Alternative climatic steady states near the Permian-Triassic Boundary

Due to spatial scarcity and uncertainties in sediment data, initial and boundary conditions in deep-time climate simulations are not well constrained. On the other hand, depending on these conditions, feedback mechanisms in the climate system compete and balance differently. This opens up the possibility to obtain multiple steady states in numerical experiments. Here, we use the MIT general circulation model to explore the existence of such alternative steady states around the Permian-Triassic Boundary (PTB). We construct the corresponding bifurcation diagram, taking into account processes on a timescale of thousands of years, in order to identify the stability range of the steady states and tipping points as the atmospheric CO2 content is varied. We find three alternative steady states with a difference in global mean surface air temperature of about 10 °C. We also examine how these climatic steady states are modified when feedbacks operating on comparable or longer time scales are included, namely vegetation dynamics and air-sea carbon exchanges. Our findings on multistability provide a useful framework for explaining the climatic variations observed in the Early Triassic geological record, as well as some discrepancies between numerical simulations in the literature and geological data at PTB and its aftermath.

Clair L, Mann J, Teran R, Lovelace DM. Fossil amphibian offers insights into the interplay between monsoons and amphibian evolution in palaeoequatorial Late Triassic systems

The severe greenhouse climate and seasonality of the early to mid-Late Triassic are thought to have limited terrestrial diversity at lower latitudes, but direct adaptations to these harsh conditions remain limited in vertebrates at the palaeoequator. Here, we present Ninumbeehan dookoodukah gen. et sp. nov., an early amphibian with specialized adaptations for seasonal estivation from the upper Jelm Formation of the Late Triassic of Wyoming, USA. Ninumbeehan are found in an association of vertebrate estivation burrows across a locally dense horizon, offering insights into the evolution and ecology of vertebrates amid the challenging conditions of low-latitude Late Triassic ecosystems. Estivation chambers were excavated within point bar deposits of an ephemeral river system, recording the cyclical signature of Triassic megamonsoons and documenting a vertebrate response to annual climate extremes across tens to hundreds of seasons. Phylogenetic analysis recovers Ninumbeehan within a group of temnospondyls characterized by fossorial adaptation, underscoring the widespread adoption of burrowing and estivation in total group Lissamphibia. Ninumbeehan hints at the pivotal role seasonal dynamics played in shaping amphibian evolution.

Mega El Niño instigated the end-Permian mass extinction

The ultimate driver of the end-Permian mass extinction is a topic of much debate. Here, we used a multiproxy and paleoclimate modeling approach to establish a unifying theory elucidating the heightened susceptibility of the Pangean world to the prolonged and intensified El Niño events leading to an extinction state. As atmospheric partial pressure of carbon dioxide doubled from about 410 to about 860 ppm (parts per million) in the latest Permian, the meridional overturning circulation collapsed, the Hadley cell contracted, and El Niños intensified. The resultant deforestation, reef demise, and plankton crisis marked the start of a cascading environmental disaster. Reduced carbon sequestration initiated positive feedback, producing a warmer hothouse and, consequently, stronger El Niños. The compounding effects of elevated climate variability and mean state warming led to catastrophic but diachronous terrestrial and marine losses.

Discriminating conodont recording bias: a case study from the Nanzhang-Yuan'an Lagerstätte

The Early Triassic Nanzhang-Yuan'an Lagerstätte of Hubei Province, South China, preserves abundant marine reptiles in the uppermost part of the Jialingjiang Formation and provides detailed insights into marine organisms, including newly discovered and well preserved conodont clusters of the Family Ellisonidae. These conodont elements allow us to assess the bias introduced during the acquisition process. We examined conodont elements preserved on the bedding planes and those acquired after the acid-dissolving method to analyze their attributes and length distributions. We identified a biased preservation of different conodont elements related to their morphologies. After the acid-dissolving procedures, the bias increased, and all different elements were affected, with larger individuals being particularly prone to destruction. Among them, the P elements of Ellisonidae were the least affected, while the S elements were the most affected. This study further indicates that paleobiological interpretations based on fossil size or morphology could be obscured if the influence of post-mortem effect is ignored.

Biogeographic climate sensitivity controls Earth system response to large igneous province carbon degassing

Periods of large igneous province (LIP) magmatism have shaped Earth's biological and climatic history, causing major climatic shifts and biological reorganizations. The vegetation response to LIP-induced perturbations may affect the efficiency of the carbon-climate regulation system and the post-LIP climate evolution. Using an eco-evolutionary vegetation model, we demonstrate here that the vegetation's climate adaptation capacity, through biological evolution and geographic dispersal, is a major determinant of the severity and longevity of LIP-induced hyperthermals and can promote the emergence of a new climatic steady state. Proxy-based temperature reconstructions of the Permian-Triassic, Triassic-Jurassic, and Paleocene-Eocene hyperthermals match the modeled trajectories of bioclimatic disturbance and recovery. We conclude that biological vegetation dynamics shape the multimillion-year Earth system response to sudden carbon degassing and global warming episodes.

Lithium isotopic evidence for enhanced reverse weathering during the Early Triassic warm period

Elevated temperatures persisted for an anomalously protracted interval following pulsed volcanic carbon release associated with the end-Permian mass extinction, deviating from the expected timescale of climate recovery following a carbon injection event. Here, we present evidence for enhanced reverse weathering-a CO2 source-following the end-Permian mass extinction based on the lithium isotopic composition of marine shales and cherts. We find that the average lithium isotopic composition of Lower Triassic marine shales is significantly elevated relative to that of all other previously measured Phanerozoic marine shales. Notably, the record generated here conflicts with carbonate-based interpretations of the lithium isotopic composition of Early Triassic seawater, forcing a re-evaluation of the existing framework used to interpret lithium isotopes in sedimentary archives. Using a stochastic forward lithium cycle model, we demonstrate that elevated reverse weathering is required to reproduce the lithium isotopic values and trends observed in Lower Triassic marine shales and cherts. Collectively, this work provides direct geochemical evidence for enhanced reverse weathering in the aftermath of Earth's most severe mass extinction.

Cenozoic history of the tropical marine biodiversity hotspot

The region with the highest marine biodiversity on our planet is known as the Coral Triangle or Indo-Australian Archipelago (IAA)1,2. Its enormous biodiversity has long attracted the interest of biologists; however, the detailed evolutionary history of the IAA biodiversity hotspot remains poorly understood3. Here we present a high-resolution reconstruction of the Cenozoic diversity history of the IAA by inferring speciation-extinction dynamics using a comprehensive fossil dataset. We found that the IAA has exhibited a unidirectional diversification trend since about 25 million years ago, following a roughly logistic increase until a diversity plateau beginning about 2.6 million years ago. The growth of diversity was primarily controlled by diversity dependency and habitat size, and also facilitated by the alleviation of thermal stress after 13.9 million years ago. Distinct net diversification peaks were recorded at about 25, 20, 16, 12 and 5 million years ago, which were probably related to major tectonic events in addition to climate transitions. Key biogeographic processes had far-reaching effects on the IAA diversity as shown by the long-term waning of the Tethyan descendants versus the waxing of cosmopolitan and IAA taxa. Finally, it seems that the absence of major extinctions and the Cenozoic cooling have been essential in making the IAA the richest marine biodiversity hotspot on Earth.

