Phylogenetic Relationships of the Families , , , and Ghilodontidae (Pisces: )

RICHARD P. VARI

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 378 SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION

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S. Dillon Ripley Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 378

Phylogenetic Relationships of the Families Curimatidae, Prochilodontidae, Anostomidae, and (Pisces: Characiformes)

Richard P. Vari

SMITHSONIAN INSTITUTION PRESS City of Washington 1983 ABSTRACT Vari, Richard P. Phylogenetic Relationships of the Families Curimatidae, Prochilodontidae, Anostomidae, and Chilodontidae (Pisces: Characi- formes). Smithsonian Contributions to Zoology, number 378, 60 pages, 41 figures, 1 table, 1983.—A series of osteological and soft anatomical systems in the families Curimatidae, Prochilodontidae, Anostomidae, and Chilodontidae were examined to reconstruct the phylogenetic relationships of these taxa and determine whether they are a monophyletic assemblage. Numerous adapta- tions associated with the food gathering and manipulation systems along with those in other portions of the body provided data useful in the reconstruction of the phylogenetic relationships of these taxa. The evidence of this study is congruent with the hypothesis that the four families constitute a monophyletic assemblage definable by shared derived characters. Results of the analysis indicate that the Curimatidae and Prochilodontidae are most parsimoniously interpreted to be sister groups. The assemblage formed by those two families is considered to be the sister group of the monophyletic lineage that consists of the Anostomidae and Chilodontidae. Synapomorphies define the members of each family as monophyletic units. The well-developed epibranchial organs in the Chilodontidae, Citharinidae, and the Curimatidae plus Prochilodontidae, were found to represent three distinct, nonhomologous kinds of pharyngeal outpocketings. The most parsi- monious interpretation of those data and other available information on ostariophysan phylogeny is that such diverticuli have been acquired several times independently among characiforms and their near relatives. This con- clusion agrees with the hypothesis proposed by Nelson (1967) but indicates that Bertmar, Kapoor, and Miller's concept (1969) of epibranchial organs as the ancestral condition for teleosts is not parsimonious, at least when applied to ostariophysan fishes.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavemosa (Linnaeus).

Library of Congress Cataloging in Publication Data Vari, Richard P. Phylogenetic relationships of the families Curimatidae, Prochilodontidae, Anostomidae, and Chilodontidae (Pisces, Characiformes) (Smithsonian contributions to zoology ; no. 378) Bibliography: p. Supt. of Docs, no.: SI 1.27:378 1. Curimatidae—Classification. 2. Prochilodontidae—Classification. 3. Anostomidae—Clas- sification. 4. Chilodontidae—Classification. 5. Fishes—Classification. 6. Fishes—Latin America—Classification. I. Title. II. Series. QL1.S54 no. 378 [QL638.C89] 591s [597'.53] 82-600338 Contents

Page Introduction 1 Acknowledgments 3 Systematic Procedures 3 Methods and Materials 4 Terminology 6 Abbreviations 6 Character Description and Analysis 7 Teeth and Jaws 7 Gill Arches 11 Epibranchial Organs 21 Hyoid Apparatus 24 Suspensorium and Circumorbital Series 25 Pectoral Girdle 33 Neurocranium 36 Vertebral Column and Ribs 41 Myology 42 Phylogenetic Reconstruction 46 The Four-Family Assemblage 46 Curimatidae and Prochilodontidae 47 Family Curimatidae 48 Family Prochilodontidae 49 Anostomidae and Chilodontidae Clade 50 Family Anostomidae 50 Family Chilodontidae 51 Discussion 52 Comparisons with Previous Classifications 54 Resumen 56 Literature Cited 58

in

Phylogenetic Relationships of the Families Curimatidae, Prochilodontidae, Anostomidae, and Chilodontidae (Pisces: Characiformes)

Richard P. Vari

Introduction tive analysis of phylogenetic relationships within that family necessitated the recognition of an The Curimatidae, Prochilodontidae, Anostom- appropriate outgroup, thereby allowing the po- idae, and Chilodontidae form a speciose, morpho- larization of intrafamilial character variation. A logically diverse assemblage of characiform fishes prerequisite for the determination of the sister widely distributed in Neotropical freshwaters. group to curimatids was an explicit, corraborated Members of these families occur in the Atlantic hypothesis of the phylogenetic placement of cur- drainages of from northern Co- imatids within a taxonomically more encompass- lombia to the Rio Negro of and inhabit ing assemblage of characiforms. the rivers and streams of the Pacific drainages of Widely divergent opinions have been advanced the region from Puntarenas Province of Costa on the exact relationships of the Curimatidae to Rica south to central Peru. Curimatids, prochil- other characiforms (Table 1). Giinther (1864:288) odontids, anostomids, and chilodontids inhabit a united the then-known members of the Curima- broad variety of freshwater ecosystems ranging tidae (Curimatus), Prochilodontidae {Prochilodus), from stagnant ox-bow lakes through sluggish riv- Chilodontidae (), Hemiodontidae ers to rapidly flowing streams. In certain ecologi- (Hemiodus), and Parodontidae (Saccodon, Parodon) cal settings they represent a significant proportion (families Greenwood et al., 1966) in his of the fish biomass (Lowe-McConnell, 1975:109), suprageneric group Curimatina, and placed the and many members of these taxa are exploited described genera of the present day Anostomidae by commercial and subsistence fisheries through- (, , ) in the Anostoma- out the Neotropics (Lowe-McConnell, 1975:74; tina group. Boulenger (1904:576), in a significant Smith, 1981:140; Goulding, 1981:60). shift, incorporated the Neotropical curimatids The results reported in this paper are an out- (Curimatus) and prochilodontids (Prochilodus) into growth of phylogenetic and revisionary studies his subfamily Citharininae, together with the Old originally centered on the Curimatidae. An effec- World characiform genera Citharinus and Cithari- dium. His Anostominae included the present day Richard P. Vari, Department of Vertebrate Zoology, National Museumanostomids (Anostomus, Leporinus, Nanognathus of Natural History, Smithsonian Institution, Washington, D.C. 20560. [? = ]) and genera today considered SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

either characids {Characidium, Chorimycterus [= TABLE 1.—Classifications of the four-family assemblage Characidium]) or lebiasinids (Nanostomus [= Nan- discussed in the text nostomus]). The chilodontid taxa described at that time (Caenotropus with as a ) were Author Classification united by Boulenger in the Hemiodontidae to- Gunther, 1864 Curimatina group gether with various hemiodontids (Hemiodus) and Curimatus, Prochilodus, parodontids (Saccodon, Parodon). Regan (1911:20) Caenotropus, Hemiodus, Saccodon, Parodon rejected Boulenger's transatlantic grouping of Anostomatina group Neotropical curimatids and prochilodontids with Anostomus, Rhytiodus, Leporinus some Old World characiforms. Furthermore, he Boulenger, 1904 Characinidae [in part] disagreed with Giinther's recognition of a sepa- Citharininae rate solely for anostomoids and that au- Citharinus, Citharidium, Curimatus, Prochilodus thor's alignment of the chilodontids with hemio- Anostominae dontids. Rather, he incorporated the present day Anostomus, Leporinus, Curimatidae (Curimatus), Prochilodontidae (Pro- Characidium, Chorimycterus, chilodus), Anostomidae (Anostomus, Rhytiodus, Le- Nanostomus, Nanognathus porinus, ) and Chilodontidae (Caenotropus) Hemiodontinae in his family Anostomidae with the last two Caenotropus, Hemiodus, Saccodon, Parodon groups combined in his subfamily Anostominae. Regan, 1911 Anostomidae Gregory and Conrad (1938:347) followed Regan Curimatinae in considering these four families to be a single Curimatus, Anodus taxon, but at the subfamily level. Eigenmann Prochilodontinae (1917:38-39), in contrast, placed the Anostomi- Prochilodus Anostominae nae, Chilodinae, Prochilodinae, Hemiodontinae, Anostomus, Rhytiodus, Leporinus, Elopomorphinae, and Curimatinae (= the Anos- Leporellus, Caenotropus tomidae, Chilodontidae, Prochilodontidae, Hem- Gregory and Conrad, Anostominae (=Anostomidae of iodontidae, Anodinae, and Curimatidae of 1938 Regan, 1911) Greenwood et al., 1966) as "an offshoot of the Greenwood et al., Curimatidae, Prochilodontidae, 1966 Anostomidae, Chilodontidae Cheirodontinae" without any explicit comment Gery, 1977b Anostomidae on the relationships of the individual components. Anostominae Gery (1961:108) presented a dendrogram of his Schizodon, Leporinus, , hypothesized phytogeny of anostomids and their Rhytiodus, , Anosto- presumed relatives. That outgroup included cur- mus, , Sartor, imatids, prochilodontids, hemiodontids and lebi- Gnathodolus Leporellinae asinids but not chilodontids. However, exact con- Leporellus cepts of phylogenetic relationship cannot be re- Curimatidae trieved from Gery's figure (1961, fig. 24). More Chilodinae recently Gery (1977b:210) united curimatids, pro- Caenotropus, Chilodus chilodontids, chilodontids, and anodontines in his Prochilodinae Semaprochilodus, Prochilodus, family Curimatidae but retained a separate An- Ichthyoelephas ostomidae for anostomids (see Table 1 for in- Curimatinae cluded genera). No explicit statement on the Curimata, Curimatella, Curima- degree to which that classification reflects under- topsis lying phylogenetic concepts was provided, nor Anodinae Anodus were the characters that support this grouping of taxa discussed. NUMBER 378

The classifications summarized above gener- loan and exchange of specimens, information and ally were advanced without a discussion of the other assistance: D.E. Rosen and C.L. Smith, basis for the different groupings of taxa or with American Museum of Natural History; P.H. only a cursory presentation of the anatomical Greenwood and G.J. Howes, British Museum information underlying the taxonomic decisions (Natural History); N. Menezes, Museu do Zool- of the different authors. The absence of such data ogia, Universidad de Sao Paulo; and F. Mago made it impossible to determine the extent to Leccia and A. Machado Allison, Museo de Biol- which those classifications reflected phylogenetic ogia, Universidad Central de . I would rather than phenetic concepts. Thus, an evalua- like to thank G. J. Howes, A. Machado Allison tion of the relative merits of the classifications as and particularly S.H. Weitzman for spending phylogenetic indicators was difficult, if not im- many hours discussing questions of characiform possible. anatomy and phylogeny. This study was partially Roberts (1973:221) was the only author to supported by the Smithsonian Institution Neo- explicitly state his concepts on the relationships tropical Lowland Research Program. S.L. Jewett, of a subgroup of these four families and to detail J.R. Gomon, and K. Bruwelheide provided tech- the characters associated with his hypotheses. nical assistance, which facilitated various aspects Contrary to his predecessors, Roberts rejected the of the study. The comments and criticisms of S.H. hypothesis of a close phylogenetic relationship of Weitzman, J.C. Tyler, and R. Winterbottom con- the Curimatidae and Prochilodontidae. Rather tributed greatly to the improvement of this paper. he stated that "the evidence favoring relationship Antonio Machado Allison generously provided between Prochilodontidae and Anostomidae is the Spanish translation of the resumen. relatively strong. . . ." He did not, however, com- ment on what relationship he envisioned for cur- Systematic Procedures imatids relative to the lineage purportedly formed by those two families or propose an alternative The relationships of the Curimatidae, Prochil- sister group for the Curimatidae. odontidae, Anostomidae, and Chilodontidae are Curimatids have, therefore, been inconsistently analyzed using the methodology of phylogenetic associated with a broad range of Neotropical and reconstruction first formalized by Hennig (1950, Old World characiform groups. Similarly, hy- 1966). The goal of phylogenetic systematics (al- potheses on the relationships of prochilodontids, ternatively termed or cladism) is the anostomids, and chilodontids to each other and grouping of taxa in a series of nested units that characiform outgroups have differed in explicit- reflect the best estimate of the natural hierarchi- ness and inclusiveness. Furthermore, during the cal history of groups of organisms. century-old discussion on the relationships of Taxa are grouped on the basis of the possession these families, no phylogenetic hypothesis has of shared derived characters (synapomorphies), been put forward that uses criteria considered which are considered the ooly valid basis for acceptable in this study: the possession of shared hypotheses of common ancestry. Hypotheses of derived characters. The conjunction of these fac- relationship derived from the possession of shared tors made it impossible to evaluate which, if any, primitive characters (symplesiomorphies) and of the previous classifications was an accurate phylogenetic speculations based on concepts of representation of the phylogenetic history of cur- overall phenetic similarity or degrees of difference imatids and their close relatives. It was in an are either not useful tests of phylogenetic hy- attempt to resolve this question that this study potheses or incongruent with the aim of this was undertaken. study, that is, the advancement of hypotheses of ACKNOWLEDGMENTS.—I am greatly indebted to the phylogenetic histories of the taxa under ex- the following individuals and institutions for the amination. SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

