The Proetida likely represent the only surviving trilobite clade past the Devonian mass extinction event(s). Although members of order Proetida have long been studied, the global phylogenetic relationships across this pivotal time are still unresolved. I used a Bayesian phylogenetic approach to construct a subordinal level tree for members within the superfamily Proetoidea. Two models, a relaxed and strict clock model, were compared and used to assess past reconstructions of clades within the order. The trees from both models highlight key relationships among proetides across the Devonian and show paraphyly in groups that have been considered monophyletic in the past. Trees from both models also suggest that major groups, e.g., the genus Gerastos Goldfuss, 1843 and the family Phillispidae (which represents the most diverse post-Devonian proetide group under current taxonomic schemes) are polyphyletic. This in turn suggests, in a paleobiological context, a more complex pattern of survivorship over the Late Devonian than previously suggested as well as pervasive parallelisms toward certain ‘Gerastos’ or ‘phillipsid’ morphotypes.

The Cambrian Explosion saw the widespread development of mineralized skeletons. At this time, nearly every major animal phylum independently evolved strategies to build skeletons through either agglutination or biomineralization. Although most organisms settled on a single strategy, Salterella Billings, 1865 employed both strategies by secreting a biocalcitic exterior shell that is lined with layers of agglutinated sediments surrounding a central hollow tube. The slightly older fossil, Volborthella Schmidt, 1888, shares a similar construction with agglutinated grains encompassing a central tube but lacks a biomineralized exterior shell. Together these fossils have been grouped in the phylum Agmata Yochelson, 1977, although no phylogenetic relationship has been suggested to link them with the broader metazoan tree, which limits their contribution to our understanding of the evolution of shells in early animals.

To understand their ecology and place them in a phylogenetic context, we investigated Salterella and Volborthella fossils from the Wood Canyon and Harkless formations of Nevada, USA, the Illtyd Formation of Yukon, Canada, and the Shady Formation of Virginia, USA. Thin-section petrography, acid maceration, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray tomographic microscopy were used to provide new insights into these enigmatic faunas. First, morphological similarities in the aperture divergence angle and ratio of central tube diameter to agglutinated layer thickness suggest Salterella and Volborthella are related. Second, both fossils exhibit agglutinated grain compositions that are distinctive from their surrounding environments and demonstrate selectivity on the part of their producers. Finally, the calcitic shell composition and simple layers of blocky prismatic shell microstructure in Salterella suggest a possible cnidarian affinity. Together these data point to these organisms being sessile, semi-infaunal filter or deposit feeders and an early experimentation in cnidarian biomineralization chronicling a hypothesized transition from an organic sheath in Volborthella to a biomineralized shell in Salterella.

Pelmatozoa is an informal grouping of filter-feeding echinoderms including crinoids, paracrinoids, rhombiferans, and eocrinoids that possess a theca, an erect stalk, and feeding appendages. Although crinoids were major constituents of marine communities with high diversity and abundance throughout the Paleozoic, most other pelmatozoans had relatively low species diversity and/or short temporal durations. It has been proposed that these different diversification trajectories could have resulted from crinoids outcompeting other filter-feeding pelmatozoans during the early Paleozoic, although this hypothesis involving niche overlap has never been formally tested. Here, we tested this hypothesis using the incredibly diverse pelmatozoan fauna of the Late Ordovician (Sandbian) Bromide Formation of Oklahoma, which preserves a rich, ecologically complex fauna that developed as a result of the Great Ordovician Biodiversification Event. We developed a framework to quantitatively characterize pelmatozoan feeding ecology using multivariate analysis of ecomorphological traits and explored niche space occupation and potential competition between crinoids, rhombiferans, paracrinoids, eocrinoids, and diploporans from the Bromide fauna. Results revealed key ecological factors controlling niche differentiation and showed that crinoids, paracrinoids, and rhombiferans occupy nonoverlapping regions of niche space, indicating competition between groups was unlikely. Although the competition hypothesis was not supported, narrow niche space occupation suggests that paracrinoids and rhombiferans were more ecologically limited than crinoids, which might have played a role in their differential diversification dynamics. These results elucidate both the nature of interactions between pelmatozoan taxa and the potential mechanisms driving their evolutionary trajectories, as well as the complexity of ecological communities that arose during the Ordovician radiation.

