species, Lasarchopyge benedettoi new genus and species, Lasarchopyge correae new genus and species, Lasarchopyge new species A, and Paratoernquistia sanchezae new genus and species. Phylogenetic analysis suggests that the Toernquistiidae Hupe, 1953 (including Chornatopyge, Lasarchopyge, Mesotaphraspis, Paratoernquistia, and Toernquistia) is closely related to but distinct from the Dimeropygidae Hupd, 1953 (including Ischyrotoma, Ischyrophyma and Dimeropyge). It is difficult to find unique synapomorphies that unite toernquistiids and dimeropygids into a monophyletic group that excludes other proetides (e.g., hystricurids), although details of their ontogenies are similar. Several species of Toernquistiidae are known from the Argentine Precordillera (one species previously described), and other species of this family have been described from Australia, Baltica, China, Kazakhstan and Laurentia. Members of the Dimeropygidae are known only from Baltica and Laurentia.

A growth series is described for a new species of Ceratocara Ramskold, 1991, C. argentina, from the Upper Ordovician (Caradoc) part of the Las Aguaditas Formation, near Jachal in San Juan Province, Argentine Precordillera. Another new species of Ceratocara, C. shawi, is described from the Middle Ordovician (lower Chazy) Crown Point Formation of New York. A phylogenetic analysis is presented for these species, other well-known Ordovician species of Ceratocara, and some Ordovician species of Ceratocephala, with Ceratocephalina tridens Whittington, 1956, as outgroup. The analysis presented supports the monophyly of both Ceratocara and Ceratocephala Warder, 1838, their divergence having occurred by the middle Arenig. The ontogenies of the Ceratocara species from Argentina and New York, complete from protaspid to holaspid growth stages, are some of the best preserved odontopleurid ontogenies described to date. Material of Ceratocephala triacantheis Whittington and Evitt, 1954, from the Crown Point Formation of the Chazy Group of New York, is discriminated from that of Ceratocara shawi.

The acastomorph calmoniid trilobite Andinacaste Eldredge and Branisa, 1980, has been known from the basal Devonian (Lower Lochkovian) of Bolivia. Andinacaste espejensis n. sp., described from probable Lower Lochkovian strata of the Los Espejos Formation in the Precordillera of San Juan Province, is the first Argentine record of this genus. Accordingly, Andinacaste is identified as a typical component of basal Devonian trilobite assemblages over a broad geographic range in Andean South America.

Lower Devonian calmoniid trilobites from three localities in San Juan province, Argentina, belong to the new taxa of the Boullia-Paraboulia clade. Morphological differences of two new Argentine species do not conform to the model based on Bolivian taxa. Calmoniids from below the Scaphiocoelia do not exhibit the gradual transformation of an acastomorph ancestor but show fast diversification within the calmoniide. Ghost lineages enhance taxonomic diversity of Lochkovian, suggesting the occurrence of calmoniid radiation in the earliest Devonian.

The homalonotid trilobite Burmeisteria Salter, 1865 is revised from material from the Lower Devonian of central western Argentina (the Talacasto Formation in the Precordillera Basin). In contrast to other closely related Devonian marine basins from South America (mainly Bolivia, Brazil and Uruguay), the only species recognized in Argentina include Burmeisteria herschelii (Murchison, 1839) and B. notica (Clarke, 1913). New observations on the structure of the carapace indicate that structures sometimes interpreted as granules with taxonomic meaning are, in fact, taphonomic characters that represent the fillings of pore canals exposed by decortication. The antero-ventral process of the rostral plate may be a locking device during enrollment, which allowed long-term defensive behavior with a minimum of muscular energy. Burmeisteria is an upper Silurian to Middle Devonian endemic representative of southwestern Gondwanan (Malvinokaffric) basins. In the Argentine Precordillera Basin, this genus is virtually restricted to a sandy, Pragian, stratigraphic interval capped by a marker bed first reported by Keidel in 1921. [ABSTRACT FROM AUTHOR]

Trilobites have traditionally been considered fully marine. Through the integration of ichnological, palaeobiological and sedimentological datasets within a sequence-stratigraphic and strati­graphic palaeobiology framework, we challenge this assumption. This analysis is based on the study of incised fluvio-estuarine valley deposits from the Furongian Tilcara Member (TM) and the latest Furongian Pico de Halcón Member (PHM) of the Santa Rosita Formation, the early late Tremadocian Cardonal Formation (CF), and the Dapingian–Darriwilian Alto del Cóndor Formation (ACF), from Cordillera Oriental of northwest Argentina. These valleys were incised into wave-dominated shallow-marine strata and filled with transgressive deposits that accumulated in tide-dominated estuaries. Whereas the TM lacks any body or trace fossil evidence of the presence of trilobites in estuarine settings, the other three units reveal that trilobites were able to inhabit these settings. The PHM and CF are host to trilobite trace fossils in outer estuarine facies, both containing various ichnospecies of Cruziana (e.g., C. omanica and C. semiplicata in the TM) and Rusophycus (e.g., R. latus in both units). In addition, the PHM also contains body fossils of the olenid trilobite Neoparabolina frequens argentina in the same deposits in which the trace fossils are preserved, as well as from middle estuarine facies. The ACF displays trilobite trace fossils of the C. rugosa group in inner, middle, and outer estuarine deposits, illustrating further landward incursions. This unit also contains body fossils of the asaphid trilobite Ogyginus sp. Accordingly, our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer to middle portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner, middle, and outer estuarine zones by asaphids (Dapingian–Darriwilian). Our study indicates that these trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. It is suggested that tolerance to salinity stress arose independently among different trilobite groups as a result of the broad array of behaviors and adaptations of trilobites during the Ordovician radiation. We speculate that the assumption that all trilobites were stenohaline may have resulted in the misinterpretation of some tide-dominated estuarine deposits as fully marine. [ABSTRACT FROM AUTHOR]

The ontogenies of three new species of Telephinidae, Telephina calandria, Telephina chingolo, and Telephina problematica are described from Arenig-Caradoc strata in the Argentine Precordillera, and compared with the larval stages of some other Proetida, including other telephinids. New findings reveal 1) a radical metamorphosis in the ontogenies of these Telephina species late in the meraspid period, not previously described among Trilobita; and 2) distinctive hypostomes of Telephinidae containing long, thin anterolaterally and dorsally splayed anterior wings. Early ontogenies of different species currently assigned to the genus Telephina fall into at least two distinct morphological and life history groups, and hypostomes (if correctly assigned in previous works) vary significantly. The three new species strengthen the hypothesis of a phylogenetic connection between Oopsites and Telephina. Three morphological types of protaspid instars are described for proetide trilobites. Two are anaprotaspides, and the third is a metaprotaspis. They always occur in the same sequence in the ontogeny, but no cases are known of all three types in the same species. These larval types are important for understanding the systematics and life cycles of the Proetida. Benthic/pelagic transitions identify four life history patterns among the the Proetida. The best larval synapomorphy for the Proetida is the distinctive metaprotaspid larval type, which is absent in very few proetides (some Telephinidae), perhaps as a result of heterochronic displacement of this stage into the meraspid period.