The descriptions of two co-occurring cardioid crustaceans from the Ballagan Formation (Tournaisian, Lower Carboniferous) of Chirnside, Scottish Borders, help to resolve the taxonomy of the genus Tealliocaris. Tealliocaris robusta Peach, 1908 is assigned to Schramocaris to form S. robusta (Peach, 1908) comb. nov. on the basis of morphological characters such as the rugosity and position of the branchial carinae as well as the nature of the pleon, and becomes the earliest representative of this genus in Scotland. A new species of Tealliocaris is also recognised from this locality and is described as T. briggsi sp. nov., based on the smooth carapace, lack of pleonic grooves and the number of spines on the scaphocerite and lateral margin of the anterior carapace. The systematic position of the Pendleian specimens identified by Peach (1908) as ‘Tealliocaris robusta var.’ is finally resolved and described as T. weegie sp. nov.

The Early Mississippian site of Willie's Hole in south-eastern Scotland hosts some of the earliest terrestrial tetrapods. This study reports on the palaeoenvironment, micropalaeontology and palaeoecology of this important locality. The 8 m thick section comprises saline–hypersaline lake facies (dolostones, evaporites), fluvial facies (conglomerate lags, rippled, planar-laminated, and cross-bedded sandstones and siltstones) and overbank facies (laminated grey siltstones, sandy siltstones, very fine sandstones and palaeosols). Numerous exposure surfaces characterised by rooting, desiccation or brecciation indicate the repeated wetting and drying of the floodplain. Vertebrate, invertebrate and plant fossils are concentrated in the overbank facies association, particularly in sandy siltstones. Macro- and microfossils present are tetrapods, rhizodonts, actinopterygians, gyracanthids, dipnoans, chondrichthyans (Ageleodus), bivalve molluscs, eumalacostracans, myriapods (diplopods), eurypterids, scorpions, branchiopods, ostracods, Spirorbis, Serpula, Calcitarcha, Monocraterion trace fossils, plant stems, arborescent lycopsids (Stigmaria, Lepidodendron) and megaspores of the creeping lycopsid Oxroadia conferta. Various palaeoenvironments coexisted on a tropical, coastal, low-lying floodplain: evaporitic saline lakes, small meandering river channels, brackish salinity temporary lakes, wet marshes and sub-aerial dry land with scrubby vegetation and trees. Tetrapods inhabited waterlogged floodplain marshes and were transported post-mortem by meteoric flooding events into brackish lakes and pools. The abundance of tetrapod and other fossils is attributed to taphonomic concentration and preferential preservation during rapid burial. The Willie's Hole succession gives a window into the rich ecology and habitats on coastal floodplains after life recovered from the end-Devonian extinction and tetrapods walked on land.

The Southern Uplands-Down-Longford Terrane (SUDLT) saw exploration for coal in Ordovician-Silurian marine rocks for several centuries, including well after it was understood that land plant coals would not occur in such rocks. Some lithologies were so carbonaceous that a fuel of sorts was mined. The record of this exploration and mining activity is mostly forgotten, but there are diverse sources to show that it was widespread. Exploration was mostly inspired by outcrops of Moffat Shale, in which deformation and hydrocarbon generation left coal-like products. The hydrocarbon origin conferred high calorific value to the fuel, so it did burn and encouraged exploration. The deposits show that an accretionary prism can be a reservoir of locally abundant carbon.

A new species, Mesolepis arabellae, is described from material recently recovered from the shales of the Scottish Lower Coal Measure Formation. Up until now, three British species of Mesolepis have been named: Mesolepis scalaris Young, Mesolepis wardi Young, and Mesolepis micropterus Traquair. A fourth member of the genus, Mesolepis pustulosa Pruvost from the coalfields of Northern France, was named on scale description alone, though the validity of this taxon is uncertain. The new material described here varies from other Mesolepis species in its caudal peduncle morphology and overall body shape. Micro-computed tomography of the new species reveals the presence of teeth on the premaxilla and dentary and a splint-like fused prearticular and coronoid element, with implications for a possible feeding behaviour of Mesolepis. Additional information on the homogeneous Mesolepis wardi is also presented.

