Exceptional Fossil Research Articles

Molluscan systematics: historical perspectives and the way ahead.

Mollusca, the second-most diverse animal phylum, is estimated to have over 100,000 living species with great genetic and phenotypic diversity, a rich fossil record, and a considerable evolutionary significance. Early work on molluscan systematics was grounded in morphological and anatomical studies. With the transition from oligo gene Sanger sequencing to cutting-edge genomic sequencing technologies, molecular data has been increasingly utilised, providing abundant information for reconstructing the molluscan phylogenetic tree. However, relationships among and within most major lineages of Mollusca have long been contentious, often due to limited genetic markers, insufficient taxon sampling and phylogenetic conflict. Fortunately, remarkable progress in molluscan systematics has been made in recent years, which has shed light on how major molluscan groups have evolved. In this review of molluscan systematics, we first synthesise the current understanding of the molluscan Tree of Life at higher taxonomic levels. We then discuss how micromolluscs, which have adult individuals with a body size smaller than 5 mm, offer unique insights into Mollusca's vast diversity and deep phylogeny. Despite recent advancements, our knowledge of molluscan systematics and phylogeny still needs refinement. Further advancements in molluscan systematics will arise from integrating comprehensive data sets, including genome-scale data, exceptional fossils, and digital morphological data (including internal structures). Enhanced access to these data sets, combined with increased collaboration among morphologists, palaeontologists, evolutionary developmental biologists, and molecular phylogeneticists, will significantly advance this field.

A light in the dark: a mid-Cretaceous bioluminescent firefly with specialized antennal sensory organs.

The beetle superfamily Elateroidea comprises the most biodiverse bioluminescent insects among terrestrial light-producing animals. Recent exceptional fossils from the Mesozoic era and phylogenomic studies have provided valuable insights into the origin and evolution of bioluminescence in elateroids. However, due to the fragmentary nature of the fossil record, the early evolution of bioluminescence in fireflies (Lampyridae), one of the most charismatic lineages of insects, remains elusive. Here, we report the discovery of the second Mesozoic bioluminescent firefly, Flammarionella hehaikuni Cai, Ballantyne & Kundrata gen. et sp. nov., from the Albian/Cenomanian of northern Myanmar (ca 99 Ma). Based on the available set of diagnostic characters, we interpret the specimen as a female of stem-group Luciolinae. The fossil possesses deeply impressed oval pits on the apices of antennomeres 3-11, representing specialized sensory organs likely involved in olfaction. The light organ near the abdominal apex of Flammarionella resembles that found in extant light-producing lucioline fireflies. The growing fossil record of lampyrids provides direct evidence that the stunning light displays of fireflies were already established by the late Mesozoic.

A paleoenvironmental and ecological analysis of biomarkers from the Eocene Fossil Basin, Green River Formation, U.S.A.

Exceptionally well-preserved fossil specimens in the Fossil Basin of the Green River Formation (GRF) have made it the subject of extensive paleontological study, but the organic molecular framework that evolved during a key paleoclimatic and fossil-bearing interval during the early Eocene is poorly understood. Whereas the organic geochemistry of the larger co-eval GRF basins has been extensively characterized, our molecular understanding of the fossil-bearing layers in the Fossil Basin and the drivers of the exceptional fossilization therein remain unresolved. To bridge this gap, sediments from the famous 18″-layer — the fossiliferous horizon that is extensively quarried for exceptional soft-tissue fossils — were sampled for organic and isotopic geochemical characterisation. The results show that the Fossil Basin sedimentary archive is geochemically distinct from other GRF basins, as exemplified by the absence of the classical biomarker β-carotane and minimal evidence for the large green algal blooms that predominate in the other GRF lake basins. Photic zone euxinia (PZE), anoxia, and a freshwater cap enabled development of a productive and diverse ecosystem. Salinity and density stratification prevented vertical mixing of the water column and supported preservation of decaying carcasses. In contrast to other GRF basins, the small areal extent and ellipsoid shape of the Fossil Basin focussed terrestrial and freshwater inputs into the lake, resulting in ideal conditions for preservation of an exceptional fossil record.

