Euan Neilson Kerr Clarkson (Fig. 1) was one of the most widely known invertebrate palaeontologists for over half a century. His international reputation sprang from the quality of his diverse research, his widely acclaimed textbook, numerous contributions to the operation of the science and the boundless enthusiasm and genuine interest that encouraged innumerable students, amateurs and professional palaeontologists.
Euan Clarkson in the field in the Cautley district, Cumbria, in 1987.
Among his many honours, he was elected a Fellow of the Royal Society of Edinburgh in 1984 and for most of the following 20 years he served on the editorial board of its Earth Sciences Transactions which subsequently became the present Earth and Environmental Science Transactions of the Royal Society of Edinburgh, including two periods as its chair. He co-convened four conferences organised by the Society and co-edited the resultant volumes in the journal. It is therefore very fitting that this special issue of EESTRSE is published in his memory, and we feel privileged to have had the opportunity to edit it. Its title, ‘A Palaeontological Odyssey’, reflects the life-long journey that Euan so happily took through the subject and was inspired by the title of a paper he wrote on the history of research on the Silurian rocks and fossils of his beloved Pentland Hills to the South of Edinburgh, ‘Pentland Odyssey’ (Clarkson Reference Clarkson2000). The narrative style in that paper epitomises the delight that Euan Clarkson felt for his science and which inspired so many who had the fortune to meet him and, especially, work with him.
1. Euan Clarkson: a brief biography
Euan Clarkson was born in Newcastle upon Tyne in NE England, where, as a child, his fascination with fossils was first developed by seeing ammonites in the local museum. Happily, he was able to develop that early interest into a remarkably productive career. Following national service, he obtained his BA (1960) and PhD (1964) at the University of Cambridge, England. He married another Cambridge graduate, Cynthia Cowie, in 1962 and they had four sons, John, Peter, Tom and Matt.
After Cambridge, Euan spent his entire career in Edinburgh, being appointed assistant lecturer at Edinburgh University in 1963 and rising through the hierarchy to become professor in 1998. He was awarded a DSc by the University of Edinburgh in 1983 and became professor emeritus on his retirement in 2002. He fulfilled numerous departmental and administrative roles within the university and more widely as an external examiner and very popular visiting lecturer. He was an excellent and highly dedicated teacher in the lecture theatre, laboratory and the field, and he stimulated many earth science and final year zoology students to undertake palaeobiological PhDs. His influence in palaeontological education went beyond his own institution with the publication of his textbook Invertebrate Palaeontology and Evolution. He spent nearly three years writing the first edition and the book evolved through four editions between 1979 and 1998 (see Clarkson Reference Clarkson1998, xv). Its lucid style and clear, informative illustrations (most drawn by Euan himself) ensured that it became the standard palaeontological textbook in many parts of the world. The writing of the book equipped Euan with a vast breadth of knowledge of invertebrate fossils that he brought to bear both in his own teaching and in his research. His writing skills beyond those of his extensive research output were evident in his later years, with books aimed at a general rather than academic readership co-written with his Edinburgh University colleague Brian Upton: Edinburgh Rock: the Geology of Lothian (2006) and Death of an Ocean: A Geological Borders Ballad (2009).
In addition to his many editorial contributions on behalf of the Royal Society of Edinburgh noted above, Euan Clarkson served on numerous palaeontological and wider geological bodies, including several terms on the councils of the Palaeontological Association (including being its president, 1998–2000) and the Edinburgh Geological Society (including president, 1986–1988). He was a trustee of the Natural History Museum, London (1987–1992), vice-president of the Palaeontographical Society (1990–1992), an editor of the Scottish Journal of Geology (1978–1983), a member of the Scottish Examination Board Geology Subject Panel (1985–1990) and a member of the editorial board of the journal Lethaia. He was involved in the organising of the annual meeting of the Palaeontological Association in 1980 and 2000 (in Edinburgh), the first and second meetings on Scandinavian Cambrian Alum Shales (1995 in Bornholm and Scania; 1997 in Lindköping, Västergötland), the Third International Meeting on Trilobites and their Relatives (Oxford, 2001) and Royal Society of Edinburgh conferences on ‘Fossil Arthropods as Living Organisms’ (1984), ‘Environments and Physiology of Fossil Organisms’ (1998), ‘Volcanism and Early Terrestrial Biotas’ (1992) and ‘The Southern Uplands Terrane’ (1999). He co-edited field excursion guides to parts of Southern Scotland (McAdam & Clarkson Reference McAdam and Clarkson1986; McAdam et al. Reference McAdam, Clarkson and Stone1993), enthusiastically led field excursions for several organisations and gave guest lectures in many countries around Europe and in South America.
