A Homerian Silurian Arthropod had a Unique Brood Caring Mode

Tiny individuals attached to a new Silurian arthropod suggest a unique mode of brood care

Authors:

Briggs et al

Abstract:

The ∼430-My-old Herefordshire, United Kingdom, Lagerstätte has yielded a diversity of remarkably preserved invertebrates, many of which provide fundamental insights into the evolutionary history and ecology of particular taxa. Here we report a new arthropod with 10 tiny arthropods tethered to its tergites by long individual threads. The head of the host, which is covered by a shield that projects anteriorly, bears a long stout uniramous antenna and a chelate limb followed by two biramous appendages. The trunk comprises 11 segments, all bearing limbs and covered by tergites with long slender lateral spines. A short telson bears long parallel cerci. Our phylogenetic analysis resolves the new arthropod as a stem-group mandibulate. The evidence suggests that the tethered individuals are juveniles and the association represents a complex brooding behavior. Alternative possibilities—that the tethered individuals represent a different epizoic or parasitic arthropod—appear less likely.

Tortotubus: a Fossil Fungus From Aeronian Silurian Sweden

A fossil dating from 440 million years ago is not only the oldest example of a fossilised fungus, but is also the oldest fossil of any land-dwelling organism yet found. The organism, and others like it, played a key role in laying the groundwork for more complex plants, and later animals, to exist on land by kick-starting the process of rot and soil formation, which is vital to all life on land.

This early pioneer, known as Tortotubus, displays a structure similar to one found in some modern fungi, which likely enabled it to store and transport nutrients through the process of decomposition. Although it cannot be said to be the first organism to have lived on land, it is the oldest fossil of a terrestrial organism yet found. The results are published in the Botanical Journal of the Linnean Society.

"During the period when this organism existed, life was almost entirely restricted to the oceans: nothing more complex than simple mossy and lichen-like plants had yet evolved on the land," said the paper's author Dr Martin Smith, who conducted the work while at the University of Cambridge's Department of Earth Sciences, and is now based at Durham University. "But before there could be flowering plants or trees, or the animals that depend on them, the processes of rot and soil formation needed to be established."

Working with a range of tiny microfossils from Sweden and Scotland, each shorter than a human hair is wide, Smith attempted to reconstruct the method of growth for two different types of fossils that were first identified in the 1980s. These fossils had once been thought to represent parts of two different organisms, but by identifying other fossils with 'in-between' forms, Smith was able to show that the fossils actually represented parts of a single organism at different stages of growth. By reconstructing how the organism grew, he was able to show that the fossils represent mycelium - the root-like filaments that fungi use to extract nutrients from soil.

It's difficult to pinpoint exactly when life first migrated from the seas to the land, since useful features in the fossil record that could help identify the earliest land colonisers are rare, but it is generally agreed that the transition started early in the Palaeozoic era, between 500 and 450 million years ago. But before any complex forms of life could live on land, there needed to be nutrients there to support them. Fungi played a key role in the move to land, since by kick-starting the rotting process, a layer of fertile soil could eventually be built up, enabling plants with root systems to establish themselves, which in turn could support animal life.

link.

Evidence of Heavy Metal Poisoning From Ordovician Mass Extinction in Marine Plankton

Several Palaeozoic mass extinction events during the Ordovician and Silurian periods (ca. 485 to 420 to million years ago) shaped the evolution of life on our planet. Although some of these short-lived, periodic events were responsible for eradication of up to 85% of marine species, the exact kill-mechanism responsible for these crises remains poorly understood.

An international team led by Thijs Vandenbroucke (researcher at the French CNRS and invited professor at UGent) and Poul Emsbo (US Geological Survey) initiated a study to investigate a little known association between 'teratological' or 'malformed' fossil plankton assemblages coincident with the initial stages of these extinction events.

In a paper just published in Nature Communications, they present evidence that malformed fossil remains of marine plankton from the late Silurian (415 million years ago) contain highly elevated concentrations of heavy metals, such as iron, lead, and arsenic. These are well-known toxins that cause morphologic abnormalities in modern aquatic organisms; which led the authors to conclude that metal poisoning caused the malformation observed in these ancient organisms and may have contributed to their extinction and that of many other species.

link.

