The fish clade Pelagiaria, which includes tunas as its most famous members, evolved remarkable morphological and ecological variety in a setting not generally considered conducive to diversification: the open ocean. Relationships within Pelagiaria have proven elusive due to short internodes subtending major lineages suggestive of rapid early divergences. Using a novel sequence dataset of over 1000 ultraconserved DNA elements (UCEs) for 94 of the 286 species of Pelagiaria (more than 70% of genera), we provide a time-calibrated phylogeny for this widely distributed clade. Some inferred relationships have clear precedents (e.g. the monophyly of ‘core’ Stromateoidei, and a clade comprising ‘Gempylidae’ and Trichiuridae), but others are unexpected despite strong support (e.g. Chiasmodontidae + Tetragonurus ). Relaxed molecular clock analysis using node-based fossil calibrations estimates a latest Cretaceous origin for Pelagiaria, with crown-group families restricted to the Cenozoic. Estimated mean speciation rates decline from the origin of the group in the latest Cretaceous, although credible intervals for root and tip rates are broad and overlap in most cases, and there is higher-than-expected partitioning of body shape diversity (measured as fineness ratio) between clades concentrated during the Palaeocene–Eocene. By contrast, more direct measures of ecology show either no substantial deviation from a null model of diversification (diet) or patterns consistent with evolutionary constraint or high rates of recent change (depth habitat). Collectively, these results indicate a mosaic model of diversification. Pelagiarians show high morphological disparity and modest species richness compared to better-studied fish radiations in contrasting environments. However, this pattern is also apparent in other clades in open-ocean or deep-sea habitats, and suggests that comparative study of such groups might provide a more inclusive model of the evolution of diversity in fishes.

The Late Cretaceous (Cenomanian-Maastrichtian) Chalk Group and Eocene (Ypresian) London Clay Formation are two British marine deposits that yield globally significant assemblages of fossil actinopterygian (ray-finned) fishes. Materials from these units, especially the Chalk, featured prominently in the work of Arthur Smith Woodward. Here we summarize the history of study of actinopterygian fossils from the Chalk and London Clay, review their geological and palaeoenvironmental context and provide updated faunal lists. The Chalk and London Clay are remarkable for preserving fossil fishes in three dimensions rather than as the flattened individuals familiar from many other famous Lagerstätten, as well as capturing detailed 'snapshots' of marine fish faunas that bracket the major taxonomic shift that took place near the CretaceousPalaeogene boundary.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

Micro-computed tomography (lCT) scanning now represents a standard tool for non-destructive study of internal or concealed structure in fossils. Here we report on otoliths found in situ during routine lCT scanning of threedimensionally preserved skulls of Palaeogene and Cretaceous fishes. Comparisons are made with isolated otolith-based taxa to attempt correlations between the body fossil and otolith fossil records. In situ otoliths previously extracted mechanically from specimens of Apogon macrolepis and Dentex laekeniensis match our lCT models. In some cases, we find a high degree of congruence between previously independent taxonomic placements for otolith and skeletal remains (Rhinocephalus, Osmeroides, Hoplopteryx). Unexpectedly, in situ otoliths of the aulopiform Apateodus match isolated otoliths of Late Cretaceous age previously interpreted as belonging to gempylids, a group of percomorph fishes that do not appear in the body fossil record until the Palaeogene. This striking example of convergence suggests constraints on otolith geometry in pelagic predators. The otoliths of Apateodus show a primitive geometry for aulopiforms and lack the derived features of Alepisauroidea, the lizardfish clade to which the genus is often attributed. In situ otoliths of Early Cretaceous fishes (Apsopelix and an unidentified taxon) are not well preserved, and we are unable to identify clear correlations with isolated otolith morphologies. We conclude that the preservation of otoliths suitable for lCT scanning appears to be intimately connected with the taphonomic history, lithological characteristics of surrounding matrix, and syn-and postdepositional diagenetic effects.

The monotypic scombrid fish Micrornatus is represented by a single skull from the early Eocene (Ypresian) London Clay Formation of southeastern England. Although Arthur Smith Woodward substantially increased the diversity of scombrids and scombrid-like taxa known from this deposit, he seems not to have studied the fossil that would later be recognized as Micrornatus. Here we re-examine this specimen using computed microtomography, with two principal aims: first, a revised anatomical account with an emphasis on concealed features; and, second, 'proof-of-concept' for the tomographic study of fish crania from the London Clay. Scans reveal new details of the braincase, suspensorium and ventral hyoid arch. We compare the cranial anatomy of Micrornatus with other members of Eocoelopomini, a group also containing the genera Eocoelopoma, Palaeothunnus and possibly Landanichthys. Clarification of the taxonomy and phylogeny of early fossil scombrids is needed, and we suggest that computed tomography will be a useful tool for revealing the anatomical evidence needed to accomplish this goal.

