1. Volume synopsis

The title of this special issue encapsulates Tim’s core interests and research philosophy, underscoring the intricate connections between extinct organisms, their habitats and their reciprocal interactions. Appropriately, the articles presented here are diverse in scope and nature, and are organised in three thematic sections.

The first section comprises two papers that delve into the environmental, ecological, geological and stratigraphic contexts of tetrapod-yielding Mississippian localities. Bennett et al. provide critical new data on the Willie’s Hole site in southeastern Scotland, detailing the ecology and habitats of its preserved biotas. Willie’s Hole showcases an extraordinarily diverse community of aquatic and terrestrial animals (e.g., molluscs, annelids, arthropods and vertebrates) and plants (represented by stems, arborescent lycopsids and creeping lycopsid megaspores) that thrived in a tropical, coastal and low-lying floodplain periodically inundated by seawater from storm surges. Numerous distinct environments coexisted within this floodplain, including evaporitic saline lakes, narrow meandering river channels, transient brackish lakes, wet marshlands and subaerial drylands featuring sparse vegetation and scattered trees. Fossils typically occur within concentration deposits resulting from the accumulation of organisms transported by episodic flooding events. The study increases and refines our knowledge of Carboniferous environments during a critical stage in the restructuring of biological communities following the end-Devonian mass extinction event (Otoo et al. Reference Otoo, Clack, Smithson, Bennett, Kearsey and Coates2019).

Marshall et al. present a detailed chronostratigraphic account of Tournaisian tetrapod localities within the Ballagan Formation, Scotland (Clack et al. Reference Clack, Bennett, Carpenter, Davies, Fraser, Kearsey, Marshall, Millward, Otoo, Reeves, Ross, Ruta, Smithson, Smithson and Walsh2016), based upon an extensive repository of palynological data. Their work further refines the stratigraphic placement of the whatcheeriid tetrapod Pederpes finneyae (Clack Reference Clack2002; Clack & Finney Reference Clack and Finney2005), which occurs within sediments representing a small section at the top of the Ballagan Formation, and that of the enigmatic, possibly whatcheeriid- or Crassigyrinus-like Occidens portlocki (Clack & Ahlberg Reference Clack, Ahlberg, Arratia, Wilson and Cloutier2004), reinterpreted as being latest Viséan or early Namurian in age. The authors highlight the distinctiveness of the Ballagan Formation through meticulous comparisons with Blue Beach in Nova Scotia, Canada, a renowned site for Tournaisian tetrapod discoveries (Anderson et al. Reference Anderson, Smithson, Mansky, Meyer and Clack2015). Unlike the perpetually wet environments at Blue Beach, however, those in the Ballagan Formation were characterised by seasonal dryness and are slightly older. The new stratigraphic context for the Ballagan tetrapods offers ample scope for future analyses of the tempo and mode of tetrapod diversification during the Carboniferous Period.

The second section of this issue consists of three palaeoichthyological papers. An additional paper, by Lebedev et al., was intended to be part of this volume but was accidentally printed in a prior issue of EESTRSE (available at https://doi.org/10.1017/S1755691022000251). In that paper, the authors investigate the morphology, development and possible function of the enlarged, coiled tooth whorl of eugeneodontiforms, one of the most elusive and iconic clades of extinct chondrichthyans (cartilaginous fish) (Lebedev Reference Lebedev2009). They introduce a new family of eugeneodontiforms to place four genera previously assigned to two distinct families. One of these families accommodates a new genus and species from the Upper Pennsylvanian of Russia, represented by two tooth whorls, one of them very large and exceptionally well-preserved. Using a combination of traditional photography and microtomography, the authors reveal the histology and pattern of growth of the tooth whorl in astounding detail. The wealth of data gleaned from palaeohistological analyses forms the basis for a comprehensive discussion of tooth crown development in eugeneodontiforms.