U-Pb geochronology reveals that hydrothermal dolomitization was coeval to the deposition of the Burgess Shale lagerstätte

Fault-controlled, hydrothermal dolomitization often occurs at margins between shallow-water carbonate platforms and deep-water sedimentary basins. In western Canada, for example, the platform margin between the Cathedral Formation and the Burgess Shale Formation has been dolomitized at temperatures up to ~200 °C, with local magnesite, talc, and clinochlore mineralization. At the same time, the Burgess Shale Formation includes exceptional fossils that provide key evidence of the radiation of the animal phyla during the Cambrian Period (541 to 485.4 Ma). This lagerstätte and Mg-rich minerals within the adjacent and underlying strata, however, have been critically understudied. Here we show, using carbonate U-Pb geochronology, that western Canada was tectonically active and subject to hydrothermal dolomitization during the Middle Cambrian (Miaolingian Epoch) to Middle Ordovician (488.1 ± 18.8 Ma). These results extend the latest stages of rifting along the western margin of Laurentia into the Paleozoic, while also suggesting that the dolomitization of the Cathedral Formation occurred at the same time as the deposition of the Burgess Shale lagerstätte.

Fossil evidence for the ancient link between clonal fragmentation, six-fold symmetry and an epizoic lifestyle in asterozoan echinoderms.

Asexual reproduction by means of splitting, also called fissiparity, is a common feature in some asterozoan groups, especially in ophiactid brittle stars. Most fissiparous brittle stars show six instead of the usual five rays, live as epibionts on host organisms, and use clonal fragmentation to rapidly colonize secluded habitats and effectively expand the margins of their distribution area. While the biology and ecology of clonal fragmentation are comparatively well understood, virtually nothing is known about the evolution and geological history of that phenomenon. Here, we describe an exceptional fossil of an articulated six-armed brittle star from the Late Jurassic of Germany, showing one body half in the process of regeneration, and assign it to the new species Ophiactis hex sp. nov. Phylogenetic inference shows that the fossil represents the oldest member of the extant family Ophiactidae. Because the Ophiactis hex specimen shows an original six-fold symmetry combined with a morphology typically found in epizoic ophiuroids, in line with recent fissiparous ophiactid relatives, we assume that the regenerating body half is an indication for fissiparity. Ophiactis hex thus shows that fissiparity was established as a means of asexual reproduction in asterozoan echinoderms by the Late Jurassic.

First report in the fossil record of a shark tooth embedded in a pinniped bone

There are now many examples in the fossil record of shark bite marks preserved on biogenic materials including coprolites, ammonoids, sea star ossicles, an echinoid, and bone and calcified cartilage. These exceptional fossils document evidence of exploratory behavior, active predation, and/or scavenging. However, only a small subset report on the presence of shark teeth embedded in fossilized bone or cartilage. Although a few shark tooth-marked seal bones are known from the fossil record, no direct evidence of predation or scavenging in the form of a shark tooth embedded in a fossil seal bone has yet been documented. Herein, we describe the first shark tooth embedded in a seal (Phocidae Gray, 1821) bone, a calcaneum (CMM-V-6964), that was surface collected in Mosaic’s South Fort Meade Mine, Hardee County, Fort Meade, Florida, United States. The isolated bone originated from within the Bone Valley Member of the Peace River Formation (Hawthorn Group). The partial tooth is identified as having come from an Early Pliocene great white shark, Carcharodon carcharias (Linnaeus, 1758). This discovery also represents the first C. carcharias tooth ever found embedded in a fossil bone. The embedded tooth may have come about as a result of active predation or scavenging. The extant macropredatory sharks, Carcharodon carcharias (great white shark), Notorynchus cepedianus (Péron, 1807) (sevengill shark), Somniosus microcephalus (Bloch & Schneider, 1801) (the Greenland shark), and Somniosus antarcticus Whitley, 1939 (sleeper shark), are known to actively prey upon seals (Pinnipedia Illiger, 1811). If this peculiar fossil association resulted from active predation, the seal did not survive the encounter because there is no evidence of healing in the area around the embedded shark tooth.

