N. Emilio Vaccari

Infaunal molting in Trilobita and escalatory responses against predation

The outstanding fossil record of trilobites contrasts with our limited knowledge of their lifestyles and strategies. Aspects such as infaunalism and behavioral defensive skills in this group have yet to be demonstrated conclusively. We report new insights based on a striking sclerite configuration exhibited by three phacopid trilobite species, part of a late Silurian–Early Devonian Paciphacops ( Paciphacops ) Maksimova, 1972, lineage. An unusual molt pattern provides compelling evidence of infaunal behavior, which accounts for a hiding, antipredatory adaptation. In addition, strengthening of the exoskeleton and acquisition of spines indicate an evolutionary trend toward morphological defensive strategies. Both trends in active and passive traits are considered escalatory in nature, thus providing unequivocal support for understanding the ecological role of trilobites as a main prey group in the context of the global diversification of predators recorded during middle Paleozoic time.

The Aulacopleurid Trilobite Maurotarion Alberti, 1969, in the Silurian-Devonian of Argentina: Systematic, Phylogenetic and Paleobiogeographic Significance

Abstract Five new species of Maurotarion Alberti, 1969 from the Silurian Lipeón Formation and Lower Devonian Talacasto Formation of Argentina are recognized. The comparisons with Bolivian and South African species support a Malvinokaffric clade based on librigenal synapomorphies, here erected as Maurotarion (Malvinotarion) new subgenus. The Malvinokaffric origin of the family would not be a migration from lower paleolatitudes but an Early Silurian stock of rare cosmopolitan ancestors which underwent a great Devonian radiation. Two lineages can be recognized within Malvinokaffric Maurotarion. The Silurian-Pragian dereimsi lineage is a plesiomorphic one resembling Silurian representatives and involves M. (Malvinotarion) dereimsi, M. (Malvinotarion) talacastoense new species, M. (Malvinotarion?) new species A, M. (Malvinotarion?) new species B, M. (Malvinotarion) sp., and eventually M. (Malvinotarion?) cf. dereimsi. The isaacsoni lineage ranges from the Lower Pragian to Eifelian exhibiting a defined morphologic trend in the librigena. This lineage comprises M. (Malvinotarion) isaacsoni, M. (Malvinotarion) sp. A from South Africa, M. (Malvinotarion) gaucho new species, M. (Malvinotarion) haudei new species and M. (Malvinotarion) legrandi. A Lochkovian diversification probably took place yet an adequate assessment remains difficult. In contrast, a great evolutionary burst is recognized during the Emsian and is related to Pragian-Emsian global relative sea level curves which are coincident with those proposed from Bolivian and Argentinian basins.

Paleoecological dynamics of Furongian (late Cambrian) trilobite-dominated communities from northwestern Argentina

Abstract The Cambrian–Ordovician boundary interval is a critical moment in the ecology of trilobite communities. To understand this transition, we studied—at three different spatial scales—changes in the structure of olenid-dominated communities included in the Parabolina fauna, which flourished in the latest Cambrian, largely storm-dominated, successions of northwestern Argentina. At the local (∼meter) scale, species-poor communities occur in shoreface deposits. Relatively flat species-abundance distributions (SADs) and high evenness characterize upper offshore to offshore transition settings of the early highstand systems tract (HST), whereas uneven SADs in species-poor communities are typical of the lower offshore and shelf environments of the transgressive systems tract (TST). This pattern is unlikely to be caused by a change in time averaging and is consistent with the intermediate disturbance hypothesis predicting unimodal diversity gradients. The pattern is thus interpreted to be related to a trend in intensity and frequency of storm disturbance along local shallowing-upward gradients. At the regional scale (∼100 km), the diversity trend across the sampled west-east transect is rather variable and does not match the depth or oxygen-related gradients. At the biogeographic scale, the patterns of abundance of two key taxa (Parabolina and Asaphellus) show contrasting abundance and occupancy patterns between the Cordillera Oriental siliciclastic settings and the more carbonate-rich settings of Famatina (Argentina) and Oaxaca (Mexico). The presence of these genera in settings spatially adjacent, but environmentally different from their preferred habitats can represent a signature of source-sink dynamics. Low sample evenness values for the Cordillera Oriental contrast with those of coeval Laurentian communities, implying that a secular increase in evenness took place earlier in Laurentia than in Gondwana.

Kainella Walcott, 1925 (Trilobita, Ordovícico Temprano) en el noroeste de Argentina y sur de Bolivia. Importancia bioestratigráfica

Abstract. Kainella Walcott (trilobita, Early Ordovician) In Northwestern Argentina And Southern bolivia. Biostratigraphic Significance. The Tremadocian Kainella meridionalis Zone in the Central Andean Basin is is reassessed. This zone has been widely used for regional and intercontinental correlations, but such correlations mostly involved an extended interval that corresponds, in fact, to the whole range of the genus. Species of Kainella recorded in northwestern Argentina and southern Bolivia exhibit a relatively wide geographic distribution and a constrained stratigraphic range. On the basis of their record a succession of biozones is proposed, ranging from the basal Tremadocian to possibly the early middle Tremadocian. Three biozones are proposed on the basis of integrated information drawn from several localities, i.e., the K. andina, K. meridionalis, and K. teiichii zones. In addition, the Jujuyaspis keideli Subzone is here upgraded to the rank of zone. The definition of this succession of biozones is a significant progress in the establishment of a high resolution biostratigraphic framework based on trilobites, leading to more precise correlations in the future.