The interrelationships of early actinopterygian (ray-finned) fish remain in a state of flux. A review of the taxonomy and validity of numerous Palaeozoic taxa is essential for establishing a robust phylogenetic framework for this group. Mo et al. scrutinise Rhadinichthys, one of the taxonomically most speciose and stratigraphically longest ranging of all Palaeozoic actinopterygian genera, representing a classic example of a ‘wastebasket taxon’. The authors present a thorough redescription of the type species, R. ornatissimus, and revise a second species, R. bearsdeni, previously classified under its own genus, Woodichthys. Out of 27 species presently assigned to Rhadinichthys, two are validated, two are proposed as potential candidates for inclusion, while the remaining species are either reassigned to separate genera or deemed undiagnosable due to insufficient or poorly preserved material. The novel diagnosis, precise taxonomic delimitation and exhaustive account of Rhadinichthys render this genus highly suitable for inclusion in current and future phylogenetic analyses of ray-finned fish (Caron et al. Reference Caron, Venkataraman, Tietjen and Coates2023; Giles et al. Reference Giles, Feilich, Warnock, Pierce and Friedman2023).

Friedman et al. advance our knowledge of the neurocranium of Durialepis edentatus, an Early Devonian, ‘porolepidid’-grade dipnomorph sarcopterygian (lobe-finned fish) from Germany, and give us an exhaustive comparative account of neurocranial data across major lineages of porolepiforms (an extinct fish clade closely related to lungfish). Their paper complements a previous contribution discussing the skull anatomy of this taxon (Mondéjar-Fernández et al. Reference Mondéjar-Fernández, Friedman and Giles2021). Aided by advanced computed microtomography, their re-examination of Durialepis emphasises the utility of braincase features in investigations of porolepiform inter- and intrarelationships. The authors describe the intricate endocranial anatomy of this taxon, reconstruct the pathway of several cranial nerves and vessels, and present a detailed three-dimensional model of the ear region and adjacent sections. Among the most intriguing features of Durialepis is a complex network of tubuli in the rostral region, suggesting a broader occurrence of these structures in sarcopterygians than previously thought.

The Late Devonian saw the demise of many vertebrate groups, including several lineages of lungfish. Carboniferous lungfish, typically associated with freshwater and estuarine environments, are thought to belong to a larger radiation known as the phaneropleuriforms. Using computed microtomography, Pardo et al. report on a lungfish occiput from the Tournaisian of Blue Beach, Nova Scotia, marking the first Tournaisian lungfish occurrence from North America. The short and tall occiput of the new taxon shares traits with two Devonian lungfish families, the holodontids and dipterids, but has no obvious characteristics in common with phaneropleuriforms. These findings indicate that a wider range of lungfish lineages persisted through the end-Devonian mass extinction event than formerly hypothesised (see also Challands et al. Reference Challands, Smithson, Clack, Bennett, Marshall, Wallace-Johnson and Hill2019). Differences in faunal composition between the Blue Beach Member of Nova Scotia and the Ballagan Formation of Scotland are explained in terms of different palaeoenvironments or palaeobiogeographical barriers between Europe and Atlantic Canada. The possible persistence of marine or estuarine lungfish into the mid-Tournaisian suggests that the turnover of marine durophagous lungfish across the end-Devonian mass extinction was perhaps not complete and may have temporarily disrupted the marine trophic levels of the earliest Carboniferous.

The third section of this issue includes four papers on early tetrapods. Ahlberg et al. explore the evolutionary remodelling of the braincase and middle ear regions during the fish–tetrapod transition. By analysing new braincase data from two notable Devonian tetrapods, Ventastega curonica and Acanthostega gunnari, the authors provide detailed neurocranial comparisons with various other primitive tetrapods and derived tetrapodomorph fish. The new findings from Ventastega and Acanthostega both enhance and complicate the sequence of character transformations underpinning the emergence of tetrapods. A new partial skull of Ventastega shows direct evidence of an intertemporal bone, a unique feature among known Devonian tetrapods, and offers a clearer depiction of suture patterns than previous studies. A small arcuate plate, sealing the narrow space between the basioccipital and the basiphenoid, is identified for the first time in Ventastega and newly recognised in Acanthostega. The otoccipital region of the neurocranium of Ventastega suggests that this taxon is more primitive than Acanthostega in several respects, such as the presence of a co-ossified exoccipital–basioccipital complex and dorsally fused exoccipitals.

