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examples from southwest and northeast Japan. Science 286, 937±939 (1999). Saurischia Seeley 1888 27. Gorbatov, A., Kostoglodov, V., Gerardo, S. & Gordeev, E. Seismicity and structure of the Kamchatka Theropoda Marsh 1881 subduction zone. J. Geophys. Res. 102, 17883±17898 (1997). 28. Engdahl, E. R., van der Hilst, R., Kirby, S. H. & Ekstrom, G. A global survey of slab structures and Abelisauroidea Bonaparte 1991 internal processes using a combined data base of high-resolution earthquake hypocenters, tomo- Masiakasaurus knop¯eri gen. et sp. nov. graphic images and focal mechanism data. Seismol. Res. Lett. 69, 153±154 (1998). Etymology. From masiaka (Malagasy, meaning vicious), sauros 29. Hochstaedter, A. G., Kepezhinskas, P., Defant, M., Drummond, M. & Koloskov, A. Insights into the volcanic arc mantle wedge from magnesian lavas from the Kamchatka arc. J. Geophys. Res. 101, 697± (Greek, meaning lizard) and knop¯eri (after singer/songwriter 712 (1996). Mark Knop¯er, whose music inspired expedition crews). 30. Kepezhinskas, P. et al. Trace element and Sr-Nd-Pb isotopic constraints on a three-component model Holotype. Universite d'Antananarivo (UA) 8680, well-preserved of Kamchatka arc petrogenesis. Geochim. Cosmochim. Acta 61, 577±600 (1997). right dentary with several teeth (Fig. 1). 31. Kersting, A. B. & Arculus, R. J. Klyuchevskoy Volcano, Kamchatka, Russia: the role of high-¯ux, Referred specimens. Field Museum of Natural History (FMNH PR recharged, tapped and fractionated magma chamber(s) in the genesis of high-Al2O3 from high-MgO basalt. J. Petrol. 35, 1±42 (1994). 2108±2182): maxilla; dentaries; splenial; cervical, dorsal, sacral and 32. Ozerov, A. Y., Ariskin, A. A., Kyle, P., Bogoyavlenskaya, G. E. & Karpenko, S. F. Petrological- caudal vertebrae; dorsal rib; humeri; manual phalanges and ungual; geochemical model for genetic relationships between basaltic and andesitic magmatism of Klyu- pubes; femora; tibiae; tibia/®bula/astragalocalcaneum; metatarsals chenskoi and Bezymyannyi volcanoes, Kamchatka. Petrology 5, 550±569 (1997). II and III; pedal phalanges and unguals. UA 8681±8696: dentary; cervical, dorsal, and caudal vertebrae; femora; tibia/astragalocalca- Acknowledgements neum; pedal phalanges; and unguals. We thank P. Kelemen and K. Furlong for discussions; J. Morris and M. Defant for Localities and horizon. All specimens are from the Anembalemba comments on the manuscript; and A. Bellousov, M. Bellousova, M. Ejzak, A. Koloskov, Member of the Upper Cretaceous (Maastrichtian) Maevarano G. Ponomarov and V. Ponomareva for assistance in the ®eld. This work was supported by the US NSF (G.M.Y. and J.M.L.), the German Science Foundation, the Volkswagen Formation, Mahajanga Basin, near the village of Berivotra, north- 8 Foundation and the European Union (INTAS) (to G.W. and T.C.), the Russian Founda- western Madagascar . With few exceptions, elements attributable to tion for Basic Research (O.V. and T.C.), and by a grant from the Whitaker Foundation to Masiakasaurus, including the holotype dentary (UA 8680), were Dickinson College. recovered as isolated specimens from a 3-m2 area in one strati- Correspondence and requests for materials should be addressed to G.M.Y. graphic horizon of a single locality, MAD 93-18. (e-mail: [email protected]). Diagnosis. Differs from all known theropods in that the four dentary teeth most rostral in position are procumbent, with the ®rst tooth set in a large, ventrally expanded alveolus that is almost horizontal in orientation. Also differs from all known theropods in that it has a strongly heterodont lower dentition: the ®rst four teeth ...... are elongate and weakly serrated, with labiolingually positioned carinae. Each of these four teeth terminates in a pointed apex that A bizarre predatory dinosaur from the hooks caudally. The teeth become increasingly recurved and trans- versely compressed with increasing caudal position in the jaw, and Late Cretaceous of Madagascar possess more standard, mesiodistally positioned carinae. Description. Together, the specimens referred to Masiakasaurus Scott D. Sampson*, Matthew T. Carrano² & Catherine A. Forster² knop¯eri account for about 40% of the skeleton (Fig. 1). The concentration of isolated Masiakasaurus elements at MAD 93-18 * Utah Museum of Natural History and Department of Geology and Geophysics, includes remains of at least six individuals. All of these specimens University of Utah, 1390 East Presidents Circle, Salt Lake City, Utah 84112-0050, are assigned to a single species, despite many of the elements (for USA example, femora, tibiae and vertebrae) being represented by several ² Department of Anatomical Sciences, Health Sciences Center, specimens, as none shows evidence of belonging to more than one State University of New York, Stony Brook, New York 