Seconded: Terrestrial Plants NOT Responsible for Climate Change During Ordovician (and Silurian)

Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times?

Authors:

Edwards et al

Abstract:

The Ordovician and Silurian periods were times of major geological activity as regards palaeogeography, volcanism and climate change, the last of these evidenced by a series of cooling episodes and glaciations that climaxed in the Hirnantian (Late Ordovician). The presence of cryptospores in the Darriwilian (Middle Ordovician) marked the advent of higher plants on land. A critical survey of direct (mega- and microfossils) and some indirect evidence in succeeding rocks indicates the presence of algae, Bacteria, Cyanobacteria, Fungi, probable lichens, cryptophytes and basal tracheophytes. Similar associations of photosynthesizers and decomposers occur today in cryptogamic covers (CCs), for example biological crusts, except that bryophytes replace cryptophytes (basal embryophytes) and tracheophytes are absent. Thus, extant CCs, which make significant contributions today to global carbon and nitrogen fixation and prevention of erosion, provide an excellent analogue for the impacts of early land vegetation on both lithosphere and atmosphere. As a prerequisite to assessing impacts in Ordovician–Silurian times, with particular consideration of parameters used by climate modellers, the effects of a number of abiotic factors on the growth and survival of extant cryptogamic ground covers and their environmental impacts are reviewed. Factors include photosynthetically active radiation, ultraviolet radiation, temperature, water, oxygen, carbon dioxide, nitrogen, phosphorus, iron, surface roughness and albedo. A survey of the nature and extent of weathering facilitated by such vegetation concludes that it was limited based on depth of weathering when compared with that from rooted tracheophytes today, with minor effects on carbon dioxide drawdown. As global net productivity from Ordovician–Silurian CCs was very probably lower than today, and while the small fraction of intractable material in their organic carbon would have resulted in a more rapid turnover of terrestrial biomass, we conclude that there was decreased possibility of long-term organic carbon burial. Hence, there would have been very limited increase in atmospheric oxygen and decrease in carbon dioxide resulting from carbon burial.

note previous paper from earlier this month.

Jawless Fish (Ostracoderms) Went Extinct due to Environmental Factors, Range Restriction, not Competition With Jawed Fish

Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history

Authors:

Sansom et al

Abstract:

The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem–gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates.

A Eurypterid Lagerstätte From Pridoli Silurian Pennsylvania

A NEW EURYPTERID LAGERSTÄTTE FROM THE UPPER SILURIAN OF PENNSYLVANIA

Authors:

Vrazo et al

Abstract:

Eurypterids are generally rare in the fossil record, but occasionally occur in abundance. The genus Eurypterus, in particular, is well known from certain upper Silurian Lagerstätten of the northern Appalachian basin (New York and Ontario), but occurs far less frequently in the central and southern Appalachian basin (Pennsylvania, Maryland, and West Virginia, respectively). The recent discovery of an exceptionally preserved mass assemblage of Eurypterus in the upper Tonoloway Formation (upper Ludlow–Přídolí) of Pennsylvania provides new information on the behavior and life habitat of the genus in this region. Eurypterids at this locality are found in thinly laminated, calcareous shale deposited within the lower intertidal to shallow subtidal zone of a coastal mudflat or sabkha. Rare associated fauna of limited diversity, and evaporitic and desiccation features in associated beds, suggest a stressed environment with variable salinity and possible hypoxic conditions. Most eurypterids are disarticulated and fragmentary, but several fully articulated, exceptionally preserved specimens are present. Exoskeletal features and taphonomic indices values indicate a molt rather than death assemblage, and the presence of arthropod trackways suggests that Eurypterus sp. may have molted en masse in the vicinity of the burial site. Sequence stratigraphic interpretation of the site suggests that preservation of eurypterid remains is the result of occupation of ephemeral environmental (salinity/oxygen) conditions during a transgression. The occurrence of this new Lagerstätte within the upper Silurian succession of the central Appalachians, an interval which had heretofore yielded only rare, fragmentary remains, indicates that eurypterids were more prevalent in this region than previously thought.

