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Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy
Gondwana Research, V 7, No. I , p p . 165-173. 0 2004 International Association for Gondwana Research, Japan. ISSN: 1342-937X
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Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy Ross J. Damiani Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg,South Africa, E-mail: damianirCdgeosciences.wits.ac.za (Manuscript received August 30,2002; accepted February 4,2003)
Abstract The Permo-Triassic Beaufort Group (Karoo Basin) of South Africa is biostratigraphically subdivided into eight, temporally successive assemblage zones based on therapsids (‘mammal-like reptiles’). The Temnospondyli, fossil tetrapods usually regarded as extinct amphibians, are second only to therapsids in terms of diversity and abundance in these strata, with nine higher-level taxa (‘families’) known. Temnospondyls are also playing an increasingly important role in biostratigraphy and correlation of the Beaufort strata. The lower Beaufort Group (Late Permian) contains six of the eight biozones, but only one temnospondyl ‘family’, the Rhinesuchidae, whose record in the Karoo is the richest in the world. However, rhinesuchid taxonomy remains in flux and the group is thus of limited biostratigraphic utiliv. The Early Triassic Lystrosaurus Assemblage Zone (middle Beaufort Group) contains the Rhinesuchidae, Amphibamidae, Lydekkerinidae, Tbpilakosauridae, Rhytidosteidae, Mastodonsauridae and Trematosauridae, although the biostratigraphy of temnospondyls within this biozone is poorly constrained. The uppermost reaches of the Lystrosaurus biozone contain a paucity of fossils but includes ‘Kestrosaurus’ (Mastodonsauridae) and ?Trematosuchus (Trematosauridae), taxa previously thought to pertain to the lower part of the overlying Cynognathus biozone. The late Early to Middle Triassic CynognathusAssemblage Zone (upper Beaufort Group) hosts the Mastodonsauridae, Trematosauridae, Brachyopidae, Laidleriidae and, possibly, the Rhytidosteidae. Based largely on the spatial and temporal distribution of mastodonsaurids, this biozone has been biostratigraphically subdivided into a lower A, middle B and upper C subzones, characterised by differing ages and faunas.
Key words: Temnospondyls, Beaufort Group, Karoo, South Africa, stereospondyls.
Introduction The Temnospondyliwas a highly diverse and successful group of fossil tetrapods that existed from the Early Carboniferous to the Early Cretaceous (Milner, 1990). They are usually regarded as fossil amphibians and as being ancestral to some or all of the living lissamphibian groups. Temnospondyls are near-ubiquitous components of non-marine sedimentary rocks, especially of Permian and Triassic age, where they have played an important role in local biostratigraphy and global correlation of nonmarine strata (e.g., Hancox et al., 1995; Ivakhnenko et al., 1997; Ochev and Shishkin, 1989; Lucas, 1998). One of the richest sources of temnospondyls is the Permo-TriassicBeaufort Group of the Karoo Basin, South Africa, which preserves a complete Late Permian to early Middle Triassic sedimentary sequence and associated vertebrate fauna and has long been recognised as the global standard for the non-marine Permo-Triassic (e.g., Cosgriff, 1984; Lucas, 1998). These rocks are renowned primarily for their rich and abundant therapsid (‘mammal-
like reptile’) fauna, which, because of the paucity of basinwide lithostratigraphic markers, has been used for the biostratigraphic subdivisionof the group and stratigraphic correlation with faunas elsewhere (Kitching, 1977; Keyser and Smith, 1979; Rubidge, 1995). Although largely neglected relative to the therapsids, temnospondyls form the second most important vertebrate taxon in the Beaufort Group in terms of diversity and abundance. In recent years, there has been a resurgence in Beaufort Group temnospondyl studies. They are now playing an important role in interpreting the basin development of the Karoo (Hancox and Rubidge, 1997; Hancox, 19981, local biostratigraphy (Hancox et al., 1995; Shishkin et al., 1995), and correlation of non-marine tetrapod faunas (Lucas, 1998; Damiani, 1999; Hancox et al., 2000; Shishkin, 2000). This paper surveys the diversity of Beaufort Group temnospondyls and summarises the biostratigraphic occurrence of all valid taxa. A detailed taxonomic review of all temnospondyl material from the Karoo is presented elsewhere, along with figures of representative genera (Damiani and Rubidge, in press).
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Abbreviations for South African geographical regions used in the text are as follows: ECP, Eastern Cape Province; FSP, Free State Province; KZN, Kwa-Zulu Natal; WCP, Western Cape Province.
Geological Setting The Karoo Supergroup of South Africa preserves a 12 km thick succession of mainly sedimentary rocks that accumulated in a retroarc foreland basin (Karoo Basin) during the Late Carboniferous to Early Jurassic in southwestern Gondwana (Catuneanu e t al., 1998) (Fig. 1). Lithostratigraphically, the Karoo Supergroup is subdivided into five main groups. These are, in ascending stratigraphic order, the Dwyka (Late Carboniferous), Ecca (Early Permian), Beaufort (Late Permian-MiddleTriassic), ‘Stormberg’(Late Triassic-EarlyJurassic) and Drakensberg groups, broadly representing deposition in glacial (Dwyka), marine (Ecca) and terrestrial (Beaufort and Stormberg) environments (Smith, 1990). The Drakensberg lavas terminated sedimentation in the basin in the Middle Jurassic (Smith, 1990). The fill of the Karoo Basin is intimately linked to orogenesis of the Cape Fold Belt in the south (Catuneanu et al., 1998), and the basin may be subdivided into a southern area (proximal Karoo facies) and a northern area (distal Karoo facies). The Beaufort Group strata are fluvially derived and typically consist of alternating mudstone and sandstone
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units with characteristic upward-fining textures, red and purple colours, abundant vertebrate fossils, desiccation cracks and palaeosol horizons, suggesting sediment accumulation on vast, semi-arid alluvial plains by floodplain aggradation (Smith, 1990; Rubidge, 1995). Eight biostratigraphic assemblage zones (Figs. 1,2), which are broadly linked to the lithostratigraphy in the various parts of the basin (Keyser and Smith, 1979; Rubidge, 1995), are currently recognized (Rubidge, 1995), namely (in ascending order) the Eodicynodon, Tapinocephalus, Pristerognathus, Tropidostoma, Cistecephalus, Dicynodon, Lystrosaurus and C’ognathus Assemblage zones. The first six of these biozones are of Late Permian age, ranging from the Kazanian to the Tatarian (Rubidge, 1995). The Lystrosaurus Assemblage Zone is broadly Early Triassic in age (Groenewald and Kitching, 1995; Hancox, 2000), although the Permo-Triassic boundary occurs within the lowest part of that biozone and is defined by the last appearance of Dicynodon, whose range overlaps that of Lystrosaurus (Smith, 1995; Smith and Ward, 2001). The upper reaches of the Lystrosaurus biozone appear to be lower Olenekian in age (Neveling, 2002). The Cjmognathus Assemblage Zone is of Early-MiddleTriassic age (Hancox 2000) and has been informally subdivided into a lower ‘A‘ zone (upper Olenekian), which is predominantly exposed in the north of the basin, a middle ‘B’ zone (early Anisian), which occurs within ‘classic’ Cynognathus biozone exposures in the south of the basin, and a reduced, upper ‘C’ zone (late Anisian), restricted to the southernmost reaches of the basin (Hancox et al. 1995; Hancox, 1998). This subdivision is based largely on the spatial and temporal distribution of mastodonsaurid temnospondyls. Most recently, Neveling (2002) restricted the Cynognathus biozone to subzone B, renamed subzone A the Kestrosaurus Assemblage Zone, and considered subzone C to represent a new biozone. In this paper, the terminology of Hancox et al. (1995) will be used for subdivision within the Cynognathus biozone.
Temnospondyl Diversity and Distribution Dissorophoidea:Amphibamidae Diversity
Fig. 1. Geographic distribution of the biozones of the Beaufort Group, with the extent of the Karoo Basin outlined. Transect line connects the proximal (southern) and distal (northern) Karoo facies. Biozone abbreviations: Cis-Cistecephalus, Cyn-Cynognathus, Dic-Dicynodon, Eod-Eodicynodon, Ly-Lystrosaurus, Pris-Pristerognathus, Tap-Tapinocephalus, Tro- Tropidostoma. Modified from Rubidge (1995).
