Juan J. Rustán

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.

The Trilobite Reedops (Phacopidae) in the Lower Devonian of Argentina (Malvinokaffric Realm)

Abstract The trilobite Reedops is documented from strata probably corresponding to the middle part of the Talacasto Formation in the Sierra de las Minitas, at the northernmost extent of the Precordillera in La Rioja Province, northwestern Argentina. The specimens resemble the type species of the genus, R. bronni, indicating a Pragian (Early Devonian) age for the strata, and suggesting the occurrence at this time of faunal exchange between the Old World Realm, particularly the Bohemian area, and the Malvinokaffric Realm. The taxon represents the first Early Devonian macrofaunal element in the Malvinokaffric Realm with global biostratigraphical significance.

First Middle Devonian Bivalves from Argentina, New Records from the Punta Negra Formation and Insights on Middle Paleozoic Faunas from the Precordillera Basin

Abstract. Middle Devonian bivalves from Argentina are reported for the first time, based on records of the Precordilleran Punta Negra Formation (Emsian—Frasnian?), San Juan Province. This finding is the youngest Devonian record of bivalves from southernmost South America. The impoverished bivalve association in the Punta Negra Formation includes five shallow infaunal deposit feeders, i.e. Nuculites argentinum Sánchez, Anthracoleda (Pseudoleda) minuta Sánchez, Praenucula sp., Deceptrix sp. and Praectenodonta sp. The distribution of the Silurian—Devonian bivalves from Precordillera shows a decreasing diversity trend during this interval, due to potential biases in sampling and paleoecology and thus suggesting that this trend might be apparent. Early and Middle Devonian bivalves from Precordillera show a strong cosmopolitan paleobiogeographic signature, in contrast with other geographically related basins showing endemic (Malvinokaffric Realm) signals during the Devonian. Contrarily, an endemic composition is recorded in the Precordillera Basin when based on coeval Malvinokaffric groups such as ostracods and trilobites. Although more information is needed, the cosmopolitan character of Devonian bivalve assemblages from the Argentine Precordillera Basin might be interpreted under the light of a unique history driving biogeographic processes affecting different taxonomic groups in different ways.

First report of Devonian bactritids (Cephalopoda) from South America: paleobiogeographic and biostratigraphic implications

Abstract. Devonian bactritids are described for the first time from South America. They come from siliciclastic rocks of the Talacasto Formation in the Precordillera Basin, west-central Argentina. The host strata span the Lochkovian—Emsian and contain other non-ammonoid cephalopods as well, thus refuting the alleged virtual absence of cephalopods in circumpolar Devonian basins from southwestern Gondwana (the Malvinokaffric Realm). We report Bactrites gracilis and Devonobactrites? sp., whose wide distribution contrasts with the endemic paleobiogeographic signature of some other taxonomic groups in these basins. Furthermore, new Lochkovian and Pragian records of Bactrites sp. provide new insights into the earliest bactritid records worldwide.

The phacopid trilobite Echidnops taphomimus n. sp. from the Lower Devonian of Argentina; insights into infaunal molting, eye architecture and geographic distribution

Abstract. Some Silurian-Devonian Argentinian trilobites characterized by infaunal behavior during molting are considered. After a taxonomic reappraisal, a species previously referred to a lineage of the phacopid Paciphacops is proposed as Echidnops taphomimus new species, from the Lower Devonian (probably late Lochkovian) of the Talacasto Formation, Argentine Precordillera. The visual surface of E. taphomimus indicates that a irregular pattern of lens arrangement, typical of early phacopids such as the Ordovician Ormathops, can also be recognized in more derived Devonian relatives, providing new insights on some evolutionary aspects of visual development. Echidnops is recognized in Australia and Argentina, recording an unusual distribution pattern in trilobites from the Lower Devonian of southern South America, otherwise mostly linked to faunas of related Gondwanan, austral circum-polar Devonian basins of the Malvinokaffric Realm. In accordance with proposed increasing predation pressure in the context of the Mid Paleozoic Marine Revolution, evidence indicates that the infaunal molting behavior, as defensive strategy, arose in several trilobite groups during Silurian-Devonian times, rather than in a single endemic lineage of Paciphacops species.

The new genus Talacastospongia: insights on the first record of a Devonian sponge from South America

Abstract. The Lower Devonian (Lochkovian) hexactinellid sponge Talacastospongia minima new genus new species is reported from the lower beds of the Talacasto Formation in the Argentine Precordillera. It represents the first Devonian sponge from South America and the best record in the paleobiogeographic context of the Malvinokaffric Realm, otherwise virtually devoid of spiculate sponges. This discovery provides some tentative insights on the age and oldest record of the Family Pileolitidae. The paleogeographical context for this new finding shows a high latitude setting with a notable scarcity of hexactinellid sponges recorded to date in Devonian Malvinokaffric basins, and the absence of calcareous spiculate sponges (heteractinids) and hypercalcified sponges (stromatoporoids, sphinctozoans).