Ludlow Silurian had Sufficient Atmospheric Oxygen to Support Meter Long Fish

The largest Silurian vertebrate and its palaeoecological implications

Authors:

Choo et al

Abstract:

An apparent absence of Silurian fishes more than half-a-metre in length has been viewed as evidence that gnathostomes were restricted in size and diversity prior to the Devonian. Here we describe the largest pre-Devonian vertebrate (Megamastax amblyodus gen. et sp. nov.), a predatory marine osteichthyan from the Silurian Kuanti Formation (late Ludlow, ~423 million years ago) of Yunnan, China, with an estimated length of about 1 meter. The unusual dentition of the new form suggests a durophagous diet which, combined with its large size, indicates a considerable degree of trophic specialisation among early osteichthyans. The lack of large Silurian vertebrates has recently been used as constraint in palaeoatmospheric modelling, with purported lower oxygen levels imposing a physiological size limit. Regardless of the exact causal relationship between oxygen availability and evolutionary success, this finding refutes the assumption that pre-Emsian vertebrates were restricted to small body sizes.

Early Silurian Red Beds of South China are Unique Globally

Pigmentation of the Early Silurian shallow marine red beds in South China as exemplified by the Rongxi Formation of Xiushan, southeastern Chongqing, central China

Authors:

Zhang et al

Abstract:

The origin and pigmentation of red beds have long been investigated, but mainly on continental settings and carbonate facies (including deep marine red beds). This paper focuses on the shallow marine clastic red beds developed in South China during the Silurian. Based on the sedimentological and geochemical analyses on red layers, green layers and laminae of the Rongxi Formation (Llandovery, Lower Silurian) of Xiushan, southeastern Chongqing, known as the ‘lower red beds’ (LRBs), the following observations are made: 1) the LRBs are primary red beds whereas the green layers are secondary (i.e., formed during early diagenesis); 2) the color differentiation of sediments shows little relevance to the bottom redox potential shift but has a close relationship to grain size and sediment sorting which may be caused by sea level changes and tides. The controlling factors of LRBs pigmentation are significantly different from those of deep marine red beds, and some coeval red beds in North America and Europe. It is noted that, among the shallow marine clastic red beds, the sedimentological and geochemical signatures from the laminae seem to better indicate the environmental conditions than those derived from the layers.

Was There a Third Pulse to the Ordovician Extinction?

The early Rhuddanian survival interval in the Lower Silurian of the Oslo Region: A third pulse of the end-Ordovician extinction

Author:

B. Gudveig Baarli

Abstract:

Ordovician/Silurian boundary layers with Rhuddanian strata are exposed as a long, continuously fossiliferous sequence in the Solvik Formation in the Asker area, central Oslo Region, Norway. Brachiopods belonging to Benthic Assemblage 5 are preserved in the lower parts of the formation. This level is investigated for the presence of a survival interval after the last end-Ordovician extinction event. The criteria for a survival interval include taxa that are dwarfed, long ranging, eurytopic, often opportunistic, as well as assemblages that show low density and diversity.

Four species, Isorthis prima, Leangella scissa, Dicoelosia osloensis and Eoplectodonta duplicata, were collected and measured. The three former were dwarfed as compared to a younger Aeronian fauna belonging to the same Benthic Assemblage. Detailed investigations showed a statistically significant two-step reduction in size for all but D. osloensis. The first interval, immediately above the last end-Ordovician extinction event, display dwarfed brachiopods, but diversity is high and the number of long-ranging and eurytopic species is low due to the presence of globally and locally “relict” Ordovician species. The second interval, the upper parts of lower Rhuddanian, shows all the characteristics of a survival interval in which the sizes are statistically significantly smaller than both those in the interval below and those in the Aeronian interval above. No lithological change within lower Rhuddanian strata could be linked to the pronounced reduction in size. The second step in size reduction may be related to global occurrence of anoxia in the deep oceans with a pulse of anoxic water pushed onto the shelf at that time. It is coeval with a short negative ∂13C excursion found in some locales, signifying a brief period of global warming. The results suggest a protracted extinction event through parts of the early Rhuddanian and a third and final extinction event followed by a clear survival interval.

