47

Journal of Vertebrate Paleontology 23(1):47–53, March 2003q 2003 by the Society of Vertebrate Paleontology

A NEW SPECIES OF LEPIDOTES (NEOPTERYGII: SEMIONOTIFORMES: SEMIONOTIDAE)FROM THE SANTANA FORMATION, LOWER CRETACEOUS OF NORTHEASTERN BRAZIL

PAULO M. BRITO and VALERIA GALLODepartamento de Biologia Animal e Vegetal, Universidade do Estado do Rio de Janeiro, Rua Sao Francisco Xavier, 524,

Rio de Janeiro, Rio de Janeiro 20550-900, Brazil, pmbrito@uerj.br

ABSTRACT—A new species of Lepidotes is described on the basis of two nearly complete specimens from the ?AlbianRomualdo Member of the Santana Formation, in the Araripe Basin, northeast Brazil. The new species differs from theother species of Lepidotes previously recorded in western Gondwanaland by the apomorphic presence of an axe-shapedhyomandibula, and by a unique combination of other characters. This is the first record of an articulated Lepidotesfrom the Santana Formation of the Araripe Basin.

INTRODUCTION

The family Semionotidae is a highly diverse group of Me-sozoic Neopterygii, with a world-wide distribution and con-firmed temporal range from the Middle Triassic to the LateCretaceous.

Several obstacles have hindered cladistic analysis of the Se-mionotidae and their relatives. Firstly, many members of thisgroup are poorly preserved or are known only from isolatedbones, teeth and scales; secondly, the anatomy of the internalbones of many semionotid taxa (such as the majority of Bra-zilian Early Cretaceous forms) is virtually unknown due to theirmode of fossilization; and thirdly, not unexpectedly there islittle or no ontogenetic data. A further problem is the absenceof a convincing close outgroup for a conclusive phylogeneticanalysis.

The aim of this contribution is to describe a new species ofSemionotidae collected from the Romualdo Member of the San-tana Formation (Early Cretaceous, ?Albian), northeastern Bra-zil, and to provide additional comments on other semionotidsfrom western Gondwana. Previous records of semionotids inthis basin include Araripelepidotes temnurus from the Santana(Agassiz, 1841; Santos, 1990) and Crato formations (Brito etal., 1998), disarticulated remains of a large-sized cf. Lepidotes(Brito et al., 1994), and an isolated scale of Semionotidae (Gal-lo-da-Silva and Azevedo, 1996) from the Neocomian MissaoVelha/Brejo Santo formations.

The Santana Formation is one of the most important Creta-ceous fossil vertebrate localities, yielding a diverse well-pre-served fish fauna including chondrichthyans, actinopterygiansand coelacanths (Santos and Valenca, 1968; Wenz and Brito,1990; Maisey, 1991), as well as turtles, dinosaurs, pterosaurs,and crocodiles (Kellner, 1998).

MATERIAL AND METHODS

The present study is based on three partial specimens,housed, respectively, in the Laboratoire de Paleontologie, Mu-seum national d’Histoire naturelle (MNHN-BCE 387; Fig. 1),Museu Nacional/UFRJ (MN 4791-V; Fig. 2) and Universidadedo Estado do Rio de Janeiro (UERJ.PMB-VP80; Fig. 3). Dueto the state of preservation of this last specimen, it is provi-sionally attributed to the new species.

The holotype was collected in the early 1960’s and misiden-tified as an Araripelepidotes temnurus. Specimen MN 4791-Vhas been acid prepared using the transfer technique of Toombsand Rixon (1959). The other semionotids used for comparison

were acid or mechanically prepared. These specimens are listedin Gallo-da-Silva (1998).

Anatomical Abbreviations ACH, anterior ceratohyal;ANG, angular; AO, antorbital; ?a.pr.PSPH, ascending processof parasphenoid; ASPH, autosphenotic; BR, branchiostegalrays; CBR, ceratobranchial; CL, cleithrum; DPAL, dermopal-atine; DPT, dermopterotic; DSPH, dermosphenotic; DSPL,dentalosplenial; EPI, epiotic; EXO, exoccipital; EXSC, extras-capular; FR, frontal; HYM, hyomandibula; IO, infraorbital;IOP, interopercle; md.s.c., mandibular sensory canal; MTP,metapterygoid; MX, maxilla; OP, opercle; op.pr.HYM, oper-cular process of hyomandibula; or.s.c., oral sensory canal;OSPH, orbitosphenoid; PA, parietal; PCH, posterior cerato-hyal; PCL, postcleithrum; PMX, premaxilla; PO, postorbital;POP, preopercle; PRO, prootic; PSPH, parasphenoid; PT,posttemporal; RO, rostral; SCL, supracleithrum; SO, supraor-bitals; SOP, subopercle; VO, vomer.

