Nipping the Cambrian "explosion" in the bud?

In recent years, two schools of thought have emerged with regard to the Cambrian "explosion". One argues that it was very quick, with phyla tumbling into existence in a virtual geological instant. The other view has a more relaxed temporal perspective. It looks to slow aeons of cryptic metazoan history, which led to a final breakthrough in the Cambrian, not in evolution but of fossilization potential. Yet both views have serious difficulties. Now, in a recent issue of Biological Reviews, Graham Budd and S?ren Jensen(1) argue for a third way. In an intriguing blend of functional morphology, the fossil record and cladistic thinking, they suggest that the assembly of metazoan bodyplans took place in a surprisingly straightforward manner.     

Correlating the global Cambrian–Ordovician boundary: Precise comparison of the Xiaoyangqiao section,Dayangcha, North China with the Green Point GSSP section,Newfoundland, Canada

The Cambrian–Ordovician boundary interval exposed at the Xiaoyangqiao section, North China is presented. The distribution of stratigraphically important fossils in the Xiaoyangqiao section revealed several nearly coeval graptolite, conodont, trilobite, and acritarch bioevents in the uppermost Cambrian–lowermost Ordovician carbonate-siliciclastic sedimentary sequence. The precise correlation to the Green Point GSSP section, western Newfoundland, Canada allows for the identification of the corresponding GSSP level in the Xiaoyangqiao section. The combined data from the Xiaoyangqiao section and the Green Point GSSP section provide a series of events that all can be applied as proxies for identification of the Cambrian–Ordovician boundary horizon outside the GSSP. Based on this, the Xiaoyangqiao section, Dayangcha, is here strongly recommended as a candidate for an Auxiliary Boundary Stratigraphic Section and Point section (ASSP) for the base of the Ordovician System, because it provides one of the best and most complete Cambrian–Ordovician transitions in the world and because the first planktic graptolites are from the Xiaoyangqiao section.     

Revision of the Cambrian Agnostina (Trilobita?) from Russia

Cambrian genera and species of Agnostina (?Trilobita) found in Russia are revised. Agnostid trilobite species are used as index taxa in chronostratigraphic subdivisions of the traditional Middle and Upper Cambrian in both regional and global stratigraphic scales. The correlation of the regional and international stratigraphic schemes largely depends on the state of knowledge of the regional agnostid fauna. Therefore, an up-to-date revision of this group based on the Russian collections taking into account their global diversity is very timely. For this study we reexamined the type collections of agnostids, including the holotypes of species described by Russian authors. This paper contains new photographic images of the holotypes housed in Russian museums. The compiled data offered solutions for some difficult taxonomic problems of the families Agnostidae, Ptychagnostidae, Peronopsidae, and some genera of Pseudagnostidae, Diplagnostidae. Apart from listing the diversity, this paper serves as the basis for studying the biogeography and evolution of this interesting arthropod group.     

What can DNA Tell us About the Cambrian Explosion?

Molecular data is ideal for exploring deep evolutionary historybecause of its universality, stochasticity and abundance. Thesefeatures provide a means of exploring the evolutionary historyof all organisms (including those that do not tend to leavefossils), independently of morphological evolution, and withina statistical framework that allows testing of evolutionaryhypotheses. In particular, molecular data have an importantrole to play in examining hypotheses concerning the tempo andmode of evolution of animal body plans. Examples are given wheremolecular phylogenies have led to a re-examination of some fundamentalassumptions in metazoan evolution, such as the immutabilityof early developmental characters, and the evolvability of bauplancharacters. Molecular data is also providing a new and controversialtimescale for the evolution of animal phyla, pushing the majordivisions of the animal kingdom deep into the Precambrian. Therehave been many reasons to question the accuracy and precisionof molecular date estimates, such as the failure to accountfor lineage-specific rate variation and unreliable estimationof rates of molecular evolution. While these criticisms havebeen largely countered by recent studies, one problem has remaineda challenge: could temporal variation in the rate of molecularevolution, perhaps associated with "explosive" adaptive radiations,cause overestimation of diversification dates? Empirical evidencefor an effect of speciation rate, morphological evolution orecological diversification on rates of molecular evolution isexamined, and the potential for rate-variable methods for moleculardating are discussed.     

The Ordovician Radiation: A Follow-up to the Cambrian Explosion?

