Journal of Vertebrate Paleontology 23(1):47–53, March 2003 q 2003 by the Society of Vertebrate Paleontology
A NEW SPECIES OF LEPIDOTES (NEOPTERYGII: SEMIONOTIFORMES: SEMIONOTIDAE) FROM THE SANTANA FORMATION, LOWER CRETACEOUS OF NORTHEASTERN BRAZIL ´ RIA GALLO PAULO M. BRITO and VALE Departamento de Biologia Animal e Vegetal, Universidade do Estado do Rio de Janeiro, Rua Sa˜o 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 ?Albian Romualdo Member of the Santana Formation, in the Araripe Basin, northeast Brazil. The new species differs from the other species of Lepidotes previously recorded in western Gondwanaland by the apomorphic presence of an axe-shaped hyomandibula, and by a unique combination of other characters. This is the first record of an articulated Lepidotes from the Santana Formation of the Araripe Basin.
were acid or mechanically prepared. These specimens are listed in Gallo-da-Silva (1998). Anatomical Abbreviations ACH, anterior ceratohyal; ANG, angular; AO, antorbital; ?a.pr.PSPH, ascending process of parasphenoid; ASPH, autosphenotic; BR, branchiostegal rays; CBR, ceratobranchial; CL, cleithrum; DPAL, dermopalatine; DPT, dermopterotic; DSPH, dermosphenotic; DSPL, dentalosplenial; EPI, epiotic; EXO, exoccipital; EXSC, extrascapular; FR, frontal; HYM, hyomandibula; IO, infraorbital; IOP, interopercle; md.s.c., mandibular sensory canal; MTP, metapterygoid; MX, maxilla; OP, opercle; op.pr.HYM, opercular process of hyomandibula; or.s.c., oral sensory canal; OSPH, orbitosphenoid; PA, parietal; PCH, posterior ceratohyal; PCL, postcleithrum; PMX, premaxilla; PO, postorbital; POP, preopercle; PRO, prootic; PSPH, parasphenoid; PT, posttemporal; RO, rostral; SCL, supracleithrum; SO, supraorbitals; SOP, subopercle; VO, vomer.
INTRODUCTION The family Semionotidae is a highly diverse group of Mesozoic Neopterygii, with a world-wide distribution and confirmed temporal range from the Middle Triassic to the Late Cretaceous. Several obstacles have hindered cladistic analysis of the Semionotidae and their relatives. Firstly, many members of this group are poorly preserved or are known only from isolated bones, teeth and scales; secondly, the anatomy of the internal bones of many semionotid taxa (such as the majority of Brazilian Early Cretaceous forms) is virtually unknown due to their mode of fossilization; and thirdly, not unexpectedly there is little or no ontogenetic data. A further problem is the absence of a convincing close outgroup for a conclusive phylogenetic analysis. The aim of this contribution is to describe a new species of Semionotidae collected from the Romualdo Member of the Santana Formation (Early Cretaceous, ?Albian), northeastern Brazil, and to provide additional comments on other semionotids from western Gondwana. Previous records of semionotids in this basin include Araripelepidotes temnurus from the Santana (Agassiz, 1841; Santos, 1990) and Crato formations (Brito et al., 1998), disarticulated remains of a large-sized cf. Lepidotes (Brito et al., 1994), and an isolated scale of Semionotidae (Gallo-da-Silva and Azevedo, 1996) from the Neocomian Missa˜o Velha/Brejo Santo formations. The Santana Formation is one of the most important Cretaceous fossil vertebrate localities, yielding a diverse well-preserved fish fauna including chondrichthyans, actinopterygians and coelacanths (Santos and Valenc¸a, 1968; Wenz and Brito, 1990; Maisey, 1991), as well as turtles, dinosaurs, pterosaurs, and crocodiles (Kellner, 1998).