SYSTEMATIC PALEONTOLOGY

Infraclass NEOPTERYGII Regan, 1923Order SEMIONOTIFORMES Arambourg and Bertin, 1958Family SEMIONOTIDAE sensu Olsen and McCune, 1991

Genus LEPIDOTES Agassiz, 1832LEPIDOTES WENZAE, sp. nov.

(Figs. 1–6)

Diagnosis Medium-sized Lepidotes with moderate predor-sal elevation; length of the skull about 33% of length of thepostcranial skeleton; dermal bones each ornamented with sev-eral conspicuous tubercles of ganoine; single pair of extrasca-pulars; extrascapulars sutured together along sagittal plane; su-bopercle with short anterodorsal process; opercle almost twiceas high as wide; three postcleithra; strong and toothed maxilla;lower jaw with two longitudinal sensory canals; axe-shaped hy-omandibula; scales without ornamentation.

Holotype MNHN-BCE 387, a partial specimen from theRomualdo Member, Santana Formation, lacking the rostral partof the skull, as well as the posterior portion of the body andthe paired and unpaired fins (Fig. 1).

Paratype MN 4791-V, a semi-complete specimen, from thesame geological unit, lacking part of the dermal bones and thepectoral, pelvic and anal fins (Fig. 2).

Etymology Specific name in honor of Dr. Sylvie Wenz.

DESCRIPTION

All measurements are taken from specimen MN 4791-V (Fig.2). The head measures 96 mm from the anteriormost point of

48 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 23, NO. 1, 2003

FIGURE 1. Lepidotes wenzae, sp. nov. (holotype, MNHN-BCE 387). Scale bar equals 3 cm.

FIGURE 2. Lepidotes wenzae, sp. nov. (paratype, MN 4791-V). Scale bar equals 4 cm.

49BRITO AND GALLO—NEW SEMIONOTID FROM THE SANTANA FORMATION

FIGURE 3. Lepidotes cf. L. wenzae (UERJ.PMB-VP80). Scale barequals 2 cm.

FIGURE 4. Lepidotes wenzae, sp. nov. (holotype, MNHN-BCE 387). Skull in dorso–lateral view plus some rows of scales. A, Photograph; B,line drawing of A. Scale bar equals 3 cm.

the skull to the posterior border of the opercle. The length ofthe cranium is approximately 33% that of the postcranial skel-eton. The standard length of the specimen is estimated to be330 mm, but this may be off slightly due to the torsion of thecaudal fin. All dermal bones are ornamented by several con-spicuous ganoine tubercles.

Rostral Bones Only the antorbital and the rostral are pre-served.

The antorbitals (Fig. 6) are tubular, boomerang-shaped bones(sensu Thies, 1989). Their anterior arms and the lateral arms ofthe rostral form an ossified tube complex for enclosure of theanteriormost part of the lateral-line sensory system. Thesebones partially surround both the nasal process and the tooth-bearing part of the premaxilla, and do not contact the frontals.

This pattern is found in the majority of the semionotids, but isunknown in Araripelepidotes.

Dermal Skull The anteriormost part of the skull roof isonly partially preserved in both examined specimens (Fig. 4).

The frontals (Fig. 4) are the longest elements of the dermalskull, having a length approximately three times that of theparietals, and extending from the rostral bone posteriorly to theparietals and dermopterotics. They have an ornamentation ofconspicuous tubercles of ganoine. The frontals are almost equalin width throughout their length, with a constriction over theorbit. The suture between the frontals is almost straight, withvery few interdigitations. The supraorbital sensory canal runslongitudinally, close to the lateral margin of the bone.

The parietals (Fig. 4) are subrectangular and well-developed,slightly longer than wide, asymmetrical, and joined togetheralong the cranial midline through a straight suture. The suturewith the frontals is sinuous. The lateral borders of the parietalsare almost linear and overlay the dermopterotics. The sensorycanal reaches the anterior half of the bone. Pit-lines cannot beobserved.