Numerous oligochaete cocoons, previously interpreted as cladoceran crustaceans, are described from the upper Permian (Lopingian) freshwater Karaungir Lagerstätte in eastern Kazakhstan. The cocoons appear as small, wrinkled, ovoid capsules, prolonged into a neck at one pole and a long slender stalk at the other; both extensions are covered with minute ridges forming a striated pattern. By their size range and distinct (although limited) morphological features, the cocoons are identical to those of the extant freshwater genus Rhynchelmis Hoffmeister, 1843 (Oligochaeta: Lumbriculidae) and thus represent the oldest undoubted record of the Clitellata. We interpret Archedaphnia Smirnov, 1970 (= Propleuroxus Smirnov, 1970, n. syn.) as a genus for fossil microdrile oligochaete cocoons similar to those of Rhynchelmis, and synonymize all five species described in Archedaphnia and Propleuroxus under Archedaphnia kazakhstanica Smirnov, 1970 sensu lato.

The family Glassiidae from Silurian and Devonian strata exhibits barrel-shaped and medially directed spiralia as primary characteristics. Membership in this family is small with five known genera, of which only two possess recognized spiralia. This paper aims to investigate the two Devonian glassiides: Karbous Havlíček, 1985 and Trigonatrypa Havlíček, 1990. In mature specimens, the type species K. aperinus Havlíček, 1985 and the species K. hassiacus (Siehl, 1962) show dorsally directed spiralia. Karbous is here placed in the family Karpinskiidae based on similar internal characteristics. The type species of Trigonatrypa was not available for study. A closely related species, T. baucis (Barrande, 1847), was sectioned and found to possess medially directed spiralia. The type species is likely to have the same kind of spiralia. Therefore, the case for placing Trigonatrypa in the Glassiidae is strengthened.

When studying extinct organisms, which phylogenetic methods are the most useful to determine patterns of evolutionary relationship? How well do current classifications reflect the patterns discovered? Using Athyridida (Upper Ordovician–Lower Jurassic) as a case study, we utilize parsimony, Bayesian Mk, asymmetrical rates, and fossilized birth–death process models, with and without character partitions, to compare results from different methods of inference, to test previous phylogenetic hypotheses and examine morphological character evolution in this long-lived group of extinct brachiopods. Because different phylogenetic methods utilize different models of evolution involving different sets of assumptions, they can result in different patterns of relationship, making it necessary to test multiple methods and then evaluate thoughtfully the various results obtained.

We discovered that the four main athyridide higher taxa we focus on largely maintain their coherence as clades in most of the analyses, but relationships among them vary substantially, with implications for the evolution of characters important in their classification. We were able to characterize in detail the athyridide external valve characters that are more variable than internal characters, quantifying the commonly held impression that internal features are more likely to be homologues and thus more reliable in identifying relationships than external characters. Because taxa in classifications are still frequently used as clade proxies in macroevolutionary studies, it is necessary to obtain and compare the most robust hypotheses of relationship among named taxa in order to evaluate both character homology and homoplasy and taxonomic fidelity to hypotheses of evolution.

Pterygotids were Paleozoic marine and marginal marine large apex predatory arthropods. However, their evolution remains poorly understood due to the scarcity of their fossils and the delicate nature of their exoskeletons. The well-studied Devonian Xiaxishancun Formation in Qujing City, Yunnan, China contains various Agnatha and three eurypterid species. Our study focuses on the eurypterid material assigned to Erettopterus qujingensis Ma et al., 2022 and Pterygotus wanggaii Ma et al., 2023. The two species were discovered from the same locality, both with individuals of different developmental stages (juveniles more common), suggesting that this area could represent a breeding site, in agreement with mass molt behavior and the occurrence of other pterygotids in shallow waters. Moreover, the coexistence of heavily armed Agnatha with Pterygotus wanggaii in the Xiaxishancun Formation, alongside their robust chelicerae, supports the hypothesis that some pterygotids were piscivorous. In addition, due to ambiguity of pterygotid cheliceral dentition nomenclature, we introduce a new framework to define the cheliceral denticle types of pterygotids based on their relative positions: TD, terminal denticle; MD, median denticle (including: MMD, modified MD, and OMD, ordinary MD); BD, basal denticle. A key diagnostic feature in the cheliceral denticles of E. qujingensis is established: movable finger ends in a curved TD, 3 MMD’s present, 9 OMDs between MMD1 and MMD2 (OMD4 and OMD8 slightly enlarged); fixed finger ends in an acute TD’, 3 MMD’s present (MMD’2 being the largest), 8 OMD’s between MMD’1 and MMD’2 (OMD’5 slightly enlarged), 15 OMD’s between MMD’2 and MMD’3 (OMD’1 and OMD’10-12 slightly enlarged). This cheliceral diagnosis distinguishes E. qujingensis from Pterygotus wanggaii by its distinct number of MMDs.