SYSTEMATIC PALEONTOLOGY Infraclass NEOPTERYGII Regan, 1923 Order SEMIONOTIFORMES Arambourg and Bertin, 1958 Family SEMIONOTIDAE sensu Olsen and McCune, 1991 Genus LEPIDOTES Agassiz, 1832 LEPIDOTES WENZAE, sp. nov. (Figs. 1–6) Diagnosis Medium-sized Lepidotes with moderate predorsal elevation; length of the skull about 33% of length of the postcranial skeleton; dermal bones each ornamented with several conspicuous tubercles of ganoine; single pair of extrascapulars; extrascapulars sutured together along sagittal plane; subopercle with short anterodorsal process; opercle almost twice as high as wide; three postcleithra; strong and toothed maxilla; lower jaw with two longitudinal sensory canals; axe-shaped hyomandibula; scales without ornamentation. Holotype MNHN-BCE 387, a partial specimen from the Romualdo Member, Santana Formation, lacking the rostral part of the skull, as well as the posterior portion of the body and the paired and unpaired fins (Fig. 1). Paratype MN 4791-V, a semi-complete specimen, from the same geological unit, lacking part of the dermal bones and the pectoral, pelvic and anal fins (Fig. 2). Etymology Specific name in honor of Dr. Sylvie Wenz.
MATERIAL AND METHODS The present study is based on three partial specimens, housed, respectively, in the Laboratoire de Pale´ontologie, Museum national d’Histoire naturelle (MNHN-BCE 387; Fig. 1), Museu Nacional/UFRJ (MN 4791-V; Fig. 2) and Universidade do Estado do Rio de Janeiro (UERJ.PMB-VP80; Fig. 3). Due to the state of preservation of this last specimen, it is provisionally attributed to the new species. The holotype was collected in the early 1960’s and misidentified as an Araripelepidotes temnurus. Specimen MN 4791-V has been acid prepared using the transfer technique of Toombs and Rixon (1959). The other semionotids used for comparison
DESCRIPTION All measurements are taken from specimen MN 4791-V (Fig. 2). The head measures 96 mm from the anteriormost point of
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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.
BRITO AND GALLO—NEW SEMIONOTID FROM THE SANTANA FORMATION
FIGURE 3. Lepidotes cf. L. wenzae (UERJ.PMB-VP80). Scale bar equals 2 cm.
the skull to the posterior border of the opercle. The length of the cranium is approximately 33% that of the postcranial skeleton. The standard length of the specimen is estimated to be 330 mm, but this may be off slightly due to the torsion of the caudal fin. All dermal bones are ornamented by several conspicuous ganoine tubercles. Rostral Bones Only the antorbital and the rostral are preserved. The antorbitals (Fig. 6) are tubular, boomerang-shaped bones (sensu Thies, 1989). Their anterior arms and the lateral arms of the rostral form an ossified tube complex for enclosure of the anteriormost part of the lateral-line sensory system. These bones partially surround both the nasal process and the toothbearing part of the premaxilla, and do not contact the frontals.
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This pattern is found in the majority of the semionotids, but is unknown in Araripelepidotes. Dermal Skull The anteriormost part of the skull roof is only partially preserved in both examined specimens (Fig. 4). The frontals (Fig. 4) are the longest elements of the dermal skull, having a length approximately three times that of the parietals, and extending from the rostral bone posteriorly to the parietals and dermopterotics. They have an ornamentation of conspicuous tubercles of ganoine. The frontals are almost equal in width throughout their length, with a constriction over the orbit. The suture between the frontals is almost straight, with very few interdigitations. The supraorbital sensory canal runs longitudinally, close to the lateral margin of the bone. The parietals (Fig. 4) are subrectangular and well-developed, slightly longer than wide, asymmetrical, and joined together along the cranial midline through a straight suture. The suture with the frontals is sinuous. The lateral borders of the parietals are almost linear and overlay the dermopterotics. The sensory canal reaches the anterior half of the bone. Pit-lines cannot be observed. The dermopterotics (Fig. 4) are subrectangular, twice as long as wide, and contact the frontals and the dermosphenotics anteriorly, a character found in all semionotids except Araripelepidotes (Maisey, 1991). The infraorbital canal runs laterally through 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 the same size as the dermopterotics. The extrascapulars articulate anteriorly with the parietals and the dermopterotics, and posteriorly with the posttemporal. Their lateral borders are convex and overlap the opercle. The extrascapulars completely enclose the occipital sensory canal, which is oriented transversely in the posterior third of these bones. An extension of the supratemporal sensory canal runs longitudinally close to the distal margin of the extrascapulars.