11794-8081, USA taxon of small-bodied non-avian theropod. Two osteological fea- ...... tures (closure of the vertebral sutures and fusion of the crural and Here we report the discovery of a small-bodied (,1.8 m) pre- tarsal elements) indicate that the largest materials represent adult or datory dinosaur from the Late Cretaceous (Maastrichtian) of near-adult individuals of this small-bodied taxon. Madagascar. Masiakasaurus knop¯eri, gen. et sp. nov., repre- The maxilla, which is represented by a single partial specimen sented by several skull elements and much of the postcranial (Fig. 1; FMNH PR 2183), has a pronounced, raised external rim skeleton, is unique in being the only known theropod with a forming the perimeter of the extensive antorbital fossa. Although highly procumbent and distinctly heterodont lower dentition. lacking accessory foramina, a deep accessory fossa occupies the Such a derived dental morphology is otherwise unknown among rostral portion of the antorbital fossa. Seven alveoli are preserved dinosaurs. Numerous skeletal characteristics indicate that and, although a small portion of the caudal alveolar margin is Masiakasaurus is a member of Abelisauroidea, an enigmatic missing, it is unlikely that the maxillary tooth count exceeded ten. clade of Gondwanan theropods. Previously, small-bodied abeli- Unerupted teeth, which are preserved in the third and ®fth alveoli, are sauroids were known only from Argentina1±3. The occurrence of transversely compressed, recurved and bear moderate serrations. Masiakasaurus on Madagascar suggests that small-bodied abeli- Although the ®rst tooth is absentÐand thus the crown orientation sauroids, like their larger-bodied counterparts, were more cos- cannot be determined with con®denceÐthe ®rst alveolus is mopolitan, radiating throughout much of Gondwana and oriented at about 458 to the horizontal, indicating that the rostrally paralleling the diversi®cation of small coelurosaur theropods in positioned teeth in the upper jaw may have been procumbent. Laurasia. The specialized dentary (Fig. 2), represented by four specimens, Several expeditions4±7 have recovered abundant, well-preserved has a greatly emarginated caudal end that indicates an enlarged skeletal remains of dinosaurs and other vertebrates from the Upper intramandibular fenestra, as in Abelisauridae. The number of tooth Cretaceous (Maastrichtian) Maevarano Formation of northwestern positions in the dentary of Masiakasaurus varies from 10 to 12. The Madagascar. The non-avian dinosaur fauna includes a large abeli- slightly enlarged ®rst alveolus is oriented almost horizontally to saurid theropod, Majungatholus atopus5, and at least two titano- such an extent that the ®rst tooth is directed forward. The ®rst four saurian sauropods. Remains of at least ®ve species of birds have also teeth are radially arrayed, and become progressively more vertical been recovered, including the basal avian Rahonavis ostromi7. Our and parasagittal with increased caudal position. study describes a previously unknown small-bodied form recovered The bizarre morphologies of these ®rst four teeth are unique from the same deposits. among theropods. The caudal carina is labial (lateral), whereas the

504 © 2001 Macmillan Magazines Ltd NATURE | VOL 409 | 25 JANUARY 2001 | www.nature.com letters to nature rostral carina has migrated to a lingual (medial) position, resulting using these teeth to assist in procuring prey items. Although the in a tooth with a convex rostral face and a slightly concave caudal speci®c diet of Masiakasaurus remains speculative, such a deviation face. The carinae of these teeth converge to a sharp, caudolaterally in dental morphology probably indicates a marked divergence from hooked tip, and a series of longitudinal grooves cover the caudal the typical theropod diet. surface of the tooth between the carinae. Further back in the The cervical vertebrae are moderately elongate and lack any dentary, the teeth gradually assume a more typical theropod vertical offset of the cranial face over the caudal face. The centra form, being recurved and transversely compressed, as the carinae are broad, rather than tall, with no obvious pneumatic features. In migrate into more rostral and caudal positions. Although hetero- contrast, the neural arches are heavily pneumatized. The neural donty has been described for other theropod taxa (for example, spines are cranially positioned, greatly abbreviated in length, and ref. 9), the degree of dental differentiation does not approach that of are short dorsoventrallyÐexceeded in height by the postzygapo- Masiakasaurus. Modern mammals with procumbent dentitions, physes. The postzygapophyses are elongate and swept back, forming such as some caenolestid marsupials, are often insectivorous, a deep, V-shaped notch that terminates cranially at the neural spine.

