The Mastodonsauroidea, previously and more widely known as the Capitosauroidea, ranks among the most common and best known Mesozoic temnospondyls. Mastodonsauroids exhibit wide morphological variation and significant homoplasy and their taxonomy and relationships have been in a state of flux. Since the first description of a mastodonsauroid there have been 56 genera and 118 species proposed. A comprehensive review of all these taxa has reduced the content of the group t o 14 genera and 44 species. Most species previously included in the Mastodonsauroidea are undiagnostic at the generic level and designated incertae sedis within the Mastodonsauridae, Heylerosauridae, Mastodonsauroidea or Stereospondyli. Where applicable, definitions, diagnoses and a list of synonyms of all fully diagnosable taxa within the Mastodonsauroidea are given. A computer-based phylogenetic analysis of mastodonsauroid temnospondyls based on 47 cranial characters and 25 terminal taxa was performed. The analysis included the 14 genera of mastodonsauroids as well as selected well-known members of the Lydekkerinidae and Trematosaurrdae. The results supported a monophyletic Mastodonsauroidea with Benthosuchus as the sister group to a clade consisting of the Heylerosauridae and the Mastodonsauridae. The name Mastodonsauridae replaces the name 'Capitosauridae', because Mastodonsaurus was found t o fall within the clade that includes most of the traditional 'capitosaurid genera. The composition of the Mastodonsauroidea was shown t o be similar to that traditionally assumed for the 'Capitosauroidea', and to exclude the Rhinesuchidae, a group often placed within the 'Capitosauroidea'. The Mastodonsauroidea must have a ghost lineage extending back to at least the Late Permian, when the common ancestor of the Mastodonsauroidea and the Trematosauroidea diverged from rhinesuchid ancestors. We can therefore expect to find Late Permian representatives of the Mastodonsauroidea, perhaps present as inconspicuous elements of non-stereospondyl dominated Late Permian faunas. C 2001 The Linnean Society of London ADDITIONAL KEY WORDS: Temnospondyls -Capitosauroidea -Capitosauridaetaxonomy -Mastodonsauridae -Heylerosauridae -Benthosuchusphylogeny. 382 R. J. DAMIANI Table 1. Previous classifications of the 'Capitosauridae'. Taxa in inverted commas were considered paraphyletic. The list is not exhaustive but gives some indication of the lack of consensus in 'Capitosauroid classification

New fossils from the Upper Permian Moradi Formation of northern Niger provide an insight into the faunas that inhabited low-latitude, xeric environments near the end of the Palaeozoic era (approximately 251 million years ago). We describe here two new temnospondyl amphibians, the cochleosaurid Nigerpeton ricqlesi gen. et sp. nov. and the stem edopoid Saharastega moradiensis gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40-90 million years earlier. Coupled with a scarcity of therapsids, the new finds suggest that faunas from the poorly sampled xeric belt that straddled the Equator during the Permian period differed markedly from well-sampled faunas that dominated tropical-to-temperate zones to the north and south. Our results show that long-standing theories of Late Permian faunal homogeneity are probably oversimplified as the result of uneven latitudinal sampling.

A 251 million year old partial burrow cast containing an articulated skeleton of the mammal-like carnivore Thrinaxodon liorhinus is the oldest evidence for burrowing by a cynodont synapsid. The burrow cast comes from terrestrial flood plain sediments close to the Permian-Triassic boundary in the Karoo of South Africa. Together with those of the later cynodont Trirachodon, the Thrinaxodon burrow cast indicates that burrow-making was broadly distributed in basal synapsids and has a long history in non-mammalian synapsid evolution. A reconstruction of its appendicular skeleton in cross-section indicates that Thrinaxodon was able to adopt a facultatively mammalian stance within its burrow shaft. Burrows of cynodont design are more common in Triassic rocks than previously realized, and suggest that burrowing may represent an adaptive response by cynodonts to the environmental conditions associated with the mass extinction event that punctuated the end of the preceding Permian period. The widespread occurrence of burrowing among extant mammals implies that the ancient synapsid ability to burrow conferred a strong adaptive value in the evolution of Mammalia.