In keeping with the general scientific principle conventional orientation if drawn from the right of parsimony, the hypothesis of the phylogenetic side of the specimen. Anatomical illustrations history of a group that necessitates the fewest ad were prepared using a Zeiss microscopic camera hoc assumptions about character transformations lucida. The osteological material and myological is preferred. Monophyletic groups consist of all preparations examined are deposited in the descendants of a common ancestor, exclusive of USNM collections of the National Museum of any not descended from that common Natural History, Smithsonian Institution; the ancestor. The traditional alternative definitions American Museum of Natural History (AMNH); of are of such generality as to include and Museo de Biologia, Universidad Central de all possible combinations of taxa or are dependent Venezuela (MBUCV). It was impossible to ex- on arbitrary taxonomic ranks, or both, and are, amine each character in all members of the as- therefore, often meaningless in application and semblage under discussion given the extremely information content. large number of species involved, the rarity of The polarity of character transformation series some nominal forms, and the myriad taxonomic (plesiomorphy vs apomorphy: primitive vs de- problems in this assemblage. A wide spectrum of rived) is determined by outgroup comparison or genera and species were examined, but it is pos- data from ontogenetic transformations. Outgroup sible that in some cases the hypothesized distri- comparisons to characiforms and if necessary bution of a character may differ from that noted other otophysan or ostariophysan groups were herein. used to determine the polarity of characters that The following specimens are the basis for illus- vary within the assemblage under examination. trations or observations noted in the text. (Meas- The ontogenetic and phylogenetic polarities are urement in mm is standard length (SL)). considered equivalent for any character that un- dergoes developmental changes in one of two CURIMATIDAE sister groups. The ontogenetically later stage in the transforming lineage is, therefore, considered Curimata cyprinoides (Linneaus), USNM 231433; 2 specimens, 17.5-21.7 mm; Surinam, Corantijn River. apomorphous relative to its homologue in the Curimata vitatta Kner, USNM 231434; 1 specimen, 81.7 mm; nontransforming group. This procedure is more , Rio Negro (Figures 5, 6, 15-17). parsimonious than assuming that the transition Curimatopsis evelynae Gery, USNM 214794; 4 specimens, 25.7- was primitively present in the common ancestor 34.9 mm; Brazil, Rio Negro. of both groups and was secondarily lost in one Curimatopsis macrolepis (Steindachner), USNM 231436; 1 lineage (detailed discussions of the theory behind, specimen, 51.3 mm; Peru. Curimatopsis macrolepis (Steindachner), USNM 190285; 1 and methods of application of, the above meth- specimen, 34.1 mm; Peru, Iquitos. odologies can be found in Nelson and Platnick, Potamorhina laticeps (Valenciennes), USNM 121325; 1 speci- 1981, and Wiley, 1981). men, 129.3 mm; Venezuela, Lake Maracaibo Basin (Fig- ures 1, 2, 25). Potamorhina latior (Spix), AMNH 48677; 1 specimen, 73.1 Methods and Materials mm; Bolivia, Rio Mamore (Figure 27). Psectrogaster amazonica Eigenmann and Eigenmann, AMNH Osteological and cartilaginous skeletal systems 40088SD; 1 specimen, 139.2 mm; Bolivia, Rio Guapore were examined in cleared and counterstained (Figures 7, 8, 33, 35). specimens prepared in a modified version of the alizarin Red S-alcian blue method of Dingerkus PROCHILODONTIDAE and Uhler (1977). Previously cleared specimens hhthyoelephas species, USNM 231437; 1 specimen, 110.2 mm; stained solely in alizarin Red S, along with dry Ecuador (Figures 15, 28). skeletal materials, were supplemental sources of Prochilodus mgricans Agassiz, USNM 231438; 1 specimen, 144.3 mm; Bolivia, Tumpasa. osteological data. Drawings were reversed into Prochilodus rubrotaeniatus Schomburgk, USNM 225419; 1 spec- NUMBER 378

imen, 108.7 mm; Surinam, Corantijn River (Figures 1, 2, imens, 71.3-78.3 mm; Surinam, Corantijn River (Figures 22, 39, 40). 3,4, 13-15). Prochilodus species, USNM 231538; 3 specimens, 29.3-35.2 Camegiella strigata (Giinther), USNM 225245; 5 specimens, mm; Amazon River. 23.4-25.6 mm; Surinam, Corantijn River. Semaprochilodus taemurus (Steindachner), USNM 231536; 1 Chalceus macrolepidotus Cuvier, USNM 231547; 1 specimen, specimen, 74.7 mm; Brazil, Rio Negro, vicinity of Manaus 39.9 mm; aquarium material. (Figure 9). Crenuchus spilurus Giinther, USNM 225630; 4 specimens, Semaprochilodus taemurus (Steindachner), USNM 231537; 1 21.7-28.2 mm; Surinam, Nickerie District, Lana Creek. specimen, 34.7 mm; Brazil, Amazon River. Gasteropelecus stemicla (Linneaus), USNM 226337; 5 speci- mens, 29.7-32.5 mm; Surinam, Corantijn River. ANOSTOMIDAE Hydrolycus pectoralis (Giinther), USNM 231548; 1 specimen, Anostomus plicatus Eigenmann, USNM 225396; 2 specimens, 167.1 mm; Peru, Rio Ucayali. 75.8 95.3 mm; Surinam, Nickerie District, Matappi Rhaphiodon vulpinnis Agassiz, USNM 231549; 4 specimens, Creek. 41.7-44.3 mm; Brazil, Rio Solimoes. Anostomus species, USNM 231540; 1 specimen, 81.3 mm; no Salminus maxillosus Valenciennes, USNM 194213; 1 specimen, data (Figures 20, 26). 214.7 mm; Venezuela, Rio Nitiado-Seco. Gnathodolus bidens Myers, USNM 231539; 1 specimen, 76.2 mm; aquarium material. HEMIODONTIDAE species, USNM 179514; 2 specimens, 75.3-77.0 Anodus elongatus Spix, USNM 231550; 1 specimen, 120.3 mm; mm; Brazil, Rio Urubu (Figure 11). Peru, Rio Ucayali. Upormus fasctatus (Bloch), USNM 103847; 1 specimen, 73.2 Bivibranchia protractila Eigenmann, USNM 194363; 1 speci- mm; aquarium material (Figure 29). men, 62.8 mm; Brazil, Mato Grosso, upper Rio Juruena. Leporinus megalepis Giinther, USNM 231541; 1 specimen, 68.2 Hemiodopsis ocellata Vari, USNM 225593; 1 specimen, 99.6 mm; no data (Figure 23). mm; Surinam, Corantijn River. Leporinus reinhardti Lutken, AMNH 40104SD; 1 specimen, Hemiodus species, USNM 231551; 2 specimens, 55.7-57.1 170.0 mm; Bolivia, Rio Guapore (Figures 33, 34). mm; Brazil, Mato Grosso, Rio Arinos. Leporinus striatus Kner, USNM 231948; 26 specimens 68.5- Micromischodus sugillatus Roberts, USNM 205527; 1 specimen, 178.5 mm; , Rio Salado (Figure 38). 96.1 mm; Brazil, Para. Rhytiodus microlepis Kner, USNM 163850; 1 specimen, 131.7 mm; Peru, Iquitos. PARODONTIDAE Schizodon fasciatum Agassiz, USNM 179507; 1 specimen, 49.3 mm; Brazil, Rio Urubu (figures 1, 2, 15). Parodon suborbitalis Valenciennes, USNM 231552; 2 speci- Myers and Fernandez-Yepez, mens, 55.0-58.1 mm; Colombia, Rio Salado. MBUCV V-4252; 1 specimen, 71.2 mm; Venezuela, Ri'o Saccodon dariensis (Meek and Hildebrand), USNM 208505; 1 Paragua. specimen, 73.3 mm; Panama, Rio Membrillo.

CHILODONTIDAE HEPSETIDAE Caenotropus labyrinthicus (Kner), USNM 231543; 1 specimen, Hepsetus odoe (Bloch), USNM 231553; 1 specimen, 96.2 mm; 58.5 mm; Brazil, Rio Negro. Togo, Kama. Caenotropus labyrinthicus (Kner), USNM 231544; 1 specimen, 64.2 mm; Venezuela, upper Rio Negro (Figure 11). ClTHARINIDAE Caenotropus maculosus (Eigenmann), USNM 231545; 2 speci- Citharinus citharus Geoffrey, USNM 52146; 1 specimen, 218.7 mens, 42.7-46.3 mm; Guyana (Figures 1, 2, 10, 12, 18, 19, mm; Egypt, Nile River. 21,24, 30-32). Citharinus species, USNM 231554; 2 specimens, 56.3-64.5 Caenotropus maculosus (Eigenmann), USNM 231546; 1 speci- mm; Volta, Black Volta River. men, 97.5 mm; Surinam, Saramaca River. Chtlodus punctatus Miiller and Troschel, USNM 231542; 13 DlSTICHODONTIDAE specimens, 27.1-38.2 mm; Peru, Rio Nanay (Figures 11, 36, 37). Nannocharax inlermedius Boulenger, USNM 231555; 2 speci- mens, 50.7-63.4 mm; West Africa. Neolebias olbrechtsi Poll, USNM 227394; 4 specimens, 25.3- Acestrorhynchus falcatus (Bloch), USNM 225614; 2 specimens, 29.7 mm; Zaire. 81.0-85.1 mm; Surinam, Nickerie District, Sisa Creek. Paradistichodus dimidiatus Pellegrin, USNM 231556; 2 speci- Brycon falcatus Miiller and Troschel, USNM 226161; 2 spec- mens, 45.6-47.3 mm; Ghana, Dayi River. SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

In addition to the listed specimens, a large BB basibranchial (1 to 4) number of dry skeletons, stained and cleared BOC basioccipital glycerine preparations and alcohol preserved BR branchiostegal ray specimens in the collections of AMNH and C ceratobranchial (1 to 5) CEN centrum USNM were examined in the comparative studies CL cleithrum associated with the present analysis. COR coracoid TERMINOLOGY.—Osteological nomenclature CR ceratobranchial ridge follows Weitzman (1962) with the following mod- CSI cavum sinus imparis ifications. As suggested by Roberts (1969:402), CTS connective tissue sheet DEN dentary "vomer" is substituted for "prevomer," and "in- DH dorsal hypohyal tercalar" for "opisthotic." The element tradition- DO dilatator operculi ally termed "epihyal" is instead referred to as E epibranchial (1 to 5) "posterior ceratohyal." The "ceratohyal" of many EAF efferent artery foramen previous authors is more correctly termed "ante- ECT ectopterygoid rior ceratohyal." This shift in terminology is a EOM epibranchial organ muscle EPI epioccipital consequence of the lack of serial homology be- ER epibranchial ridge tween the so-called epihyal and the epibranchials EXT extrascapular and the resultant misleading inference of homol- FR frontal ogy inherent in the continued use of "epihyal" FM foramen magnum (Nelson, 1969:480-481). The use of "epioccipital" FS foramen for scaphium rather than "epiotic" follows Patterson (1975). H hypobranchial (1 to 3) HA hyohyoidei abductores Nelson's substitution (1973) of "angulo-articular" HI hyohydoides inferior for "articular" and "retroarticular" for "angular" HYO hyomandibula is more reflective of the homologies of these ele- I interhyal ments among teleosts than previous terminologies INT interopercle and is utilized in this paper. Myological termi- LAP levator arcus palatini nology is that of Winterbottom (1974). LE lateral ethmoid LIG ligament Unless noted otherwise, the concepts of the LOC lateral occipital foramen characiform families used in this paper are those MES mesopterygoid of Greenwood et al. (1966) with the following MET metapterygoid modifications. The Cynodontidae of those au- METH mesethmoid MX maxilla thors is considered a tribe in the Characidae NC neural canal rather than a distinct family in keeping with the NS neural spine results of Howes (1976). The Ichthyboridae of OP opercle Greenwood et al. is placed within the Disticho- OPF opercular flange dontidae following Vari (1979:339). The termi- PA parietal nology utilized for the major groups of osatrio- PAL palatine PAP pterotic articular process physan fishes is that of Fink and Fink (1981). PAR parasphenoid ABBREVIATIONS.—The following abbreviations PB infrapharyngobranchial (1 to 4) are used in the text and illustrations. PC posterior ceratohyal PCL postcleithrum (1 to 3) A division of the adductor mandibulae PMX premaxilla (1 to 3 and w) POST posttemporal AAP adductor arcus palatini PP parapophysis AA angulo-articular PR pleural rib AC anterior ceratohyal PRE preopercle B basihyal PTE pterotic BTP basihyal tooth plate PZ prezygapophysis NUMBER 378