Fifty years ago, Alec Panchen formally named and described the ‘anthracosaur’ Eoherpeton watsoni from the Late Viséan or Namurian of Scotland (Panchen Reference Panchen1975). A decade later, Tim Smithson released a comprehensive redescription of the cranial and postcranial anatomy of this tetrapod (Smithson Reference Smithson1985). Using computed microtomography, Porro et al. present a thorough re-examination of the skull morphology of Eoherpeton. Their study both reveals new cranial traits and amends previous accounts of specific cranial features, culminating with the production of a three-dimensional digital model of the skull. The authors shed new light on the morphology and distribution of teeth in the anterior portion of the palate (especially on the vomer), clarify the configuration of the basipterygoid processes and jaw articulation, enable a complete visualisation of the pterygoid and identify a substantial pterygoid flange. The skull architecture of Eoherpeton is investigated from a biomechanical standpoint: a general conclusion from their paper is that this animal was capable of exerting a strong bite through the force generated by its jaw adductor musculature. The restudy of Eoherpeton is a valuable addition to the literature on anthracosaurs – a group of early tetrapods that is central to discussions about the taxonomic composition of the amniote stem group – and dictates a significant re-evaluation of trait polarity near the base of the tetrapod crown group.

Ruta et al. present a detailed redescription of the lower jaw of the temnospondyl amphibian Trimerorhachis from the Early Permian of North America, revealing both previously unknown features and lesser-known aspects of its jaw construction. Their work illuminates the course of sutures around the symphyseal region, the architecture of the precoronoid fossa (an excavation located posterior or posterolingual to the dentary fangs), the proportions and distribution of foramina on the medial surface of the jaw ramus, the presence of a prominent adductor process on the angular, the extent of Meckelian ossifications within the adductor fossa, and the morphology of the coronoids, including variations in the size, shape and arrangement of coronoid denticles. The authors provide a revised diagnosis of Trimerorhachis based on jaw characteristics and discuss presumed diagnostic jaw traits in two other Trimerorhachis species, T. rogersi and T. mesops.

In a different authorship combination, Ruta et al. conduct an in-depth analysis of rates, shifts and trends in skull-length evolution in temnospondyl amphibians, the most speciose group of early tetrapods, using a range of comparative phylogenetic methods applied to a newly assembled, time-calibrated supertree. Temnospondyls exhibit greater variation in skull dimensions among groups than within groups, indicating rapid diversification of this trait early in their evolutionary history as well as during major diversification events. Changes in skull length generally follow a driven trend, characterised by a sustained and directional pattern of change mirrored across distinct temnospondyl lineages, and with an overall increase from Carboniferous through to Permian and Mesozoic. However, whereas trait values and evolutionary rates tend to increase over time across the entire group, individual lineages display contrasting patterns, with some showing no temporal trends and others characterised by varying degrees of increase or decrease. Reduction in skull length is predominantly observed in terrestrial groups, whereas most aquatic temnospondyls tend to achieve large or even gigantic sizes.

2. Timothy R. Smithson: a biography

Born in 1954, Tim was brought up in Yorkshire and Lincolnshire, eventually settling in Barton-upon-Humber, where his father served as a headteacher. Tim pursued his undergraduate studies at the University of Newcastle upon Tyne from 1972 to 1975, earning a BSc (Hons) in Zoology in 1975. Following his graduation, he gained further research experience at Newcastle working as a junior research associate in Alec Panchen’s lab from 1976 to 1979. During this time, Tim focussed on fossil material that would become the centrepiece of his doctoral dissertation. Despite his deep engagement in research, Tim also served as a part-time lecturer at Gateshead College from 1977 to 1978, marking the beginning of a long series of educational and managerial roles. During this period, he formed a close association with Stan Wood, who was Alec’s research technician at the time, leading to a collaboration and friendship that spanned decades and resulted in significant palaeontological discoveries that have continually enhanced our understanding of the vertebrates’ transition to life on land.

