Pondering the Precambrian #9

Proterozoic:

There is evidence from the Proterozoic that Earth's day was 18 hours long.

NeoProterozoic:

Ediacaran:

The evolution of biological productivity and primary producers across the Ediacaran/Cambrian boundary

The Hüttenberg Anomaly appears to have been evidence of the Ediacaran oxygenation event.

Oxygenation variations in the atmosphere and shallow waters in the Yangzte platform.

Did anoxia kill off the Ediacaran benthic communities?

The Doushantuo fossils from China get examined closer.

Bilateral animal trackways and metazoan burrows have been discovered in the Ediacaran Dengying formation.

Two new disc critters from the Ediacaran have been found.  One was named for Sir David Attenborough.  The other for Barrack Obama.

Why did rangeomorphs grew so large during the Ediacaran?

What caused the mass extinction of the Ediacaran Biota?

Cryogenian:

Argonite fans were present in the bottom sediments during the Marinoan Glaciation.

Tonian:

India and Suixian sedimentary group were connected and either were on the margin of the supercontinent of Rodinia or were on a separate plate.

MesoProterozoic:

Evidence of an island arc from the Calymmian has been found.

PaleoProterozoic:

Australia was not connected to Laurentia from 1.8 gya to 1.65 gya during the Nuna/Columbia supercontinet.

During a continent breakup, there appears to have been enhanced terrestrial input into Chinese carbonates.

There is evidence of oceanic crust subduction from China.

During the Siderian, continental microbes and their 'crusts' on rocks might have helped seed the oceans with nitrogen.

Archean:

NeoArchean:

Continents rising above the ocean changed the climate and environment, permanently, on earth.  

Did the dawn of plate tectonics trigger a NeoArchean Snowball Earth episode?

The interplay between crustal arcs and mantle plumes was important in the Archean.

There is no support of wide spread increases in oxygen in shallow waters from South Africa leading up to the Great Oxygenation Event.

MesoArchean:

There might be evidence of two separate turns of the Wilson Cycles in Chinese deposits during the Archean.

Yet, it seems crustal production was periodic prior to 2.7 gya.

PaleoArchean:

Evidence of microbial mats was found from the PaleoArchean.

Hadean:

The Earth might have been able to form a high silica crust during the Hadean, less than 350 million years after its formation.

Origin of Life:

How primordial life might have replicated itself.

Experimental Paleontology:

Fish eggs were used to test how precambrian embryos might have been silicified.  

How Birds got Their Wings

Saccorhytus coronarius: a Basal Deuterostome From the Ediacaran/Cambrian Boundary

Researchers have identified traces of what they believe is the earliest known prehistoric ancestor of humans -- a microscopic, bag-like sea creature, which lived about 540 million years ago.

Named Saccorhytus, after the sack-like features created by its elliptical body and large mouth, the species is new to science and was identified from microfossils found in China. It is thought to be the most primitive example of a so-called "deuterostome" -- a broad biological category that encompasses a number of sub-groups, including the vertebrates.

If the conclusions of the study, published in the journal Nature, are correct, then Saccorhytus was the common ancestor of a huge range of species, and the earliest step yet discovered on the evolutionary path that eventually led to humans, hundreds of millions of years later.

link.

Tumor Found in 255 Million Year old Gorgonopsid Tooth Fossil

When paleontologists at the University of Washington cut into the fossilized jaw of a distant mammal relative, they got more than they bargained for -- more teeth, to be specific.

As they report in a letter published Dec. 8 in the Journal of the American Medical Association Oncology, the team discovered evidence that the extinct species harbored a benign tumor made up of miniature, tooth-like structures. Known as a compound odontoma, this type of tumor is common to mammals today. But this animal lived 255 million years ago, before mammals even existed.

"We think this is by far the oldest known instance of a compound odontoma," said senior author Christian Sidor, a UW professor of biology and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture. "It would indicate that this is an ancient type of tumor."

Before this discovery, the earliest known evidence of odontomas came from Ice Age-era fossils.

"Until now, the earliest known occurrence of this tumor was about one million years ago, in fossil mammals," said Judy Skog, program director in the National Science Foundation's Division of Earth Sciences, which funded the research. "These researchers have found an example in the ancestors of mammals that lived 255 million years ago. The discovery suggests that the suspected cause of an odontoma isn't tied solely to traits in modern species, as had been thought."

