Well-preserved Fossil Research Articles

Spathiurus dorsalis Davis, 1887, from the Upper Cretaceous of Haqel, Lebanon, and the evolutionary history of Ionoscopiformes

New and well-preserved fossil fish material from the Upper Cretaceous (Cenomanian) of Haqel, Lebanon, is assigned to Spathiurus dorsalis Davis, 1887. Spathiurus dorsalis and Amphilaphurus major are found to be synonymous. A complete re-description of this taxon is provided and delivers new recognized anatomical information, mainly cranial features. Spathiurus dorsalis displays diagnostic characters of ionoscopids and consequently is designated as a new member of this family. A phylogenetic analysis was performed to place this taxon within the Halecomorphi. The studied taxon was recovered as the sister genera of Ionoscopus petrarojae, both derived compared to ‘Ionoscopus’ cyprinoides, suggesting that the latter should be placed in a distinct genus. The validated placement of Spathiurus within the Ionoscopidae extends the stratigraphic range of this family from the Albian to the Cenomanian and becomes the first record of an ionoscopiform from the Upper Cretaceous and from the Middle East.

Elevated CO<sub>2</sub>, increased leaf-level productivity, and water-use efficiency during the early Miocene

Abstract. Rising atmospheric CO2 is expected to increase global temperatures, plant water-use efficiency, and carbon storage in the terrestrial biosphere. A CO2 fertilization effect on terrestrial vegetation is predicted to cause global greening as the potential ecospace for forests expands. However, leaf-level fertilization effects, such as increased productivity and water-use efficiency, have not been documented from fossil leaves in periods of heightened atmospheric CO2. Here, we use leaf gas-exchange modeling on a well-preserved fossil flora from early Miocene New Zealand, as well as two previously published tropical floras from the same time period, to reconstruct atmospheric CO2, leaf-level productivity, and intrinsic water-use efficiency. Leaf gas-exchange rates reconstructed from early Miocene fossils, which grew at southern temperate and tropical latitudes when global average temperatures were 5–6 ∘C higher than today, reveal that atmospheric CO2 was ∼450–550 ppm. Early Miocene CO2 was similar to projected values for 2040 CE and is consistent with an Earth system sensitivity of 3–7 ∘C to a doubling of CO2. The Southern Hemisphere temperate leaves had higher reconstructed productivity than modern analogs, likely due to a longer growing season. This higher productivity was presumably mirrored at northern temperate latitudes as well, where a greater availability of landmass would have led to increased carbon storage in forest biomass relative to today. Intrinsic water-use efficiency of both temperate and tropical forest trees was high, toward the upper limit of the range for modern trees, which likely expanded the habitable range in regions that could not support forests with high moisture demands under lower atmospheric CO2. Overall, early Miocene elevated atmospheric CO2 sustained globally higher temperatures, and our results provide the first empirical evidence of concomitant enhanced intrinsic water-use efficiency, indicating a forest fertilization effect.

Effects of seawater Mg2+ /Ca2+ ratio and diet on the biomineralization and growth of sea urchins and the relevance of fossil echinoderms to paleoenvironmental reconstructions.

