What Drove the Giant Marsupial Predators (sparassodontans) of South America to Extinction?

Extinction of South American sparassodontans (Metatheria): environmental fluctuations or complex ecological processes?

Authors:

Lópes-Aguirre et al

Abstract:

Sparassodontans are a diverse but now extinct group of metatherians that were apex predators in South America during most of the Cenozoic. Studying their decline has been controversial mainly due to the scarcity of the fossil record, and different methodological approaches have led to contradictory hypotheses. In an effort to explore questions about their extinction, we developed a novel multi-model statistical approach to analyse all of the currently available data at a continental scale. Using multiple regression analysis and new advances in beta diversity analysis, we used all currently available fossil data at a continental scale to test four competing hypotheses to account for the decline of sparassodontans: competition with placental carnivorans, competition with avian phorusrhacids, non-competitive ecological interactions, and environmental fluctuations. Our results show that the sparassodontan extinction was a gradual process with species disappearing throughout the Cenozoic. Multiple regression analysis supported non-competitive ecological interactions as the best extinction model. Native South American ungulates, African migrants (caviomorph rodents and platyrrhine primates) and didelphimorphians were the groups with the highest statistical significance. Sparassodontan beta diversity increased between South American Land Mammal Ages after the Paleocene–Eocene boundary. Our results demonstrate that ecological modelling techniques illuminate aspects of extinction processes whilst mitigating the limitations of the fossil record. Our study suggests that non-competitive ecological interactions could have been the main driver for sparassodontan extinction rather than, as commonly assumed, a result of competition and/or abiotic fluctuations.

Ecological and Biological Shifts During the Late Ediacaran NeoProterozoic

Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils

Authors:

Boag et al

Abstract:

The mid-late Ediacaran Period (∼579–541 Ma) is characterized by globally distributed marine soft-bodied organisms of unclear phylogenetic affinities colloquially called the “Ediacara biota.” Despite an absence of systematic agreement, previous workers have tested for underlying factors that may control the occurrence of Ediacaran macrofossils in space and time. Three taxonomically distinct “assemblages,” termed the Avalon, White Sea, and Nama, were identified and informally incorporated into Ediacaran biostratigraphy. After ∼15 years of new fossil discoveries and taxonomic revision, we retest the validity of these assemblages using a comprehensive database of Ediacaran macrofossil occurrences. Using multivariate analysis, we also test the degree to which taphonomy, time, and paleoenvironment explain the taxonomic composition of these assemblages. We find that: (1) the three assemblages remain distinct taxonomic groupings; (2) there is little support for a large-scale litho-taphonomic bias present in the Ediacaran; and (3) there is significant chronostratigraphic overlap between the taxonomically and geographically distinct Avalonian and White Sea assemblages ca. 560–557 Ma. Furthermore, both assemblages show narrow bathymetric ranges, reinforcing that they were paleoenvironmental—ecological biotopes and spatially restricted in marine settings. Meanwhile, the Nama assemblage appears to be a unique faunal stage, defined by a global loss of diversity, coincident with a noted expansion of bathymetrically unrestricted, long-ranging Ediacara taxa. These data reinforce that Ediacaran biodiversity and stratigraphic ranges of its representative taxa must first statistically account for varying likelihood of preservation at a local scale to ultimately aggregate the Ediacaran macrofossil record into a global biostratigraphic context.

Coprolites Give Evidence of Early Triassic Polar Predators

An Early Triassic polar predator ecosystem revealed by vertebrate coprolites from the Bulgo Sandstone (Sydney Basin) of southeastern Australia

Authors:

Niedźwiedzki et al

Abstract:

Vertebrate trace fossils often provide a measure of cryptic biodiversity, and are especially pertinent when skeletal remnants are exceptionally rare. The Lower Triassic (lower Olenekian) Bulgo Sandstone at Long Reef in the Sydney Basin of southeastern Australia constitutes just such a deposit, having yielded isolated bones of giant capitosaurian temnospondyls and proterosuchid archosauriforms, together with abundant coprolites that are geochemically rich in elemental phosphate and carbon denoting vertebrate predators. Microstructural analysis of these preserved droppings reveals occasional bone fragments, fish scales, insect cuticles, plant material and bacterial traces (pseudomorph voids), as well as silicate mineral particles. REE concentrations indicate that burial and early diagenesis occurred explicitly within fluvial sediments. Furthermore, external morphological characterization permits attribution of spiral coprolites to chondrichthyan or osteichthyan fishes, polygonal, ovoid–spherical and typically flattened feces to temnospondyls, and conspicuously large cylindrical droppings to archosauriforms or other amniote apex predators. Collectively, the Bulgo Sandstone coprolite assemblage thus offers new insights into ecosystem structure and palaeoenvironment in what was an earliest Triassic near polar setting. Such data compliments the documented skeletal record, but indicates a greater range of aquatic and possibly terrestrial carnivores — the latter being enigmatically sparse in the Australian Triassic and yet detected here via the hitherto underexplored trace fossil evidence of their ecological presence.

Cenozoic Theropod Dinosaurs in South America Revisited

Cenozoic dinosaurs in South America – revisited

Authors:

Molnar et al

Abstract:

Of course there were Cenozoic dinosaurs (theropods) in South America, phorusrhacid (‘terror’) birds among others, but that is not the subject here. Why did anyone think there were Cenozoic (non-avian) theropods in South America? Because of a misinterpretation of Ameghino’s belief that derived mammals lived along with dinosaurs in Late Cretaceous Argentina. But also because isolated theropod teeth were found associated with derived (Eocene) mammal fossils. These turned out to be the teeth of Sebecus icaeorhinus. This is a small crocodylomorph, skull length c. 450 mm. More recently discovered sebecosuchians were substantially larger: Barinasuchus arveloi had an (estimated) skull length of c. 1000 mm, similar to that of Daspletosaurus (1000 mm). These crocodylomorphs are generally believed to have been terrestrial animals, presumably preying on large mammals. Thus, although there were no large non-avian theropods in Cenozoic South America, there were crocodylomorphs that seem to have been ecological vicars of large theropods. The reconstruction of terrestrial trophic networks for large terrestrial tetrapods after the Cretaceous-Paleogene extinctions seems to have been slower than often supposed. At (or near) the Cretaceous-Paleogene boundary, large herbivores turned over from archosaurs to mammals, but turnover of large carnivores was slower. In South America, dinosaur-size crocodylomorphs lived as late as the Miocene. Thus modern terrestrial ecosystems do not, trophically, reflect those of even the Early Neogene in some southern continents. Sebecosuchians, at least in South America, seem to have been unaffected by the Cretaceous-Paleogene extinctions.

Feeding ecology and habitat preferences of top predators from two Miocene Neogene Locales

Feeding ecology and habitat preferences of top predators from two Miocene carnivore-rich assemblages

Authors:

Domingo et al

Abstract:

Carnivore-rich fossil sites are uncommon in the fossil record and, accordingly, provide valuable opportunities to study predators from vantages that are rarely applied to ancient faunas. Through stable isotopes of carbon and a Bayesian mixing model, we analyze time-successive (nearly contemporaneous), late Miocene carnivoran populations from two fossil sites (Batallones-1 and Batallones-3) from central Spain. Stable isotopes of carbon in tooth enamel provide a reliable and direct methodology to track ancient diets. These two carnivoran-dominated fossil sites display differences in the composition and abundance of the carnivoran species, with some species present at both sites and some present only at one site. This disparity has been interpreted as the consequence of habitat differences between Batallones-1, the older site, and Batallones-3, the younger site. However, carbon isotope values of carnivore and herbivore tooth enamel suggest a common habitat of C3 woodland originally present at both sites. The differences in the carnivoran faunas rather may be the consequence of the dynamics of species entrance and exit from the Madrid Basin during the time elapsed between Batallones-1 and Batallones-3 and changes in population densities due to biotic factors. We infer higher levels of interspecific competition in Batallones-3 than in Batallones-1 because of the larger number of similar-sized, sympatric predators; the clear overlap in their δ13C values (except for the amphicyonid Magericyon anceps); and similarity of their preferred prey: the hipparionine horses. Finally, carbon stable isotopic composition of Indarctos arctoides teeth implies that this ursid was a carnivorous omnivore rather than a herbivorous omnivore. This work demonstrates the insights that stable isotopes can provide in characterizing the feeding ecology and trophic interactions of ancient carnivoran taxa.