QUA quadrate logenetic reconstruction are discussed. Similarly, RA retroarticular S scaphium only intrafamilial character differences pertinent SAP supracleithral articular process to the phylogenetic reconstruction at the familial SC scapula level are detailed. Osteological and soft anatom- SCL supracleithrum ical systems are discussed separately other than SMX supramaxilla where the functional association between the two SPH sphenotic systems would make a divided discussion less SPO suprapreopercle SOP subopercle efficacious. ST sternohyoideus Among the hypothesized derived characters SYM symplectic discovered during the study, a minority were UP upper pharyngeal tooth plate (4 and 5) found to have distributions incongruent with the V vomer most parsimonious phylogenetic reconstruction VH ventral hypophyal based on the overall distribution of synapomor- phies. Such homoplasies are recognizable only in the context of the final phylogenetic hypothesis Character Description and Analysis and will be summarized as a group in the "Dis- cussion" section. In to simplify the evalua- The phylogenetic analysis of the present study tion of homoplasies, such characters and their has three primary goals: first, to advance an distributional incongruities relative to the arrived explicit hypothesis of the phylogenetic relation- at phylogeny will also be discussed at appropriate ship of the Curimatidae within the Characi- points in the character descriptions. formes; second, to examine the hypothesized monophyly of the Curmatidae and closely related groups; and third, to evaluate the utility of pre- TEETH AND JAWS vious alternate classifications as indicators of the phylogenetic history of the Curimatidae and as- The feeding habits of curimatids, prochilodon- sociated lineages. tids, anostomids, and chilodontids range from In this section the characters that show phylo- microphagous filtration of food items from the genetically significant variation in the anatomical substrate and water column to micropredation systems examined in the present study are dis- and macrovegetation cropping. The diversity of cussed, along with data that bear on polarity jaw forms in this assemblage reflects the differing determinations for each character transition se- requirements for dealing with that spectrum of ries. The evidence from the analyzed characters food items. is brought together in the "Phylogenetic Recon- Characiforms most commonly have a single struction" to advance the most parsimonious hy- tooth row on the maxilla and one or two rows of pothesis of the phylogenetic history of the taxa moderate-sized teeth on the dentary and premax- under consideration. The resultant phylogeny illa. The maxilla of chilodontids, curimatids, and serves as the basis for the evaluation of the utility anostomids differs from the above pattern in of previously advanced classifications as indica- being edentulous throughout ontogeny. The tors of phylogenetic relationships among curi- question of the possible presence of maxillary matids and closely related taxa (see "Compari- teeth in prochilodontids is difficult to resolve. The sons with Previous Classifications"). prochilodontid suctorial mouth bears multiple The purpose of this study is the advancement rows of numerous small teeth on hypertrophied of a phylogenetic hypothesis rather than a de- lips (Roberts, 1973:217). Portions of the dentition tailed description of the osteology and soft anat- overlap the maxilla but are associated with the omy of the involved taxa. Thus, only anatomical fleshy lips rather than being attached to the bone systems that show variation relevant to the phy- itself. Neither phylogenetic nor ontogenetic data 8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY permit a determination of whether the oral disk cuspidate premaxillary and dentary teeth (see dentition proximal to the maxilla is homologous also Gery, I977b:231). Excepting the absence of with the primitively present maxillary dentition. maxillary teeth, this dentition pattern agrees in An assumption of the nonhomology of the mul- form and distribution with that of various gen- tiple tooth rows near the maxilla with the primi- eralized characiforms. Ontogenetically, however, tive, attached maxillary teeth would make an the curimatid premaxilla and dentary undergo a edentulous maxilla synapomorphous for prochil- progressive loss of dentition, with adult curima- odontids, anostomids, chilodontids, and curima- tids being endentulous (Figure ID). This ontoge- tids although not unique to these groups among netic information and the broad distribution of characiforms. Alternatively, it is possible that the jaw teeth in characiforms and more inclusive oral disk dentition proximal to the prochilodontid ostariophysan groups indicate that this absence maxilla is derived from the plesiomorphous max- of jaw dentition is derived within characiforms. illary teeth. If the latter situation approximates Totally edentulous jaws are limited in chara- the actual phylogenetic history of portions of the ciforms to the Curimatidae and the Anodus, prochilodontid oral disk dentition, then the ab- considered by some authors (Eigenmann and Ei- sence of maxillary dentition is not a shared de- genmann, 1889; Fernandez-Yepez, 1948) as a rived character for the four taxon unit but would member of that family. Roberts (1974) demon- rather be a synapomorphy for the Anostomidae, strated that Anodus actually shares numerous de- Curimatidae, and Chilodontidae. That single rived characters with, and is most closely related character phylogenetic scheme is incongruent to, the Hemiodontidae. The other members of with the pattern of relationships considered most the Hemiodontidae possess well-developed teeth; parsimonious, based on the overall distribution of therefore, the absence of jaw dentition in Anodus all synapomorphies. Within the context of the phylogenetic hypothesis incorporating all exam- ined characters (p. 46), two equally parsimonious explanations could account for the phylogenetic distribution of edentulous maxillae among these taxa. First, the maxillary teeth were indepen- dently lost in the ancestral curimatid and the common ancestor of chilodontids and anostom- ids. Second, maxillary dentition was lost, or al- ready absent, in the common ancestor of the four families but re-acquired in prochilodontids. The conjunction of the uncertain homology of por- tions of the prochilodontid dentition with ques- tions about character polarity in the system makes it impossible to appropriately use the ab- sence of attached maxillary dentition in the res- olution of phylogenetic relationships within the unit that consists of curimatids, prochilodontids, chilodontids, and anostomids. Departures from the generalized characiform pattern of premaxillary and dentary dentition distinguish each of the families under discussion. FIGURE 1.—Upper jaws: A, Caenotropus maculosus, USNM Juvenile curimatids (Curimatopsis macrolepis, Curi- 231545 (row of reduced teeth not shown); B, Schizodon fascia- mata cyprinoides, and various undetermined Curi- turn, USNM 179507; c, Prochilodus rubrotaeniatus, USNM 225419 (multiple rows of reduced teeth not shown); D, mata species) have a single row of attached uni- Potamorhina laticeps, USNM 121325, left side, lateral view. NUMBER 378 is most parsimoniously considered a loss achieved distinctive in their thickness, multiserrate non- independent of that in curimatids. symmetrical cutting edges, increased relative The teeth of chilodontids and prochilodontids sizes, and the congruent reduction in tooth num- are significantly smaller than those in most char- ber (Figure 1B). These shifts from the moderate- aciforms and attach to the fleshy covering of the sized, more nearly symmetrical, and more nu- jaws rather than onto the premaxilla and dentary. merous teeth that evidently are primitive for the The significance of these similarities in these two Characiformes are considered synapomorphous taxa is difficult to evaluate. Differences in the for the subunits of the Anostomidae and are very morphology and distribution of jaw dentition in likely correlated with their leaf cropping and the two families raise questions as to the homol- micropredatory food habits. ogy of the tooth size reduction and the absence of The various distinctive dentitional synapomor- direct tooth to jaw articulation in the lineages. phies of the Curimatidae, Prochilodontidae, Chil- The absence of jaw dentition in adult curimatids odontidae, and Anostomidae are reflected in their could also be considered the terminal state of a jaw forms. The overall morphology of the curi- transition series whose intermediate stage might matid upper jaw is little altered relative to that have included the precursor of the detached jaw of other characiforms (Figure ID). The derived teeth in prochilodontids and chilodontids. Avail- reduction in the overall strength of the involved able ontogenetic data does not assist in the eval- bones, the lessening of the medial interconnec- uation of the preferability of either of these two tions between the premaxillae, and the loosening scenarios. These uncertanties render it impossible of the articulation between the maxilla and pre- to appropriately use the dentition morphology in maxilla are all congruent with the absence of jaw the Chilodontidae, Prochilodontidae, and Curi- dentition in adult curimatids. These changes are matidae for the resolution of phylogenetic rela- presumably correlated with the lack of firm ma- tionships in the four-family unit. Neither the nipulation of food items by the jaws in this mi- hypothesis of the homology of prochilodontid- crophagous family. chilodontid dentitional form nor the hypothesis Unique types of highly derived upper jaws that considers that condition to be a precursor to characterize each of the other three families. The the edentulous jaws of curimatids is congruent chilodontid maxilla (Figure 1A) is greatly en- with the arrived at phylogeny (see "Phylogenetic larged with the well-developed dorsal maxillary Reconstruction"). process ligamentously attached medially to the Chilodontids retain the primitive single tooth mesethmoid's anterolateral surface. The chilo- row on each jaw, whereas prochilodontids have a dontid premaxilla is small relative to the mor- unique, pronounced increase in the number of phology typical for characiforms and especially functional teeth and replacement tooth rows. so in comparison to the enlarged maxilla in the Roberts (1973:217) reported about 600 functional family. The reduced chilodontid premaxilla teeth in an Ichthyoelephas specimen of 97.2 mm SL forms a limited portion of the upper jaw margin and 12 replacement tooth rows in larger prochil- with the paired bones not in contact medially. odontid specimens. That dentition pattern con- Rather, the distal portion of the anteroventrally trasts with a maximum of less than 60 teeth and enlarged mesethmoid lies between the premaxil- 2 or 3 replacement tooth rows elsewhere in the lae. In addition to separating those primitively order. The pronounced increases in the number conjoined elements, that portion of the meseth- of teeth and replacement tooth series are, thus, moid also forms the midsection of the arc of the considered shared derived characters for the upper jaw (Figure 32). The dentition associated members of the Prochilodontidae. with the chilodontid upper jaw is reduced in size Anostomids retain the single row of premaxil- and not in direct contact with the premaxilla and lary and dentary teeth common to many chara- maxilla, but rather attached to the fleshy lips. ciforms. The teeth of anostomids are, nonetheless, The latter modification permits the maintenance 10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY of a continuous row of teeth along the upper jaw forms outside of the family. Equally unusual is despite the intercalation of the mesethmoid be- the strong bony process that extends posteroven- tween the premaxillae. Chilodontids also have a trally from the medial surface of the maxilla. supernumerary upper jaw ossification: the supra- That spur serves as the attachment area for the maxilla, situated along the posterodorsal margin maxillo-mandibular ligament, which terminates of the maxilla (Figure 1A). The association of the ventrally on the dentary. robust, enlarged maxilla and a reduced premax- Congruent with the modifications of the upper illa is not approximated among characiforms jaw among the four families under discussion are other than chilodontids; neither did outgroup various changes in the form of the lower jaw comparisons in that order uncover a mesethmoid elements. As in the case of the upper jaw, the that so distinctly separates the premaxillae. A mandibular elements in curimatids are the least discrete supramaxilla is known elsewhere in the modified relative to those of most characiforms. order only in the characid Chalceus macrolepidotus. The curimatid lower jaw (Figure 2D) is distin- Present concepts on phylogenetic relationships guished from the generalized characiform condi- within characiforms indicates that the relation- tion primarily in the lack of teeth and tooth ships of Chalceus lie with the Neotropical family associated structures, most notably the dentary Characidae, an assemblage that is not an imme- replacement tooth trench. The dentary of curi- diate sister group to the Chilodontidae. The com- matids is relatively elongate and overlaps the mon possession of a supramaxilla in Chalceus and triangular angulo-articular. The retroarticular is the Chilodontidae is, therefore, considered to rep- a small lateral ossification along the ventral mar- resent two independent acquisitions of that ossi- gin of the latter bone. The other three families fication. have the lower jaw foreshortened to differing The Anostomidae, the hypothesized sister degrees compared to the relatively elongate man- group of the Chilodontidae, has the relative sizes dible of curimatids. Such a foreshortening, al- of the upper jaw elements reversed. Anostomids though hypothesized to be derived, has a phylo- have a very robust, triangular, tooth-bearing pre- genetic distribution incongruent with the phylog- maxilla with a relatively smaller maxilla located eny arrived at here (p. 46); thereby representing along the posteroventral margin of the premax- at least two separate trends towards lower-jaw illa. The overall form of the premaxilla is the shortening. result of the apomorphous expansion of the as- The lower jaw of chilodontids is little modified cending premaxillary process that results in a other than in being foreshortened (Figure 2A). distinctly triangular element (Figure 1B). The absence in chilodontids of direct contact of The highly specialized, fleshy suctorial mouth the teeth with the dentary is correlated with the of prochilodontids is supported in part by distinc- absence of a replacement tooth trench. As noted tively structured upper jaw bones (Figure lc). above, that attribute also occurs, evidently inde- The outwardly curved premaxilla and maxilla pendently, in the edentulous curimatids. Anos- form rounded surfaces which serve as expanded tomids, in contradistinction, have a transversely attachment areas for the multilayered fleshy lips widened dentary that reflects the expansion of that bear the numerous rows of functional and the replacement tooth trench. The widened re- replacement teeth. The pronounced fenestration placement tooth trench has both an increased of the maxilla is especially unusual, with one or attachment area for the enlarged functional teeth more large fenestra along the lateral surface of (Figure 2B) and space for development of the the element and a number of smaller apertures relatively large replacement dentition. Another often arranged in posteroventrally aligned linear unusual aspect of the anostomid dentary replace- series. Neither the outward curvature of the pre- ment tooth trench is the large fenestra on the maxilla and maxilla nor the high degree of fenes- bone's ventral surface. A total ventral enclosure tration of the latter are found among characi- of the trench is typical for characiforms, and the NUMBER 378 11

