sues et al, 2002

535

Journal of Vertebrate Paleontology 22(3):535–547, September 2002q 2002 by the Society of Vertebrate Paleontology

IRRITATOR CHALLENGERI, A SPINOSAURID (DINOSAURIA: THEROPODA) FROM THELOWER CRETACEOUS OF BRAZIL

HANS-DIETER SUES1, EBERHARD FREY2, DAVID M. MARTILL3, and DIANE M. SCOTT4

1Department of Palaeobiology, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6 andDepartment of Zoology, University of Toronto, Toronto, Ontario, M5S 3G5, Canada, [email protected];2Abteilung fur Geowissenschaften, Staatliches Museum fur Naturkunde Karlsruhe, Erbprinzenstrasse 13,

D-76133 Karlsruhe, Germany;3School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth PO1 3QL, U.K.;

4Department of Zoology, University of Toronto at Mississauga, Mississauga, Ontario, L5L 1C6, Canada

ABSTRACT—The holotype of Irritator challengeri Martill et al., 1996 from the Romualdo Member of the SantanaFormation (Lower Cretaceous) in northeastern Brazil represents the most complete skull of a spinosaurid known todate. The now fully prepared specimen provides much new information on the cranial structure in these enigmaticpredatory dinosaurs. The skull is remarkably narrow, especially in the region of the elongated snout. The maxillae arein broad contact along the midline, forming an extensive secondary bony palate. The maxillary teeth have straight orslightly recurved, conical crowns, with thin, fluted enamel and distinct but smooth carinae. As in Baryonyx walkeri,the anterior and ventral processes of the lacrimal meet at a more acute angle than in most non-avian theropod dinosaurs.The braincase is short anteroposteriorly but deep dorsoventrally, extending ventrally far below the occipital condyle.Irritator challengeri most closely resembles Spinosaurus aegyptiacus in the structure of its teeth, but more extensivecomparisons between the two taxa are currently impossible due to the limited amount of cranial material known forthe latter.

INTRODUCTION

The Romualdo Member of the Santana Formation in north-eastern Brazil is well-known for the abundance, taxonomic di-versity, and often exceptional preservation of its vertebrate fos-sils, especially fishes (Maisey, 1991; Martill, 1993). In recentyears, skeletal remains of dinosaurs have been repeatedly re-ported from this unit (Frey and Martill, 1995; Kellner and Cam-pos, 1996; Kellner, 1996, 1999; Martill et al., 1996; Martill etal., 2000). Although the material recovered to date is fragmen-tary, it is typically well preserved. The most remarkable amongthese fossils is the nearly complete skull of an unusual theropoddinosaur, which is housed in the collections of the StaatlichesMuseum fur Naturkunde Stuttgart (SMNS 58022). In its unpre-pared state, it was originally identified as the skull of a largepterosaur. Its dinosaurian affinities were first recognized byMartill et al. (1996), who designated this specimen as the ho-lotype of a new taxon, Irritator challengeri, which they placedin the Maniraptora. Kellner (1996) found no evidence in sup-port of maniraptoran affinities and referred Irritator to the Spi-nosauridae, a group of rather poorly known but distinctive te-tanuran theropods. This assignment has been widely accepted(Charig and Milner, 1997; Sereno et al., 1998; Taquet and Rus-sell, 1998), and is fully supported by the present study.

The Santana Formation is a poorly defined stratigraphic unitof the Araripe Group in the intracontinental Araripe Basin ofnortheastern Brazil. Strata of the Araripe Group crop out at thefoot of the Chapada do Araripe, a vast plateau on the bordersof the states of Ceara, Pernambuco, and Piauı, with possiblecorrelative deposits in basins to the south and west (Martill,1993). The Santana Formation constitutes a diverse suite ofsedimentary rocks. In its lower portion, a series of variegatedclays and silty clays with channel sandstones, conglomerates,and thin bituminous shales is overlain by silty, greyish-greenclays with abundant carbonate concretions. The matrix enclos-ing the holotype of Irritator challengeri closely corresponds tothat of the concretions from the Romualdo Member of this unit.

The Romualdo Member is a well-known source of vertebratefossils, and there is little doubt that the specimen described herewas derived from it. As partial confirmation of this provenance,preparation of the skull yielded fossils of the ostracod Patter-soncypris as well as isolated scales of the ichthyodectid fishCladocyclus, both of which are commonly found in concretionsfrom the Romualdo Member. D. M. M. recently showed a pho-tograph of the unprepared skull to several fossil dealers in San-tana do Cariri. One dealer who had also worked as a collectorrecalled the specimen and recollected that it was found nearBuxexe, a site near Santana do Cariri. The nature of the con-cretion as well as its color and texture are consistent with con-cretions from this region. Buxexe is a small farming communitylocated at about 650 m above sea-level on the flanks of theChapada do Araripe in the south of Ceara, about 5 km southof the famous fossil-producing region of Santana do Cariri. Itis only accessible by rough track. There are several localitiesin this region where fossils are collected from the RomualdoMember, and teams of local collectors move from place toplace. It is possible that the holotype of Irritator challengericame from one of several localities in the valley of the CaririacuRiver, and we are unable to determine the provenance of thisspecimen more precisely than to confirm its derivation from theRomauldo Member of the Santana Formation.

Despite the abundance and taxonomic diversity of its fossils,the precise stratigraphic age of the Romualdo Member remainsuncertain (Martill, 1993). Gardner (1846) considered the San-tana Formation Cretaceous in age based on lithological simi-larities to the Cretaceous strata in the south of England. Braun(1966) proposed an Early Cretaceous age for this formation onthe basis of similarities to the Wealden strata of northwesternEurope. Lima (1978) regarded the Santana Formation as Aptianin age based on palynological data. More recent work by Ponset al. (1990) suggested a late Aptian to early Albian date forthe underlying Crato Formation and a mid- to late Albian agefor bituminous shales with fossils of the aspidorhynchid fishVinctifer from the Romualdo Member. Between the Crato For-

536 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 22, NO. 3, 2002

FIGURE 1. Skull and mandible of Irritator challengeri, SMNS 58022 (holotype), in A, left lateral and B, right lateral views. Scale bar equals5 cm. Most of the dentigerous portion of the right maxilla was broken off during collection and has been reattached to the snout for the purposeof this drawing. Areas in white represent matrix and/or epoxy filler; uniform grey shading indicates opening. Abbreviations used in Figs. 1–4:an, angular; ao.f, antorbital fenestra; ar, articular; b.p, basipterygoid process; bo, basioccipital; bs, basisphenoid; ch, choana; d?, dentary?; e.m.f,external mandibular fenestra; e.n, external naris; f, frontal; f.c, facet for coronoid; f.m, metotic foramen; f.o, fenestra ovalis; g.f, glenoid fossa;it.f, infratemporal fenestra; l, lacrimal; ls, laterosphenoid; ls.c, laterosphenoid condyle; m, maxilla; m.a, maxillary antrum; n, nasal; n.c, nasalcrest; n.p, nasal projection; o, orbit; o.c, occipital condyle; os, orbitosphenoid; p, parietal; p.s, process on basisphenoid/parasphenoid rostrum; pl,palatine; pm, premaxilla; pn, lateral pneumatic recess on basisphenoid; pn.o, ‘‘postnasal fenestra’’ (see text for discussion); po, postorbital; po.p,paroccipital process; pr, prootic; prf, prefrontal; pt, pterygoid; q, quadrate; qj, quadratojugal; r, basisphenoid recess; s, stapes; sa, surangular;so, supraoccipital; sq, squamosal; v, vomer; v.f, foramen for V. cerebralis media; x, hole produced by post-mortem damage. Roman numeralsrepresent foramina for passage of cranial nerves; V1 denotes groove for ramus ophthalmicus of N. trigeminus.

mation and the Romualdo Member of the Santana Formation,there exists a significant (if variable) thickness of strata, whichincludes several intervals of non-deposition (Silva, 1983). Thusthe concretion-bearing horizon of the Romauldo Member isprobably younger than early Albian. Berthou (1990) suggesteda mid- to late Albian age for the concretions from the RomualdoMember, but palynological data for this horizon are inadequate(Maisey, 2000). Dates based exclusively on the vertebrate as-semblage are somewhat unreliable due to uncertainties regard-ing the stratigraphic ranges for most taxa. Furthermore, manyvertebrate taxa described from the Santana Formation may havebeen endemic to the Araripe Basin. However, Vinctifer, whichis frequently found in concretions from the Romualdo Member,has also been reported from the upper Aptian of Colombia(Schultze and Stohr, 1996) and the Aptian and lower Albian ofVenezuela (Moody and Maisey, 1994). Several fish taxa fromthe Romualdo Member also occur in Aptian- to Cenomanian-age strata of Morocco, including the giant coelacanthid Maw-sonia (Wenz, 1981) and the amiid Calamopleurus (Forey andGrande, 1998). On balance, the age of the Romualdo Memberis probably late Early Cretaceous (Albian; Maisey, 2000), butit could be as young as Cenomanian.