Quantifying the effects of exceptional fossil preservation on the global availability of phylogenetic data in deep time.

Fossil deposits with exceptional preservation ("lagerstätten") provide important details not typically preserved in the fossil record, such that they hold an outsized influence on our understanding of biodiversity and evolution. In particular, the potential bias imparted by this so-called "lagerstätten effect" remains a critical, but underexplored aspect of reconstructing evolutionary relationships. Here, we quantify the amount of phylogenetic information available in the global fossil records of 1,327 species of non-avian theropod dinosaurs, Mesozoic birds, and fossil squamates (e.g., lizards, snakes, mosasaurs), and then compare the influence of lagerstätten deposits on phylogenetic information content and taxon selection in phylogenetic analyses to other fossil-bearing deposits. We find that groups that preserve a high amount of phylogenetic information in their global fossil record (e.g., non-avian theropods) are less vulnerable to a "lagerstätten effect" that leads to disproportionate representation of fossil taxa from one geologic unit in an evolutionary tree. Additionally, for each taxonomic group, we find comparable amounts of phylogenetic information in lagerstätten deposits, even though corresponding morphological character datasets vary greatly. Finally, we unexpectedly find that ancient sand dune deposits of the Late Cretaceous Gobi Desert of Mongolia and China exert an anomalously large influence on the phylogenetic information available in the squamate fossil record, suggesting a "lagerstätten effect" can be present in units not traditionally considered lagerstätten. These results offer a phylogenetics-based lens through which to examine the effects of exceptional fossil preservation on biological patterns through time and space, and invites further quantification of evolutionary information in the rock record.

Ecological structure of diversity-dependent diversification in Phanerozoic marine bivalves.

Rigorous analysis of diversity-dependence-the hypothesis that the rate of proliferation of new species is inversely related to standing diversity-requires consideration of the ecology of the organisms in question. Differences between infaunal marine bivalves (living entirely within the sediment) and epifaunal forms (living partially or completely above the sediment-water interface) predict that these major ecological groups should have different diversity dynamics: epifaunal species may compete more intensely for space and be more susceptible to predation and physical disturbance. By comparing detrended standing diversity with rates of diversification, origination, and extinction in this exceptional fossil record, we find that epifaunal bivalves experienced significant, negative diversity-dependence in origination and net diversification, whereas infaunal forms show little appreciable relationship between diversity and evolutionary rates. This macroevolutionary contrast is robust to the time span over which dynamics are analysed, whether mass-extinction rebounds are included in the analysis, the treatment of stratigraphic ranges that are not maximally resolved, and the details of detrending. We also find that diversity-dependence persists over hundreds of millions of years, even though diversity itself rises nearly exponentially, belying the notion that diversity-dependence must imply equilibrial diversity dynamics.

Oviposition abundance and diversity in the Middle Pennsylvanian: the exceptional fossil lagerstätte Piesberg, northwest Germany

Oviposition abundance and diversity in the Middle Pennsylvanian: the exceptional fossil lagerstätte Piesberg, northwest Germany

A new fossil dolphin with tusk-like teeth from New Zealand and an analysis of procumbent teeth in fossil cetaceans

ABSTRACT Studies involving anatomical description and taxonomy of fossil odontocetes offer insights into their evolutionary history and diversity. This study analyses tusk-like teeth in odontocetes including the description of a new species, Nihoroa reimaea, from the Waitaki valley, North Otago, New Zealand. Dental features of Nihoroa reimaea, a gracile, longirostrine odontocete with procumbent tusk-like anterior teeth and slightly denticulate cheek teeth, are described in detail. A comparative analysis of tusk-like teeth from New Zealand specimens and from elsewhere in the world was performed allowing a classification of tusk-like teeth in odontocetes and highlighting the differences between true tusks and rooted procumbent teeth. Correlation analyses revealed significant associations between rostrum proportions and tooth crown morphology. This study contributes to the understanding of tusk-like teeth and illuminates their significance in odontocete evolution. Nihoroa reimaea expands our knowledge of fossil cetaceans and highlights the importance of New Zealand's exceptional fossil record of odontocetes with tusk-like teeth.

