Coníferas permineralizadas en la cuenca de Cañadón Asfalto, Chubut, Argentina: impacto evolutivo y taxonómico

Intensivos trabajos de campo realizados durante los últimos seis años en la cuenca de Cañadón Asfalto, Chubut, han permitido un notable incremento en el conocimiento taxonómico de la biota. Distintas sedimentitas de esta cuenca han sido referidas al Jurásico Inferior, Medio y Superior, constituyendo además una de las secuencias del Jurásico continental mejor representadas en Gondwana. En la presente contribución se describe el contenido de una nueva flora permineralizada, con excepcionales características de preservación, ubicada en estratos de la Formación Cañadón Calcáreo (Jurásico Superior - Cretácico Inferior?), al norte de la localidad de Cerro Cóndor. La asociación está compuesta por conos megasporangiados asignados a los géneros Pararaucaria y Araucaria, además de plántulas, maderas y conos indeterminados. Araucaria sp. está compuesta por conos megasporangiados de gran tamaño, de hasta 20cm de largo y 10cm de ancho, que por sus características anatómicas puede ser asignada a una nueva especie. De igual forma, Paraucaria sp. presenta mayor tamaño y dos óvulos por complejo ovulífero como principales rasgos que la diferencian de la única especie descripta previamente para el género (P. patagonica Wieland). La descripción de esta nueva especie permite avanzar sobre la discusión sistemática que atañe al género, el cual ha sido relacionado con distintas familias de coníferas, incluyendo Cupressaceae sensu lato y Pinaceae. El hallazgo de la asociación Araucaria / Pararaucaria en Chubut, extiende tanto geográfica como estratigráficamente la distribución de los bosques clásicamente conocidos de la Formación La Matilde del Jurásico Medio de la provincia de Santa Cruz.Sesiones libresFacultad de Ciencias Naturales y Muse

Evolution and Relationships of the Conifer Seed Cone Telemachus: Evidence from the Triassic of Antarctica

This is the publisher's version, also available electronically from http://www.jstor.org/stable/10.1086/651948The seed cone Telemachus is known from several Triassic localities in Gondwana. New specimens from two localities in Antarctica provide additional information about the type species, Telemachus elongatus, based on details of morphology and anatomy revealed by using a modified transfer technique on the compressed plants. Seed cones of T. elongatus are up to 6.0 cm long and characterized by conspicuous, elongate bracts. A second Antarctic species, described here as Telemachus antarcticus, is segregated, based on a shorter bract and differences in cone size. Newly recognized features of the genus include the shape, size, and disposition of the ovules; vascularization of the ovuliferous complex; and scale and bract histology. As a result of this new information, it is now possible to compare Telemachus with the permineralized Middle Triassic conifer seed cone Parasciadopitys from the Central Transantarctic Mountains. The similarities between the two genera make it possible to relate organs in different preservational modes and to develop a more complete concept for this widely distributed Gondwana conifer. Placing the Telemachus plant within a phylogenetic context makes it possible to evaluate the relationship with other so‐called transitional conifers, an informal group that has been interpreted as intermediate between Paleozoic and modern conifers

Seed Cone Anatomy of Cheirolepidiaceae (Coniferales): Reinterpreting Pararaucaria patagonica Wieland

Premise of the study: Seed cone morphology and anatomy reflect some of the most important changes in the phylogeny and evolutionary biology of conifers. Reexamination of the enigmatic Jurassic seed cone Pararaucaria patagonica reveals previously unknown systematically informative characters that demonstrate affinities with the Cheirolepidiaceae. This paper documents, for the first time, internal anatomy for seed cones of this important extinct Mesozoic conifer family, which may represent the ghost lineage leading to modern Pinaceae. Methods: Morphology and anatomy of cones from the Jurassic La Matilde Formation in Patagonia are described from a combination of polished wafers and thin section preparations. New photographic techniques are employed to reveal histological details of thin sections in which organic cell wall remains are not preserved. Specific terminology for conifer seed cones is proposed to help clarify hypotheses of homology for the various structures of the cones. Key results: Specimens are demonstrated to have trilobed ovuliferous scale tips along with a seed enclosing pocket of ovuliferous scale tissue. Originally thought to represent a seed wing in P. patagonica, this pocket-forming tissue is comparable to the flap of tissue covering seeds of compressed cheirolepidiaceous cones and is probably the most diagnostic character for seed cones of the family. Conclusions: Pararaucaria patagonica is assigned to Cheirolepidiaceae, documenting anatomical features for seed cones of the family and providing evidence for the antiquity of pinoid conifers leading to the origin of Pinaceae. A list of key morphological and anatomical characters for seed cones of Cheirolepidiaceae is developed to facilitate assignment of a much broader range of fossil remains to the family. This confirms the presence of Cheirolepidiaceae in the Jurassic of the Southern Hemisphere, which was previously suspected from palynological records.Keywords: Conifers, Seed cones, Cheirolepidiaceae, Jurassic, Pararaucaria, Patagoni

A new cupressaceous wood from the Lower Cretaceous of central Patagonia reveals possible clonal growth habit