There was a major diversification known as the Ordovician Radiation,in the period immediately following the Cambrian. This eventis unique in taxonomic, ecologic and biogeographic aspects. While all of the phyla but one were established during the Cambrianexplosion, taxonomic increases during the Ordovician were manifestat lower taxonomic levels although ordinal level diversity doubled.Marine family diversity tripled and within clade diversity increasesoccurred at the genus and species levels. The Ordovician radiationestablished the Paleozoic Evolutionary Fauna; those taxa whichdominated the marine realm for the next 250 million years. Communitystructure dramatically increased in complexity. New communitieswere established and there were fundamental shifts in dominanceand abundance. Over the past ten years, there has been an effort to examinethis radiation at different scales. In comparison with the Cambrianexplosion which appears to be more globally mediated, localand regional studies of Ordovician faunas reveal sharp transitionswith timing and magnitudes that vary geographically. These transitionssuggest a more episodic and complex history than that revealedthrough synoptic global studies alone. Despite its apparent uniqueness, we cannot exclude the possibilitythat the Ordovician radiation was an extension of Cambrian diversitydynamics. That is, the Ordovician radiation may have been anevent independent of the Cambrian radiation and thus requiringa different set of explanations, or it may have been the inevitablefollow-up to the Cambrian radiation. Future studies should focuson resolving this issue.     

Butterflies of the Cambrian benthos? Shield position in bradoriid arthropods

Mode of preservation and method of recovery strongly influences our understanding of the life habits of extinct organisms. Bradoriid arthropods were abundant, and diverse members of early Cambrian ecosystems and most life reconstructions display these animals with the two shields of the carapace open in a ‘butterfly’ configuration. This favoured reconstruction is largely based on the abundance of ‘crack‐out’ specimens preserved in this position (e.g. Kunmingella from the early Cambrian of China). In contrast, large collections of acid processed bradoriids from the Arrowie Basin of South Australia (Cambrian Stage 3) are preserved with a narrow gape at the ventral margin or completely closed with the carapace folded along the dorsal midline. The relative abundance of conjoined, closed (or partially closed) specimens from the lower Cambrian Hawker Group succession suggests that at least some bradoriid taxa were capable of withdrawing appendages and tightly closing the shields, challenging the common view that the majority of bradoriids usually held their carapaces open in a ‘butterfly’ configuration during life. New data show that layers of the bradoriid carapace are continuous through the dorsal fold with no evidence for complex articulating structures as in ostracod hinges. The relatively pliable, sclerotized or lightly mineralized calcium phosphate composition of the carapace and the simple, flexible dorsal fold facilitated opening and closing of the shields. Despite not being closely related, ostracods share close biomechanical and ecological similarities with bradoriids. The evolution of more complex articulating hinge structures – together with well‐developed musculature – in ostracods during the Early Ordovician, may have provided more efficient means for shield articulation and movement, thus promoting the ecological success of ostracods throughout the Phanerozoic.     

Fossil microphytoplankton dynamics across the Ordovician–Silurian boundary

A critical review of all available data on acritarch biostratigraphy and diversity dynamics across the Late Ordovician through the early Silurian, permits a better appreciation of the potential of acritarchs for the recognition of the systemic boundary. This analysis also reveals the response of marine microphytoplankton populations to the Late Ordovician palaeoenvironmental crisis (Hirnantian glaciation). Previous zonal schemes are improved, and an updated acritarch biostratigraphic chart is proposed, plotted against the most recent chronostratigraphic subdivisions. Sections from Anticosti Island (Québec, Canada), Algeria, Morocco, and Estonia preserve the best palynological record for the investigated interval. The present analysis shows that no true mass-extinction event occurred in latest Ordovician times in connection with the well known glacial event. “Pre-glacial” Ashgill acritarch suites are dominated by species of Baltisphaeridium, Multiplicisphaeridium, Ordovicidium, Orthosphaeridium, and netromorph acritarchs. An important proportion of these taxa (excluding Ordovicidium and Orthosphaeridium) survive the onset of glacial conditions in Hirnantian (latest Ordovician) times and continues through the early Silurian. The development of morphological polymorphism appears as a response (a survival strategy?) to the establishment of glacial conditions.In glacial-related sediments of Hirnantian age in North Africa, acritarch assemblages display a burst of relative abundance and intra-specific morphological variability (polymorphism) of long-ranging taxa such as Veryhachium, Multiplicisphaeridium, Dactylofusa, Poikilofusa, and Evittia. The extinction of several species characteristic of Upper to uppermost Ordovician strata occurs near the boundary, in “post-glacial” Ashgill (uppermost Hirnantian). This extinction event is counterbalanced by the almost contemporaneous (within the limits of stratigraphic resolution) appearance of several new taxa showing already a clear “Silurian affinity”, e.g., Tylotopalla, Cymbosphaeridium, and Visbysphaera. This origination event is observable in, and correlatable between the North African, the Bohemian and the Anticosti sections, making it global in extent.The completion of the palynological turnover and the establishment of a diverse Silurian acritarch suite occurs well above the base of the Silurian, during Aeronian times. The strong survival capability of the oceanic plankton through periods of palaeoenvironmental crisis in latest Ordovician times (but also throughout the Phanerozoic) could have played an important role in the post-extinction rebounds of metazoan clades, by assuring the continuity of marine trophic resources to consumers and avoiding irreversible disruptions of the trophic chains.     