It has been argued that skeletal Mg/Ca ratio in echinoderms is mostly governed by Mg2+ and Ca2+ concentrations in the ambient seawater. Accordingly, well-preserved fossil echinoderms were used to reconstruct Phanerozoic seawater Mg2+ /Ca2+ ratio. However, Mg/Ca ratio in echinoderm skeleton can be affected by a number of environmental and physiological factors, the effects of which are still poorly understood. Notably, experimental data supporting the applicability of echinoderms in paleoenvironmental reconstructions remain limited. Here, we investigated the effect of ambient Mg2+ /Ca2+ seawater ratio and diet on skeletal Mg/Ca ratio and growth rate in two echinoid species (Psammechinus miliaris and Prionocidaris baculosa). Sea urchins were tagged with manganese and then cultured in different Mg2+ /Ca2+ conditions to simulate fluctuations in the Mg2+ /Ca2+ seawater ratios in the Phanerozoic. Simultaneously, they were fed on a diet containing different amounts of magnesium. Our results show that the skeletal Mg/Ca ratio in both species varied not only between ossicle types but also between different types of stereom within a single ossicle. Importantly, the skeletal Mg/Ca ratio in both species decreased proportionally with decreasing seawater Mg2+ /Ca2+ ratio. However, sea urchins feeding on Mg-enriched diet produced a skeleton with a higher Mg/Ca ratio. We also found that although incubation in lower ambient Mg2+ /Ca2+ ratio did not affect echinoid respiration rates, it led to a decrease or inhibition of their growth. Overall, these results demonstrate that although skeletal Mg/Ca ratios in echinoderms can be largely determined by seawater chemistry, the type of diet may also influence skeletal geochemistry, which imposes constraints on the application of fossil echinoderms as a reliable proxy. The accuracy of paleoseawater Mg2+ /Ca2+ calculations is further limited by the fact that Mg partition coefficients vary significantly at different scales (between species, specimens feeding on different types of food, different ossicle types, and stereom types within a single ossicle).

The first theropod dinosaur (Coelurosauria, Theropoda) from the base of the Romualdo Formation (Albian), Araripe Basin, Northeast Brazil

The Romualdo Formation (Araripe Basin) is worldwide known for the large number of well-preserved fossils but the dinosaur record is rather scarce. Here we describe a new coelurosaur, which is the first tetrapod recovered from the basal layers of this stratigraphic unit that consist of dark shales. Aratasaurus museunacionali gen. et sp. nov. is known by an incomplete but articulated right hind limb with the distal portion of the femur, proximal half of tibia and incomplete pes. The new species differs from other coelurosaurs by a medial fossa in the tibia and digits II, III and IV being symmetric. The phylogenetic analysis recovered Aratasaurus museunacionali closely related to Zuolong salleei, forming a basal coelurosaur lineage. The paleohistology indicate that the specimen is a juvenile, with an estimated body length around 3.12 m. The new taxon represents the first occurrence of basal coelurosaurians in the Araripe Basin and suggests a widespread distribution of this group during the Lower Cretaceous.

Lontras Shale (Paraná Basin, Brazil): Insightful analysis and commentaries on paleoenvironment and fossil preservation into a deglaciation pulse of the Late Paleozoic Ice Age

The Lontras Shale is a fossil site located in Mafra, Santa Catarina, south of Brazil. This Late Paleozoic (Pennsilvanian - Cisularian) stratum holds an important place with great potential for the synthesis of knowledge about paradigmatic events that happened on Gondwana. This marine fossil site, preserved into a 1.1 m black shale, comprises a combination of different kinds of preservation, in broad taphonomical spectra, including hard and/or soft-tissues of aquatic (e.g., fishes, poriferans and ammonoids) and terrestrial biotas (e.g., insect and woods), among other organisms that were well preserved under still unrevealed process and conditions. Considering the prevailing depositional settings and aiming to present fossil diagenetic aspects that led to some special preservation modes, we performed chemical analyses of sponges and insects by means of energy-dispersive spectroscopy (EDS), synchrotron micro-X-ray fluorescence (micro-XRF) and Raman spectroscopy. To date, we have identified the majority of fossils preserved as carbonaceous compressions or phosphatized forms. The well-preserved fossils have so far permitted new insights into metazoan evolution, especially regarding Insecta, Porifera, and Conodonta. Our findings not only allow suggestions regarding the chemical remains of soft tissues on these specimens but also can provide background data for future analyses of these groups in similar depositional settings.