Euan Clarkson’s achievements were marked by the awards of the Clough Medal of the Edinburgh Geological Society (1993), the Keith Medal of the Royal Society of Edinburgh (1997), the T. Neville George Medal of the Geological Society of Glasgow (1999), the Coke Medal of the Geological Society (2010) and the Lapworth Medal of the Palaeontological Association (2012).
2. Research topics
Euan had an encyclopaedic knowledge of fossil invertebrates, their distributions, lifestyles and habitats. His work was increasingly collaborative, involving colleagues from around the world, and it encompassed a remarkably wide range of research topics, taxonomic groups and geographical regions. His research had a global reach and has made fundamental and lasting contributions to the earth sciences. Here, we summarise six key areas and cite a number of Euan’s most influential publications within them.
2.1. Trilobite vision and functional morphology
A significant part of Euan’s research was centred on trilobites, especially their taxonomy, ontogeny, evolution and palaeo-ecology. He described trilobites from every Palaeozoic System from the Cambrian to the Carboniferous and from several parts of Europe, China and South America. Euan’s thesis on the Functional Morphology in Trilobites supervised by Martin Rudwick (1964, University of Cambridge) set the scene for much of his subsequent distinguished career. His earlier papers were focused on trilobite vision (Clarkson Reference Clarkson1966a, Reference Clarkson1966b, Reference Clarkson1967a, Reference Clarkson1967b, Reference Clarkson1968, Reference Clarkson and Westermann1969a, Reference Clarkson1969b, Reference Clarkson1971, Reference Clarkson1973, Reference Clarkson1975; Clarkson & Levi-Setti Reference Clarkson and Levi-Setti1975), culminating in an invited review for the Palaeontological Association (Clarkson Reference Clarkson1979). Trilobite vision was a common thread throughout Euan’s career continuing into his later years, advancing our understanding on how and what trilobites and other ancient arthropods saw (e.g., Clarkson et al. Reference Clarkson, Levi-Setti and Horváth2006; Schoenemann et al. Reference Schoenmann, Clarkson and Castellani2014, Reference Schoenemann, Pärnaste and Clarkson2017; Schoenemann & Clarkson Reference Schoenemann and Clarkson2017, Reference Schoenemann and Clarkson2020, Reference Schoenemann and Clarkson2021, Reference Schoenemann and Clarkson2023).
Vision was not the only function examined. Euan published papers on the functional morphology of the odontopleurids (Clarkson Reference Clarkson1969c), the enrolment mechanisms of a number of trilobite species (Clarkson & Henry Reference Clarkson and Henry1969, Reference Clarkson and Henry1973; Henry & Clarkson Reference Henry and Clarkson1975) and adaptations in some trilobites to a deep-water benthic setting (Clarkson Reference Clarkson1967a; Feist & Clarkson Reference Feist and Clarkson1989) or life in the plankton (Schoenemann et al. Reference Schoenemann, Clarkson, Ahlberg, Dies Álvarez, Rábano, Gozalo and García-Bellido2008). Through these studies we have a much clearer perspective on the life and times of the Trilobita.