Trace element evidence for diverse origins of superheavy pyrite in Neoproterozoic sedimentary strata

Sedimentary pyrite has long been used as an archive of marine environments in Earth history. To capture reliable paleoenvironmental signals, however, we need to first evaluate pyrite in sedimentary strata as it can be altered and masked by later diagenetic and/or hydrothermal processes. Here, we trained two supervised machine learning algorithms on a large LA-ICP-MS pyrite trace element database to distinguish pyrite of different origins. The analysis validates that two models built on the co-behavior of 12 trace elements (Co, Ni, Cu, Zn, As, Mo, Ag, Sb, Te, Au, Tl, and Pb) can be used to accurately predict pyrite origins. Further statistical analysis suggests four trace element clusters behaving differently among sedimentary (syngenetic and early diagenetic), synsedimentary hydrothermal (syngenetic hydrothermal), and post-sedimentary hydrothermal (epigenetic hydrothermal) pyrite, which is probably driven by chemical and physical properties of source fluids, interactions between elements, competition among coprecipitating minerals, and pyrite growth rate. Armed with this initial success and aided by new LA-ICP-MS trace element data from 9 samples, we then demonstrated the efficacy of this approach in identifying the origins of pyrite from two Neoproterozoic sedimentary successions in South China. The first set of samples contain isotopically superheavy pyrite (i.e., whose bulk-sample δ34S values greater than those of contemporaneous seawater sulfate and whose origins remain controversial) from the Cryogenian Tiesi’ao and Datangpo formations. The second set of samples contain pyritic rims (associated with fossiliferous chert nodules and thought to be critical in exceptional fossil preservation) from the Ediacaran Doushantuo Formation. For the superheavy pyrite, the models consistently show high confidence levels (mostly > 80 % probability) in identifying its genesis type, and three out of four samples were given sedimentary origins. For the pyritic nodule rims, the models suggest that early diagenetic pyrite was subsequently altered by hydrothermal fluids and therefore shows mixed signals. The study highlights the importance of pyrite trace elements in deciphering and distinguishing the origins of pyrite in sedimentary strata.

Skeletal elements controlled soft-tissue preservation in echinoderms from the Early Ordovician Fezouata Biota

Exceptional fossils preserve non-biomineralized tissues in the geological record and provide crucial information on the evolution of life on Earth. Exceptionally preserved fossils are rarely discovered complete, challenging their morphological description and their palaeontological interpretation. Although decay experiments reconstructing degradation sequences in modern animals are necessary to better understand taphonomic processes involved in exceptional preservation, their applicability to some enigmatic and/or extinct fossil taxa remains limited. Here, based on a representative sample of 423 specimens collected from a single stratigraphic level from the Early Ordovician Fezouata Biota, we reconstruct the degradation sequence of both skeletal remains and soft tissues of stylophorans, an extinct clade of echinoderms. The rare preservation of the water vascular system can be explained by the rapid post-mortem opening of the cover plates resulting from the fast decay of associated muscles and the action of ligaments. In contrast, the proximal aulacophore and associated stylocone formed a particularly decay-resistant closed module, thus favouring the preferential preservation of included soft parts (fore-gut). The non-random location and frequency of pyritised intra-skeletal structures strongly suggest that skeletal elements dictated the preservation of underlying soft parts. As such, taphonomic investigations should not only focus on the environment surrounding a decaying animal, but also on the different environments created within a particular carcass.

The fossil record of appendicular muscle evolution in Synapsida on the line to mammals: Part II-Hindlimb.