Ecological disruption close to the Ordovician‐Silurian boundary

Following a long period of stability there was substantial ecological disruption in the late Ordovician, accompanied by widespread extinction. The ecological upheaval was spread over a period of time (1 My?) and varied in intensity between different groups.

The greatest change in brachiopod faunas occurred in the tropics, where there were widespread extinctions. In temperate regions the community structure, although disrupted, was not destroyed. The deep shelf associations (Benthic Assemblages 4–5) of the Rawtheyan persisted in an attenuated form into the Hirnantian when they were supplemented by genera of the ”Hirnantia fauna” and then became strongly re‐established in the Llandovery.

Trilobites, in contrast to brachiopods, suffered a worldwide extinction in the late Ashgill. Approximately 40% of trilobite genera became extinct at, or near, the Rawtheyan‐Hirnantian boundary.

Analysis of the distribution of Rawtheyan trilobite and brachiopod genera supports a correlation between geographical distribution and survival. Global range charts for brachiopod and trilobite genera, incorporating ecological and palaeogeographical data, have been compiled for this study.     

Can fast early rates reconcile molecular dates with the Cambrian explosion?

Molecular dates consistently place the divergence of major metazoan lineages in the Precambrian, leading to the suggestion that the 'Cambrian explosion' is an artefact of preservation which left earlier forms unrecorded in the fossil record. While criticisms of molecular analyses for failing to deal with variation in the rate of molecular evolution adequately have been countered by analyses which allow both site-to-site and lineage-specific rate variation, no analysis to date has allowed the rates to vary temporally. If the rates of molecular evolution were much higher early in the metazoan radiation, molecular dates could consistently overestimate the divergence times of lineages. Here, we use a new method which uses multiple calibration dates and an empirically determined range of possible substitution rates to place bounds on the basal date of divergence of lineages in order to ask whether faster rates of molecular evolution early in the metazoan radiation could possibly account for the discrepancy between molecular and palaeontological date estimates. We find that allowing basal (interphylum) lineages the fastest observed substitution rate brings the minimum possible divergence date (586 million years ago) to the Vendian period, just before the first multicellular animal fossils, but excludes divergence of the major metazoan lineages in a Cambrian explosion.     

Zooplankton in Svalbard fjords on the Atlantic–Arctic boundary

Zooplankton abundance and community structures were studied in three west Spitsbergen fjords at the beginning of the warm phase, which seem to have entered in 2006. Sampling was conducted in summer 2007 at stations distributed along transects in Hornsund, Isfjorden and Kongsfjorden. Variations in zooplankton standing stocks and community structures (assessing taxonomic diversity and zoogeographical affiliations) were analysed in relation to the environmental variables using multivariate techniques. The hydrographic conditions in Hornsund were influenced by the cold Arctic Water, whereas those in Isfjorden and especially in Kongsfjorden were, to a greater extent, under the influence of the warm Atlantic Water. High abundances of both meroplankton and holoplankton organisms were observed in Kongsfjorden, with high contributions of boreal and ubiquitous species (Calanus finmarchicus and Oithona similis, respectively). In Hornsund at the same time, the zooplankton consisted mainly of boreo-Arctic and Arctic species, the abundances of which were comparable along the West Spitsbergen Shelf. Our results indicate that the difference in hydrography had measurable effects on the zooplankton community in the study area. Furthermore, by comparing regions of contrasting oceanographic conditions, we present evidence as to how the zooplankton structure will change in the Arctic ecosystems if the warming trends continue to operate with the same dynamics. The advection of Atlantic waters to the Arctic seas may lead to changes in zooplankton structure, with increased abundance and contributions of boreal and small ubiquitous species. The ‘warmer Arctic fjords’ scenarios may also induce more rapid development of both holoplankton and meroplankton populations and, consequently, modify the trophic interactions in plankton communities.     

