Five new species ofMaurotarionAlberti, 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 asMaurotarion(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 MalvinokaffricMaurotarion.The Silurian-Pragiandereimsilineage is a plesiomorphic one resembling Silurian representatives and involvesM.(Malvinotarion)dereimsi, M.(Malvinotarion)talacastoensenew species,M.(Malvinotarion?) new species A,M.(Malvinotarion?) new species B,M.(Malvinotarion) sp., and eventuallyM. (Malvinotarion?)cf.dereimsi.Theisaacsonilineage ranges from the Lower Pragian to Eifelian exhibiting a defined morphologic trend in the librigena. This lineage comprisesM.(Malvinotarion)isaacsoni, M.(Malvinotarion) sp. A from South Africa,M.(Malvinotarion)gauchonew species,M.(Malvinotarion)haudeinew species andM.(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.
Silurian and Devonian corals occur abundantly in siliciclastic rocks of the Argentine Precordillera. They are distributed along a Silurian stormdominated shallow-water platform, a transitional restricted nearshore environment, and a Devonian muddy platform setting. Four main associations of rugose and tabulate corals have been recorded: a Silurian association, a lowermost Devonian and two associations in Lower Devonian rocks. The Silurian shallow-water platform coral association shows abundant colonies of a tabulate pleurodictyform coral. The type and the domical form of corals indicate high-energy environments. The lowermost Devonian coral association shows the abundance of the tabulate coral Argentinella argentina, which could have formed patches in protected low-energy environments. The Lower Devonian coral associations correspond to a muddy platform environment. The first one includes rugose and hemispherical tabulate corals and the second is composed of tabulate corals assigned to Parastriatopora sanjuanina, and Parastriatopora sp. They are long stick-like, fasciculate forms, grouped in apparently life position. Rugose and tabulate corals in the Upper Silurian and Lower Devonian of Argentina constitute lowdiversity associations of western Gondwana, developed in mid-to high-latitudes. The morphologies acquired by corals are related to water energy. Laminar or encrusting forms were more competitive in the Silurian shallow-water, high-energy environments. Slender branching forms with a high profile typically inhabited Devonian relatively deeper water or protected settings. The stratigraphic distribution observed partially followed the well-known pattern in which shallow-water faunas disappeared during regressive events and are replaced by new forms in the subsequent transgressive sequence. The turnover pattern detected across the Silurian-Devonian transitional interval is in agreement with that previously recognized on the basis of the accompanying fauna.
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.
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 phacopidPaciphacopsis proposed asEchidnops taphomimusnew species, from the Lower Devonian (probably late Lochkovian) of the Talacasto Formation, Argentine Precordillera. The visual surface ofE.taphomimusindicates that a irregular pattern of lens arrangement, typical of early phacopids such as the OrdovicianOrmathops, can also be recognized in more derived Devonian relatives, providing new insights on some evolutionary aspects of visual development.Echidnopsis 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 ofPaciphacopsspecies.
The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic section located in Western Argentina (Precordillera Basin). Palynological evidence indicates an Early Mississippian (probably Tournaisian) age for this new succession. The two identified early seeds generas, Pseudosporogonites cf. hallei and Warsteinia sancheziae n. sp. were up to now considered as restricted to the Devonian of Laurussia. This finding suggests a dispersal of earliest spermatophytes between Laurussia and Gondwana during Devonian/ Tournaisian times, thus accounting for the Rheic Ocean as a surmountable biogeographic barrier for continental biotas. Alternatively, contrasting biogeographic hypotheses dealing with early spermatophytes rising in paleotropics and then displacing herbaceous communities of non-spermatophytes typical from cool high latitudinal regions, are explored for explaining the recognized paleobiogeographical pattern. The new information supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and more similar to those reported from Laurussia. In addition, their discovery in a sedimentary environment associated to glacigenic deposits, show that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana.
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