end-Triassic Extinction Research Articles

Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions

The end-Triassic extinction (ETE) on land was synchronous with the initial lavas of the Central Atlantic Magmatic Province (CAMP) and occurred just after the brief 26 thousand year (kyr) reverse geomagnetic polarity Chron E23r that can be used for global correlation. Lava-by-lava paleomagnetic secular variation data, previously reported from Morocco and northeastern United States combined with our data for the North Mountain Basalt from the Fundy Basin of Canada show that the initial phase of CAMP volcanism occurred in only five directional groups or pulses each occupying less than a century. The first four directional groups occur during a ~40 kyr period based on available astrochronology and U-Pb geochronology. The coincidence of the initial major pulse of CAMP volcanism with the ETE points to short-lived volcanic winters albedo-induced by sulfate aerosols as a plausible key agent of the extinctions in the tropical continental realm, whereas looser correlations allow prolonged CO2 emissions to contribute to more long-ranging effects in the marine realm via ocean acidification and longer-term warming.

The Permian – Triassic boundary in Peninsular India and the extinction of the Glossopteridales

The Glossopteridales was a distinctive order of gymnospermous seed-plants that occurred widely in the Permian of Gondwana. Some authors have suggested that they may also have occurred in the Triassic and so had survived the catastrophic Permian – Triassic extinction event. This suggestion was mainly based on records from peninsular India such as from the Panchet Formation, which traditionally was regarded as Triassic in age. This paper reviews the evidence for a Triassic age for these floras and it is argued that they are in fact late Permian. There is no clear evidence that the Glossopteridales survived the P/T biotic crisis in India and only unequivocal evidence is in China that they survived into the Triassic.

Unveiling a new oceanic anoxic event at the Norian/Rhaetian boundary (Late Triassic)

The latest Triassic was characterised by protracted biotic extinctions concluding in the End-Triassic Extinction (~ 200 Ma) and a global carbon cycle perturbation. The onset of declining diversity is closely related to reducing conditions that spread globally from upper Sevatian (uppermost Norian) to across the Norian-Rhaetian boundary, likely triggered by unusually high volcanic activity. We correlate significant organic carbon cycle perturbations to an increase of CO2 in the ocean–atmosphere system, likely outgassed by the Angayucham igneous province, the onset of which is indicated by the initiation of a rapid decline in 87Sr/86Sr and 188Os/187Os seawater values. A possible causal mechanism involves elevated CO2 levels causing global warming and accelerating chemical weathering, which increased nutrient discharge to the oceans and greatly increased biological productivity. Higher export production and oxidation of organic matter led to a global O2 decrease in marine water across the Norian/Rhaetian boundary (NRB). Biotic consequences of dysoxia/anoxia include worldwide extinctions in some fossil groups, such as bivalves, ammonoids, conodonts, radiolarians.

Bone Connectivity and the Evolution of Ichthyosaur Fins

After the end-Triassic extinction, parvipelvian ichthyosaurs diversified and became dominant elements of marine ecosystems worldwide. By the Early Jurassic, they achieved a thunniform body plan that persisted for the last 100 m.y.a of their evolution. Diversification and extinctions of thunniform ichthyosaurs, and their swimming performance, have been studied from different perspectives. The transformation of limbs into hydrofoil-like structures for better control and stability during swimming predates thunniform locomotion. Despite their importance as control surfaces, fin evolution among thunnosaurs remains poorly understood. We explore ichthyosaur fin diversity using anatomical networks. Our results indicate that, under a common hydrofoil controller fin, the bone arrangement diversity of the ichthyosaur fin was greater than traditionally assumed. Changes in the connectivity pattern occurred stepwise throughout the Mesozoic. Coupled with other lines of evidence, such as the presence of a ball-and-socket joint at the leading edge of some derived Platypterygiinae, we hypothesize that fin network disparity also mirrored functional disparity likely associated with different capabilities of refined maneuvering. The ball-and-socket articulation indicates that this local point could be acting like a multiaxial intrafin joint changing the angle of attack and thus affecting the maneuverability, similar to the alula of flying birds. Further studies on large samples and quantitative experimental approaches would be worthy to test this hypothesis.