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Evidence Pareiasaurs had a Lifestyle Very Different From Modern Megafauna

Bone microstructure of pareiasaurs (Parareptilia) from the Karoo Basin, South Africa: implications for growth strategies and lifestyle habits

Authors:

Canoville et al

Abstract:

Numerous morphological studies have been carried out on pareiasaurs; yet their taxonomy and biology remain incompletely understood. Earlier works have suggested that these herbivorous parareptiles had a short juvenile period as compared to the duration of adulthood. Several studies further suggested an (semi-) aquatic lifestyle for these animals, but more recent investigations have proposed a rather terrestrial habitat.

Bone paleohistology is regarded as a powerful tool to assess aspects of tetrapod paleobiology, but few studies have been conducted on pareiasaurs. The present study assesses intra and inter-specific histovariability of pareiasaurs and provides fresh insights into their paleobiology, thereby permitting a re-evaluation of earlier hypotheses. Our sample comprises various skeletal elements and several specimens covering most of the taxonomic and stratigraphic spectrum of South African pareiasaurs, including large and basal forms from the Middle Permian, as well as smaller and more derived forms from the Late Permian.

Our results concerning size of elements and histological tissues show that for pareiasaurs, element size is not a good indicator of ontogenetic age, and furthermore, suggest that the specific diversity of the Middle Permian pareiasaurs may have been underestimated. The bone histology of these animals shows that they experienced a relatively rapid growth early in ontogeny. The periosteal growth later slowed down, but seems to have been protracted for several years during adulthood. Pareiasaur bone microanatomy is unusual for continental tetrapods, in having spongious stylopod diaphyses and thin compact cortices. Rigorous paleoecological interpretations are thus limited since no modern analogue exists for these animals.

Nasutoceratopsini Ceratopsian From Campanian Cretaceous Alberta, Canada

A basal ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada

Authors:

Ryan et al

Abstract:

A partial skull (CMN 8804) of a ceratopsid from the upper unit of the Campanian Oldman Formation of Alberta is the first Canadian example of the newly established Nasutoceratopsini, a new subclade of Centrosaurinae defined as the stem-based clade of centrosaurine ceratopsids more closely related to Nasutoceratops titusi than to Centrosaurus apertus. The new clade is diagnosed, in part, by having a parietosquamosal frill lacking modified epimarginals; a small nasal horncore; large, rostrolaterally directed postorbital horncores; and a relatively short, deep face. Although the CMN 8804 taxon closely resembles Nasutoceratops, its phylogenetic position within Nasutoceratopsini is unresolved. The CMN 8804 taxon would have been contemporaneous with dinosaurs from the lower portion of the Dinosaur Park Formation 200 km to the northwest in Dinosaur Provincial Park. The presence of the CMN 8804 taxon in Alberta, and the approximately contemporaneous Nasutoceratops in Utah, indicates that the nasutoceratopsins persisted in both north and south Laramidia well after the first appearance (i.e., Coronosaurus brinkmani) of the newly defined Centrosaurini. This stem-based clade is composed of centrosaurine ceratopsids with well-adorned parietosquamosal frills and short postorbital horncores that are more closely related to Centrosaurus apertus than Pachyrhinosaurus canadensis. The rarity of nasutoceratopsins in the well-sampled sediments of Laramidia suggests that they may have had different ecological preferences than centrosaurins, or that their relatively non-diagnostic, fragmentary remains may be misidentified as other centrosaurins. The temporally (∼79–76 Ma) and geographically (Utah to Alberta) large distributions of Nasutoceratopsini weakens the hypothesis of distinct north and south Laramidian provinciality.

A FEATHERED Dinosaur Tail Found Trapped in Amber From Cenomanian Cretaceous Myanmar

A Feathered Dinosaur Tail with Primitive Plumage Trapped in Mid-Cretaceous Amber

Authors:

Xi et al

Abstract:

In the two decades since the discovery of feathered dinosaurs, the range of plumage known from non-avialan theropods has expanded significantly, confirming several features predicted by developmentally informed models of feather evolution. However, three-dimensional feather morphology and evolutionary patterns remain difficult to interpret, due to compression in sedimentary rocks. Recent discoveries in Cretaceous amber from Canada, France, Japan, Lebanon, Myanmar, and the United States reveal much finer levels of structural detail, but taxonomic placement is uncertain because plumage is rarely associated with identifiable skeletal material. Here we describe the feathered tail of a non-avialan theropod preserved in mid-Cretaceous (∼99 Ma) amber from Kachin State, Myanmar, with plumage structure that directly informs the evolutionary developmental pathway of feathers. This specimen provides an opportunity to document pristine feathers in direct association with a putative juvenile coelurosaur, preserving fine morphological details, including the spatial arrangement of follicles and feathers on the body, and micrometer-scale features of the plumage. Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis. Beneath the feathers, carbonized soft tissues offer a glimpse of preservational potential and history for the inclusion; abundant Fe2+ suggests that vestiges of primary hemoglobin and ferritin remain trapped within the tail. The new finding highlights the unique preservation potential of amber for understanding the morphology and evolution of coelurosaurian integumentary structures.

Synapsids Developed the Diaphragm for Breathing Very Early

A caseian point for the evolution of a diaphragm homologue among the earliest synapsids

Authors:

Lambertz et al

Abstract:

The origin of the diaphragm remains a poorly understood yet crucial step in the evolution of terrestrial vertebrates, as this unique structure serves as the main respiratory motor for mammals. Here, we analyze the paleobiology and the respiratory apparatus of one of the oldest lineages of mammal-like reptiles: the Caseidae. Combining quantitative bone histology and functional morphological and physiological modeling approaches, we deduce a scenario in which an auxiliary ventilatory structure was present in these early synapsids. Crucial to this hypothesis are indications that at least the phylogenetically advanced caseids might not have been primarily terrestrial but rather were bound to a predominantly aquatic life. Such a lifestyle would have resulted in severe constraints on their ventilatory system, which consequently would have had to cope with diving-related problems. Our modeling of breathing parameters revealed that these caseids were capable of only limited costal breathing and, if aquatic, must have employed some auxiliary ventilatory mechanism to quickly meet their oxygen demand upon surfacing. Given caseids’ phylogenetic position at the base of Synapsida and under this aquatic scenario, it would be most parsimonious to assume that a homologue of the mammalian diaphragm had already evolved about 50 Ma earlier than previously assumed.

pop sci write up.

Romer's Gap Plugged: 5 new Tetrapods From Tournaisian Mississippian Carboniferous Scotland

Phylogenetic and environmental context of a Tournaisian tetrapod fauna

Authors:

Clack et al

Abstract:

The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

pop sci write up.

Ozimek volans: a Carnian Triassic Gliding Protorosaur

An early Late Triassic long-necked reptile with a bony pectoral shield and gracile appendages

Authors:

Dzik et al

Abstract:

Several partially articulated specimens and numerous isolated bones of Ozimek volans gen. et sp. nov., from the late Carnian lacustrine deposits exposed at Krasiejów in southern Poland, enable a reconstruction of most of the skeleton. The unique character of the animal is its enlarged plate-like coracoids presumably fused with sterna. Other aspects of the skeleton seem to be comparable to those of the only known specimen of Sharovipteryx mirabilis from the latest Middle Triassic of Kyrgyzstan, which supports interpretation of both forms as protorosaurians. One may expect that the pectoral girdle of S. mirabilis, probably covered by the rock matrix in its only specimen, was similar to that of O. volans gen. et sp. nov. The Krasiejów material shows sharp teeth, low crescent scapula, three sacrals in a generalized pelvis (two of the sacrals being in contact with the ilium) and curved robust metatarsal of the fifth digit in the pes, which are unknown in Sharovipteryx. Other traits are plesiomorphic and, except for the pelvic girdle and extreme elongation of appendages, do not allow to identify any close connection of the sharovipterygids within the Triassic protorosaurians.

Evidence of Simple Multicellarity in Tonian NeoProterozoic Fossils From China

Electron microscopy reveals evidence for simple multicellularity in the Proterozoic fossil Chuaria

Authors:

Tang et al

Abstract:

Multicellularity arose multiple times in the evolutionary history of eukaryotes, and simple multicellularity may have a deep history tracing back to the Paleoproterozoic. However, complex multicellular organisms with cellular and tissue differentiation did not appear in the fossil record until the Mesoproterozoic, and it is not until the Ediacaran Period (635–541 Ma) when diverse assemblages of complex multicellular eukaryotes evolved. In the intervening Tonian Period (ca. 1000–720 Ma), the fossil record of multicellular organisms is poorly documented. To address this knowledge gap, we investigated Chuaria and associated carbonaceous compression fossils from the Tonian Liulaobei Formation in North China. These fossils have been variously interpreted as unicellular or multicellular organisms. Our analysis using backscattered-electron scanning electron microscopy (BSE-SEM) revealed direct evidence for simple multicellularity in some of these fossils and suggests that Chuaria may have had a multicellular vegetative stage in its life cycle. This study demonstrates that BSE-SEM has the potential to unveil the hidden diversity of multicellular organisms in the Tonian Period, thus enriching our knowledge about the multiple origins of multicellularity in this critical geological period before Cryogenian glaciations.