and more inclusive hypotheses of relationships indicate that these rotations in trench position were achieved independently (page 46; Vari, 1979). The medial fenestra opening into the re- placement tooth trench in the Prochilodontidae has not been encountered elsewhere in the order.

GILL ARCHES The hypothesized plesiomorphous condition of the characiform gill arches' ventral portion is comparable to that illustrated in Figures 3 and 4. Medially there are three ossified basibranchials, DEN each bordered by paired hypobranchials. The unossified posteriormost fourth basibranchial is an anteriorly wider, overall triangular element. FIGURE 2.—Lower jaws: A, Caenotropus maculosus, USNM The three pairs of hypobranchials are associated 231545 (row of reduced teeth not shown); B, Schizodon fascia- turn, USNM 179507; c, Prochilodus rubrotaeniatus, USNM with the first through third basibranchials. The 225419 (multiple rows of reduced teeth not shown); D, hypobranchials typically are unelaborated, with Potamorhina laticeps, USNM 121325, left side, lateral view. the exception of hypobranchial 3 which often has an anteroventral, prong-shaped process. When anostomid form of aperture is not approximated present, that protrusion extends lateral to the in any other characiform examined for the pres- ventral aorta and is variously developed in differ- ent study. The anostomid retroarticular lies in a ent characiform groups. Ceratobranchials 1 to 3 distinct pocket formed by the angulo-articular attach to the lateral margins of the associated and dentary (Figure 2B), contrary to the gener- hypobranchials, whereas the fourth and fifth cer- alized condition in which enclosure by the bor- atobranchials are in direct contact with the unos- dering bones is minimal. sified fourth basibranchial. The first through The prochilodontid lower jaw is particularly third ceratobranchials are elongate, dorsoven- noteworthy for the alteration of its retroarticular trally flattened bones that lack any pronounced and dentary (Figure 2c). The prochilodontid re- dorsal ridges or processes. Ceratobranchial 4 has troarticular is greatly reduced relative to the typ- a comparable overall form and a definite ridge ical characiform condition. Equally distinctive is along its ventromedial edge, which serves as the the repositioning of the retroarticular along the attachment area for a connective tissue band. anteromedial surface of the angulo-articular, Ceratobranchial 5 is expanded anteromedially which results in its being barely visible in lateral into a flattened, largely horizontal plate, which view. This is a significant shift in size and position bears a patch of moderately developed, unicus- from the larger, laterally located retroarticular in pidate, dorsally, or posterodorsally directed teeth. other characiforms. The numerous rows of re- This hypothesized primitive condition of the placement teeth on the lower jaw of prochilodon- gill arches among characiforms is modified, often tids are contained in a greatly widened, laterally markedly, among members of the families Curi- rotated replacement trench with a large medial matidae, Prochilodontidae, Anostomidae, and fenestra. A rotation of the dentary replacement Chilodontidae. The phylogenetic distribution of tooth trench onto the anterior surface of the the various, derived restructurings are congruent dentary also characterizes the Citharinidae (Vari, with the recognition of the four-taxon assemblage 1979:267). The trench size in that family does not as a natural evolutionary unit and with its divi- approximate the condition in prochilodontids, sion into two monophyletic subunits. One subunit 12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

BB,

BB-

FIGURE A.—Bryconfakatus, USNM 226161, ventral portion of FIGURE 3.—Btyconfalcalus, USNM 226161, ventral portion of gill arches, ventral view (denser stippling represents carti- gill arches, dorsal view (denser stippling represents cartilage). lage). H,

BB. BB,

BB

BB

FIGURE b.—Cunmata vittata, USNM 231434, ventral portion FIGURE 6.—Curimata vittata, USNM 231434, ventral portion of gill arches, dorsal view (denser stippling represents carti- of gill arches, ventral view (denser stippling represents car- lage). tilage). NUMBER 378 13 consists of curimatids and prochilodontids, the other of anostomids and chilodontids. -< ' Ef , i The most readily apparent difference between the basic form of the ventral portion of the gill arches common to prochilodontids and curima- tids and the hypothesized plesiomorphous condi- tion of these elements for characiforms is the FIGURE 7.—Psectrogaster amazomca, AMNH 40088SD, cerato- marked reduction or absence of dentition on the branchial 4, left side, lateral view (arrow points to ventral lower pharyngeal (fifth ceratobranchial) in the process). adults of these families (Figure 5). Fifth cerato- branchial dentition is present in postlarvae of ess extends from the fourth certobranchial's an- both families. In specimens of Prochilodus of ~ 35 teromedial surface in prochilodontids and curi- mm SL, six to eight unicuspidate teeth are ar- matids (Figures 6, 7). This process is an apomor- ranged in two parallel rows along the postero- phous elaboration of the ridge on the medial medial portion of the bone. The progressive on- portion of the fourth ceratobranchial in other togenetic loss in lower results in characiforms. In a similar fashion the anterior the fifth ceratobranchials of prochilodontids corner of the third hypobranchial is often antero- being edentulous in — 85 mm SL specimens. ventrally prolonged in characiforms into a prong- Similarly curimatids under ~ 25 mm SL com- shaped process that extends lateral to the ventral monly have a patch of unicuspidate teeth on the aorta. Curimatids have the ventral portion of that fifth ceratobranchial. An ontogenetic loss of pha- process apomorphously further expanded ven- ryngeal dentition that leads to toothless fifth cer- trally and posteriorly to form a vertical wall that atobranchials is common to the vast majority of extends lateral to, and evidently partially sup- curimatid species, particularly those that attain ports, the ventral aorta (Figures 6, 8). Anterior an adult standard length over 50 mm. In some of and posterior extensions of this process' ventral the smaller species, however, the reduction is not margin are positioned along the lateral wall of carried to its ultimate limit. Fully grown Curima- the blood vessel. The degree of development of topsis species (i.e., ~ 25 mm SL) retain a distinct, these secondary processes vary among different albeit greatly reduced, patch of teeth on the fifth subunits of the family. ceratobranchial. Certain hemiodontids {Anodus, Hemiodus, Hem- Within the Characiformes a reduction or elim- iodopsis (Vari, 1982a: 191), Micromischodus and Bi- ination of lower pharyngeal dentition also occurs vibranchia) and chilodontids (Caenotropus) also in the Neotropical genus Anodus (Roberts, have prominent ventral processes of the third 1974:223) and the African family Citharinidae (Vari, 1979:303). Various shared derived char- acters unite these taxa respectively to the Hem- iodontidae (Roberts, 1974) and Distichodontidae (Vari, 1979). The latter families otherwise have a full complement of lower pharyngeal dentition. The reduction or elimination of fifth ceratobran- chial dentition in Anodus and the Citharinidae is consequently most parsimoniously considered a homoplasy relative to the comparable adaptation common to curimatids and prochilodontids. The lower portion of the gill arches also pro- FIGURE 8.—Psectrogaster amazomca, AMNH 40088SD, basi- vides some other phylogenetically interesting branchial 3 and hypobranchial 3, left side, lateral view, characters. A prominent, anteriorly directed proc- showing ventral process of hypobranchial 3. 14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

hypobranchial. The hypobranchial projections in

those taxa arise from the ventrolateral margin of Hv *V the main body of the hypobranchial rather than the ventromedial portion of the element as in BB2 curimatids. Those structures are consequently considered nonhomologous with the adaptations BB- in the latter family; a hypothesis congruent with the arrived at hypothesis of relationships. The first basibranchial is the final phylogenet- CR ically significant character discovered in the ven- tral portion of the gill arches in curimatids and prochilodontids. Most characiforms have a rela- tively well-developed conical or elongate first ba- sibranchial that extends distinctly anterior to the first hypobranchial (Figures 3, 10). In prochilo- dontids, however, basibranchial 1 is a small, tri- angular element approximate to the anterior mar- gin of basibranchial 2 and barely extends ante- riorly to the level of the anterior terminus of the first hypobranchial (Figure 9). This reductional trend is carried further in the Curimatidae, which lack a separate, ossified first basibranchial (Figure 5). Available evidence does not permit a decision as to whether the conical cartilagenous process FIGURE 10.—Caenotropus maculosus, USNM 231545, ventral anterior to the ossified second basibranchial of portion of gill arches, dorsal view (denser stippling represents curimatids represents the unossified remnant of cartilage).