Dissorophoids are small, predominantly PermoCarboniferous terrestrial temnospondyls widely cited in connection with the origin of the Lissamphibia, and are represented in the Karoo by the small taxon Micropholis stowii (Huxley, 1859). Within the Dissorophoidea, M. stowii was initially placed in its own higher-level taxon, the Micropholidae, later referred by some workers to the Dissorophidae, but is now recognised as belonging to the Gondwana Research, V. 7, No. I, 2004
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TEMNOSPONDYL BIOSTRATIGRAPHY
I L mp.
Tup.
Brrch.
Lai. Lydek.
Mastod.
Rhines.
Rhyt.
Tremat.
I
anognatlius
?Procolophon
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.-
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Lystrosaurus
Dicynodoir LJ
Cistecephalus Tropidosioma Pristerognatltus Tapinoceplialus Eodicynodon
Fig. 2. Biostratigraphic subdivision of the Beaufort Group (Karoo Basin), showing the stratigraphic occurrence of all valid temnospondyl species. Hatched bars indicate uncertainty in the stratigraphic occurrence. See text for discussion. Taxon abbreviations: Amp, Amphibamidae; Brach, Brachyopidae; Lai, Laidleriidae; Lydek, Lydekkerinidae; Mastod, Mastodonsauridae; Rhines, Rhinesuchidae; Rhyt, Rhytidosteidae; Tremat, Trematosauridae; mp, mpilakosauridae. Modified from Rubidge (1995).
Amphibamidae. M. stowii is of particular importance as representing the last dissorophoid.
Distribution Micropholis stowii occurs in local abundance in the Lystrosaurus Assemblage Zone (Kitching, 1978) and has been recovered from a number of localities in both the north and south of the basin. Stratigraphically it occurs from near the base of the Triassic part of the Lystrosaurus biozone (Smith and Ward, 2001) through to the upper reaches of that biozone (unpublished data). Dvinosauria: Tupilakosauridae Diversity The Tupilakosauridae are small, probably fully aquatic, rare relict survivors of the Palaeozoic Dvinosauria (Warren, 1999; Yates and Warren, 2000), and are represented in the Karoo by Thabanchuia oomie (Warren, 19991, the most Gondwana Research, V 7, No.1,2004
recently described and complete tupilakosaurid. Elsewhere, tupilakosaurids are represented by Tupilakosaurus from the Early Triassic of East Greenland and Russia, Slaugenhopia from the Lower Permian of Texas and, possibly, Kourerpeton from the ?Upper Permian of North America (Warren, 1999; Milner et al., 2002).
Distribution Thabanchuia oornie comes from a single locality near Thaba Nchu (FSP) in the north of the basin, in strata from which Lystrosaurus specimens had also been collected and thus considered to pertain to the Lystrosaurus Assemblage Zone (Warren, 1999). However, both the underlying Late Permian Dicynodon Assemblage Zone and overlying Early-MiddleTriassic Cynognathus Assemblage Zone also outcrop near Thaba N'chu (Kitching, 1977; Welman et al., 1991), and Lystrosaurus is now known to also occur in the uppermost Permian (Smith, 1995).
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Stereospondyli: Brachyopidae Diversity Four species representing three genera of the cosmopolitan, medium to large-sized, aquatic Brachyopidae have been described from the Karoo, namely Batrachosuchus browni (Broom, 1903), ‘Batrachosuchus’ watsoni (Haughton, 1925), Vanastega plurimidens (Damiani and Kitching, 2003) and Bathignathus poikilops (Damiani and Jeannot, 2002). Additional fragmentary material referred to Batrachosuchus sp. has been described by a number of authors (see Damiani and Rubidge (in press) for a review). The genus Batrachosuchus has been considered the archetypal brachyopid (Warren and Marsicano, 2000), although ‘Batrachosuchus’watsoni was recently transferred to a new genus, Bathignathus, by Damiani and Jeannot (2002).
Distribution ‘Batrachosuchus’watsoni and B. browni are known only from their near-complete, holotype skulls, which are presumed to have come from near Burgersdorp (ECP) and Aliwal North (ECP), respectively, both in the south of the basin. Their horizon is undoubtedly the Cynognathus Assemblage Zone, as both subzones A and B, but not C, occur in those districts. Vanastega plurimidens is represented by cranial material from a single locality near Burgersdorp (ECP), in strata of subzone B of the Cynognathus biozone. In contrast to all other brachyopids which occur in the south of the basin, Bathignathus poikilops comes from a locality near Paul Roux (FSP) in the north of the basin, and pertains to subzone A of the Cynognathus biozone. The brachyopid material described as Batrachosuchus sp. comes from the Cynognathus biozone in the Burgersdorp (ECP) and Aliwal North (ECP) districts in the south of the basin; the Burgersdorpmaterial pertains to subzone B, whereas that from Aliwal North may pertain to either subzone A or B. Stereospondyli: Laidleriidae Diversity This enigmatic higher-level taxon is currently known only from the Karoo and is represented by a single, nearcomplete skeleton, Laidleria gracilis (Kitching, 1957; Warren, 1998), that has also variously been considered a trematosaurid, a rhytidosteid, a plagiosaurid relative, or incertae sedis within the Temnospondyli.
Distribution Laidleria gracilis comes from a locality in the Engcobo District (ECP), in the south of the basin; the horizon is presumed to be the Cynognathus Assemblage Zone,
although the underlying Lystrosaurus Assemblage Zone also crops out in this area (Kitching, pers. comm.).
Stereospondyli: Lydekkerinidae Diversity The Lydekkerinidae are small, terrestrial, cosmopolitan Early Triassic temnospondyls with a centre of diversity in the Karoo. Five species have been named from the Karoo, although only three are now considerd valid (Shishkin et al., 1996). These are the genotype for the Lydekkerinidae, Lydekkerina huxleyi (Lydekker, 1889; Broom, 1915), Broomulus dutoiti (Broom, 1930; Romer, 1947) and Eolydekkerina magna (Shishkin et al., 1996). Both B. dutoiti and E. magna are known only from a single individual that includes mainly cranial material, whereas L. huxleyi is known from hundreds of specimens, including complete or near-complete skeletons, and is the most abundant temnospondyl taxon in the Karoo.
Distribution The holotype and original referred material of L. huxleyi described by Lydekker (1889, 1890) came from an unknown locality near Edenburg (FSP), in the north of the basin, in strata that are presumed to pertain to the Lystrosaurus biozone based on the co-occurrence of Lydekkerina with Lystrosaurus elsewhere. There is no other record of fossil material from the Edenburg district. The majority of all known L. huxleyi specimens, as well as B. dutoiti, come from the famous Lystrosaurus biozone locality of Harrismith Commonage (Kitching, 1977,1978), near the town of Harrismith (FSP) in the north of the basin. A few Lydekkerina specimens have also been recovered farther south. E. magna comes from Lystrosaurus biozone strata near the Bethulie district (FSP), in the south of the basin. Shishkin et al. (1996) believed E. magna and L. huxleyi to be restricted to the lower and upper part of the Lystrosaurus biozone, respectively. However, the latter species is also known to occur in the lower part of the Lystrosaurus biozone (Smith and Ward, 2001), so that its range probably overlaps that of E. magna.
Stereospondyli: Mastodonsauridae Diversity The Mastodonsauridae were large, primarily aquatic temnospondyls with a cosmopolitan distribution during the Triassic. Eight species have been named from the Karoo, of which five are considered valid by Damiani and Rubidge (in press) : the basal taxa Parotosuchus haughtoni (Broili and Schroder, 1937; Chernin, 1978; Damiani, 2001a) and Watsonisuchusmagnus (Watson, 1962; Ochev, 19661, the more derived Xenotosuchus africanus (Broom, Gondwana Research, V. 7, No. 1, 2004
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1909; Morales and Shishkin, 2002), and the highly derived Jammerbergia formops and Paracyclotosaurusmorganorum (Hancox et al., 2000; Damiani and Hancox, 2003). The validity of the basal taxon Kestrosaurus dreyeri (Haughton, 1925) is uncertain (Damiani, 2001b), while ‘Parotosuchus’ dirus (Chernin, 1978), like K. dreyeri, is represented by fragmentary material. In any case, the five valid species of mastodonsaurids makes them the most diverse Triassic higher-level taxon in the Karoo.