Evidence of Wild Fires From Barremian Cretaceous Jordan

Fire in a Weichselia-dominated coastal ecosystem from the Lower Cretaceous (Barremian) of the Kurnub Group in NW Jordan

Authors:

Abu Hamad et al

Abstract:

Large intervals of the Cretaceous are considered as a ‘high-fire’ period in Earth's history. However, so far most studies dealing in greater detail with the fossil evidence of palaeo-wildfires, i.e. fossil charcoal, originate from the northern hemisphere (i.e. North America, Europe, Asia) whereas there are large stratigraphic and geographic gaps on the Cretaceous southern continents. The present paper deals with the fossil contents (plant macro-remains, palynomorphs and charcoal) of a lignite lens from the lower part of the Lower Cretaceous Kurnub Group near King Talal Dam in Jordan. The data provide evidence for the repeated occurrence of palaeo-wildfires in coastal ecosystems on the northern margin of Gondwana during the Barremian. The fossil content of the lens indicates that the vegetation, which was repeatedly affected by fire, has been dominated by the matoniaceous tree fern Weichselia reticulata. Palynological data from the lignite, as well as the repeated occurrence of wildfires point to an at least seasonally dry (or at least less humid) climate during deposition of the lignite.

Late Cenozoic onset of the latitudinal diversity gradient of North American mammals

Late Cenozoic onset of the latitudinal diversity gradient of North American mammals

Authors:

Marcot et al

Abstract:

The decline of species richness from equator to pole, or latitudinal diversity gradient (LDG), is nearly universal among clades of living organisms, yet whether it was such a pervasive pattern in the geologic past remains uncertain. Here, we calculate the strength of the LDG for terrestrial mammals in North America over the past 65 My, using 27,903 fossil occurrences of Cenozoic terrestrial mammals from western North America downloaded from the Paleobiology Database. Accounting for temporal and spatial variation in sampling, the LDG was substantially weaker than it is today for most of the Cenozoic and the robust modern LDG of North American mammals evolved only over the last 4 My. The strength of the LDG correlates negatively with global temperature, suggesting a role of global climate patterns in the establishment and maintenance of the LDG for North American mammals.

pop sci write up.

The Oceans Recovered From the Permian Mass Extinction Quickly

Reptiles rapidly invaded the seas soon after a global extinction wiped out most life on Earth, according to a new study led by University of California, Davis, researchers.

Global climate change -- likely triggered by massive volcanic eruptions -- killed off more than 95 percent of all species about 250 million years ago, at the end of the Permian period. Land reptiles colonized the ocean in just 3.35 million years at the beginning of the Triassic, a speedy recovery in geologic time, the researchers report today (June 13) in the journal Scientific Reports.

"Our results fit with the emerging view that the recovery was faster than previously thought," said study co-author Ryosuke Motani, professor of paleobiology at UC Davis' Department of Earth and Planetary Sciences.

The research was led by Wanlu Fu, now of the Laboratory of Orogenic Belt and Crustal Evolution at Peking University. Fu conducted the research while an in-residence doctoral student working with study co-author Isabel Montañez, professor of geochemistry at UC Davis. Co-authors include scientists from the University of Wisconsin and the University of Milan in Italy. The fossils and rock samples were collected from Majiashan in Chaohu, South China.

link.

Late Triassic Reefs of China

Paleoecology, biogeography, and evolution of reef ecosystems in the Panthalassa Ocean during the Late Triassic: Insights from reef limestone of the Sambosan Accretionary Complex, Shikoku, Japan

Authors:

Peybernes et al

Abstract:

Upper Triassic reefs from the Panthalassa Ocean have been understudied in comparison to their Tethyan counterparts and are therefore pivotal to understanding the global reef evolution during the Late Triassic. To fill this gap, Upper Triassic reef limestone from ten localities of the Sambosan Accretionary Complex at Shikoku Island (Japan) has been investigated. Biotic assemblages, quantitative microfacies analysis, and integrated biostratigraphy allow us to characterize two types of reefs, those attributed to the Ladinian?–Early Carnian and those attributed to the Late Carnian–Rhaetian? At the regional scale, our data refine the biostratigraphic framework of the Upper Triassic Sambosan limestone. At the global scale, multivariate analyses support a strong paleobiogeographic affinity of the Western Panthalassa reef biota with those of the South Tethys Ocean during the Ladinian–Carnian and Norian–Rhaetian. Additionally, they indicate connections with East Panthalassa reefs during the Norian–Rhaetian.