We report a new stratigraphic section in the Argentine Precordillera (Zanja Honda, west of Pachimoco, San Juan Province), recording the Silurian-Devonian transition. It corresponds to particular siliciclastics of the uppermost 75 m of the Los Espejos Formation (LEF) exhibiting coquines at the base, noduliferous dark siltstones above, then greenish-brown sandstones, and subsequently, a reddish, massive, fine-grained sandstone interval. The overlying shaly lower interval of the Talacasto Formation records the homalonotid trilobite Burmeisteria notica (Clarke, 1913a), indicating the Lochkovian-Pragian interval. Brachiopods and trilobites of the basal coquinites are typical of the upper Silurian of the LEF elsewhere. However, Slovinograptus Urbanek, 1997, the youngest graptolite from southwestern Gondwana, indicates the Silurian-Devonian transition in the basal coquine. The dalmanitid Pachimocaspis pachimocensis new genus new species comes from this and other undoubted Silurian underlying coquinites. The brachiopod and trilobite associations disappear in the overlying dark nodular siltstone interval, replaced by an earliest Lochkovian Orthostrophia meridionalis Benedetto in Benedetto et al., 1992 brachiopod association and a monospecific Pachimocaspis pachimocensis n. gen. n. sp. Thus, we recognize a neat faunal turnover around the Silurian-Devonian boundary as in other southern South American localities. We refer to Pachimocaspis pachimocensis n. gen. n. sp. pygidia from the Silurian-Devonian of Bolivia and the lowest Pragian of the Talacasto Formation from Las Aguaditas locality in the Precordillera Basin. Pachimocaspis pachimocensis n. gen. n. sp. lacks the typical pygidial dalmanitid morphology, exhibiting instead a subelliptical shape with no caudal spine. Also, thoracic pleural tips are variably blunt along the thorax in contrast with the evenly spinose dalmanitid morphology. The morphology of this taxon challenges its systematic position in regarding Silurian-Devonian subfamilies from high paleolatitudes, resembling instead extra-Gondwanic, early Silurian synphoriines.

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Mecochirid lobsters (Glypheidea, Mecochiridae) are iconic decapod crustaceans from the Jurassic and Cretaceous. The composition of the family in terms of included genera strongly fluctuated during the twentieth century because of the lack of study of the type specimens, which are herein illustrated. On the basis of the type material of different species housed in German, French, British, and Romanian museums and universities, Eumorphia von Meyer, 1847 (type species Carcinium sociale von Meyer, 1841) is re-established as a valid mecochirid genus. Six species are considered, including the new species Eumorphia fabianmuelleri (Callovian, Germany), and the synonymization of Romaniacheiros Franţescu et al., 2018 with Eumorphia is proposed. The composition of the revised family Mecochiridae is discussed.

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The Ovatoryctocara granulata Chernysheva, 1962 assemblage is a diverse fossil fauna that is important for global biostratigraphic correlation within Cambrian Series 2, Stage 4. The assemblage includes more than 60 invertebrate species in North Greenland from Freuchen Land to western Peary Land, but systematic documentation of all the fossils from the assemblage remains to be done. Here we expand on previous work by describing new mollusks and the problematic Stenothecoides from this assemblage in North Greenland, mainly from Freuchen Land. The identified taxa include Stenothecoides sp., Capitoconus borealis, Dorispira tippik Peel and Kouchinsky, 2022, Dorispira sp., Ressericonella pipalukae Oh and Peel, 2024, Ressericonella? sp., Mellopegma georginense Runnegar and Jell, 1976, Mellopegma simesi (MacKinnon, 1985), Yochelcionella gracilis Atkins and Peel, 2004, Eotebenna arctica Peel, 1989, Pelagiella sp., and three helcionelloid species in open nomenclature. These mollusks and stenothecoids facilitate faunal comparisons of North Greenland with Stage 4 to Miaolingian strata from other paleocontinents such as Siberia, Gondwana (Australia), and peri-Gondwana (North China), as well as within Laurentia.