Ecological Implications of Mass Extinction are Separate From Taxonomic Implications

Contrasting the ecological and taxonomic consequences of extinction

Authors:

Christie et al

Abstract:

Extinction in the fossil record is most often measured by the percentage of taxa (species, genera, families, etc.) that go extinct in a certain time interval. This is a measure of taxonomic loss, but previous work has indicated that taxonomic loss may be decoupled from the ecological effects of an extinction. To understand the role extinction plays in ecological change, extinction should also be measured in terms of loss of functional diversity. This study tests whether ecological changes increase correspondingly with taxonomic changes during the Late Ordovician M4/M5 extinction, the Ordovician/Silurian mass extinction, and the Late Devonian mass extinction. All three extinctions are evaluated with regional data sets from the eastern United States. Ecological effects are measured by classifying organisms into ecological lifestyles, which are groups based on ecological function rather than evolutionary history. The taxonomic and ecological effects of each extinction are evaluated with additive diversity partitioning, detrended correspondence analysis, and relative abundance distributions. Although the largest taxonomic changes occur in the Ordovician/Silurian extinction, the largest ecological changes occur in the Late Devonian extinction. These results suggest that the ecological consequences of extinction need to be considered in addition to the taxonomic effects of extinction.

After Devonian Hangenberg Extinction, Fish Crushed Their Food

Trends in shell fragmentation as evidence of mid-Paleozoic changes in marine predation

Authors:

Salamon et al

Abstract:

Recent observations indicate that shell fragmentation can be a useful tool in assessing crushing predation in marine communities. However, criteria for recognizing shell breakage caused by durophagous predators versus physical factors are still not well established. Here, we provide data from tumbling and aquarium experiments to argue that physical and biotic processes lead to different patterns of shell damage, specifically that angular shell fragments are good indicators of durophagous predation. Using such angular shell fragments as a predation proxy, we analyze data from 57 European Paleozoic localities spanning the Ordovician through the Mississippian. Our results reveal a significant increase in angular shell fragments (either occurring as isolated valves or present in regurgitalites) in the Mississippian. The timing of this increase is coincident with the increased diversity of crushing predators as well as marked anti-predatory changes in the architecture and mode of life of invertebrate prey observed after the end-Devonian Hangenberg extinction (359 Ma). More specifically, the observed trend in shell fragmentation constitutes strong and independent confirmation of a recently suggested end-Devonian changeover in the primary method of fish predation from shearing to crushing. These results also highlight the important effect of extinction events, not only on taxonomic diversity, but also on the nature of predator-prey interactions.

Evidence of the Collison of the Precambrian Kokchetav Microcontinent With Future Asia During Paleozoic

Formation of the Kokchetav subduction-collision zone (northern Kazakhstan): Insights from zircon U-Pb and Lu-Hf isotope systematics

Authors:

Glorie et al

Abstract:

The Kokchetav subduction-collision zone is located in the western part of the ancestral Central Asian Orogenic Belt. This zone is built up by the Precambrian Kokchetav microcontinent which includes a HP-UHP metamorphic belt, and the North Kokchetav tectonic zone (NKTZ) which represents an accretionary complex between the Kokchetav microcontinent and the adjacent Stepnyak island-arc. The entire region is widely intruded by Palaeozoic granitoids which were emplaced after the collision of the Stepnyak island-arc with the Kokchetav microcontinent. We present zircon U-Pb ages and Lu-Hf systematics in zircon to better characterize the tectonic evolution of the Kokchetav subduction-collision zone.

The Lu-Hf results indicate that the Kokchetav basement rocks are derived from late Neoarchaean – early Palaeoproterozoic (~ 2.5 Ga) crust. For the granite-gneiss basement of the Kokchetav microcontinent, early Mesoproterozoic (Grenville-age, ~ 1.17-1.14 Ga) zircon U-Pb crystallization ages were obtained. For the NKTZ, two main age-components were recognized: (1) an oldest Mesoproterozoic age-component (~ 1.20-1.05 Ga) similar as for the Kokchetav microcontinental zircons, and (2) a younger Early Cambrian (540-520 Ma) or Late Cambrian - Early Ordovician (~ 490-480 Ma) age-component. Th/U ratios (< 0.1) are indicative of a metamorphic origin for both Early Cambrian and Late Cambrian - Early Ordovician zircon populations. The oscillatory zoned Mesoproterozoic zircons have higher Th/U ratios (> 0.1) and are typical of a magmatic protolith. The distinction between both zircon types is supported by characteristic cathodoluminescence images. These results confirm previous observations, indicating early Palaeozoic high-grade metamorphism (~ 540-520 Ma) and collisional deformation (~ 490-480 Ma) of the Mesoproterozoic Kokchetav zone as a result of subduction-accretion and collision of the Stepnyak island-arc to the Kokchetav microcontinent. For two additional samples of the Balkashin granitic complex Early Devonian (~ 415-395 Ma) zircon crystallization ages (magmatic Th/U ratios) were obtained. The occurrence of a Mesozoic xenocryst within these leucogranites may indicate that they were emplaced in a continental-arc setting.

