Abstract

This special issue of the Earth and Environmental Science Transactions of the Royal Society of Edinburgh (EESTRSE) celebrates the career and scientific achievements of Professor Jennifer (Jenny) Alice Clack FRS, FLS, Professor Emeritus and Curator of Vertebrate Palaeontology at the University Museum of Zoology, Cambridge. In recognition of Jenny’s professional services and outstanding accomplishments in vertebrate palaeontology, and to mark her official retirement in 2015, we have assembled 21 original research papers from 55 international scientists. The breadth of topics reflects Jenny’s wide-ranging interests. Beside vertebrate palaeontology, these include (but are not limited to) comparative anatomy, development, phylogeny, macroevolution, biomechanics, palaeoecology, palaeobiogeography, geology, and stratigraphy. The contributors to this volume include many of Jenny’s colleagues, collaborators, former students, and long-time friends. We are especially delighted to see the scientific endeavours of several young scientists at early stages of their careers alongside those of established professionals – a solid testament to Jenny’s scholarly influence.
The planning of this volume started in the late spring of 2017, when we submitted a formal proposal to the Editorial Board of EESTRSE. Key contributions to the study of early vertebrates, many authored by Jenny herself, have featured in the pages of EESTRSE. Two and a half decades ago, a seminal volume on the Scottish fossil site of East Kirkton, published in what was then known as the Transactions of the Royal Society of Edinburgh: Earth Sciences, opened a new era in the study of Palaeozoic vertebrates, particularly Carboniferous tetrapods. As recently as the summer of 2018, EESTRSE issued a special volume dedicated to the life and work of the late Stan Wood, whose painstaking fossil collecting efforts greatly expanded our knowledge of the Carboniferous world. For these reasons, EESTRSE appeared to us to represent an excellent venue for a Festschrift in honour of Jenny, and an appropriate vehicle for consolidating the UK’s long-standing tradition of research on early vertebrates.
Alongside the planning of the volume, we also organized a one-day conference in Jenny’s honour. This was held at the University of Cambridge on 13th December 2017 (Dunne & Armfield, 2018) and proved to be immensely successful. It was hosted by the Department of Zoology and the University Museum of Zoology and received generous sponsorship from The Linnean Society, The Palaeontological Association, and Dunedin Academic Press. Many of the volume contributors took part in the conference and we thank all our colleagues for their prompt and enthusiastic responses to our invitation to contribute research papers, for attending to manuscript revisions in a timely fashion, and for providing intellectually stimulating outputs. We acknowledge the demanding task of all our referees, who acted with courtesy and professionalism in reviewing the original manuscripts and, often, their revised versions. Special thanks go to some of our contributors for their generous offer to referee colleagues’ manuscripts when we experienced difficulties with reviewer selection. We also thank Rob Clack and Sarah Wallace-Johnson for their very helpful comments, corrections, and additions to the biographical section below, and for providing many of the photographs we have used to illustrate it. We are grateful to the Royal Society of Edinburgh for making this volume possible, and to our Editor-in-Chief, Stig Walsh, for coordinating various stages of its production. We would like to take this opportunity to thank Vicki Hammond, former Journals and Archive Officer at the Royal Society of Edinburgh, for providing unwavering support, strong encouragement, and prompt technical assistance with countless aspects of manuscript handling, and for attending to our numerous queries with competence and kindness. Vicki has been a driving force behind EESTRSE for many years, until her retirement in 2018, and greatly facilitated our editorial efforts during the initial stages of this Festschrift production. After Vicki’s retirement, we were delighted to receive equally strong support and invaluable help from Susie Bloor, Technical Editor at Cambridge University Press, who guided us through all final stages of volume editing, ensuring a steady and fast delivery of the revised manuscripts to her production team. Last but not least, our thanks go to Amy Woolf (Cambridge University Press) and Sharon Nickels (Sunrise Setting Ltd.) for their painstaking work with last minute’s queries concerning proof corrections, typographic and iconographic glitches, and paper layouts.

1. Volume synopsis
Although early tetrapods feature prominently in Jenny’s work, several other vertebrate groups have captured her interest throughout her career. Five palaeoichthyological papers – two on actinopterygians and three on sarcopterygians – discuss various aspects of osteichthyan biology. Coates and Tietjen describe a new genus of stem-group ray-finned fish and examine the structural and functional variety of pectoral fins in early members of this clade. Friedman et al. present evidence for durophagy in their study of Eurynotus crenatus and discuss the diversification of feeding ecologies in ray-finned fish following the end-Devonian mass extinction. Smithson et al. address dipnoan diversity in the latest early Carboniferous through a re-examination of historically important fossil material collected by Ramsay Traquair and present new data on the ontogeny of lungfish tooth plates. Lebedev and Clément introduce us to new tetrapodomorph taxa from the middle–late Devonian of northwestern Russia. Kamska et al. discuss the morphology and ontogeny of the humerus of the large Devonian tetrapodomorph Hyneria lindae and present palaeohistological evidence in support of the slow skeletal development, large genome size, and possible neotenic nature of this near-tetrapod relative.