The dermopterotics (Fig. 4) are subrectangular, twice as longas wide, and contact the frontals and the dermosphenotics an-teriorly, a character found in all semionotids except Araripe-lepidotes (Maisey, 1991). The infraorbital canal runs laterallythrough the anterior third of the bone.

Only one pair of extrascapulars is found in L. wenzae (Fig.4). They are symmetrical, subtriangular bones, wider than long,joined together along the cranial midline, and approximately thesame size as the dermopterotics. The extrascapulars articulateanteriorly with the parietals and the dermopterotics, and pos-teriorly with the posttemporal. Their lateral borders are convexand overlap the opercle. The extrascapulars completely enclosethe occipital sensory canal, which is oriented transversely inthe posterior third of these bones. An extension of the supra-temporal sensory canal runs longitudinally close to the distalmargin of the extrascapulars.

50 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 23, NO. 1, 2003

FIGURE 5. Lepidotes wenzae, sp. nov. (holotype, MNHN-BCE 387). Skull in ventral view. A, Photograph; B, line drawing of A. Scale barequals 3 cm.

FIGURE 6. Lepidotes wenzae, sp. nov. (paratype, MN 4791-V). Detail of the skull and first rows of scales. A, Photograph; B, line drawing ofA. Scale bar equals 2 cm.

Orbital Bones The circumorbital series is incompletelypreserved in both specimens. However, the series seems to beentire as in all species of Lepidotes other than L. lennieri(Wenz, 1967; Olsen and McCune, 1991) and L. tendaguruensis(Arratia and Schultze, 1999), consisting of supraorbitals, der-mosphenotic, and infraorbitals.

There are two articulated quadrangular supraorbitals (Fig. 4).The contact between the first supraorbital and the infraorbitalseries could not be observed; the dorsal part of these bonesruns along the border of the frontals, and the posterior supra-orbital contacts the dermosphenotic.

The dermosphenotic (Fig. 4) is a large trapezoidal bone thatforms the posterodorsal angle of the orbit. It contacts the frontaldorsally, the dermopterotic and the postorbital posteriorly, and

an infraorbital ventrally. Unlike in Araripelepidotes, the der-mosphenotic does not separate the frontal from the dermopter-otic, and the parietal does not contact the dermosphenotic. Thejunction of the infraorbital and supraorbital sensory canalsseems to be near the anteroventral portion of the dermopterotic.

The total number of infraorbital elements cannot be deter-mined. However at least two infraorbitals are visible on theholotype (Fig. 4). They are small, rectangular elements and bearthe infraorbital canal.

The sclerotic ring is not preserved.Cheek Dermal Bones The posterior cheek region is com-

pletely closed with two postorbital plates and the preopercle(Fig. 4).

At least two large, anamestic postorbital plates (Fig. 4) are

51BRITO AND GALLO—NEW SEMIONOTID FROM THE SANTANA FORMATION

present, lying along the anterior edge of the preopercle. Thepreopercle (Figs. 4, 6) is a narrow and crescent-shaped bone,tightly articulated with the opercular bones. The preopercularsensory canal runs the entire length of this bone and some largepores occur along its anterior edge. The dorsal edge of the preo-percle contacts the dermopterotic, where the preopercular canalcommunicates with the supratemporal canal.

Opercular Series This series consists of three bones: theopercle, the subopercle, and the interopercle (Figs. 4, 6).

The opercle (Figs. 4, 6) is almost twice as high as wide, andthe distal part has an anterior surface pointing rostrally anddownwards, upon which rests the subopercle. The anterior bor-der is straight, and partially covered by the preopercle. Its pos-terior border is strongly convex and widely overlaps the supra-cleithrum. The dorsal border reaches the dermal roof, whereasits ventral sinuous border abuts the subopercle.

The subopercle (Fig. 6) has a subtriangular shape and is lo-cated between the preopercle and the cleithrum. It has a shortanterodorsal process. The interopercle (Fig. 6) is triangular andits anterior tip runs toward the ventral tip of the preopercle.