the reduced firstbasibranchia l of prochilodontids. Nonetheless, an ossified first basibranchial is widespread in otophysans and its reduction and BB- ultimate loss are, thus, considered synapomor- phies of different levels of universality within the prochilodontid-curimatid lineage. The lack of an unossified first basibranchial also occurs homo- plasiously in the examined adults of at least some anostomids {Rhytiodus microlepis, irinae (Winterbottom, 1980:40)) and parodontids (Par- odon suborbitalis). The primary shared derived character for an- ostomids and chilodontids in the gill arches' ven- tral portion involves the fifth ceratobranchial dentition (Figure 10). Chilodontids and anostom- ids have enlarged bi- or multicuspidate teeth rather than the relatively small or moderately FIGURE 9.—Semaprochilodus taeniurus, USNM 231536, ventral developed unicuspidate pharyngeal dentition portion of gill arches, anterior region, dorsal view (denser common to most characiforms. Bicuspidate pha- stippling represents cartilage). ryngeal teeth with unequally developed cusps are NUMBER 378 15

universal among anostomids (Figure 11A). The elaboration of the distal portion of the fifth cer- atobranchial dentition progresses further in Caen- otropus and Chilodus in which the lower pharyngeal teeth have three cusps of markedly different size aligned along the longitudinal body axis. This dentition is comparable to that of the upper portions of the Caenotropus gill arches, as illus- trated in Figure UB. Lower pharyngeal dentition enlarged to the degree found in chilodontids and anostomids has not been reported or observed elsewhere among characiforms (Roberts, 1969:424; Winterbottom, 1980:2). Consequently, its possession is most ap- FIGURE 12.—Caenotropus maculosus, USNM 231545, fifth propriately considered a shared derived charac- ceratobranchial, left side, dorsal view. ter. Non-unicuspidate pharyngeal dentition is known to occur in only one other characiform, branchial apparatus into the system. Most no- the hemiodontid Bivibranchia, which has tricuspi- table are the modifications of the fourth and fifth date teeth on the fifth ceratobranchial (Roberts, ceratobranchials. The enlarged fourth cerato- 1974, fig. 37). The equally developed, transversely branchial (Figures 10, 21) has greatly expanded or obliquely transversely oriented, tooth cusps of posterior and posteroventral surfaces that form a Bivibranchia do not appear to be homologous with broad curved plate which closely approximates the anteroposteriorly oriented cusps of markedly neighboring portions of the enlarged fifth cera- different size found in chilodontids and anostom- tobranchial (Figures 10, 12, 21). The increased ids. Furthermore, as discussed by Roberts, Bivi- size and modified form of the fourth ceratobran- branchia is evidently most closely related to hem- chial are seemingly unique to chilodontids among iodontids, a family otherwise characterized by ostariophysans. The lower pharyngeal (fifth cer- unicuspidate pharyngeal teeth. The anatomical atobranchial) of chilodontids is similarly totally and phylogenetic data concordantly indicate that restructured (Figures 10, 12) relative to the con- the tricuspidate dentition of Bivibranchia is a hom- dition basic for characiforms (Figure 3). Most oplasy relative to the apomorphous bi- or multi- distinctive is the great expansion of the ventral cuspidate tooth forms common to the Chilodon- portion of ceratobranchial 5 into a broad, cup- tidae and Anostomidae. shaped plate that extends under and closely ap- Although numerous fish groups with promi- proximates the posterior and ventral surfaces of nent epibranchial organs have associated altera- the enlarged fourth ceratobranchial (Figures 10, tions of the gill arches' dorsal portion, chilodon- 21). Dorsomedially the fifth ceratobranchial is a tids are unusual, if not unique, in also incorpo- flattened, fenestrated plate that extends ante- rating elements of the ventral portion of the riorly along the dorsal surface of the cartilagenous fourth basibranchial. Posteriorly the tooth-bear- ing portion of the bone is expanded dorsally and FIGURE 11.—Form of fifth up- rotated anteriorly. This results in the associated per pharyngeal tooth plate den- dentition being oriented directly anteriorly or tition, left side, lateral view: having only a slight dorsal inclination contrary A, Laemolyta species, USNM to the plesiomorphous dorsal or moderately an- 179514; B, Caenotropus labyrinlhi- terodorsal orientation of these teeth in other char- cus, USNM 231544; c, , USNM 231542. (Scale aciforms. The chilodontid gill arches also have = 0.1 mm.) prominent dorsal ridges that arise from the main 16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY chilodontidae and the second of the Anostomidae and Chilodontidae. The hypothesized plesiomorphous characiform morphology of the gill arches' dorsal portion is comparable to that illustrated for Brycon (Figures 13, 14). Four infrapharyngobranchials occur along the midline. The first, a small, rod-like or triangular element associated with the first epi- branchial, is ligamentously attached dorsally to the neurocranium. Infrapharyngobranchials 2 and 3 are triangular, anteriorly directed elements that contact their respective epibranchials lat- PB2 erally. The fourth infrapharyngobranchial is a flattened cartilage that extends between the third FIGURE 13.—Bryconfalcatus, USNM 226161, dorsal portion of infrapharyngobranchial and the fourth epibran- gill arches, left side, ventral view (denser stippling represents chial. Epibranchials 1 through 3 are elongate, cartilage). flattened structures unelaborated other than for proximal uncinate processes. The fourth epibran- body of ceratobranchials 1, 2, and 3 (Figure 10). chial is a more complex triangular bone with a Such elaborations are distinctive relative to the well-developed, dorsally directed process above primitive, flattened dorsal surface of these ele- the fifth upper pharyngeal tooth plate. Postero- ments in other characiforms. Whether, and how, laterally, the fourth epibranchial articulates with these ridges are functionally related to the epi- the relatively small, rod-shaped, cartilaginous branchial organs is unknown. Ceratobranchial fifth epibranchial (Figures 13-15). The fourth ridges also occur in the hemiodontid Bivibranchia. and fifth epibranchials diverge dorsally, with an In that genus the margins of the ridges are intervening groove that serves as the passage for straight and the main body of the entire cerato- the fifth efferent branchial artery. Upper pharyn- branchial is bowed ventrally; a system different geal tooth plate 4 is attached to the ventral from the chilodontid form of ceratobranchial surface of the fourth infrapharyngobranchial, ridge. Furthermore, Bivibranchia apparently is not closely related to the assemblage formed by chil- odontids and anostomids. The conjunction of PEL, these factors leads to an assumption that the ceratobranchial elaborations in Bivibranchia and the Chilodontidae are homoplasious. Characiforms as a whole more typically dem- onstrate alterations of the gill arches' dorsal por- tion than restructurings of the branchial appara- tus' ventral region. This dichotomy is apparent among curimatids, prochilodontids, anostomids, and chilodontids, all of which have some of the most pronounced alterations of the dorsal por- tions of the gill arches among characiforms. Once again some modifications are synapomorphous for the four-family unit, while others delineate FIGURE 14.—Bryconfalcatus, USNM 226161, dorsal portion of two subgroups within the assemblage. The first gill arches, left side, dorsal view (denser stippling represents subgroup consists of the Curimatidae and Pro- cartilage). 17

nocharax and Neolebias (Vari, 1979:303-305). Re- duced dentition on the fourth upper pharyngeal EAF tooth plate also characterizes the Neotropical hemiodontid genus Anodus. Although derived, the reduction or loss of dentition on the fourth upper pharyngeal tooth plate does not delimit a natural assemblage. The species of Hemigrammocharax, Nannocharax, and Neolebias that have reduced den- tition on the fourth upper pharyngeal tooth plate are all relatively small forms with congruent re- ductions in the overall ossification of other head parts. Furthermore, the data on relationships within and between these distichodontid genera make it most parsimonious to conclude that this UP, loss of dentition was achieved independently in each lineage and that a complete pattern of pha- ryngeal dentition was ancestral for distichodon- tids (Vari, 1979:305). The citharinids Citharidium FICURE 15.—Fourth and fifth epibranchials, fifth upper pharyngeal tooth plate, and associated dentition, right side, and Citharinus, which also lack teeth on the fourth medial view: A, Brycon falcatus, USNM 226161; B, Curimata upper pharyngeal tooth plate, are hypothesized vittala, USNM 231434; c, Ichthyoeltphas species, USNM to form the sister assemblage to the Distichodon- 231437; D, Schizodon fasciatum, USNM 179507. (Scales = 1.0 tidae (Vari, 1979:324). The presence of dentition mm; stippling represents cartilage). on the fourth upper pharyngeal tooth plate in characiform outgroups and most members of the while upper pharyngeal tooth plate 5 is joined Distichodontidae indicates that the edentulous dorsally to the fourth epibranchial's ventral sec- nature of the element in citharinids, although tion. The two tooth plates together form a contin- most simply considered a synapomorphy for the uous, flattened bony sheet that bears a patch of members of that family, is a homoplasy relative small unicuspidate teeth, which oppose those on to the comparable condition in curimatids, pro- the fifth ceratobranchial. Comparable small uni- chilodontids, anostomids, and chilodontids. A cuspidate dentition often also occurs in small number of derived characters place Anodus, in patches on the ventral surfaces of the second and which UP4 lacks teeth, within the Hemiodontidae third infrapharyngobranchials. (Roberts, 1974:429). The remaining members of Curimatids, prochilodontids, anostomids, and that family have the more typical plesiomorphous chilodontids have in common a pronounced re- characiform pattern of complete pharyngeal den- duction in the amount and distribution of pha- tition, which is consequently considered the prim- ryngeal dentition. Most notable is their lack of itive condition for the Hemiodontidae. teeth on the fourth upper pharyngeal tooth plate Curimatids, prochilodontids, anostomids, and (UP4), a condition here considered to be derived chilodontids or subunits of that assemblage share within characiforms relative to the previously restructurings of the fourth upper pharyngeal described presumed primitive condition. Re- tooth plate. All four families lack the plesiomor- duced or absent dentition on the fourth upper phous close contact of the fourth and fifth upper pharyngeal tooth plate is not unique to this par- pharyngeal tooth plates (Figures 16-19). The ab- ticular assemblage within the order. Among Old sence of that immediate association of those ele- World characiforms, an edentulous UP4 occurs in ments is thus hypothesized to be a shared derived all citharinids and in some, but not all, species of character for the quadrifamilial grouping. Curi- the distichodontid genera Hemigrammocharax, Nan-matids and prochilodontids have a somewhat 18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY '5 PB, PB3

UP,

FIGURE 16.—Curimata vitlata, USNM 231434, dorsal portion of gill arches, left side, ventral view (denser stippling repre- sents cartilage). FIGURE \9.—Caenotropus maculosus, USNM 231545, dorsal PB portion of gill arches, left side, dorsal view (denser stippling PB, represents cartilage).

FIGURE 17.—Curimata vitlata, USNM 231434, dorsal portion of gill arches, left side, dorsal view (denser stippling repre- sents cartilage).

FIGURE 20.—Anostomus species, USNM 231540, dorsal por- ER tion of gill arches, left side, dorsal view (denser stippling represents cartilage).