Acceleration of phosphorus weathering under warm climates

The release of phosphorous (P) via chemical weathering is a vital process that regulates the global cycling of numerous key elements and shapes the size of the Earth's biosphere. It has long been postulated that global climate should theoretically play a prominent role in governing P weathering rates. Yet, there is currently a lack of direct evidence for this relationship based on empirical data at the global scale. Here, using a compilation of temperature and P content data of global surface soils (0 to 30 cm), we demonstrate that P release does enhance at high mean annual surface temperatures. We propose that this amplification of nutrient supply with warming is a critical component of Earth's natural thermostat, and that this relationship likely caused expanded oceanic anoxia during past climate warming events. The potential acceleration of phosphorus loss from soils due to anthropogenic climate warming may pose threats to agricultural production, terrestrial and marine ecosystems, and alter marine redox landscapes.

Sedimentary records of sea level fall during the end-Permian in the upper Yangtze region (southern China): Implications for the mass extinction

Sea level fall is considered one of the significant factors leading to the end-Permian mass extinction (EPME). We studied the relative sea level changes in the Beifengjing and Shangsi sections, and the results indicate that a sea level fall occurred in the Upper Yangtze region during the Permian-Triassic transition. Considering that there is no significant change in fossil abundance in the strata following the two sea level falls observed in the Beifengjing section, we conclude that the reduction in shallow marine habitat for sea level fall solely was insufficient to cause the mass extinction. However, sea level fall did exacerbate the input of terrestrial debris into the ocean, leading to the deterioration of the marine environment. We propose that the combined adverse effects of volcanic eruptions, sea level falls, and other events exceeded the threshold for biological survival, ultimately resulting in the catastrophic EPME.

Respiratory protein-driven selectivity during the Permian-Triassic mass extinction

Extinction selectivity determines the direction of macroevolution, especially during mass extinction; however, its driving mechanisms remain poorly understood. By investigating the physiological selectivity of marine animals during the Permian-Triassic mass extinction, we found that marine clades with lower O2-carrying capacity hemerythrin proteins and those relying on O2 diffusion experienced significantly greater extinction intensity and body-size reduction than those with higher O2-carrying capacity hemoglobin or hemocyanin proteins. Our findings suggest that animals with high O2-carrying capacity obtained the necessary O2 even under hypoxia and compensated for the increased energy requirements caused by ocean acidification, which enabled their survival during the Permian-Triassic mass extinction. Thus, high O2-carrying capacity may have been crucial for the transition from the Paleozoic to the Modern Evolutionary Fauna.

Oxygen isotope ensemble reveals Earth's seawater, temperature, and carbon cycle history

Earth's persistent habitability since the Archean remains poorly understood. Using an oxygen isotope ensemble approach-comprising shale, iron oxide, carbonate, silica, and phosphate records-we reconcile a multibillion-year history of seawater δ18O, temperature, and marine and terrestrial clay abundance. Our results reveal a rise in seawater δ18O and a temperate Proterozoic climate distinct to interpretations of a hot early Earth, indicating a strongly buffered climate system. Precambrian sediments are enriched in marine authigenic clay, with prominent reductions occurring in concert with Paleozoic and Cenozoic cooling, the expansion of siliceous life, and the radiation of land plants. These findings support the notion that shifts in the locus and extent of clay formation contributed to seawater 18O enrichment, clement early Earth conditions, major climate transitions, and climate stability through the reverse weathering feedback.

The great catastrophe: causes of the Permo-Triassic marine mass extinction

The marine losses during the Permo-Triassic mass extinction were the worst ever experienced. All groups were badly affected, especially amongst the benthos (e.g. brachiopods, corals, bryozoans, foraminifers, ostracods). Planktonic populations underwent a fundamental change with eukaryotic algae being replaced by nitrogen-fixing bacteria, green-sulphur bacteria, sulphate-reducing bacteria and prasinophytes. Detailed studies of boundary sections, especially those in South China, have resolved the crisis to a ∼55 kyr interval straddling the Permo-Triassic boundary. Many of the losses occur at the beginning and end of this interval painting a picture of a two-phase extinction. Improved knowledge of the extinction has been supported by numerous geochemical studies that allow diverse proposed extinction mechanisms to be studied. A transition from oxygenated to anoxic-euxinic conditions is seen in most sections globally, although the intensity and timing shows regional variability. Decreased ocean ventilation coincides with rapidly rising temperatures and many extinction scenarios attribute the losses to both anoxia and high temperatures. Other kill mechanisms include ocean acidification for which there is conflicting support from geochemical proxies and, even less likely, siltation (burial under a massive influx of terrigenous sediment) which lacks substantive sedimentological evidence. The ultimate driver of the catastrophic changes at the end of the Permian was likely Siberian Trap eruptions and their associated carbon dioxide emissions with consequences such as warming, ocean stagnation and acidification. Volcanic winter episodes stemming from Siberian volcanism have also been linked to the crisis, but the short-term nature of these episodes ( Collapse

Key Words

• ocean acidification
• ocean anoxia
• productivity collapse
• siltation
• volcanic winter

Collapse

MESH Headings Collapse

Grants

• NERC

Collapse

Affiliation(s)

Paul B Wignall School of Earth & Environment, University of Leeds, Leeds LS2 9JT, UK
David P G Bond School of Environmental Sciences, University of Hull, Hull HU6 7RX, UK

Collapse

Theory and classification of mass extinction causation

Theory regarding the causation of mass extinctions is in need of systematization, which is the focus of this contribution. Every mass extinction has both an ultimate cause, i.e. the trigger that leads to various climato-environmental changes, and one or more proximate cause(s), i.e. the specific climato-environmental changes that result in elevated biotic mortality. With regard to ultimate causes, strong cases can be made that bolide (i.e. meteor) impacts, large igneous province (LIP) eruptions and bioevolutionary events have each triggered one or more of the Phanerozoic Big Five mass extinctions, and that tectono-oceanic changes have triggered some second-order extinction events. Apart from bolide impacts, other astronomical triggers (e.g. solar flares, gamma bursts and supernova explosions) remain entirely in the realm of speculation. With regard to proximate mechanisms, most extinctions are related to either carbon-release or carbon-burial processes, the former being associated with climatic warming, ocean acidification, reduced marine productivity and lower carbonate δ13C values, and the latter with climatic cooling, increased marine productivity and higher carbonate δ13C values. Environmental parameters such as marine redox conditions and terrestrial weathering intensity do not show consistent relationships with carbon-cycle changes. In this context, mass extinction causation can be usefully classified using a matrix of ultimate and proximate factors. Among the Big Five mass extinctions, the end-Cretaceous biocrisis is an example of a bolide-triggered carbon-release event, the end-Permian and end-Triassic biocrises are examples of LIP-triggered carbon-release events, and the Late Ordovician and Late Devonian biocrises are examples of bioevolution-triggered carbon-burial events. Whereas the bolide-impact and LIP-eruption mechanisms appear to invariably cause carbon release, bioevolutionary triggers can result in variable carbon-cycle changes, e.g. carbon burial during the Late Ordovician and Late Devonian events, carbon release associated with modern anthropogenic climate warming, and little to no carbon-cycle impact due to certain types of ecosystem change (e.g. the advent of the first predators around the end-Ediacaran; the appearance of Paleolithic human hunters in Australasia and the Americas). Broadly speaking, studies of mass extinction causation have suffered from insufficiently critical thinking-an impartial survey of the extant evidence shows that (i) hypotheses of a common ultimate cause (e.g. bolide impacts or LIP eruptions) for all Big Five mass extinctions are suspect given manifest differences in patterns of environmental and biotic change among them; (ii) the Late Ordovician and Late Devonian events were associated with carbon burial and long-term climatic cooling, i.e. changes that are inconsistent with a bolide-impact or LIP-eruption mechanism; and (iii) claims of periodicity in Phanerozoic mass extinctions depended critically on the now-disproven idea that they shared a common extrinsic trigger (i.e. bolide impacts).