Distribution The Mastodonsauridae has the widest temporal and geographic distribution amongst Triassic temnospondyls from the Karoo. The basal taxon W. magnus is from subzone A of the Cynognathus Assemblage Zone in the Burgersdorp district (ECP), southern Karoo, while I? haughtoni is from the same subzone in both the Rouxville (FSP) and Paul Roux (FSP) districts in the south and north of the basin, respectively (Damiani, 2001a). K. dreyeri also pertains to subzone A and is also known from the south and north of the basin, while a possible new species of Kestrosaurus has been described from subzone A in the north of the basin. Unsurprisingly, the more derived X. africanus pertains to subzone B of the Cynognathusbiozone and specimens are known from the Burgersdorp (ECP) and Rouxville (FSP) districts in the south of the basin. The highly derived P. morganorum comes from the Sterkstroom district (ECP) in the extreme south of the basin, and is currently the only temnospondyl from subzone C of the Cynognathus biozone. The equally derived J. formops is from an unknown horizon, likely subzone A or B of the Cynognathus biozone (Damiani and Hancox, in press), in the Wepener district (FSP). Fragmentary mastodonsaurid material referrable to Watsonisuchussp. (Damiani et al., 2001) and Kestrosaurus sp. (Neveling, 2002) has also been described from the Lystrosaurus Assemblage Zone. This material possibly pertains to an ‘impoverished’fauna that may be interposed between the Lystrosaurus and Cynognathus biozones (Neveling et al., 1999; Neveling, 2002; Damiani et al., 2000) and referred to by earlier workers as the Procolophon Zone (e.g., Broom, 1906).
Stereospondyli: Rhinesuchidae Diversity The Rhinesuchidae are large, semi-aquatic temnospondyls known only from Gondwana, with a centre of diversity in the Karoo. They are the only known higherlevel temnospondyl taxon from the Permian (lower Beaufort Group) of the Karoo, and are relatively rare components of that fauna (Kitching, 1978). They are nevertheless a critical taxon in temnospondyl phylogeny Gondwana Research, V. 7, No. I, 2004
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as they represent the sister-group to the great Mesozoic radiation of the Stereospondyli (Milner, 1990; Schoch and Milner, 2000; Yates and Warren, 2000), which includes all of the known Mesozoic temnospondyls except for relict members of the Dvinosauria and Dissorophoidea. Seventeen species of rhinesuchids have been named from the Karoo, with most based on poorly preserved material. Although their taxonomy remains in a state of flux, the most recent estimates of the number of valid taxa are about six or seven (Schoch and Milner, 2000; Damiani and Rubidge, in press). These include two species of the genotype Rhinesuchus that are characterized by relatively broad skulls, R. whaitsi (Broom, 1908) and R. capensis (Haughton, 1925), the narrow-skulled Rhinesuchoides tenuiceps (Olson and Broom, 1937), the medium-sized Laccosaurus watsoni (Haughton, 1925), the giant, possibly fully aquatic Uranocentrodon senekalensis (van Hoepen, 1911, 1915; unpublished d a t a ) and the small, paedomorphic, relict taxon Broomistega putterilli (Broom, 1930; Shishkin and Rubidge, 2000).
Distribution The stratigraphic distribution of rhinesuchids within the Beaufort Group remains necessarily tenuous because of the poor state of rhinesuchid taxonomy. Consequently, the following discussion will be limited to the holotype specimens of each taxon. Except for U.senekalensis and B. putterilli, all rhinesuchid species come from the south of the basin where all six Permian biozones are exposed; only the uppermost of the Permian biozones, the Dicynodon Assemblage Zone, is also exposed in the north (Rubidge, 1995; Fig. 1). Rhinesuchus whaitsi and R. tenuiceps come from the Prince Albert district (WCP) and pertain t o the Tapinocephalus Assemblage Zone. Laccosaurus watsoni and R. capensis come from the Graaff Reinet district (ECP) and pertain to the Dicynodon and, possibly, the Tropidostoma Assemblage zones, respectively. Uranocentrodon senekalensis comes from the north of the basin near Senekal (FSP) and was long considered to pertain to the Lystrosaurus biozone which outcrops extensively in that area. However, it has recently been shown to occur below the Permo-Triassic boundary and to belong to the underlying Dicynodon biozone (Latimer et al., 2002). The sole Lystrosaurus biozone rhinesuchid is the relict B. putterilli, which occurs in the Harrismith Commonage (FSP) and Bergville (KZN) districts in the northern Karoo.
Stereospondyli: Rhyfidosteidae Diversity The Rhytidosteidae were medium-sized, aquatic piscivores and are amongst the rarest of Karoo
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temnospondyls, with only three known specimens representing two species. These are the genotype for the group, Rhytidosteus capensis (Owen, 1884), and Pneumatostega potamia (Cosgriff and Zawiskie, 1979).
Distribution The holotype and only known specimen of R. capensis is from an unknown locality in the Free State Province, and has variously been considered as from either the Lystrosaurus or Cynognathus biozones (Damiani and Rubidge, in press). Shishkin et al. (1995) considered R. capensis to pertain to subzone A of the Cynognathus biozone based on the presence of fragmentary Rhytidosteus material in the upper Olenekian of Russia. Pneurnatostega potamia is represented by two specimens from the Lystrosaurus biozone in the Middelburg and Colesberg districts (ECP) in the southern Karoo.
Stereospondyli: Trernatosauridae Diversity Trematosaurids were medium-sized, aquatic piscivores with a cosmopolitan distribution during the Triassic. The group is traditionally subdivided into the generalized, short-snouted trematosaurines and the specialized, longs no u t e d 1o n ch o r h yn c h in e s. U n t i1 re cent 1y, o n 1y trematosaurines were known with certainty from the Karoo, namely the taxa Trernatosuchussobeyi (Haughton, 1915; Watson, 1919) and the highly derived Microposaurus casei (Haughton, 1925; Damiani, in press). ‘Trematosaurus’ kannemeyeri (Broom, 1909) is a poorly preserved partial skull that Hammer (1987) transferred to the 1on ch o rh y n ch i n e Ap ha n e ram m a s p . Addition a 1 lonchorhynchine material includes an undescribed specimen referred initially to T. sobeyi (Haughton, 1925) and later to Aphanerarnrna sp. (Hammer, 1987), and a partial skull reported by Damiani and Welman (2001). All of this material is currently being restudied by the author.
Distribution The trematosaurine T. sobeyi is known from the Queenstown (ECP) and Paul Roux (FSP) districts in the south and north of the basin, respectively, in strata pertaining to subzone A of the Cynognathus biozone. Recently, Damiani et al. (2000) described a trematosaurine mandible possibly referrable to T. sobeyi from the uppermost part of the underlying Lystrosaurus biozone, in an impoverished, ‘intermediate’biozone once referred to as the Procolophon Zone (cf. Neveling et al., 1999; Neveling, 2002). The more derived M. casei pertains to subzone B of the Cynognathus biozone and is known from a number of specimens from a single locality near
Burgersdorp (ECP) in the southern Karoo. The possible lonchorhynchine ‘T’. kannemeyeri is from an unknown locality in the Free State Province and is thus of unknown horizon. However, the lonchorhynchine reported by Damiani and Welman (2001) comes from the Bethulie district (FSP) in the south of the basin and appears to have been low in the Lystrosaurus biozone, while the undescribed specimen referred to above is from subzone A of the Cynognathus biozone in the south of the basin.
Discussion The stratigraphic distribution of temnospondyls in the Beaufort Group strata is summarized in figure 2. Included in the biostratigraphic subdivisions are the as yet informal threefold subdivision of the Cynognathus biozone (Hancox et al., 1995), and a ‘Procolophon Zone’ between the Lystrosaurus and Cynognathus biozones (cf. Damiani et al., 2000; Neveling, 2002). Note that the bars shown in Figure 2 do not imply the strict temporal range associated with individual taxa, but do indicate each taxon’s maximum presumed stratigraphic range. As alluded to in the text, many of the temnospondyl taxa from the Karoo are known from few specimens and, in some cases, from only a single specimen. Furthermore, a number of these taxa are represented by poorly preserved material so that their anatomy is inadequately known. This problem stems, in part, from the scant attention given to temnospondyls by Karoo palaeontologists and collectors over the last century. Amongst Karoo temnospondyls, only members of the Mastodonsauridae can be regarded as both sufficiently common and well known to be utilized as index taxa in biostratigraphic subdivision of the Beaufort strata, namely the Cynognathus Assemblage Zone (Hancox et al. 1995; Shishkin e t al. 1 9 9 5 ) . The Brachyopidae and Trematosauridae are also represented by relatively well known species, but are at present not common enough for use as index taxa. Furthermore, the ranges of some trematosaurid taxa may cut across more than one assemblage zone and additional material is required to resolve the taxonomy of Karoo trematosaurids. The Amphibamidae, lbpilakosauridae and Laidleriidae are represented in the Karoo by a single species each and are thus of limited biostratigraphic use. However, the amphibamid species Micropholis stowii, which apparently occurs throughout the Lystrosaurus Assemblage Zone, appears to be divisible into two morphotypes (R. Schoch, pers. comm.) that possibly represent separate species. It remains to be seen whether the stratigraphic ranges of these morphotypes are concurrent. Within the Lydekkerinidae, Lydekkerina huxleyi is known from hundreds of specimens, and the species apparently occurs Gondwana Research, V. 7, No. 1,2004
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throughout the Lystrosaurus biozone. A detailed study in progress on the variability within L. huxteyi should determine if more than one species is present, which may or may not have biostratigraphic implications. Finally, the Rhinesuchidae are at present the only Permian temnospondyls known from the Karoo and are relatively common and widely distributed across the assemblage zones. As such, they have considerable potential for use in Karoo biostratigraphy. However, their taxonomy is at present problematic and a forthcoming revision of their anatomy and taxonomy should provide the necessary framework for a biostratigraphic analysis.