Ever since Stromer’s (1915) original description of Spino-saurus aegyptiacus, the distinctive skeletal structure of theseenigmatic predatory dinosaurs has intrigued paleontologists.The most noteworthy features of S. aegyptiacus are the enor-mously elongated (up to 1.65 m tall) neural spines on the dorsal

vertebrae (Stromer, 1915, 1934a, 1936) and the conical toothcrowns with distinct but smooth carinae (Stromer, 1934b). Al-though isolated teeth and bones referable to Spinosauridae arenot uncommon in the Albian- to Cenomanian-age continentalstrata of North Africa (Stromer, 1915, 1936; Bouaziz et al.,1988; Buffetaut, 1989; Russell, 1996; Kellner and Mader, 1997;Sereno et al., 1998; Taquet and Russell, 1998; Benton et al.,2000), little has been known to date about the structure of theskull of these theropods. So far, only the fragmentary and large-ly disarticulated cranial remains of the holotype of Baryonyxwalkeri (BMNH R9951; Charig and Milner, 1986) from theWealden (Lower Cretaceous: Barremian) of Surrey (England)have been described in detail (Charig and Milner, 1997); Serenoet al. (1998:1301, note 18) reidentified several of these bones.

D. M. S. has fully prepared the holotype of Irritator chal-lengeri (SMNS 58022) using only mechanical means. Prepa-ration proved to be slow and difficult due to the hardness ofthe calcareous matrix, which includes numerous spaces filledby dark brown, sparry calcite. It has invalidated a number ofobservations originally reported by Martill et al. (1996), andthe specimen now provides a wealth of information on the cra-nial structure of this unusual theropod dinosaur. We present herea detailed description of the holotype of Irritator challengeri,which represents the most complete skull of a spinosauridknown to date and thus is of great interest.

Anatomical terminology (including positional terms) em-ployed in this paper largely follows the standard English-lan-

537SUES ET AL.—SKULL OF IRRITATOR

FIGURE 1. Continued.

guage usage of comparative anatomy rather than the nomencla-ture of veterinary anatomy.

Institutional Abbreviations BMNH, The Natural HistoryMuseum (formerly British Museum [Natural History]), London;SMNS, Staatliches Museum fur Naturkunde Stuttgart.

SYSTEMATIC PALEONTOLOGY

THEROPODA Marsh, 1881TETANURAE Gauthier, 1986

SPINOSAUROIDEA Stromer, 1915 sensu Sereno et al., 1998SPINOSAURIDAE Stromer, 1915 sensu Sereno et al., 1998

IRRITATOR CHALLENGERI Martill et al., 1996

Holotype SMNS 58022, nearly complete skull, lacking theanterior portion of the snout and preserved together with bonesfrom both mandibular rami in a large calcareous concretion(Figs. 1, 2).

Locality and Horizon Romualdo Member of the SantanaFormation, Chapada do Araripe, northeastern Brazil. See pre-ceding discussion concerning stratigraphic age and provenance.

Diagnosis Nasals with prominent median bony crest thatterminates posteriorly in knob-like, somewhat dorsoventrallyflattened projection. Dorsal surface of parietals facing postero-dorsally and vertical axis of braincase inclined anteroventrally.Posterior surface of basisphenoid with deep, dorsoventrally ovalmedian recess. Surangular with broad lateral shelf.

As the holotype of Irritator challengeri represents the onlysubstantially complete skull currently known for any spino-saurid, it is not clear at what taxonomic level the individualfeatures listed above are diagnostic. Furthermore, the cranialstructure of related basal tetanuran theropods remains poorlyknown. Among Spinosauridae, Irritator challengeri most close-ly resembles Spinosaurus aegyptiacus Stromer, 1915, withwhich it shares several apomorphic character-states in the den-tition: Maxillary tooth crowns straight or slightly recurved andconical rather than labiolingually compressed; carinae of tooth

crowns distinct but devoid of serrations; enamel thin, with ver-tical ridges (‘‘fluting’’) on both the labial and lingual surfacesof the crown (Stromer, 1915, 1934b; Sereno et al., 1998). In-deed, Irritator may well prove to be congeneric with Spinosau-rus, but the current lack of cranial material for the latter makesdetailed comparisons between the two taxa impossible.

Comments Kellner and Campos (1996) described a newtaxon of spinosaurid theropod, Angaturama limai, on the basisof the poorly preserved anterior end of a snout with brokenteeth from the Romualdo Member of the Santana Formation.Direct comparisons with the holotype of Irritator challengeriare not possible because the two specimens represent differentregions of the skull and we were unable to examine or obtaina cast of the holotype of A. limai. However, the photographspublished by Kellner and Campos (1996:figs. 2A, 4) and Kell-ner (1996:figs. 2, 3) show that the premaxillae of Angaturamaare remarkably narrow transversely and form a median crestdorsally, matching the narrow snout and the dorsomedian creston the nasals of Irritator. In the preserved portion of the rightmaxilla (Kellner and Campos, 1996:figs. 2A, 3), the anterior(second and third) teeth are large as in Irritator. Furthermore,as in Irritator, the tooth crowns are round rather than labiolin-gually compressed in transverse section and have distinct butsmooth anterior (mesial) and posterior (distal) carinae at leastnear the base of the crown (Kellner and Campos, 1996:fig. 2C).Thus we follow Charig and Milner (1997) in considering An-gaturama limai a subjective junior synonym of Irritator chal-lengeri, which has priority by one month. Sereno et al. (1998:1301) even suggested that the holotype of ‘‘Angaturama limai’’might represent the rostral end of the snout of SMNS 58022.The family-level taxon Irritatoridae Martill et al., 1996 onlycomprises (and thus, in a phylogenetic classification, is redun-dant with) Irritator challengeri, which we refer to Spinosauri-dae Stromer, 1915 sensu Sereno et al., 1998 (including Baryo-nychidae Charig and Milner, 1986).


FIGURE 2. Skull of Irritator challengeri, SMNS 58022 (holotype),in dorsal view. Scale bar equals 5 cm.

DESCRIPTION

The retouched photograph of SMNS 58022 published byMartill et al. (1996:fig. 2) presented a left lateral view of thethen largely unprepared fossil. The principal openings of theskull (shown in black for contrast) were still filled with matrixbut the latter has since been removed to reveal additional detail,including previously unrecorded cranial bones. The allegedfrontoparietal crest does not belong to the specimen as no actualcontact can be established between this fragment of indeter-minate bone and the skull roof. The dorsal surfaces of the rightfrontal and both parietals as well as the posterodorsal portionof the supraoccipital have been largely destroyed, possibly dueto exposure along the edge of the concretion containing theskull.

SMNS 58022 was preserved lying on its side in an earlydiagenetic calcareous concretion. The crude initial preparationundertaken by the local collector inflicted considerable damageto the fossil because the hard limestone of the concretion doesnot always separate cleanly from the enclosed bone. Thus pres-ervation of the bony surfaces on the left side of the skull (in-cluding the braincase) is generally poor, with extensive fractur-ing as well as loss of bone in many places. However, the bonesof the right side of the skull are, for the most part, excellentlypreserved. The skull has been subjected to some crushing,mainly on the left side of the snout and the right side of thepostorbital region. The anterior end of the snout, comprisingmost of both premaxillae and the anterior ends of both maxillae,is broken off. The broken surface is clean and unweathered,suggesting that the rostral portion of the snout was lost onlyduring or after the recovery of the fossil. Numerous large andsmall fractures, some due to septarian cracking of the surround-ing concretion, traverse the cranial bones. A major break ex-tends almost vertically through the skull at the level of theanterior ends of the antorbital fenestrae and was crudely re-paired with epoxy car-body filler by the collector. Some bonysurfaces sustained damage during a poorly executed attempt byan unknown party to employ acid preparation.

The right postorbital, squamosal, and quadrate, the left quad-ratojugal, and the right angular as well as both coronoids, den-taries (except possibly the posterior part of the left element)and splenials were probably already lost prior to fossilization.The parietals, premaxillae, and supraoccipital are only incom-pletely preserved. Most of the tooth-bearing portion of the rightmaxilla was separated from the skull during collecting and isnow preserved as a detached fragment. The left jugal wasslightly rotated clockwise anteroventrally. The left postorbitalbecame detached along its sutural contacts and dropped into theleft orbit prior to burial. Similarly, the left squamosal and quad-rate were disarticulated. The former is now preserved medialto the left jugal, whereas the latter was displaced forward andis now exposed through the right antorbital fenestra. The leftpterygoid became separated and somewhat rotated clockwiseventrally; its lateral surface was exposed by preparation. Theposterior portion of the left mandibular ramus is no longer inarticular contact with the skull, but lies close to it and its lateralsurface is visible. The posterior portion of the right mandibularramus was displaced so that the ventral edge of the surangular(which is exposed in both lateral and medial views) is nowadjacent to the alveolar margin of the right maxilla.

Skull

In dorsal view, discounting some crushing on both sides, theskull is remarkably narrow throughout its entire length. Thelong and low snout is subtriangular in transverse section at itsbroken anterior end where it is much deeper (75 mm) than wide(48 mm). Although the anterior end of the snout is not pre-served, the length of the preorbital region of the skull was more


than twice that of the postorbital region and significantly ex-ceeded the greatest height of the skull. The sides of the snoutare relatively flat and steeply inclined dorsomedially. The longaxes of the antorbital fenestra and orbit extend posterodorsally.Similarly, the postorbital region of the skull roof faces poster-odorsally, and the vertical axis of the braincase extends ante-roventrally. The skull has an estimated length of about 600 mm,assuming rostral proportions similar to those for Baryonyxwalkeri (Charig and Milner, 1997) and measured from the tipof the snout to the occipital condyle. (The much higher estimatepublished by Martill et al. [1996] was based on the then largelyunprepared specimen including the alleged frontoparietal crest.)It is about 165 mm high at the level of the preorbital bar. Asthe sutures between the basioccipital, exoccipital-opisthotic,and supraoccipital are still discernable, SMNS 58022 may rep-resent an individual that was not fully mature at the time ofdeath (see Currie and Zhao, 1994). The external surfaces of thecranial bones are smooth where this condition can be confi-dently assessed on the specimen. However, Carr (pers. comm.)noted the presence of ‘‘immature’’ bone grain on the surangular.