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The cranial anatomy of the plagiosaurid temnospondyl Plagiosuchus pustuliferus, from the Middle Triassic of Germany, is described in detail on the basis of a newly discovered skull and mandibular material. The highly derived skull is characterized by huge orbitotemporal fenestrae, a reduction of the circumorbital bones -the prefrontal, postfrontal and (probably) postorbital are lost -and the expansion of the jugal to occupy most of the lateral skull margin. Ventrally the extremely long subtemporal vacuities correlate with the elongate adductor fossa of the mandible. The dentition is feebly developed on both skull and mandible. Ossified ?ceratobranchials and 'branchial denticles' indicate the presence of open gills clefts in life. The remarkably divergent cranial morphology of P. pustuliferus highlights the extraordinary cranial diversity within the Plagiosauridae, probably unsurpassed within the Temnospondyli. Specific structural aspects of the skull -including an extremely short marginal tooth row, feeble dentition and an elongated chamber for adductor musculature -together with evidence for a hyobranchial skeleton, suggests that P. pustuliferus utilized directed suction feeding for prey capture.

We describe the edopoid temnospondyl Nigerpeton ricqlesi from the Upper Permian Moradi Formation of northern Niger on the basis of two partial skulls and tentatively associated postcranial material. This crocodile-like taxon displays several edopoid characters states such as a long prenarial region with enlarged premaxillae, elongated vomers, large, posteriorly tapering choanae. and a jugal that broadens anteriorly. Nigerpeton possesses a unique carnivorous dentition. lt is autapomorphic in its possession of an extremely elongate snout bearing a maxillary bulge that accommodates three hypertrophied caniniform teeth. inner premaxillary tusks, and anterior paired fenestrae, which pierce the skull roof. ln addition, both the maxilla and dentary tooth rows show the sporadic appearance of 'doubled' tooth positions. The lateral-line system is present at the adult stage, which suggests an aquatic habitat for this taxon. A phylogenetic analysis of Edopoidea and its relatives places Nigerpeton as the sister taxon to the Permo-Carboniferous genus Chenoprosopus from the U.S.A. As with other members of the Moradi tetrapod fauna, the discovery of Nigerpeton strengthens support for the hypothesis that West Africa hosted an endemic fauna at the close of the Paleozoic Era. Biogeographically, we propose that Late Carboniferous and Permian edopoids were geographically widespread and that they twice crossed the Central Pangean mountain chain (between Laurussia and Gondwana) during their evolution. This distribution was later fragmented with the onset of Late Permian climatic warming. Institutional Abbreviations-AMNH, American Museum of Natural History, New York; MCZ, Museum of Comparative Zoology, Harvard University, Cambridge; MNHN, Museum national d'Histoire naturelle, Paris; MNN, Musee National du Niger, Niamey. SYSTEMATIC PALEONTOLOGY TEMNOSPONDYLI Zittel, 1887-1890 EDOPOIDEA Romer, 1945 COCHLEOSAURIDAE Broili in Zittel and Broili, 1923 COCHLEOSAURINAE Broili in Zittel and Broili, 1923 Definition--A node-based taxon including Cochleosaurus and Chenoprosopus and all descendants of their most recent common ancestor.Diagnosis--Cochleosaurids diagnosed by the following synapomorphic characters: depression in vomer anterior to choana (character 21 in the present phylogenetic analysis, unambiguous synapomorphy of the clade); elongate and narrow sphenethmoid (character 32, state 2, unambiguous synapomorphy of the clade); and pineal foramen closed in skulls greater than 120 mm in midline length (character 1, convergent with Saharastega).

A reptile specimen from the Lystrosaurus Assemblage Zone of the Beaufort Group, lowermost Triassic of South Africa, represents a new procolophonoid parareptile. Sauropareion anoplus gen. et sp. nov. is identi¢ed as the sister taxon of Procolophonidae in a phylogenetic analysis of procolophonoids. Stratigraphic calibration of the most parsimonious tree reveals that four of the six procolophonoid lineages originating in the Permian Period extended into the succeeding Triassic Period. This relatively high taxic survivorship (67%) across the Permo-Triassic boundary strongly suggests that procolophonoids were little if at all a¡ected by the mass extinction event that punctuated the end of the Palaeozoic Era (ca. 251 million years ago).

The small tetrapod Candelaria barbouri, from the Middle Triassic of southern Brazil, is the first example of an owenettid procolophonoid outside Africa and Madagascar. Candelaria barbouri was originally described as a primitive procolophonid; however, a re-examination of the holotype, as well as new material, reveals that C. barbouri is in fact the youngest member of the Owenettidae, extending the chronological range of the group by more than 10 million years. The recognition of C. barbouri as an owenettid points to a broader diversity and distribution for owenettids than hitherto thought. In addition, C. barbouri is the first member of the Owenettidae to exhibit temporal fenestrae, a discovery that draws attention to the significance of this feature in 'anapsid' reptiles.