Shell chemistry of the boreal Campanian bivalve <i>Rastellum diluvianum</i> (Linnaeus, 1767) reveals temperature seasonality, growth rates and life cycle of an extinct Cretaceous oyster

Abstract. The Campanian age (Late Cretaceous) is characterized by a warm greenhouse climate with limited land-ice volume. This makes this period an ideal target for studying climate dynamics during greenhouse periods, which are essential for predictions of future climate change due to anthropogenic greenhouse gas emissions. Well-preserved fossil shells from the Campanian (±78 Ma) high mid-latitude (50∘ N) coastal faunas of the Kristianstad Basin (southern Sweden) offer a unique snapshot of short-term climate and environmental variability, which complements existing long-term climate reconstructions. In this study, we apply a combination of high-resolution spatially resolved trace element analyses (micro-X-ray fluorescence – µXRF – and laser ablation inductively coupled plasma mass spectrometry – LA-ICP-MS), stable isotope analyses (IRMS) and growth modeling to study short-term (seasonal) variations recorded in the oyster species Rastellum diluvianum from the Ivö Klack locality. Geochemical records through 12 specimens shed light on the influence of specimen-specific and ontogenetic effects on the expression of seasonal variations in shell chemistry and allow disentangling vital effects from environmental influences in an effort to refine paleoseasonality reconstructions of Late Cretaceous greenhouse climates. Growth models based on stable oxygen isotope records yield information on the mode of life, circadian rhythm and reproductive cycle of these extinct oysters. This multi-proxy study reveals that mean annual temperatures in the Campanian higher mid-latitudes were 17 to 19 ∘C, with winter minima of ∼13 ∘C and summer maxima of 26 ∘C, assuming a Late Cretaceous seawater oxygen isotope composition of −1 ‰ VSMOW (Vienna standard mean ocean water). These results yield smaller latitudinal differences in temperature seasonality in the Campanian compared to today. Latitudinal temperature gradients were similar to the present, contrasting with previous notions of “equable climate” during the Late Cretaceous. Our results also demonstrate that species-specific differences and uncertainties in the composition of Late Cretaceous seawater prevent trace element proxies (Mg∕Ca, Sr∕Ca, Mg∕Li and Sr∕Li) from being used as reliable temperature proxies for fossil oyster shells. However, trace element profiles can serve as a quick tool for diagenesis screening and investigating seasonal growth patterns in ancient shells.

Formation of Siderite in Microbial Microcosms Derived from a Marine Sediment

Exceptionally well-preserved fossils are frequently encased by carbonate concretions. The initial steps of their formation in marine and freshwater sediments are induced by microbial activity. The role of the involved microbial communities, however, is not well understood. In this study, siderite (FeCO3) formation in microbial microcosms is observed, with various fatty acyl compounds (lipids, surfactants) as substrates and Wadden Sea sediment samples as inocula. In actively growing microcosms, sulfate-reducing bacteria (the genus Desulfofrigus in particular) dominate the microbial community and submicroscopic siderite precipitates on bacterial cell surfaces were identified. We suggest that these biologically induced mineralization processes may, in the natural environment, initiate the formation of large concretions under suboxic conditions in coastal sediments.

ŻYCIE I ŚMIERĆ PÓŹNOJURAJSKICH SKRZYPŁOCZY (XIPHOSURA) Z OWADOWA-BRZEZINEK W ŚWIETLE INTERDYSCYPLINARNYCH BADAŃ PALEOŚRODOWISKOWYCH

Skrzypłocze (Xiphosura) są jednymi z najdziwniejszych istot w królestwie zwierząt. Grupa ta, współcześnie obejmująca cztery reliktowe gatunki, przetrwała właściwie niezmieniona od ordowiku (480 milionów lat), i była świadkiem masowych wymierań, stąd powszechnie używana jest jako przykład „żywych skamieniałości” lub „stabilomorfów”. Niniejsza praca poświęcona jest opisowi nowych i doskonale zachowanych skamieniałości skrzypłoczy z górnej jury (tyton) kamieniołomu Owadów-Brzezinki, który jest jednym z najważniejszych stanowisk paleontologicznych opisanych w ostatnim czasie w Polsce. Kamieniołom ten znany jest z wyjątkowo dobrze zachowanych skamieniałości organizmów morskich i lądowych. Odkrycie licznych okazów młodocianych skrzypłoczy w kamieniołomie Owadów-Brzezinki stanowi istotny wkład w badania nad paleobiologią tych stawonogów oraz paleoekologią ich środowiska życia. Praca ta podsumowuje ostatnie badania nad tymi unikatowymi skamieniałościami i tym, jaki wkład badania te wnoszą w lepsze poznanie tej grupy zwierząt. Szczegółowe oględziny doskonale zachowanych egzoszkieletów tych skrzypłoczy, a także analiza osadu, w którym je znaleziono, pozwoliły na stworzenie scenariusza paleośrodowiskowego, według którego najbardziej prawdopodobną przyczyną epizodu masowej śmiertelności skrzypłoczy była infekcja glonowa.