Morphological evolution of the vertebrate skull has been explored across a wide range of tetrapod clades using geometric morphometrics, but the application of these methods to teleost fishes, accounting for roughly half of all vertebrate species, has been limited. Here we present the results of a study investigating three-dimensional morphological evolution of the neurocranium across 114 species of Pelagiaria, a diverse clade of open-ocean teleost fishes that includes tuna and mackerel. Despite showing high shape disparity overall, taxa from all families fall into three distinct morphological clusters. Convergence in shape within clusters is high, and phylogenetic signal in shape data is significant but low. Neurocranium shape is significantly correlated with body elongation and significantly but weakly correlated with size. Diet and habitat depth are weakly correlated with shape, and non-significant after accounting for phylogeny. Evolutionary integration in the neurocranium is high, suggesting that convergence in skull shape and the evolution of extreme morphologies are associated with the correlated evolution of neurocranial elements. These results suggest that shape evolution in the pelagiarian neurocranium reflects the extremes in elongation found in body shape but is constrained along relatively few axes of variation, resulting in repeated evolution towards a restricted range of morphologies.

Character list pertaining to the gill arches, taken from Davis (2010) Gill Arches1. Second epibranchial uncinate process: absent (0), present, enlarged (1), present, not enlarged, end of second pharyngobranchial displaced posterolaterally (2), present, not enlarged, end of second pharyngobranchial displaced posteriorly (3)2. Cartilaginous condyle on dorsal surface of third pharyngobranchial: PB3 with cartilaginous condyle articulating with EB2 (0), PB3 without cartilaginous condyle articulating with EB2(1) (Baldwin & Johnson [2],1996). 3. Fourth pharyngobranchial toothplate: UP4 present (0), UP4 absent (1) (Baldwin & Johnson [3], 1996). 4. Articulation of first pharyngobranchial: PB1 articulates at distal tip of EB1 (0), PB1 articulates at proximal base of cartilaginous tip of EB1 (1) (Baldwin & Johnson [4], 1996). 5. Gill rakers or toothplates: Gill rakers long, lathlike (0), gill rakers present as tooth-plates (1), single elongate gill raker on EB1 (2) (Baldwin & Johnson [5], 1996). 6. Second pharyngobranchial with extra uncinate process: PB2 without extra uncinate process (0), PB2 without extra uncinate process but with expanded proximal base (1), PB2 with extra uncinate process (2) (Baldwin & Johnson [6], 1996). 7. Second pharyngobranchial toothplate: UP2 present (0), UP2 absent (1)

Gempylids' (snake mackerels) and trichiurids (cutlassfishes) are pelagic fishes characterized by slender to eel-like bodies, deep-sea predatory ecologies, and large fanglike teeth. Several hypotheses of relationships between these groups have been proposed, but a consensus remains elusive. Fossils attributed to 'gempylids' and trichiurids consist almost exclusively of highly compressed body fossils and isolated teeth and otoliths. We use micro-computed tomography to redescribe two three-dimensional crania, historically assigned to †Eutrichiurides winkleri and †Progempylus edwardsi, as well as an isolated braincase (NHMUK PV OR 41318). All from the London Clay Formation (Eocene, Ypresian), these specimens represent some of the oldest fossils identified as trichiuroids. We find that †Eutrichiurides winkleri does not show diagnostic characters of †Eutrichiurides, and it is assigned to a new genus. To investigate the placement of these fossils relative to extant lineages, we combine existing morphological character sets for 'gempylids' and trichiurids along with published mitogenomic data. Our analyses recover a monophyletic Trichiuridae nested within a paraphyletic 'Gempylidae'. The taxon formerly known as †Eutrichiurides winkleri is considered Trichiuroidea incertae sedis, while †Progempylus edwardsi and NHMUK PV OR 41318 are recovered within the 'gempylid' grade. Using previously published descriptions and character optimizations from our phylogenetic analyses we suggest possible placements for laterally compressed body fossils assigned to Trichiuroidea ( †Argestichthys, †Abadzekhia, †Chelifichthys, †Anenchelum, †Eutrichiurides, †Musculopedunculus).

Many modern groups of marine fishes first appear in the fossil record during the early Palaeogene (66–40 Ma), including iconic predatory lineages of spiny-rayed fishes that appear to have originated in response to ecological roles left empty after the Cretaceous/Palaeogene extinction. The hypothesis of extinction-mediated ecological release likewise predicts that other fish groups have adopted novel predatory ecologies. Here, we report remarkable trophic innovation in early Palaeogene clupeiforms (herrings and allies), a group whose modern representatives are generally small-bodied planktivores. Two forms, the early Eocene (Ypresian) † Clupeopsis from Belgium and a new genus from the middle Eocene (Lutetian) of Pakistan, bear conspicuous features indicative of predatory ecology, including large size, long gapes and caniniform dentition. Most remarkable is the presence of a single, massive vomerine fang offset from the midline in both. Numerous features of the neurocranium, suspensorium and branchial skeleton place these taxa on the engraulid (anchovy) stem as the earliest known representatives of the clade. The identification of large-bodied, piscivorous anchovies contributes to an emerging picture of a phylogenetically diverse guild of predatory ray-finned fishes in early Palaeogene marine settings, which include completely extinct lineages alongside members of modern marine groups and taxa that are today restricted to freshwater or deep-sea environments.