Were Gorgonopsid Sabre Teeth for Mating Display Purposes?!

Hollywood celebrities spend large amounts of dollars on it. The hunky stud at the local pub thinks he knows it. But the age-old secret has been carefully kept for millions of years. Yet, it seemed obvious to pre-mammalian reptiles that went so far as to evolve mouths full of beautifully crafted teeth. It's your beautifully bleached smile that makes you sexy!

Mammals, like us, have a set of dentition that are neatly divided into three distinct types of teeth -- the incisors at the front of your mouth, the molars in your cheeks, and the canines, that Dracula-type teeth that separates the molars from the incisors. The origin of this separation can be traced back to 300 million years ago, when our ancestors still looked like sprawling reptiles, the pre-mammalian therapsids.

These creatures, like the gorgonopsians (a group of therapsids), had long, sometimes sabre-like canines that was often interpreted as a deadly hunting device. However, there was a problem. Some herbivorous species that only grazed on plants, like the dicynodonts (herbivorous animals, varying in sizes from a rat to an ox, and like warthogs, had two tusks, that gave them their name, which means "two dog tooth").

So, if not for hunting, what were these impressive sets of pointy teeth for? Defence against predators? Nope! These prehistoric characters used them to seduce the beauties!

link.

The rebuttal to this would be immediately after the gorgons went extinct, a therocephalian genus went through rapid convergent evolution to develop its own sabre teeth implying there was an empty ecological niche.

Ernietta from the late Edicaran NeoProterozoic Namibia was Weirdly Assymetrical

Ernietta from the late Edicaran Nama Group, Namibia

Authors:

Elliott

Abstract:

Ernietta plateauensis Pflug, 1966 is the type species of the Erniettomorpha, an extinct clade of Ediacaran life. It was likely a gregarious, partially infaunal organism. Despite its ecological and taxonomic significance, there has not been an in-depth systematic description in the literature since the original description fell out of use. A newly discovered field site on Farm Aar in southern Namibia has yielded dozens of specimens buried in original life position. Mudstone and sandstone features associated with the fossils indicate that organisms were buried while still exposed to the water column rather than deposited in a flow event. Ernietta plateauensis was a sac-shaped erniettomorph with a body wall constructed from a double layer of tubes. It possessed an equatorial seam lying perpendicular to the tubes. The body is asymmetrical on either side of this seam. The tubes change direction along the body length and appear to be constricted together in the dorsal part of the organism.

A New Dinosauromorph & Carnivorous Sauropod Ancestor Fossils Discovered in Norian/Rhaetian Triassic Brazil

A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet

Authors:

Cabreira et al

Abstract:

Dinosauromorpha includes dinosaurs and other much less diverse dinosaur precursors of Triassic age, such as lagerpetids [1]. Joint occurrences of these taxa with dinosaurs are rare but more common during the latest part of that period (Norian-Rhaetian, 228–201 million years ago [mya]) [2, 3]. In contrast, the new lagerpetid and saurischian dinosaur described here were unearthed from one of the oldest rock units with dinosaur fossils worldwide, the Carnian (237–228 mya) Santa Maria Formation of south Brazil [4], a record only matched in age by much more fragmentary remains from Argentina [5]. This is the first time nearly complete dinosaur and non-dinosaur dinosauromorph remains are found together in the same excavation, clearly showing that these animals were contemporaries since the first stages of dinosaur evolution. The new lagerpetid preserves the first skull, scapular and forelimb elements, plus associated vertebrae, known for the group, revealing how dinosaurs acquired several of their typical anatomical traits. Furthermore, a novel phylogenetic analysis shows the new dinosaur as the most basal Sauropodomorpha. Its plesiomorphic teeth, strictly adapted to faunivory, provide crucial data to infer the feeding behavior of the first dinosaurs.