SIMS U-Pb geochronology for the Jurassic Yanliao Biota from Bawanggou section, Qinglong (northern Hebei Province, China)

ABSTRACT The Yanliao Biota is notable for producing rare and well-preserved Jurassic vertebrate fossils. Many discoveries in the Bawanggou section, northern Hebei Province have greatly enhanced our knowledge of important vertebrate fossils from the Yanliao Biota, including an arboreal euharamiyidan mammal, maniraptoran theropods, salamanders and pterosaurs. However, lacking of precise dating for the sediments bearing these fossils in the Bawanggou section hampered further understanding of the evolution of this biota. Here we report a chronology based on secondary ion mass spectrometry (SIMS) U-Pb zircon analyses from the Tiaojishan Formation bearing the Yanliao Biota in the Bawanggou section. Three bentonite layers dated to 159.0 ± 1.1 Ma, 159.5 ± 0.8 Ma, and 159.8 ± 0.8 Ma, respectively, were found to be interstratified with the fossil-bearing layer in this area. These data place the Yanliao Biota from Qinglong in the Oxfordian Stage of the Upper Jurassic and provide stringent constraints on vertebrates discovered in the Bawanggou section. Previous biostratigraphic studies and our geochronology show that fossil assemblage in the Bawanggou section is coeval with the Linglongta Biota (late Yanliao Biota) preserved in the Daxishan section (western Liaoning Province).

Mesozoic sooty mould beetles as living relicts in New Zealand.

New Zealand is an island continent that completed its split from the Gondwanan continent at 52 Ma, harbouring an iconic biota of tuatara, kiwi and weta. The sooty mould community is a distinctive trophic element of New Zealand forest ecosystems that is driven by plant-feeding sternorrhynchan Hemiptera. These produce honeydew, which supports fungal growth, which in turn supports numerous endemic invertebrates, including endemic New Zealand beetle families. Ancient New Zealand insect fossils are rare but a single fossil of a sooty mould cyclaxyrid was recently described from Cretaceous Burmese amber, a family that was previously known from two extant New Zealand species. Well-preserved fossils like this one are recasting Earth history, and, based on a wealth of additional specimens, we re-evaluate the taxonomy of Cretaceous cyclaxyrids and one Eocene species here transferred to Cyclaxyridae. Cyclaxyridae are highly tied to the sooty mould community and have now been discovered to occur in disparate biogeographic realms in deep time. Our discovery indicates that the family, and perhaps the sooty mould community in general, was widespread in Pangaea from at least the Cretaceous and survived as a relict in New Zealand. Persistence of a sooty mould ecosystem in New Zealand and fungal specialization may not necessarily be an evolutionary 'dead-end' for cyclaxyrids and other insects.

A New Genus and Species of Lymexylidae (Insecta: Coleoptera) from Mid-Cretaceous Amber of Northern Myanmar

The ship-timber beetle Cretoquadratus engeli gen. et sp.n. has been described and classified based on a moderately well-preserved fossil specimen found inside mid-Cretaceous amber from the Hukawng Valley in northern Myanmar. The newly created taxon is placed within Atractocerinae, and the new species can be easily distinguished from all other extinct and recent members of the subfamily due to the presence of media veins and branches, including M1, M2, M3, and M4. Cretoquadratus engeli is the oldest known representative of (Atractocerinae) Lymexylidae, with the exception of Cratoatractocerus grimaldii Wolf-Schwenninger, 2011, which was deposited in the Lower Cretaceous of Brazil. The palaeobiomigratory significancehas been briefly discussed.

Cretaceous fossil reveals a new pattern in mammalian middle ear evolution.