Patterns of extinction and recovery across the Triassic–Jurassic boundary interval in three resilient Southern Tethyan carbonate platforms

During the end-Triassic extinction (ETE), carbonate platform biocalcifiers suffered high extinction rates that have been linked to volcanically-induced global changes in climate and carbon cycle. Most studies have been focused on the classical sections of the Northern Calcareous Alps (NCA, Austria) and Lombardy Basin (Italy), where the extinction of the aragonitic Dachstein-type biota (involutinid foraminifera and megalodontid bivalves) coincides with the demise of the carbonate platform and with the initial negative carbon isotope excursion (CIE) of the reference sections for the Triassic/Jurassic Boundary (TJB).In this study, we present a detailed facies analysis, bio- and carbon-isotope stratigraphy of three Southern Tethyan carbonate platform sections, Mt. Messapion (Greece), Valle Agricola and Mt. Sparagio (southern Italy) that instead show persisting carbonate productivity across the TJB and potentially preserve the most detailed record of timing and patterns of the ETE in these ecosystems.In the studied sections, the disappearance of the Dachstein-type biota is observed within a positive δ13Ccarb excursion that, according to our study, correlates with that documented in the Schattwald beds (NCA) and Malanotte Fm (Lombardy Basin) above the initial CIE. This level represents the true extinction of the Dachstein-type biota, while the disappearance in the Northern Tethyan sections of the NCA and Lombardy Basin represents a pseudoextinction coinciding with the carbonate platform demise. Above the ETE, Southern Tethyan carbonate platform sections are characterized either by microbial laminites or ooid and oncoid limestones and low-diversity associations.This study reveals a possible paleogeographic and/or latitudinal control on the response of biocalcifiers and carbonate platform ecosystems during the ETE. The Dachstein-type biota was resilient to the environmental perturbations associated with the initial CIE in Southern Tethys, but probably failed to survive subsequent and/or prolonged stress. Despite extinctions, Southern Tethyan carbonate platforms adapted to environmental disturbances through a shift of the dominant carbonate production style from aragonitic biocalcification to chemical and microbially-mediated CaCO3 precipitation. The ecosystem recovery was slow and aragonitic biocalcifiers (dasycladacean algae) reappeared during the early Sinemurian.

Climate-forced Hg-remobilization associated with fern mutagenesis in the aftermath of the end-Triassic extinction

The long-term effects of the Central Atlantic Magmatic Province, a large igneous province connected to the end-Triassic mass-extinction (201.5 Ma), remain largely elusive. Here, we document the persistence of volcanic-induced mercury (Hg) pollution and its effects on the biosphere for ~1.3 million years after the extinction event. In sediments recovered in Germany (Schandelah-1 core), we record not only high abundances of malformed fern spores at the Triassic-Jurassic boundary, but also during the lower Jurassic Hettangian, indicating repeated vegetation disturbance and stress that was eccentricity-forced. Crucially, these abundances correspond to increases in sedimentary Hg-concentrations. Hg-isotope ratios (δ202Hg, Δ199Hg) suggest a volcanic source of Hg-enrichment at the Triassic-Jurassic boundary but a terrestrial source for the early Jurassic peaks. We conclude that volcanically injected Hg across the extinction was repeatedly remobilized from coastal wetlands and hinterland areas during eccentricity-forced phases of severe hydrological upheaval and erosion, focusing Hg-pollution in the Central European Basin.

A phytosaur osteoderm from a late middle Rhaetian bone bed of Bonenburg (North Rhine-Westphalia, Germany): Implications for phytosaur extinction

A phytosaur osteoderm from a late middle Rhaetian bone bed of Bonenburg (North Rhine-Westphalia, Germany): Implications for phytosaur extinction

Marine Strontium Isotope Evolution at the Triassic‐Jurassic Transition Links Transient Changes in Continental Weathering to Volcanism of the Central Atlantic Magmatic Province

AbstractThe end‐Triassic extinction (ETE) is one of the most severe biotic crises in the Phanerozoic. This event was synchronous with volcanism of the Central Atlantic Magmatic Province (CAMP), the ultimate cause of the extinction and related environmental perturbations. However, the continental weathering response to CAMP‐induced warming remains poorly constrained. Strontium isotope stratigraphy is a powerful correlation tool that can also provide insights into the changes in weathering regime, but the scarcity of 87Sr/86Sr data across the Triassic‐Jurassic boundary (TJB) hindered the use of this method. Here we present new high‐resolution 87Sr/86Sr data from bulk carbonates at Csővár, a continuous marine section that spans 2.5 Myrs across the TJB. We document a continuing decrease in 87Sr/86Sr ratio from the late Rhaetian to the ETE, terminated by a 300 kyr interval of a flat trend and followed by a transient increase in the early Hettangian that levels off. We suggest that the first in the series of perturbations is linked to the influx of non‐radiogenic Sr from the weathering of freshly erupted CAMP basalts, leading to a delay in the radiogenic continental weathering response. The subsequent rise in 87Sr/86Sr after the TJB is explained by intensified continental crustal weathering from elevated CO2 levels and reduced mantle‐derived Sr flux. Using Sr flux modeling, we also find support for such multiphase, prolonged continental weathering scenarios. Aggregating the new data set with published records employing an astrochronological age model results in a highly resolved Sr isotope reference curve for an 8.5 Myr interval around the TJB.