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.
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FIGURE 5. Lepidotes wenzae, sp. nov. (holotype, MNHN-BCE 387). Skull in ventral view. A, Photograph; B, line drawing of A. Scale bar equals 3 cm.
Orbital Bones The circumorbital series is incompletely preserved in both specimens. However, the series seems to be entire 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, dermosphenotic, and infraorbitals. There are two articulated quadrangular supraorbitals (Fig. 4). The contact between the first supraorbital and the infraorbital series could not be observed; the dorsal part of these bones runs along the border of the frontals, and the posterior supraorbital contacts the dermosphenotic. The dermosphenotic (Fig. 4) is a large trapezoidal bone that forms the posterodorsal angle of the orbit. It contacts the frontal dorsally, the dermopterotic and the postorbital posteriorly, and
an infraorbital ventrally. Unlike in Araripelepidotes, the dermosphenotic does not separate the frontal from the dermopterotic, and the parietal does not contact the dermosphenotic. The junction of the infraorbital and supraorbital sensory canals seems to be near the anteroventral portion of the dermopterotic. The total number of infraorbital elements cannot be determined. However at least two infraorbitals are visible on the holotype (Fig. 4). They are small, rectangular elements and bear the infraorbital canal. The sclerotic ring is not preserved. Cheek Dermal Bones The posterior cheek region is completely closed with two postorbital plates and the preopercle (Fig. 4). At least two large, anamestic postorbital plates (Fig. 4) are
FIGURE 6. Lepidotes wenzae, sp. nov. (paratype, MN 4791-V). Detail of the skull and first rows of scales. A, Photograph; B, line drawing of A. Scale bar equals 2 cm.
BRITO AND GALLO—NEW SEMIONOTID FROM THE SANTANA FORMATION present, lying along the anterior edge of the preopercle. The preopercle (Figs. 4, 6) is a narrow and crescent-shaped bone, tightly articulated with the opercular bones. The preopercular sensory canal runs the entire length of this bone and some large pores occur along its anterior edge. The dorsal edge of the preopercle contacts the dermopterotic, where the preopercular canal communicates with the supratemporal canal. Opercular Series This series consists of three bones: the opercle, the subopercle, and the interopercle (Figs. 4, 6). The opercle (Figs. 4, 6) is almost twice as high as wide, and the distal part has an anterior surface pointing rostrally and downwards, upon which rests the subopercle. The anterior border is straight, and partially covered by the preopercle. Its posterior border is strongly convex and widely overlaps the supracleithrum. The dorsal border reaches the dermal roof, whereas its ventral sinuous border abuts the subopercle. The subopercle (Fig. 6) has a subtriangular shape and is located between the preopercle and the cleithrum. It has a short anterodorsal process. The interopercle (Fig. 6) is triangular and its anterior tip runs toward the ventral tip of the preopercle. Only four plate-like branchiostegal rays (Fig. 6) are preserved in the paratype, the first one being the largest. They are situated between the interopercle and the posterior angle of the subopercle. As in all semionotiforms (sensu Olsen and McCune, 1991) there is no gular plate. Neurocranium Although the braincase is not completely preserved and only a few bones have been recognized in both specimens (Figs. 5, 6), the degree of fusion of the neurocranial bones found in L. wenzae is very similar to that described for L. gloriae (Thies, 1989) and Araripelepidotes temnurus (Wenz and Brito, 1996). The orbitosphenoid (Fig. 5) is a median Y-shaped bone divided into two wings, which posteriorly surround the anterior part of the anterior fontanelle, forming an interorbital septum. A small fenestra is present in each wing of the posterodorsal edge of the bone, in a position similar to the passage for the anterior cerebral vein in Araripelepidotes temnurus. Both wings are fused anteriorly along the midline, forming the passage for the olfactory nerve (I). This bone is very similar to the orbitosphenoid described in A. temnurus (Wenz and Brito, 1996). The autosphenotic (Fig. 6) is a pyramidal bone, with a spongy inner region, found near the postorbital process. The exoccipital (Fig. 5) is massive. In internal view the impression of the posterior semicircular canal is clearly visible. The vagus foramen (X) is not preserved, although the bone presents, on its posterolateral face, a series of small foramina that probably mark the occipital nerves. The small epiotic (Fig. 5) is formed by a head