The evolution of the mammalian middle ear is thought to provide an example of 'recapitulation'-the theory that the present embryological development of a species reflects its evolutionary history. Accumulating data from both developmental biology and palaeontology have suggested that the transformation of post-dentary jaw elements into cranial ear bones occurred several times in mammals1,2. In addition, well-preserved fossils have revealed transitional stages in the evolution of the mammalian middle ear1,3,4. But questions remain concerning middle-ear evolution, such as how and why the post-dentary unit became completely detached from the dentary bone in different clades of mammaliaforms. Here we report a definitive mammalian middle ear preserved in an eobaatarid multituberculate mammal, with complete post-dentary elements that are well-preserved and detached from the dentary bones. The specimen reveals the transformation of the surangular jaw bone from an independent element into part of the malleus of the middle ear, and the presence of a restricted contact between the columelliform stapes and the flat incus. We propose that the malleus-incus joint is dichotomic in mammaliaforms, with the two bones connecting in either an abutting or an interlocking arrangement, reflecting the evolutionary divergence of the dentary-squamosal joint4. In our phylogenetic analysis, acquisition of the definitive mammalian middle ear in allotherians such as this specimen was independent of that in monotremes and therians. Our findings suggest that the co-evolution of the primary and secondary jaw joints in allotherians was an evolutionary adaptation allowing feeding with unique palinal (longitudinal and backwards) chewing. Thus, the evolution of the allotherian auditory apparatus was probably triggered by the functional requirements of the feeding apparatus.

Palynological, megafloral and mesofossil record from the Bajo Grande area (Anfiteatro de Ticó Formation, Baqueró Group, Upper Aptian), Patagonia, Argentina

The late Aptian flora of Baqueró is one of the best known and accurately dated Cretaceous plant associations from Gondwana, recognized for their well-preserved fossil remains. The Cerro Bayo (Bajo Grande area, Argentinean Patagonia) is one of its classical locations and includes the northernmost fossiliferous outcrops of the Baqueró Group, which belong to the Anfiteatro de Ticó Formation. It yields diverse and numerous plant megafossils and reproductive structures with associated pollen. We report a complete systematic study of a palynological association with 124 species, including 26 that are identified for the first time in the unit. This allowed the first record of three major botanical groups not reported before (i.e., lycophytes, hornworts and angiosperms), as well as algae and fungal spores. The same fossiliferous levels also yielded megafloral remains and the first record of a mesofossils assemblage for the Baqueró flora. By integrating all these floristic data sources, relative abundance analyses, and sedimentological data it is possible to propose a paleoenvironmental reconstruction of the Bajo Grande area during the late Aptian: a diverse forest growing in a temperate to warm climate with subtle variations between those associations from floodplains with water instability within a delta and those that grew into a more stable area out of the flooding influence. Thus, the presumed xeromorphic features identified in the Cerro Bayo flora (sunken stomata, papillae, epicuticular waxes) may have been related to contemporaneous volcanic activity recorded in Patagonia rather than to dry conditions.

Cretaceous amber fossils highlight the evolutionary history and morphological conservatism of land snails

Other than hard bones and shells, it is rare for soft tissues to fossilize, but occasionally they are well-preserved in amber. Here, we focus on both modern and fossilized species of the land snail superfamily Cyclophoroidea. Phylogenetic relationships within the Cyclophoroidea were previously studied using extant species, but timing of divergence within the group remains unclear. In addition, it is difficult to observe morphological traits such as the chitinous operculum and periostracum of fossil snails due to their poor preservation potential. Here we describe nine species including a new genus and five new species of well-preserved fossil cyclophoroideans from the mid-Cretaceous Burmese amber. These fossils include not only the shell, but also the chitinous operculum and periostracum, soft body, and excrements. We present the first estimation of divergence time among cyclophoroidean families using fossil records and molecular data, suggesting extreme morphological conservatism of the Cyclophoroidea for nearly 100 million years.

Cranial anatomy and taxonomy of the erythrosuchid archosauriform 'Vjushkovia triplicostata' Huene, 1960, from the Early Triassic of European Russia.