Depth and hierarchies in the predictive brain: From reaction to action

The human brain is a prediction device, a view widely accepted in neuroscience. Prediction is a rational and efficient response that relies on the brain's ability to create and employ generative models to optimize actions over unpredictable time horizons. We argue that extant predictive frameworks while compelling, have not explicitly accounted for the following: (a) The brain's generative models must incorporate predictive depth (i.e., rely on degrees of abstraction to enable predictions over different time horizons); (b) The brain's implementation scheme to account for varying predictive depth relies on dynamic predictive hierarchies formed using the brain's functional networks. We show that these hierarchies incorporate the ascending processes (driven by reaction), and the descending processes (related to prediction), eventually driving action. Because they are dynamically formed, predictive hierarchies allow the brain to address predictive challenges in virtually any domain. By way of application, we explain how this framework can be applied to heretofore poorly understood processes of human behavioral thermoregulation. Although mammalian thermoregulation has been closely tied to deep brain structures engaged in autonomic control such as the hypothalamus, this narrow conception does not translate well to humans. In addition to profound differences in evolutionary history, the human brain is bestowed with substantially increased functional complexity (that itself emerged from evolutionary differences). We argue that behavioral thermoregulation in humans is possible because, (a) ascending signals shaped by homeostatic sub-networks, interject with (b) descending signals related to prediction (implemented in interoceptive and executive sub-networks) and action (implemented in executive sub-networks). These sub-networks cumulatively form a predictive hierarchy for human thermoregulation, potentiating a range of viable responses to known and unknown thermoregulatory challenges. We suggest that our proposed extensions to the predictive framework provide a set of generalizable principles that can further illuminate the many facets of the predictive brain. This article is categorized under: Neuroscience > Behavior Philosophy > Action Psychology > Prediction.

A new phosphate purification method for igneous weathering profiles

RATIONALE

The oxygen isotope composition of phosphate (δ18 OPO4 ) is widely employed for reconstructing paleotemperature and tracing biogeochemical phosphorus cycling. However, existing phosphate purification protocols do not work well for igneous rocks and igneous weathering profiles (IWPs). A reliable purification method is needed for measuring δ18 OPO4 in these materials.

METHODS

Our phosphate purification method includes two steps of cation exchange resin treatment separated by a step of calcium phosphate precipitation (R-Ca-R method). In addition, the silver phosphate precipitation in our procedure is featured by slow evaporation to crystallization until the appearance of ammonium nitrate or silver nitrate crystals. We evaluated our methods on weathered and pristine igneous rocks, phosphorite rocks, KH2 PO4 , and (NH4 )2 HPO4 solutions.

RESULTS

Our purification method converted over 99.9% phosphate in solution to calcium phosphate, which can be easily decalcified by cation resin. The improved silver phosphate precipitation method produced high phosphate yields (97.1%-99.5%) and retained original δ18 OPO4 within analytical uncertainty (2σ = 0.6‰). We applied the purification and precipitation method on five igneous rocks and IWPs, and obtained δ18 OPO4 values ranging from 6.4‰ to 8.0‰. Duplicate phosphate extractions yielded δ18 OPO4 values differing by less than 0.3‰.

CONCLUSIONS

We developed a new phosphate purification method that is applicable to phosphate extraction in igneous rocks and IWPs. We also proposed a reliable indicator for the termination of silver phosphate precipitation. Our method can achieve high phosphate yield and reproducible δ18 OPO4 value.

Bayesian analyses indicate bivalves did not drive the downfall of brachiopods following the Permian-Triassic mass extinction

Certain times of major biotic replacement have often been interpreted as broadly competitive, mediated by innovation in the succeeding clades. A classic example was the switch from brachiopods to bivalves as major seabed organisms following the Permian-Triassic mass extinction (PTME), ~252 million years ago. This was attributed to competitive exclusion of brachiopods by the better adapted bivalves or simply to the fact that brachiopods had been hit especially hard by the PTME. The brachiopod-bivalve switch is emblematic of the global turnover of marine faunas from Palaeozoic-type to Modern-type triggered by the PTME. Here, using Bayesian analyses, we find that unexpectedly the two clades displayed similar large-scale trends of diversification before the Jurassic. Insight from a multivariate birth-death model shows that the extinction of major brachiopod clades during the PTME set the stage for the brachiopod-bivalve switch, with differential responses to high ocean temperatures post-extinction further facilitating their displacement by bivalves. Our study strengthens evidence that brachiopods and bivalves were not competitors over macroevolutionary time scales, with extinction events and environmental stresses shaping their divergent fates.

A Highly Diverse Olenekian Brachiopod Fauna from the Nanpanjiang Basin, South China, and Its Implications for the Early Triassic Biotic Recovery

As one of the predominant benthic organisms in the Palaeozoic, brachiopod was largely eliminated in the Permian-Triassic boundary mass extinction, and then highly diversified in the Middle Triassic. Since fossil data from the Early Triassic are rarely reported, the recovery patterns of Early Triassic brachiopods remain unclear. This study documents a well-preserved fauna that is the most diverse Olenekian brachiopod fauna so far (age constrained by conodont biostratigraphy) from the Datuguan section of ramp facies in South China. This fauna is composed of 14 species within nine genera, including six genera (Hirsutella, Sulcatinella, Paradoxothyris, Dioristella, Neoretzia and Isocrania) found in the Early Triassic for the first time and three new species, including Paradoxothyris flatus sp. nov., Hirsutella sulcata sp. nov. and Sulcatinella elongata sp. nov. The Datuguan fauna indicates that the diversity of Olenekian brachiopod fauna has been underestimated, which can be caused by a combination of reduced habitats (in geographic size and sedimentary type) compared with the end-Permian, great bed thickness making it difficult to find fossils and most species in the fauna having low abundance. Based on the faunal change in the Datuguan section and environmental changes in South China, it can be inferred that brachiopod recovery in the studied section occurred in the latest Spathian rather than the Smithian when the environment started to ameliorate. Global brachiopod data also indicates that the initial recovery of brachiopods happened in the Spathian, and many genera that widely occurred in the Middle or Late Triassic had originated in the Olenekian.