The oval external naris is about three times longer antero-posteriorly than tall dorsoventrally (76 mm vs. approximately25 mm for the left naris). It is situated well behind the anteriorend of the elongate snout. The large antorbital fenestra has alongest (posterodorsal) diameter of about 145 mm (left open-ing). Its anterior margin is rounded, but its dorsal and ventralmargins converge posterodorsally, giving the opening anobliquely ellipsoidal outline. The ‘‘preantorbital fenestra’’ and‘‘maxillary process’’ identified by Martill et al. (1996:fig. 3a,‘‘mxp’’ and ‘‘p.an.f’’) are, in fact, the choana and part of thepalatine and vomer, respectively; these structures are exposedin lateral view through the antorbital fenestra on both sides ofthe snout. The maxilla lacks accessory antorbital (maxillary)and promaxillary fenestrae. Only the posterior edge of the me-dial wall of the antorbital fossa was exposed along the antero-dorsal margin of the antorbital fenestra. Posteriorly, the antor-bital fossa is weakly incised onto the lateral surface of the lac-rimal and does not extend onto the lateral surface of the jugal.The tall, somewhat keyhole-shaped orbit is round and widest inits dorsal portion (which housed the eyeball), but, more ven-trally, its anterior and posterior margins converge anteroven-trally. The longest (posterodorsal) diameter of the right orbit is130 mm. The small ‘‘supratemporal fenestra’’ identified byMartill et al. (1996:fig. 3a, ‘‘stf’’) represents an artificial holein the left sidewall of the braincase just behind the dorsal con-dyle of the laterosphenoid. The medial margins of the actualsupratemporal fenestrae are formed by the more or less verticallateral surfaces of the parietals and laterosphenoids. The great-est anteroposterior diameter of the (right) infratemporal fenestrais 77 mm.

Premaxilla Only the posterodorsal extremity of the pre-maxilla is preserved. Posteriorly, the premaxilla bifurcates toform the anterior and anteroventral margins of the external nar-is. The short ventral process of this bifurcation contributes tothe shelf-like ventral margin of the narial fenestra, whereas the(now largely destroyed) dorsal process contacted the anteriorend of the nasal.

Maxilla Anteriorly, the maxilla forms a greatly elongatedand dorsoventrally deep subnarial ramus, which contributesmost of the concave ventral margin of the external naris andseparates the nasal and premaxilla below this opening. The lat-eral surfaces of the maxillae are only slightly inclined dorso-medially towards each other. Most of the lateral portion of theright maxilla has been broken off, exposing a large, conicalmaxillary antrum (sensu Witmer, 1997a), which extends in thebody of the bone forward to the posteroventral margin of theexternal naris. The maxilla is deeply embayed posteriorly bythe anterior and ventral margins of the antorbital fenestra and

forms the medial bony wall to the antorbital fossa and maxillaryantrum. The medial wall of the maxillary antrum is perforatedby a large oval opening, as in Allosaurus (Witmer, 1997a). Me-dially, the maxillae broadly contact each other to form a sec-ondary bony palate; a distinct ridge, which is clearly visible intransverse section at the broken anterior end of the snout, ex-tends along their median suture. The slender ascending processof the maxilla curves posterodosally and tapers towards theposterior end, which overlaps the anterior ramus of the lacrimalabove the antorbital fenestra.

The left maxilla preserves nine tooth crowns or stumps ofcrowns; the first and third tooth show details of the crown. Mostof the dentigerous portion of the right maxilla was separatedfrom the skull by the collector but can be readily fitted backonto it, using a major vein of dark, sparry calcite traversing thebone and a broken anterior tooth as landmarks (Fig. 1B). Theright maxilla holds nine mostly damaged teeth, and there is thebroken base and a partial impression in the matrix of the tenthcrown at the incomplete posterior end of the bone. The brokendorsal surface of the posterior part of this jaw fragment showsoblique cross-sections of the functional teeth and of sometimestwo replacement teeth in different stages of eruption. The deep-ly implanted, vertically oriented teeth are well separated fromeach other more anteriorly. Posteriorly, the maxillary tooth rowterminates below the anterior end of the antorbital fenestra, wellforward of the orbit. The broken anterior end of the snout re-veals that the long, apparently slender root of the first preservedtooth in the left maxilla extends dorsally close to the level ofthe ventral margin of the external naris. The roots of the teethfrom opposing sides converge medially, almost reaching themidline. The first and second preserved tooth in the left maxillahave the tallest crowns, with heights of 32 and over 40 mm,respectively, and a mesiodistal diameter of about 13 mm; theirrelative position in the maxilla is uncertain due to the loss ofthe anterior end of that bone. The crowns of the more posteriormaxillary teeth are shorter. The left maxilla preserves nine teethpartially or completely, and the complete tooth row probablycomprised at least 11 teeth. The crown of the last tooth in theleft maxilla was in the process of eruption at the time of death,and only its tip is exposed. All tooth crowns are conical, ta-pering rather evenly towards the apex, and straight or at mostslightly recurved. They are round in transverse section ratherthan labiolingually flattened as is typical for theropod teeth. Thelumen of the pulp cavity is small. The anterior (mesial) andposterior (distal) carinae extend the full height of the crown toits apex. They are distinct but devoid of serrations; their relativeposition on the tooth crowns does not vary along the maxillarytooth row. The thin enamel is preserved in extensive patcheson several maxillary tooth crowns. At higher magnification, ithas a granular texture, as in Baryonyx (Charig and Milner, 1997:fig. 19; Sereno et al., 1998:fig. 2E). The labial surface of theleft first and the right eighth tooth crown bears fine, short enam-el ‘‘wrinkles’’ that extend obliquely toward the posterior carina,and the carina appears ‘‘beaded’’ at higher magnification on theright eighth tooth (Fig. 5). The enamel is distinctly fluted onall maxillary teeth, with vertical ridges extending the height ofthe crown on both the labial and lingual surfaces. The labialsurfaces of the well-preserved seventh and eighth right toothcrowns each bear seven vertical ridges. In Baryonyx walkeri,only the lingual surface of the tooth crowns is fluted (Charigand Milner, 1997), but fluting is present on both the labial andlingual surfaces of tooth crowns referred to Spinosaurus fromthe Kem Kem beds of southern Morocco (Kellner and Mader,1997).

Nasal The long, narrow nasals form much of the anteriorportion of the skull roof, extending from the external nares backbeyond the anterior margin of the orbit. Dorsally, a longitudinalcrest is developed along the straight internasal suture (which is


still discernable more anteriorly). Its height cannot be deter-mined with certainty due to extensive breakage along much ofits dorsal edge. The crest appears to reach its greatest depth inthe region above the antorbital fenestra. Posteriorly, it decreasesin height and terminates in a median knob-like, somewhat dor-soventrally flattened projection (part of which has been abrad-ed) that projects over the anterior end of the frontals and ap-pears to be flanked on either side by a narrow opening in theskull roof. The latter is situated on either side of the posteriorend of the nasals at their sutural contacts with the prefrontallaterally and the frontal posteriorly. The presence of a ‘‘post-nasal fenestra’’ in Baryonyx walkeri was inferred by Charig andMilner (1997) on the basis of the shape of the posterior end ofthe fused nasals. However, it is likely that the openings inSMNS 58022 are the result of dorsal displacement of the nasals,which has slightly separated these bones at their sutural contactswith the frontal, lacrimal, and prefrontal. This interpretation issupported by the fact that the left opening is less distinct thanthe right. Additional cranial material is needed to confirm thepresence of the postnasal fenestra in Baryonyx and Irritator.

The nasal contacts the maxilla laterally along a nearlystraight, forward-sloping suture. Anteriorly, it is emarginatedby the posterior margin of the external naris. The nasal doesnot enter into the dorsal margin of the antorbital fenestra andfossa. The nasals are not fused medially throughout their entirelength, and the internasal suture is clearly visible anteriorlywhere the dorsal surface of the snout was damaged.

Lacrimal The lacrimal forms the slightly thickened poster-odorsal margin of the antorbital fenestra and the anteroposte-riorly broad bony bar separating the orbit from the antorbitalfenestra. The long axes of its anterior and ventral processesenclose an angle of only about 408, similar to the condition inBaryonyx (about 358; Charig and Milner, 1997). The ventralprocess of the lacrimal is distinctly inclined posterodorsallyand, in lateral view, flares ventrally to form a broad flange,which reaches its greatest anteroposterior width at the suturalcontacts with the jugal and maxilla. The extensive anterior por-tion of this flange contacts the maxilla in an interdigitating su-ture; its posterior portion is thicker and forms the anterior mar-gin of the orbit. The slender anterior process of the lacrimalcontacts the nasal dorsally and medially, and is overlapped bythe tapering dorsal process of the maxilla anteriorly close to theposterodorsal apex of the antorbital fenestra. Posterodorsally,the lateral surface of the better preserved right lacrimal bears aprominent, anteriorly facing recess at the junction of the ante-rior and ventral rami. This recess is partially concealed in lateralview by a thick bony ridge along the posterodorsal margin ofthe lacrimal, but it is more exposed than in Baryonyx walkeri.It contains no obvious openings into the body of the lacrimal,but it is possible that several pits within the recess may repre-sent foramina that are still filled with matrix. Dorsally, the lac-rimal is narrowly exposed on the skull roof. Its posterodorsalcornual process is lower and smoother than the tuberosity in B.walkeri (Charig and Milner, 1997:fig. 5A).