Erythrosuchidae are a globally distributed and important group of apex predators that occupied Early and Middle Triassic terrestrial ecosystems following the Permo-Triassic mass extinction. The stratigraphically oldest known genus of Erythrosuchidae is Garjainia Ochev, 1958, which is known from the late Early Triassic (late Olenekian) of European Russia and South Africa. Two species of Garjainia have been reported from Russia: the type species, Garjainia prima Ochev, 1958, and ‘Vjushkovia triplicostata’ von Huene, 1960, which has been referred to Garjainia as either congeneric (Garjainia triplicostata) or conspecific (G. prima). The holotype of G. prima has received relatively extensive study, but little work has been conducted on type or referred material attributed to ‘V. triplicostata’. However, this material includes well-preserved fossils representing all parts of the skeleton and comprises seven individuals. Here, we provide a comprehensive description and review of the cranial anatomy of material attributed to ‘V. triplicostata’, and draw comparisons with G. prima. We conclude that the two Russian taxa are indeed conspecific, and that minor differences between them result from a combination of preservation or intraspecific variation. Our reassessment therefore provides additional information on the cranial anatomy of G. prima. Moreover, we quantify relative head size in erythrosuchids and other early archosauromorphs in an explicit phylogenetic context for the first time. Our results show that erythrosuchids do indeed appear to have disproportionately large skulls, but that this is also true for other early archosauriforms (i.e. proterosuchids), and may reflect the invasion of hypercarnivorous niches by these groups following the Permo-Triassic extinction.

Two new species of fossil Paratydeidae (Acari: Trombidiformes) from the late Eocene amber highlight ultraslow morphological evolution in a soil-inhabiting arthropod lineage

We describe two species of soil mite of the family Paratydeidae from the late Eocene Rovno amber: Scolotydaeus vlaskini sp. nov. and Tanytydeus pogrebnyaki sp. nov. This is the first formal description of fossils from the family Paratydeidae. These exceptionally well-preserved fossils have very similar morphologies compared to extant species, suggesting that Paratydeidae is a lineage that has experienced extremely slow rates of phenotypic evolution. To infer rates of morphological evolution in this group, we used a combination of tip dating (from the fossils) and internal node dating (based on molecular outgroup time-calibrated analysis) in a Bayesian phylogenetic framework. This analysis inferred Paratydeidae as an ancient lineage, originating 242 Ma (stem group) and diversifying 150 Ma (crown group), having ultraslow average rates of morphological evolution, i.e. 4.53e-04 changes per site per million years, which is equivalent to one change in any of the characters per 46.0 million years, per each branch of the tree. Based on our divergence time estimates, we suggest that the present global distribution of the group could be explained by their early evolution on the Pangaean supercontinent. Analysis of character state distributions in the fossil specimens suggests later extinction of ancestral taxa in the Palaearctic.http://zoobank.org/urn:lsid:zoobank.org:pub:265A36D2-B6AE-4150-B5B6-59054D33CEA0

Araucaria Section Eutacta Macrofossils from the Cenozoic of Southeastern Australia

Premise of research. We collate and interpret previously undescribed foliar material of Araucaria section Eutacta from Australian Cenozoic sediments.Methodology. The fossils we describe here were collected over several decades and were identified by direct comparisons with extant and fossil species using light and scanning electron microscopy.Pivotal results. Fossil leaves and leafy shoots of three new species of Araucaria section Eutacta (A. macrophylla, A. mollifolia, and A. balfourensis), along with new records of the previously described A. planus, are described from eight localities in southeastern Australia, spanning the early Eocene to the early Miocene.Conclusions. These well-preserved fossils add significantly to our knowledge of Araucaria and confirm the dominance of the section Eutacta compared with other sections in the region during that time. The range of leaf morphology exhibited is similar to that seen in extant New Caledonian species and probably reflects past phases of radiation in similar wet climates.

Mechanistic Morphogenesis of Organo-Sedimentary Structures Growing Under Geochemically Stressed Conditions: Keystone to Proving the Biogenicity of Some Archaean Stromatolites?