A number of early tetrapods occur in different localities from the Ballagan Formation in Scotland. These localities are within the 12 Myr time duration of the Tournaisian so it is important to be able to place them within a chronology to better understand the evolutionary relationships of the tetrapods. Palynology is used to recognise distinct assemblages in the Norham West Mains Farm borehole and the Burnmouth coastal section which become a composite standard. The Willie's Hole tetrapods (Koilops, Mesanerpeton and Perittodus) come from the lower part of the Ballagan Formation with Auchenreoch Glen (Pederpes) somewhat higher. The oldest tetrapods are from the Harbour beds at Burnmouth with the Ross end cliffs tetrapods (Aytonerpeton, Diploradus and Ossirarus) the youngest assemblage. It is not possible to place the Coldstream tetrapods as the spore assemblage is low diversity. Tantallognathus from Tantallon is early Viséan in age. Occidens portlocki, an isolated partial tetrapod jaw from a historic collection in Northern Ireland, is not of Tournaisian age and hence not from within Romer's Gap, but it can be dated as Brigantian (latest Viséan) age. The other significant Romer's Gap locality from Blue Beach, Nova Scotia, Canada, is different in age span and palaeoenvironment.

Rhadinichthys is one of the most wide-ranging and speciose genera of Palaeozoic actinopterygians. A classic variety of ‘palaeoniscoid’, Rhadinichthys species are generally small (~10–15 cm) and known mostly from dermal skeletal remains that show features commonplace among early ray-finned fishes. For this reason, the genus has long been considered a poorly diagnosed wastebasket taxon in need of revision and rarely included in systematic analyses. In the present work, syntypes of Rhadinichthys ornatissimus, the type species, are re-examined and supplemented with better-preserved material from other localities in the Scottish Midland Valley. A neotype is nominated and a more precise diagnosis presented with a suite of genus-level apomorphies. Unexpectedly, these traits are also evident in the monotypic Lower Carboniferous actinopterygian genus Woodichthys, which the neotype of R. ornatissimus closely resembles. As a result, the genus Woodichthys is subsumed within the redefined Rhadinichthys, and the single Woodichthys species is reassigned as R. bearsdeni, comb. nov., bringing with it a set of endoskeletal data. Some of these data are new, derived from μCT scans of the skull of the R. bearsdeni holotype, yielding renderings that update the original description of its skull table, parasphenoid, neurocranium, and otoliths. Further new data concerning the hyoid arch are obtained from a new specimen of R. bearsdeni from a site close by the original Bearsden locality. Redefined in this way, Rhadinichthys presents a data-rich operational taxonomic unit better suited for systematic studies. However, in so doing, it also releases a cluster of fossil species no longer anchored to a genus and now in need of rediagnoses.

Continental drift of Baltica from the Tremadocian subpolar latitudes to subtropical latitudes in the Katian was the main factor controlling the succession of the Ordovician Baltic conodont communities. These faunas were gradually enriched during the Floian as a result of immigrations from the regions experiencing warmer climate. Reinterpretation of quantitative data in terms of population approach to fossil assemblages shows how some of these immigrants evolved anagenetically in place, changing their contribution to the secondary productivity of the ecosystem. The composition of the fauna became surprisingly uniform, at least since the numerical domination by the presumably indigenous Baltoniodus lineage was established during the Dapingian. Baltoniodus was supplemented by another indigenous lineage of Trapezognathus-Lenodus-Eoplacognathus, which continued its subordinate occurrence during the Darriwilian. The early Sandbian transgression resulted in immigration of the Amorphognathus lineage that emerged allopatrically in an unknown region but then began evolving anagenetically until the end of the Ordovician. Conodonts with coniform apparatus elements added complexity to the general picture of immigrations and disappearances, but only the lineage of Protopanderodus rectus seems to have differentiated geographically its contribution to the biological productivity. Several brief cooling and warming episodes did not result in any long-term transformations of the conodont communities. Most intriguing was the immigration of the Yaoxianognathus lineage that probably gave rise to all of the post-Ordovician ozarkodinids. By that time, Yaoxianognathus had its close relative in the tropical North American Midcontinent, but the source area was probably in the Darriwilian of the Argentinian part of Gondwana. Forms with thin P1 elements of basal cone walls, like Scabbardella or Hamarodus, are indicators of glacial Gondwanan influences. The lineage of Sagittodontina, associated with these in the Małopolska microcontinent (with Gondwanan affinities), was subordinate in Baltica until it had been influenced by the Hirnantian glaciation that ended the Baltic conodont fauna.