Tim embarked on his PhD project at Newcastle in 1976, working on Scottish Namurian anthracosaurs under Alec’s supervision. The exceptional quality of his work quickly earned him a strong reputation in the vertebrate palaeontological community. While still a postgraduate student, Tim was offered a postdoctoral fellowship (1979–1980) to carry out research in Robert (Bob) Carroll’s lab at McGill University in Montreal. This brief departure from anthracosaurs enabled Tim to expand his scientific interests. At McGill, he investigated the cranial anatomy of the colosteid tetrapod Greererpeton burkemorani from the Late Mississippian of West Virginia. His meticulous observations and detailed scientific illustrations provided the basis for a monograph on Greererpeton, which remains a fundamental reference for early tetrapod researchers (Smithson Reference Smithson1982).

Upon returning to the UK to complete his thesis, Tim resided in Leicester, where he was employed for a short period by the University of Leicester and redeployed his drawing skills as an archaeological illustrator. In 1982 he returned to the University of Newcastle, having been awarded a Sir James Knott Fellowship (1982–1984), and he obtained his PhD in 1983. By 1984–1985, Tim had resumed his collaboration with his esteemed friend Stan Wood, with whom he shared a passion for fieldwork. The two worked together for two months at the East Kirkton Quarry.

Facing limited employment opportunities, Tim left academia to retrain and build a successful new career. A natural teacher, he returned to the North East and began his long stint in further education and management. He started as a lecturer at Northumberland College (part-time in 1985–1986; full-time in 1986–1989), then moved to Cambridge Regional College, where he served as Senior Lecturer (1989–1995), Head of the School of Science, Maths, and IT (1995–1999) and Head of Research and Business Development (1999–2000). Living in Cambridge allowed him to reconnect, both personally and academically, with two old friends and colleagues from Alec’s lab, Mike Coates and Jenny Clack.

In 2000, Tim joined Aylesbury College as Director of Curriculum and Quality, and was promoted to Vice-Principal a year later, overseeing a £30 million new build project. He left in 2006 to work for the South-West Learning and Skills Council, initially as Partnership Director for Wiltshire (2006–2009). In 2007, he was promoted to Partnership Director for Gloucestershire and later based in Bristol after the Learning and Skills Council was integrated into the Department for Education. Tim was appointed Senior Manager in 2012, the year he returned to research as a postdoctoral research assistant on the highly successful, NERC-funded TW:eed Project (https://tetrapods.org) at the University of Cambridge, a position he held until 2017.

Throughout his extensive career in post-16 education, which might have been more than enough for most people, Tim not only continued to pursue his research interests and publications but also worked with Stan Wood to highlight the importance of the fossil discoveries they had made at Burnmouth in the Scottish Borders.

3. Research, exploration and mentoring

Beyond his pivotal role in discovering and describing novel fossil specimens, Tim has demonstrated exceptional proficiency in the theoretical application of his findings. In 1987, in collaboration with his former PhD supervisor Alec Panchen, he produced a seminal, detailed demonstration of how fossils may influence the phylogenetic relationships of extant groups (Panchen & Smithson Reference Panchen and Smithson1987), a study that has since been extensively cited in numerous related research endeavours.

Tim’s research has consistently underscored the indispensable nature of fieldwork as a cornerstone of rigorous scientific inquiry. His unique position – straddling academia and teaching – has enabled him to approach his work pragmatically, applying his knowledge to real-world scenarios to solve problems and improve processes yielding tangible benefits. A remarkable example of this is his ability to foster robust relationships with fellow researchers, collectors, landowners and authorities, which have allowed him to establish valuable and fruitful collaborative networks. Frequently partnering with Stan Wood, Tim has devoted considerable time to exploring prospective new sites and re-examining established milieus in Scotland, particularly in the Borders region and Fife. One such site, the Dora Bone Bed near Cowdenbeath, provided critical material that informed a substantial part of Tim’s doctoral research. His extensive field activities in the pursuit of tetrapods within the elusive ‘Romer’s Gap’ time interval laid the foundation for the TW:eed Project (2012–2017) led by Tim’s colleague and friend, the late Professor Jenny Clack at the University of Cambridge, which was predicated on Tim’s preliminary investigations and findings. Tim is distinguished among contemporary vertebrate palaeontologists for his commitment to extensive, primary data gathering, encompassing the entire process from site prospecting, through fossil extraction and preparation, to publication, rather than relying solely on museum collections. While he has utilised such collections, he has also made significant contributions of specimens to various institutions.