Out of the ocean: the timescale of molluscan evolution based on phylogenomics revealed the ages of mollusks’ evolutionary transitions into the novel environment

Being the phylum with the second largest biodiversity, mollusks are widely distributed in marine, freshwater, and land, conquered almost all habitats on the earth. Throughout geological time, several molluscan lineages independently colonized freshwater and land, evolving independently in new habitats. Resolving the timing of their colonization for novel environments is the basis of understanding the complex evolution of Mollusca. Herein, we obtained an elaborate single–copy orthologs set including 107 genes with a total length of 3,447,675 amino acid sites across 134 mollusks to reconstruct the phylogeny of Mollusca. The phylogenetic analysis recovered the “Aculifera+ Conchifera” topology with well–supported. By the divergence times estimation with fossil calibration, we revealed Cambrian rapid diversification of all molluscan classes. What’s more, our results provided the times of three major independent colonization of novel environments and consistent with previous studies. The freshwater mussels (Bivalvia: Unionida) colonized freshwater about 233 Mya, ancient origin and late diversification make this order to become the main represent of the freshwater bivalves. The orders Stylommatophora and Basommatophora (Gastropoda: Pulmonata) respectively colonized land and freshwater about 201 Mya, the Triassic–Jurassic mass extinction may have provided the opportunities for their colonization. Ampullariidae (Gastropoda) colonized freshwater about 156 Mya, their lungs may have contributed to the adaption of tropical freshwater environment and make them survive. Our results probably offer the most comprehensive time–scale of molluscan evolution, could provide some insights into the habitat transition and evolution of Mollusca.

Different wildfire types promoted two-step terrestrial plant community change across the Triassic-Jurassic transition

Frequent wildfires associated with emplacement of the Central Atlantic Magmatic Province (CAMP) are thought to have been important drivers of two significant changes in terrestrial plant communities and diversity during the Triassic-Jurassic Mass Extinction (TJME, ca. 201.51 Ma). ​However, it remains to be investigated whether these two changes are potentially related to different wildfire types. To better understand this relationship, we used a new method to reanalyze fossil pollen and spores across the Triassic-Jurassic transition in the Jiyuan Basin from the North China Plate. Results show that two peaks in wildfire frequency experienced different types of wildfires, with each linked to significant changes in plant communities and diversity losses. In the first wildfire peak, canopy fires dominated and are accompanied by significant losses of canopy forming plants, while in the second wildfire peak, ground cover fires dominated accompanied by significant losses of ground cover plants. ​Changes in atmospheric humidity conditions were an important control on the two different wildfire peaks. Relatively humid climatic conditions corresponded to the prevalence of canopy fires and hindered the spread and development of ground cover fires in wet surface conditions. Conversely, relatively arid climatic conditions corresponded with the prevalence of ground cover fires in dry surface environments. Our results provide a potential relationship between terrestrial plant communities and wildfire types, which is important to further understanding of terrestrial environmental and floral changes driven by Large Igneous Provinces.

Recognition of an extended record of euglenoid cysts: Implications for the end-Triassic mass extinction

The enigmatic non-pollen palynomorph Chomotriletes, occurs consistently within sediments associated with the end-Triassic mass-extinction. Based on a detailed palynological survey and other published records from Europe, Chomotriletes is prevalent within the uppermost Rhaetian Contorta and Triletes Beds and its equivalents elsewhere. Chomotriletes is now a senior synonym for Permian Circulisporites, Meso- to Cenozoic Pseudoschizaea, and Quaternary to Recent Concentricystes. Its widespread occurrence has significance for our understanding of the end-Triassic mass-extinction, but its biological affinity and ecological preference have remained contentious for almost a century. We undertook a TEM examination of a Holocene and a Pliocene example of Concentricystes and found their structure to be a close match to the wall of Jurassic Pseudoschizaea from Italy that has been interpreted to belong to cysts of the Euglenophyceae. Together with a nascent understanding of a deep time record of the euglenoid, Moyeria, Chomotriletes helps document a terrestrial signature of the Euglenophyceae in the fossil record. An extensive literature survey indicates that Chomotriletes is associated with wetlands and riverine floodplain soils, and that it inhabited mainly temperate to tropical latitudes and continues to do so to the present day. Its presence in ancient marine sediments therefore indicates transport via weathering and erosion. The association with wetlands is in line with the ecological preferences of species of the Euglenophyceae. The presence of euglenoid cysts in association with the end-Triassic extinction fits a scenario in which enhanced rainfall followed by strong soil erosion resulted in the release and redeposition of Chomotriletes into shallow marine settings.