reduced fourth upper pharyngeal tooth plate that no longer retains its primitive direct contact pos- teriorly with the elements of the fifth gill arch (Figure 16). In addition to its separation from the fifth upper pharyngeal tooth plate, UP4 is also apomorphously altered into a curved sheet that surrounds the ventral, lateral, and sometimes por- tions of the dorsal surfaces of the fourth infra- pharyngobranchial (Figures 16, 17); a marked FIGURE \8.—Caenotropus maculosus, USNM 231545, dorsal shift from the flat tooth plate form typical for portion of gill arches, left side, ventral view (denser stippling characiforms. Anostomids and chilodontids re- represents cartilage). tain the flattened form of the fourth upper pha- NUMBER 378 19 ryngeal tooth plate hypothesized to be primitive that element (Roberts, 1973, fig.22) . Comparable but have the posterior portion of the element teeth occur at some point in the ontogeny of shifted laterally (Figure 18). Consequently, the various curimatids. The majority of curimatid posterior portion of UP4 now contacts the antero- species have carried the trend towards tooth re- lateral surface of the main body of the fourth duction further and have very few teeth on the epibranchial rather than the anterior margin of fifth upper pharyngeal tooth plate, or have an the fifth upper pharyngeal tooth plate. The edentulous bone. Roberts (1973:219) reported marked reorientation of the tooth plate apparent that "in Curimatidae third and fourth epibran- in anostomids is more pronounced in chilodon- chial and fifth ceratobranchial toothplates bear tids. numerous conical teeth . . .." Observations asso- Subunits of the four-family assemblage under ciated with the present study have shown, how- consideration have the form of the fifth upper ever, that curimatids are characterized by the pharyngeal tooth plate (UP5) modified in differ- marked reduction or absence of teeth on the fifth ent ways relative to the hypothesized plesiomor- upper pharyngeal tooth plate, the absence of phous flattened plate common to most characi- teeth on the fifth ceratobranchial, and an eden- forms. Prochilodontids have a transversely com- tulous fourth upper pharyngeal tooth plate. Else- pressed fifth upper pharyngeal tooth plate mov- where among characiforms, a reduction in the ably articulated with the fourth epibranchial UP5 dentition comparable to that in curimatids (Figure 15c; Roberts, 1974, fig. 22). In the An- is known only in the Old World family Cithar- ostomidae and Chilodontidae the fifth upper pha- inidae (Vari, 1979:303). However, numerous syn- ryngeal tooth plate is vertically thickened relative apomorphies unite the Curimatidae to the Pro- to the condition generalized for characiforms. chilodontidae (see "Phylogenetic Reconstruc- Among chilodontids, this thickened plate is ad- tion") and various derived characters indicate ditionally rotated posterodorsally. As a conse- that the Citharinidae forms the sister group to quence, the primitively ventral surface of UP5 is the Distichodontidae (Vari, 1979:324). Given oriented to face posteriorly (Figures 18, 19). The those more inclusive hypotheses of relationship, it various restructurings of the fifth upper pharyn- is simplest to consider the edentulous nature of geal tooth plate in prochilodontids, anostomids, the fifth upper pharyngeal tooth plate in cithar- and chilodontids are not known to occur else- inids to be a homoplasy relative to the reduced where among characiforms. Therefore, they are dentition on that bone in curimatids. This con- considered derived characters of differing levels vergent reduction in the UP5 dentition in the of universality. In the Curimatidae, UP5 is apo- microphagous curimatids and citharinids may be morphously expanded posteriorly and postero- a consequence of the decreased utility of pharyn- ventrally into a curved, somewhat convoluted geal teeth in fishes with that feeding habit. The ossification (Figures 15B, 16) that contacts and congruent, hypothesized homoplasious expansion matches the curved dorsal surface of the fifth of the fifth upper pharyngeal tooth plate is pos- ceratobranchial. A posterior extension of UP5 sibly associated with the food concentrating func- somewhat comparable to that in curimatids oc- tion of the epibranchial organs. curs in the Old World citharinids (Vari, 1979, fig. The enlarged bi- or multicuspidate dentition 28). The pronounced difference in the morphol- on the fifth upper pharyngeal tooth plate of ogy of the bony plates in the two families and the anostomids and chilodontids is comparable to overall distribution of derived characters within that on the fifth ceratobranchial. Anostomids characiforms indicates that these are analogous have totally bicuspidate pharyngeal dentition rather than homologous changes. (Figures 11A, 15D). Caenotropus (family Chilodon- Distinctive modifications of the fifth upper tidae) has tricuspidate pharyngeal teeth on both pharyngeal tooth plate dentition distinguish sub- ventral and dorsal portions of the gill arches units of the four-family assemblage. Prochilodon- (Figure 11B). The dentition on the fifth upper tids have reduced teeth with swollen bases on pharyngeal tooth plate of Chilodus (Chilodonti- 20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY dae) is quadricuspidate (Figure 1 lc) and opposes Nelson (1967) and the suprapharyngobranchial the tricuspidate teeth on the fifthceratobranchial . process of Bertmar et al. (1969)) is expanded and Enlarged non-unicuspidate UP5 dentition is lim- reoriented anteriorly, thereby extending over the ited to the preceding families among characiforms dorsal surface of the fourth infrapharyngobran- examined, with the single exception of the hem- chial (Figures 15B,C, 17). The resultant sheet of iodontid Bivibranchia (Roberts, 1974, fig. 37). As bone and cartilage runs parallel to, and is closely in the case of the lower pharyngeal dentition, the associated with, the lateral surface of the pharyn- supernumerary tooth cusps on the teeth in the geal outpocketing of the epibranchial organ. This upper portion of the gill arches in this hemiodon- vertical plate in these taxa is also extended pos- tid are evidently nonhomologous with those of teriorly and posterodorsally by a significant an- anostomids and chilodontids. terodorsal expansion of the cartilaginous fifth An overall restructuring of many other ele- epibranchial, which attaches to the rear of the ments in the dorsal portions of the gill arches fourth epibranchial (Figures 15B,C). The enlarged occurs in anostomids and chilodontids. The form form of the cartilage contrasts with the usual of the anteromedial process of the third epibran- characiform condition of a relatively small fifth chial of anostomids is distinctive among characi- epibranchial dorsally separated from the fourth. forms. This transversely widened portion of the The dorsal contact between the fourth and fifth bone has a distinct process that is somewhat epibranchials in curimatids and prochilodontids dorsally recurved, thereby extending over the results in the encirclement of fifth efferent bran- dorsal surface of the fourth infrapharyngobran- chial artery. Comparable expansions of the fourth chial (Figure 20). The third infrapharyngobran- and fifth epibranchials with a resultant enclosure chial of anostomids and chilodontids is trans- of the efferent artery are associated with well- versely widened posteriorly relative to the ple- developed epibranchial organs in various fish siomorphous characiform condition. This expan- groups (Nelson, 1967:76, 83). However, other sion is most pronounced in chilodontids (Figures than curimatids and prochilodontids, no chara- 18, 19), in which the associated third epibranchial ciform with well-developed epibranchial organs has an elongate slender medial process that ex- is known to have such an association of these tends dorsally to the fourth infrapharyngobran- elements. chial. Chilodontids have pronounced ridges on In anostomids (Figure 15D) and chilodontids, the ventral surfaces of epibranchial 1, 2, and 3 the form of the fourth epibranchial is dramati- that oppose the dorsal ridges on the three ante- cally altered relative to the condition hypothe- riormost ceratobranchials (Figure 18). Most sized to be plesiomorphous for characiforms. The highly developed is the process on epibranchial dorsal process of the bone in these families is 3. Once again the ridge form in the Chilodontidae considerably thickened transversely and foreshor- differs in detail from that of the hemiodontid tened longitudinally. Furthermore, the primary Bivibranchia. The anatomical differences and the axis of the process also has a posterodorsal align- data associating Bivibranchia phylogenetically ment rather than the dorsal or anterodorsal ori- with the Hemiodontidae (Roberts, 1974) indicate entation that characterizes other characiforms. that the ridges in that genus and the Chilo- The anterior portion of the fourth epibranchial, dontidae are evidently analogous rather than which articulates with the cartilaginous fourth homologous elaborations of the involved cerato- infrapharyngobranchial, has undergone a consid- branchials. erable vertical expansion in anostomids and chil- Epibranchial 4 is notably modified in the Cur- odontids. That expanded portion of the bone and imatidae, Prochilodontidae, Anostomidae, and the posteriorly reoriented dorsal process delimit Chilodontidae. In curimatids and prochilodon- a distinct, transversely aligned notch along the tids, the primitively dorsally directed process of dorsal surface of the bone (Figures 15D, 19, 20). the fourth epibranchial (the dorsal extension of The notch serves as an attachment area for the NUMBER 378 21 very large obliquus dorsal is muscle that extends Moderately developed pharyngeal outpocket- anteriorly to the fourth infrapharyngobranchial. ings associated with the fourth and fifth epibran- In no other characiform examined has such a chials have been reported in some African char- highly developed form of this upper pharyngeal acids and distichodontids (Daget, 1958, 1959, muscle been found. The alteration of the overall 1960; Bertmar, 1961:156). Highly developed epi- form of the fourth epibranchial is carried further branchial organs, however, are present within the in chilodontids (Figures 18, 19), which have the suborder only in the African Citharinidae (Sage- ventromedial surface of that element rotated pos- mehl, 1885, 1887; Daget, 1962a, 1962b) and the terodorsally. As a consequence the dentition on Neotropical Chilodontidae, Prochilodontidae, the associated fifth upper pharyngeal tooth plate and Curimatidae (Kner, 1861; Heim, 1935) (for points posteroventrally rather than ventrally as Hemiodontidae, see p. 22). Although well-devel- in other characiforms. oped epibranchial organs are hypothesized to be Chilodontids also have a number of modifica- derived for characiforms, they apparently are not tions of the upper portions of the gill arches that a shared derived character for all the taxa pos- are associated with their unique form of epibran- sessing them. Pronounced differences between the chial organ. three types of highly developed epibranchial or- gans in the group cast doubt on the homology of EPIBRANCHIAL ORGANS these adaptations, as do present concepts of higher level phylogenetic relationships among Epibranchial organs have been reported in a characiforms. number of fish groups including clupeiods, osteo- The epibranchial organ in the citharinids Cith- glossiforms, and ostariophysans. Within the Os- aridium and Citharinus is an elaborate system of tariophysi (sensu Rosen and Greenwood, 1970, foliate lobes and dichotomously branching inter- and Fink and Fink, 1981), such a system is known nal tubes supported by numerous bony spicules in some gonorhynchiforms, characiforms, and cy- (Daget, 1962a, figs. 6-8). Epibranchial organs of priniforms. The typical teleostean epibranchial that type are presently unknown elsewhere organ is primarily associated with the fourth epi- among teleostean fishes (Bertmar et al., 1969, branchial and consists of paired dorsal diverticuli table 1). This unique anatomy suggests that the of the branchial chamber. Each diverticulum citharinid epibranchial organ is a synapomorphy communicates posteroventrally with the pharynx for the members of that family, analogous rather via an aperture in the posterodorsal region of the than homologous with the well-developed pha- branchial chamber. Most early students studying ryngeal diverticuli in some other characiforms. the system suggested that the epibranchial organs That hypothesis is congruent with more inclusive in characiforms had a respiratory function (e.g., concepts of relationships based on shared derived Sagemehl, 1887; Rauther, 1910). Subsequent re- characters and the lack or poor development of search by Heim (1935) on the Old World chara- epibranchial diverticuli in distichodontids, the ciforms Distichodus (Distichodontidae) and Cith- hypothesized sister group to citharinids (see Vari, arinus (Citharinidae) and the New World genera 1979:322, for a further discussion). Curimatus (Curimatidae) and Prochilodous (Prochil- The epibranchial organs of curimatids and pro- odontidae), followed by Anglescu and Gneri's chilodontids are elongate, longitudinally aligned (1949) research on Prochilodus and Bertmar's study sacs with both longitudinal and circular muscles (1961) on Citharinus indicate that epibranchial in their walls (Heim, 1935:64, 71). Commencing organs in the examined taxa are not accessories at the posterodorsal limits of the branchial cham- of the respiratory system. Rather they serve to ber, the diverticuli then extend dorsally and an- sense food items in, and concentrate them from, terodorsally over the fourth infrapharyngobran- the water column and/or substrate (see Bertmar chial, the fourth and fifth upper pharyngeal tooth et al., 1969, for a detailed discussion). plates, and part of the tooth epibranchial. The 22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

medial surfaces of the sacs are in contact or chilodontids. Bertmar et al. (1969:20) erroneously slightly separated, with each diverticulum en- considered the epibranchial organ of the chilo- closed laterally by the enlarged cartilaginous fifth dontid Caenotropus to be equivalent to the ex- epibranchial and anteriorly expanded osseous panded, sac-like epibranchial organs of curima- and cartilaginous dorsal process of the fourth tids and prochilodontids. They also described the epibranchial. Although Bertmar et al. (1969:20) epibranchial organ of the chilodontid Microdus as state that the hemiodontid Hemiodus and the chil- "more convoluted and heliciform . .. than that of odontid Caenotropus have large, sac-like epibran- other characoids." As alluded to above, the epi- chial diverticuli, the present study has not found branchial organ of Caenotropus is nonhomologous such pharyngeal outpocketings in those genera. with that in curimatids and prochilodontids. The only hemiodontid with a noticeable poster- Rather it is like that described by Bertmar et al. odorsal epibranchial pouch is Anodus, which was for Microdus, which is an older, although preoc- not placed in the Hemiodontidae at the time of cupied, generic name for species now placed in the study by Bertmar et al. The diverticulum in Caenotropus (Gery, 1964:6). Anodus is relatively small outpocketing at the pos- Several features of the chilodontid epibranchial terodorsal limit of the branchial apparatus and is organ are unknown among other characiform formed largely by a cartilage associated with the groups. Foremost among these are the restructur- fifth ceratobranchial. It, furthermore, does not ings of the fourth and fifth ceratobranchials and extend dorsal of the fourth epibranchial and their incorporation into the epibranchial organ fourth infrapharyngobranchial. The Anodus pha- system (see "Gill Arches"). The exact functional ryngeal diverticulum thus differs in both position significance of the expansion of the apparatus and structure relative to the sac-like, muscular, into the ventral portions of the gill arches is dorsally located epibranchial organs of curima- uncertain. However, the adjoining surfaces of the tids and prochilodontids; the two forms of diver- expanded ceratobranchials form two broadly ticuli are consequently considered nonhomolo- curved, matching plates (Figures 10, 21) with the gous. adjacent surfaces in close contact and covered by The cited presence of sac-like epibranchial or- sheets of smooth connective tissue. Laterally this gans in Caenotropus is a misinterpretation of the covering layer is developed into a series of radially system in that genus. The pharyngeal diverticu- arranged, interdigitating ridges (Gery, 1964, fig. lum of chilodontids, including Caenotropus, is com- 2), which presumably filter food particles from posed largely of cartilage and connective tissue the water passed from the oral cavity. sheets and differs in numerous details from that The dorsal portions of the epibranchial organs of curimatids and prochilodontids. Those differ- also incorporate atypical elements. The postero- ences and available data on phylogenetic rela- dorsal margin of the fifth ceratobranchial is tionships of chilodontids support the hypothesis joined to a broad, shell-shaped connective tissue that the pharyngeal diverticulum in the Chilo- sheet (Figure 21). That structure extends upward dontidae is nonhomologous with the sac-like mus- above the level of the dorsal portions of the cular epibranchial organ of some other characi- epibranchials and forms the posterior wall of a forms. Thus, the sac-like epibranchial organ form partially helical, medially spiraling epibranchial of the Curimatidae and Prochilodontidae is ap- chamber. The anterior wall of the transversely parently synapomorphously limited to those fam- oriented chamber is largely formed by the carti- ilies among characiforms, with the reports by laginous fifth epibranchial, which is significantly Bertmar et al. (1969) of large sac-like epibranchial expanded vertically and transversely relative to organs in the Hemiodontidae and Chilodontidae the condition in other characiforms (Figure 21). being evidently erroneous. The fifth epibranchial's ventral margin is at- The final highly developed epibranchial organ tached by a connective tissue sheet to the poster- form within the Characiformes is common to all oventral margin of the fourth epibranchial. That NUMBER H78 23