This paper is the second in a two-part series that charts the evolution of appendicular musculature along the mammalian stem lineage, drawing upon the exceptional fossil record of extinct synapsids. Here, attention is focused on muscles of the hindlimb. Although the hindlimb skeleton did not undergo as marked a transformation on the line to mammals as did the forelimb skeleton, the anatomy of extant tetrapods indicates that major changes to musculature have nonetheless occurred. To better understand these changes, this study surveyed the osteological evidence for muscular attachments in extinct mammalian and nonmammalian synapsids, two extinct amniote outgroups, and a large selection of extant mammals, saurians, and salamanders. Observations were integrated into an explicit phylogenetic framework, comprising 80 character-state complexes covering all muscles crossing the hip, knee, and ankle joints. These were coded for 33 operational taxonomic units spanning >330 Ma of tetrapod evolution, and ancestral state reconstruction was used to evaluate the sequence of muscular evolution along the stem lineage from Amniota to Theria. The evolutionary history of mammalian hindlimb musculature was complex, nonlinear, and protracted, with several instances of convergence and pulses of anatomical transformation that continued well into the crown group. Numerous traits typically regarded as characteristically "mammalian" have much greater antiquity than previously recognized, and for some traits, most synapsids are probably more reflective of the ancestral amniote condition than are extant saurians. More broadly, this study highlights the utility of the fossil record in interpreting the evolutionary appearance of distinctive anatomies.

The fossil record of appendicular muscle evolution in Synapsida on the line to mammals: Part I-Forelimb.

This paper is the first in a two-part series that charts the evolution of appendicular musculature along the mammalian stem lineage, drawing upon the exceptional fossil record of extinct synapsids. Here, attention is focused on muscles of the forelimb. Understanding forelimb muscular anatomy in extinct synapsids, and how this changed on the line to mammals, can provide important perspective for interpreting skeletal and functional evolution in this lineage, and how the diversity of forelimb functions in extant mammals arose. This study surveyed the osteological evidence for muscular attachments in extinct mammalian and nonmammalian synapsids, two extinct amniote outgroups, and a large selection of extant mammals, saurians, and salamanders. Observations were integrated into an explicit phylogenetic framework, comprising 73 character-state complexes covering all muscles crossing the shoulder, elbow, and wrist joints. These were coded for 33 operational taxonomic units spanning >330 Ma of tetrapod evolution, and ancestral state reconstruction was used to evaluate the sequence of muscular evolution along the stem lineage from Amniota to Theria. In addition to producing a comprehensive documentation of osteological evidence for muscle attachments in extinct synapsids, this work has clarified homology hypotheses across disparate taxa and helped resolve competing hypotheses of muscular anatomy in extinct species. The evolutionary history of mammalian forelimb musculature was a complex and nonlinear narrative, punctuated by multiple instances of convergence and concentrated phases of anatomical transformation. More broadly, this study highlights the great insight that a fossil-based perspective can provide for understanding the assembly of novel body plans.

Variations in preservation of exceptional fossils within concretions

Concretions are an interesting mode of preservation that can occasionally yield fossils with soft tissues. To properly interpret these fossils, an understanding of their fossilization is required. Probabilistic models are useful tools to identify variations between different Konservat-Lagerstätten that are separated spatially and temporally. However, the application of probabilistic modeling has been limited to Early Paleozoic Konservat-Lagerstätten preserved in shales. In this paper, the patterns of preservation of three concretionary Konservat-Lagerstätten—the Carboniferous Mazon Creek (USA) and Montceau-les-Mines (France), and the Silurian Herefordshire Lagerstätte (UK)—are analyzed using a statistical approach. It is demonstrated that the degree of biotic involvement, i.e., the degree to which a carcass dictates its own preservation, is connected to internal organ conditional probabilities—the probabilities of finding an internal organ associated with another structure such as biomineralized, sclerotized, cuticularized, or cellular body walls. In concretions that are externally forced with little biological mediation (e.g., Herefordshire), all internal organ conditional probabilities are uniform. As biological mediation in concretion formation becomes more pronounced, heterogeneities in conditional probabilities are introduced (e.g., Montceau-les-Mines and Mazon Creek). The three concretionary sites were also compared with previously investigated Konservat-Lagerstätten preserving fossils in shales to demonstrate how the developed probability framework aids in understanding the broad-scale functioning of preservation in Konservat-Lagerstätten.