Globally limited but severe shallow-shelf euxinia during the end-Triassic extinction

One of the most severe extinctions of complex marine life in Earth’s history occurred at the end of the Triassic period (~201.4 million years ago). The marine extinction was initiated by large igneous province volcanism and has tentatively been linked to the spread of anoxic conditions. However, the global-scale pattern of anoxic conditions across the end-Triassic event is not well constrained. Here we use the sedimentary enrichment and isotopic composition of the redox-sensitive element molybdenum to reconstruct global–local marine redox conditions through the extinction interval. Peak δ98Mo values indicate that the global distribution of sulfidic marine conditions was similar to the modern ocean during the extinction interval. Meanwhile, Tethyan shelf sediments record pulsed, positive δ98Mo excursions indicative of locally oxygen-poor, sulfidic conditions. We suggest that pulses of severe marine de-oxygenation were restricted largely to marginal marine environments during the latest Triassic and played a substantial role in shallow-marine extinction phases at that time. Importantly, these results show that global marine biodiversity, and possibly ecosystem stability, were vulnerable to geographically localized anoxic conditions. Expanding present-day marine anoxia in response to anthropogenic marine nutrient supply and climate forcing may therefore have substantial consequences for global biodiversity and wider ecosystem stability.

Temporal fenestration in a Procolophon trigoniceps specimen (Procolophonoidea) from the Lower Triassic of Brazil.

The parareptiles diversified widely during the Permian and persisted in Pangean ecosystems until the end of the Triassic. However, most parareptiles succumbed to the Permian-Triassic extinction, leading to the exclusive survival of procolophonoids. Procolophonoidea stands out as one of the most diverse parareptile clades, with about 40 species across Pangean land masses. The Early Triassic species Procolophon trigoniceps is known from South Africa, Antarctica, and Brazil. The majority of cranial materials of this procolophonoid are described as anapsid in temporal morphology, however, some skulls discovered in South Africa were found to exhibit temporal fenestration. Once thought to have systematic significance for the genus Procolophon, temporal fenestration was lately proposed to be an anomalous or pathological feature in P. trigoniceps. In this study, we describe new cranial material of P. trigoniceps from the Sanga do Cabral Formation of Brazil that clearly displays temporal fenestration. Aside from the fenestra, the specimen closely resembles more complete Brazilian P. trigoniceps skulls. The recurrent presence of the feature and the varying morphologies exhibited by the temporal fenestrae of P. trigoniceps may substantiate its characterization as an anomalous trait within the species. Furthermore, the occurrence of temporal fenestration in P. trigoniceps specimens from both South America and South Africa underscores parallels between these two Early Triassic ecosystems.

The relationships and paleoecology of Pachystropheus rhaeticus, an enigmatic latest Triassic marine reptile (Diapsida: Thalattosauria)

ABSTRACT Pachystropheus rhaeticus is a primarily marine diapsid reptile found in Upper Triassic (Rhaetian) deposits in Britain and continental Europe. Although known for a long time, Pachystropheus remains an enigma. It was identified as the oldest choristodere based on similarities between postcranial bones and a sole cranial element. Here, we re-study all available Pachystropheus material, including new specimens, identifying all skeletal elements that are plausibly referrable to the genus. We reject some previous dubious identifications and show that reports of an ectopterygoid, the only cranial element of Pachystropheus described, were incorrect and that supposed skull elements belong to coelacanth fishes. Furthermore, we present CT data for the first time and new palynological data from Pachystropheus-bearing strata, providing a clearer picture of its stratigraphic distribution and the paleoecology of the Penarth Group. The reassessment of its phylogeny using new character informative data, places Pachystropheus as the last of the thalattosaurs, a lineage of marine reptiles abundant throughout the Triassic. We demonstrate that a specimen of Pachystropheus previously reported from the Lower Jurassic is more likely from the Late Rhaetian, and therefore the taxon does not extend across the end-Triassic Extinction. Moreover, this extends the known geological range of thalattosaurs from the Norian–Rhaetian boundary to the latest Rhaetian. Similarities in the postcranial skeleton between Pachystropheus and other askeptosauroid thalattosaurs, particularly Endennasaurus acutirostris, suggest it was able to move on land, but was most likely a primarily marine predator with an ecological niche distinct from coeval marine reptiles (placodonts, ichthyosaurs) and carnivorous fishes (hybodont sharks, actinopterygians).