Entelgnathus primordialis: Earliest Known Jawed Fish From Pridoli Silurian China

A Silurian placoderm with osteichthyan-like marginal jaw bones

Authors:

Min Zhu et al (I'm going to start doing shorter authors and whatnot, not enough time in the day now)

Abstract:

The gnathostome (jawed vertebrate) crown group comprises two extant clades with contrasting character complements. Notably, Chondrichthyes (cartilaginous fish) lack the large dermal bones that characterize Osteichthyes (bony fish and tetrapods). The polarities of these differences, and the morphology of the last common ancestor of crown gnathostomes, are the subject of continuing debate. Here we describe a three-dimensionally preserved 419-million-year-old placoderm fish from the Silurian of China that represents the first stem gnathostome with dermal marginal jaw bones (premaxilla, maxilla and dentary), features previously restricted to Osteichthyes. A phylogenetic analysis places the new form near the top of the gnathostome stem group but does not fully resolve its relationships to other placoderms. The analysis also assigns all acanthodians to the chondrichthyan stem group. These results suggest that the last common ancestor of Chondrichthyes and Osteichthyes had a macromeric dermal skeleton, and provide a new framework for studying crown gnathostome divergence.

pop sci link too.

A Collision of Sea Mounts and Plates From the Silurian to Carboniferous

Restoring the Silurian to Carboniferous northern active continental margin of the Mongol-Okhotsk Ocean in Mongolia - Hangay-Hentey accretionary wedge and seamount collision

Authors:

1. Désirée Ruppen (a)

2. Alice Knaf (a)

3. Denise Bussien (a)

4. Wilfried Winkler (a)

5. Anaad Chimedtseren (b)

6. Albrecht von Quadt (c)

Affiliations:

a. Geological Institute, Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland

b. Mongolian University of Science and Technology, Ulaanbaatar 210646, P.O.Box 46/225, Mongolia

c. Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland

Abstract:

Trapped between the Siberian Craton to the north, and the Tarim and North China blocks to the south, the Mongol-Okhotsk Belt represents a young portion of the Central Asian Orogenic Belt. The Andean-type orogeny was caused by the closure of the Mongol-Okhotsk Ocean, whose timing and mode of geodynamic evolution still needs to be clarified in more detail. This paper investigates the lithostratigraphic units of the Gorkhi Formation, which are comprised in the Hangay-Hentey terrane representing the accretionary prism of the northern continental margin of the Mongol-Okhotsk Ocean. In the tectonically disrupted slices of the Gorkhi Formation we identify a typical ocean plate stratigraphy with pelagic to hemipelagic and turbiditic sequences. Locally, shallow marine limestones are found associated with mafic volcanic rocks. XRF and LA-ICPMS measurements of these volcanic rocks clearly indicate an OIB signature. The geochemistry together with lithostratigraphic observations permit us to reconstruct the evolution of a seamount, ranging from its growth in shallow water depths and drowning due to subduction-related subsidence linked with subsequent radiolarian chert, hemipelagic shale and turbiditic sandstone cover sedimentation. Calc-alkaline felsic dikes later intruded the accreted silt and sandstone deposits. Standard sandstone provenance analysis, detrital zircon U-Pb laser ablation ICP-MS dating and Hf isotope ratios in the sandstones document a prevailing continental volcanic arc sourcing during Carboniferous from the northern margin of the Mongol-Okhotsk Ocean.

A Gorgeously Preserved Silurian Ostracod

'It is exciting to discover that a common group of fossils that we thought we knew a lot about may well have been hood-winking us as to their true identity, which we now realise because we have their beautifully fossilised soft-parts. A case of a 'wolf in sheep's clothing''- Professor David Siveter, University of Leicester

An international team of researchers have made an extremely rare discovery of a species of animal - related to crabs, lobsters and shrimps – that is new to science.

