Naturalis
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Rhexoxylon cortaderitaense (Menéndez) comb. nov., a species of permineralized stems newly assigned to the Corystospermaceae, from the Triassic of Argentina
(2008) Bodnar, Josefina
Anatomically preserved stems of Late Triassic corystosperms from the upper Cortaderita Formation in San Juan province, Argentina are described and assigned to Rhexoxylon cortaderitaense (Mene´ndez) comb. nov. These specimens were originally attributed to conifers, a group not closely related to corystosperms. The silicified axes preserve features of the cortex, pith, and secondary vascular system. Like all Rhexoxylon species, these axes have two discontinuous cambial rings that develop centrifugal secondary xylem (normal secondary xylem) and centripetal secondary xylem (inverted secondary xylem). Both types of xylem are separated by a band of parenchymatous tissue developed by a remnant cambium. The centrifugal xylem is divided by parenchymatous rays following differential cambial activity. The secondary xylem is pycnoxylic with uniseriate rays; tracheids have mainly biseriate and alternate bordered pits on radial and tangential walls, and one simple oval pit in cross-fields. The distinctive feature of R. cortaderitaense is the conspicuous amount of centripetal secondary vascular tissues not forming perimedullar bundles, this being interpreted as an apomorphic trait. This interpretation of the character modifies previous hypothesized phylogenetic relationships of corystosperm wood taxa.
La antártida argentina
(1948) Sgrosso, Pascual
Manual of Neotropical Diptera. Simuliidae
(2009) Coscarón, Sixto
The Neotropical Simuliidae have been most recently monographed by Coscarón & Coscarón Arias (2007), with the exception of the small genus Pedrowygomyia Coscarón & Miranda Esquivel, 1998 (revised by Coscarón & Miranda Esquivel, 1998) and the large genus Gigantodax Enderlein, 1915 (revised by Wygodzinsky & Coscarón, 1989). Basic information about black flies’ bionomics (pp. 15-16), behavior (pp.16-17), morphology (pp. 22-330, collection and preparation of material (pp. 34-35), methods of study (pp. 36-37) and bibliography (pp. 648-670) may be found in Coscarón & Coscarón Arias (2007). Some additional references are added in the ensuing paragraphs.
Biostratigraphy and biochronology of the Monte Hermoso Formation (early Pliocene) at its type locality, Buenos Aires Province, Argentina
(2013) Tomassini, Rodrigo Leandro; Montalvo, Claudia Inés; Deschamps, Cecilia Marcela; Manera de Bianco, Teresa
The Monte Hermoso Formation, cropping out at its type locality of Farola Monte Hermoso (Buenos Aires Province), is a classical fossiliferous unit of the South American Neogene, highlighted by the abundance and diversity of its vertebrate remains. However, its biostratigraphy and age have been largely debated, and numerous discrepancies and controversies have been stated. In this regard, the result of the analysis of new materials recovered from the different levels of this formation, following a strict control of stratigraphic provenance, is here reported. As well, the provenance of specimens of previous collections has been evaluated. The studied assemblage consists of Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. These latter are the most numerous and belong to the Didelphimorphia, Polydolopimorphia, Rodentia, Notoungulata, Litopterna and Xenarthra. The recorded taxa suggest no important faunistic variations among the different levels of the Monte Hermoso Formation that would imply significant chronological differences, and hence, justify the recognition of two biostratigraphic units. The analysis of the first and last records as well as the taxa considered as exclusive, does not support the validity of the biozones of Trigodon gaudryi and Neocavia depressidens previously proposed. On this basis, a new scheme for the Monte Hermoso Formation at its type locality is proposed, including a new single biostratigraphic unit. This unit is the Eumysops laeviplicatus Range Zone, which represents the biostratigraphic base for the Montehermosan Stage/Age of the early Pliocene.
On the genus Tomaxellia (Coniferae) from the Lower Cretaceous of Patagonia (Argentina) and its male and female cones
(1968) Archangelsky, Sergio
This paper reports the organic attachment of male and female cones to twigs previously described as Tomaxellia biforme Archangelsky. The male cones produce Classopollis pollen, while the scales of the female StIWCtWeS are comparable to the Rhaeto-Liassic northern genus Cheirolepidium. A new interpretation of the possible femqle cone of Cheirolepidium is presented, based on the new evidence now available with the knowledge of Tomaxeellia cones. Other female cones found in Mesozoic formations may be comparable to some extent with Tomaxellia, such as Indostrobus (Cretaceous of India) or Paruraucaria (Jurassic of Argentina), and they may be grouped in the family Cheirolepidiaceaa. Comparisons with older conifer genera with known female cones are also included (Voltziaceae). Some morphological changes of the female cones,
which probably took place during the Mesozoic (in these particular groups) are also inferred.