EOM joins its counterpart on the posterodorsal surface of the epibranchial organ. The posterior portion of the muscle band arises in part on the postero- CTS ventral margin of the fifth ceratobranchial and partially on the posterior surface of the shell- shaped connective tissue band surmounting that bone. The anterior and posterior muscle bundles join on the posterior surface of the epibranchial organ slightly ventral to the dorsal border of the epibranchial organ. The resultant common mus- cle band extends dorsally from this point of con- tact to insert on the neurocranium. Although the exact homology of these epibranchial organ mus- cles is uncertain, they are considered a synapo- morphy for all chilodontids because of the lack of any comparable musculature in the branchial apparatus of other characiforms. The concurrent presence in chilodontids of well-developed pharyngeal dentition and large epibranchial organs runs counter to the general pattern noted by Nelson (1967:81), in which the development of large epibranchial diverticuli is FIGURE 21.—Caenotropus maculosus, USNM 231545, fourth typically accompanied by a reduction or elimi- and fifth branchial arches and anterior portion of epibran- nation of pharyngeal dentition. The functional chial organ muscle, right side, anterolateral view. significance of the association of such seemingly disparate adaptations—a large epibranchial or- common connective tissue band then continues gan correlated with filter-feeding and enlarged ventrally to attach to the fourth ceratobranchial's pharyngeal teeth usually associated with shred- dorsolateral surface. This soft tissue complex in- ding of larger food items—is unknown. An in- terconnects the dorsal cul-de-sac with the space depth examination of food habits in the group delimited by the expanded fourth and fifth cera- may resolve the question. tobranchials; an association between the dorsal The possession of epibranchial organs has been and ventral portions of the branchial apparatus hypothesized to be the ancestral condition for limited to chilodontids among fishes. various groups of fishes by Bertmar et al. Chilodontids lack the circular and longitudinal (1969:44). They consequently suggested that the musculature found in the sac-like epibranchial absence of these adaptations in members of var- organs of curimatids and prochilodontids. Rather ious lineages was achieved by repeated indepen- their epibranchial organs are formed largely of dent losses. Nelson (1967), in contrast, advanced nonmuscular tissue with only a single, narrow, the suggestion that the presence of such epibran- vertical muscle band that extends along the ex- chial diverticuli in different groups of fishesrep - ternal surface of the anterior and posterior walls resented independent acquisitions and that the of the epibranchial portion of the diverticulum absence of these pharyngeal outpocketings con- (Figure 21). The muscle segment on the anterior stituted the ancestral state for teleostean fishes. face of the epibranchial organ arises from the The scope of this study is too limited to analyze primitively dorsal surface of the fourth epibran- which of these hypotheses is most parsimonious chial. It extends dorsally from its origin to pass for all subunits of the Teleostei. However, the over the upper edge of the fifth epibranchial and morphology of well-developed epibranchial or- 24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY gans in characiforms indicates that the three forms of the diverticuli in chilodontids, citharin- ids, and the unit formed by curimatids and pro- chilodontids are analogous, homoplasious devel- BTP opments. The hypothesis that these diverticuli B arose independently in each lineage is also the most parismonious within the context of our pres- ent knowledge of relationships within the Char- aciformes. Similarly, the epibranchial organ in the cyprinid Hypopthalmichthys is an analog of the various systems in characiforms, with that genus most closely related to other cyprinids that lack the adaptation (Howes, 1981). Comparable ar- guments apply to the pharyngeal diverticuli of various gonorhynchiformes. Therefore, the ana- FIGURE 22.—Prochilodus rubrotaematus, USNM 225419, hyoid tomical and phylogenetic evidence concordantly arch: A, left side, lateral view (branchiostegal rays removed); B, left side, dorsal view. (Stippling represents cartilage.) indicates that, for the Ostariophysi, the hypoth- esis that large epibranchial organs are apomor- by the edentulous basihyal tooth plate (e.g., Le- phous independent acquisitions as stated by Nel- porinus, Figure 23). Four branchiostegal rays are son, is more parsimonious than the hypothesis of common to most characiforms, three attached to Bertmar et al., who considered such outpocket- the anterior ceratohyal and one to the posterior. ings ancestral for all teleosts. The relative width of these elements is variable within the order, but the degree of overlap be- tween neighboring rays is usually not extensive. HYOID APPARATUS The median urohyal typically has a moderately The four families under discussion possess a developed laminar vertical process and horizontal series of hyoid arch alterations congruent with lateral wings. adaptations of other portions of the oral appara- The hyoid arches of curimatids differ from tus. The generalized and presumed plesiomor- those just described only in the lateral expansion phous hyoid arch form for characiforms is com- of the anterior portions of the basihyal and basi- parable to that in Brycon (Weitzman, 1962, fig. hyal tooth plate, which results in a distinctly 1 lc). The arch's lateral portion consists of ventral triangular basihyal complex. The anterolateral and dorsal hypohyals followed posteriorly by an- expansion of these elements is carried further in terior and posterior ceratohyals. The hypohyals prochilodontids (Figure 22B) in which the ante- are transversely wide, complex bones, whereas the rior margin of the complex is apomorphously ceratohyals are distinctly compressed, laterally greatly developed transversely. This enlargement unelaborated elements. The anterior ceratohyal progresses ontogenetically to result in a squat T- is approximately twice as long as the posterior shaped basihyal complex in larger individuals. (e.g., Prochilodus, Figure 22). The hyoid series is Several other alterations of the hyoid arches char- completed posterodorsally by a rod-like interhyal, acterize the Prochilodontidae. Smaller individ- which attaches ligamentously to the dorsal sur- uals of the family have a distinctive ventrally face of the posterior ceratohyal (e.g., Leporinus, notched interhyal straddling a corresponding de- Figure 23). In the majority of characiforms the pression in the dorsal surface of the posterior basihyal is a relatively elongate element, ossified ceratohyal (Roberts, 1973:219). Large specimens approximate to the hypohyals and cartilaginous that were examined have the interhyal notch less anteriorly. The ossified and cartilaginous portions pronounced, but there is often (always?) a distinct of the element are both partially overlain dorsally sesamoid cartilage in the ligament that joins the NUMBER 378 25 interhyal to the posterior ceratohyal. Neither an equivalent interhyal form nor a comparable in- dependent ossification in the ligament have been encountered in the characiform outgroups ex- BTP amined. Prochilodontids also have a marked broadening of the branchiostegal rays, particu- larly the most lateral element, and a unique form of urohyal with highly developed, laterally di- rected ventral wings. Once again these apomor- VH phous modifications are not found in curimatids, anostomids, and chilodontids, but are present, evidently as homoplasies, in some distichodontids FIGURE 24.—Caenotropus maculosus, USNM 231545, hyoid (Nannocharax) and parodontids (Parodon). arch: A, left side, lateral view (branchiostegal rays removed); B, left side, dorsal view. (Stippling represents cartilage.) The overall hyoid arch form of anostomids and chilodontids is unique within characiforms. Sin- most notably in a subunit of the Distichodontidae gularly notable is the longitudinal foreshortening (e.g., Paradistichodus), in which it was apparently and transverse expansion of the lateral portions achieved independently. of the system (compare Figures 23 and 24 with The thickening of the lateral elements in the 22). Anostomids and chilodontids also share a hyoid arch, particularly the anterior and posterior posteroventrally slanting joint between the ante- ceratohyals, is most pronounced in the Chilodon- rior and posterior ceratohyals. The degree of tidae. Another notable feature of the hyoid arch obliqueness differs significantly within anostom- of that family is the prominent horizontal ridge ids, but a distinctly nonvertical joint is by far the extending from the posterior portion of the ante- most common condition in both families. Most rior ceratohyal onto the adjoining region of the other characiforms have a vertical articulation posterior ceratohyal. Chilodontids also have a between these elements. However, an oblique thickened, complex interhyal with a distinct me- area of contact between these elements occurs dial process that extends onto a depression on the sporadically in some other characiform groups, dorsomedial surface of the posterior ceratohyal. This process serves as the point of attachment for the ligament that joins the interhyal to the me- tapterygoid and quadrate. Such an attachment is a pronounced shift from the usual insertion of the ligament on the dorsal portion of the main body of the interhyal and is not known in the other characiform groups examined. This medial proc- ess of chilodontids is somewhat similar to the medial portion of the ventrally notched prochil- odontid interhyal. However, the Hgamentous at- tachments of the interhyal in prochilodontids are of the type generalized for characiforms rather than comparable to those of chilodontids.