Ecomorphological diversifications of Mesozoic marine reptiles

Ecomorphological diversifications of Mesozoic marine reptiles: the roles of ecological opportunity and extinction

Authors:

Stubbs et al

Abstract:

Mesozoic marine ecosystems were dominated by several clades of reptiles, including sauropterygians, ichthyosaurs, crocodylomorphs, turtles, and mosasaurs, that repeatedly invaded ocean ecosystems. Previous research has shown that marine reptiles achieved great taxonomic diversity in the Middle Triassic, as they broadly diversified into many feeding modes in the aftermath of the Permo-Triassic mass extinction, but it is not known whether this initial phase of evolution was exceptional in the context of the entire Mesozoic. Here, we use a broad array of disparity, morphospace, and comparative phylogenetic analyses to test this. Metrics of ecomorphology, including functional disparity in the jaws and dentition and skull-size diversity, show that the Middle to early Late Triassic represented a time of pronounced phenotypic diversification in marine reptile evolution. Following the Late Triassic extinctions, diversity recovered, but disparity did not, and it took over 100 Myr for comparable variation to recover in the Campanian and Maastrichtian. Jurassic marine reptiles generally failed to radiate into vacated functional roles. The signatures of adaptive radiation are not seen in all marine reptile groups. Clades that diversified during the Triassic biotic recovery, the sauropterygians and ichthyosauromorphs, do show early diversifications, early high disparity, and early burst, while less support for these models is found in thalattosuchian crocodylomorphs and mosasaurs. Overall, the Triassic represented a special interval in marine reptile evolution, as a number of groups radiated into new adaptive zones.

The Implications of Resource Partitioning in Miocene Neogene Herbivores for Hominoid Rudapithecus hungaricus

Stable isotopes show resource partitioning among the early Late Miocene herbivore community at Rudabánya II: Paleoenvironmental implications for the hominoid, Rudapithecus hungaricus

Author:

Eastham et al

Abstract:

Examining how species use and partition resources within an environment can lead to a better understanding of community assembly and diversity. The rich early Late Miocene (early Vallesian) deposits at Rudabánya II (R. II) in northern central Hungary preserve an abundance of forest dwelling taxa, including the hominoid Rudapithecus hungaricus. Here we use the carbon and oxygen stable isotope compositions of tooth enamel carbonate from 10 genera of medium to large-bodied mammals to evaluate resource use and partitioning among the herbivore community, and to reconstruct the paleoenvironment of Rudapithecus. The range of stable carbon and oxygen isotope values (δ13CE and δ18OE) displayed by the R. II fauna indicates a variable forest environment, which included both open and closed canopy habitats. The relatively low δ13CE and δ18OE values found in all sampled taxa are consistent with high levels of precipitation and humidity. Significant differences in stable isotope values were observed among the sampled fauna, supporting the interpretation of resource specialization and partitioning. Higher δ13CE values found in Aceratherium incisivum (Rhinocerotidae), Lucentia aff. pierensis (Cervidae), Hippotherium intrans (Equidae), Tetralophodon longirostris (Gomphotheriidae), Propotamochoerus palaeochoerus and Parachleuastochoerus kretzoii (Suidae) suggest foraging in more open canopy habitats, while lower δ13CE values found in Miotragocerus sp. (Bovidae), Dorcatherium naui (Tragulidae), and Micromeryx flourensianus (Moschidae) imply a preference for more densely canopied habitats. Several of the sampled taxa yielded relatively higher δ18OE and δ13CE values indicative of fruit consumption, including the small ruminants, cervid, and bovid. The analyzed isotope values reflect a moderate degree of dietary niche overlap between taxa. An abundance of plant resources likely allowed for the coexistence of this diverse community of predominantly browsing herbivores. Within the gradient of more open to closed canopy forest, it is likely that Rudapithecus occupied dense closed canopy habitats where access to fruit was relatively continuous. The progressive fragmentation and replacement of humid forests by more open and seasonal woodlands during the late Vallesian would have had a significant influence on the extinction of this fossil ape.