Acknowledgments I am grateful to Prof. B. S. Rubidge (University of the Witwatersrand), the University of the Witwatersrand, and the National Research Foundation of South Africa for financial support. Dr R.R. Schoch (Berlin) provided unpublished information on Micropholis stowii. The manuscript was improved through comments by Drs. A.A. Warren (Melbourne) and S.G. Lucas (Albuquerque).
References Broili, F. and Schroder, J. (1937) Beobachtungen an Wirbeltieren der Karrooformation. XXVII. Uber einen Capitosauriden aus der Cynognathus-Zone. Sitz.-Ber. bayer. Akad. Wiss. Munchen, v. 1937, pp. 98-117. Broom, R. (1903) On a new stegocephalian (Batrachosuchus browni) from the Karroo beds of Aliwal North South Africa. Geol. Mag., v. 10, pp. 499-501. Broom, R. (1906) On the Permian and Triassic faunas of South Africa. Geol. Mag., v. 3, pp.29-30. Broom, R. (1908) On a new labyrinthodont Rhinesuchus whaitsi, from the Permian beds of South Africa. Ann. S. Afr. Mus., v. 4, pp. 373-376. Broom, R. (1909) Notice of some new South African fossil amphibians and reptiles. Ann. S. Afr. Mus., v. 7, pp. 270-278. Broom, R. (1915) On the Triassic stegocephalians Brachyops, Bothriceps, and tydekkerina gen. nov. Proc. Zool. SOC.Lond., V. 1915, pp. 363-368. Broom, R. (1930) Notes on some labyrinthodonts in the Transvaal Museum. Ann. Transvaal Mus., v. 14, pp. 1-10. Catuneanu, O., Hancox, P.J. and Rubidge, B.S. (1998) Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Res., v. 10, pp. 417-439. Chernin, S. (1978) Three capitosaurs from the Triassic of South Africa: Parotosuchus africanus (Broom 1909); Kestrosaurus dreyeri Haughton 1925, and Parotosuchus dirus sp. nov. Palaeont. afr., v. 21, pp. 79-100. Cosgriff, J.W. (1984) The temnospondyl labyrinthodonts of the earliest Triassic. J. Vert. Paleontol., v. 4, pp. 30-46. Cosgriff, J.W. and Zawiskie, J.M. (1979) A new species of the Rhytidosteidae from the Lystrosaurus Zone and a review of the Rhytidosteoidea. Palaeont. Afri., v. 22, pp. 1-27. Gondwana Research, V. 7, No. 1, 2004
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Damiani, R.J. (1999) Parotosuchus (Amphibia, Temnospondyli) in Gondwana: biostratigraphic and palaeobiogeographic implications. S. Afri. J. Sci., v. 95, pp. 458-460. Damiani, R.J. (2001a) Parotosuchus (Amphibia, Temnospondyli) from the Cynognathus Assemblage Zone (Early Triassic) of South Africa: cranial morphology and relationships. Alcheringa, v. 25, pp. 351-379. Damiani, R.J. (2001b) A systematic revision and phylogenetic analysis of the Triassic mastodonsauroids (Temnospondyli: Stereospondyli). Zool. J. Linn. SOC.,v. 133, pp. 379-482. Damiani, R. Cranial anatomy and relationships of Microposaurus casei, a temnospondyl from the Middle Triassic of South Africa. J. Vert. Paleontol. (in press). Damiani, R.J. and Hancox, P.J. (2003) New mastodonsaurid temnospondyls from the Cynognathus Assemblage Zone (Upper Beaufort Group; Karoo Basin) of South Africa. J. Vert. Paleontol., v. 23, pp. 54-66. Damiani, R.J. and Jeannot, A.M. (2002) A brachyopid temnospondyl from the lower Cynognathus Assemblage Zone in the northern Karoo Basin, South Africa. Palaeont. Afri., V. 38, pp. 57-69. Damiani, R.J. and Kitching, J.W. (2003) A new brachyopid temnospondyl from the Cynognathus Assemblage Zone, Upper Beaufort Group, South Africa. J. Vert. Paleontol., V. 23, pp. 67-78. Damiani, R. J. and Rubidge, B.S. A review of the South African temnospondyl amphibian record. Palaeont. Afri., (in press). Damiani, R.J. and Welman, J. (2001) A long-snouted trematosaurid amphibian from the Early Triassic of South Africa. S. Afri. J. Sci., v. 97, pp. 318-320. Damiani, R.J., Neveling, J. and Hancox, P.J. (2001) First record of a mastodonsaurid (Temnospondyli, Stereospondyli) from the Early Triassic Lystrosuurus Assemblage Zone (Karoo Basin) of South Africa. N. Jb. Geol. Palaont. Abh., v. 221, pp. 133-144. Damiani, R.J., Neveling, J., Hancox, J. and Rubidge, B. (2000) First trematosaurid temnospondyl from the Lystrosaurus Assemblage Zone of South Africa and its biostratigraphic implications. Geol. Mag., v. 137, pp. 659-665. Groenewald, G.H. and Kitching, J.W. (1995) Biostratigraphy of the Lystrosaurus Assemblage Zone. In: Rubidge, B.S. (Ed.), Biostratigraphy of the Beaufort Group (Karoo Supergroup). SACS Biostratigraphic Series No. l.,Council for Geoscience, Pretoria, pp. 35-39. Hammer, W.R. (1987) Paleoecology and phylogeny of the Trematosauridae. Geophys. Monogr. Ser., v. 41, pp. 73-83. Hancox, P.J. (1998) A stratigraphic, sedimentological and palaeoenvironmental synthesis of the Beaufort-Molten0 contact in the Karoo Basin. Unpub. Ph.D. thesis, Univ. Witwatersrand, Johannesburg. Hancox, P.J. (2000) The continental Triassic of South Africa. Zbl. Geol. Palaont. Teil I, v. 1998, pp. 1285-1324. Hancox, P.J. and Rubidge, B.S. (1997) The role of fossils in interpreting the development of the Karoo Basin. Palaeont. Afri., v. 33, pp. 41-54. Hancox, P.J., Damiani, R.J. and Rubidge, B.S. (2000) First occur re n ce of Pa racyc I o t 0sa u rus (Te mn o s p o nd y 1i, Capitosauridae) in the Karoo Basin of South Africa and its biostratigraphic implications. S. Afri. J. Sci., v. 96, pp. 135-137. Hancox, P.J., Shishkin, MA., Rubidge, B.S. and Kitching, J.W. (1995) A threefold subdivision of the Cynognathus
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Assemblage Zone (Beaufort Group, South Africa) and its palaeogeographical implications. S. Afri. J. Sci., v. 91, pp. 143-144. Haughton, S.H. (1915) Investigations in South African fossil reptiles and Amphibia (Parts 1to 4). Ann. S. Afri. Mus., v. 12, pp. 47-63. Haughton, S.H. (1925) Investigations in South African fossil reptiles and Amphibia (Part 13). Ann. S. Afri. Mus., v. 22, pp. 227-261. Huxley, TH. (1859) On some amphibian and reptilian remains from South Africa and Australia. Quart. J. Geol. SOC.Lond., V. 15, pp. 642-658. Ivakhnenko, M.F., Golubev, V.K., Gubin, Y.M., Kalandadze, N.N., Novikov, I.V., Sennikov, A.G. and Rautian, A.S. (1997) Permian and Triassic tetrapods of Eastern Europe. GEOS, Moscow (in Russian). Keyser, A.W. and Smith, R.M.H. (1979) Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin. Ann. Geol. Surv. S. Afri., v. 12, pp. 1-35. Kitching, J.W. (1957) A new small stereospondylous labyrinthodont from the Triassic beds of South Africa. Palaeont. Afri., v. 5, pp. 67-82. Kitching, J.W. (1977) The distribution of the Karroo vertebrate fauna. Bernard Price Inst. Palaeontol. Res. Mem., v. 1, pp. 1-131. Kitching, J.W. (1978) The stratigraphic distribution and occurrence of South African fossil Amphibia in the Beaufort Beds. Palaeont. Afri., v. 21, pp. 101-112. Latimer, E.M., Hancox, P.J., Rubidge, B.S, Shishkin, M.A. and Kitching, J.W. (2002) The temnospondyl amphibian Uranocentrodon, another victim of the end-Permian extinction event. S. Afri. J. Sci., v. 98, pp. 191-193. Lucas, S.G. (1998) Global Triassic tetrapod biostratigraphy and biochronology. Palaeogeogr., Palaeoclimatol., Palaeoecol., V. 143, pp. 347-384. Lydekker, R. (1889) Note on the occurrence of a species of Bothriceps in the Karoo system of South Africa. Ann. Mag. Nat. Hist., v. 6, pp. 