Epibionts on the lingulate brachiopod Diandongia from the Early Cambrian Chengjiang Lagerst?tte,South China

The classic Chengjiang Lagerstätte (Lower Cambrian, Atdabanian stage: Yu''anshan Formation) Yunnan, southwestern China, has yielded, besides the exceptional and often controversial soft-bodied fossils, a fauna of primitive/early lingulid brachiopods. Diandongia pista (Rong 1974) is one of the commonest and most strongly mineralized of the phosphatic brachiopods from the Lagerstätte. The shells of this species have been found to commonly serve as a basibiont host. Epibionts comprise the coeval brachiopod Longtancunella chengjiangensis and the cone-shaped cnidarian-related Archotuba conoidalis, as well as rounded smaller-sized epizoans (lesser than 2 mm). A principle morphological analysis demonstrates that the ovoid and rounded organisms that often occur along the commissure of D. pista resemble small juvenile or immature brachiopods. Epibiont-bearing shells of D. pista with soft-tissue preservation demonstrate that the host brachiopods were overgrown while alive, and provide an argument for D. pista having a semi-infaunal life style with only the slim pedicle embedded in sediment. The epibiotic association sheds direct light on the ecology of Cambrian brachiopods in soft-substrate marine environments. The Chengjiang fossils demonstrate that the Early Cambrian brachiopods, as compared with recent lingulids, occupied different and a wider spectrum of ecological niches and tiers of space.     

Pelmatozoan arms from the Middle Cambrian of Australia: bridging the gap between brachioles and brachials?

The early Middle Cambrian Monastery Creek Phosphorite (Beetle Creek Formation, Queensland, Australia) contains an assemblage of disarticulated echinoderm ossicles that are exquisitely preserved. Amongst this material we recognize pelmatozoan brachials, radials, basals and holomeric columnals. Although we cannot reconstruct the complete animal with precision, these elements represent the oldest known pelmatozoan with crinoid-like appendages. Key elements include isotomously to heterotomously branched uniserial appendage plates with a tripartite adoral food groove, a longitudinal central canal interpreted as housing entoneural nerve, and differentiated articulation facets. There are also epispire-bearing radials bearing one to four arm insertion-facets, each one pierced by a central neural canal. These canals run internal towards the oral area beneath the external food groove. Co-occuring material includes single truncated cone-shaped basals and holomeric columnals, both with a similar articulation pattern, and irregular, epispire-bearing thecal plates. This mosaic of crinozoan (uniserial isotomous to heterotomous arms with neural canal), blastozoan (epispire-bearing thecal plates, appendage leading to oral thecal food groove without direct connection with body cavity) and apomorphic characters (circumoral instead of basal entoneural plexus) is unexpected and demonstrates that crinoid-like pelmatozoans with uniserial, branched arms appeared significantly earlier than the Tremadocian, when the first articulated crinoid skeletons are found. It also raises questions about the polyphyletic appearance of feeding appendages among pelmatozoan echinoderms.     

‘Playing’ at the ethnic boundary: strategic boundary making/unmaking among ethnic Chinese groups in Australia

The sociological literature has constructed a systematic typology of ‘modes’ and ‘means’ of strategic ethnic boundary making/unmaking. Through exploring different strategies, scholars illustrate the processes and contexts of boundary expansion or contraction. Other scholars also distinguish ethnic elements and ‘moral' values attached to certain ethnicities but not to others. This paper acknowledges dynamic boundary making/unmaking and moral aspects of ethnicity, while exploring the different degrees to which national and pan-national identity nest within each other among ethnic Chinese groups, as well as how ethnic boundary becomes a field where people ‘play' in their everyday interactions. Based on participant observations and in-depth interviews from two pan-Chinese worksites in Australia, the paper argues that different interpretations of ethnic identity as well as how different identities (national and pan-national) are nested give people room to ‘play' at the ethnic boundary and result in different outcomes. This paper also shows that people can cross the ethnic boundary (between Taiwanese/Hong Kongese and PRC-Chinese) without expanding/contracting the existing categories or ‘repositioning/transvaluing' their ethnic statuses.     