Morphologically diverse organo-sedimentary structures (including microbial mats and stromatolites) provide a palaeobiological record through more than three billion years of Earth history. Since understanding much of the Archaean fossil record is contingent upon proving the biogenicity of such structures, mechanistic interpretations of well-preserved fossil microbialites can reinforce our understanding of their biogeochemistry and distinguish unambiguous biological characteristics in these structures, which represent some of the earliest records of life. Mechanistic morphogenetic understanding relies upon the analysis of geomicrobiological experiments. Herein, we report morphological-biogeochemical comparisons between micromorphologies observed in growth experiments using photosynthetic mats built by the cyanobacterium Coleofasciculus chthonoplastes (formerly Microcoleus) and green anoxygenic phototrophic Chloroflexus spp. (i.e., Coleofasciculus–Chloroflexus mats), and Precambrian organo-sedimentary structures, demonstrating parallels between them. In elevated ambient concentrations of Cu (toxic to Coleofasciculus), Coleofasciculus–Chloroflexus mats respond by forming centimetre-scale pinnacle-like structures (supra-lamina complexities) associated with large quantities of EPS at their surfaces. µPIXE mapping shows that Cu and other metals become concentrated within surficial sheath-EPS-Chloroflexus-rich layers, producing density-differential micromorphologies with distinct fabric orientations that are detectable using X-ray computed micro-tomography (X-ray µCT). Similar micromorphologies are also detectable in stromatolites from the 3.481 Ga Dresser Formation (Pilbara, Western Australia). The cause and response link between the presence of toxic elements (geochemical stress) and the development of multi-layered topographical complexities in organo-sedimentary structures may thus be considered an indicator of biogenicity, being an indisputably biological and predictable morphogenetic response reflecting, in this case, the differential responses of Coleofasciculus and Chloroflexus to Cu. Growth models for microbialite morphogenesis rely upon linking morphology to intrinsic (biological) and extrinsic (environmental) influences. Since the pinnacles of Coleofasciculus–Chloroflexus mats have an unambiguously biological origin linked to extrinsic geochemistry, we suggest that similar micromorphologies observed in ancient organo-sedimentary structures are indicative of biogenesis. An identical Coleofasciculus–Chloroflexus community subjected to salinity stress also produced supra-lamina complexities (tufts) but did not produce identifiable micromorphologies in three dimensions since salinity seems not to negatively impact either organism, and therefore cannot be used as a morphogenetic tool for the interpretation of density-homogeneous micro-tufted mats—for example, those of the 3.472 Ga Middle Marker horizon. Thus, although correlative microscopy is the keystone to confirming the biogenicity of certain Precambrian stromatolites, it remains crucial to separately interrogate each putative trace of ancient life, ideally using three-dimensional analyses, to determine, where possible, palaeoenvironmental influences on morphologies. Widespread volcanism and hydrothermal effusion into the early oceans likely concentrated toxic elements in early biomes. Morphological diversity in fossil microbialites could, therefore, reflect either (or both of) differential exposure to ambient fluids enriched in toxic elements and/or changing ecosystem structure and tolerance to elements through evolutionary time—for example, after incorporation into enzymes. Proof of biogenicity by deducing morphogenesis (i.e., a process preserved in the fossil record) overcomes many of the shortcomings inherent to the proof of biogenicity by descriptions of morphology alone.

Strontium isotope stratigraphy and paleomagnetic age constraints on the evolution history of coral reef islands, northern South China Sea

