Timothy R. Smithson

Earliest Carboniferous tetrapod and arthropod faunas from Scotland populate Romer's Gap

Devonian tetrapods (limbed vertebrates), known from an increasingly large number of localities, have been shown to be mainly aquatic with many primitive features. In contrast, the post-Devonian record is marked by an Early Mississippian temporal gap ranging from the earliest Carboniferous (Tournaisian and early Viséan) to the mid-Viséan. By the mid-Viséan, tetrapods had become effectively terrestrial as attested by the presence of stem amniotes, developed an essentially modern aspect, and given rise to the crown group. Up to now, only two localities have yielded tetrapod specimens from the Tournaisian stage: one in Scotland with a single articulated skeleton and one in Nova Scotia with isolated bones, many of uncertain identity. We announce a series of discoveries of Tournaisian-age localities in Scotland that have yielded a wealth of new tetrapod and arthropod fossils. These include both terrestrial and aquatic forms and new taxa. We conclude that the gap in the fossil record has been an artifact of collection failure.

Phylogenetic and environmental context of a Tournaisian tetrapod fauna

The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

What made Stan Wood a great collector

Stan Wood was an exceptional fossil collector who, over a collecting career of more than 40 years, provided British palaeontology with an abundance and variety of new Carboniferous fossils, the like of which had not been collected since Victorian times. So, what made him a great collector? Here, with the help of Stans family, his friends and colleagues, we try to provide the answer. There is no single factor that stands out, but a complex mixture of innate and learned behaviours that together produced a unique talent. Although he acquired an Open University degree in geology, Stan was largely self-taught as a collector and, in doing so, became an accomplished and confident field geologist. He was naturally curious, persistent and very observant, with a photographic memory. He was tough, very strong and enjoyed hard physical work. He was congenial, unorthodox and a calculated risk taker. He asked questions, tested ideas and had a healthy disregard for authority. He was systematic, kept detailed records and shared his discoveries. He not only loved collecting fossils but, in the process, discovered in himself the essential qualities of a true scientist.

A new tetrapod from Romer's Gap reveals an early adaptation for walking

A new early tetrapod, Mesanerpeton woodi gen. et sp. nov. , collected by Stan Wood from the Ballagan Formation, Tournaisian CM palynozone, at Willies Hole, Scottish Borders, is described. It includes vertebrae like those of Crassigyrinus, with poorly developed neural arches, a well ossified ulna with a large olecranon, and a humerus that is structurally intermediate between the pleisiomorphic condition of Devonian taxa and that of all later forms. A comparative analysis of this new material and other tetrapodomorph humeri revealed how an increase in humeral torsion transformed the course of the brachial artery and median nerve through the bone, from an entirely ventral path to one in which the blood vessel and nerve passed through the entepicondyle from the dorsal to the ventral surface. Increasing humeral torsion is suggested to improve walking in early tetrapods by potentially contributing to an increase in stride length, and is one of a number of changes to limb morphology during the Early Carboniferous that led to the development of terrestrial locomotion.