Litorosuchus somnii: A new Armored and Aquatic Archosauriform From Ladinian Triassic China

A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria

Authors:

Li et al

Abstract:

Reptiles have a long history of transitioning from terrestrial to semi-aquatic or aquatic environments that stretches back at least 250 million years. Within Archosauria, both living crocodylians and birds have semi-aquatic members. Closer to the root of Archosauria and within the closest relatives of the clade, there is a growing body of evidence that early members of those clades had a semi-aquatic lifestyle. However, the morphological adaptations to a semi-aquatic environment remain equivocal in most cases. Here, we introduce a new Middle Triassic (245–235 Ma) archosauriform, Litorosuchus somnii, gen. et sp. nov., based on a nearly complete skeleton from the Zhuganpo Member (Ladinian [241–235 Ma]) of the Falang Formation, Yunnan, China. Our phylogenetic analyses suggest that Litorosuchus is a stem archosaur closely related to the aberrant Vancleavea just outside of Archosauria. The well-preserved skeleton of L. somnii bears a number of morphological characters consistent with other aquatic-adapted tetrapods including: a dorsally directed external naris, tall neural spines and elongate chevrons in an elongated tail, a short and broad scapula, webbed feet, long cervical vertebrae with long slender ribs, and an elongated rostrum with long and pointed teeth. Together these features represent one of the best-supported cases of a semi-aquatic mode of life for a stem archosaur. Together with Vancleavea campi, the discovery of L. somnii demonstrates a growing body of evidence that there was much more diversity in mode of life outside Archosauria. Furthermore, L. somnii helps interpret other possible character states consistent with a semi-aquatic mode of life for archosauriforms, including archosaurs.

A Fossilized Dinosaur Brain was Found

An unassuming brown pebble, found more than a decade ago by a fossil hunter in Sussex, has been confirmed as the first example of fossilised brain tissue from a dinosaur.

The fossil, most likely from a species closely related to Iguanodon, displays distinct similarities to the brains of modern-day crocodiles and birds. Meninges - the tough tissues surrounding the actual brain - as well as tiny capillaries and portions of adjacent cortical tissues have been preserved as mineralised 'ghosts'.

The results are reported in a Special Publication of the Geological Society of London, published in tribute to Professor Martin Brasier of the University of Oxford, who died in 2014. Brasier and Dr David Norman from the University of Cambridge co-ordinated the research into this particular fossil during the years prior to Brasier's untimely death in a road traffic accident.

The fossilised brain, found by fossil hunter Jamie Hiscocks near Bexhill in Sussex in 2004, is most likely from a species similar to Iguanodon: a large herbivorous dinosaur that lived during the Early Cretaceous Period, about 133 million years ago.

Finding fossilised soft tissue, especially brain tissue, is very rare, which makes understanding the evolutionary history of such tissue difficult. "The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing," said co-author Dr Alex Liu of Cambridge's Department of Earth Sciences, who was one of Brasier's PhD students in Oxford at the time that studies of the fossil began.

link.

2nd link.

Ediacaran Soft Bodied Fossils Were Preserved due to Silicia Rich Oceans?

Exceptional preservation of soft-bodied Ediacara Biota promoted by silica-rich oceans

Authors:

Tarhan et al

Abstract:

The Ediacara Biota, Earth's earliest fossilized ecosystem of complex, macroscopic, multicellular organisms, occurs in terminal Ediacaran strata worldwide, yet how the fossils are preserved remains controversial. Ediacara assemblages consist of exceptionally preserved soft-bodied forms of enigmatic morphology and phylogenetic affinity. Many of these fossil assemblages are anactualistically preserved as casts and molds in sandstones ("Ediacara-style" preservation). Here we present evidence from the Ediacara Member of South Australia that Ediacara-style preservation was due to rapid, early-stage precipitation of silica cements, facilitated by the high silica saturation state of the oceans prior to the appearance of prolific silica biomineralizers. An early silicification model provides a coherent, mechanistic and empirically supported explanation for the widespread preservation of soft-bodied organisms of Ediacaran–early Paleozoic age as sandstone casts and molds. The prevalence of early silicification confirms that Ediacara-style fossil assemblages can provide an accurate window into life on the Ediacaran seafloor that can be used to reconstruct critical steps in the development and diversification of early animal ecosystems.