475-476. Lydekker, R. (1890) Catalogue of the fossil Reptilia and Amphibia in the British Museum (Natural History). Part N. Taylor and Francis, London. Milner, A.R. (1990) The radiations of temnospondyl amphibians. Syst. Ass. Spec. Vol., v. 42, pp. 321-349. Milner, A.R., Sequeira, S.E.K. and Schoch, R. (2002) Dvinosaurian temnospondyls in the Permian. J. Vert. Paleontol., v. 22, pp. 88A. Morales, M. and Shishkin, M.A. (2002) A re-assessment of Parotosuchus aficanus (Broom), a capitosauroid temnospondyl amphibian from the Triassic of South Africa. J. Vert. Paleontol., v. 22, pp. 1-11. Neveling, J. (2002) Biostratigraphic and sedimentological investigation of the contact between the Lystrosaurus and Cynognathus Assemblage zones. Unpub. Ph.D. thesis, Univ. Witwatersrand, Johannesburg. Neveling, J., Rubidge, B.S. and Hancox, PJ. (1999) A lower Cynognathus Assemblage Zone fossil from the Katberg Formation (Beaufort Group, South Africa). S. Afri. J. Sci., V. 95, pp. 555-556. Ochev, V.G. (1966) Systematics and phylogeny of capitosauroid labyrinthodonts. Saratov State Univ. Press, Saratov
(in Russian). Ochev, V.G. and Shishkin, M.A. (1989) On the principles of global correlation of the continental Triassic on the tetrapods. Acta Palaeont. Polon., v. 34, pp. 149-173. Olson, E.C. and Broom, R. (1937) New genera and species of tetrapods from the Karroo beds of South Africa. J. Paleontol., V. 11, pp. 613-619. Owen, R. (1884) On a labyrinthodont amphibian (Rhytidosteus capensis) from the Trias of the Orange Free State, Cape of Good hope. Quart. J. Geol. SOC.Lond., v. 40, pp. 333-338. Romer, A.S. (1947) Review of the Labyrinthodontia. Bull. Mus. Comp. Zool. Ham, v. 99, pp. 1-352. Rubidge, B.S. (1995) Biostratigraphy of the Beaufort Group (Karoo Supergroup). SACS Biostratigraphic Series No. 1. Council for Geosci., Pretoria. Schoch, R.R. and Milner, A.R. (2000) Stereospondyli. Handbuch der Palaoherpetologie, Teil 3B. Verlag Dr. Friedrich Pfeil, Munchen. Shishkin, M.A. (2000) Olenekian-Anisianboundary in the history of land tetrapods. In: Gradinaru, E. (Ed.), Workshop on the Lower-Middle Triassic (Olenekian-Anisian) boundary, 7-10 June. Tulcea, Romania, pp. 60-69. Shishkin, M.A. and Rubidge, B.S. (2000) A relict rhinesuchid (Amphibia: Temnospondyli) from the Lower Triassic of South Africa. Palaeontology, v. 43, pp. 653-670. Shishkin, M.A., Rubidge, B.S. and Hancox, PJ. (1995) Vertebrate biozonation of the Upper Beaufort Series of South Africa - a new look on correlation of the Triassic biotic events in Euramerica and southern Gondwana. In: Sun, A. and Wang, Y. (Eds.), Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers, 1995. China Ocean Press, Beijing, pp. 39-41. Shishkin, M.A., Rubidge, B.S. and Kitching, J.W. (1996) A new lydekkerinid (Amphibia, Temnospondyli) from the lower Triassic of South Africa: implications for evolution of the early capitosauroid cranial pattern. Phil. Trans. R. SOC. Lond. B, v. 351, pp. 1635-1659. Smith, R.M.H. (1990) A review of stratigraphy and sedimentary environments of the Karoo Basin of South Africa. J. Afri. Earth Sci., v. 10, pp. 117-137. Smith, R.M.H. (1995) Changing fluvial environments across the Permian-Triassic boundary in the Karoo Basin, South Africa and possible causes of tetrapod extinctions. Palaeogeogr., Palaeoclim., Palaeoecol., v. 117, pp. 81-104. Smith, R.M.H. and Ward, P.D. (2001) Pattern of vertebrate extinctions across an event bed at the Permian-Triassic boundary in the Karoo Basin of South Africa. Geology, v. 29, pp. 1147-1150. Van Hoepen, E.C.N. (1911) Korte, voorlopige beschrijving van te Senekal gevonden Stegocephalen. Ann. Transvaal Mus., V. 3, pp. 102-106. Van Hoepen, E.C.N. (1915) Stegocephalia of Senekal, O.F.S. Ann. Transvaal Mus., v. 5, pp. 125-149. Warren, A.A. (1998) Laidleria uncovered: a redescription of Laidleria gracilis Kitching (1957), a temnospondyl from the C’ognathus Zone of South Africa. Zool. J. Linn. SOC.,v. 122, pp. 167-185. Warren, A.A. (1999) Kamo tupilakosaurid: a relict from Gondwana. Trans. R. SOC.Edinb. Earth Sci., v. 89, pp. 145-160. Warren, A.A. and Marsicano, C.A. (2000) A phylogeny of the Gondwana Research, V. 7, No. 1,2004
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Brachyopoidea (Temnospondyli, Stereospondyli). J. Vert. Paleontol., v. 20, pp. 462-483. Watson, D.M.S. (1919) The structure, evolution and origin of the Amphibia. The “Orders” Rachitomi and Stereospondyli. Phil. Trans. R. SOC.Lond. B, v. 209, pp. 1-73. Watson, D.M.S. (1962) The evolution of the labyrinthodonts. Phil. Trans. R. SOC.Lond. B, v. 245, pp. 219-265. Welman, J., Groenewald, G.H. and Kitching, J.W. (1991)
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Confirmation of the occurrence of Cynognathus Zone (Kannemeyeria-Diademodon Assemblage-zone) deposits (uppermost Beaufort Group) in the northeastern Orange Free State, South Africa. S. Afri. J. Geol., v. 94, pp. 245-248. Yates, A.M. and Warren, A.A. (2000) The phylogeny of the ‘higher’ temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyli. Zool. J. Linn. SOC.,v. 128, pp. 77-121.
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Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy Ross J. Damiani Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg,South Africa, E-mail: damianirCdgeosciences.wits.ac.za (Manuscript received August 30,2002; accepted February 4,2003)
Abstract The Permo-Triassic Beaufort Group (Karoo Basin) of South Africa is biostratigraphically subdivided into eight, temporally successive assemblage zones based on therapsids (‘mammal-like reptiles’). The Temnospondyli, fossil tetrapods usually regarded as extinct amphibians, are second only to therapsids in terms of diversity and abundance in these strata, with nine higher-level taxa (‘families’) known. Temnospondyls are also playing an increasingly important role in biostratigraphy and correlation of the Beaufort strata. The lower Beaufort Group (Late Permian) contains six of the eight biozones, but only one temnospondyl ‘family’, the Rhinesuchidae, whose record in the Karoo is the richest in the world. However, rhinesuchid taxonomy remains in flux and the group is thus of limited biostratigraphic utiliv. The Early Triassic Lystrosaurus Assemblage Zone (middle Beaufort Group) contains the Rhinesuchidae, Amphibamidae, Lydekkerinidae, Tbpilakosauridae, Rhytidosteidae, Mastodonsauridae and Trematosauridae, although the biostratigraphy of temnospondyls within this biozone is poorly constrained. The uppermost reaches of the Lystrosaurus biozone contain a paucity of fossils but includes ‘Kestrosaurus’ (Mastodonsauridae) and ?Trematosuchus (Trematosauridae), taxa previously thought to pertain to the lower part of the overlying Cynognathus biozone. The late Early to Middle Triassic CynognathusAssemblage Zone (upper Beaufort Group) hosts the Mastodonsauridae, Trematosauridae, Brachyopidae, Laidleriidae and, possibly, the Rhytidosteidae. Based largely on the spatial and temporal distribution of mastodonsaurids, this biozone has been biostratigraphically subdivided into a lower A, middle B and upper C subzones, characterised by differing ages and faunas.