Early Devonian organic-walled phytoplankton and miospores from the Precordillera Basin of San Juan, Argentina: biostratigraphic and paleobiogeographic implications

ABSTRACT The palynological assemblages of the Talacasto and Punta Negra formations, from the Argentinean Precordillera, were analysed. Marine phytoplankton is dominant in both stratigraphic units. ?Cymatiosphaera florida, Evittia sommeri, Palacanthus ledanoisii, Riculasphaera fissa, Schizocystia pilosa, Tysanoprobolus polykion and Winwaloeusia distracta are among the most age-significant phytoplankton species of the Talacasto Formation, while Amicosporites sp. cf. A. streelii, Dictyotriletes emsiensis Morphon, Dictyotriletes favosus and ?Knoxisporites riondae prove the most biostratigraphically significant miospore species. A Lochkovian to probably late Pragian age is interpreted based on the marine and terrestrial palynomorphs. The lower part of the Punta Negra Formation contains phytoplankton species such as Cordobesia oriental, Cordobesia uruguayensis, Duvernaysphaera stellata, Navifusa bacilla, Polyedryxium fragosulum and Pterospermella sp. cf. P. pernambucensis as well as the miospores Acinosporites sp. cf. A. lindlarensis and Apiculatasporites microconus, which suggests an early Emsian age. Taxa such as Cordobesia, Schizocystia and Winwaloeusia support affinities of the Argentinean assemblages with Gondwana.

Teresa María Sánchez (1945–2011)

Teresa nació el 25 de enero de 1945 en Pehuajó (Provincia de Buenos Aires). En 1969 se graduó como Licenciada en Zoología de la Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata y en 1984 recibió el título de Doctora en Paleontología de la Facultad de Ciencias, Universidad de Bretaña Occidental (Brest, Francia). Era Investigadora Principal del CONICET y Profesora Titular en la carrera de Ciencias Biológicas, de la Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, a cargo de las cátedras de Paleontología e Introducción a la Biología. Inició sus investigaciones en Paleontología con el estudio de vertebrados cretácicos de Argentina. Las circunstancias políticas de la década del 70 impulsaron su exilio a Venezuela. Allí, llevo a cabo un cambio radical en su tema de investigación, comenzando a desarrollar su doctorado acerca de la paleoecología de las comunidades marinas y faunas de moluscos bivalvos del Paleozoico Superior de la Sierra de Perijá (Venezuela). Desde su regreso al país en 1983 y junto a su esposo, el Dr. Juan Luis Benedetto, gestó un equipo de trabajo dedicado a la investigación de los más diversos aspectos de la biota marina del Paleozoico Inferior. En este marco Teresa realizó una importante contribución a la formación de recursos humanos, dirigiendo numerosas tesis doctorales y becas del CONICET, CONICOR y SECyT-UNC. Sus investigaciones estuvieron centradas en el estudio taxonómico y paleoecológico de los bivalvos del Paleozoico Inferior de Argentina. Fue una verdadera pionera en la investigación de la radiación temprana del grupo en nuestro país y de las relaciones de estas formas con representantes más jóvenes. Paralelamente, fue precursora de otra línea de investigación vinculada a la reconstrucción de los ecosistemas del Paleozoico Inferior argentino y a eventos bióticos de gran escala. Sus contribuciones en ambas temáticas, publicadas en las más prestigiosas revistas científicas, han merecido un importante reconocimiento internacional, constituyendo referencias obligadas para los especialistas. En los últimos meses estuvo abocada a la redacción de tres capítulos para el nuevo volumen Bivalvia y Rostroconchia del Treatise on Invertebrate Paleontology. La docencia también fue su vocación y su pasión. Se desempeñó como docente en la Facultad de Ciencias Naturales de la Universidad Nacional de Salta, en la Facultad de Ciencias Puras y Naturales de la Universidad Mayor de San Andrés (La Paz, Bolivia), en la Escuela de Geología, Minas y Geofísica, Facultad de Ingeniería de la Universidad Central de Caracas (Venezuela), en la Facultad de Ciencias Exactas, FísicoQuímicas y Naturales de la Universidad Nacional de Río Cuarto, y en la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de Córdoba. Es importante destacar también la publicación de una importante obra de difusión: “La historia de la vida en pocas palabras” un libro ameno y atractivo para el público general que, además, se ha tornado en libro de consulta para estudiantes de grado. Asimismo, desempeñó una labor activa en la gestión científico-tecnológica, tanto en el ámbito universitario como en organismos científicos provinciales y nacionales. Teresa ha sido la gestora del Centro de Investigaciones Paleobiológicas (CIPAL) dependiente de la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de Córdoba que alberga numerosos investigadores y becarios. Como directora del mencionado Centro siempre propició un ámbito de trabajo, de respeto y de libertad. En todos sus roles, como investigadora, docente, paleontóloga, divulgadora, colega, compañera y amiga, Teresa ha dejado huellas. Tenía una personalidad abierta, leal y afectuosa, era espontánea. Tenía la virtud de saber escuchar y ponerse rápidamente en el lugar del otro, con una palabra adecuada y especial para cada uno siempre a mano, poniendo el afecto y la comprensión por encima de todas las diferencias. Quienes firmamos esta nota, discípulos, compañeros, colegas y amigos, tuvimos el placer de compartir con ella el trabajo cotidiano. Hoy tenemos la satisfacción y la responsabilidad de haber recibido un enorme legado: su entusiasmo genuino por el conocimiento, la dedicación y el compromiso con el trabajo científico, el valor y la fortaleza para enfrentar las adversidades de la vida, la honestidad para apreciar los logros ajenos, la defensa de las convicciones, la pasión por la Paleontología.