Delamaran trilobites from the La Laja Formation, San Juan, Argentina

Abstract The La Laja Formation lies exposed almost continuously along the western margin of two hill ranges, i.e., the Sierra Chica de Zonda and Sierra de Villicum. This limestone unit bears a remarkable fauna of Cambrian trilobites. In this work we analyse the Delamaran trilobite fauna from the upper part of the El Estero Member and the lower third of the Soldano Member of the La Laja Formation. Taxa described are Glossopleura walcotti Poulsen, Glossopleura lodensis (Clark), Fieldaspis sp., and Prozacanthoides zondaensis n. sp. The Poliella denticulata, Mexicella mexicana?, and Glossopleura walcotti Zones are documented; these had been previously included in a hiatus. Trilobites-based correlations are established between the La Laja Formation and olistoliths of the Western Precordillera. Additional correlations are also suggested between the Precordillera and different localities in Laurentia. Finally, we discuss the biogeographic implications of the described material. Delamaran taxa reported from the La Laja Formation are characteristic and so far restricted to Laurentia. Analysis of the trilobite fauna from this unit supports the allochtonous origin of the Precordillera.

A revision of the Devonian Malvinokaffric dalmanitid trilobite Dalmanitoides Delo, 1935, on the basis of new data from Argentina

In light of new information on holotypes and additional material from the Lower Devonian type areas from Argentina, the dalmanitid trilobite Dalmanitoides Delo, 1935, is rediagnosed and considered a dalmanitine rather than a synphoriine. Comparisons suggest that Gamonedaspis Braniša and Vaněk, 1973, is a junior synonym of Dalmanitoides, so that this Early-Middle Devonian genus includes at least five species: four formally named from South America, D. drevermanni (Delo, 1935), D. boehmi (Knod, 1908), D. scutata (Braniša and Vaněk, 1973), and D. accola (Clarke, 1913), together with a species from South Africa herein treated in open nomenclature (D. sp. A). Although the number of Dalmanitoides species suggests a diversification of cosmopolitan dalmanitines already present in Malvinokaffric basins, a close relationship with the boreal and slightly older Roncellia Lespérance and Bourque, 1971, would suggest migration from the Eastern Americas Paleobiogeographical Realm during the Early Devonian as origin of the clade, which is in accordance with paleobiogeographic patterns recognized on the basis of evidence from synphoriine distributions. Juan José Rustán. CIPAL CICTERRA (Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba CONICET), Av. Vélez Sársfield 299, 5000, Córdoba, Argentina and Museo de Ciencias Naturales, Universidad Nacional de La Rioja, Av. René Favaloro s/n 5300La Rioja, Argentina, juanjorustan@gmail.com N. Emilio Vaccari. CIPAL CICTERRA (Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba CONICET), Av. Vélez Sársfield 299, 5000, Córdoba, Argentina and Museo de Ciencias Naturales, Universidad Nacional de La Rioja, Av. René Favaloro s/n 5300La Rioja, Argentina, evaccari@efn.uncor.edu

The Upper Ordovician Trinucleid Trilobite Bancroftolithus from the Precordillera of Argentina

Abstract The trinucleid trilobite Bancroftolithus Baldis and Pöthe, 1995 includes a group of species from Sandbian strata of the Argentine Precordillera. The monotypic Hunickenolithus Baldis and Pöthe, 1995 from the Las Aguaditas Formation at its type locality in San Juan Province is placed in the synonymy of Bancroftolithus. Of four nominal taxa from the Las Aguaditas Formation, B. pozensis Baldis and Pöthe, 1995, and B. hughesi Baldis and Pöthe, 1995 are retained, and both are revised based on new collections from the type locality that include ontogenetic series from the protaspid period. Two protaspid stages are recognized in both species. Three additional species (Bancroftolithus alki n. sp., B. cf. B. pozoensis, Bancroftolithus sp.) from broadly coeval strata in the Las Plantas Member of the Las Vacas Formation in La Rioja Province are identified as the closest relatives of the Las Aguaditas species. Bancroftolithus alki also occurs in the Los Azules Formation in San Juan Province. The five species included in this regional clade exhibit significant morphological differences in the lower lamellae, an unusual feature among the Trinucleidae. Bancroftolithus is evidently most closely related to the Australian Katian genus Parkesolithus. The two are not convincingly assigned to any of the existing trinucleid subfamilies.

Kainella Walcott, 1925 (Trilobita, Ordovícico Temprano) en el noroeste de Argentina y sur de Bolivia: Paleontología sistemática

Abstract Kainella Walcott, 1925 (Trilobita, Early Ordovician) in Northwestern Argentina and Southern Bolivia. Systematic Paleontology. A taxonomic study is presented involving different species of Kainella from the Central Andean Basin. These early Tremadocian species come from the Santa Rosita, Cardonal, and Devendeus formations, and also from the Guayoc Chico Group; all units lie exposed at numerous localities in the Argentine Cordillera Oriental. Also analyzed are Kainella species from the Iscayachi Formation exposed in the Yunchará Segment in southern Bolivia. A group of eight species is recognized, suggesting a significantly greater diversity than previously assessed. An emmended diagnosis of K. meridionalis Kobayashi is provided, and a lectotype is designated. On this basis, some of the former assignments to this species are now rearranged into the taxa described herein. Complete morphological information is provided on K. andina Suárez Soruco, based on new collections from its type locality (Cuesta de Erquis), and from Argentina. The new species K. teiichii sp. nov., K. morena sp. nov., Kainella sp. nov. A and Kainella sp. nov. B are described and illustrated. Also, K. colombiana Harrington and Kay from the Güéjar Group (Tremadocian-Floian, Sierra de La Macarena, Colombia) is tentatively referred to Naustia Ludvigsen of Late Cambrian age.