Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago.

The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial. Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis, which may have been eukaryotic, evidence for morphological and taxonomic biodiversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization. The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration, may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.

[Taphonomy of the gastropod cf. Donaldina robusta (Heterobranchia: Streptacididae) from the Middle Pennsylvanian, La Joya Formation, Sonora, Mexico]. / Tafonomía del gasterópodo cf. Donaldina robusta (Heterobranchia: Streptacididae) del Pensilvánico Medio, Formación La Joya, Sonora, México.

Gastropods are an important component in most of the fossil record; however, investigations have focused mainly on the characterization of the tafofacies and signatures in determined environments. We present qualitative and quantitative taphonomic data for the gastropod cf. Donaldina robusta assemblages from the La Joya Formation of the Sierra Agua Verde, Sonora State, (NW) Mexico. We analyzed 176 shells. Good preservation received ahigh taphonomic grade (A) and poor preservation a D. The shells were complete in 72% of cases (taphonomic grade B). Less than 10% are corroded or are parallel to the layer (grade A). This rock is petrographycally classified as wackestone, sedimentologically it is characterized by middle sorting (grade B) and low grading (grade A). The fossiliferous assemblage grades as A and B. Biostratinomic features of the skeletal assemblage are characteristic of sedimentologic concentrations of autochthonous-parautochthonous elements at the accumulation site. There was minimal reworking and transport in an environment of low energy, locally produced during a short period of accumulation.

Terreneuvian orthothecid (Hyolitha) digestive tracts from northern Montagne Noire, France; taphonomic, ontogenetic and phylogenetic implications.

More than 285 specimens of Conotheca subcurvata with three-dimensionally preserved digestive tracts were recovered from the Terreneuvian (early Cambrian) Heraultia Limestone of the northern Montagne Noire, southern France. They represent one of the oldest occurrences of such preserved guts. The newly discovered operculum of some complete specimens provides additional data allowing emendation of the species diagnosis. Infestation of the U-shaped digestive tracts by smooth uniseriate, branching to anastomosing filaments along with isolated botryoidal coccoids attests to their early, microbially mediated phosphatisation. Apart from taphonomic deformation, C. subcurvata exhibits three different configurations of the digestive tract: (1) anal tube and gut parallel, straight to slightly undulating; (2) anal tube straight and loosely folded gut; and (3) anal tube straight and gut straight with local zigzag folds. The arrangement of the digestive tracts and its correlation with the mean apertural diameter of the specimens are interpreted as ontogenetically dependent. The simple U-shaped gut, usually considered as characteristic of the Hyolithida, developed in earlier stages of C. subcurvata, whereas the more complex orthothecid type-3 only appears in largest specimens. This growth pattern suggests a distinct phylogenetic relationship between these two hyolith orders through heterochronic processes.

Tafonomía del gasterópodo cf. Donaldina robusta (Heterobranchia: Streptacididae) del Pensilvánico Medio, Formación La Joya, Sonora, México

Taphonomy of the gastropod cf. Donaldina robusta Heterobranchia: Streptacididae) from the Middle Pennsylvanian, La Joya Formation, Sonora, Mexico. Gastropods are an important component in most of the fossil record; however, investigations have focused mainly on the characterization of the tafofacies and signatures in determined environments. We present qualitative and quantitative taphonomic data for the gastropod cf. Donaldina robusta assemblages from the La Joya Formation of the Sierra Agua Verde, Sonora State, (NW) Mexico. We analyzed 176 shells. Good preservation received a high taphonomic grade (A) and poor preservation a D. The shells were complete in 72% of cases (taphonomic grade B). Less than 10% are corroded or are parallel to the layer (grade A). This rock is petrographycally classified as wackestone, sedimentologically it is characterized by middle sorting (grade B) and low grading (grade A). The fossiliferous assemblage grades as A and B. Biostratinomic features of the skeletal assemblage are characteristic of sedimentologic concentrations of autochthonous-parautochthonous elements at the accumulation site. There was minimal reworking and transport in an environment of low energy, locally produced during a short period of accumulation. Rev. Biol. Trop. 58 (1): 183-194. Epub 2010 March 01.

Los gasterópodos son un componente importante en la mayoría de los registros fósiles, sin embargo, las investigaciones se han centrado principalmente en la caracterización de las tafofacies y firmas tafonómicas en ambientes particulares. Se presentan los datos tafonómicos cualitativos y cuantitativos para el ensamblaje del gasterópodo cf. Donaldina robusta de la Formación La Joya de la Sierra Agua Verde, Sonora, (NW) México. Se analizaron 176 conchas. Una buena preservación recibió un grado tafonómico alto (A) y una preservación pobre D. Las conchas estaban completas en el 72% de los casos (grado tafonómico B). Menos del 10% estaban corroídas y se encontraban paralelas a la capa (grado A). Esta roca según la petrografía es clasificada como "wackestone", de acuerdo a los sedimentos se encuentra en una categoría intermedia (grado B) y baja (grado A). Los ensambles fosilíferos tienen grados tanto A como B. Las características biostratinómicas del ensamblaje esquelético tienen concentraciones de sedimentos de los elementos autóctonos-parautóctonos típicas del sitio de la acumulación. Durante un corto período de acumulación, en un ambiente de baja energía, hubo reelaboración y transporte mínimo de la producción local.