Fossils can reveal large differences between the geographic range that a species could potentially inhabit and the more restricted realized distribution where individuals presently occur. Extant great penguins (Aptenodytes Miller, 1778) include emperor and king penguins, which have polar and subpolar ranges, respectively. New evidence now reveals that the fundamental niche for great penguins includes much warmer environments. Here, we report the first skull of an extinct great penguin that lived in Zealandia during the mid-Piacenzian Warm Period (mPWP) when global temperatures were ~3°C above those of the preindustrial era. Because estimated sea-surface temperatures in Zealandia during the mPWP were 10–20°C warmer than those experienced by living emperor and king penguins, we hypothesize that the exclusion of great penguins from lower latitudes today reflects constraints more complex than climate pressures alone. Terrestrial predation might be an overlooked factor because Aptenodytes appears to have gone extinct in Zealandia coincident with the arrival of large raptors like Haast’s eagle, Hieraaetus moorei (Haast, 1872), and Forbes’ harrier, Circus teauteensis Forbes, 1892.

Abrupt appearance of the dikelocephalid trilobite genus Osceolia in later Cambrian strata of the upper Mississippi Valley immediately above a flooding surface is succeeded by widespread regional occurrence among approximately eight parasequences in the early part of a falling stage systems tract. All of Osceolia’s sclerite types are illustrated for the first time. The taxonomy is revised to recognize two species, of which O. tumerispina is new and known only from a dolomitic horizon at a single locality. All five of Ulrich and Resser’s (1930) Osceolia species are synonymized within O. osceola (Hall, 1863), a species widespread in regional dolomitic mudstones and feldspathic sandstones. Osceolia osceola shows notable polymorphism in the presence of an axial ledge in the anterior cranidial border. Holaspid ontogenetic variation evident within bedding-plane collections of O. osceola scales with that occurring among collections and across facies. Collection-related morphological differences among the samples beyond those related to size are subtle. The occurrence of larger individuals in more distal settings may reflect ontogenetically related habitat preference. Osceolinae Ulrich and Resser, 1930 is rejected. The closest relatives of the two Osceolia species may occur outside of the upper Mississippi Valley. Material of a local, stratigraphically older, and possibly related Ulrich and Resser 1930 nomen nudum is figured and described for the first time. Osceolia’s cranidial morphotype was converged upon several times during the evolution of Cambrian trilobites among relatives both phylogenetically close and distant.

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The phylogenetic relationships among arthropods remain contentious because morphological studies face challenges in resolving certain branches. Particularly difficult are relationships within and between the stem arthropods, owing largely to too few well-preserved fossil representatives. Additional fossil evidence, particularly from exceptional deposits like the Silurian Waukesha Lagerstätte in Wisconsin, helps to bolster our views on the evolutionary history of arthropods by providing well-preserved examples of novel taxa that could fit between early diverging stem-arthropod clades and modern euarthropods, thus building possible bridges between the two. Formed in karstification-induced troughs of the Manistique Formation paleoslope, the Waukesha Lagerstätte preserves a unique biota of organisms from the Telychian Age, mostly through secondary precipitation of francolite. Perhaps most well known from this deposit are the many peculiar and enigmatic arthropod taxa that could help resolve early arthropod cladistic relationships. We add to the growing body of work on the diversity, phylogeny, and taxonomic descriptions of the Waukesha biota by detailing a previously unnamed bivalved arthropod, informally called ‘the butterfly animal’ in past literature—which we here designate as Papiliomaris kluessendorfae n. gen. n. sp. We also conducted a Bayesian phylogenetic analysis that placed several recently described Waukesha taxa as basal members of the ‘Mandibulate’ clade within the Euarthropoda.

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Precambrian organic-walled microfossils preserved in fine-grained sedimentary rocks constitute the earliest fossil record of eukaryotic life. The Mesoproterozoic–Neoproterozoic transition coincided with major innovations in the evolution of early eukaryotes, including the radiation of crown-group lineages, represented in these rocks by candidate red algae, green algae, and fungi. However, the diversity of these early eukaryotes is yet to be fully explored. Here, we present a systematic description of the microfossil assemblage preserved in exceptional detail within sedimentary phosphatic nodules and bands in the Diabaig Formation of the ca. 1-Ga Torridon Group of northwest Scotland. Recent work has highlighted the lacustrine or estuarine nature of its depositional environment and confirmed that these fossils may include the oldest known non-marine eukaryotes. We identified 11 morphotaxa from newly collected material, including the new genus and species Minimarmilla multicatenaria, two undoubted eukaryotes, and two probable eukaryotes. The latter include Pterospermopsimorpha sp., and a new network-forming unnamed taxon. These microfossils present an important window on eukaryotic diversification in non-marine aquatic environments during the Mesoproterozoic–Neoproterozoic.