and a robust process twice as long as the head. Although Thies (1989) considered the presence of two pockets in the epiotic as a putative autapomorphy for Lepidotes, we could not observe these pockets in our material. The parasphenoid (Fig. 5) is incomplete with only the anterior branch preserved, as well as part of the ascending process and the posterior edge of the bone. It appears to have been a stout bone. It is laminated, with grooves for the foramina of the pseudobranchial efferent and internal carotid arteries as well as for the spiracular canal. The tooth patch cannot be seen. The vomer (Fig. 6) is not completely visible, but it appears to be a median bone as in other adult Lepidotes. We counted at least five styliform vomerine teeth, which have distally expanded crowns set off by a constriction. At least one tooth is ornamented with proximal striae. Upper Jaw The upper jaw consists of a premaxilla and maxilla (Figs. 4–6). The premaxilla (Fig. 6) has a long nasal process and a short anterior oral border. Due to its poor preservation only one styliform tooth can be seen along the oral border of the bone.
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The maxilla (Figs. 4, 5) is a strong bone that ends, posteriorly, just anterior to the orbit. Anteriorly each maxilla bears a medially directed articular process, which extends between the vomer and premaxilla. The anterior ventral edge of the bone bears at least eleven small teeth arranged in a single row. These teeth are sharp-edged, expanded at their distal extremity, and more or less conical. Lower Jaw Only the dentalosplenial and part of the angular (Fig. 6), and a probable coronoid are preserved. The dentalosplenial (Fig. 6) is a strong bone forming the major part of the lower jaw. This bone is characterized by a strong curvature in its postero-inferior region. The height of the dentalosplenial is constant along the dentigerous margin, then expanded posteriorly where it takes part in the coronoid process. As in other semionotids, excepting Araripelepidotes and Pliodetes, this bone has a posterior apophysis extending along the ventral edge of the angular. The dentalosplenial bears at least ten styliform teeth arranged in a single row. The angular (Fig. 6) is a high bone that forms the posteroinferior edge of the lower jaw and also takes part in the coronoid process. The contact between the dentalosplenial and the angular 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 anterior half of the dentalosplenial and can be identified as the oral canal (sensu Thies, 1989); the ventral one reaches the angular and is here identified as the mandibular canal. Suspensorium and Hyoid Arch The bones of these complexes are not in their natural positions; however, it is possible to determine their original orientation. The hyomandibula (Fig. 5) is a long, slender, axe-shaped bone, almost vertically oriented. The bone has an expanded dorsal and a narrow ventral extremity; the dorsal edge possesses two well-developed, obliquely disposed articular heads. Dorsally, there is a slightly accentuated hyomandibular fossa. The opercular process is stout and ellipsoid. The dorsal one-third is pierced by the foramen for the hyomandibular branch of the facial nerve (VII). The metapterygoid (Fig. 5) is a complex bone, presenting two branches: a medial fan-shaped edge, and the anterior reflected lamella, which are separated by a notch through which passes the trigeminal nerve (V). The dermopalatine (Fig. 4) is disarticulated from the pterygoid series. The bone is small, but stout and massive, and bears a median tooth and two transverse rows of teeth. These teeth have a long base with an enlarged occlusal surface. The anterior and posterior ceratohyals (Fig. 5) are disarticulated from each other. The anterior ceratohyal is long, laterally thinned, and hourglass-shaped, about three times as long as wide. The dorsal border is slightly concave whereas the ventral is slightly convex. The anterior end is not as high as the posterior one. The bone is devoid of fenestrae, but does present a canal for passage of the efferent hyoid artery, which extends to the posterior ceratohyal. The posterior ceratohyal is nearly round, 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 incomplete, isolated, long, narrow, stick-shaped bones. Two of them exhibit a groove on their ventral surface, probably for the branchial arteries. Tooth plates are not preserved. Pectoral Girdle The posttemporal, supracleithrum, cleithrum, and post-cleithrum are preserved (Fig. 6). The posttemporal (Fig. 6) is narrower than the extrascapular and subtriangular with a convex border; the supratemporal sensory canal runs along the bone’s ventral edge.