The stability and collapse of marine ecosystems during the Permian-Triassic mass extinction

The history of Earth's biodiversity is punctuated episodically by mass extinctions. These are characterized by major declines of taxon richness, but the accompanying ecological collapse has rarely been evaluated quantitatively. The Permian-Triassic mass extinction (PTME; ∼252 mya), as the greatest known extinction, permanently altered marine ecosystems and paved the way for the transition from Paleozoic to Mesozoic evolutionary faunas. Thus, the PTME offers a window into the relationship between taxon richness and ecological dynamics of ecosystems during a severe extinction. However, the accompanying ecological collapse through the PTME has not been evaluated in detail. Here, using food-web models and a marine paleocommunity dataset spanning the PTME, we show that after the first extinction phase, community stability decreased only slightly despite the loss of more than half of taxonomic diversity, while community stability significantly decreased in the second phase. Thus, taxonomic and ecological changes were unequivocally decoupled, with species richness declining severely ∼61 ka earlier than the collapse of marine ecosystem stability, implying that in major catastrophes, a biodiversity crash may be the harbinger of a more devastating ecosystem collapse.

Volcanic CO2 degassing postdates thermogenic carbon emission during the end-Permian mass extinction

Massive carbon dioxide (CO₂) emissions are widely assumed to be the driver of the end-Permian mass extinction (EPME). However, the rate of and total CO₂ released, and whether the source changes with time, remain poorly understood, leaving a key question surrounding the trigger for the EPME unanswered. Here, we assimilate reconstructions of atmospheric Pco₂ and carbonate δ¹³C in an Earth system model to unravel the history of carbon emissions and sources across the EPME. We infer a transition from a CO₂ source with a thermogenic carbon isotopic signature associated with a slower emission rate to a heavier, more mantle-dominated volcanic source with an increased rate of emissions. This implies that the CO₂ degassing style changed as the Siberian Traps emplacement evolved, which is consistent with geochemical proxy records. Carbon cycle feedbacks from terrestrial ecosystem disturbances may have further amplified the warming and the severity of marine extinctions.

Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction

Land plants can adjust the concentration of protective ultraviolet B (UV-B)-absorbing compounds (UACs) in the outer wall of their reproductive propagules in response to ambient UV-B flux. To infer changes in UV-B radiation flux at Earth's surface during the end-Permian mass extinction, we analyze UAC abundances in ca. 800 pollen grains from an independently dated Permian-Triassic boundary section in Tibet. Our data reveal an excursion in UACs that coincide with a spike in mercury concentration and a negative carbon-isotope excursion in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, global carbon and mercury cycle perturbations, and ozone layer disruption. Because enhanced UV-B radiation can exacerbate the environmental deterioration induced by massive magmatism, ozone depletion is considered a compelling ecological driver for the terrestrial mass extinction.

A diverse diapsid tooth assemblage from the Early Triassic (Driefontein locality, South Africa) records the recovery of diapsids following the end-Permian mass extinction

Mass extinctions change the trajectory of evolution and restructure ecosystems. The largest mass extinction, the end-Permian, is a particularly interesting case due to the hypothesized delay in the recovery of global ecosystems, where total trophic level recovery is not thought to have occurred until 5-9 million years after the extinction event. Diapsids, especially archosauromorphs, play an important role in this recovery, filling niches left vacant by therapsids and anapsids. However, the nature of lineage and ecological diversification of diapsids is obscured by the limited number of continuous, well-dated stratigraphic sections at the Permian-Triassic boundary and continuing through the first half of the Triassic. The Karoo Basin of South Africa is one such record, and particularly the late Early Triassic (Olenekian) Driefontein locality fills this gap in the diapsid fossil record. We collected a total of 102 teeth of which 81 are identified as diapsids and the remaining 21 as identified as temnospondyls. From the sample, seven distinct tooth morphotypes of diapsids are recognized, six of which are new to the locality. We used a combination of linear measurements, 3D geomorphometrics, and nMDS ordination to compare these morphotypes and made inferences about their possible diets. Although the morphotypes are readily differentiated in nMDS, the overall morphological disparity is low, and we infer five morphotypes are faunivorous with the other two potentially omnivorous or piscivorous based on their morphological similarities with dentitions from extant diapsids, demonstrating an unsampled taxonomic and ecological diversity of diapsids in the Early Triassic based on teeth. Although ecological specialization at Driefontein may be low, it records a diversity of diapsid taxa, specifically of archosauromorph lineages.

The hierarchy of factors predicting the latitudinal diversity gradient

The numerous explanations for why Earth's biodiversity is concentrated at low latitudes fail to explain variation in the strength and even direction of the gradient through deep time. Consequently, we do not know if today's gradient is representative of what might be expected on other planets or is merely an idiosyncrasy of Earth's history. We propose a hierarchy of factors driving the latitudinal distribution of diversity: (i) over geologically long time spans, diversity is largely predicted by climate; (ii) when climatic gradients are shallow, diversity tracks habitat area; and (iii) historical contingencies linked to niche conservatism have geologically short-term, transient influence at most. Thus, latitudinal diversity gradients, although variable in strength and direction, are largely predictable on our planet and possibly others.

Palaeoecology of the Hiraiso Formation (Miyagi Prefecture, Japan) and implications for the recovery following the end-Permian mass extinction

The Hiraiso Formation of northeast Japan represents an important and under-explored archive of Early Triassic marine ecosystems. Here, we present a palaeoecological analysis of its benthic faunas in order to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition. In addition, we utilise redox proxies to make inferences about the redox state of the depositional environments. We then use this data to explore the pace of recovery in the Early Triassic, and the habitable zone hypothesis, where wave aerated marine environments are thought to represent an oxygenated refuge. The age of the Hiraiso Formation is equivocal due to the lack of key biostratigraphical index fossils, but new ammonoid finds in this study support an early Spathian age. The ichnofossils from the Hiraiso Formation show an onshore-offshore trend with high diversity and relatively large faunas in offshore transition settings and a low diversity of small ichnofossils in basinal settings. The body fossils do not, however, record either spatial or temporal changes, because the shell beds represent allochthonous assemblages due to wave reworking. The dominance of small burrow sizes, presence of key taxa including Thalassinoides, Rhizocorallium and Holocrinus, presence of complex trace fossils, and both erect and deep infaunal tiering organisms suggests that the benthic fauna represents an advanced stage of ecological recovery for the Early Triassic, but not full recovery. The ecological state suggests a similar level of ecological complexity to late Griesbachian and Spathian communities elsewhere, with the Spathian marking a globally important stage of recovery following the mass extinction. The onshore-offshore distribution of the benthic faunas supports the habitable zone hypothesis. This gradient is, however, also consistent with onshore-offshore ecological gradients known to be controlled by oxygen gradients in modern tropical and subtropical settings. This suggests that the habitable zone is not an oxygenated refuge that is only restricted to anoxic events. The lack of observed full recovery is likely a consequence of a persistent oxygen-limitation (dysoxic conditions), hot Early Triassic temperatures and the lack of a steep temperature/water-depth gradient within the habitable zone.

The PhanSST global database of Phanerozoic sea surface temperature proxy data

Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary, geochemical, diagenetic, and proxy calibration studies.