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A highly diversified fauna of brachyurans is described from the lower Eocene Serraduy Formation of Huesca, northeastern Spain. Fifteen new and first-reported taxa of brachyurans are described including three new genera, ten new species, and five taxa in open nomenclature. New taxa include: Carpilius feldmanni n. sp., Ceronnectes rugosus n. sp., Eohexapus simplex n. sp., Galenopsis ossoi n. sp., Matutsalen rotundus n. gen. n. sp., Microboschettia elegans n. gen. n. sp., Parhalimede antiqua n. sp., Locomius parthenopimimus n. gen. n. sp., Liocarcinus tridentatus n. sp., and Xanthilites robustus n. sp. Five additional genera have been recognized from fragmented material only including Alponella sp., Lovaroides sp., Paromola sp., ?Rhinolambrus sp., and ?Spinirostrimaia sp. Moreover, based on new specimens, we provide new data on Ilerdapatiscus guardiae and Aragolambrus collinsi. New information supports previous considerations about reef settings that are comparable to modern reef ecosystems as environments of diversified decapod crustaceans in the early Eocene.

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Benthic gastropods are not commonly useful for biostratigraphic zonation. The gastropod genus Plocezyga is abundant throughout the marine units of the Desmoinesian through Virgilian Pennsylvanian strata in the United States. The protoconch of Plocezyga gives evidence that it had a planktonic time within its life cycle, which would give it a wider regional distribution. It has been found that Plocezyga is able to biostratigraphically zone the Pennsylvanian of the United States by use of first-occurrence range zones. The upper Atokan stage through the Virgilian Stage can be zoned using of the first occurrences of Plocezyga conica, P. excellens, P. ampla new species, P. costata, P. subquadrata, P. ornata, P. acuminata, P. obscura, and P. procera new species. The lower and upper boundary of the Desmoinesian as well as the lower boundary of the Missourian Stage are defined by these gastropod zones. Six new species are proposed: Plocezgya ampla from upper Desmoinesian units; Gamizyga lenterotunda from Missourian units; and Plocezyga pingurestis, Plocezyga procera, Cyclozyga promohumera, and Cyclozyga diversarevolvi from Virgilian units.

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New, well-preserved specimens of the paracrinoids Wellerocystis and Implicaticystis provide new morphological data. All specimens originate from reef facies in the Kimmswick Limestone (Upper Ordovician, Sandbian–Katian) at a single locality near St Louis, Missouri, USA. Wellerocystis is characterized by an ovoid theca largely composed of imperforate plates arranged in vertical columns lacking pore-structures but with fine granular sculpture; four recumbent branched uniserial ambulacra with up to seven branches in total; a mouth frame of four plates, one of which also contributes to the periproct frame; a sinuous hydropore; and circular gonopore. The stem is unknown; its facet is small and circular, similar to that of Platycystites. Implicaticystis is characterized by a circular, heteromorphic stem, ovoid theca composed of externally concave, perforate plates with foerstepores, internal pararhombs, and a mouth frame of three plates plus two lateral plates each bearing two facets for erect, uniserial, hemipinnate pseudoarms. Foerstepores connect to tubes that pass through the theca near plate sutures. Internal lamellae of pararhombs support thecal plates much as A-frames support ridged rooves. Erect versus recumbent and branched ambulacra evolved repeatedly in pelmatozoans so both are less useful in classifying paracrinoids than presence or absence of unique pore-structures. The sister group of paracrinoids could have included Columbocystis, rhipidocystids, and cryptocrinitids. Columbocystis is commonly mentioned in discussions in this context, but its asymmetrical facets suggest it had biserial feeding appendages, unlike uniserial paracrinoid appendages.

This work expands the knowledge on the diversity of Ordovician cephalopod assemblages of peri-Gondwana by describing 16 straight-shelled, annulated and/or reticulately ornamented specimens from the late Darriwilian and late Katian strata of the Prague Basin (Central Bohemia). Preservation facilitated the micro-CT investigation of internal shell structures in one of the specimens; in other specimens, the siphuncle and septa are not preserved, and these specimens are thus left in open nomenclature. In total, six species are recognized with one new species established: Anthoceras? sp. A, Anthoceras? sp. B, Sactorthoceras pustulatum new species, Dawsonoceras? sp. indet., Kionoceras? sp. indet., and Palaeodawsonocerina obscurum new combination. In addition, the holotype of Orthoceras evictum was examined and re-interpreted as a conulariid rather than a cephalopod. Paleogeographically, these taxa indicate mixed Baltican, Avalonian and peri-Gondwanan affinities for the late Darriwilian and late Katian cephalopod assemblages.

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