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The supracleithrum (Figs. 4 and 6) is a smooth, triangular bone with a straight anterior and a convex posterior border. It is bounded anteriorly by the posterior margin of the opercle. It reaches the dorsal process of the cleithrum as well as contacting the first scale of the lateral line. The cleithrum (Fig. 4) is a well-developed crescent-shaped bone. Its vertical arm is shorter and narrower than the horizontal one. Although the horizontal arm is long, its anteroventral tip reaches just to the middle of the opercle and subopercle. A series of three large postcleithra (Fig. 6) is preserved, with the dorsalmost one larger than the other two. Fins Only the pectoral, dorsal, and caudal fins are available in the studied material (Figs. 2, 3). The pectoral fin is low on the body. Its lepidotrichia articulate with the distal radials. There are at least three basal fulcra and nine lepidotrichia. The dorsal fin is short, starting in the middle part of the body just behind the dorsal scale row, and includes at least seven lepidotrichia. The caudal fin is not well preserved on any of our specimens; in MN 4791-V at least 14 lepidotrichia and three epaxial fulcra were counted. Scales The body of the fish is covered by slender ganoid scales (Figs. 1–3), which are smooth, without any kind of ornamentation, and show peg-and-socket articulations. The anterior scales are larger, strongly imbricate, and higher than long. Posteriorly, the scales become diamond-shaped, and in the caudal peduncle they are shorter. The median dorsal scales are modified, forming a slightly pronounced crest. The scales of the lateral line are readily recognized by the presence of a wellmarked 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 in the paratype, the exact number of rows cannot be determined. There are at least 28 rows of scales, extending from the posterior border of the supracleithrum to the posterior part of the dorsal fin. DISCUSSION AND CONCLUSIONS Although the monophyletic condition of the semionotids seems to be widely accepted (Olsen and McCune, 1991; Arratia and Schultze, 1999), the interrelationships of its genera as well as the exact taxonomic position of some species are in need of much work. ‘‘Lepidotes’’ is a paraphyletic or polyphyletic taxon, and cannot be diagnosed by any synapomorphy. It is currently defined either by primitive characters, or by characters not present in all the species of the genus such as presence of a single median vomer, more than one postorbital plate, dentalosplenial with a long posterior process, two pockets in the epiotic, and dorsal ridge scales lacking a posterior spine (for a discussion see Thies, 1989). The following combination of characters allows assignment of the new taxon to the genus Lepidotes: at least two postorbital plates (only one plate is found in Semionotus and Paralepidotus, while there are three plates in Araripelepidotes and a mosaic of plates in Pliodetes), a predorsal elevation (not found in Araripelepidotes and Pliodetes), styliform marginal teeth and more robust internal teeth, and conspicuous scales along the median dorsal line (also found in Semionotus and Pliodetes). We have compared Lepidotes wenzae with nine Western Gondwanian semionotids: the distinct taxa Araripelepidotes temnurus (from the same locality as L. wenzae) and Pliodetes nigeriensis (from the Lower Cretaceous of Gadoufaoua, Niger Republic), as well as with seven other nominal species of Lepidotes from the Mesozoic of Brazil (the almost complete Lepidotes piauhyensis from the Parnaı´ba basin, L. roxoi and L. souzai from the Recoˆncavo basin, the fragmentary taxa L. llewellyni, L. mawsoni, and L. oliveirai from the Recoˆncavo basin, and L. dixseptiensis from the Potiguar basin).