Abstract Understanding the history of the response of coral reefs to past climate changes can provide valuable information for predicting the future response of modern reefs. However, dating such ancient biotic carbonate is still challenging because of its sensitivity to diagenetic alteration processes, scarcity of well-preserved fossils, and low magnetic mineral content. There have been a long debates about the origin and evolutionary history of coral reefs in the northern South China Sea, mainly due to the lack of direct and reliable age constraints. This provides us with a good opportunity to verify the practicability of different dating approaches, especially the strontium (Sr) isotope analysis of bulk carbonate. Here, we retrieved a 972.55-m-long core from the Xisha Islands to provide a credible chronologic constraint on the carbonate platform evolution. The lithostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy were analyzed throughout the whole reef sequence. The lithostratigraphic results show that the 873.55 m reef sequence developed on an ancient volcaniclastic basement and experienced multiple evolutionary phases. The 87Sr/86Sr results of all 100 bulk carbonate samples vary from 0.708506 to 0.709168 and show a monotonic increase with decreasing depth, except for a few outliers. Trace-element criteria and stable isotope (δ18O and δ13C) methods were applied to these bulk carbonate samples, and results imply that the primary or near-primary seawater 87Sr/86Sr values were likely preserved, although different degrees of diagenetic alteration occurred. In addition, the paleomagnetic results indicate 10 normal polarity and eight reversed polarity magnetozones. Based on the 87Sr/86Sr ratios of the selected 58 samples and paleomagnetic reconstruction of polarity reversals, the bottom of the reef sequence is dated to 19.6 Ma, and the observed polarity chronozones extend from chron C6 (19.722–18.748 Ma) at 866.60 m to present at the top. Based on the new data, we propose a new chronologic framework for the evolutionary history of the reef islands, where: (1) the reefs initiated in the early Miocene (19.6 Ma) and were drowned until 16.26 Ma; (2) during 16.26–10.66 Ma, lagoon to lagoon slope environments prevailed; (3) the lagoon environment progressively transformed into a reef crest environment from 10.66 to 4.36 Ma and 4.36 to 1.59 Ma; and (4) the reef started to be drowned again during 1.59–0 Ma. Our study provides a new and reliable chronologic constraint on the general evolutionary history of the reef islands in the northern South China Sea. Furthermore, the 87Sr/86Sr results from bulk carbonate indicate that strontium isotope stratigraphy is a powerful dating tool only when rigid sample selection, sequential leaching procedures, and strict trace-element and isotopic criteria are applied.

Significant shift in the terrestrial ecosystem at the Paleogene/Neogene boundary in the Tibetan Plateau

<p indent=0mm>The shift from the Paleogene to the Neogene represents an important timeline in the history of life on Earth: A point when the biotic realm approached that of nature today. The uplift of the Tibetan Plateau in the Cenozoic Era has imposed profound influence on the evolution of the terrestrial ecosystem by creating a sustainable life system in a freezing climate. A reconstruction of this epic scene on the plateau relies on fossil discoveries. Based on a recent study of numerous well-preserved fossils from the Paleogene and Neogene deposits of the Lunpola and Nima basins in the central Tibetan Plateau, we recognized therein, for the first time, the turnover of the Late Oligocene tropical or subtropical ecosystem, and the subsequent transition toward a plateau-type biotic assemblage during the Early Miocene epoch. The fossil biota consisting of fishes, insects and plants from the Upper Oligocene suggests that in 26−24 Ma, the hinterland of the Tibetan Plateau was a warm and humid lowland nourished by tropical moisture from the Indian Ocean, which would have been able to reach northern Tibet then. This biota, represented by climbing perches and palms, shows typical tropical or subtropical climatic patterns and maintained a paleoelevation no higher than <sc>2300 m</sc> in the depositional areas. In the Early Miocene, the Tibetan ecosystem underwent comprehensive transformation into the one we recognize today. Primitive snow carps, which are endemic to the plateau today, emerged and, in an “Ascending with the Modifications” mode, evolved into more and more specialized species all the way up until the Pliocene epoch. The vegetation of the Early Miocene was dominated by temperate broad-leaved forests mixed with abundant coniferous trees and booming herbs, hence showing a cool climatic setting. Some mammals adapted to the temperate forest, e.g., <italic>Plesiaceratherium</italic> (a kind of extinct rhinos), appeared at the center of the plateau during the Early Miocene, and gave way to the ancestors of the Ice Age mammals, e.g., the woolly rhino of the Pliocene epoch. Such a dramatic transformation of the Tibetan ecosystem around the Paleogene and Neogene boundary was due to the cooling-down effect accompanying the rise of the main body of the plateau to ca. <sc>3000 m</sc> and the global climate evolution toward icehouse conditions during the Cenozoic.