Spore Diversity Trends From Eifelian/Givetian Devonian Argentina

Spore diversity trends in the Middle Devonian of the Chaco-Salteño Plain, northwestern Argentina

Author:

Noetinger et al

Abstract:

Devonian deposits in northwestern Argentina were historically studied with stratigraphical purposes, since these layers conform the source rocks of the producing basins of the region. A fairly well preserved palynomorph assemblage, from the Tonono Formation, provides an opportunity to perform the first quantitative analysis to study the evolution of diversity in the succession. Two associations are here defined by both, stratigraphic distribution of species and cluster analysis, ranging from the lower Eifelian to the lower Givetian. Rarefaction analysis reveals the existence of a relatively rich miospore population. Species richness increases while there is a drop in diversity and evenness towards the top of the column. The increment of the marine components towards the latter section indicates shifts in the shoreline. The influx of warmer water into higher latitudes, as highlighted by the arrival of the brachiopod Tropidoleptus, could have favored the inception of new spore species in the settled community. These results add to evidence that some groups build up the number of species in disturbed settings, and evenness is reduced with each new species introduced.

Palaeoenvironmental Changes Recorded in Givetian-Frasnian Devonian Reef Systems From Australia

Changes of palaeoenvironmental conditions recorded in Late Devonian reef systems from the Canning Basin, Western Australia: A biomarker and stable isotope approach

Authors:

Tulipani et al

Abstract:

Although the Late Devonian extinctions were amongst the largest mass extinction events in the Phanerozoic, causes, nature and timing of these events remain poorly restrained. In addition to the most pronounced biodiversity loss at the Frasnian-Famennian (F-F) boundary and the end Famennian, there were also less extensively studied extinction pulses in the Middle to Late Givetian and the Frasnian. Here we used a combination of palynological, elemental, molecular and stable isotope analyses to investigate a sedimentary record of reef-systems from this time period in the Canning Basin, Western Australia.

The acquired data generally showed distinct variations between sediments from (i) the time around the Givetian-Frasnian (G-F) boundary and (ii) later in the Frasnian and indicated a distinct interval of biotic stress, particularly for reef-builders, in the older sediments. Alterations of pristane/phytane ratios, gammacerane indices, Chlorobi biomarkers, δDkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic/euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column. Simultaneous excursions in δ13C profiles of carbonates, organic matter (OM) and hydrocarbons in the older sediments reflect the stratification-induced enhancement of OM-recycling by sulfate reducing bacteria. Alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans (MTTCs) and perylene indicate an increased terrigenous nutrient input via riverine influx, which would have promoted stratification, phytoplankton blooms and the development of lower water column anoxia.

The detected palaeoenvironmental conditions around the G-F boundary may reflect a local or global extinction event. Our data furthermore suggest a contribution of the higher plant-expansion and photic zone euxinia to the Late Devonian extinctions, consistent with previous hypotheses. Furthermore, this work might contribute to the understanding of variations in Devonian reef margin and platform-top architecture, relevant for petroleum exploration and development in the global Devonian hydrocarbon resources.

A Cryptic Coral-crinoid "Hanging Garden" From Eifelian/Givetian Devonian Morocco

Cryptic coral-crinoid "hanging gardens" from the Middle Devonian of southern Morocco

Authors:

Jakubowicz et al

Abstract:

An unusual and exceptionally well preserved cryptic community of cnidarians, crinoids, sponges, and microbes developed in a submarine cavity of Middle Devonian age in the Hamar Laghdad area (Morocco). The biota encrusted the cavity roof and grew predominantly in an upside-down position, forming spectacular "hanging gardens." The investigated assemblage differs strikingly from both its Paleozoic and modern analogues; it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings, and is the first report of a cryptic paleoecosystem dominated by rugose corals. The results support the view that during the middle Paleozoic there was no distinct polarization between open-surface and cryptic faunas in deep-water environments, but keen competition for space already existed in Devonian cryptic assemblages. The regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community.

Schinderhannes bartelsi, a Penguin-winged Anomalocarid?

A missing link in the evolution of the front claw of living scorpions and horseshoe crabs was identified with the discovery of a 390 million-year-old fossil by researchers at Yale and the University of Bonn, Germany.

The specimen, named Schinderhannes bartelsi, was found fossilized in slate from a quarry near Bundenbach in Germany, a site that yields spectacularly durable pyrite-preserved fossils — findings collectively known as the Hunsrück Slate. The Hunsrück Slate has previously produced some of the most valuable clues to understanding the evolution of arthropods – including early shrimp-like forms, a scorpion and sea spiders as well as the ancient arthropods trilobites.

"With a head like the giant Cambrian aquatic predator Anomalocaris and a body like a modern arthropod, the specimen is the only known example of this unusual creature," said Derek Briggs, director of Yale's Peabody Museum of Natural History and an author of the paper appearing in the journal Science.

Scientists have puzzled over the origins of the paired grasping appendages found on the heads of scorpions and horseshoe crabs. The researchers suggest that Schinderhannes gives a hint. Their appendages may be an equivalent to those found in the ancient predatory ancestor, Anomalocaris — even though creatures with those head structures were thought to have become extinct by the middle of the Cambrian Period, 100 million years before Schinderhannes lived.

The fossil's head section has large bulbous eyes, a circular mouth opening and a pair of segmented, opposable appendages with spines projecting inward along their length. The trunk section is made up of 12 segments, each with small appendages, and a long tail spine. Between the head and trunk, there is a pair of large triangular wing-like limbs — that likely propelled the creature like a swimming penguin, according to Briggs. Unlike its ancestors from the Cambrian period, which reached three feet in length, Schinderhannes is only about 4 inches long.

So the Anomalocarid line didn't die out in the Cambrian. ha! This sucker is Devonian! Knock down a family from getting wiped out in the Cambrian Extinction.