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Summary: Contemporary glaciers are inhabited by streptophyte algae that balance photosynthesis and growth with tolerance of low temperature, desiccation and UV radiation. These same environmental challenges have been hypothesised as the driving force behind the evolution of land plants from streptophyte algal ancestors in the Cryogenian (720–635 million years ago).We sequenced, assembled and analysed the metagenome‐assembled genome of the glacier alga Ancylonema nordenskiöldii to investigate its adaptations to life in ice, and whether this represents a vestige of Cryogenian exaptations.Phylogenetic analysis confirms the placement of glacier algae within the sister lineage to land plants, Zygnematophyceae. The metagenome‐assembled genome is characterised by an expansion of genes involved in tolerance of high irradiance and UV light, while lineage‐specific diversification is linked to the novel screening pigmentation of glacier algae. We found no support for the hypothesis of a common genomic basis for adaptations to ice and to land in streptophytes. Comparative genomics revealed that the reductive morphological evolution in the ancestor of Zygnematophyceae was accompanied by reductive genome evolution.This first genome‐scale data for glacier algae suggests an Ancylonema‐specific adaptation to the cryosphere, and sheds light on the genome evolution of land plants and Zygnematophyceae. See also the Commentary on this article by Kunz et al., 244: 1125–1127. [ABSTRACT FROM AUTHOR]

Background: The sea spiders (Pycnogonida Latreille, 1810) of the Hunsrück Slate (Lower Devonian, ~400 million years ago) are iconic in their abundance, exquisite pyritic preservation, and in their distinctive body plan compared to extant sea spiders (Pantopoda Gerstäcker, 1863). Consequently, the Hunsrück sea spiders are important in understanding the deep evolutionary history of Pycnogonida, yet they remain poorly characterised, impacting upon attempts to establish a time-calibrated phylogeny of sea spiders. Methods: Here, we investigated previously described and new material representing four of the five Hunsrück pycnogonids: Flagellopantopus blocki Poschmann & Dunlop, 2006; Palaeoisopus problematicus Broili, 1928; Palaeopantopus maucheri Broili, 1929; and Pentapantopus vogteli Kühl, Poschmann & Rust, 2013; as well as a few unidentified specimens. Using X-ray microtomography and Reflectance Transformation Imaging, we describe new fossils, provide evidence for newly revealed anatomical features, and interpret these data in comparison to extant species. We also reinterpret the previously published illustration of the (probably lost) holotype of Palaeothea devonica Bergström, Stürmer & Winter, 1980. Results: We provide the first detailed description of the cephalic appendages of Palaeoisopus problematicus and revise the interpretation of the organisation of its ocular tubercle. Furthermore, we provide new insights into the structure of the legs and the proboscis of Palaeopantopus maucheri, the first description of the body of Flagellopantopus blocki and describe a new specimen of Pentapantopus vogteli, demonstrating that it had eight legs, in contrast to previous interpretations. We argue that, contrary to previous suggestions, Palaeothea devonica probably had a different body plan from extant pantopods. We discuss the ecological traits of the Hunsrück pycnogonids based on their morphological adaptations, and conclude that there is no compelling evidence of Pantopoda in the Devonian. Through comparative interpretation of the legs as well as general morphology, we can divide the Hunsrück pycnogonids into two morphological groups, while Pantopoda constitutes a third morphological group. [ABSTRACT FROM AUTHOR]

Mesoraphidiidae is an extinct family of the order Raphidioptera with an evolutionary history that is largely unexplored. Here, we uncovered the evolutionary history of Mesoraphidiidae using phylogenetic comparative approaches, based on an updated morphological dataset, with an additional description of two new genera and species with distinct cephalic elongation, Dracoraphidia brachystigma gen. et sp. nov. and Teratocephala macrostigma gen. et sp. nov. from mid-Cretaceous Myanmar amber. Phylogenetic analysis shows their affinity to the subfamily Alloraphidiinae. Our results show that the radiation of species diversity and morphological disparity of Mesoraphidiidae dates back to the Lower Cretaceous and experienced a distinct peak approximately 130–118 million years ago (Ma). This timeframe aligns with the Cretaceous Terrestrial Revolution (KTR), a period from 125 to 80 Ma marked by the proliferation of flowering plants and their interactions with insects. The habitat preference of mesoraphidiid larvae to gymnosperm plants might have led to their extinction during the KTR, with the associated decline of gymnosperm diversity. Despite reduction in the occupation of morphospace by Mesoraphidiinae, there is surprising expansion of morphospace occupation by Alloraphidiinae in the Upper Cretaceous, possibly related to cephalic elongation, which may have enhanced pollen-feeding or predation ability, in response to extrinsic changes to biodiversity and ecosystems during the KTR. This study enriches our understanding of the macroevolution of snakeflies during the Mesozoic and provides new evidence for the impact of the KTR on insects. [ABSTRACT FROM AUTHOR]

Vertebrate evolution has been punctuated by three whole genome duplication events that have been implicated causally in phenotypic evolution, from the origin of phenotypic novelties to explosive diversification. Arguably, the most dramatic of these is the 3R whole genome duplication event associated with the origin of teleost fishes which comprise more than half of all living vertebrate species. However, tests of a causal relationship between whole genome duplication and teleost diversification have proven difficult due to the challenge of establishing the timing of these phenomena. Here we show, based on molecular clock dating of concatenated gene alignments, that the 3R whole genome duplication event occurred in the early–middle Permian (286.18 to 267.20 million years ago; Ma), 52.02 to 12.84 million years (Myr) before the divergence of crown-teleosts in the latest Permian–earliest Late Triassic (254.36 to 234.16 Ma) and long before the major pulses of teleost diversification in Ostariophysi and Percomorpha (56.37 to 100.17 Myr and at least 139.24 to 183.29 Myr later, respectively). The extent of this temporal gap between putative cause and effect precludes 3R as a deterministic driver of teleost diversification. However, these age constraints remain compatible with the expectations of a prolonged rediploidization process following whole genome duplication which, through the effects of chromosome rearrangement and gene loss, remains a viable mechanism to explain the evolution of teleost novelties and diversification. [ABSTRACT FROM AUTHOR]

Attempts to explain the origin and diversification of vertebrates have commonly invoked the evolution of feeding ecology, contrasting the passive suspension feeding of invertebrate chordates and larval lampreys with active predation in living jawed vertebrates. Of the extinct jawless vertebrates that phylogenetically intercalate these living groups, the feeding apparatus is well-preserved only in the early diverging stem-gnathostome heterostracans. However, its anatomy remains poorly understood. Here, we use X-ray microtomography to characterize the feeding apparatus of the pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855). The apparatus is composed of 13 plates arranged approximately bilaterally, most of which articulate from the postoral plate. Our reconstruction shows that the oral plates were capable of rotating around the transverse axis, but likely with limited movement. It also suggests the nasohypophyseal organs opened internally, into the pharynx. The functional morphology of the apparatus in Rhinopteraspis precludes all proposed interpretations of feeding except for suspension/deposit feeding and we interpret the apparatus as having served primarily to moderate the oral gape. This is consistent with evidence that at least some early jawless gnathostomes were suspension feeders and runs contrary to macroecological scenarios that envisage early vertebrate evolution as characterized by a directional trend towards increasingly active food acquisition. [ABSTRACT FROM AUTHOR]