Taphonomy of early life (2.1 Ga) in the francevillian basin (Gabon): Role of organic mineral interactions

The taphonomy of early soft-bodied organisms in Palaeoproterozoic sediments is not yet clearly understood, even though some locations where these fossils are found present all the conditions for exceptional fossil preservation. Indeed, the degree of fossil preservation has received attention, but better knowledge of the environmental conditions and associated taphonomic processes is also essential. In the Gabonese Francevillian Basin, the discovery of macrofossils (2.1 Ga) of multicellular organisms in black shales is an outstanding example of this degree of preservation. Indeed, the biological diversity, as a wide variety of fossil morphologies are observed, is associated with two major taphonomic processes – moulding (lenticular-shaped forms) or early pyritization, while the fossil host rocks were not deeply buried and were affected only by weak to moderate diagenesis. However, usually, the mechanisms of this preservation remain difficult to assess, as the original taphonomic processes are impacted by diagenesis and still misunderstood. In this way, by closely observing fossil mineralization in four morphotypes of macrofossils and associated host rocks from mineralogical and textural points of view, this work aims to provide some keys to a taphonomic comprehension of soft-bodied organism preservation. After the deposition of dead organisms on the clayey sediment, an illitization process, which depends on the availability of dissolved K driven by bacterial activity, started from the first stages of preservation by moulding the lenticular-shaped forms and proceeded in the pores of the other macrofossils after their pyritization. At the fossil level, the intensity of illitization is controlled by the mode of preservation and the evolution of the associated permeability. In the nonpyritized lenticular-shaped specimens, illitization was not achieved, preserving I-S mixed-layer minerals, while in the pyritized forms, the illitization degree was more extensive. In comparison, I-S mixed-layer minerals are almost absent in pyritized abiotic concretions. A second process, which occurred later, consists of general chloritization from fluid circulation. Our detailed results show that each specimen behaved like a microsystem with its own physico-chemical and mineralogical evolution during preservation/diagenesis. This finding allows us to propose a conceptual model of the taphonomic history, describing the fossilization stages for each type of specimen.

Institutional Drivers of Voluntary Carbon Reduction Target Setting—Evidence from Poland and Hungary

Governments worldwide have launched climate policies to mitigate greenhouse gas emissions (GHG). These policies aim to enhance businesses to be active actors in the process of decarbonisation. Therefore, the main objective of this paper is to identify the drivers of voluntary corporate decarbonisation illustrated by climate target-setting practices. In particular, this paper aims at diagnosing whether European Union (EU)-wide and country-level policies foster material corporate commitment to mitigating the carbon footprint in two countries that are exceptionally heavily dependent on fossil fuels: Poland and Hungary, which are characterised by a specific political-economic situation. This analysis focuses on policies related to the EU sustainable finance initiative that enhances companies to voluntarily reduce their GHG emissions: (1) sustainable financial sector, (2) corporate disclosure, and (3) corporate governance policy. At the country level, the national policies for state-owned enterprises (SOEs) are analysed. The empirical research is conducted based on the financial and economic data for a group of Polish and Hungarian publicly listed companies exposed to these regulations. The exposure to certain policies is approximated through selected corporate characteristics. Logistic regression analysis is applied to firm-level data gathered from Refinitive and corporate reports. The dataset covers the period 2014 to 2021, with 214 data-points. The response variable is a binary indicator of whether a company sets emission targets. The empirical research proved that state ownership, belonging to the financial sector, and performance-oriented corporate governance factors have a significantly negative impact on the probability of a company setting target emissions. On the other hand, the company’s size and leverage have a strong positive impact on the probability of setting emission targets. Also, it was confirmed that after 2020 the frequency of corporate target-setting in Poland and Hungary increased. Additionally, it was observed that Polish firms are more willing to set climate targets than Hungarian ones. Therefore, from the analysed policies, only the corporate sustainability disclosure policy proved to have a positive impact on the practices of setting climate targets in Polish and Hungarian firms. The policies related to the sustainable financial sector and to state-owned enterprises proved to have a negative impact on the probability of setting climate targets, while for the corporate governance policy, the results are mixed. In this vein, it was shown that, by a majority, policies to stimulate voluntary corporate commitment to decarbonisation are counter-effective in countries characterised by exceptional fossil fuel dependence and particular institutional features. The original value of this study stems from the applied methodology focusing on a mix of policies addressing the deep decarbonisation process in the specific country settings. The presented research contributes to an on-going debate on the drivers of voluntary corporate decarbonisation, in particular the impact that policy mixes framed under the sustainable finance agenda may have on material commitments to GHG emission reduction targets. In this context, the main findings are important for policymakers who are responsible for creating and implementing policy measures devoted to the deep decarbonisation process. It is recommended that policymakers should consider national specificities while designing policies for a Europe-wide net-zero transition and account for potential tensions arising from different goals as they may have impact on the effectiveness of the decarbonisation process. Future research may focus on the verification of the observed relationships between variables on a larger sample of the European firms to identify the key drivers of deep corporate decarbonisation.