Key words: Temnospondyls, Beaufort Group, Karoo, South Africa, stereospondyls.
Introduction The Temnospondyliwas a highly diverse and successful group of fossil tetrapods that existed from the Early Carboniferous to the Early Cretaceous (Milner, 1990). They are usually regarded as fossil amphibians and as being ancestral to some or all of the living lissamphibian groups. Temnospondyls are near-ubiquitous components of non-marine sedimentary rocks, especially of Permian and Triassic age, where they have played an important role in local biostratigraphy and global correlation of nonmarine strata (e.g., Hancox et al., 1995; Ivakhnenko et al., 1997; Ochev and Shishkin, 1989; Lucas, 1998). One of the richest sources of temnospondyls is the Permo-TriassicBeaufort Group of the Karoo Basin, South Africa, which preserves a complete Late Permian to early Middle Triassic sedimentary sequence and associated vertebrate fauna and has long been recognised as the global standard for the non-marine Permo-Triassic (e.g., Cosgriff, 1984; Lucas, 1998). These rocks are renowned primarily for their rich and abundant therapsid (‘mammal-
like reptile’) fauna, which, because of the paucity of basinwide lithostratigraphic markers, has been used for the biostratigraphic subdivisionof the group and stratigraphic correlation with faunas elsewhere (Kitching, 1977; Keyser and Smith, 1979; Rubidge, 1995). Although largely neglected relative to the therapsids, temnospondyls form the second most important vertebrate taxon in the Beaufort Group in terms of diversity and abundance. In recent years, there has been a resurgence in Beaufort Group temnospondyl studies. They are now playing an important role in interpreting the basin development of the Karoo (Hancox and Rubidge, 1997; Hancox, 19981, local biostratigraphy (Hancox et al., 1995; Shishkin et al., 1995), and correlation of non-marine tetrapod faunas (Lucas, 1998; Damiani, 1999; Hancox et al., 2000; Shishkin, 2000). This paper surveys the diversity of Beaufort Group temnospondyls and summarises the biostratigraphic occurrence of all valid taxa. A detailed taxonomic review of all temnospondyl material from the Karoo is presented elsewhere, along with figures of representative genera (Damiani and Rubidge, in press).
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Abbreviations for South African geographical regions used in the text are as follows: ECP, Eastern Cape Province; FSP, Free State Province; KZN, Kwa-Zulu Natal; WCP, Western Cape Province.
Geological Setting The Karoo Supergroup of South Africa preserves a 12 km thick succession of mainly sedimentary rocks that accumulated in a retroarc foreland basin (Karoo Basin) during the Late Carboniferous to Early Jurassic in southwestern Gondwana (Catuneanu e t al., 1998) (Fig. 1). Lithostratigraphically, the Karoo Supergroup is subdivided into five main groups. These are, in ascending stratigraphic order, the Dwyka (Late Carboniferous), Ecca (Early Permian), Beaufort (Late Permian-MiddleTriassic), ‘Stormberg’(Late Triassic-EarlyJurassic) and Drakensberg groups, broadly representing deposition in glacial (Dwyka), marine (Ecca) and terrestrial (Beaufort and Stormberg) environments (Smith, 1990). The Drakensberg lavas terminated sedimentation in the basin in the Middle Jurassic (Smith, 1990). The fill of the Karoo Basin is intimately linked to orogenesis of the Cape Fold Belt in the south (Catuneanu et al., 1998), and the basin may be subdivided into a southern area (proximal Karoo facies) and a northern area (distal Karoo facies). The Beaufort Group strata are fluvially derived and typically consist of alternating mudstone and sandstone
0
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I . .
units with characteristic upward-fining textures, red and purple colours, abundant vertebrate fossils, desiccation cracks and palaeosol horizons, suggesting sediment accumulation on vast, semi-arid alluvial plains by floodplain aggradation (Smith, 1990; Rubidge, 1995). Eight biostratigraphic assemblage zones (Figs. 1,2), which are broadly linked to the lithostratigraphy in the various parts of the basin (Keyser and Smith, 1979; Rubidge, 1995), are currently recognized (Rubidge, 1995), namely (in ascending order) the Eodicynodon, Tapinocephalus, Pristerognathus, Tropidostoma, Cistecephalus, Dicynodon, Lystrosaurus and C’ognathus Assemblage zones. The first six of these biozones are of Late Permian age, ranging from the Kazanian to the Tatarian (Rubidge, 1995). The Lystrosaurus Assemblage Zone is broadly Early Triassic in age (Groenewald and Kitching, 1995; Hancox, 2000), although the Permo-Triassic boundary occurs within the lowest part of that biozone and is defined by the last appearance of Dicynodon, whose range overlaps that of Lystrosaurus (Smith, 1995; Smith and Ward, 2001). The upper reaches of the Lystrosaurus biozone appear to be lower Olenekian in age (Neveling, 2002). The Cjmognathus Assemblage Zone is of Early-MiddleTriassic age (Hancox 2000) and has been informally subdivided into a lower ‘A‘ zone (upper Olenekian), which is predominantly exposed in the north of the basin, a middle ‘B’ zone (early Anisian), which occurs within ‘classic’ Cynognathus biozone exposures in the south of the basin, and a reduced, upper ‘C’ zone (late Anisian), restricted to the southernmost reaches of the basin (Hancox et al. 1995; Hancox, 1998). This subdivision is based largely on the spatial and temporal distribution of mastodonsaurid temnospondyls. Most recently, Neveling (2002) restricted the Cynognathus biozone to subzone B, renamed subzone A the Kestrosaurus Assemblage Zone, and considered subzone C to represent a new biozone. In this paper, the terminology of Hancox et al. (1995) will be used for subdivision within the Cynognathus biozone.
Temnospondyl Diversity and Distribution Dissorophoidea:Amphibamidae Diversity
Fig. 1. Geographic distribution of the biozones of the Beaufort Group, with the extent of the Karoo Basin outlined. Transect line connects the proximal (southern) and distal (northern) Karoo facies. Biozone abbreviations: Cis-Cistecephalus, Cyn-Cynognathus, Dic-Dicynodon, Eod-Eodicynodon, Ly-Lystrosaurus, Pris-Pristerognathus, Tap-Tapinocephalus, Tro- Tropidostoma. Modified from Rubidge (1995).
Dissorophoids are small, predominantly PermoCarboniferous terrestrial temnospondyls widely cited in connection with the origin of the Lissamphibia, and are represented in the Karoo by the small taxon Micropholis stowii (Huxley, 1859). Within the Dissorophoidea, M. stowii was initially placed in its own higher-level taxon, the Micropholidae, later referred by some workers to the Dissorophidae, but is now recognised as belonging to the Gondwana Research, V. 7, No. I, 2004
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kSSEMBLAGE ZONE
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TEMNOSPONDYL BIOSTRATIGRAPHY
I L mp.
Tup.
Brrch.
Lai. Lydek.
Mastod.
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Tremat.
I
anognatlius
?Procolophon
--------
.-
cq
4)
Lystrosaurus
Dicynodoir LJ
Cistecephalus Tropidosioma Pristerognatltus Tapinoceplialus Eodicynodon
Fig. 2. Biostratigraphic subdivision of the Beaufort Group (Karoo Basin), showing the stratigraphic occurrence of all valid temnospondyl species. Hatched bars indicate uncertainty in the stratigraphic occurrence. See text for discussion. Taxon abbreviations: Amp, Amphibamidae; Brach, Brachyopidae; Lai, Laidleriidae; Lydek, Lydekkerinidae; Mastod, Mastodonsauridae; Rhines, Rhinesuchidae; Rhyt, Rhytidosteidae; Tremat, Trematosauridae; mp, mpilakosauridae. Modified from Rubidge (1995).
Amphibamidae. M. stowii is of particular importance as representing the last dissorophoid.