A new Liassophlebiidae (Odonata: Heterophlebioidea) from strata close to the Triassic-Jurassic boundary in Somerset, UK

ABSTRACT Liassophlebiidae is an extinct family of damsel-dragonflies found in Upper Triassic and Lower Jurassic strata of Europe, Asia and Antarctica. Whilst Liassophlebiidae is well represented by Lower Jurassic fossils, their lowest occurrence in the Upper Triassic has hitherto only been suggested by three fragmentary specimens. These were originally ascribed to two species: Liassophlebia withersi and Liassophlebia batheri, but the latter is now considered nomen dubium. Here we describe a fourth, better preserved specimen that is likely to be Rhaetian (Late Triassic) in age. The specimen, BRSMG Cg3101 a+b, was collected from Bowdens Quarry, Somerset, UK, from the lower part of the White Lias Formation. The specimen comprises an incomplete forewing attributed to Liassophlebia due to: the small number of antenodals, antesubnodals and crossveins between RP and MA based RP3/4 in the base of RP2 opposite the subnodus; a straight and elongate secondary longitudinal vein in the postdiscoidal area; numerous cells and secondary veins in radial and median areas. The specimen is likely to represent a new species and provides stronger evidence than the previous three specimens of the presence of Liassophlebiidae during the late Rhaetian. Its stratigraphical position suggests that Liassophlebiidae arose in the immediate aftermath of the Triassic-Jurassic mass extinction.

Biological extinction and photic-zone anoxia across the Triassic–Jurassic transition: insights from the Qiangtang Basin, eastern Tethys

The end-Triassic mass extinction (ETME) is one of the five catastrophic extinction events. However, the driving mechanisms of biodiversity loss during this interval remain controversial. In this study, we investigate the marine sediment geochemistry and fauna across the Triassic–Jurassic boundary in the Wenquan section of Qiangtang Basin, and the triggering mechanism of the Late Triassic extinction in the eastern Tethys Ocean. Our study shows that the main pulse of the ETME occurred in Bed 8, manifesting as the disappearance of four brachiopod species, a significant decrease of other faunas, and the ‘Lilliput effect’ on bivalves. Analyses of pyrite framboids and redox-sensitive trace elements suggest the development of photic zone anoxia near the T/J boundary and coincident with the Late Triassic extinction. Thus, the development of abrupt and intense photic-zone anoxia could play an important role in the end-Triassic extinction. Supplementary material: Supplementary tables giving element contents and palaeontological data are available at https://doi.org/10.6084/m9.figshare.c.6771606

Komlopteris: A persistent lineage of post-Triassic corystosperms in Gondwana

Komlopteris is a genus that includes the youngest representative of the so-called ‘seed ferns’, an informal group of gymnosperms that were prevalent during the Mesozoic but largely went extinct at the end of the Cretaceous. New fossil material, morphological data, and an extensive literature review allowed us to clarify the systematics of Gondwanan post-Triassic leaves of the Komlopteris lineage that were formerly assigned to diverse genera. Trends in diversity and distribution were identified. Ten species of Komlopteris were recognized in Jurassic to Eocene strata across Gondwana. Earliest records of the genus derive from South America soon after the end-Triassic extinction event. The genus reached its peak diversity and range in the Late Jurassic and Early Cretaceous and declined markedly after the Aptian. Its youngest representation is in mid-Cretaceous to Eocene deposits of southeastern Gondwana. Although never dominant, Komlopteris represents an important subsidiary component of austral Jurassic–Paleogene plant fossil assemblages. Striking morphological similarities to Dicroidium and Kurtziana, and co-occurrence with low concentrations of Alisporites/Falcisporites-type pollen, suggest that Komlopteris was a gymnosperm belonging to Umkomasiales (=Corystospermales) that survived the end-Triassic and end-Cretaceous biotic crises in climatically buffered humid habitats of high southern latitudes. Arthropod induced leaf damage was rare on Komlopteris foliage and recognized only in two Late Jurassic–Early Cretaceous species.