Porolepiforms represent one of the key lineages of early lobe-finned fishes. They include two taxonomic groupings: the paraphyletic ‘porolepidids’, characterised by rhombic scales and extensive development of cosmine on dermal bones; and the monophyletic, more nested holoptychiids, characterised by round scales and lack of cosmine. Braincases and endocasts represent important sources of information bearing on sarcopterygian interrelationships, but the level of detail available for these structures is highly uneven. Among porolepiforms, the braincase and endocast is best known for the Middle Devonian holoptychiid Glyptolepis groenlandica, but even here there is lack of detail compared to the most completely understood examples from other sarcopterygian lineages. Here we address this deficiency through micro-computed tomographic study of the intact neurocranium of Durialepis edentatus and Early Devonian (Emsian) ‘porolepidid’-grade porolepiforms from the Eifel region of Germany. We present some revisions to external details of the braincase reported by a prior study, the most significant of which is identification of the occipital arch. Scans reveal substantial new data on internal structure of the braincase. The endocranial cavity of the ethmosphenoid division closely agrees with details reported for Glyptolepis and Powichthys, and we agree with past studies that argue for a close relationship between the latter genus and porolepiforms. Durialepis edentatus shows a dense network of canals in the snout comparable to the rostral tubuli of several other sarcoptergians. We also provide the first model of the posterior cranial endocast in a porolepiform. Drawing on additional tomographic data for Glyptolepis paucidens and an unnamed Scottish holoptychiid, we review patterns of character distribution in porolepiform braincases and endocasts, amplifying support for clades including Porolepiformes + Powichthys and for Holoptychiidae.

Lungfishes achieved high diversity in the Devonian, but most of these lineages went extinct in the late Devonian mass extinctions. Carboniferous lungfish are generally thought to belong to one larger diversification, Phaneropleuriformes, typically associated with freshwater and estuarine environments. We here use μCT to describe a lungfish occiput from the Tournaisian of Blue Beach, Nova Scotia, Canada, the first lungfish occurrence from the Tournaisian of North America. The occiput is short and high with well-developed dorsolateral cristae, two pairs of spinal nerves posterior to the vagus nerve, and a short triangular posterior stem of the parasphenoid. Although this specimen is too incomplete to place into a phylogenetic analysis, we identify characteristics shared with both holodontids and dipterids and absent within Phaneropleuriformes, suggesting the persistence of a wider range of lungfish lineages through the end-Devonian mass extinction events, in line with recent findings from the Tournaisian-aged Ballagan Formation of Scotland. Differences in the faunal composition of the Blue Beach Member of Nova Scotia and the Ballagan Formation of the Scottish Borders may be a consequence of different paleoenvironments in these roughly coeval formations or of palaeobiogeographical barriers to dispersal between Europe and Atlantic Canada. The possible persistence of a marine or estuarine lungfish into the mid-Tournaisian shows turnover of the marine durophage guild across the Hangenberg extinction was not complete, but may have been sufficient to disrupt incumbency in earliest Carboniferous marine trophic guilds.

The braincase and middle ear region underwent a dramatic reconfiguration during the fish–tetrapod transition, involving the loss of the intracranial joint and associated structures, as well as the loss of the lateral commissure and the transformation of the hyomandibula into a stapes. The earliest examples of the tetrapod condition are seen in Devonian stem tetrapods. Complete otoccipital regions have only been described from two genera, Ichthyostega and Acanthostega, which differ greatly from each other. Here we present the first complete otoccipital region of Ventastega, together with new data on Acanthostega that modify the published reconstruction. In lateral view, both braincases are similar in shape, with large fenestrae vestibuli and anteroposteriorly short, but tall, exoccipitals. However, in occipital view the exoccipital-basioccipital complex of Ventastega resembles that of Eusthenopteron and differs substantially from Acanthostega. Remarkably, both braincases contain an arcual plate, a sarcopterygian fish characteristic known in taxa with an intracranial joint, such as Eusthenopteron and Latimeria, but never before seen in a tetrapod. The hypophysial region of Acanthostega contains an interorbital foramen similar to that in post-Devonian tetrapods, contrasting with Ventastega which has a solid braincase wall with small foramina similar to the condition in Eusthenopteron. The suture pattern of the skull roof of Ventastega is fully resolved and the presence of an intertemporal bone is confirmed.