Figure 1 Skeletal anatomy of Masiakasaurus knop¯eri, based on a composite of isolated emphasize contacts between individual elements. j, Pedal ungual (FMNH PR 2155) in specimens from locality MAD 93-18. a, Partial right maxilla (FMNH PR 2183) in medial lateral view. k, Right metatarsals II (FMNH PR 2129) and III (FMNH PR 2151) in cranial view. Dashed lines indicate reconstructed outline of the element. b, Posterior cervical view. Scale bars, 1 cm. am, acetabular margin; aof, antorbital fossa; as, astragalus; bg, vertebra (FMNH PR 2139) in left lateral view. c, Left pubis (FMNH PR 2108) in dorsal view. blood groove; ca, calcaneum; cn, cnemial crest; dp, deltopectoral crest; epi, epipophysis; d, Left femur (FMNH PR 2117) in cranial view. e, Medial caudal vertebra (FMNH PR 2126) ®, ®bula; hh, humeral head; idp, interdental plates; ip, pit for ilio-pubic articulation; lt, in left lateral view. f, Partial right humerus (FMNH PR 2143) in medial view. g, Left pubis lesser trochanter; mc, mediodistal crest; mt2, metatarsal II; mt3, metatarsal III; ns, neural (FMNH PR 2108) in lateral view. h, Proximal left tibia (FMNH PR 2118) in lateral view. i, spine; pb, pubic boot; pf, pubic fenestra; poz, postzygapophysis; pop, parapophysis; pp, Left tibia/®bula/astragalocalcaneum (FMNH PR 2112) in cranial view. Dashed lines palatal process; prz, prezygapophysis; ti, tibia; ts, trochanteric shelf.

Figure 2 Dentary and lower dentition of Masiakasaurus knop¯eri. a, Holotype dentary (UA Reconstructed dentary with full complement of teeth in right lateral view. f, Reconstructed 8680) in right lateral view. The tooth in position four has been displaced caudally post dentary in dorsal view, showing relative sizes and orientations of alveoli. c, carina; emf, mortem. b±d, Scanning electron microscope photographs of isolated dentary teeth external mandibular fenestra; lg, longitudinal groove; s, serration. Tooth positions are (FMNH uncatalogued). b, Anterior tooth, position 2±4 in lingual view. c, Anterior tooth, numbered sequentially from cranial to caudal positions. Scale bars, 10 mm (a, e±f); position 1±3, in lingual view. d, Anterior tooth, position 1±3, in lateral view. e, 5mm(b±d).