Predicting Reproductive Strategies for Insight into Paleoecology & Evolution

Prediction of offspring in extant and extinct mammals to add light on paleoecology and evolution

Author:

Andrea

Abstract:

Reproductive strategies can be inferred from adult body mass, although offspring characteristics can give more accurate tools to predict life histories. In fossil mammals, adult body mass estimation incorporates error to the possible predictions, and additionally, there are not estimators of the offspring. Here I test the significance of two measurements, the inter-acetabulum width and the lumbar length, as predictors of offspring body mass, litter weight, and litter size in extant and fossil mammals. The inter-acetabulum width is the best measurement to estimate offspring body mass and litter weight, whereas litter size can be estimated from the division of litter weight on offspring body mass. The possibility of estimating these offspring variables gives a new approximation to study the history of life, paleoecology, and evolution of fossil species. Ecological aspects as developmental and maturity time, can be combined to study population growth, faunal interaction and evolution in fossil taxa. Some interpretative factors are proposed as start point to study fossil fauna taking into account offspring and reproductive information.

Ecological Changes During the Glacial & Interglacials of the late Paleozoic ice age of Pennsylvanian Carboniferous Argentina

Compositional turnover and ecological changes related to the waxing and waning of glaciers during the late Paleozoic ice age in ice-proximal regions (Pennsylvanian, western Argentina)

Author:

Balseiro

Abstract:

The late Paleozoic ice age (LPIA) had a profound effect on the biota. Despite much research having been focused on paleotropical regions or global-scale analyses, regional ecological changes have seldom been studied in ice-proximal basins. Here, I study the compositional turnover and diversity structure across the main Carboniferous glacial event recorded in western Argentina and the subsequent nonglacial interval. Brachiopod and bivalve data from western Argentina suggest that the transition from glacial to nonglacial climates caused major compositional changes. Turnover, however, was not uniform across the bathymetric gradient, being higher in deep environments. Because extirpation was concentrated in brachiopods, but immigration was similar in both clades, the taxonomic structure of the region was significantly modified. Although regional hierarchical diversity structure and occupancy distributions remained stable, dissecting the analysis in brachiopods and bivalves underscores that both clades had different responses to climate change. Brachiopods, on the one hand, show stability in the diversity structure and a very slight decrease in occupancies of intermediate genera, while bivalves show an important rise in diversity, both at the environment and regional scale, and an increase in genera with intermediate occupancies. The bathymetric diversity gradient was also modified from hump shaped with maximum diversity in the deep subtidal to a linear gradient with maximum values toward the offshore. However, relative compositional differences within environments remained stable, with maximum values at intermediate depths both in glacial and nonglacial intervals. Moreover, local-scale coexistence between brachiopods and bivalves changed in the nonglacial interval, showing significant segregation, which indicates relevant modifications in community assembly dynamics. Results from western Argentina highlight the magnitude of regional-scale ecological changes during the LPIA in ice-proximal regions, suggesting that the waxing and waning of glaciers was able to cause regional taxonomic turnover and medium-scale ecological changes even during intervals of relative macroevolutionary quiescence.

Yes, Neandertals Were Omnivores

Ecological niche of Neanderthals from Spy Cave revealed by nitrogen isotopes of individual amino acids in collagen

Authors:

Naito et al

Abstract:

This study provides a refined view on the diet and ecological niche of Neanderthals. The traditional view is that Neanderthals obtained most of their dietary protein from terrestrial animals, especially from large herbivores that roamed the open landscapes. Evidence based on the conventional carbon and nitrogen isotopic composition of bulk collagen has supported this view, although recent findings based on plant remains in the tooth calculus, microwear analyses, and small game and marine animal remains from archaeological sites have raised some questions regarding this assumption. However, the lack of a protein source other than meat in the Neanderthal diet may be due to methodological difficulties in defining the isotopic composition of plants. Based on the nitrogen isotopic composition of glutamic acid and phenylalanine in collagen for Neanderthals from Spy Cave (Belgium), we show that i) there was an inter-individual dietary heterogeneity even within one archaeological site that has not been evident in bulk collagen isotopic compositions, ii) they occupied an ecological niche different from those of hyenas, and iii) they could rely on plants for up to ∼20% of their protein source. These results are consistent with the evidence found of plant consumption by the Spy Neanderthals, suggesting a broader subsistence strategy than previously considered.

The Paleoecology of Eocene Paleogene British Columbia

Why did the Stegosaurs go Extinct in the Cretaceous?