Aptenoperissus burmanicus: A Wingless Parasitic Wasp Found in Cretaceous Burmese Amber

Bizzare wingless parasitic wasp from mid-Cretaceous Burmese amber (Hymenoptera, Ceraphronoidea, Aptenoperissidae fam. nov.)

Authors:

Rasnitsyn et al

Abstract:

A strange wingless female parasitic wasp from mid-Cretaceous Burmese amber is described as Aptenoperissus burmanicus sp. et gen. nov. in the new family Aptenoperissidae (Hymenoptera, Ceraphronoidea). Diagnostic characters of the female Aptenoperissus burmanicus sp. et gen. nov. include its wingless, streamlined and heavily sclerotized body lacking any apparent trace of a wasp waist, and geniculate antenna composed of a long, thin, stick-like scape, standard pedicel and 22 uniform flagellomeres. Also the body has 9 externally visible segments with no evidence of segment fusion implying the presence of a completely hidden segment. All tibiae have paired spurs and the hind femora are saltatory and incrassate. The double fore-tibial spur combined with unquestionable diagnostic features of Apocrita (primarily an internalized needle-like thin and acute ovipositor) suggest placement within the superfamily Ceraphronoidea s.str. with the Maimetshidae as a sister group of the crown Ceraphronoidea, composed of the Ceraphronidae, Megaspilidae, Stigmaphronidae, and Radiophronidae. The fossil is hypothesized to live semicryptically on the forest floor or tree trunk and to parasitize immature holometabolous insects. Diagnostic features of a respective male are suggested to test the hypothesized position of the new taxon.

Triopticus primus: a Triassic Archosauromorph Convergent With Pachycephalosaur Dinosaurs

A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives

Authors:

Stocker et al

Abstract:

Similarities in body plan evolution, such as wings in pterosaurs, birds, and bats or limblessness in snakes and amphisbaenians, can be recognized as classical examples of convergence among animals [1, 2, 3]. We introduce a new Triassic stem archosaur that is unexpectedly and remarkably convergent with the “dome-headed” pachycephalosaur dinosaurs that lived over 100 million years later. Surprisingly, numerous additional taxa in the same assemblage (the Otis Chalk assemblage from the Dockum Group of Texas) demonstrate the early acquisition of morphological novelties that were later convergently evolved by post-Triassic dinosaurs. As one of the most successful clades of terrestrial vertebrates, dinosaurs came to occupy an extensive morphospace throughout their diversification in the Mesozoic Era [4, 5], but their distant relatives were first to evolve many of those “dinosaurian” body plans in the Triassic Period [6, 7, 8]. Our analysis of convergence between archosauromorphs from the Triassic Period and post-Triassic archosaurs demonstrates the early and extensive exploration of morphospace captured in a single Late Triassic assemblage, and we hypothesize that many of the “novel” morphotypes interpreted to occur among archosaurs later in the Mesozoic already were in place during the initial Triassic archosauromorph, largely non-dinosaurian, radiation and only later convergently evolved in diverse dinosaurian lineages.

link.

Evidence of Eukaryote Fossils From the NeoArchean?

Tubular microfossils from ∼2.8 – 2.7 Ga-old lacustrine deposits of South Africa: a sign for early origin of eukaryotes?

Authors:

Kaźmierczak et al

Abstract:

Unequivocal evidence for Archean eukaryotic life has been long sought for and is a matter of lively debate. In the absence of unambiguous fossils this debate has focused on biogeochemical signatures and molecular phylogenies. Most researchers agree that fossil forms comparable with modern eukaryotic cells can be credibly identified only in Proterozoic (∼1.8-1.6 Ga) and younger rocks. Herein, we report for the first time, Neoarchean mineralized tubular microfossils from ∼2.8-2.7 Ga lacustrine deposits of South Africa. The exceptional preservation of these microfossils allows recognition of important morphological details in petrographic thin section and in HF-macerates that links them to modern siphonous (coenocytic) green or yellow-green microalgae (Chlorophyta and Xanthophyta). The microfossil identification is supported by Raman spectroscopic analyses, EPMA, SEM/BSE and SEM/EDS microprobe analytical results, NanoSIMS elemental mapping and micro-tomographic sectioning of the thalli. All results point to indigenous, bona fide eukaryotic microfossils of algal affinity. These Neoarchean microalgae-like remains and their assumingly combined in vivo and early post-mortem precipitated mineral envelopes greatly improve our knowledge of early life and its habitats and may have far-reaching consequences for the studies of the evolution of life.