Did changes in terrigenous components of deep-sea cherts across the end-Triassic extinction relate to Central Atlantic magmatic province volcanism?

The end-Triassic mass extinction event (ETE) is considered to be linked with the emplacement of the Central Atlantic magmatic province (CAMP), yet their temporal relation and underlying nature of global environmental and biotic changes remain controversial. A drastic radiolarian faunal turnover was associated with deep-sea acidification and changes in the chemical composition of pelagic terrigenous components, which were interpreted as the results of increased CAMP-derived materials, such as Fe2O3/Al2O3, MgO/Al2O3, and SiO2/Al2O3, without statistical tests. Here, we re-examined these CAMP-like signatures in terms of changes in the chemical composition of the Triassic–Jurassic pelagic deep-sea chert succession in Japan. Our newly compiled dataset suggests that changes in Fe2O3/Al2O3 and MgO/Al2O3 across the ETE were not significant, and thus, they may not be appropriate proxies for CAMP-derived material, potentially due to the dissolution of iron by ocean acidification and the formation of chlorite during diagenesis, respectively. Decreased SiO2/Al2O3 was also considered to have been reflected in increased CAMP-related dust flux and/or decreased biosiliceous productivity, but a slight increase in the Al2O3/TiO2 ratio (a biosiliceous productivity proxy) and an increase in shale bed thickness (dust flux proxy) across the radiolarian ETE imply increased eolian dust flux rather than decreased productivity. Furthermore, statistically significant Na enrichment at the radiolarian ETE level might be related to CAMP volcanism and/or associated changes in the source areas of eolian dust.

A revision and histological investigation of Saltoposuchus connectens (Archosauria: Crocodylomorpha) from the Norian (Late Triassic) of south-western Germany

Abstract Crocodylomorpha is the stem-lineage of modern crocodylians and the only pseudosuchian (i.e. crocodylian-line archosaurs) clade that survived the Triassic–Jurassic mass extinction event. Its earliest members, the non-crocodyliform crocodylomorphs, also known as ‘sphenosuchians’, were terrestrial and mostly small-bodied (<2 m long), although some large-bodied forms are known. Saltoposuchus connectens is one of the first described crocodylomorph species but it remains poorly studied, in part due to its contentious taxonomy. Here, all referred Saltoposuchus specimens are described in detail for the first time and its taxonomy is revised, with additional taxonomic implications for the British crocodylomorph Terrestrisuchus gracilis and the coelophysoid theropod Procompsognathus triassicus. Saltoposuchus connectens is clearly distinguished from Terrestrisuchus gracilis based on both cranial and postcranial features. The phylogenetic analysis finds that Saltoposuchus connectens, Terrestrisuchus gracilis, and Litargosuchus leptorhynchus form a clade of gracile, long-legged crocodylomorphs, identified as Saltoposuchidae Crush 1984. A histological section of a femur reveals highly vascularized fibrolamellar tissue in the second-largest specimen of Saltoposuchus connectens (SMNS 12596), indicating sustained high growth rates. A similar pattern was previously observed in Terrestrisuchus sp., contrasting with slower growth rates in the crocodylomorph Hesperosuchus agilis. These findings suggest that saltoposuchids had a high resting metabolic rate and active lifestyle.

Independent rediploidization masks shared whole genome duplication in the sturgeon-paddlefish ancestor

Whole genome duplication (WGD) is a dramatic evolutionary event generating many new genes and which may play a role in survival through mass extinctions. Paddlefish and sturgeon are sister lineages that both show genomic evidence for ancient WGD. Until now this has been interpreted as two independent WGD events due to a preponderance of duplicate genes with independent histories. Here we show that although there is indeed a plurality of apparently independent gene duplications, these derive from a shared genome duplication event occurring well over 200 million years ago, likely close to the Permian-Triassic mass extinction period. This was followed by a prolonged process of reversion to stable diploid inheritance (rediploidization), that may have promoted survival during the Triassic-Jurassic mass extinction. We show that the sharing of this WGD is masked by the fact that paddlefish and sturgeon lineage divergence occurred before rediploidization had proceeded even half-way. Thus, for most genes the resolution to diploidy was lineage-specific. Because genes are only truly duplicated once diploid inheritance is established, the paddlefish and sturgeon genomes are thus a mosaic of shared and non-shared gene duplications resulting from a shared genome duplication event.