Without doubt, stegosaurs were adversely affected by new conditions in the Cretaceous. Available data suggests that, right after their Jurassic heyday, stegosaurs suffered a loss of diversity similar to what sauropods endured - 57-89%. After this first setback, they were further battered, by Barremian time c. 127 Ma. Plated dinosaurs apparently vanished everywhere, except in Asia, where their last occurrences are dated Aptian-Albian. By mid K at the latest, Stegosauria was entirely gone. What caused plated beasts to wane and die out?

In their 2009 paper, Diversity patterns amongst herbivorous dinosaurs and plants during the Cretaceous, Butler et al. note an apparent correlation between the waning of certain plants (cycads, cycadophytes and bennattitalles) and the demise of stegosaurs. Citing earlier works suggesting an ecological association of plated dinosaurs and cycads (and close relatives) they suggest the disappearance of stegosaurs, from the start of the early Cretaceous to its end, mirrored the decline of such vegetation.

With their narrow snouts, stegosaurs do appear to have been specialized feeders, essentially limited to a specific type of plant. Ergo, they may have been vulnerable to loss of such flora. The available evidence however, suggests other factors may have been equally important, if not more so.

link.

Just What Were the Noeggerathiales Plants?

Paleoecology of Noeggerathiales, an enigmatic, extinct plant group of Carboniferous and Permian times

Authors:

Pfefferkorn et al

Abstract:

Noeggerathiales are late Paleozoic plants of uncertain systematic position. They may either be late survivors of the Devonian progymnosperms or represent a sister group to ferns and sphenopsids. Noeggerathiales carry cycad-like or fern-like leaves on small, unbranched stems. They produce microspores and megaspores in cone-like structures in which sporangia are attached adaxially to sporophylls. Noeggerathiales are rare in Carboniferous and Permian fossil floras in the Euramerican floral realm (Europe and North America). Most floras do not even contain a single specimen. In the Cathaysian floral realm (China) they are more common and some fossil floras contain Noeggerathiales in substantial or even large numbers. The paleoenvironmental and taphonomic interpretations of these occurrences allow us to deduce the paleoecological preferences of Noeggerathiales. Noeggerathiales were tropical plants as can be derived from the pattern of their occurrence and the fact that tuft-trees can survive only in frost free climates. The single growing point of a tuft tree would be endangered by frost and the investment in the large leaves is so high that they have to function for at least two to three years. In Euramerica Noeggerathiales are not present in wet tropical lowland floras on clastic substrates or on most peat-deposits. However, they occur at the margin of smaller basins and on peat that was fertilized by volcanic ash. In North America several occurrences of Noeggerathialean plants are known from the base of sedimentary sections, an indication that these Noeggerathiales were part of the extrabasinal or hinterland floras. They were present before sedimentation began and could therefore be preserved by the earliest sedimentation events. Hinterland or extrabasinal floras often grew in environments that experienced a wet–dry seasonality. In China Noeggerathiales occur in species-rich lowland assemblages preserved in sediments of wet lowlands indicating that these forms were adapted to wetter conditions. The pattern indicates a plant group that was adapted to tropical climate and needed nutrient rich soil, but could withstand wet–dry seasonality. By Permian times Noeggerathiales living on the North and South China microcontinents had adapted to ever-wet climates but still needed nutrient-rich environments.

The First Report of a Forest From Mid to Late Permian China

First report of a phytogeographically mixed (transitional) Middle–Late Permian fossil wood assemblage from the Hami area, northwest China, and implications for Permian phytogeographical, paleogeographical and paleoclimatic evolution in central Asia

Authors:

Wei et al

Abstract:

A diverse and well-preserved fossil wood assemblage is described, for the first time, from the Middle Permian Taerlang Formation and the Upper Permian Quanzijie Formation in the vicinity of the Tianshan Town, Hami City of northwestern China. On the basis of wood microstructure, the fossil woods are classified into three genera and five species, including one new genus: Prototianshanoxylon gen. nov. and two new species: Prototianshanoxylon erdaogouense sp. nov., Prototianshanoxylon hamiense sp. nov. The new genus is characterized by window-like cross-field pitting and mixed tracheid radial wall pitting that suggest a transitional type between araucarioid-type and protopinoid-type pittings.