Scientists from the universities of Leicester, Oxford, Imperial and Yale have announced their discovery of a new and scientifically important fossil species of ostracod in the journal, Proceedings of The Royal Society B. The research was funded by the Natural Environment Research Council.

The discovered species, which is up to 10 millimetres long, is special because it is exceptionally well preserved, complete with not only the shell but also the soft parts – its body, limbs, eyes, gills and alimentary system. Such discoveries are extremely rare in the fossil record.

The discovery of the tiny shelled arthropod was made in 425 million year old rocks in Herefordshire, Welsh Borderland. The rocks at the site date to the Silurian period of geological time, when southern Britain was a sea area on a small continent situated in warm, southerly subtropical latitudes. The ostracods and associated marine animals living there were covered by a fall of volcanic ash that preserved them frozen in time.

Professor David Siveter, of the University of Leicester Department of Geology, said: "The two ostracod specimens discovered represent a genus and species new to science, named Pauline avibella. The genus is named in honour of a special person and avibella means 'beautiful bird', so-named because of the fancied resemblance of a prominent feature of the shell to the wing of a bird."

"Ostracods are the most abundant fossil arthropods, occurring ubiquitously as bivalved shells in rocks of the last 490 million years, and are common in most water environments today. The find is important because it is one of only a handful preserving the fossilised soft-tissues of ostracods. Its assignment to a particular group of ostracods based on knowledge of its biology is at odds with its shell form, thus urging caution in interpreting the classification of fossil ostracods based on shell characters alone."

"The preservation of soft-parts of animals is a very rare occurrence in the fossil record and allows unparalleled insight into the ancient biology, community structure and evolution of animals - key facts that that would otherwise be lost to science. The fossils known from the Herefordshire site show soft-part preservation and are of global importance."

The fossils were reconstructed 'virtually', by using a technique that involves grinding each specimen down, layer by layer, and photographing it at each stage. Ten millimetres is relatively tiny, but at an incremental level of 20 µm (micrometres) that yields 500 slices, which can then be pieced together in a computer to provide a full, three-dimensional image of each fossil, outside and in.

Drakozoon in Real 3D!

A unique blob-like creature that lived in the ocean approximately 425 million years ago is revealed in a 3D computer model in research published today in the journal Biology Letters. The model is helping researchers to understand what primitive species on early Earth looked like and how they might have evolved into the types of creatures that are on Earth today.

The scientists, from Imperial College London, have developed a detailed 3D model of the only known fossilised specimen in the world of a creature called Drakozoon. The specimen was found by one of the team approximately 6 years ago in the Herefordshire Lagerstätte, one of England's richest deposits of soft-bodied fossils.

Drakozoon lived in the ocean during the Silurian Period, 444 to 416 million years ago, and today's model hints at how it lived.

The research reveals that Drakozoon was a cone-shaped, blob-like creature with a hood and it probably had a leathery exterior skin. It appears to have survived in the ocean by attaching itself to hard surfaces such as rock. It was approximately 3mm long, and used filament-bearing tentacles to catch and eat organic particles in seawater. It pulled its hood down over its body for protection against predators, pulling it back again to expose its tentacles when danger passed.

Dr Mark Sutton, from the Department of Earth Science and Engineering at Imperial College London, says:

"Excitingly, our 3D model brings back to life a creature that until recently no one knew even existed, and provides us with a window into the life of Drakozoon. We think this tiny blob of jelly survived by clinging onto rocks and hard shelled creatures, making a living by plucking microscopic morsels out of seawater. By looking at this primitive creature, we also get one tantalising step closer to understanding what the earliest creatures on Earth looked like."

Scientists have debated what the first relatives of all creatures on Earth may have resembled and how their bodies evolved. Some scientists think the creatures had repeated units, similar to a caterpillar with its many segments and legs, while others think that their bodies were structured in more free-form ways, similar to slugs.

In today's study, the researchers analysed their 3D model and discovered that Drakozoon had eight deep ridges on either side of its body. They suggest that these deep ridges are the genetic remnants from a time when Drakozoon had a body made of repeated units, supporting the theory that the earliest creatures on Earth were also made of repeated units.