A new genus and species, Austrocupressinoxylon barcinense, based on remains of cupressaceous wood is described for the Lower Cretaceous of central Patagonia, Argentina. The studied specimens are silicified fragments of picnoxylic and homoxylic wood that exhibit a combination of characters not previously reported, therefore a new genus is erected. The characters are: 1- growth ring boundaries distinct, 2- transition from earlywood to latewood gradual, 3- axial parenchyma diffuse,4- radial tracheid pitting predominantly abietinean,5- cross-field pitting cupressoid, arranged in both cupressoid and araucarioid patterns, 6- rays uniseriate heterocellular, 7- end and horizontal walls of ray parenchyma cells smooth or slightly nodular, and 8- ray tracheids with smooth walls. The cross-field pitting patterns and the presence of ray tracheids are two traits of particular interest in the context of systematic affinities. The fragments were collected from two stumps found in life position attached to each other by a main root, consequently, the disposition of the stumps suggests a case of clonal growth by root suckering. This is the second report of such mechanisms in the fossil records worldwide and the first one for South America.Facultad de Ciencias Naturales y Muse

Unstable taxa in cladistic analysis: identification and the assessment of relevant characters.

Abstract A common problem in phylogenetic analysis is the presence of unstable taxa that are depicted in multiple positions in optimal topologies. These uncertainties are reflected in strict consensus trees with polytomies that hamper the interpretation of the phylogenetic results. We propose a protocol for detecting unstable branches (either terminal taxa or clades) and identifying particular characters related to their instability in cladistic analysis. This procedure is based on an iterative evaluation of the agreement of triplets among the optimal topologies (i.e. most-parsimonious trees, MPTs) and examination of character optimizations on these trees. Different types of characters underlying the unstable behaviour of taxa are detected: those with conflicting scorings that support alternative positions of problematic taxa and those with missing data in the unstable taxa that could reduce their instability if they are scored. The entire process is automated through a TNT script that provides a list of characters related to the instability of each unstable taxon. The outcome of this procedure can be used as a guide for further research efforts focused on the revision or addition of (morphological or molecular) phylogenetic data for elucidating the affinities of unstable taxa

Contribución al conocimiento palinoestratigráfico de la Formación Cañadón Calcáreo en su localidad tipo, provincia del Chubut, Argentina

Los depósitos continentales silicoclásticos de la Formación Cañadón Calcáreo (Cuenca Cañadón Asfalto) afloran en el área de la Estancia Flores (S 43°17'30" y W 69°59'40"), margen oriental del valle medio del río Chubut. Esta es la localidad tipo para esta controvertida unidad, cuya base no aflora en el área. Regionalmente se ha propuesto que las sedimentitas de la Formación Cañadón Calcáreo se sobreponen discordantemente sobre la Formación Lonco Trapial y/o sobre la Formación Cañadón Asfalto, y son cubiertas por el Grupo Chubut (Cretácico). En la base de la unidad diez niveles de pelitas negras carbonosas de ambiente palustre contienen palinomorfos bien preservados y restos de algas. Hasta el momento se han identificado más de 98 especies de esporas y granos de polen distribuidos en 53 géneros, muchas de las cuales representan nuevos registros para Argentina. La diversidad y composición de esta palinoflora está caracterizada por el Complejo Callialasporites y variedad de especies de Araucariacites, Classopollis, Podosporites - Microcachryidites, Trilobosporites, Klukisporites - Ischyosporites, Aequitriradites, Retitriletes, Antulsporites, Nevesisporites, Concavissimisporites e Interulobites, entre otros géneros de típica ocurrencia jurásica. Es llamativa la escasa presencia de granos hilados referidos a las Araucariaceae, representados por los géneros Cyclusphaera, Coptospora y Balmeiopsis, que comienzan su registro en el Jurásico Superior y son muy abundantes en las asociaciones gondwánicas a partir del Cretácico Inferior. Por otra parte, en la asociación de la Formación Cañadón Calcáreo están ausentes las esporas de Schizaceae del género Cicatricosisporites (=Ruffordiaspora), que representan un evento biocronológico clave en secuencias gondwánicas, y cuya introducción (first appearance datum) se refiere al Tithoniano medio - tardío (Zona Cicatricosisporites autraliensis). La ausencia de este taxón en la secuencia estudiada sumado a las características generales del espectro microflorístico mencionado sugiere que la Formación Cañadón Calcáreo no es más joven que Tithoniano.Sesiones libresFacultad de Ciencias Naturales y Muse

A new species of Athrotaxites (Athrotaxoideae, Cupressaceae) from the Upper Cretaceous Raritan Formation, New Jersey, USA.

A new species of anatomically preserved Cupressaceae is described from the Upper Cretaceous Raritan Formation (New Jersey, USA). The fossils are charcolified isolated ovuliferous complexes that were studied by means of a combination of MEB images and Micro-CT, allowing the observation of morphological and anatomical characters. Each ovuliferous complex bears 3-4 anatropous winged seeds, disposed in one row on a thin medial part of the adaxial side of the ovuliferous complex. Based on the combination of characters such as ovuliferous complex morphology, arrangement of vascular tissues and resin canals, seed number and their morphology, orientation and disposition, these fossils are placed within a new species of the fossil genus Athrotaxites. The developmental stage of the specimens is analyzed base on comparisons with living representatives of the subfamily Athrotaxoideae (i.e., Athrotaxis spp.), which supports a post-pollination stage for these fossils. In addition, the new species is compared with other extant and extinct representatives of basal cupressaceous subfamilies. This new record from the Upper Cretaceous sediments of New Jersey further supports a wider distribution of the subfamily Athrotaxoideae during the middle part of the Mesozoic, as it has been also noted for other basal representatives of the family Cupressaceae.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author