Extinction magnitude of animals in the near future

There have been five major mass extinctions and some minor mass extinctions of animals since early animal diversification 540-520 Myr ago. It is said that a sixth mass extinction is already underway. However, the future extinction magnitude has not been quantitatively estimated. Here, I show that the sixth major mass extinction (defined as > 60% species loss) will be avoided, but a minor mass extinction, 20-50% animal species loss (1% now), will occur when humans cause nuclear war and/or fail to stop increasing greenhouse gas (GHG) emissions, pollution, and deforestation until 2060-2080 CE. When humans decrease GHG emissions, pollution, and deforestation in 40 years and prevent nuclear war in the future, 10-15% animal species loss will occur. Humans should stop not only industrial GHG emissions but also deforestation, environmental pollution, and nuclear war to prevent this mass extinction. When humans fail to stop these processes, significant decreases in biodiversity and the human population and a collapse of ecological balance will occur on Earth.

A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China

The Smithian-Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian-Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ13Ccarb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ7 and UAZ8 thus leaving some flexibility for future refinement and updating.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13358-022-00259-x.

An 80-million-year sulphur isotope record of pyrite burial over the Permian-Triassic

Despite the extensive use of sulphur isotope ratios (δ³⁴S) for understanding ancient biogeochemical cycles, many studies focus on specific time-points of interest, such as the end-Permian mass extinction (EPME). We have generated an 80 million-year Permian-Triassic δ³⁴S_evap curve from the Staithes S-20 borehole, Yorkshire, England. The Staithes δ³⁴S_evap record replicates the major features of the global curve, while confirming a new excursion at the Olenekian/Anisian boundary at ~ 247 million years ago. We incorporate the resultant δ³⁴S_evap curve into a sulphur isotope box model. Our modelling approach reveals three significant pyrite burial events (i.e. PBEs) in the Triassic. In particular, it predicts a significant biogeochemical response across the EPME, resulting in a substantial increase in pyrite burial, possibly driven by Siberian Traps volcanism. Our model suggests that after ~ 10 million years pyrite burial achieves relative long-term stability until the latest Triassic.

Breathless through Time: Oxygen and Animals across Earth's History

AbstractOxygen levels in the atmosphere and ocean have changed dramatically over Earth history, with major impacts on marine life. Because the early part of Earth's history lacked both atmospheric oxygen and animals, a persistent co-evolutionary narrative has developed linking oxygen change with changes in animal diversity. Although it was long believed that oxygen rose to essentially modern levels around the Cambrian period, a more muted increase is now believed likely. Thus, if oxygen increase facilitated the Cambrian explosion, it did so by crossing critical ecological thresholds at low O₂. Atmospheric oxygen likely remained at low or moderate levels through the early Paleozoic era, and this likely contributed to high metazoan extinction rates until oxygen finally rose to modern levels in the later Paleozoic. After this point, ocean deoxygenation (and marine mass extinctions) is increasingly linked to large igneous province eruptions-massive volcanic carbon inputs to the Earth system that caused global warming, ocean acidification, and oxygen loss. Although the timescales of these ancient events limit their utility as exact analogs for modern anthropogenic global change, the clear message from the geologic record is that large and rapid CO₂ injections into the Earth system consistently cause the same deadly trio of stressors that are observed today. The next frontier in understanding the impact of oxygen changes (or, more broadly, temperature-dependent hypoxia) in deep time requires approaches from ecophysiology that will help conservation biologists better calibrate the response of the biosphere at large taxonomic, spatial, and temporal scales.

Successive climate crises in the deep past drove the early evolution and radiation of reptiles

Climate change-induced mass extinctions provide unique opportunities to explore the impacts of global environmental disturbances on organismal evolution. However, their influence on terrestrial ecosystems remains poorly understood. Here, we provide a new time tree for the early evolution of reptiles and their closest relatives to reconstruct how the Permian-Triassic climatic crises shaped their long-term evolutionary trajectory. By combining rates of phenotypic evolution, mode of selection, body size, and global temperature data, we reveal an intimate association between reptile evolutionary dynamics and climate change in the deep past. We show that the origin and phenotypic radiation of reptiles was not solely driven by ecological opportunity following the end-Permian extinction as previously thought but also the result of multiple adaptive responses to climatic shifts spanning 57 million years.

Resilience of infaunal ecosystems during the Early Triassic greenhouse Earth

The Permian-Triassic mass extinction severely depleted biodiversity, primarily observed in the body fossil of well-skeletonized animals. Understanding how whole ecosystems were affected and rebuilt following the crisis requires evidence from both skeletonized and soft-bodied animals; the best comprehensive information on soft-bodied animals comes from ichnofossils. We analyzed abundant trace fossils from 26 sections across the Permian-Triassic boundary in China and report key metrics of ichnodiversity, ichnodisparity, ecospace utilization, and ecosystem engineering. We find that infaunal ecologic structure was well established in the early Smithian. Decoupling of diversity between deposit feeders and suspension feeders in carbonate ramp-platform settings implies that an effect of trophic group amensalism could have delayed the recovery of nonmotile, suspension-feeding epifauna in the Early Triassic. This differential reaction of infaunal ecosystems to variable environmental controls thus played a substantial but heretofore little appreciated evolutionary and ecologic role in the overall recovery in the hot Early Triassic ocean.

Marine siliceous ecosystem decline led to sustained anomalous Early Triassic warmth

In the wake of rapid CO2 release tied to the emplacement of the Siberian Traps, elevated temperatures were maintained for over five million years during the end-Permian biotic crisis. This protracted recovery defies our current understanding of climate regulation via the silicate weathering feedback, and hints at a fundamentally altered carbon and silica cycle. Here, we propose that the development of widespread marine anoxia and Si-rich conditions, linked to the collapse of the biological silica factory, warming, and increased weathering, was capable of trapping Earth's system within a hyperthermal by enhancing ocean-atmosphere CO2 recycling via authigenic clay formation. While solid-Earth degassing may have acted as a trigger, subsequent biotic feedbacks likely exacerbated and prolonged the environmental crisis. This refined view of the carbon-silica cycle highlights that the ecological success of siliceous organisms exerts a potentially significant influence on Earth's climate regime.

Ocean temperatures through the Phanerozoic reassessed

The oxygen isotope compositions of carbonate and phosphatic fossils hold the key to understanding Earth-system evolution during the last 500 million years. Unfortunately, the validity and interpretation of this record remain unsettled. Our comprehensive compilation of Phanerozoic δ¹⁸O data for carbonate and phosphate fossils and microfossils (totaling 22,332 and 4615 analyses, respectively) shows rapid shifts best explained by temperature change. In calculating paleotemperatures, we apply a constant hydrosphere δ¹⁸O, correct seawater δ¹⁸O for ice volume and paleolatitude, and correct belemnite δ¹⁸O values for ¹⁸O enrichment. Similar paleotemperature trends for carbonates and phosphates confirm retention of original isotopic signatures. Average low-latitude (30° S–30° N) paleotemperatures for shallow environments decline from 42.0 ± 3.1 °C in the Early-to-Middle Ordovician to 35.6 ± 2.4 °C for the Late Ordovician through the Devonian, then fluctuate around 25.1 ± 3.5 °C from the Mississippian to today. The Early Triassic and Middle Cretaceous stand out as hothouse intervals. Correlations between atmospheric CO₂ forcing and paleotemperature support CO₂’s role as a climate driver in the Paleozoic.