Tim has been an exemplary guide and source of inspiration to numerous students, helping them to navigate the intricacies of vertebrate anatomy and the publication process. His steadfast dedication and genuine passion for his field continue to inspire and support junior and senior colleagues in their efforts to advance the study of Palaeozoic vertebrates in a region replete with untapped potential. As a result, Scotland is a globally significant location for studying the early stages of vertebrate terrestrialisation and the emergence of the modern tetrapod fauna. Tim would be the last person to advertise his successes and influence. His work with many prominent colleagues should not overshadow the fact that his findings have set much of the agenda for the exploration of post-Devonian tetrapods, with the bulk of his research embedded in Scottish rocks and establishing a scientific trajectory that has continued through several decades of both independent and collaborative, often funded work.

4. A brief timeline of collecting history before the TW:eed Project

The following account summarises the most significant field-related activities that Tim undertook, with a brief description of the major outputs related to each.

4.8. Broomhouse

Broomhouse is located on Whiteadder Water, upstream from Willie’s Hole towards Preston Bridge. Like Willie’s Hole, it was originally known for its fossil crustaceans and was included in Schram’s (1979) monograph on British Carboniferous Malacostraca. Familiar with Schram’s work, Stan Wood visited Broomhouse in early 2009 after his success at Willie’s Hole. Once again, Stan found fossil vertebrates, including tooth plates similar to those of a new lungfish he had first discovered at Burnmouth in 2007. This lungfish was later named Xylognathus macrustenus in Stan’s honour (Smithson et al. Reference Smithson, Richards and Clack2016).

Figure 1

Photograph of Tim Smithson, with lime trees in the background and the parish church behind them in Stoke by Clare, Suffolk. Photograph credit: Lesley Agar, 2021.

5. Concluding remarks

Tim has had an extraordinary career. As one of Alec Panchen’s ‘academic children’ in Newcastle upon Tyne, he quickly gained recognition for his pioneering work on early tetrapods. Through this work, Tim and other PhD students of Alec laid the groundwork for a comprehensive and far-reaching perspective on the evolutionary history of Palaeozoic groups, which later became central to our understanding of the anatomical, functional and ecological innovations that led to the emergence of limbed vertebrates from fish ancestors. Tim shared and enhanced Alec’s vision, elevating research on early tetrapods to new heights. With extensive fieldwork experience before his PhD, he recognised the potential of new discoveries and the importance of meticulously revising existing data. These elements have been pivotal throughout his career. Early on, he mastered a variety of self-taught skills, including scientific illustration and photography, many of which he applied in fields unrelated to his scientific pursuits. He developed a keen eye for subtle comparative anatomical details and created superb specimen renditions that enrich his scientific output.

Tim embraced cladistics with a constructively critical approach that persists today. In collaboration with Alec Panchen, he made significant contributions to understanding the interrelationships of major groups of early tetrapods, providing the first detailed analysis of character polarity and distribution in these organisms. Many of the challenging hypotheses proposed by Tim and Alec have stood the test of time, broadening the scope of scientific work in this field and informing much of the current research. We still find ourselves deeply engaged in reading those papers, appreciating their depth more than ever.

Throughout his career, Tim’s interests expanded significantly. He continued to produce influential papers on the taxonomy, phylogeny, palaeoecology and environment of early tetrapods – as well as the occasional Carboniferous sharks and lungfish – while maintaining an active interest in the geology and sedimentology of the sites he has fondly explored for over five decades. Thanks to Tim’s meticulous efforts, valuable material is now available for in-depth research, providing impetus for new research projects. Tim remains a great inspiration for all of us. He exemplifies the qualities of a dedicated research scientist: an inquisitive and critical mind, boundless curiosity, unwavering determination, immense passion and innovative thinking. In addition, his enthusiasm is captivating, and surfaces in his inspiring writing and personal interactions. Lastly, he combines solid scientific knowledge with a friendly personality and a steadfast collegial attitude.

In recognition of his contributions, Tim was honoured with the Edinburgh Geological Society’s 2021–22 Clough Medal, an esteemed award bestowed upon individuals whose research has greatly enhanced our knowledge of the geology of Scotland and/or northern England.