Lepidotes wenzae mainly differs from Pliodetes nigeriensis and Araripelepidotes temnurus in the presence of a coronoid process, a toothed maxilla, and the predorsal elevation (see Maisey, 1991; Thies, 1996; Wenz and Brito, 1996; Wenz, 1999). Lepidotes wenzae is readily distinguished from Lepidotes roxoi, L. souzai, and L. llewellyni by its smooth squamation. In these three other taxa the scales are thicker and ornamented with longitudinal, parallel ridges. L. wenzae also differs from L. roxoi and L. souzai in the number and arrangement of postorbital plates (two postorbital plates disposed in a single row in L. wenzae, versus numerous plates disposed in more than one row in the other forms) (Woodward, 1908; Santos, 1953; Jain and Robinson, 1963). Lepidotes wenzae differs from L. piauhyensis in the outline of the predorsal elevation (moderate in L. wenzae versus very accentuated in L. piauhyensis) and the shape of the hyomandibular (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 and the shape of the opercle only with L. piauhyensis (Gallo-daSilva, 1998). Lepidotes oliveirai and L. dixseptiensis are known only by disarticulated scales. Although these scales are morphologically similar to those of L. wenzae, these taxa are primarily known from non-marine deposits of, respectively, Wealden and Upper Cretaceous age. Lepidotes wenzae presents a combination of characters differentiating it from all the other Western Gondwanan species: presence of a moderate predorsal elevation, length of the skull about 33% of the length of the postcranial skeleton, dermal bones each ornamented with several conspicuous tubercles of ganoine, single pair of extrascapulars sutured together along the midline, subopercle with short anterodorsal process, opercle almost twice as high as wide, three postcleithra, strong and toothed maxilla, two longitudinal sensory canals in the lower jaw, axe-shaped hyomandibula, and slender ganoid scales without ornamentation. ACKNOWLEDGMENTS We are most grateful to Sylvie Wenz (Museum national d’Histoire naturelle, Paris), who encouraged one of us (PMB) to study the specimen housed in the Paris Museum. The manuscript was improved by review and suggestions by Lance Grande (Field Museum of Natural History), Detlev Thies (University of Hannover), David Martill (Portsmouth University), and an anonymous referee. For the loan of the specimens and facilities we are grateful to H. Lelie`vre and D. Gouget (Museum national d’Histoire naturelle, Paris), and A. W. A. Kellner and S. A. Azevedo (Museu Nacional, Rio de Janeiro). The photograph of the holotype was made by D. Serrette. PMB has a research fellowship grant from the CNPq (Brazilian Federal Government) and PMG and VG have a research fellowship grant from the UERJ/FAPERJ (Rio de Janeiro State Government). LITERATURE CITED Agassiz, L. R. 1832. Untersuchungen u¨ber die fossilen Fische der LiasFormation. Neues Jahrbuch fu¨r Mineralogie, Geognosie, Geologie und Petrefaktenkunde 3:139–149. ——— 1841. On the fossil fishes found by Mr. Gardner in the Province of Ceara´, in the North of Brazil. Edinburg New Philosophical Journal 30:82–84. Arambourg, C., and L. Bertin. 1958. Super-ordre des Holoste´ens et des Halecostomi (Holostei et Halecostomi); pp. 2173–2203 in P.-P. Grasse´ (ed.), Traite´ de Zoologie: Anatomie, syste´matique, biologie, 13. Masson et Cie, Paris. Arratia, G., and H.-P. Schultze. 1999. Semionotiform fish from the Up-
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