544 Journal of Vertebrate Paleontology 23(3):544–555, September 2003  2003 by the Society of Vertebrate Paleontology A REVISION OF THE EARLY TRIASSIC ‘‘CAPITOSAURS’’ (STEGOCEPHALI, STEREOSPONDYLI) FROM MADAGASCAR, WITH REMARKS ON THEIR COMPARATIVE ONTOGENY J. SEBASTIEN STEYER* Laboratoire de Pale ´ontologie, UMR 8569 du CNRS, Muse ´um national d’Histoire naturelle, 8 rue Buffon, 75005 Paris, France ABSTRACT—The ‘‘capitosaurs’’ from the Lower Triassic of Madagascar are revised. Benthosuchus madagascariensis Lehman, 1961, and Wetlugasurus milloti Lehman, 1961, are combined in the new combination Watsonisuchus mada- gascariensis on the basis of the most complete growth series among capitosaurians. A phylogenetic analysis showed that the genus Watsonisuchus is justified, although its species W. madagascariensis is not the most derived within the genus. The skull growth of W. madagascariensis clearly shows an allometric trend, but the fact that adults have more dermo-sensory grooves than juveniles suggests surprisingly that they may have become progressively more aquatic during growth. The ontogeny of W. madagascariensis is compared with that of other temnospondyls. Different longi- rostrine conditions are observed in Permian and Triassic stereospondylomorphs (archegosaurians and capitosaurians, respectively). They are interpreted as convergences rather than are a synapomorphy of the clade. INTRODUCTION The first discovery of a temnospondyl amphibian from Mad- agascar was a mandible from the Sakamena Formation (previ- ously considered as Permian, but now considered to be Triassic) of the southwestern part of the island. It was briefly reported by Piveteau (1926), and referred to Rhinesuchus (Uranocentro- don) cf. senekalensis by Romer (1947). From 1954 onwards, numerous stereospondyls were collected and described, includ- ing trematosaurs, ‘‘capitosaurs’’ (sensu Milner 1990, Schoch and Milner 2000, or Mastodonsauroidea sensu Damiani, 2001, see below; Lehman 1961, 1963, 1966, 1974), metoposaurs (Du- tuit, 1978), and some problematical genera such as Deltace- phalus Swinton, 1956 (Hewison, 1996), and Mahavisaurus Lehman, 1966. Lehman (1961) described a well-preserved series of ‘‘capi- tosaur’’ specimens from the Early Triassic of northwestern Madagascar, erecting the new species Benthosuchus madagas- cariensis and Wetlugasaurus milloti. These two taxa are prob- lematical because both their assignment and definition have been often discussed, but without complete redescription of the holotypes. Apart from a re-evaluation of Benthosuchus mada- gascariensis by Warren and Hutchinson (1988a), the knowledge and the understanding of these Malagasy ‘‘capitosaurs’’ has re- mained dormant for the last 40 years. With recent discoveries of new material and the application of new phylogenetic analytical techniques (Maryanska and Shishkin, 1996; Shishkin et al., 1996; Schoch, 1997; Mukherjee and Sengupta, 1998; Warren and Hutchinson, 1998b; Warren et al., 1998; Damiani, 2001), the taxonomy and phylogeny of ‘‘capitosaurs’’ have become the objects of intense debate. This article is part of a program of re-evaluation of the Malagasy temnospondyls described by Lehman. Its aim is to redescribe the ‘‘capitosaurs’’ on the basis of additional preparation and casting of the holotypes. Institutional Abbreviations BMNH, Natural History Mu- seum, London; IGS, Institut de Ge ´ologie de Strasbourg (France); MCZ, Museum of Comparative Zoology, Harvard; MNHN, Muse ´um national d’Histoire naturelle, Paris; MSNM, * Present address: Department of Palaeobiology and Palaeoecology, Geological Institute, Academy of Sciences, Rozvojova ´135, CZ-165 00, Prague 6, Czech Republic, steyer@gli.cas.cz Museo di Storia Naturale di Milano (Italy); RHM, Rhinopolis Associative Museum (Gannat, France); UMZC, University Mu- seum of Zoology, Cambridge. Anatomical Abbreviations aa, area aspera (of the ptery- goid, sensu Bystrow and Efremov, 1940); af, adductor fossa; ag, arcadian groove; ang, angular; apf, anterior palatal fossa; ar, articular; car, crista articularis; cf, crista falciformis; ch, choana; cl, clavicle; cle, cleithrum; cli, crista lingualis; cm, cris- ta muscularis; co, crista obliqua of the posterior ramus of the pterygoid; co1, co2, co3, coronoid 1, 2, or 3; cp, cultriform process of the parasphenoid; ct, crista terminalis; cte, crista tabularis externa; d, dentary; dsc, dermo-sensory canal (or sen- sory-line groove); ect, ectopterygoid; eo, exoccipital; f, frontal; gf, glenoid fossa; h, humerus; hp, hamate process on the glen- oid fossa; icl, interclavicle; j, jugal; l, lacrimal; m, maxilla; mf, magnum foramen; mef, meckelian foramen; n, nasal; oc, oc- cipital condyle; of, optic foramen; p, parietal; pa, prearticular; pal, palatine; pf, prefrontal; pm, premaxilla; po, postorbital; pof, postfrontal; pqf, prequadratum foramen; prp, prescapular process; pp, postparietal; ps, postsplenial; psp, parasphenoid; pt, pterygoid; q, quadrate; qb, quadrate boss; qj, quadratojugal; qr, quadrate ramus; r, rib; s, stapes; sa, surangular; sc, scapu- locoracoid; sf, symphyseal foramen; soc, supraoccipital; sp, splenial; sph, sphenethmoid (endocranium); sq, squamosal; st, supratemporal; stf, supratemporal fenestra; syp, symphyseal plateau; t, tabular; tf, temporal fossa; tm, torus marginalis of the pterygoid; ueo, undifferentiated endochondral ossification; v, vomer; ve, vertebra; IX-X, glossopharyngeal and vagus fo- ramen. SYSTEMATIC PALEONTOLOGY STEGOCEPHALI Cope, 1868 (sensu Laurin, 1998) TEMNOSPONDYLI Zittel, 1888 STEREOSPONDYLI Zittel, 1887 (sensu Yates and Warren, 2000) Superfamily MASTODONSAUROIDEA Lydekker, 1885 (sensu Damiani, 2001) (= ‘‘CAPITOSAUROIDS’’Watson, 1919 [Milner, 1990; Schoch and Milner, 2000; sensu Yates and Warren, 2000]) Definition A node-based taxon including Benthosuchus, Wetlugasaurus, Eocyclotosaurus, and all descendants of their