Only four plate-like branchiostegal rays (Fig. 6) are pre-served in the paratype, the first one being the largest. They aresituated between the interopercle and the posterior angle of thesubopercle. As in all semionotiforms (sensu Olsen and Mc-Cune, 1991) there is no gular plate.

Neurocranium Although the braincase is not completelypreserved and only a few bones have been recognized in bothspecimens (Figs. 5, 6), the degree of fusion of the neurocranialbones found in L. wenzae is very similar to that described forL. gloriae (Thies, 1989) and Araripelepidotes temnurus (Wenzand Brito, 1996).

The orbitosphenoid (Fig. 5) is a median Y-shaped bone di-vided into two wings, which posteriorly surround the anteriorpart of the anterior fontanelle, forming an interorbital septum.A small fenestra is present in each wing of the posterodorsaledge of the bone, in a position similar to the passage for theanterior cerebral vein in Araripelepidotes temnurus. Both wingsare fused anteriorly along the midline, forming the passage forthe olfactory nerve (I). This bone is very similar to the orbi-tosphenoid described in A. temnurus (Wenz and Brito, 1996).

The autosphenotic (Fig. 6) is a pyramidal bone, with aspongy inner region, found near the postorbital process.

The exoccipital (Fig. 5) is massive. In internal view the im-pression of the posterior semicircular canal is clearly visible.The vagus foramen (X) is not preserved, although the bonepresents, on its posterolateral face, a series of small foraminathat probably mark the occipital nerves.

The small epiotic (Fig. 5) is formed by a head and a robustprocess twice as long as the head. Although Thies (1989) con-sidered the presence of two pockets in the epiotic as a putativeautapomorphy for Lepidotes, we could not observe these pock-ets in our material.

The parasphenoid (Fig. 5) is incomplete with only the ante-rior branch preserved, as well as part of the ascending processand the posterior edge of the bone. It appears to have been astout bone. It is laminated, with grooves for the foramina of thepseudobranchial efferent and internal carotid arteries as well asfor the spiracular canal. The tooth patch cannot be seen.

The vomer (Fig. 6) is not completely visible, but it appearsto be a median bone as in other adult Lepidotes. We countedat least five styliform vomerine teeth, which have distally ex-panded crowns set off by a constriction. At least one tooth isornamented with proximal striae.

Upper Jaw The upper jaw consists of a premaxilla andmaxilla (Figs. 4–6).

The premaxilla (Fig. 6) has a long nasal process and a shortanterior oral border. Due to its poor preservation only one sty-liform tooth can be seen along the oral border of the bone.

The maxilla (Figs. 4, 5) is a strong bone that ends, posteri-orly, just anterior to the orbit. Anteriorly each maxilla bears amedially directed articular process, which extends between thevomer and premaxilla. The anterior ventral edge of the bonebears at least eleven small teeth arranged in a single row. Theseteeth are sharp-edged, expanded at their distal extremity, andmore or less conical.

Lower Jaw Only the dentalosplenial and part of the an-gular (Fig. 6), and a probable coronoid are preserved.

The dentalosplenial (Fig. 6) is a strong bone forming themajor part of the lower jaw. This bone is characterized by astrong curvature in its postero-inferior region. The height of thedentalosplenial is constant along the dentigerous margin, thenexpanded posteriorly where it takes part in the coronoid pro-cess. As in other semionotids, excepting Araripelepidotes andPliodetes, this bone has a posterior apophysis extending alongthe ventral edge of the angular. The dentalosplenial bears atleast ten styliform teeth arranged in a single row.

The angular (Fig. 6) is a high bone that forms the postero-inferior edge of the lower jaw and also takes part in the coro-noid process. The contact between the dentalosplenial and theangular is sigmoidal.

A fragment of a probable coronoid is present in the paratype.It bears two or three robust teeth arranged in one row.

Two longitudinal sensory canals are present in the lower jaw(Fig. 6). The more dorsal opens through the pores on the an-terior half of the dentalosplenial and can be identified as theoral canal (sensu Thies, 1989); the ventral one reaches the an-gular and is here identified as the mandibular canal.

Suspensorium and Hyoid Arch The bones of these com-plexes are not in their natural positions; however, it is possibleto determine their original orientation.