Examining the ontogeny of the Pennsylvanian cladid crinoid Erisocrinus typus Meek and Worthen, 1865

AbstractCrinoids were major constituents of late Carboniferous (Pennsylvanian) marine ecosystems, but their rapid disarticulation rates after death result in few well-preserved specimens, limiting the study of their growth. This is amplified for cladids, who had among the highest disarticulation rates of all Paleozoic crinoids due to the relatively loose suturing of the calyx plates. However, Erisocrinus typus Meek and Worthen, 1865 has been found in unusually large numbers, most preserved as cups but some as nearly complete crowns, in the Barnsdall Formation in Oklahoma. The Barnsdall Formation, a Koncentrat Lagerstätte, is composed predominantly of fine- to medium-grained sandstone, overlain by mudstone and shale; severe compaction of the fossils in the mudstone and shale layer in this formation allowed for exceptional preservation of the plates. Herein, we summarize a growth study based on 10 crowns of E. typus, showcasing a well-defined growth series of this species from the Barnsdall Formation, including fossils from juvenile stages of development, which are rarely preserved. We used high-resolution photographs imported into ImageJ and recorded measurements of the cup and arms for all nondistorted or disarticulated plates. Results show that the plates of the cup grew anisometrically with both positive and negative allometry. The primibrachial plates of E. typus grew with positive allometry. The brachial plates started as uniserial (i.e., cuneiform) as juveniles but shifted to be biserial. Erisocrinus typus broadly shares similar growth trajectories with other cladids. These growth patterns provide insight into feeding strategies and can aid in understanding crinoid evolutionary paleoecological trends.

Exceptional fossil preservation and evolution of the ray-finned fish brain.

Brain anatomy provides key evidence for the relationships between ray-finned fishes1, but two majorlimitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology-like other aspects of their anatomy2,3-are specialized relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull4-8. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalus wildi, an approximately 319-million-year-old ray-finned fish. This example of a well-preserved vertebrate brain provides a window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalus indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies1 and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes1,9. Our findings, along with a growing set of studies in other animal groups10-12, point to the importance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues13-15.

Exceptional soft tissue preservation reveals a cnidarian affinity for a Cambrian phosphatic tubicolous enigma.

Exoskeletal dwelling tubes are widespread among extant animals and early fossil assemblages. Exceptional fossils from the Cambrian reveal independent origins of tube dwelling by several clades including cnidarians, lophophorates, annelids, scalidophorans, panarthropods and ambulacrarians. However, most fossil tubes lack preservation of soft parts, making it difficult to understand their affinities and evolutionary significance. Gangtoucunia aspera (Wulongqing Formation, Cambrian Stage 4) was an annulated, gradually expanding phosphatic tube, with occasional attachments of multiple, smaller juveniles and has previously been interpreted as the dwelling tube of a 'worm' (e.g. a scalidophoran), lophophorate or problematicum. Here, we report the first soft tissues from Gangtoucunia that reveal a smooth body with circumoral tentacles and a blind, spacious gut that is partitioned by septa. This is consistent with cnidarian polyps and phylogenetic analysis resolves Gangtoucunia as a total group medusozoan. The tube of Gangtoucunia is phenotypically similar to problematic annulated tubular fossils (e.g. Sphenothallus, Byronia, hyolithelminths), which have been compared to both cnidarians and annelids, and are among the oldest assemblages of skeletal fossils. The cnidarian characters of G. aspera suggest that these early tubular taxa are best interpreted as cnidarians rather than sessile bilaterians in the absence of contrary soft tissue evidence.