2.2. The Cambrian Alum Shale
A significant part of Euan’s research was devoted to the Cambrian rocks of southern Sweden, in particular the environments and fossils of the Alum Shale Formation. This combined studies on upper Cambrian trilobites, their ontogeny, microevolution and habitats, with his passion for Sweden, his ‘second academic home’. Ahlberg & Harper (Reference Ahlberg and Harper2026) have summarised his impact on our understanding of the fascinating life of the Trilobita in the Baltic basin. In this research he combined with his Swedish colleagues and others on studies on olenid and other trilobites (e.g., Clarkson et al. Reference Clarkson, Ahlgren and Taylor2003, Reference Clarkson, Ahlgren and Taylor2004; Ahlberg et al. Reference Ahlberg, Szaniawski, Clarkson and Bengtson2005, Reference Ahlberg, Månsson, Clarkson and Taylor2006; Cederström et al. Reference Cederström, Ahlberg and Clarkson2009; Månsson & Clarkson Reference Månsson and Clarkson2012) and their biodiversity changes through the upper Cambrian (Ahlberg et al. Reference Ahlberg, Månsson, Clarkson and Taylor2006). These studies formed a platform for continuing studies on the life in deep-water environments off the ancient coasts of Baltica and elsewhere.
2.3. The Southern Uplands of Scotland
The Ordovician and Silurian rocks of the Southern Uplands were a key focus of Charles Lapworth’s earlier researches, using a detailed graptolite zonation to solve some of the tectonics of this part of the Caledonides while using this evidence to bolster the establishment of the Ordovician System. The plate tectonic history of the terrane proved to be the focus of considerable controversy (Floyd et al. Reference Floyd, Clarkson and Stone2000) and Euan had great scope for his passion for fieldwork in exploring this upland tract, publishing with colleagues on some key localities and describing a considerable variety of both macrofossil and microfossil faunas (Armstrong et al. Reference Armstrong, Clarkson and Owen1990, Reference Armstrong, Owen, Scrutton, Clarkson and Taylor1996; Scrutton & Clarkson Reference Scrutton and Clarkson1991; Clarkson et al. Reference Clarkson, Harper, Owen and Taylor1992; Owen & Clarkson Reference Owen and Clarkson1992; Owen et al. Reference Owen, Harper and Clarkson1996; Danelian & Clarkson Reference Danelian and Clarkson1998) from the terrane and from the adjacent Midland Valley Terrane at Girvan (Clarkson & Tripp Reference Clarkson and Tripp1982; Clarkson et al. Reference Clarkson, Harper and Höey1998; Vanderbroucke et al. Reference Vanderbroucke, Verniers and Clarkson2003). These studies drew attention to the importance of fossil biotas in understanding the evolution of mountain belts.
2.4. The Pentland Hills
Harper et al. (Reference Harper, Candela and Gallagher2026) have listed and briefly summarised Euan’s many forays into these iconic hills to the immediate south of Edinburgh, their rocks and fossils, commencing from his appointment at Edinburgh University (Clarkson Reference Clarkson2000). Although Euan’s primary interest was the many aspects of the trilobite animal, he quickly realised the significance of the abundance and diversity of the whole fossil biota. He encouraged colleagues and students to engage with him in the many opportunities the Silurian rocks offered. He initially focused on the taxonomy of the trilobites (Clarkson et al. Reference Clarkson, Eldredge and Henry1977; Clarkson & Howells Reference Clarkson and Howells1981) but his investigations diversified into a range of topics including sedimentary environments (Clarkson et al. Reference Clarkson, Harper and Taylor2000) and even bentonites (Batchelor & Clarkson Reference Batchelor and Clarkson1993). The ‘Pentlands Field Guide’ (Clarkson et al. Reference Clarkson, Harper, Taylor and Anderson2007) is a window into the rich biotas of the Pentlandian Biotic Complex (Harper et al. Reference Harper, Candela and Gallagher2026); Euan co-authored many of the chapters and the book highlights the wide range of collaborators he attracted to Edinburgh and its environs. These studies established the Pentland Hills as one of the premier sites for Silurian research.