The hyomandibula (Fig. 5) is a long, slender, axe-shapedbone, almost vertically oriented. The bone has an expandeddorsal and a narrow ventral extremity; the dorsal edge possessestwo well-developed, obliquely disposed articular heads. Dor-sally, there is a slightly accentuated hyomandibular fossa. Theopercular process is stout and ellipsoid. The dorsal one-third ispierced by the foramen for the hyomandibular branch of thefacial nerve (VII).

The metapterygoid (Fig. 5) is a complex bone, presentingtwo branches: a medial fan-shaped edge, and the anterior re-flected lamella, which are separated by a notch through whichpasses the trigeminal nerve (V).

The dermopalatine (Fig. 4) is disarticulated from the ptery-goid series. The bone is small, but stout and massive, and bearsa median tooth and two transverse rows of teeth. These teethhave a long base with an enlarged occlusal surface.

The anterior and posterior ceratohyals (Fig. 5) are disarticu-lated from each other. The anterior ceratohyal is long, laterallythinned, and hourglass-shaped, about three times as long aswide. The dorsal border is slightly concave whereas the ventralis slightly convex. The anterior end is not as high as the pos-terior one. The bone is devoid of fenestrae, but does present acanal for passage of the efferent hyoid artery, which extends tothe posterior ceratohyal. The posterior ceratohyal is nearlyround, having one third the length of the anterior ceratohyal.The interhyal is not preserved.

Branchial Apparatus Only the ceratobranchials (Fig. 5)are preserved from the branchial arch. They are three incom-plete, isolated, long, narrow, stick-shaped bones. Two of themexhibit a groove on their ventral surface, probably for the bran-chial arteries. Tooth plates are not preserved.

Pectoral Girdle The posttemporal, supracleithrum, cleith-rum, and post-cleithrum are preserved (Fig. 6).

The posttemporal (Fig. 6) is narrower than the extrascapularand subtriangular with a convex border; the supratemporal sen-sory canal runs along the bone’s ventral edge.

52 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 23, NO. 1, 2003

The supracleithrum (Figs. 4 and 6) is a smooth, triangularbone with a straight anterior and a convex posterior border. Itis bounded anteriorly by the posterior margin of the opercle. Itreaches the dorsal process of the cleithrum as well as contactingthe first scale of the lateral line.

The cleithrum (Fig. 4) is a well-developed crescent-shapedbone. Its vertical arm is shorter and narrower than the horizontalone. Although the horizontal arm is long, its anteroventral tipreaches just to the middle of the opercle and subopercle.

A series of three large postcleithra (Fig. 6) is preserved, withthe dorsalmost one larger than the other two.

Fins Only the pectoral, dorsal, and caudal fins are availablein the studied material (Figs. 2, 3).

The pectoral fin is low on the body. Its lepidotrichia articulatewith the distal radials. There are at least three basal fulcra andnine lepidotrichia. The dorsal fin is short, starting in the middlepart of the body just behind the dorsal scale row, and includesat least seven lepidotrichia. The caudal fin is not well preservedon any of our specimens; in MN 4791-V at least 14 lepidotri-chia and three epaxial fulcra were counted.

Scales The body of the fish is covered by slender ganoidscales (Figs. 1–3), which are smooth, without any kind of or-namentation, and show peg-and-socket articulations. The ante-rior scales are larger, strongly imbricate, and higher than long.Posteriorly, the scales become diamond-shaped, and in the cau-dal peduncle they are shorter. The median dorsal scales aremodified, forming a slightly pronounced crest. The scales of thelateral line are readily recognized by the presence of a well-marked notch on their posterior portion.

The scales are arranged in transverse rows in an anterodorsal/posteroventral direction. Due to the torsion of the caudal fin inthe paratype, the exact number of rows cannot be determined.There are at least 28 rows of scales, extending from the pos-terior border of the supracleithrum to the posterior part of thedorsal fin.

DISCUSSION AND CONCLUSIONS

Although the monophyletic condition of the semionotidsseems to be widely accepted (Olsen and McCune, 1991; Arratiaand Schultze, 1999), the interrelationships of its genera as wellas the exact taxonomic position of some species are in need ofmuch work. ‘‘Lepidotes’’ is a paraphyletic or polyphyletic tax-on, and cannot be diagnosed by any synapomorphy. It is cur-rently defined either by primitive characters, or by charactersnot present in all the species of the genus such as presence ofa single median vomer, more than one postorbital plate, den-talosplenial with a long posterior process, two pockets in theepiotic, and dorsal ridge scales lacking a posterior spine (for adiscussion see Thies, 1989).