Phytogeographically, the fossil wood assemblage is characterized by an admixture of elements of both temperate Angaran (represented by wood specimens with moderately to well defined growth rings in their secondary xylem) and tropical–subtropical north subregion of the Cathaysian floras (with wood specimens lacking well-defined growth rings). Such a phytogeographically mixed fossil wood assemblage is interpreted to represent a transitional and complex climate condition between a cool temperate and tropical to subtropical zones, showing both seasonal variation and unstable climate conditions. Previously, similarly mixed floras have already been found to exist widely in northern China ranging in age from Early to Late Permian, but the mechanisms thought to be responsible for their formation were varied and remain controversial. In this study, the formation of these mixed Permian floras of North China is linked to the closure of the Tianshan–Hingan seaway coupled with the collision and amalgamation of Siberia with North China and the Tarim block, in a manner much like closing a pair of scissors with the closure of the seaway proceeding gradually and progressively from west to the east.

Cambrian Burgess Shale Ecologies Were Stable (!) Temporally and Geographically

Paleocommunity Analysis of the Burgess Shale Tulip Beds, Mount Stephen, British Columbia: Comparison with the Walcott Quarry and Implications for Community Variation in the Burgess Shale

Authors:

O'Brien et al

Abstract:

The Tulip Beds locality on Mount Stephen (Yoho National Park, British Columbia) yields one of the most abundant and diverse (~10,000 specimens in 110 taxa) Burgess Shale fossil assemblages in the Canadian Rockies. Detailed semi quantitative and quantitative analyses of this assemblage suggest strong similarities with the Walcott Quarry on Fossil Ridge. Both assemblages are dominated by epibenthic, sessile, and suspension feeding taxa, mostly represented by arthropods and sponges and have comparable diversity patterns, despite sharing only about half the genera. However, the Tulip Beds has a higher relative abundance of suspension feeders and taxa of unknown affinity compared to the Walcott Quarry. These biotic variations are probably largely attributable to ecological and evolutionary differences between the two temporally distinct communities that adapted to similar, but not identical, environmental settings. For instance, the Tulip Beds is farther away from the Cathedral Escarpment than the Walcott Quarry. The Tulip Beds and Walcott Quarry assemblages are more similar to each other than either one is to the assemblages of the Chengjiang biota, although the relative diversity of major taxonomic groups and ecological patterns are similar in all assemblages. The conserved diversity patterns and ecological structures among sites suggest that the ecological composition of Cambrian Burgess Shale-type communities was relatively stable across wide geographic and temporal scales.

Extraordinary Claim: Mesozoic Tetrapod PaleoDiversity Stagnated

Near-Stasis in the Long-Term Diversification of Mesozoic Tetrapods

Authors:

Benson et al

Abstract:

How did evolution generate the extraordinary diversity of vertebrates on land? Zero species are known prior to ~380 million years ago, and more than 30,000 are present today. An expansionist model suggests this was achieved by large and unbounded increases, leading to substantially greater diversity in the present than at any time in the geological past. This model contrasts starkly with empirical support for constrained diversification in marine animals, suggesting different macroevolutionary processes on land and in the sea. We quantify patterns of vertebrate standing diversity on land during the Mesozoic–early Paleogene interval, applying sample-standardization to a global fossil dataset containing 27,260 occurrences of 4,898 non-marine tetrapod species. Our results show a highly stable pattern of Mesozoic tetrapod diversity at regional and local levels, underpinned by a weakly positive, but near-zero, long-term net diversification rate over 190 million years. Species diversity of non-flying terrestrial tetrapods less than doubled over this interval, despite the origins of exceptionally diverse extant groups within mammals, squamates, amphibians, and dinosaurs. Therefore, although speciose groups of modern tetrapods have Mesozoic origins, rates of Mesozoic diversification inferred from the fossil record are slow compared to those inferred from molecular phylogenies. If high speciation rates did occur in the Mesozoic, then they seem to have been balanced by extinctions among older clades. An apparent 4-fold expansion of species richness after the Cretaceous/Paleogene (K/Pg) boundary deserves further examination in light of potential taxonomic biases, but is consistent with the hypothesis that global environmental disturbances such as mass extinction events can rapidly adjust limits to diversity by restructuring ecosystems, and suggests that the gradualistic evolutionary diversification of tetrapods was punctuated by brief but dramatic episodes of radiation.