2.5. The Granton Shrimp Bed
Carboniferous rocks are well exposed in some classic localities on the south coast of the Firth of Forth at and near Granton, Edinburgh. Euan published over 20 papers on the faunas and sedimentology of these remarkable Lagerstätte deposits, especially those of the Granton Shrimp Bed (Briggs & Clarkson Reference Briggs and Clarkson1983; Briggs et al. Reference Briggs, Clark and Clarkson1991). Here, whilst primarily studying the crustaceans, Euan discovered the conodont animal (see Briggs et al. Reference Briggs, Clarkson and Aldridge1983; Aldridge et al. Reference Aldridge, Briggs, Smith, Clarkson and Clark1993) and helped unravel its anatomy and affinities (Briggs et al. Reference Briggs, Clarkson and Aldridge1983; Aldridge et al. Reference Aldridge, Briggs, Clarkson and Smith1986, Reference Aldridge, Briggs, Smith, Clarkson and Clark1993). Many of the publications formed a series in the Transactions of the Royal Society of Edinburgh from 1983 to the early 1990s, along with the documentation of other exceptionally preserved lower Carboniferous faunas from southern Scotland and NE England (Clarkson Reference Clarkson1985; Cater et al. Reference Cater, Briggs and Clarkson1989; Clarkson et al. Reference Clarkson, Milner and Coates1993). Many fossil groups were described, but Euan’s main focus was on the arthropods, their systematics, phylogeny, taphonomy and palaeoecology (Briggs & Clarkson Reference Briggs and Clarkson1985a, Reference Briggs and Clarkson1985b, Reference Briggs and Clarkson1989).
3. Contents of this special issue
The 17 articles presented in this special issue (Table 1) cover some of the diversity of Euan’s many research interests. Topics range from Cambrian to Carboniferous faunas, and although there is a strong focus on trilobites and other arthropods, many Palaeozoic phyla are represented in this issue. Most of the authors were friends of Euan Clarkson for most or all of their research careers. Many were also among his scientific collaborators. His enthusiasm, encouragement and comradeship are greatly missed.
A list of the papers comprising this special issue in memory of Euan Clarkson, highlighting their topics and their major findings. The papers are placed in approximate order of the Palaeozoic System to which they each relate. This echoes the stratigraphical span of Euan’s research and their scope reflects many of the fields in which he made important contributions.
Euan Clarkson’s research on Cambrian olenid trilobites, especially at Andrarum in Sweden, led to major advances in understanding their ontogenetic development, evolution and palaeoecology. Ahlberg & Harper (Reference Ahlberg and Harper2026) summarise his work, often in collaboration with colleagues in Lund University and elsewhere, that generated influential studies on the Alum Shales and its trilobite faunas.
Guo et al. (Reference Guo, Yang, Schoenemann and Zhang2026) describe an exceptionally preserved new species of the bivalved euarthropod Cassicaris from the Xiaoshiba Lagerstätte (lower Cambrian, Stage 3), Kunming, China. This careful study offers new insights into the early Cambrian evolution of the group, paying particular attention to the diversity of their lifestyles and morphological disparity.
Tortello (Reference Tortello2026) describes Cambrian trilobites from two allochthonous limestone blocks from the Precordillera of Mendoza, Argentina. These descriptions include the first records of Dunderbergia, Sigmocheilus and Litocephalus from South America. The trilobites indicate that one block is of late Guzhangian age and the other of late Paibian age. They confirm the Laurentian affinities of the Cambrian faunas of the Precordillera.
The study by Mottequin et al. (Reference Mottequin, Candela, Crônier, Laibl, Marion and Servais2026) reviews fossil reports from the Stavelot-Venn Inlier in Belgium and western Germany, and finds that macrofossils are extremely rare. Only a few brachiopod fossils from the Cambrian and Lower Ordovician are confirmed; previous reports of trilobites, phyllocarids and sponges cannot be validated.
The study of an exhaustive dataset of Cambrian (Miaolingian) to Silurian radiolarian species occurrences by Danelian & Monnet (Reference Danelian and Monnet2026) discriminates three evolutionary faunas. The dynamics of change of these faunas, at the family level, are observed and correlate with major biotic and climatic changes in the Ordovician.
Lissens et al. (Reference Lissens, Vancoppenolle, Ingham and Vandenbroucke2026), through the study of a comprehensive dataset of chitinozoans from Girvan, Scotland, propose the development of a solid framework of chitinozoan biostratigraphy. This framework provides more accurate stratigraphical correlations between Avalonia, Baltica and Laurentia in the Late Ordovician.
Ingham & Owen (Reference Ingham and Owen2026) describe and discuss two species of the rare and rather unusual trilobite Bohemilla from the Upper Ordovician of Girvan, SW Scotland. They are among the youngest known occurrences of the genus and mark its extension to the Laurentian margin of the Iapetus Ocean, and are associated with deep-water trilobite faunas.
