A review of the South African temnospondyl amphibian record

INTRODUCTION The Karoo Basin of South Africa preserves a continuous sequence of sedimentary rocks from the Late Carboniferous through to the Middle Jurassic periods (Smith 1990). Within this thick succession, the Permo-Triassic Beaufort Group and overlying Triassic-Jurassic Stormberg Group preserve a rich fossil biota that documents the evolution of terrestrial life during the late Palaeozoic and early to middle Mesozoic eras. These rocks are world renowned primarily for their therapsid (‘mammal-like reptile’) fauna, the diversity and abundance of which have allowed for the biostratigraphic subdivision of the sequence (Kitching 1977; Kitching & Raath 1984; Rubidge 1995). Less well known amongst Karoo fossil vertebrates are the temnospondyl amphibians, which are surpassed only by therapsids in terms of diversity and abundance. The Temnospondyli was the largest, most diverse and most successful group of fossil amphibians, ranging in time from the Early Carboniferous to the Early Cretaceous (Milner 1990). Temnospondyls were superficially salamander-like in appearance with a total body length that varied from below 1 m to 6 m or more, most being above 1 m. They have also been widely linked to the origin of some or all of the modern lissamphibian groups (e.g. Milner 1988; Bolt 1991; Trueb & Cloutier 1991). Temnospondyls have been recovered from all continents and are near-ubiquitous components of non-marine sedimentary rocks of Permian and Triassic age. This abundance has led to their playing an important and sometimes critical role in local biostratigraphy and global correlation of nonmarine strata of Triassic age (e.g. Hancox et al. 1995; Ivakhnenko et al. 1997; Ochev & Shishkin 1989; Lucas 1998). In the Karoo the temnospondyl fauna is dominated by members of the great Mesozoic radiation of temnospondyls known as the Stereospondyli (Milner 1990; Yates & Warren 2000), with members of the Palaeozoic lineages Dvinosauria and Dissorophoidea making up the non-stereospondyl component. The Permo-Triassic Beaufort Group contains all but one of the higher-level temnospondyl taxa known from the Karoo, with most of these occurring in the Triassic part of the Group. The overlying TriassicJurassic ‘Stormberg Group’ has received far less attention palaeontologically, a fact reflected in the considerably lower diversity of tetrapods, including temnospondyls (Kitching & Raath 1984). Despite this overall rich temnospondyl record, relatively little research has been directed towards Karoo temnospondyls. In recent years, however, there has been a resurgence of interest in South African temnospondyls, especially in taxonomic studies (see review below), their role in interpreting the basin development of the Karoo (Hancox & Rubidge 1997; Hancox 1998), and in local biostratigraphy and correlation of nonmarine tetrapod faunas (Hancox et al. 1995; Shishkin et al. 1995; Lucas 1998; Damiani 1999; Hancox et al. 2000; Shishkin 2000). The only previous review of Karoo temnospondyls was that of Kitching (1978), a paper which was concerned primarily with documenting the total numbers and stratigraphic distribution of the temnospondyl fauna of the Beaufort Group. Since then, a significant number of new temnospondyl taxa have been described, additional information has been obtained through redescriptions of older material, and stratigraphic and biostratigraphic advances have been made. The aim of this paper is to summarize the taxonomy as well as stratigraphic occurrence of all known temnospondyls from the Karoo. It is not the intention here to critically reassess the relationships of each temnospondyl species discussed, although we provide a brief summary of the taxonomic history of those species whose relationships have been controversial. In the review below, higher-level taxa are arranged in alphabetical order, whereas individual species within each higher-level taxon are listed in chronological order of description. Synonomy lists include only those references in which a change in a taxon name has occurred. Note that the relationships of the Brachyopidae and Chigutisauridae