Prefrontal The rather large prefrontal is triangular in lat-eral view and robust. Its lateral edge forms the rugose, thickanterior portion of the dorsal rim of the orbit, which continuesanterolaterally onto the lacrimal. Its ventral process extends faranteroventrally along the medial surface of the lacrimal. Pos-teromedially, the prefrontal inserts into a broad anterolateralnotch on the frontal. Dorsally, it is well exposed on the skullroof and forms the lateral margin of the postnasal fenestra.

Frontal The frontals broadly contact the parietals along atransverse suture posteriorly. Dorsally, they form a distinctridge along their median sutural contact. Their lateral marginsconverge only slightly anteriorly. The supratemporal fossa ex-tends forward onto the dorsal surface of the posterolateral por-tion of the frontal. Most of the dorsal surface of the frontal is

gently concave transversely and smooth. Ventrally, low cristaecranii border a narrow median sulcus for the olfactory tracts ofthe forebrain; the interfrontal suture is discernable in the roofof this groove. The frontal forms the thin posterior portion ofthe dorsal rim of the orbit.

Parietal In dorsal view, the parietals are much expandedanteriorly and posteriorly so that their lateral edges borderingthe supratemporal fossae are distinctly concave. They form anearly straight transverse suture with the frontals anteriorly. Theinterparietal suture can still be traced more anteriorly, but mostof the posterodorsally facing dorsal surface of the parietals hasbeen destroyed. The low occipital wings of the parietals extendposterolaterally as well as ventrally. Distally, each wing tapersand becomes slightly twisted to assume an almost vertical ori-entation, resting on the dorsal edge of the paroccipital process.The lateral surface of the occipital wing bears a depressed areafor contact with the squamosal.

Postorbital The postorbital is represented by the disartic-ulated left element. It formed the posterodorsal margin of theorbit and the anterior portion of the supratemporal bar. Thepostorbital is more or less T-shaped in lateral view, with a dor-sal portion formed by the anterior and posterior processes anda broad ventral process, the distal end of which is still buriedin the matrix. The anterolateral surface of the postorbital doesnot form a ‘‘horn’’ or rugosity. The anterior process curvesanteromedially to contact the frontal and parietal. It is morerobust than the short, tapering posterior process. The ventralprocess formed the more dorsal portion of the postorbital bar.It appears to lack any trace of a suborbital process.

Jugal The jugal is dorsoventrally deep and mediolaterallycompressed. Its much expanded anterior portion meets the max-illa in a deeply interdigitating suture anteriorly and the broadventral process of the lacrimal dorsally. The sutural contact be-tween the lacrimal and maxilla excludes the jugal from partic-ipating in the posterior margin of the antorbital fenestra (contraMartill et al., 1996). The dorsal edge of the jugal is notched bythe narrow ventral margin of the orbit. On the better preservedright element, a low ridge extends longitudinally above the ven-tral margin. The tall, posterodorsally directed dorsal process ofthe jugal forms a long, steeply forward-sloping surface for ar-ticular contact with the ventral process of the postorbital. Theslender posterior process of the jugal bifurcates and receivesthe anterior process of the quadratojugal posteriorly, formingthe infratemporal bar. The dorsal prong of this bifurcation ismore slender and shorter than the ventral one.

Squamosal The displaced left squamosal is preserved me-dial to the left jugal. The lateral surface of its anterior processbears a posteriorly tapering groove for the reception of the pos-terior process of the postorbital. The dorsal surface is convexanteriorly and concave posteriorly, indicating a shallow supra-temporal fossa that is bordered laterally by a low ridge. A shortposterior process arises just behind a ventral concavity on thesquamosal for the reception of the proximal head of the quad-rate. Its distal end is dorsoventrally expanded and curves ven-trally. The ventral process of the squamosal is broad antero-posteriorly.

Quadratojugal The L-shaped quadratojugal is representedby the complete right element. It forms most of the ventral andposterior margin of the large infratemporal fenestra. The quad-ratojugal has a tall, anteroposteriorly broad, and nearly verticaldorsal process, which is divided by a lateral ridge into a broadposterolaterally facing and a narrower anterolaterally orientedsurface, which probably contacted the ventral process of thesquamosal. It would have contacted the ventral process of thesquamosal dorsally. The more slender, tapering anterior processof the quadratojugal inserts into a slot on the infratemporalprocess of the jugal.

Quadrate A displaced bone partially visible through the


FIGURE 3. Braincase of Irritator challengeri, SMNS 58022 (holo-type), in occipital view. Scale bar equals 5 cm.

FIGURE 4. Braincase of Irritator challengeri, SMNS 58022 (holo-type), in right lateral view. Scale bar equals 5 cm.

FIGURE 5. Crown of the right eighth maxillary tooth of Irritatorchallengeri (SMNS 58022, holotype) in labial view. Anterior to theright of the figure. Scale bar equals 1 cm.

right antorbital fenestra right behind the palatine represents the?left quadrate. It is tall and has a vertical shaft terminating inthe proximal articular head as well as an extensive, flange-likeportion for contact with the pterygoid. The proximal head hasa rounded triangular outline in dorsal view and forms a cap thatis offset by a lip from the remainder of the bone.

Palatine The tall and thin vomeropterygoid process of thepalatine (sensu Witmer [1997a]) borders the choana and is ex-posed in lateral view through each antorbital fenestra. Anteri-orly, it forms a deep and stout flange for contact with the vomer.

Pterygoid The pterygoid is a long and thin bone. A distinctconcavity marks the articular contact for the basipterygoid pro-cess of the basisphenoid. A short but dorsoventrally deep, wing-like process for contact with the quadrate rises steeply posteriorand lateral to the basipterygoid joint. The anteriorly extendingpalatine ramus of the pterygoid is long, thin, and almoststraight.

Braincase As in Baryonyx walkeri (Charig and Milner,1997), the braincase (Figs. 3, 4) is short anteroposteriorly butdeep dorsoventrally. The sutural outlines of its constituentbones are, for the most part, still discernable, especially on thewell-preserved right lateral surface. The greatest width of thebraincase, as measured posteriorly across the (slightly abraded)distal ends of the paroccipital processes, is about 100 mm. Theforamen magnum has a concave dorsal and an almost straightventral margin. It is 25 mm wide and 20 mm high. The dorsalmargin of the opening is formed by the supraoccipital, and itslateral and ventral margins are made up by the exoccipitalsexcept for a narrow median contribution to the ventral marginfrom the basioccipital. The occipital condyle is almost hemi-spherical but is flattened dorsally. It is largely formed by thebasioccipital except for the dorsolateral corners, which are con-tributed by the exoccipitals. Its articular surface faces slightlyposteroventrally. The condyle is set off from the braincase bya short neck. The olfactory tracts extend in about the samehorizontal plane as the forebrain, and the hindbrain parallels theforebrain at a more ventral level.


Supraoccipital The supraoccipital is not fused to the ex-occipital-opisthotic (otoccipital). In occipital view, its dorsalportion bears a conspicuous, slightly posterodorsally projectingnuchal crest along the midline, which is subtriangular in coronalsection and served as the site of attachment for the ligamentumnuchae. The posterior surface of the supraoccipital is deeplyrecessed on either side of this crest, presumably for the insertionof M. rectus capitis. Breakage reveals that the supraoccipital isV-shaped in coronal section. A foramen in the notch at thedorsal contact between the forward sloping, wing-like lateralprocess (which presumably represents the fused epiotic, as inextant birds and crocodylians; Walker, 1990) and the dorso-median process of the supraoccipital on either side representsthe posterior opening for a vascular canal. This canal opensanteriorly in a small foramen situated on or close to the suturebetween the prootic and laterosphenoid, and probably servedfor the passage of V. cerebralis media (V. occipitalis externa ofauthors). Ventrally, a short median process of the supraoccipitalenters into the dorsal margin of the foramen magnum.

Orbitosphenoid The delicate orbitosphenoid is clearly dis-cernable on the right side of the braincase. Dorsally, a largeforamen, presumably for the passage of N. trochlearis (IV), issituated ventral and medial to the dorsal condyle of the later-osphenoid on the suture between the latter bone and the orbi-tosphenoid. Just ventral to this foramen on the right side of thebraincase, there are two smaller openings, at least one of whichrepresents the exit for N. oculomotoricus (III). Ventromedially,the orbitosphenoids meet and enclose between them a largeopening, which presumably represents the passage for N. op-ticus (II).

Laterosphenoid The laterosphenoid extends anterolaterallyfrom the front of the braincase. It forms a transversely expandeddorsal condyle for articular contact with the frontal, parietal,and presumably postorbital. This condyle has a smooth, round-ed articular surface. The lateral surface of the laterosphenoid isconcave anteroposteriorly and convex dorsoventrally. Posteri-orly, a single large foramen for the passage of N. trigeminus(V) and of V. cerebralis media is enclosed between the later-osphenoid and prootic. A deep sulcus, which probably carriedramus ophthalmicus of V1, and a less well developed grooveextend anterodorsally from the foramen along the almost flatanterolateral surface of the laterosphenoid toward the dorsalcondyle. This indicates that the three branches of N. trigeminusstill left the braincase together through a single common open-ing and diverged only after exiting the braincase.