The following combination of characters allows assignmentof the new taxon to the genus Lepidotes: at least two postorbitalplates (only one plate is found in Semionotus and Paralepido-tus, while there are three plates in Araripelepidotes and a mo-saic of plates in Pliodetes), a predorsal elevation (not found inAraripelepidotes and Pliodetes), styliform marginal teeth andmore robust internal teeth, and conspicuous scales along themedian dorsal line (also found in Semionotus and Pliodetes).

We have compared Lepidotes wenzae with nine WesternGondwanian semionotids: the distinct taxa Araripelepidotestemnurus (from the same locality as L. wenzae) and Pliodetesnigeriensis (from the Lower Cretaceous of Gadoufaoua, NigerRepublic), as well as with seven other nominal species of Lep-idotes from the Mesozoic of Brazil (the almost complete Lep-idotes piauhyensis from the Parnaıba basin, L. roxoi and L.souzai from the Reconcavo basin, the fragmentary taxa L. llew-ellyni, L. mawsoni, and L. oliveirai from the Reconcavo basin,and L. dixseptiensis from the Potiguar basin).

Lepidotes wenzae mainly differs from Pliodetes nigeriensisand Araripelepidotes temnurus in the presence of a coronoidprocess, a toothed maxilla, and the predorsal elevation (seeMaisey, 1991; Thies, 1996; Wenz and Brito, 1996; Wenz,1999).

Lepidotes wenzae is readily distinguished from Lepidotesroxoi, L. souzai, and L. llewellyni by its smooth squamation. Inthese three other taxa the scales are thicker and ornamentedwith longitudinal, parallel ridges. L. wenzae also differs fromL. roxoi and L. souzai in the number and arrangement of post-orbital plates (two postorbital plates disposed in a single rowin L. wenzae, versus numerous plates disposed in more thanone row in the other forms) (Woodward, 1908; Santos, 1953;Jain and Robinson, 1963).

Lepidotes wenzae differs from L. piauhyensis in the outlineof the predorsal elevation (moderate in L. wenzae versus veryaccentuated in L. piauhyensis) and the shape of the hyoman-dibular (axe-shaped in L. wenzae and stout in L. piauhyensis).On the other hand, among the other Brazilian Lepidotes, L.wenzae shares the presence of one pair of extrascapulars andthe shape of the opercle only with L. piauhyensis (Gallo-da-Silva, 1998).

Lepidotes oliveirai and L. dixseptiensis are known only bydisarticulated scales. Although these scales are morphologicallysimilar to those of L. wenzae, these taxa are primarily knownfrom non-marine deposits of, respectively, Wealden and UpperCretaceous age.

Lepidotes wenzae presents a combination of characters dif-ferentiating it from all the other Western Gondwanan species:presence of a moderate predorsal elevation, length of the skullabout 33% of the length of the postcranial skeleton, dermalbones each ornamented with several conspicuous tubercles ofganoine, single pair of extrascapulars sutured together along themidline, subopercle with short anterodorsal process, opercle al-most twice as high as wide, three postcleithra, strong andtoothed maxilla, two longitudinal sensory canals in the lowerjaw, axe-shaped hyomandibula, and slender ganoid scales with-out ornamentation.

ACKNOWLEDGMENTS

We are most grateful to Sylvie Wenz (Museum nationald’Histoire naturelle, Paris), who encouraged one of us (PMB)to study the specimen housed in the Paris Museum. The man-uscript was improved by review and suggestions by LanceGrande (Field Museum of Natural History), Detlev Thies (Uni-versity of Hannover), David Martill (Portsmouth University),and an anonymous referee. For the loan of the specimens andfacilities we are grateful to H. Lelievre and D. Gouget (Museumnational d’Histoire naturelle, Paris), and A. W. A. Kellner andS. A. Azevedo (Museu Nacional, Rio de Janeiro). The photo-graph of the holotype was made by D. Serrette. PMB has aresearch fellowship grant from the CNPq (Brazilian FederalGovernment) and PMG and VG have a research fellowshipgrant from the UERJ/FAPERJ (Rio de Janeiro State Govern-ment).

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Received 2 March 2000; accepted 8 May 2002.