The study shows that Drakozoon was an early member of a major group of invertebrate species called lophophorates. The best known lophophorates are the brachiopods, a type of spineless shellfish that are some of the most common fossils from the Silurian Period. The team found their Drakozoon specimen clinging onto the fossilised shell of a brachiopod.

Wow.

Being on rotation after the power upgrade really, really sux, however.

The Australian Trackways Referenced in the Polish Trackways Paper

Fluviodeltaic sedimentology and ichnology of part of the Silurian Grampians Group, western Victoria


1. C. Gouramanis
2. J. A. Webb (a)
3. A. A. Warren (b)

a. Department of Earth Sciences, La Trobe University, Bundoora, Vic. 3086, Australia.
b. Department of Zoology, La Trobe University, Bundoora, Vic. 3086, Australia.

Abstract:

The mid-Silurian Major Mitchell Sandstone of the Grampians Group outcrops at Mt Bepcha, western Victoria, represent a prograding fluviodeltaic sequence comprising four lithofacies and five ichnofacies. The stratigraphically lowest Interbedded Sandstone/Siltstone Facies is characterised by thin sandstone and siltstone beds with soft-sediment deformation and scours with gravelly lag deposits. This lithofacies contains Thalassinoides, Palaeophycus, Rhizocorallium and intrastratal burrows, together indicative of the Cruziana Ichnofacies, and is interpreted as a shallow-marine depositional environment on a low-energy delta front with minor tidal influences. The overlying Massive Sandstone Facies lacks silt, and consists of predominantly massive and some plane-laminated sandstone, abundant Skolithos linearis , rare Palaeophycus and a single small Cruziana problematica ; the trace-fossil assemblage is assigned to the Skolithos Ichnofacies. This facies is believed to have been deposited in a marine high-energy shoreface environment with continuously shifting sands, affected by periodic flooding events from the mouth of a nearby river. Above this is the Trough Cross-bedded Facies, which contains trough cross-bedding with gravelly lag deposits, a northwest palaeocurrent direction and large Taenidium barretti burrows (Burrowed Ichnofacies). This facies also contains abundant plane-laminated sandstone with a northeast-southwest palaeocurrent direction and ichnofossils of Scoyenia and Daedalus , representing the Scoyenia Ichnofacies. The Trough Cross-bedded Facies is interpreted to have been deposited in shallow low-sinuosity channels by overbank-flooding events, most likely on a delta plain. The uppermost facies, the Plane-laminated Facies, contains thin beds of current-lineated, plane-laminated graded coarse to fine sandstone that preserve arthropod trackways (Arthropod Ichnofacies). This facies was deposited on a periodically sheet-flooded, subaerially exposed delta plain.

Apparently, they found potential tetrapods trackways there. In the Mid Silurian. They were supposed to be very questionable. Not so much now. The authors of the polish trackways make a call not to dismiss these in light of the very nice and very derived trackways in the Holy Cross Mountains.

Does anyone have a more specific subdivision than Mid Silurian?

New Paleozoic Sediment Curve

...A new sediment curve (which shows where sediment-on-the-move is deposited), derived from sediments of the Paleozoic Era 542 to 251 million years ago, scientists report in this week's issue of the journal Science. The sediment curve covers the entire Paleozoic Era.

"The new Paleozoic sea-level sediment curve provides a way of deriving predictive models of sediment migration on continental margins and in interior seaways," said Bilal Haq, lead author of the Science paper and a marine geologist at the National Science Foundation (NSF). The paper's co-author is geologist Stephen Schutter of Murphy Oil International in Houston, Tx.

"The sediment curve is of interest to industry, and also to scientists in academia," said Haq, "as the rise and fall of sea-level form the basis for intepretations of Earth history based on stratigraphy."

Through stratigraphy, the study of rock layering (stratification), scientists can derive a sequence of time and events in a particular region. Recent advances in the field of stratigraphy, including better time-scales for when sediments were deposited, and availability of data on a worldwide basis, are allowing scientists to reconstruct sea level during the Paleozoic.

The rises and falls of sea level during this period form the basis of stratigraphic interpretations of geology not only in the sea, but on land. These sea level increases and decreases are used extensively, Haq said, in predictive models of sediment movements.

The current Science paper is a shorter version of the results of a global synthesis of Paleozoic stratigraphy on which the authors have worked for many years.

news, news, news.