Prootic The prootic is an irregularly shaped, robust ele-ment. Posteroventral to the trigeminal foramen, a slit-like open-ing for the passage of N. facialis (VII) is situated on a thickcrest, which becomes a laterally projecting flange and extendsonto the basisphenoid more ventrally. The latter represents theotosphenoidal crest (sensu Witmer, 1997b; crista prootica ofauthors). Just posterior to the crest, there is an extensive, deeprecess that continues laterally as the broad stapedial groovealong the anteroventral surface of the paroccipital process. Itcontains a pair of large foramina, which are separated from eachother by a slender crista interfenestralis. The anterior and slight-ly more dorsally situated opening represents the fenestra ovalis(fenestra vestibuli of authors) into which fitted the head of thestapes, and the posterior foramen is the metotic foramen (sensuWalker, 1990) for the passage of N. glossopharyngeus, N. va-gus, and N. accessorius (IX–XI). Although the sutural contactbetween the prootic and the exoccipital-opisthotic is not clear,at least the posterior and dorsal margins of the metotic foramenare formed by the exoccipital-opisthotic. There is no trace of afenestra pseudorotunda (cochleae).

Basioccipital and Basisphenoid Together with the basi-occipital, the basisphenoid (which appears to be indistinguish-ably fused with the parasphenoid) forms a transversely narrow,

somewhat apron-like structure that extends ventrally far belowthe occipital condyle. The basioccipital bears a median depres-sion rather than a ridge between the occipital condyle and basaltubera. The basal tubera are indistinct. Just below each tuber,an area for muscle insertion (‘‘oval scar’’ sensu Bakker et al.,1988) is developed along the posterolateral margin of the ba-sicranium. The transversely concave posterior surface of thebasisphenoid is marked by a deep, dorsoventrally oval medianrecess and, more dorsally, a median opening on the sutural con-tact between the basioccipital and basisphenoid. Both featuresare part of what is commonly referred to as the basisphenoidsinus, which is part of the median pharyngeal system (Witmer,1997b). This differs from the condition in Baryonyx walkeri(Charig and Milner, 1997:fig. 9A) where a deep median ‘‘fur-row’’ on the posterior surface of the basisphenoid tapers dor-sally to terminate on the suture between the basioccipital andbasisphenoid. The basipterygoid processes project anteroven-trally and diverge only slightly ventrolaterally. Medially, theyare linked by the transversely concave ventral edge of the bodyof the basisphenoid. The articular surface of each process facesventrally and slightly medially. Just anterior to the sella turcica,the anterodorsally projecting cultriform process arises from thebases of the basipterygoid processes. It bears a blunt, slightlyrecurved dorsomedial projection; Currie (1985) interpreted asimilar structure in Troodon as marking the posteroventral ex-tent of the (otherwise unossified) interorbital septum. Anter-oventral to the foramen for N. facialis (VII) and the otosphen-oidal crest, the anteroposteriorly gently concave lateral surfaceof the basisphenoid is marked by a prominent, dorsoventrallyoval recess. This depression contains two large foramina (whichare fully exposed on the right side of the braincase) and rep-resents the anterior (lateral) tympanic recess (Witmer, 1997b).The larger opening is situated on the anterodorsal margin ofthe depression and probably represents the posterior entranceof the canal for A. carotis interna (cerebralis), which wouldhave passed anterodorsally to the sella turcica. The other fora-men is located posteroventral to the former; it opens into thebody of the basisphenoid and may have been pneumatic in or-igin.

Exoccipital–Opisthotic As in most dinosaurs, the exoccip-ital and opisthotic appear to be indistinguishably fused into asingle element (otoccipital). The compound bones do not meetalong the midline but are separated by a narrow ventral processof the supraoccipital dorsal to the foramen magnum and by thebasioccipital below that opening. The lateral surface of the con-dylar portion of the exoccipital is pierced by a single foramenfor the passage of N. hypoglossus (XII) just anterior to theoccipital condyle. (This opening is currently exposed only onthe left side of the braincase.) The robust, short paroccipitalprocess projects posterolaterally and ventrally so that its distaltip is situated at about mid-height of the occipital condyle. Itsproximal end is thick, but the process gradually tapers postero-laterally. The distal end is neither expanded nor extended down-ward as, for example, in Allosaurus (Gilmore, 1920; Madsen,1976). In lateral view, the lower half of the distal end of theprocess bears a concavity for possible contact with the quadrate.The concave dorsolateral surface of the bone is flattened by thearticular surface for the squamosal. The ventral margin of thelatter extends anterodorsally to the proximal end of the contact.Thus the medial process of the squamosal fitted into a broadgroove formed by the otoccipital and parietal.

Stapes On the right side of the skull, a slender, rod-likebone is preserved lying across the infratemporal fenestra andthe lateral surface of postorbital process of the jugal. It is 55mm long and has slightly expanded and flattened proximal anddistal ends. The bone is identified as a stapes because it closelyresembles the stapes of Allosaurus (Madsen, 1976) and Dro-maeosaurus (Colbert and Ostrom, 1958). The presence of this


element in SMNS 58022 is noteworthy because only a fewexamples of a complete stapes in non-avian dinosaurs havebeen reported to date.

Mandible

The left mandibular ramus is represented by the articulatedsurangular, angular, articular, and prearticular, and the right bythe articulated surangular and articular. The coronoid, dentary,and splenial are not preserved for either lower jaw. A possibleexception may be the posterior end of the left dentary, but thereis no clear sutural separation from the surangular posteriorlyand the fragment in question shows no trace of alveoli.

Surangular The large surangular is a more or less verticaland dorsoventrally deep bone, which comprises most of thedorsolateral portion of the mandibular ramus behind the toothrow. A prominent shelf extends along the lateral surface of thesurangular from the level of the posterior end of the externalmandibular fenestra back to the region anterior to the glenoidfacet of the jaw joint. The dorsal surface of this shelf facesobliquely dorsolaterally and is concave anteroposteriorly aswell as transversely. Anteriorly, the shelf fades into the dorso-ventrally gently convex lateral surface of the surangular. Theposterior surangular foramen is small; it is clearly visible onthe medial surface of the right element. The medial surface ofthe surangular is broadly concave dorsoventrally except for aprominent ridge along the dorsal margin of the extensive ad-ductor fossa. Anteromedially, this ridge bears a distinct articularfacet, possibly for contact with the coronoid; the latter passesonto the dorsal surface of the surangular.

Angular The angular, which is incompletely preserved onthe left mandibular ramus, forms the distinctly concave ventralmargin of the external mandibular fenestra. Behind this open-ing, it forms a thin sheet of bone. There is no clearly discern-able sutural separation from the surangular, and it is not clearwhether the angular contacted the surangular anterior to theexternal mandibular fenestra.

Prearticular The prearticular is exposed in medial view onthe left mandibular ramus. It is a curved, long, and thin bone,which is dorsoventrally expanded at either end and borders theadductor fossa ventromedially. The prearticular is most robustat its posterior end, which covers the ventromedial aspect ofthe articular. Its dorsal edge is concave. The anterior portion ofthe prearticular forms a vertical, dorsoventrally expanded plateof bone, which presumably contacted the splenial and the me-dial surface of the dentary. A narrow surface along the dorsalmargin of the anterior end may have been for contact with thecoronoid.

Articular The articular contacts the prearticular antero-medially and the surangular laterally. Ventrally, it is plate-likeand wedged between the surangular laterally and the prearti-cular medially. The articular facet for the mandibular condyleof the quadrate is concave anteroposteriorly and delimited bytransverse bony ridges anteriorly and posteriorly. Immediatelyposterior to the posterior transverse ridge, the dorsomedial edgeof the articular is distinctly concave anteroposteriorly. A smallforamen, which may have served for passage of the chordatympani, is situated just posteromedial to the posterior trans-verse ridge. The articular forms an anteroposteriorly short re-troarticular process, which turns posteromedially behind thefacet for the mandibular condyle of the quadrate. The processis dorsolaterally-ventromedially flattened so that its anteropos-teriorly gently convex lateral surface faces dorsolaterally.

RELATIONSHIPS OF IRRITATOR CHALLENGERI

Irritator shares with Baryonyx and the probably congenericSuchomimus (see below) the following derived character-statesin the skull and dentition that are absent in most or all other

known non-avian theropod dinosaurs: (1) The skull is remark-ably narrow throughout its entire length, especially in its rostralregion. (2) The long but low external nares are situated far backon the sides of the elongated snout rather than near the rostralend of the snout. (3) The maxillae broadly contact each othermedially, forming an extensive secondary bony palate. (4) Themaxilla forms a greatly elongated subnarial ramus, which sep-arates the premaxilla and nasal below the external naris and islonger anteroposteriorly than deep dorsoventrally. (5) The max-illary teeth have straight or slightly recurved crowns that areround to subcircular in transverse section, rather than labiolin-gually flattened. (6) If the holotype of ‘‘Angaturama limai’’indeed represents the anterior end of the snout of Irritator chal-lengeri, the latter also shares with Baryonyx the apomorphicpresence of seven premaxillary teeth. (7) The fused posteriorportions of the nasals terminate in a knob-like median projec-tion posteriorly. (8) A narrow fenestra (postnasal fenestra;Charig and Milner, 1997) appears to be present between thefrontal, posterior end of the conjoined nasals, and prefrontal oneither side of the skull roof; this feature is convergently presentin the coelophysoid theropod Syntarsus (Rowe, 1989). (9) Theanterior and ventral processes of the lacrimal enclose a muchmore acute angle (about 358–408) than in other theropod taxa(about 758–908). (10) The braincase is short anteroposteriorlybut deep dorsoventrally, extending ventrally far below the oc-cipital condyle. (11) The basipterygoid processes of the basi-sphenoid are elongate and diverge only slightly ventrolaterally.These features support recognition of the family-level taxonSpinosauridae Stromer, 1915, as defined and diagnosed by Ser-eno et al. (1998).