Distribution Micropholis stowii occurs in local abundance in the Lystrosaurus Assemblage Zone (Kitching, 1978) and has been recovered from a number of localities in both the north and south of the basin. Stratigraphically it occurs from near the base of the Triassic part of the Lystrosaurus biozone (Smith and Ward, 2001) through to the upper reaches of that biozone (unpublished data). Dvinosauria: Tupilakosauridae Diversity The Tupilakosauridae are small, probably fully aquatic, rare relict survivors of the Palaeozoic Dvinosauria (Warren, 1999; Yates and Warren, 2000), and are represented in the Karoo by Thabanchuia oomie (Warren, 19991, the most Gondwana Research, V 7, No.1,2004
recently described and complete tupilakosaurid. Elsewhere, tupilakosaurids are represented by Tupilakosaurus from the Early Triassic of East Greenland and Russia, Slaugenhopia from the Lower Permian of Texas and, possibly, Kourerpeton from the ?Upper Permian of North America (Warren, 1999; Milner et al., 2002).
Distribution Thabanchuia oornie comes from a single locality near Thaba Nchu (FSP) in the north of the basin, in strata from which Lystrosaurus specimens had also been collected and thus considered to pertain to the Lystrosaurus Assemblage Zone (Warren, 1999). However, both the underlying Late Permian Dicynodon Assemblage Zone and overlying Early-MiddleTriassic Cynognathus Assemblage Zone also outcrop near Thaba N'chu (Kitching, 1977; Welman et al., 1991), and Lystrosaurus is now known to also occur in the uppermost Permian (Smith, 1995).
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Stereospondyli: Brachyopidae Diversity Four species representing three genera of the cosmopolitan, medium to large-sized, aquatic Brachyopidae have been described from the Karoo, namely Batrachosuchus browni (Broom, 1903), ‘Batrachosuchus’ watsoni (Haughton, 1925), Vanastega plurimidens (Damiani and Kitching, 2003) and Bathignathus poikilops (Damiani and Jeannot, 2002). Additional fragmentary material referred to Batrachosuchus sp. has been described by a number of authors (see Damiani and Rubidge (in press) for a review). The genus Batrachosuchus has been considered the archetypal brachyopid (Warren and Marsicano, 2000), although ‘Batrachosuchus’watsoni was recently transferred to a new genus, Bathignathus, by Damiani and Jeannot (2002).
Distribution ‘Batrachosuchus’watsoni and B. browni are known only from their near-complete, holotype skulls, which are presumed to have come from near Burgersdorp (ECP) and Aliwal North (ECP), respectively, both in the south of the basin. Their horizon is undoubtedly the Cynognathus Assemblage Zone, as both subzones A and B, but not C, occur in those districts. Vanastega plurimidens is represented by cranial material from a single locality near Burgersdorp (ECP), in strata of subzone B of the Cynognathus biozone. In contrast to all other brachyopids which occur in the south of the basin, Bathignathus poikilops comes from a locality near Paul Roux (FSP) in the north of the basin, and pertains to subzone A of the Cynognathus biozone. The brachyopid material described as Batrachosuchus sp. comes from the Cynognathus biozone in the Burgersdorp (ECP) and Aliwal North (ECP) districts in the south of the basin; the Burgersdorpmaterial pertains to subzone B, whereas that from Aliwal North may pertain to either subzone A or B. Stereospondyli: Laidleriidae Diversity This enigmatic higher-level taxon is currently known only from the Karoo and is represented by a single, nearcomplete skeleton, Laidleria gracilis (Kitching, 1957; Warren, 1998), that has also variously been considered a trematosaurid, a rhytidosteid, a plagiosaurid relative, or incertae sedis within the Temnospondyli.
Distribution Laidleria gracilis comes from a locality in the Engcobo District (ECP), in the south of the basin; the horizon is presumed to be the Cynognathus Assemblage Zone,
although the underlying Lystrosaurus Assemblage Zone also crops out in this area (Kitching, pers. comm.).
Stereospondyli: Lydekkerinidae Diversity The Lydekkerinidae are small, terrestrial, cosmopolitan Early Triassic temnospondyls with a centre of diversity in the Karoo. Five species have been named from the Karoo, although only three are now considerd valid (Shishkin et al., 1996). These are the genotype for the Lydekkerinidae, Lydekkerina huxleyi (Lydekker, 1889; Broom, 1915), Broomulus dutoiti (Broom, 1930; Romer, 1947) and Eolydekkerina magna (Shishkin et al., 1996). Both B. dutoiti and E. magna are known only from a single individual that includes mainly cranial material, whereas L. huxleyi is known from hundreds of specimens, including complete or near-complete skeletons, and is the most abundant temnospondyl taxon in the Karoo.
Distribution The holotype and original referred material of L. huxleyi described by Lydekker (1889, 1890) came from an unknown locality near Edenburg (FSP), in the north of the basin, in strata that are presumed to pertain to the Lystrosaurus biozone based on the co-occurrence of Lydekkerina with Lystrosaurus elsewhere. There is no other record of fossil material from the Edenburg district. The majority of all known L. huxleyi specimens, as well as B. dutoiti, come from the famous Lystrosaurus biozone locality of Harrismith Commonage (Kitching, 1977,1978), near the town of Harrismith (FSP) in the north of the basin. A few Lydekkerina specimens have also been recovered farther south. E. magna comes from Lystrosaurus biozone strata near the Bethulie district (FSP), in the south of the basin. Shishkin et al. (1996) believed E. magna and L. huxleyi to be restricted to the lower and upper part of the Lystrosaurus biozone, respectively. However, the latter species is also known to occur in the lower part of the Lystrosaurus biozone (Smith and Ward, 2001), so that its range probably overlaps that of E. magna.
Stereospondyli: Mastodonsauridae Diversity The Mastodonsauridae were large, primarily aquatic temnospondyls with a cosmopolitan distribution during the Triassic. Eight species have been named from the Karoo, of which five are considered valid by Damiani and Rubidge (in press) : the basal taxa Parotosuchus haughtoni (Broili and Schroder, 1937; Chernin, 1978; Damiani, 2001a) and Watsonisuchusmagnus (Watson, 1962; Ochev, 19661, the more derived Xenotosuchus africanus (Broom, Gondwana Research, V. 7, No. 1, 2004
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1909; Morales and Shishkin, 2002), and the highly derived Jammerbergia formops and Paracyclotosaurusmorganorum (Hancox et al., 2000; Damiani and Hancox, 2003). The validity of the basal taxon Kestrosaurus dreyeri (Haughton, 1925) is uncertain (Damiani, 2001b), while ‘Parotosuchus’ dirus (Chernin, 1978), like K. dreyeri, is represented by fragmentary material. In any case, the five valid species of mastodonsaurids makes them the most diverse Triassic higher-level taxon in the Karoo.
Distribution The Mastodonsauridae has the widest temporal and geographic distribution amongst Triassic temnospondyls from the Karoo. The basal taxon W. magnus is from subzone A of the Cynognathus Assemblage Zone in the Burgersdorp district (ECP), southern Karoo, while I? haughtoni is from the same subzone in both the Rouxville (FSP) and Paul Roux (FSP) districts in the south and north of the basin, respectively (Damiani, 2001a). K. dreyeri also pertains to subzone A and is also known from the south and north of the basin, while a possible new species of Kestrosaurus has been described from subzone A in the north of the basin. Unsurprisingly, the more derived X. africanus pertains to subzone B of the Cynognathusbiozone and specimens are known from the Burgersdorp (ECP) and Rouxville (FSP) districts in the south of the basin. The highly derived P. morganorum comes from the Sterkstroom district (ECP) in the extreme south of the basin, and is currently the only temnospondyl from subzone C of the Cynognathus biozone. The equally derived J. formops is from an unknown horizon, likely subzone A or B of the Cynognathus biozone (Damiani and Hancox, in press), in the Wepener district (FSP). Fragmentary mastodonsaurid material referrable to Watsonisuchussp. (Damiani et al., 2001) and Kestrosaurus sp. (Neveling, 2002) has also been described from the Lystrosaurus Assemblage Zone. This material possibly pertains to an ‘impoverished’fauna that may be interposed between the Lystrosaurus and Cynognathus biozones (Neveling et al., 1999; Neveling, 2002; Damiani et al., 2000) and referred to by earlier workers as the Procolophon Zone (e.g., Broom, 1906).