NATURE | VOL 409 | 25 JANUARY 2001 | www.nature.com © 2001 Macmillan Magazines Ltd 505 letters to nature

The humerus has a straight shaft, with a bulbous head that is the pedal unguals. In the Abelisauroidea, abelisaurids are all separated from a well-developed deltopectoral crest. The femur is relatively large-bodied theropods that are identi®ed by a suite of strongly bowed, with a greatly enlarged mediodistal crest. Proxi- derived features, and are currently known from the Late Cretaceous mally, the relatively long, slender tibia has a pronounced cnemial of India, Madagascar and Argentina2,3,5,16,17. In contrast, noasaurids crest that curves dorsolaterally; distally, this element appears to back are small-bodied forms previously represented by one, or possibly both the astragalus and calcaneum. The astragalus has a plate-like, two, fragmentary taxa restricted to the Late Cretaceous of Argen- rectangular ascending process that is fused with the ®bula along its tina1±3. Given that Masiakasaurus shares derived features with the lateral margin. Metatarsal II is relatively straight, with the proximal noasaurid Noasaurus leali from the Late Cretaceous of Argentina, two-thirds reduced to a thin shaft. The weakly curved pedal unguals such as cranially positioned cervical neural spines and reduced possess a triangular arrangement of vascular grooves on both the metatarsal II, it is possible that the new Malagasy taxon represents lateral and medial surfaces. a geographical extension of Noasauridae outside of Argentina. Masiakasaurus can be clearly diagnosed as a theropod dinosaur However, Noasaurus, as well as several other small-bodied, Late on the basis of several shared, derived characters, such as recurved, Cretaceous Gondwanan theropods from Argentina18 and India19, serrated, laterally compressed teeth, trenchant manual unguals and are represented by only a handful of elements, and thus the markedly thin-walled skeletal elements10,11. Most phylogenetic ana- phylogenetic relationships of these taxa remain obscure. lyses of Theropoda10±13 have recognized two major clades, Cerato- The placement of Masiakasaurus in the Abelisauroidea indicates sauria (Coelophysoidea and Neoceratosauria) and Tetanurae that small-bodied members of this clade, together with larger- (Spinosauroidea, Allosauroidea, Coelurosauria). However, a few bodied forms, spread throughout much of the southern super- studies14±16 have suggested that Ceratosauria is paraphyletic, with continent Gondwana by the Late Cretaceous. Thus, it seems that the Coelophysoidea and Neoceratosauria as successive sister taxa to a Late Cretaceous radiation of North American coelurosaur thero- monophyletic Tetanurae. pods into small-bodied (ornithomimid, troodontid, dromaeo- Masiakasaurus possesses a number of synapomorphies that saurid) and large-bodied (tyrannosaurid) forms12 occurred in support its membership in Abelisauroidea (Abelisauridae plus parallel with the diversi®cation of Gondwanan abelisauroid ther- Noasauridae)17 (Fig. 3). These include: a specialized caudal dentary opods. Furthermore, the peculiar dental and jaw morphology of margin with enlarged intramandibular fenestra; straight-shafted Masiakasaurus suggests that we are still far from fully appreciating humerus with enlarged, bulbous head; peg-and-socket articulation the morphological diversity of dinosaurs. M of ilium and pubis; mediodistal crest of femur hypertrophied to Received 5 May; accepted 26 October 2000. form a thin lamina; large, laterally curved and dorsally elevated 1. Bonaparte, J. F. & Powell, J. E. A continental assemblage of tetrapods from the Upper Cretaceous beds cnemial crest of the tibia; and triangular arrangement of grooves on of El Brete, northwestern Argentina (Sauropoda-Coelurosauria-Carnosauria-Aves). MeÂm. Soc. GeÂol. Fra. 139, 19±28 (1980). TRIASSIC JURASSIC CRETACEOUS 2. Bonaparte, J. F. The Gondwanian theropod families Abelisauridae and Noasauridae. Hist. Biol. 5, 1± 25 (1991). MUUpperLowerMid Lower Upper 65 144 208 3. Bonaparte, J. F. Cretaceous tetrapods of Argentina. Geowiss. Abhand. 30, 73±130 (1996). 4. Krause, D. W., Prasad, G. V. R., von Koenigswald, W., Sahni, A. & Grine, F. E. Cosmopolitanism THEROPODA among Gondwanan Late Cretaceous mammals. Nature 390, 504±507 (1997). Eoraptor 5. Sampson, S. D. et al. Predatory dinosaur remains from Madagascar: implications for the Cretaceous Herrerasaurus biogeography of Gondwana. Science 280, 1048±1051 (1998). 