Combining information from the cranial bones of Baryonyxwalkeri and ‘‘Suchomimus’’ tenerensis, Sereno et al. (1998:fig.2) reconstructed the skull of spinosaurid theropod dinosaurs aslong, low, and narrow throughout its entire length. They criti-cized the reconstruction of the skull of B. walkeri by Charigand Milner (1997:fig. 1) as exaggerating the vertical height ofthe cranium in the occipital region by ‘‘unnatural ventral dis-placement’’ of the quadrate to the paroccipital process (Serenoet al., 1998:1301). However, as the more distal portions of theparoccipital processes in the holotype of B. walkeri (BMNHR9951) are not preserved (Charig and Milner, 1997:fig. 9), it isnot obvious which reference point was used by Sereno et al.(1998) as the basis for their assertion. The skull of I. challengeridemonstrates that the more posterior region of the skull wasindeed deeper dorsoventrally than the snout (Figs. 1, 6).

The Spinosauridae had a wide, apparently mainly Gondwan-an distribution during the Early and early Late Cretaceous(Charig and Milner, 1997; Sereno et al., 1998). Stromer (1915)named Spinosaurus aegyptiacus on the basis of associated skel-etal remains from the Upper Cretaceous (Cenomanian) Baha-riya Formation of the Bahariya Oasis in the Western Desert ofEgypt. The holotype consists of an edentulous fragment of amaxilla, a partial mandible with four teeth, isolated teeth, ver-tebrae from all parts of the column, incomplete thoracic ribs,and gastralia elements (Stromer, 1915, 1936). With the possibleexception of a caudal vertebra, Stromer interpreted this materialas representing the skeletal remains of a single individual. Un-fortunately, the holotype and only known specimen was lostduring the destruction of the Palaontologische Staatssammlungin Munich by a British air raid in 1944. Stromer (1934a) iden-tified additional postcranial bones from Bahariya as ‘‘Spinosau-rus B’’ based on their proportionately smaller size and somemorphological differences. However, Sereno et al. (1998) re-assigned this material (which was destroyed along with the ho-lotype of S. aegyptiacus) to the allosauroid Carcharodontosau-rus saharicus. Buffetaut (1989) identified two jaw fragmentsand an isolated tooth from the ?Cenomanian-age Kem Kembeds of southern Morocco as Spinosaurus. Russell (1996) re-


FIGURE 6. Partial reconstruction of the skull and mandible of Irritator challengeri in left lateral view, based primarily on the better preservedright side of SMNS 58022. Scale bar equals 5 cm. Broken lines indicated restored portions. The height of the nasal crest and the depth of thepostdentary portion of the mandibular ramus are uncertain. The supralabial foramina on the lateral surface of the maxilla are based on the conditionin Baryonyx tenerensis (Sereno et al., 1998).


ferred several vertebrae from the same region to this genus, andTaquet and Russell (1998) figured and briefly reported on theanterior portion of a snout. Additional cranial material from theKem Kem beds will be described by Milner (in prep.). Russellused proportional differences in the cervical vertebrae to distin-guish a new species, Spinosaurus maroccanus, for the Moroc-can material, but Sereno et al. (1998) considered these differ-ences taxonomically insignificant and synonymized S. maroc-canus with S. aegyptiacus.

To date, the most completely known spinosaurid theropod isBaryonyx walkeri from the Lower Cretaceous (Barremian) Up-per Weald Clay of Ockley, Surrey (England; Charig and Milner,1986, 1997). Buffetaut (1989, 1992) first recognized its closerelationship to Spinosaurus. The holotype of B. walkeri is anincomplete but well-preserved skeleton (BMNH R9951), whichincludes largely disarticulated and fragmentary bones of theskull and mandible and was described in detail by Charig andMilner (1997). Sereno et al. (1998:1302) diagnosed B. walkeriby ‘‘fused nasals with a median crest terminating posteriorly ina cruciate process, a solid subrectangular lacrimal horn, amarked transverse constriction of the sacral or anterior caudalcentra, a well-formed peg-and-notch articulation between thescapula and coracoid, an everted distal margin of the pubicblade, and a very shallow fibular fossa.’’ Charig and Milner(1997) and Martill and Naish (2001) listed additional occur-rences of isolated teeth as well as isolated postcranial bonesreferable to B. walkeri (or related taxa) from the Lower Cre-taceous (mainly Barremian) of England and the Isle of Wight.A maxilla fragment from the Barremian-age Enciso Group ofLa Rioja, Spain has also been referred to Baryonyx (Viera andTorres, 1995).

Taquet (1984), Taquet and Russell (1998), and Sereno et al.(1998) reported on a series of specimens of a Baryonyx-likespinosaurid from continental strata of the Lower Cretaceous(Aptian–Albian) Tegama Group at Gadoufaoua (locality GAD5), Niger. Taquet and Russell (1998) named Cristatusaurus lap-parenti on the basis of conjoined premaxillae and associatedfragments of a maxilla and dentary. They distinguished thistaxon from Baryonyx walkeri solely on the basis of the ‘‘bre-virostrine condition’’ of the premaxilla. Sereno et al. (1998)considered this difference uninformative, and Charig and Mil-ner (1997) identified the material discovered by Taquet as Bary-onyx sp. indet. Shortly after the publication of the paper byTaquet and Russell, Sereno et al. (1998) briefly announced thediscovery of additional skeletal remains, including a snout anda partial postcranial skeleton, from the same locality. They as-signed these specimens to a new genus and species, Suchomi-mus tenerensis, which they distinguished from Baryonyx walk-eri by the broader and taller neural spines of the dorsal, sacral,and anterior caudal vertebrae, robust humeral tuberosities, muchenlarged olecranon that is offset from the humeral articulation,and hook-shaped radial ectepicondyle. There exists at presentno evidence to indicate the presence of more than one taxon ofspinosaurid in the faunal assemblage from GAD 5. We concurwith Milner (in prep.) that the anatomical differences betweenthe material reported by Sereno et al. (1998) and Baryonyxwalkeri only warrant recognition of the former as a distinctspecies of Baryonyx, B. tenerensis. The generic nomina Cris-tatusaurus and Suchomimus should be considered subjective ju-nior synonyms of Baryonyx. Buffetaut and Ingavat (1986) de-scribed some unusual teeth from the Upper Jurassic Sao KhuaFormation of northeastern Thailand as Siamosaurus suteethorniand tentatively referred this taxon to the Spinosauridae. How-ever, the currently available material is insufficient for estab-lishing even dinosaurian affinities for Siamosaurus.

Sereno et al. (1994, 1998) and Holtz (2000) have establishedthe phylogenetic position of Spinosauridae among basal Tetan-urae, obviating the need for a cladistic analysis in this paper.

Sereno et al. (1994, 1998) grouped Spinosauridae with Torvo-sauridae (comprising Eustreptospondylus from the Middle Ju-rassic [Callovian] Oxford Clay Formation of England and Tor-vosaurus from the Upper Jurassic [Kimmeridgian–Tithonian]Morrison Formation of the western United States) and Afrov-enator from the Lower Cretaceous Tiouraren beds of Niger ina clade Spinosauroidea (‘‘Torvosauroidea’’ of Sereno et al.,1994). However, the comprehensive phylogenetic analysis ofTheropoda by Holtz (2000) placed Spinosauridae as the mostbasal clade of Tetanurae and considered Eustreptospondylus,Torvosaurus, and Afrovenator as progressively more derivedwithin Tetanurae. Of the apomorphies listed by Sereno et al.(1998) in support of Spinosauroidea, Irritator shares the pres-ence of a subnarial process of the maxilla that is longer thandeep and the dorsoventrally narrow anterior ramus of the lac-rimal. However, the derived character-state ‘‘lacrimal anteriorramus, length: . . . less (1) than 65% of the ventral ramus’’cited by Sereno et al. (1998:1302) is absent in Irritator (SMNS58022, right side).

Sereno et al. (1998) distinguished two clades among Spino-sauridae: Baryonychinae, comprising Baryonyx and Suchomi-mus, and Spinosaurinae, for Spinosaurus and Irritator. At pre-sent, the latter grouping is united only by two derived featuresof the teeth (tooth crowns with distinct but non-serrated carinaeand fluted enamel on both the labial and lingual surfaces) andpossibly the wide spacing of the maxillary teeth. In Baryonyx,the carinae are very finely serrated (Martill and Hutt, 1996;Charig and Milner, 1997; Sereno et al., 1998).

The presence of a spinosaurid theropod in the Santana For-mation is not surprising in view of the connection between east-ern Brazil and West Africa during at least part of the EarlyCretaceous, which is reflected by numerous sister-group pair-ings among continental fish and tetrapod taxa from these re-gions (e.g., Forey and Grande, 1998).