Stereospondyli: Rhinesuchidae Diversity The Rhinesuchidae are large, semi-aquatic temnospondyls known only from Gondwana, with a centre of diversity in the Karoo. They are the only known higherlevel temnospondyl taxon from the Permian (lower Beaufort Group) of the Karoo, and are relatively rare components of that fauna (Kitching, 1978). They are nevertheless a critical taxon in temnospondyl phylogeny Gondwana Research, V. 7, No. I, 2004
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as they represent the sister-group to the great Mesozoic radiation of the Stereospondyli (Milner, 1990; Schoch and Milner, 2000; Yates and Warren, 2000), which includes all of the known Mesozoic temnospondyls except for relict members of the Dvinosauria and Dissorophoidea. Seventeen species of rhinesuchids have been named from the Karoo, with most based on poorly preserved material. Although their taxonomy remains in a state of flux, the most recent estimates of the number of valid taxa are about six or seven (Schoch and Milner, 2000; Damiani and Rubidge, in press). These include two species of the genotype Rhinesuchus that are characterized by relatively broad skulls, R. whaitsi (Broom, 1908) and R. capensis (Haughton, 1925), the narrow-skulled Rhinesuchoides tenuiceps (Olson and Broom, 1937), the medium-sized Laccosaurus watsoni (Haughton, 1925), the giant, possibly fully aquatic Uranocentrodon senekalensis (van Hoepen, 1911, 1915; unpublished d a t a ) and the small, paedomorphic, relict taxon Broomistega putterilli (Broom, 1930; Shishkin and Rubidge, 2000).
Distribution The stratigraphic distribution of rhinesuchids within the Beaufort Group remains necessarily tenuous because of the poor state of rhinesuchid taxonomy. Consequently, the following discussion will be limited to the holotype specimens of each taxon. Except for U.senekalensis and B. putterilli, all rhinesuchid species come from the south of the basin where all six Permian biozones are exposed; only the uppermost of the Permian biozones, the Dicynodon Assemblage Zone, is also exposed in the north (Rubidge, 1995; Fig. 1). Rhinesuchus whaitsi and R. tenuiceps come from the Prince Albert district (WCP) and pertain t o the Tapinocephalus Assemblage Zone. Laccosaurus watsoni and R. capensis come from the Graaff Reinet district (ECP) and pertain to the Dicynodon and, possibly, the Tropidostoma Assemblage zones, respectively. Uranocentrodon senekalensis comes from the north of the basin near Senekal (FSP) and was long considered to pertain to the Lystrosaurus biozone which outcrops extensively in that area. However, it has recently been shown to occur below the Permo-Triassic boundary and to belong to the underlying Dicynodon biozone (Latimer et al., 2002). The sole Lystrosaurus biozone rhinesuchid is the relict B. putterilli, which occurs in the Harrismith Commonage (FSP) and Bergville (KZN) districts in the northern Karoo.
Stereospondyli: Rhyfidosteidae Diversity The Rhytidosteidae were medium-sized, aquatic piscivores and are amongst the rarest of Karoo
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temnospondyls, with only three known specimens representing two species. These are the genotype for the group, Rhytidosteus capensis (Owen, 1884), and Pneumatostega potamia (Cosgriff and Zawiskie, 1979).
Distribution The holotype and only known specimen of R. capensis is from an unknown locality in the Free State Province, and has variously been considered as from either the Lystrosaurus or Cynognathus biozones (Damiani and Rubidge, in press). Shishkin et al. (1995) considered R. capensis to pertain to subzone A of the Cynognathus biozone based on the presence of fragmentary Rhytidosteus material in the upper Olenekian of Russia. Pneurnatostega potamia is represented by two specimens from the Lystrosaurus biozone in the Middelburg and Colesberg districts (ECP) in the southern Karoo.
Stereospondyli: Trernatosauridae Diversity Trematosaurids were medium-sized, aquatic piscivores with a cosmopolitan distribution during the Triassic. The group is traditionally subdivided into the generalized, short-snouted trematosaurines and the specialized, longs no u t e d 1o n ch o r h yn c h in e s. U n t i1 re cent 1y, o n 1y trematosaurines were known with certainty from the Karoo, namely the taxa Trernatosuchussobeyi (Haughton, 1915; Watson, 1919) and the highly derived Microposaurus casei (Haughton, 1925; Damiani, in press). ‘Trematosaurus’ kannemeyeri (Broom, 1909) is a poorly preserved partial skull that Hammer (1987) transferred to the 1on ch o rh y n ch i n e Ap ha n e ram m a s p . Addition a 1 lonchorhynchine material includes an undescribed specimen referred initially to T. sobeyi (Haughton, 1925) and later to Aphanerarnrna sp. (Hammer, 1987), and a partial skull reported by Damiani and Welman (2001). All of this material is currently being restudied by the author.
Distribution The trematosaurine T. sobeyi is known from the Queenstown (ECP) and Paul Roux (FSP) districts in the south and north of the basin, respectively, in strata pertaining to subzone A of the Cynognathus biozone. Recently, Damiani et al. (2000) described a trematosaurine mandible possibly referrable to T. sobeyi from the uppermost part of the underlying Lystrosaurus biozone, in an impoverished, ‘intermediate’biozone once referred to as the Procolophon Zone (cf. Neveling et al., 1999; Neveling, 2002). The more derived M. casei pertains to subzone B of the Cynognathus biozone and is known from a number of specimens from a single locality near
Burgersdorp (ECP) in the southern Karoo. The possible lonchorhynchine ‘T’. kannemeyeri is from an unknown locality in the Free State Province and is thus of unknown horizon. However, the lonchorhynchine reported by Damiani and Welman (2001) comes from the Bethulie district (FSP) in the south of the basin and appears to have been low in the Lystrosaurus biozone, while the undescribed specimen referred to above is from subzone A of the Cynognathus biozone in the south of the basin.
Discussion The stratigraphic distribution of temnospondyls in the Beaufort Group strata is summarized in figure 2. Included in the biostratigraphic subdivisions are the as yet informal threefold subdivision of the Cynognathus biozone (Hancox et al., 1995), and a ‘Procolophon Zone’ between the Lystrosaurus and Cynognathus biozones (cf. Damiani et al., 2000; Neveling, 2002). Note that the bars shown in Figure 2 do not imply the strict temporal range associated with individual taxa, but do indicate each taxon’s maximum presumed stratigraphic range. As alluded to in the text, many of the temnospondyl taxa from the Karoo are known from few specimens and, in some cases, from only a single specimen. Furthermore, a number of these taxa are represented by poorly preserved material so that their anatomy is inadequately known. This problem stems, in part, from the scant attention given to temnospondyls by Karoo palaeontologists and collectors over the last century. Amongst Karoo temnospondyls, only members of the Mastodonsauridae can be regarded as both sufficiently common and well known to be utilized as index taxa in biostratigraphic subdivision of the Beaufort strata, namely the Cynognathus Assemblage Zone (Hancox et al. 1995; Shishkin e t al. 1 9 9 5 ) . The Brachyopidae and Trematosauridae are also represented by relatively well known species, but are at present not common enough for use as index taxa. Furthermore, the ranges of some trematosaurid taxa may cut across more than one assemblage zone and additional material is required to resolve the taxonomy of Karoo trematosaurids. The Amphibamidae, lbpilakosauridae and Laidleriidae are represented in the Karoo by a single species each and are thus of limited biostratigraphic use. However, the amphibamid species Micropholis stowii, which apparently occurs throughout the Lystrosaurus Assemblage Zone, appears to be divisible into two morphotypes (R. Schoch, pers. comm.) that possibly represent separate species. It remains to be seen whether the stratigraphic ranges of these morphotypes are concurrent. Within the Lydekkerinidae, Lydekkerina huxleyi is known from hundreds of specimens, and the species apparently occurs Gondwana Research, V. 7, No. 1,2004
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throughout the Lystrosaurus biozone. A detailed study in progress on the variability within L. huxteyi should determine if more than one species is present, which may or may not have biostratigraphic implications. Finally, the Rhinesuchidae are at present the only Permian temnospondyls known from the Karoo and are relatively common and widely distributed across the assemblage zones. As such, they have considerable potential for use in Karoo biostratigraphy. However, their taxonomy is at present problematic and a forthcoming revision of their anatomy and taxonomy should provide the necessary framework for a biostratigraphic analysis.
Acknowledgments I am grateful to Prof. B. S. Rubidge (University of the Witwatersrand), the University of the Witwatersrand, and the National Research Foundation of South Africa for financial support. Dr R.R. Schoch (Berlin) provided unpublished information on Micropholis stowii. The manuscript was improved through comments by Drs. A.A. Warren (Melbourne) and S.G. Lucas (Albuquerque).
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