Global diversity dynamics in the fossil record are regionally heterogeneous

Global diversity patterns in the fossil record comprise a mosaic of regional trends, underpinned by spatially non-random drivers and distorted by variation in sampling intensity through time and across space. Sampling-corrected diversity estimates from spatially-standardised fossil datasets retain their regional biogeographic nuances and avoid these biases, yet diversity-through-time arises from the interplay of origination and extinction, the processes that shape macroevolutionary history. Here we present a subsampling algorithm to eliminate spatial sampling bias, coupled with advanced probabilistic methods for estimating origination and extinction rates and a Bayesian method for estimating sampling-corrected diversity. We then re-examine the Late Permian to Early Jurassic marine fossil record, an interval spanning several global biotic upheavals that shaped the origins of the modern marine biosphere. We find that origination and extinction rates are regionally heterogenous even during events that manifested globally, highlighting the need for spatially explicit views of macroevolutionary processes through geological time.

Global diversity trends in the fossil record vary regionally through time and space, affecting our ability to interpret macroevolutionary history. Here, the authors propose a method to eliminate spatial sampling bias, estimate origination and extinction rates, and generate diversity estimates, applying this method to the Late Permian to Early Jurassic marine fossil record.

Low tropical diversity during the adaptive radiation of early land plants

The latitudinal biodiversity gradient, with tropical regions acting as 'evolutionary cradles', is a cornerstone of current biogeographical and ecological theory¹. In the modern world floral biodiversity and biomass are overwhelmingly concentrated in the tropics, and it is often assumed that the tropics were evolutionary cradles throughout land plant evolutionary history. For example, the origination and diversification of angiosperms is believed to have taken place in the Cretaceous tropics² and modern gymnosperms in the Permian tropics³. Here, we show that during the first major diversification of land plants, in the Late Silurian-Early Devonian, land plant biodiversity was much lower at the equator compared to medium-high southern latitudes. Throughout this crucial interval of plant evolution, tropical vegetation remained depauperate and of very low taxonomic biodiversity, although with similar morphological disparity to the more diverse higher latitude floras. Possible explanations for this low tropical floral biodiversity include palaeocontinental configuration or adverse palaeotropical environmental conditions. We discount the possibility that it was simply a fortuitous feature of the biogeographical spread of the earliest vascular land plants.

Early evolution of beetles regulated by the end-Permian deforestation

The end-Permian mass extinction (EPME) led to a severe terrestrial ecosystem collapse. However, the ecological response of insects—the most diverse group of organisms on Earth—to the EPME remains poorly understood. Here, we analyse beetle evolutionary history based on taxonomic diversity, morphological disparity, phylogeny, and ecological shifts from the Early Permian to Middle Triassic, using a comprehensive new dataset. Permian beetles were dominated by xylophagous stem groups with high diversity and disparity, which probably played an underappreciated role in the Permian carbon cycle. Our suite of analyses shows that Permian xylophagous beetles suffered a severe extinction during the EPME largely due to the collapse of forest ecosystems, resulting in an Early Triassic gap of xylophagous beetles. New xylophagous beetles appeared widely in the early Middle Triassic, which is consistent with the restoration of forest ecosystems. Our results highlight the ecological significance of insects in deep-time terrestrial ecosystems.

Living fast in the Triassic: New data on life history in Lystrosaurus (Therapsida: Dicynodontia) from northeastern Pangea

Lystrosaurus was one of the few tetrapods to survive the Permo-Triassic mass extinction, the most profound biotic crisis in Earth’s history. The wide paleolatitudinal range and high abundance of Lystrosaurus during the Early Triassic provide a unique opportunity to investigate changes in growth dynamics and longevity following the mass extinction, yet most studies have focused only on species that lived in the southern hemisphere. Here, we present the long bone histology from twenty Lystrosaurus skeletal elements spanning a range of sizes that were collected in the Jiucaiyuan Formation of northwestern China. In addition, we compare the average body size of northern and southern Pangean Triassic-aged species and conduct cranial geometric morphometric analyses of southern and northern taxa to begin investigating whether specimens from China are likely to be taxonomically distinct from South African specimens. We demonstrate that Lystrosaurus from China have larger average body sizes than their southern Pangean relatives and that their cranial morphologies are distinctive. The osteohistological examination revealed sustained, rapid osteogenesis punctuated by growth marks in some, but not all, immature individuals from China. We find that the osteohistology of Chinese Lystrosaurus shares a similar growth pattern with South African species that show sustained growth until death. However, bone growth arrests more frequently in the Chinese sample. Nevertheless, none of the long bones sampled here indicate that maximum or asymptotic size was reached, suggesting that the maximum size of Lystrosaurus from the Jiucaiyuan Formation remains unknown.

Lethal microbial blooms delayed freshwater ecosystem recovery following the end-Permian extinction

Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. We demonstrate that climate changes and deforestation can drive recurrent microbial blooms, inhibiting the recovery of freshwater ecosystems for hundreds of millennia. From the stratigraphic successions of the Sydney Basin, Australia, our fossil, sedimentary and geochemical data reveal bloom events following forest ecosystem collapse during the most severe mass extinction in Earth’s history, the end-Permian event (EPE; c. 252.2 Ma). Microbial communities proliferated in lowland fresh and brackish waterbodies, with algal concentrations typical of modern blooms. These initiated before any trace of post-extinction recovery vegetation but recurred episodically for >100 kyrs. During the following 3 Myrs, algae and bacteria thrived within short-lived, poorly-oxygenated, and likely toxic lakes and rivers. Comparisons to global deep-time records indicate that microbial blooms are persistent freshwater ecological stressors during warming-driven extinction events.

Harmful algal and bacterial blooms are increasingly frequent in lakes and rivers. From the Sydney Basin, Australia, this study uses fossil, sedimentary and geochemical data to reveal bloom events following forest ecosystem collapse during the end-Permian event and that blooms have consistently followed warming-related extinction events, inhibiting the recovery of freshwater ecosystems for millennia.

Thresholds of temperature change for mass extinctions

Climate change is a critical factor affecting biodiversity. However, the quantitative relationship between temperature change and extinction is unclear. Here, we analyze magnitudes and rates of temperature change and extinction rates of marine fossils through the past 450 million years (Myr). The results show that both the rate and magnitude of temperature change are significantly positively correlated with the extinction rate of marine animals. Major mass extinctions in the Phanerozoic can be linked to thresholds in climate change (warming or cooling) that equate to magnitudes >5.2 °C and rates >10 °C/Myr. The significant relationship between temperature change and extinction still exists when we exclude the five largest mass extinctions of the Phanerozoic. Our findings predict that a temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.