6. Krause, D. W. et al. The Late Cretaceous vertebrate fauna of Madagascar: implications for Gondwanan Coelophysidae paleobiogeography. GSA Today 9, 1±7 (1999). Dilophosaurus 7. Forster, C. A., Sampson, S. D., Chiappe, L. M. & Krause, D. W. The theropod ancestry of birds: new TETANURAE evidence from the Late Cretaceous of Madagascar. Science 279, 1915±1919 (1998). 8. Rogers, R. R., Hartman, J. H. & Krause, D. W. Stratigraphic analysis of Upper Cretaceous strata in the Mahajanga Basin, Madagascar: implications for ancient and modern faunas. J. Geol. 108, 275±301 Ceratosaurus (2000). 9. Sereno, P. C., Forster, C. A., Rogers, R. R. & Monetta, A. M. Primitive dinosaur skeleton from Majungatholus Argentina and the early evolution of Dinosauria. Nature 361, 64±66 (1993). 1 10. Gauthier, J. in The Origin of Birds and the Evolution of Flight (ed. Padian, K.) 1±47 (Memoirs of the NEOCERATOSAURIA Abelisauridae 3 Carnotaurus California Academy of Sciences, San Francisco, 1986). Abelisaurus 2 11. Holtz, T. R. Jr The phylogenetic position of the Tyrannosauridae: implications for theropod Abelisauroidea Masiakasaurus systematics. J. Paleontol. 68, 1100±1117 (1994). Noasaurus 12. Sereno, P. C. The origin and evolution of dinosaurs. Annu. Rev. Earth Planet. Sci. 25, 435±489 (1997). 13. Sereno, P. C. The evolution of dinosaurs. Science 284, 2137±2147 (1999). 14. Rauhut, O. Elaphrosaurus bambergi and the early evolution of theropod dinosaurs. J. Vert. Paleontol.18, 71A (1998). 15. Carrano, M. T. & Sampson, S. D. Evidence for a paraphyletic `Ceratosauria' and its implications for theropod dinosaur evolution. J. Vert. Paleontol. 19, 36A (1999). Figure 3 Stratigraphically calibrated cladogram of phylogenetic relationships of 16. Forster, C. A. Gondwanan dinosaur evolution and biogeographic analysis. J. Af. Earth Sci. 28, 169±185 Abelisauroidea, including Masiakasaurus. Unambiguous synapomorphies supporting the (1999). nodes are: (1) (Neoceratosauria), lateral temporal fenestra much larger than orbit; 17. Novas, F. E. in The Encyclopedia of Dinosaurs (eds Currie, P.J. & Padian, K) 1±2 (Academic, New York, 1997). numerous foramina surrounding axial diapophysis; notched posterior iliac margin; peg- 18. Bonaparte, J. F. Los vertebrados foÂsiles de la FormacioÂn Rio Colorado, de la Ciudad de NeuqueÂny and-socket articulation between ilium and pubis; femoral fourth trochanter reduced to low cercancias, CretaÂcico Superior, Argentina. Paleontologia 4, 16±123 (1991). ridge; deeply excavated medial surface of proximal ®bula; enlarged ilio®bularis tubercle 19. Huene, F. v. & Matley, C. A. The Cretaceous Saurischia and Ornithischia of the central provinces of on ®bular shaft; (2) (Abelisauroidea): caudal dentary margin with notch for surangular; India. Palaeontol. Indica 21, 1±72 (1933). enlarged external mandibular foramen; cervical neural spine abbreviated craniocaudally; Acknowledgements seven sacral veretebrae; large rounded coracoid; humerus straight-shafted with bulbous We thank A. Rasoamiaramanana, B. Rakotosamimanana, P. Wright, B. Andriamihaja and head; hypertrophied mediodistal crest on femur; large tibial cnemial crest with laterally- the staff of the Institute for the Conservation of Tropical Environments for help with directed hook; distal; cnemial crest curved dorsally; rectangular astragalar ascending ®eldwork in Madagascar; members of the 1993, 1995, 1996, 1998 and 1999 expeditions for process; triangular set of grooves on lateral and medial pedal unguals; and (3) their efforts; F. Novas amd P. Currie for photographs of Noasaurus; D. Krause for (Abelisauridae), craniofacial elements with external sculpturing; long, shelf-like maxilla± comments on earlier drafts of the manuscript; V. Heisey for preparation; F. Grine for scanning electron microscope photography; and L. Betti-Nash and J. Higgins for assistance jugal contact; greatly exposed paradental plates bearing a series of vertical ridges and with the ®gures. This work was funded by grants from the National Science Foundation, grooves; dorsal veretebral parapophyses projecting far laterally from centrum; distal ends the National Geographic Society, and the Dinosaur Society. of caudal transverse processes expanded craniocaudally; forelimb short relative to other Correspondence and requests for materials should be addressed to S.D.S. skeletal elements. M, Middle; U, Upper. Dates are millions of years before present. (e-mail: [email protected]).

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