The early tetrapod Eoherpeton watsoni is known from the mid- to late Carboniferous (late Viséan to Namurian, approximately 346–313 Ma) of Scotland. The holotype is made up of a nearly complete but crushed skull with postcranial fragments. The skull anatomy of Eoherpeton was first described over 40 years ago; however, many details are obscured due to deformation of the specimen, including internal bone surfaces, the palatal bones and dentition, and suture morphology. Most phylogenetic analyses place Eoherpeton as an embolomere/reptilomorph on the lineage leading to amniotes, making it a key taxon for understanding anatomical changes during the fish-tetrapod transition. In this paper, we scanned the holotype using micro-computed tomography and digitally prepared the specimen. Based on these data, we present a revised description of the skull, including sutural morphology, that supplements and amends previous descriptions. New anatomical findings include the presence of a previously unknown tooth-bearing vomer, additional information on the shape of the basipterygoid processes and jaw joint, the ability to visualise the full extent of the pterygoid, and confirmation of the arrangement of the coronoid series. We also note the size of the pterygoid flange, which is larger than previously described for Eoherpeton. The pterygoid flange is widely considered to be characteristic of amniotes and serves as the origin of the medial pterygoideus muscle. The differentiation of the adductor muscles and appearance of medial pterygoideus are thought to have permitted a static pressure bite in amniotes, potentially resulting in greater bite forces and increased dietary range. Thus, the presence and extent of the pterygoid flange in Eoherpeton suggests this feature (and associated changes in feeding mechanism) may have evolved earlier than previously thought. Finally, the skull was digitally repaired and retrodeformed to create a new, hypothetical three-dimensional reconstruction of the skull of Eoherpeton.

The dvinosaur temnospondyl Trimerorhachis is one of the best-known tetrapod genera from the Early Permian of the continental United States. Although the cranial and postcranial anatomy of this taxon is known in considerable detail, no comprehensive appraisal of its lower jaw is available. The present study aims to fill this gap. We surveyed numerous, previously unfigured, mechanically prepared jaw rami of Trimerorhachis, most attributed to T. insignis, from several localities in North America. This material demonstrates remarkable phenotypic variation, clarifies aspects of the jaw construction that have remained elusive or poorly documented until now, and reveals new information, including: the course of sutures around the symphyseal region; the construction of the precoronoid fossa (an excavation situated posterior or posterolingual to the dentary fangs); the proportions and distribution of foramina on the medial surface of the ramus; the presence of a conspicuous adductor process on the angular; the extent of Meckelian ossifications inside the adductor fossa; and the morphology of the coronoids, including differences in the size, shape, and arrangement of coronoid denticles. We present a revised diagnosis of Trimerorhachis based on jaw characters, compare its jaw with those of other dvinosaurs, and comment on the presumed diagnostic jaw traits in two other Trimerorhachis species, namely T. rogersi and T. mesops.

The evolution of skull length in temnospondyl amphibians is investigated using a variety of phylogenetic comparative methods applied to a time-calibrated supertree of 288 species. Temnospondyls expressed greater among-group than within-group variation in skull dimensions, pointing to a rapid occupation of distinct regions of trait space early in their history and during major episodes of clade diversification. Consistent with this pattern is the occurrence of regime shifts along basal branches in their phylogeny, especially within a diverse clade consisting of dendrerpetids, dvinosaurs, zatracheids, and dissorophoids. An additional conspicuous shift marks the separation between the two main clades of derived stereospondyls, the trematosauroids and the capitosauroids. Mean skull length differs significantly among taxonomic groups and across three main time intervals (Carboniferous; Permian; Mesozoic). However, the distribution of skull lengths across groups varies from nearly symmetrical to markedly skewed. Despite these differences, analyses of skewness show that the evolution of skull length conformed for the most part to expectations of a driven trend, with a sustained and directional pattern of change mirrored across separate lineages. Trait values and evolutionary rates tend to increase through time across the entire group, but individual lineages show contrasting patterns, revealing either no temporal trends or varying degrees of increase/decrease through time. Reduction in skull length features predominantly in terrestrial groups, such as amphibamid dissorophoids, although exceptions are observed. In contrast, most groups exhibiting an aquatic lifestyle tend to attain large or even gigantic sizes, particularly among stereospondyls.