FUNCTIONAL INFERENCES

As noted above, Baryonyx and Irritator share a suite of cran-iodental features that distinguish them from most known non-avian theropod dinosaurs. The straight or at most slightly re-curved, conical tooth crowns in these two taxa are round oroval in transverse section, rather than labiolingually flattened,and their mesial and distal carinae have either very fine serra-tions (Baryonyx) or none at all (Irritator). This type of teethwas less suited for ‘‘grip-and-rip’’ cutting than the teeth withmore coarsely serrated carinae in other non-avian theropods(Abler, 1992), and instead may have been used primarily forimpaling and holding prey items (Charig and Milner, 1997).The long, narrow snout of Baryonyx forms an expanded anteriorend (‘‘terminal rosette’’ sensu Charig and Milner, 1997) withsix or seven teeth in each premaxilla, resembling the spatulatetip of the snout in predominantly piscivorous, longirostrine cro-codyliforms such as the extant gharial (Gavialis gangeticus)and various extinct taxa. The terminal expansion of the snoutof ‘‘Angaturama’’ is less prominent than that of Baryonyx(Kellner and Campos, 1996). The external nares are situatedwell back behind the anterior end of the snout in Baryonyx andIrritator. Taquet (1984), Buffetaut (1989), Charig and Milner(1986, 1997), Milner (1996), Martill et al. (1996) and Serenoet al. (1998) interpreted this combination of features as indi-cating piscivorous habits for spinosaurid dinosaurs. The pre-sumed gastric contents of the holotype of Baryonyx walkeri(BMNH R9951) contain etched scales of the holostean fish Lep-idotes and thus are consistent with this dietary inference (Char-ig and Milner, 1997). However, they also included abradedand(or) etched bones of a small individual of the ornithopoddinosaur Iguanodon, suggesting that B. walkeri fed on terres-trial vertebrates as well as fish. Most extant faunivorous tetra-


pods are opportunistic feeders, and there exists no reason notto assume similarly broad dietary habits for non-avian theropoddinosaurs.

The deeply implanted, vertically oriented teeth of Irritatorwith their conical, straight or at most slightly recurved crownsare suitable for apical loading parallel to their long axes, whichis consistent with their use for impaling and holding prey. Thenarrow snout with its nearly vertical sides and more or lessconvex dorsal surface would have facilitated forceful bitingdown on prey because this type of rostral shape (oreinirostralcondition) is less susceptible to dorsoventral bending stresses(Busbey, 1995). It clearly differs from the long, tubular snout(platyrostral condition) in Gavialis and various extinct crocod-yliforms that have been interpreted as piscivorous (Busbey,1995). The extensive secondary bony palate in spinosaurid the-ropods would also have served to reduce bending stresses act-ing on the snout (Thomason and Russell, 1986). We hypothe-size transmission of the vertically directed forces applied alongthe tooth row along the roots of the teeth to the occipital seg-ment of the skull through the dorsal strut formed by the nasals,which was probably further strengthened by the median crest.The posterodorsal inclination of the postorbital region of theskull suggests a reorientation of M. adductor mandibulae ex-ternus. Barghusen (1973) interpreted a comparable feature inbasal therapsids as reflecting a posterodorsal line of action forthe adductor jaw muscle to resist anteroventral displacement ofthe mandible by prey seized with the enlarged anterior teeth.This functional interpretation is equally plausible for spino-saurid theropods, which have a premaxillary dentition suitablefor seizing prey (Charig and Milner, 1997).

The skull of Irritator does not appear to be well-suited forcatching and processing large, resistant prey. Its structure dif-fers from that in other large theropod dinosaurs such as Allo-saurus (Rayfield et al., 2001) and Tyrannosaurus (Erickson etal., 1996), presumably reflecting different modes of feeding.Most likely spinosaurid theropods rapidly and forcefully seizedsmaller prey, which was then processed by dorsoventral motionof the head facilitated by the powerful neck musculature. (Ex-tensive side-to-side striking movements of the head, as em-ployed by extant crocodylians, appear unlikely in view of thenarrow occiput as well as the weak development of the basaltubera.) Whereas fish formed part of the diet in at least B. walk-eri, there is nothing to suggest that spinosaurids were exclu-sively or even predominantly piscivorous. Previous anatomicalcomparisons between the feeding apparatus of crocodylians andspinosaurid theropods were based only on superficial resem-blances.

The postcranial skeleton of Baryonyx lacks any obvious spe-cializations suggestive of an aquatic or semiaquatic mode oflife (Charig and Milner, 1997). Charig and Milner (1986, 1997)interpreted the greatly enlarged and strongly curved ungual ofmanual digit I as a ‘‘gaffing’’ device for catching fish, but thisintriguing hypothesis remains untestable in the absence of aclose analogue among extant tetrapods.

ACKNOWLEDGMENTS

We are greatly indebted to R. Wild (Staatliches Museum furNaturkunde Stuttgart) for the extended loan of the material andhis continuing interest in this study. D. Pulera (Toronto) pre-pared the drawings of the reconstructed skull reproduced in Fig.6. The remaining illustrations are the work of D. M. S. Wethank T. D. Carr (Royal Ontario Museum) who assisted ourwork through a thorough critique of the manuscript. A. C. Mil-ner (The Natural History Museum, London) and T. R. Holtz,Jr. (University of Maryland, College Park) provided construc-tive reviews. H.-D. S. gratefully acknowledges support from theRoyal Ontario Museum Foundation.

LITERATURE CITED

Abler, W. L. 1992. The serrated teeth of tyrannosaurid dinosaurs, andbiting structures in other animals. Paleobiology 18:161–183.

Bakker, R. T., M. Williams, and P. Currie. 1988. Nanotyrannus, a newgenus of pygmy tyrannosaur from the latest Cretaceous of Mon-tana. Hunteria 1(5):1–30.

Barghusen, H. R. 1973. The adductor jaw musculature of Dimetrodon(Reptilia, Pelycosauria). Journal of Paleontology 47:823–834.

Benton, M. J., S. Bouaziz, E. Buffetaut, D. Martill, M. Ouaja, M. Sous-si, and C. Trueman. 2000. Dinosaurs and other fossil vertebratesfrom fluvial deposits in the Lower Cretaceous of southern Tunisia.Palaeogeography, Palaeoclimatology, Palaeoecology 157:227–246.

Berthou, P.-Y. 1990. Le bassin d’Araripe et les petits bassins intracon-tinentaux voisins (NE de Bresil): formation et evolution dans lecadre de l’ouverte de l’Atlantique equatorial. Comparison avec lesbassins ouest-africains situes dans le meme contexte; pp. 113–134in D. de A. Campos, M. S. S. Viana, P. M. Brito, and G. Beurlen(eds.), Atas do I Simposio sobre a Bacia do Araripe e Bacias In-teriores do Nordeste, Crato, 14–16 de Junho de 1990, Anais. Crato,Ceara.

Bouaziz, S., E. Buffetaut, M. Ghanmi, J.-J. Jaeger, M. Martin, J.-M.Mazin, and H. Tong. 1988. Nouvelles decouvertes de vertebres fos-siles dans l’Albien du Sud tunisien. Bulletin de la Societe geolo-gique de France (8) 4:335–339.

Braun, O. P. G. 1966. Estratigrafia dos sedimentos da parte interior daregiao Nordeste do Brasil (bacias de Tucano-Jatoba, Mircundiba eAraripe). Boletim da Divisao de Geologia e Mineralogia do De-partamento Nacional de Producao Mineral, Rio de Janeiro 263:1–75.

Buffetaut, E. 1989. New remains of the enigmatic dinosaur Spinosaurusfrom the Cretaceous of Morocco and the affinities between Spi-nosaurus and Baryonyx. Neues Jahrbuch fur Geologie und Palaon-tologie, Monatshefte 1989:79–87.

———. 1992. Remarks on the Cretaceous theropod dinosaurs Spino-saurus and Baryonyx. Neues Jahrbuch fur Geologie und Palaon-tologie, Monatshefte 1992:88–96.

———, and R. Ingavat. 1986. Unusual theropod dinosaur teeth fromthe Upper Jurassic of Phu Wiang, northeastern Thailand. Revue dePaleobiologie 5:217–220.

Busbey, A. B. 1995. The structural consequences of skull flattening incrocodilians; pp. 173–192 in J. J. Thomason (ed.), Functional Mor-phology in Vertebrate Paleontology. Cambridge University Press,Cambridge and New York.

Charig, A. J., and A. C. Milner. 1986. Baryonyx, a remarkable newtheropod dinosaur. Nature 324:359–361.

———, and ———. 1997. Baryonyx walkeri, a fish-eating dinosaurfrom the Wealden of Surrey. Bulletin of the Natural History Mu-seum, Geology Series 53:11–70.

Colbert, E. H., and J. H. Ostrom. 1958. Dinosaur stapes. AmericanMuseum Novitates 1900:1–20.

Currie, P. J. 1985. Cranial anatomy of Stenonychosaurus inequalis(Saurischia, Theropoda) and its bearing on the origin of birds. Ca-nadian Journal of Earth Sciences 22:1643–1658.

———, and X.-J. Zhao. 1994. A new carnosaur (Dinosauria, Thero-poda) from the Jurassic of Xinjiang, People’s Republic of China.Canadian Journal of Earth Sciences 30:2037–2081. [Listed as ‘‘Oc-tober–November 1993,’’ but actually published on February 10,1994.]

Erickson, G. F., S. D. Van Kirk, J. Su, M. E. Levenston, W. E. Caler,and D. R. Carter. 1996. Bite-force estimation for Tyrannosaurusrex from tooth-marked bones. Nature 382:706–708.

Forey, P. L., and L. Grande. 1998. An African twin to the BrazilianCalamopleurus (Actinopterygii: Amiidae). Zoological Journal ofthe Linnean Society 123:179–195.

Frey, E., and D. M. Martill. 1995. A possible oviraptorosaurian theropodfrom the Santana Formation (Lower Cretaceous,?Albian) of Brazil.Neues Jahrbuch fur Geologie und Palaontologie, Monatshefte 1995:397–412.

Gardner, G. 1846. Travels in the Interior of Brazil, Principally throughthe Northern Provinces, and the Gold and Diamond Districts, dur-ing the Years 1836–1841. Reeve, Benham and Reeve, London, XVI1 562 pp.