The main stage of recovery after the end-Permian mass extinction: taxonomic rediversification and ecologic reorganization of marine level-bottom communities during the Middle Triassic

The recovery of marine life from the end-Permian mass extinction event provides a test-case for biodiversification models in general, but few studies have addressed this episode in its full length and ecological context. This study analyses the recovery of marine level-bottom communities from the end-Permian mass extinction event over a period of 15 Ma, with a main focus on the previously neglected main phase during the Middle Triassic. Our analyses are based on faunas from 37 lithological units representing different environmental settings, ranging from lagoons to inner, mid- and outer ramps. Our dataset comprises 1562 species, which belong to 13 higher taxa and 12 ecological guilds. The diversification pattern of most taxa and guilds shows an initial Early Triassic lag phase that is followed by a hyperbolic diversity increase during the Bithynian (early middle Anisian) and became damped later in the Middle Triassic. The hyperbolic diversity increase is not predicted by models that suggest environmental causes for the initial lag phase. We therefore advocate a model in which diversification is primarily driven by the intensity of biotic interactions. Accordingly, the Early Triassic lag phase represents the time when the reduced species richness in the wake of the end-Permian mass extinction was insufficient for stimulating major diversifications, whereas the Anisian main diversification event started when self-accelerating processes became effective and stopped when niche-crowding prevented further diversification. Biotic interactions that might drive this pattern include interspecific competition but also habitat construction, ecosystem engineering and new options for trophic relationships. The latter factors are discussed in the context of the resurgence of large carbonate platforms, which occurred simultaneously with the diversification of benthic communities. These did not only provide new hardground habitats for a variety of epifaunal taxa, but also new options for grazing gastropods that supposedly fed from microalgae growing on dasycladaceans and other macroalgae. Whereas we do not claim that changing environmental conditions were generally unimportant for the recovery of marine level-bottom communities, we note that their actual role can only be assessed when tested against predictions of the biotic model.

Metabolic tradeoffs control biodiversity gradients through geological time

The latitudinal gradient of increasing marine biodiversity from the poles to the tropics is one of the most conspicuous biological patterns in modern oceans.^1-3 Low-latitude regions of the global ocean are often hotspots of animal biodiversity, yet they are set to be most critically affected by anthropogenic climate change.⁴ As ocean temperatures rise and deoxygenation proceeds in the coming centuries, the volume of aerobically viable habitat is predicted to decrease in these zones.^5,6 In contrast to the slightly asymmetrical modern latitudinal biodiversity gradient,⁷ compilations of fossil occurrences indicate peaks in biodiversity may have existed much further away from the equator in the past, with transitions between climate states hypothesized to explain this trend.^8-13 We combine a new compilation of fossil mollusc occurrences, paleotemperature proxies, and biogeographic data to reveal a non-monotonic relationship between temperature and diversity in the paleontological record over the last 145 million years. We derive a metabolic model that integrates the kinetic effects of temperature on biodiversity¹⁴ with the recently described Metabolic Index that calculates aerobic habitat availability based on the effect of temperature on hypoxia sensitivity.^5,15,16 Although factors such as coastal habitat area and homeothermy are important,^17,18 we find strong congruence between our metabolic model and our fossil and paleotemperature meta-analysis. We therefore suggest that the effects of ocean temperature on the aerobic scope of marine ectotherms is a primary driver of migrating biodiversity peaks through geologic time and will likely play a role in the restructuring of biodiversity under projected future climate scenarios.

Evidence from South Africa for a protracted end-Permian extinction on land

Earth's largest biotic crisis occurred during the Permo-Triassic Transition (PTT). On land, this event witnessed a turnover from synapsid- to archosauromorph-dominated assemblages and a restructuring of terrestrial ecosystems. However, understanding extinction patterns has been limited by a lack of high-precision fossil occurrence data to resolve events on submillion-year timescales. We analyzed a unique database of 588 fossil tetrapod specimens from South Africa's Karoo Basin, spanning ∼4 My, and 13 stratigraphic bin intervals averaging 300,000 y each. Using sample-standardized methods, we characterized faunal assemblage dynamics during the PTT. High regional extinction rates occurred through a protracted interval of ∼1 Ma, initially co-occurring with low origination rates. This resulted in declining diversity up to the acme of extinction near the Daptocephalus-Lystrosaurus declivis Assemblage Zone boundary. Regional origination rates increased abruptly above this boundary, co-occurring with high extinction rates to drive rapid turnover and an assemblage of short-lived species symptomatic of ecosystem instability. The "disaster taxon" Lystrosaurus shows a long-term trend of increasing abundance initiated in the latest Permian. Lystrosaurus comprised 54% of all specimens by the onset of mass extinction and 70% in the extinction aftermath. This early Lystrosaurus abundance suggests its expansion was facilitated by environmental changes rather than by ecological opportunity following the extinctions of other species as commonly assumed for disaster taxa. Our findings conservatively place the Karoo extinction interval closer in time, but not coeval with, the more rapid marine event and reveal key differences between the PTT extinctions on land and in the oceans.

Six-fold increase of atmospheric pCO2 during the Permian-Triassic mass extinction

The Permian–Triassic mass extinction was marked by a massive release of carbon into the ocean-atmosphere system, evidenced by a sharp negative carbon isotope excursion. Large carbon emissions would have increased atmospheric pCO₂ and caused global warming. However, the magnitude of pCO₂ changes during the PTME has not yet been estimated. Here, we present a continuous pCO₂ record across the PTME reconstructed from high-resolution δ¹³C of C₃ plants from southwestern China. We show that pCO₂ increased from 426 +133/−96 ppmv in the latest Permian to 2507 +4764/−1193 ppmv at the PTME within about 75 kyr, and that the reconstructed pCO₂ significantly correlates with sea surface temperatures. Mass balance modelling suggests that volcanic CO₂ is probably not the only trigger of the carbon cycle perturbation, and that large quantities of ¹³C-depleted carbon emission from organic matter and methane were likely required during complex interactions with the Siberian Traps volcanism.

The Permian–Triassic mass extinction was accompanied by a massive release of carbon into the ocean-atmosphere system, but the magnitude of change is not well known. Here, the authors present a new record of C₃ plants from southwestern China which shows that atmospheric pCO₂ increased by a factor of six during this event.

Different triggers for the two pulses of mass extinction across the Permian and Triassic boundary

Widespread ocean anoxia has been proposed to cause biotic mass extinction across the Permian-Triassic (P-Tr) boundary. However, its temporal dynamics during this crisis period are unclear. The Liangfengya section in the South China Block contains continuous marine sedimentary and fossil records. Two pulses of biotic extinction and two mass extinction horizons (MEH 1 & 2) near the P-Tr boundary were identified and defined based on lithology and fossils from the section. The data showed that the two pulses of extinction have different environmental triggers. The first pulse occurred during the latest Permian, characterized by disappearance of algae, large foraminifers, and fusulinids. Approaching the MEH 1, multiple layers of volcanic clay and yellowish micritic limestone occurred, suggesting intense volcanic eruptions and terrigenous influx. The second pulse occurred in the earliest Triassic, characterized by opportunist-dominated communities of low diversity and high abundance, and resulted in a structural marine ecosystem change. The oxygen deficiency inferred by pyrite framboid data is associated with biotic declines above the MEH 2, suggesting that the anoxia plays an important role.