Schoenemann & Eyzenga (Reference Schoenemann and Eyzenga2026) describe a healed injury to the schizochroal eye of an Upper Ordovician phacopine trilobite. The injury had destroyed part of the visual surface and the assessment of its repair provides clues as to the possible genetic programme controlling the order of lens arrangement in such compound eyes.
Stewart (Reference Stewart2026) reports that Ordovician shelly fossils (mainly molluscs) from the Southern Uplands of Scotland are less studied than the faunas of the graptolitic shales. Their distribution suggests the Kirkcolm Formation was deposited further to the west of its present position, close to what is now Pomeroy, Co. Tyrone, Northern Ireland, and represents deeper water environments than previously thought.
The Silurian rocks of the Pentland Hills have unique and diverse fossils, different from other classic regions. The ‘Pentlandian’ was proposed as a chronostratigraphical term for these rocks but was not accepted globally. The area’s distinct fossil communities are now recognised by Harper et al. (Reference Harper, Candela and Gallagher2026) as the ‘Pentlandian Biotic Complex’.
Hughes (Reference Hughes2026) describes a long-term study of the Silurian trilobite Aulacopleura koninckii that has revealed how its segment growth was precisely controlled, providing important insights for evolutionary developmental biology.
Most of the few specimens of synziphosuran Limuloides limuloides are incomplete and consist mainly of isolated prosomas. Selden (Reference Selden2026) describes a new articulated and more complete (but lacking a telson) specimen of this species from the Wenlock (Silurian) of the Welsh Borderland, in a locality that never before yielded chelicerates. This find extends the range of known species northwest to the Welsh Borders.
Most beyrichioidean ostracods show clear shell dimorphism, but Siveter & Siveter (Reference Siveter and Siveter2026) reveal that the Silurian species Ametrobeyrichia schizopyge from the UK lacks this character. This challenges the group’s definition and suggests not all beyrichioideans used the same brood care strategy.
Methods of assessing of morphological disparity in trilobites are addressed by Randolfe et al. (Reference Randolfe, Serra, Balseiro, Dorado, Aquino, Parry, Monti, Handkamer, Vaccari, Rustán and Waisfeld2026), who analysed geometric morphometric data on Silurian to Permian trilobites. Their work shows that it is necessary to analyse multiple aspects of the trilobite body plan to reveal the full extent of their disparity. The morphospaces occupied by cephala and pygidia are poorly correlated, indicating that they each represent different aspects of biological variation.
Crônier et al. (Reference Crônier, Serobyan, Tsatryan, Hambardzumyan, Harutyunyan, Danelian, Witt, Grigoryan and Galoyan2026) describe a new species of the phacopid trilobite Omegops from the Upper Devonian of Armenia. This taxon inhabited shallow-water, near-shore habitats during the latest Fammenian; this new find represents the youngest occurrence of phacopids before their extinction during the Hangenberg Crisis at the Devonian–Carboniferous boundary.
A new species of trilobite is also described by Feist (Reference Feist2026). This species of Branikarges is the first known trochurine from the Lower Devonian of southern France and is closest to species from northern Gondwana. Silicified early growth stages enable its meraspid development to be determined and this is the first time they have been documented in the genus.
New material of the malacostracan crustacean Crangopsis collected from the Carboniferous of Scotland is described alongside historical material leading to the description and illustration of two new species by Clark (Reference Clark2026). The material reveals newly observed morphological features that enable a refined systematic position for this genus.
4. Acknowledgements
We thank all the authors who contributed their research to this special issue focused on the career and impact of Euan Clarkson. We are also deeply grateful to all the reviewers for their careful and constructive evaluations, which greatly enhanced the quality of the contributions. We warmly thank Susie Cox and the staff at Cambridge University Press for their substantial contributions throughout the editorial process, which were essential to the successful completion of this volume. Finally, we acknowledge the Royal Society of Edinburgh for the opportunity to illustrate and reflect on the life of one of its distinguished Fellows.
5. Competing interests
The authors declare none.
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