Gauthier, J. A. 1986. Saurischian monophyly and the origin of birds;


pp. 1–55 in K. Padian (ed.), The Origin of Birds and the Evolutionof Flight. Memoirs of the California Academy of Sciences 8.

Gilmore, C. W. 1920. Osteology of the carnivorous Dinosauria in theUnited States National Museum, with special reference to the gen-era Antrodemus (Allosaurus) and Ceratosaurus. United States Na-tional Museum Bulletin 110:1–159.

Holtz, T. R., Jr. 2000. A new phylogeny of the carnivorous dinosaurs.Gaia 15:5–61.

Kellner, A. W. A. 1996. Remarks on Brazilian dinosaurs. Memoirs ofthe Queensland Museum 39:611–626.

———. 1999. Short note on a new dinosaur (Theropoda, Coelurosauria)from the Santana Formation (Romualdo Member, Albian), north-eastern Brazil. Boletim do Museu Nacional, Nova Serie, Rio deJaneiro, Geologia 49:1–8.

———, and D. de A. Campos. 1996. First Early Cretaceous theropoddinosaur from Brazil with comments on Spinosauridae. Neues Jahr-buch fur Geologie und Palaontologie, Abhandlungen 199:151–166.

———, and B. J. Mader. 1997. Archosaur teeth from the Cretaceousof Morocco. Journal of Paleontology 71:525–527.

Lima, H. R. de. 1978. Consideracoes sobre a subdivisao estratigraficada Formacao Santana, Cretaceo do Nordesto do Brasil. RevistaBrasiliera de Geociencias 9:116–121.

Madsen, J. H., Jr. 1976. Allosaurus fragilis: a revised osteology. UtahGeological and Mineral Survey Bulletin 106:1–163.

Maisey, J. G. (ed.) 1991. Santana Fossils: An Illustrated Atlas. T.F.H.Publications Inc., Neptune, New Jersey, 459 pp.

———. 2000. Continental break up and the distribution of fishes ofWestern Gondwana during the Early Cretaceous. Cretaceous Re-search 21:281–314.

Marsh, O. C. 1881. Principal characters of American Jurassic dinosaurs.Part V. American Journal of Science 21:417–423.

Martill, D. M. 1993. Fossils of the Santana and Crato Formations, Bra-zil. Field Guides to Fossils, no. 5. The Palaeontological Associa-tion, Oxford, 159 pp.

———, A. R. I. Cruickshank, E. Frey, P. G. Small, and M. Clarke.1996. A new crested maniraptoran dinosaur from the Santana For-mation (Lower Cretaceous) of Brazil. Journal of the GeologicalSociety, London 153:5–8.

———, E. Frey, H.-D. Sues, and A. R. I. Cruickshank. 2000. Skeletalremains of a small theropod dinosaur with associated soft structuresfrom the Lower Cretaceous Santana Formation of northeastern Bra-zil. Canadian Journal of Earth Sciences 37:891–900.

———, and S. Hutt. 1996. Possible baryonychid dinosaur teeth fromthe Wessex Formation (Lower Cretaceous, Barremian) of the Isleof Wight, England. Proceedings of the Geologists’ Association 107:81–84.

———, and D. Naish (eds.). 2001. Dinosaurs of the Isle of Wight. FieldGuides to Fossils, no. 10. The Palaeontological Association, Lon-don, 433 pp.

Moody, J. M., and J. G. Maisey. 1994. New Cretaceous marine verte-brate assemblages from north-western Venezuela and their signifi-cance. Journal of Vertebrate Paleontology 14:1–8.

Pons, D., P.-Y. Berthou, and D. de A. Campos. 1990. Quelques obser-vations sur la palynologie de l’Aptien superieur et de l’Albien duBassin d’Araripe (NE du Bresil); pp. 241–252 in D. de A. Campos,M. S. S. Viana, P. M. Brito, and G. Beurlen (eds.), Atas do I Sim-posio sobre a Bacia do Araripe e Bacias Interiores do Nordeste,Crato, 14–16 de Junho de 1990, Anais. Crato, Ceara.

Rayfield, E. J., D. B. Norman, C. C. Horner, J. R. Horner, P. M. Smith,J. J. Thomason, and P. Upchurch. 2001. Cranial design and functionin a large theropod dinosaur. Nature 409:1033–1037.

Rowe, T. 1989. A new species of the theropod dinosaur Syntarsus fromthe Early Jurassic Kayenta Formation of Arizona. Journal of Ver-tebrate Paleontology 9:125–136.

Russell, D. A. 1996. Isolated dinosaur bones from the Middle Creta-ceous of the Tafilalt, Morocco. Bulletin du Museum nationald’Histoire naturelle, Paris, serie 4, 18, section 4, 2–3:349–402.

Schultze, H.-P., and D. Stohr. 1996. Vinctifer (Pisces, Aspidorhynchi-

dae) aus der Unterkreide (oberes Aptium) von Kolumbien. NeuesJahrbuch fur Geologie und Palaontologie, Abhandlungen 199:395–415.

Sereno, P. C., A. L. Beck, D. B. Dutheuil, B. Gado, H. C. E. Larsson,G. H. Lyon, J. D. Marcot, O. W. M. Rauhut, R. W. Sadleir, C. A.Sidor, D. Varricchio, G. P. Wilson, and J. A. Wilson. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spi-nosaurids. Science 282:1,298–1,302.

———, J. A. Wilson, H. C. E. Larsson, D. B. Dutheuil, and H.-D.Sues. 1994. Early Cretaceous dinosaurs from the Sahara. Science265:267–271.

Silva, M. A. M. da. 1983. The Araripe Basin, north-eastern Brazil:regional geology and facies analysis of a Lower Cretaceous evap-oritic depositional complex. Ph.D. dissertation, Columbia Univer-sity, New York, 290 pp.

Stromer, E. 1915. Ergebnisse der Forschungsreisen Prof. E. Stromers inden Wusten Agyptens. II. Wirbeltier-Reste der Baharıje-Stufe (un-terstes Cenoman). 3. Das Original des Theropoden Spinosaurus ae-gyptiacus nov. gen., nov. spec. Abhandlungen der Koniglich Bay-erischen Akademie der Wissenschaften, Mathematisch-Physikali-sche Klasse 28(3):1–32.

———. 1934a. Ergebnisse der Forschungsreisen Prof. E. Stromers inden Wusten Agyptens. II. Wirbeltier-Reste der Baharıje-Stufe (un-terstes Cenoman). 13. Dinosauria. Abhandlungen der BayerischenAkademie der Wissenschaften, Mathematisch-naturwissenschaftli-che Abteilung, Neue Folge 22:1–79.

———. 1934b. Die Zahne des Compsognathus und Bemerkungen uberdas Gebiss der Theropoda. Centralblatt fur Mineralogie, Geologieund Palaontologie, Abteilung B, 1934:74–85.

———. 1936. Ergebnisse der Forschungsreisen Prof. E. Stromers inden Wusten Agyptens. VII. Baharıje-Kessel und -Stufe mit derenFauna und Flora. Eine erganzende Zusammenfassung. Abhandlun-gen der Bayerischen Akademie der Wissenschaften, Mathematisch-naturwissenschaftliche Abteilung, Neue Folge 33:1–102.

Taquet, P. 1984. Une curieuse specialisation du crane de certains Di-nosaures carnivores du Cretace: le museau long et etroit des Spi-nosaurides. Comptes Rendus de l’Academie des Sciences, Paris,serie II, 299:217–222.

———, and D. A. Russell. 1998. New data on spinosaurid dinosaursfrom the Early Cretaceous of the Sahara. Comptes Rendus del’Academie des Sciences, Paris, Sciences de la terre et des planetes327:347–353.

Thomason, J. J., and A. P. Russell. 1986. Mechanical factors in theevolution of the mammalian secondary palate: a theoretical anal-ysis. Journal of Morphology 189:199–213.

Viera, L. I., and J. A. Torres. 1995. Presencia de Baryonyx walkeri(Saurischia, Theropoda) en el Weald de La Rioja (Espana). Notaprevia. Munibe, Ciencias Naturales 47:57–61.

Walker, A. D. 1990. A revision of Sphenosuchus acutus Haughton, acrocodylomorph reptile from the Elliot Formation (late Triassic orearly Jurassic) of South Africa. Philosophical Transactions of theRoyal Society of London, B, 330:1–120.

Wenz, S. 1981. Un Coelacanthe geant, Mawsonia lavocati Tabaste, del’Albien-base du Cenomanien du Sud Marocain. Annales de Pa-leontologie (Vertebres) 67:1–20.

Witmer, L. M. 1997a. The evolution of the antorbital cavity of archo-saurs: a study in soft-tissue reconstruction in the fossil record withan analysis of the function of pneumaticity. Society of VertebratePaleontology Memoir 3:1–73.

———. 1997b. Craniofacial air sinus systems; pp. 151–159 in P. J.Currie and K. Padian (eds.), Encyclopedia of Dinosaurs. AcademicPress, San Diego.

Zhao, X., and P. J. Currie. 1994. A large crested theropod from theJurassic of Xinjiang, People’s Republic of China. Canadian Journalof Earth Sciences 30:2027–2036. [Listed as ‘‘October–November1993,’’ but actually published on February 10, 1994.]

Received 7 May 2001; accepted 13 November 2001.

sues et al, 2002

Documents

university of toronto

complete skull

martill etal

university of portsmouth

royal ontario museum

fur geowissenschaften

enigmaticpredatory dinosaurs

cranial structure