Classical and non-classical taxonomy: where does the boundary pass?

Rise of non-classical science during XX century had certain influence upon development of biological taxonomy. Scientific pluralism (especially normative naturalism of Laudan), contrary to positivist and early post-positivist treatments, made taxonomy acknowledged scientific discipline of its own right. The present state of some schools of taxonomy makes it possible to consider them as a part of non-classical science and constituting the non-classical taxonomy. The latter is characterized by the following most important features. Ontological substantiation of both classificatory approaches and particular classifications is requested which invalidates such formal approaches as nominalistic and phenetic (numerical) schools. This substantiation takes a form of content-wise background preferably causal models which include certain axioms and presumptions about taxonomic diversity being studied, together with its causes, and thus define initial conditions of classificatory procedures. From this viewoint, phylogenetic classificatory approach is the most developed part of non-classical taxonomy. The entire taxonomic diversity is structured into several aspects of different levels of generality, each being outlined by a particular consideration aspect. The latter makes personal knowledge constituting an irremovable part of any scientific statement about taxonomic diversity, thus opposition of "objectively" and "subjectively" elaborated classifications becomes vague. Interrelation of various species concepts corresponding to its different consideration aspects is described by uncertainty relation principle. Classificatory algorithms are to be compatible with the conditions of a background model to ensure particular classifications obtained by their means are interpretable within the same model: this is provided by the correspondence principle. Classification is considered as a taxonomic hypothesis, i.e. a conjectural judgement about structure of particular fragment of taxonomic diversity considered within given consideration aspect; wich is to be forwarded and tested according to certain rules. Recognition of different aspects of taxonomic diversity makes it "legal" to elaborate several classifications of equal status, each reflecting a particular aspect of a fixed fragment of that diversity. This viewpoint makes classical ideas of the "ultimate" Natural (whatever might be its definition) or the best reference systems futile. In general, any pretension of an approach to be "the best" in reflecting taxonomic divesrity is contr-productive. Instead, elaboration of particular spectra of complementary classifications becomes the main task of non-classical taxonomy which describes in sum the entire taxonomic diversity. So, not opposition but correct mutual interpretation of such classifications and uniting them into the comprehensive picture of taxonomic diversity become focal points of non-classical taxonomy.     

Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion?

The study of metazoan evolution has fascinated biologists for centuries, and it will certainly keep doing so. Recent interest on the origin of metazoan body plans, early metazoan evolution, genetic mechanisms generating disparity and diversity, molecular clock information, paleontology, and biogeochemistry is contributing to a better understanding of the current phyletic diversity. Unfortunately, the pattern of the metazoan tree of life still shows some important gaps in knowledge. It is the aim of this article to review some of the most important issues related to the inference of the metazoan tree, and point towards possible ways of solving certain obscure aspects in the history of animal evolution. A new hypothesis of the metazoan diversification during the Cambrian explosion is proposed by synthesizing ideas from phylogenetics, molecular evolution, paleontology, and developmental biology.     

Revisiting the stratigraphic position of the Matuyama–Brunhes geomagnetic polarity boundary in Chinese loess

It is commonly accepted that the climate records in Chinese loess can be correlated well with that in marine sediments. However, discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives. For example, the exact stratigraphic position of the whole Matuyama–Brunhes (MB) transitional polarity zone remains uncertain in Chinese loess. In this study, an accurate transitional zone of the MB reversal from the Mangshan profile, southeast margin of the Chinese Loess Plateau (CLP), was statistically determined using multiple subsets of parallel samples. By integrating results from the central CLP, the whole MB transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between S8 and L8 over a wide region of the CLP. This conclusion further supports that the paleosol unit S8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21, and thus unambiguously supplies an accurate age control in constructing a new loess time scale.     

Is LEAFY a useful marker gene for the flower-inflorescence boundary in the Euphorbia cyathium?