Evolutionary developmental biology is an ever-expanding and rapidly changing field that Jenny has embraced with enthusiasm since its inception, through her work on vertebrates’ paired appendages and ears. Aptly, two papers focus on these two anatomical regions in light of embryological data from two new model organisms. Dickson and Pierce give novel insights into the origin and evolution of paired limbs through their analysis of pectoral fin development and musculoskeletal anatomy in anglerfish. Pfaff et al. produce a detailed account of the ontogeny of the ear region in the skate Leucoraja erinacea and discuss the relevance of cartilaginous fish in comparative evolutionary and developmental studies of vertebrate neuroanatomy.
Eight papers are devoted to early tetrapods, including two general and six taxonomic contributions. Ahlberg presents an in-depth review of the origin and diversification of tetrapods, summarizes research milestones in this area, and offers new evidence in support of alternative scenarios to the aquatic origin of limbed vertebrates. Long et al. review the body of evidence for the origin and diversification of tetrapod faunas in Gondwana. Herbst and Hutchinson use advanced methods in fossil image analysis to cast a fresh look at the osteology of one of the most problematic of all Carboniferous stem-group tetrapods, the aquatic moray eel-like predator Crassigyrinus scoticus, and describe important new details of its axial and appendicular skeleton. Bolt and Lombard investigate the complex morphology of the palate and braincase of Whatcheeria deltae from the Mississippian of North America, a key stem-group tetrapod with a mosaic of primitive and derived features. Andrew Milner discusses two trematopid temnospondyl amphibians from the Pennsylvanian of the Czech Republic, describes a new taxon, and reviews the morphology and ontogeny of trematopids alongside a detailed account of character distribution within the family. Klembara and Mikudíková offer a new account of the cranial anatomy of the Lower Permian discosauriscid seymouriamorph Discosauriscus pulcherrimus from the Czech Republic and detail major ontogenetic changes in its skull roof, palate, and braincase. Two additional tetrapod contributions concern representatives of the problematic “lepospondyls”, a collection of early tetrapod groups long suspected to form a polyphyletic assemblage rather than a distinct clade. Angela Milner gives us a captivating narrative of the history of discovery and research on the Pennsylvanian genus Keraterpeton, a representative of a group of “lepospondyls” known as the nectrideans, several of which were characterized by elongate and backward-pointing horns projecting from the skull. A detailed description of the skeletal anatomy of Keraterpeton is accompanied by a discussion of the group’s affinities. Lastly, Pardo et al. reveal the intricate morphology of an isolated aïstopod braincase from the middle Pennsylvanian of North America. The snake-like and limbless aïstopods are perhaps the most challenging of all early tetrapod groups in terms of their affinities, but the new braincase data lend support to their placement on the tetrapod stem-group.
Jenny’s approach to the study of extinct vertebrates reveals attention to the wider physical context – geological, stratigraphic, environmental – accompanying fossil data. Two papers focus on the stratigraphic and palaeoenvironmental settings for tetrapod origins. Marshall et al. provide crucial new information on the age of the uppermost part of the Old Red Sandstone – an all-time favourite in geological studies – and on the position of the Devonian-Carboniferous boundary through their detailed analysis of palynological and palaeoichthyological data from recently discovered stratigraphic sequences in central Scotland and the Scottish Borders. Millward et al. supply a detailed palaeogeographic, paleoclimatic, and palaeoenvironmental analysis of the coastal wetland habitats of northern Great Britain where some of the earliest known Carboniferous tetrapods lived.
Four macroevolutionary papers fall under the broad umbrellas of theory and practice of phylogenetic analysis, patterns and processes of phenotypic change in deep time, and tempo and mode of evolution. Tschopp and Upchurch review specimen-based approaches to the construction of cladograms from morphological data using maximum parsimony as an optimality criterion, highlighting potential and limitations intrinsic to these methodological protocols. Lee et al. address the complex question of a Laurasian vs. Gondwanan origin for dinosaurs using a new Bayesian method that simultaneously accounts for phylogeny, fossil age and location, and changes in the interconnections among geographic areas through time. Witzmann and Ruta examine the complex relationships between orbital and palatal openings in early tetrapods, especially temnospondyls, quantifying patterns of covariance between their shape and size and discussing the possible functional implications of their varying proportions. Ruta et al. tackle the morphological diversity of early tetrapod humeri, the temporal and clade-wise distribution of increases and decreases in rates of evolutionary change in this structure, and the correlation between evolutionary rates and major morphological, ecological, and functional transitions in early tetrapod history.