Preliminary bone histological analysis of Lystrosaurus (Therapsida: Dicynodontia) from the Lower Triassic of North China, and its implication for lifestyle and environments after the end-Permian extinction

Lystrosaurus represents one of the most successful dicynodonts, a survivor of the end-Permian mass extinction that remained abundant in the Early Triassic, but many aspects of its paleobiology are still controversial. The bone histology of Lystrosaurus species from South Africa and India has provided important information on their growth strategy and lifestyle, but until recently no data was available on the bone histology of Lystrosaurus from China. Here, we report on the bone microstructure of seven Lystrosaurus individuals from the Lower Triassic of Xinjiang, providing the first such data for the Chinese Lystrosaurus species. Our samples indicate that the microstructure of Lystrosaurus limb bones from China is characterized by fibrolamellar bone tissue similar to those from South Africa and India. Three ontogenetic stages were identified: juvenile, early subadult, and late subadult based on lines of arrested growth (LAGs) and bone tissue changes. Bone histology supports a rapid growth strategy for Lystrosaurus during early ontogeny. Unlike Early Triassic Lystrosaurus from South Africa, lines of arrested growth are common in our specimens, suggesting that many individuals of Chinese Lystrosaurus had reached the subadult stage and were interrupted in growth. The differences in bone histology between Lystrosaurus from South Africa and China may indicate different environmental conditions in these two regions.

Climate impacts on organisms, ecosystems and human societies: integrating OCLTT into a wider context

Physiological studies contribute to a cause and effect understanding of ecological patterns under climate change and identify the scope and limits of adaptation. Across most habitats, this requires analyzing organism responses to warming, which can be modified by other drivers such as acidification and oxygen loss in aquatic environments or excess humidity or drought on land. Experimental findings support the hypothesis that the width and temperature range of thermal performance curves relate to biogeographical range. Current warming causes range shifts, hypothesized to include constraints in aerobic power budget which in turn are elicited by limitations in oxygen supply capacity in relation to demand. Different metabolic scopes involved may set the borders of both the fundamental niche (at standard metabolic rate) and the realized niche (at routine rate). Relative scopes for aerobic performance also set the capacity of species to interact with others at the ecosystem level. Niche limits and widths are shifting and probably interdependent across life stages, with young adults being least thermally vulnerable. The principles of thermal tolerance and performance may also apply to endotherms including humans, their habitat and human society. Overall, phylogenetically based comparisons would need to consider the life cycle of species as well as organism functional properties across climate zones and time scales. This Review concludes with a perspective on how mechanism-based understanding allows scrutinizing often simplified modeling approaches projecting future climate impacts and risks for aquatic and terrestrial ecosystems. It also emphasizes the usefulness of a consensus-building process among experimentalists for better recognition in the climate debate.

Victims of ancient hyperthermal events herald the fates of marine clades and traits under global warming

Organismic groups vary non-randomly in their vulnerability to extinction. However, it is unclear whether the same groups are consistently vulnerable, regardless of the dominant extinction drivers, or whether certain drivers have their own distinctive and predictable victims. Given the challenges presented by anthropogenic global warming, we focus on changes in extinction selectivity trends during ancient hyperthermal events: geologically rapid episodes of global warming. Focusing on the fossil record of the last 300 million years, we identify clades and traits of marine ectotherms that were more prone to extinction under the onset of six hyperthermal events than during other times. Hyperthermals enhanced the vulnerability of marine fauna that host photosymbionts, particularly zooxanthellate corals, the reef environments they provide, and genera with actively burrowing or swimming adult life-stages. The extinction risk of larger sized fauna also increased relative to non-hyperthermal times, while genera with a poorly buffered internal physiology did not become more vulnerable on average during hyperthermals. Hyperthermal-vulnerable clades include rhynchonelliform brachiopods and bony fish, whereas resistant clades include cartilaginous fish, and ostreid and venerid bivalves. These extinction responses in the geological past mirror modern responses of these groups to warming, including range-shift magnitudes, population losses, and experimental performance under climate-related stressors. Accordingly, extinction mechanisms distinctive to rapid global warming may be indicated, including sensitivity to warming-induced seawater deoxygenation. In anticipation of modern warming-driven marine extinctions, the trends illustrated in the fossil record offer an expedient preview.

Archosauriform footprints in the Lower Triassic of Western Alps and their role in understanding the effects of the Permian-Triassic hyperthermal

The most accepted killing model for the Permian-Triassic mass extinction (PTME) postulates that massive volcanic eruption (i.e., the Siberian Traps Large Igneous Province) led to geologically rapid global warming, acid rain and ocean anoxia. On land, habitable zones were drastically reduced, due to the combined effects of heating, drought and acid rains. This hyperthermal had severe effects also on the paleobiogeography of several groups of organisms. Among those, the tetrapods, whose geographical distribution across the end-Permian mass extinction (EPME) was the subject of controversy in a number of recent papers. We here describe and interpret a new Early Triassic (?Olenekian) archosauriform track assemblage from the Gardetta Plateau (Briançonnais, Western Alps, Italy) which, at the Permian-Triassic boundary, was placed at about 11° North. The tracks, both arranged in trackways and documented by single, well-preserved imprints, are assigned to Isochirotherium gardettensis ichnosp. nov., and are here interpreted as produced by a non-archosaurian archosauriform (erytrosuchid?) trackmaker. This new discovery provides further evidence for the presence of archosauriformes at low latitudes during the Early Triassic epoch, supporting a model in which the PTME did not completely vacate low-latitude lands from tetrapods that therefore would have been able to cope with the extreme hot temperatures of Pangaea mainland.

A Receptor of the Immunoglobulin Superfamily Regulates Adaptive Thermogenesis

Exquisite regulation of energy homeostasis protects from nutrient deprivation but causes metabolic dysfunction upon nutrient excess. In human and murine adipose tissue, the accumulation of ligands of the receptor for advanced glycation end products (RAGE) accompanies obesity, implicating this receptor in energy metabolism. Here, we demonstrate that mice bearing global- or adipocyte-specific deletion of Ager, the gene encoding RAGE, display superior metabolic recovery after fasting, a cold challenge, or high-fat feeding. The RAGE-dependent mechanisms were traced to suppression of protein kinase A (PKA)-mediated phosphorylation of its key targets, hormone-sensitive lipase and p38 mitogen-activated protein kinase, upon β-adrenergic receptor stimulation—processes that dampen the expression and activity of uncoupling protein 1 (UCP1) and thermogenic programs. This work identifies the innate role of RAGE as a key node in the immunometabolic networks that control responses to nutrient supply and cold challenges, and it unveils opportunities to harness energy expenditure in environmental and metabolic stress.

Hurtado del Pozo et al. show that the deletion of adipocyte RAGE, whose ligands accumulate in metabolic stress, protects from obesity and cold challenges through the modulation of protein kinase A activities. This work adds RAGE to the immunometabolic networks that regulate energy expenditure in environmental and metabolic stress.

Flat latitudinal diversity gradient caused by the Permian-Triassic mass extinction

The latitudinal diversity gradient (LDG) is recognized as one of the most pervasive, global patterns of present-day biodiversity. However, the controlling mechanisms have proved difficult to identify because many potential drivers covary in space. The geological record presents a unique opportunity for understanding the mechanisms which drive the LDG by providing a direct window to deep-time biogeographic dynamics. Here we used a comprehensive database containing 52,318 occurrences of marine fossils to show that the shape of the LDG changed greatly during the Permian-Triassic mass extinction from showing a significant tropical peak to a flattened LDG. The flat LDG lasted for the entire Early Triassic (∼5 My) before reverting to a modern-like shape in the Middle Triassic. The environmental extremes that prevailed globally, especially the dramatic warming, likely induced selective extinction in low latitudes and accumulation of diversity in high latitudes through origination and poleward migration, which combined together account for the flat LDG of the Early Triassic.