The flower-like reproductive structure of Euphorbia s.l. (Euphorbiaceae) is widely believed to have evolved from an inflorescence, and is therefore interpreted as a special type of pseudanthium, termed a cyathium. However, fuzzy morphological boundaries between the inflorescence, individual flowers, and organs have fuelled the suggestion that the cyathium does not merely superficially resemble a flower but could actually share developmental genetic pathways with a conventional flower. To test this hypothesis, immunolocalizations of FLORICAULA/LEAFY (LFY), a protein associated with floral identity in many angiosperm species, were performed in developing cyathia of different species of Euphorbia. Expression of the LFY protein was found not only in individual floral primordia (as predicted from results in the model organisms Arabidopsis and Anthirrhinum), but also in the cyathium primordium and in the primordia of partial male inflorescences. These results provide further evidence that the evolution of floral traits in pseudanthial inflorescences often involves expression of floral development genes in the inflorescence apex. This finding blurs the conventional rigid distinction between flowers and inflorescences.     

International Cambrian Friendship北大核心CSCD

Professor Chang was a long-time friend and colleague.We began exchanging reprints in the 1950's and finally,in 1976 I was able to visit Nanjing and we met for the first time.Subsequently he came to the U.S.and I was able to show him some of our spectacular desert Cambrian exposures in the west.Later,he was a most gracious host as we toured much of eastern China,following an International Cambrian Symposium in Novosibirsk,dividing our time between Cambrian exposures and famous tourist sites.Our final personal meeting was in 2002 at his apartment following a Cambrian conference in Nanjing,where he was still pursuing research on Cambrian trilobites.He was the leader of his generation in Cambrian studies and his work provided important demonstrations of the significant differences between contemporaneous faunas in Laurentia and what was then eastern Gondwana.This work contributed significantly to our understanding of the biogeography of the Cambrian world,and is a lasting addition to global knowledge of the Cambrian of eastern Asia.     

Biostratigraphy and important biotic events in the Western Verkhoyansk Region around the Sakmarian–Artinskian boundary

A diverse marine invertebrate fauna was found in the Echij Formation (Sakmarian–Artinskian) at the Arkachan, Chelge, and Nizhnyaya Dielendzha sections, all Western Verkhoyansk Region, North-East of Russia. The biostratigraphic sequence of ammonoid, brachiopod, bivalve, and foraminiferal assemblages in the Echij Formation of the Western Verkhoyansk Region is studied. Five ammonoids units are identified in the Echian Regional Stage (“Horizon”): Uraloceras subsimense, Uraloceras omolonense, Neoshumardites triceps hyperboreus, Eotumaroceras endybalense, and Eotumaroceras subyakutorum beds. The first two divisions contain ammonoids of the Arkachanian association, and the last three contain the Endybalian association. The boundary between the Sakmarian and Artinskian stages is established at the base of Neoshumardites triceps hyperboreus beds. In the Sakmarian interval of the Echij Regional Stage of the Verkhoyansk Region, a brachiopod biostratigraphic sequence similar to that of the Kolyma–Omolon Region is observed: Jakutoproductus insignis, Jakutoproductus terechovi, and Jakutoproductus rugosus zones. In the lower part of the Artinskian stage, Uraloproductus stuckenbergianus beds are identified, which are characterized by a rich brachiopod assemblage (Peregoedov et al., 2009), not typical for Verkhoyansk Region. The bivalves, identified in the Lower Echij Subformation, presumably belong to the Merismopteria permiana, Cypricardinia eopermica, and Cypricardinia borealica zones of the Ogonerian Horizon of the Kolyma–Omolon Region. Bivalves of the Middle and Upper subformations are characteristic of the Edmondia gigantea and Aphanaia lima zones of the Koargychanian Regional Stage (“Horizon”). The foraminifera complex identified in the Echij Formation is compared with the complex of the lower part of the Sandy Foraminifera horizon of the northeast of the Siberian platform, to which the Tustakh Formation belongs. The beginning of the wide distribution of the Early Permian foraminifera in the Western Verkhoyansk Region was recorded at the base of the Artinskian. The Sakmarian–Artinskian boundary interval in the Verkhoyansk Region is characterized by three significant biotic events: the replacement of the brachiopod Jakutoproductus by Inoceramus-like bivalves, the first appearance of the Endybalian ammonoid association, and biotic invasions from the Uralian and North American regions. An important factor of the Late Sakmarian–Early Artinskian events was a large sea level rise (the Echian transgression), which significantly changed the environmental conditions for East Siberian marine invertebrates, and contributed to the spread of new faunas.