SUSPENSORIUM AND ClRCUMORBITAL SERIES PC

FIGURE 23.—Leporinus megalepis, USNM 231541, hyoid arch: Many of the derived characters in the suspen- A, left side, lateral view (branchiostegal rays removed); B, left sorium of curimatids, prochilodontids, anostom- side, dorsal view. (Stippling represents cartilage.) ids, and chilodontids are associated with trophic 26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY specializations. Functionally, the majority of tral expansion of the distal margin of the lateral these modifications are related either to differing ethmoid's ventral wing contacts the palatine's degrees of mobility between the suspensorium posterodorsal process (Figure 25). Although de- and neurocranium or to relative motion of sub- rived for characiforms, a close articulation of the units of the suspensory apparatus. Two distinctive lateral ethmoid and palatine, per se, is not unique suspensorium modifications, one in curimatids to curimatids within the order. Various forms of and the other in anostomids involve the relation- contact between those elements are also found in ship of the suspensorium and the neurocranium the Old World hepsetid characiform Hepsetus and and serve to further reduce mobility between in the Neotropical characid genera Salminus, Aces- those systems. trorhynchns, Rhaphiodon, Hydrolycus, and Crenuchus. Characiforms typically have a single, antero- The Hepsetus lateral ethmoid-palatine joint differs dorsal articular surface on the palatine. This car- from that in curimatids in having two distinct tilagenous portion of the bone contacts both the contact points between the bones. Furthermore, vomerine region of the neurocranium anterodor- the lateral ethmoid's anterior process serves as the sally and the cartilage associated with the upper point of articulation rather than the bone's ven- arm of the maxilla laterally (the submaxillary tral wing as in curimatids. The section of the cartilage of Daget (1964, fig. 23) and ethmopa- palatine that contacts the lateral ethmoid in Sal- latine cartilage of Fink and Fink (1981:311)). The minus is a posterior extension of the originally palatine in curimatids is apomorphously ex- anterodorsal articular surface of the bone, a situ- panded posterodorsally to form a second, carti- ation also not comparable to that in curimatids. lage-topped articular surface. That cap of carti- The common possession of various derived char- lage is continuous ventrolaterally with the rela- acters (e.g., presence of an ossified rhinosphenoid) tively thick cartilaginous mass that overlies the indicates that Acestrorhynchus, Rhaphiodon, and Hy- lateral portions of the metapterygoid and ectop- drolycus are most closely related to taxa that lack terygoid (Figure 25). A corresponding cartilage- any lateral ethmoid-palatine contact. Therefore, capped articular process formed by an anteroven- it is most parsimonious to consider the presence of the articulation in those noncurimatid genera as homoplasious relative to the condition in the Curimatidae; a hypothesis also congruent with the distribution of shared derived characters that unite the Curimatidae and its close relatives (see METH "Phylogenetic Reconstruction"). The form of the lateral ethmoid-palatine con- tact in curimatids and the characid genus Crenu- chus does not differ notably. However, Crenuchus has a median orbital ossification which may rep- resent an autapomorphous form of rhinosphen- oid. If correct, that homology would support the MET hypothesis that Crenuchus is more closely related to characiforms with a rhinosphenoid than to those, such as curimatids, that lack it. Rhino- sphenoid-bearing taxa generally lack the second- MX ary palatinejoint. Therefore, if the median orbital ossification of Crenuchus is homologous to the rhi- FIGURE 25.—Potamorhina laticeps, USNM 121325, upper jaw nosphenoid, the secondary palatine joint of that and anterior portion of suspensorium and neurocranium, left genus would be presumed homoplasious relative side, lateral view (denser stippling represents cartilage). to the articulation in curimatids. In the absence NUMBER 378 27 of a homology between the median orbital ossi- most members of that family a well-developed fication of Crenuchus and the rhinosphenoid, it lateral process on the posterodorsal portion of the can, nonetheless, be noted that Crenuchus lacks the ectopterygoid serves as the attachment point for numerous synapomorphies shared by curimatids a cord-like ligament both thicker and stronger and their close relatives. That situation is incon- than that in chilodontids. As in chilodontids, the gruent with the union of curimatids and Crenuchus ligament passes lateral to the palatine, but rather in a monophyletic assemblage as would be sug- than terminating on the anteroventral margin of gested by their common possession of indistin- the lateral ethmoid's ventral process, it attaches guishable forms of lateral ethmoid-palatine joints. in a pit-like depression on the anteroventral por- Under either alternative the lateral ethmoid-pal- tion of the bone. atine articulations in curimatids and Crenuchus A broad connective tissue sheet between the (and perhaps its close relatives) are most parsi- neurocranium, particularly the parasphenoid, moniously considered independent acquisitions. and the medial and dorsal margins of at least the In anostomids and chilodontids the contact metapterygoid and mesopterygoid portions of the between the suspensorium and lateral ethmoid is suspensorium is ubiquitous among characiforms. tightened by an alternate system. Chilodontids In some members of the order, portions of the have a discrete cord-like ligamentous band that connective tissue sheet are thickened into one or arises from the unelaborated dorsolateral surface more cord- or strap-like ligamentous bands that of the ectopterygoid. That connective tissue band join the medial margins of the suspensorium to extends posterodorsally lateral to the palatine and the vomer or adjoining areas (e.g., prochilodon- attaches to the anteroventral surface of the lateral tids and some curimatids). However, examination ethmoid's ventral wing. Anostomids have the of characiform outgroups has not revealed taxa modifications carried further (Figures 26, 38). In other than anostomids and chilodontids with a thick ligament that extends between the suspen- sorium's lateral surface and the lateral ethmoid. The presence of some form of discrete lateral ethmoid-ectopterygoid ligament is, therefore, METH considered a shared derived character for chilo- dontids and anostomids. The posterolateral proc- ess on the ectopterygoid, which serves as an at- tachment point of the ligament, and the thick- ening of that connective tissue band are further elaborations of the system synapomorphous for the members of the Anostomidae. No traces of an ectopterygoid process or the associated ligamentous band are found in the anostomid Gnathodolus, contrary to the broad dis- PAR tribution of those characters in anostomids. In Gnathodolus, the elongate, horizontally aligned ec- topterygoid is very distant from the lateral eth- moid and is flexibly attached to the dorsal margin ECT of the quadrate (Winterbottom, 1980, figs. 41, 58). The primary function of the lateral ethmoid- QUA ectopterygoid ligament in other anostomids ap- FIGURE 26.—Anostomus species, USNM 231540, lateral eth- pears to be in reducing motion between the neu- moid and anterodorsal portion of suspensorium, left side, rocranium and suspensorium. The wide separa- lateral view (denser stippling represents cartilage). tion of the ectopterygoid from the lateral ethmoid 28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY and its mobility relative to the quadrate would The preceding discussion has dealt with mod- drastically diminish, if not eliminate, the stabiliz- ifications that involve the functional relationship ing action of the ligament in Gnathodolus. The of the suspensorium with the neurocranium. A absence of the connective tissue band and of the number of other characters are found in subunits associated ectopterygoid modifications is conse- of the suspensorium. Curimatids have the least quently not unexpected from a functional view- modified form of suspensorium (Figure 27) point. As noted, the ligamentous attachment is among the four families that are the primary present in chilodontids, the sister group of the focus of this study. Nonetheless, they have several Anostomidae. Furthermore, the other anostomids derived alterations of the system, including the examined, perhaps including Synaptolaemus the secondary articular facet on the palatine dis- sister genus to the lineage containing Gnathodolus cussed above. Curimatids are also distinguished (Winterbottom, 1980), have the lateral elabora- by a horizontal shelf along the dorsomedial sur- tion of the ectopterygoid and an ectopterygoid- face of the metapterygoid and sometimes meso- lateral ethmoid ligament. (A definite statement pterygoid (Figure 27B). This evidently apomor- on the presence or absence of the ligament in phous elaboration of the metapterygoid does not Synaptolaemus cannot be made based on available occur in the family's close relatives. The some- material, but the dorsolateral process on the ec- what similar horizontal shelf on the medial sur- toptyergoid is present, although not prominent.) face of the metapterygoid described by Winter- The lack of the ligament in Gnathodolus (and bottom (1980:50) in various anostomids is formed perhaps its sister genus Sartor) is most parsimoni- by the ventral bending of the dorsal margin of ously considered a secondary loss rather than the the metapterygoid rather than via an elaboration primitive absence of the band given the presence of the medial surface of that element. of the ligament in sister groups to Gnathodolus of Roberts (1974:429) used the presence of a increasing universality. strong, posteroventrally sloping flange located on

MET B OP

QUA SOP SYM PRE INT

FIGURE 27.—Potamorhina latior, AMNH 48677: A, suspensorium, left side, lateral view; B, detail of region of metapterygoid-quadrate fenestra, left side, medial view. NUMBER 378 29

OP

QUA

SYM A SOP

PRE FIGURE 28.—Ichthyoelephas species, USNM 231437: A, suspensorium, left side, lateral view; B, quadrate, left side, ventral view. the opercle's lateral surface just above the hy- of bony ridges that extend posterodorsally at omandibula-opercle joint in the Curimatidae as approximately right angles from the main body a distinguishing feature of that family (Figure of the process. Although similar secondary pro- 27). In an earlier paper Roberts (1973:213) re- cesses also occur in larger adult curimatids, in jected previous hypotheses of a close relationship prochilodontids the processes' number and degree of curimatids and prochilodontids, citing in sup- of development increases ontogenetically, leading port of his argument the absence of an opercular to a progressive masking of the originally discrete flange in prochilodontids, among other differ- flange. The flange is still apparent in — 80 mm ences. Such an absence would, in and of itself, be SL specimens but indistinguishable in individuals actually irrelevant to the question of the interfa- of over 100 mm SL in which the ridges have milial relationships since, if unique to curimatids, coalesced into a gently sloping, thickened area on the flange would be a synapomorphy for the the opercle's lateral surface. In large specimens members of that family with no bearing on the the thickening is not apparent in lateral view question of curimatid-prochilodontid relation- (Figure 28A), but it is readily visible when the ships. That point is moot, however, since prochil- bone is examined in transmitted light. The oper- odontid juveniles have an opercular flange iden- cular modifications of curimatids and prochilo- tical to that in curimatids. The prochilodontid dontids presumably serve to strengthen the op- flange undergoes a unique ontogenetic modifica- ercle in these microphagous fishes that use a tion that leads to the condition Roberts equated suctorial feeding mode that requires the move- with the plesiomorphous, laterally unelaborated ment of relatively large water volumes through opercle. Juvenile prochilodontids of ~ 20 to 40 the oral chamber. These characters are derived at mm SL have a posteroventrally slanting, dorsally two levels of universality. The presence of an undercut opercular flange. With increasing body opercular flange or a further derived condition of size, the members of the family develop a series that process is synapomorphous for the Curima- 30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY tidae and the Prochilodontidae, while the further quadrate joint is the highly specialized Gnathodo- elaboration of the flange is a shared derived lus, in which the ectopterygoid is shifted away character for the members of the Prochilodonti- from the anterior margin of the remaining ele- dae. A distinct opercular flange also characterizes ments of the pterygoid series. Reference to the the African characiform family Citharindae reconstruction of anostomin phylogeny arrived at (Vari, 1979:295), which also consists of micropha- by Winterbottom (1980) shows that Gnathodolus is gous filter feeders. However, the flange in that a member of a lineage whose sister species, Syn- taxon differs in several features from the process aptolaemus cingulatus, lacks ectopterygoid-quadrate in curimatids and juvenile prochilodontids. Fur- mobility. That concept of relationships in con- thermore, citharinids share numerous, often junction with the immobile contact of these ele- unique, synapomorphies with, and are evidently ments in other anostomids results in the most most closely related to, distichodontids, which parsimonious hypothesis: Gnatholodus achieved ec- lack a lateral elaboration of the opercle. Thus, topterygoid-quadrate mobility independently of the opercular flange of the African family is prochilodontids. considered homoplasious with respect to that in Pronounced quadrate-preopercle mobility is the Curimatidae and Prochilodontidae. another character unique to prochilodontids in The prochilodontid "suctorial" mouth is the Characiformes. The prochilodontid quadrate unique among characiforms with its functional is laterally expanded into a prominent horizontal modifications reflected in the numerous changes shelf that serves as an expanded attachment area in the form and relationships of the elements of for portions of the adductor mandibulae muscles. the suspensorium's anterior portion. Roberts Medially the quadrate has a comparable, though (1974) has previously discussed the osteology of less pronounced process that extends along the prochilodontids, and it is only necessary to review inner surface of the preopercle (Figure 28B). The the adaptations of phylogenetic interest. In lateral horizontal notch delimited by the medial and view the prochilodontid ectopterygoid is tripar- lateral quadrate processes fits into the correspond- tite, with a definite anteroventral process (Figure ing vertical notch bordered by dorsal and ventral 28A) that contrasts with the relatively straight subdivisions of the preopercle's anterior portion margin of the ectopterygoid in most characiforms. (Figure 28). This distinctive joint permits signifi- Equally distinctive is the high mobility of the cant vertical motion of the quadrate on the pre- ectopterygoid that results from its loose ligamen- opercle. A prominent lateral quadrate shelf also tous attachments to the quadrate and mesopter- occurs among characiforms in chilodontids and ygoid. Ectopterygoid-quadrate mobility is also anostomids. The phylogenetic hypotheses of re- present in hemiodontids and parodontids. How- lationships arrived at in this study indicate, how- ever, the relationships of the involved elements in ever, that these three families do not form a those taxa differ from the condition in prochilo- monophyletic group (see "Phylogenetic Recon- dontids, and neither family has the ectopterygoid- struction") but that, rather, prochilodontids are mesopterygoid mobility characteristic of prochil- more closely related to curimatids than to the odontids. Roberts (1973:218) also reported ecto- unit that consists of anostomids and chilodontids. pterygoid-quadrate mobility in the Anostomidae. Within that hypothesis of relationships there exist The anostomids on which that observation was two equally parisomonious explanations for the based were not specifically noted, although Schi- distribution of this derived character. First, that zodon fasciatus and an unidentified Leporinus species the quadrate shelf arose in the common ancestor are figured or cited in the text. However, the of the four families and was secondarily elimi- ectopterygoid and quadrate are tightly, immov- nated in curimatids. Second, that the quadrate ably joined in the Schizodon and Leporinus material shelf was independently acquired in the ancestor examined in the present study. Indeed, the only of the Prochilodontidae and in the common anostomid studied with a mobile ectopterygoid- ancestor of the Anostomidae and Chilodontidae. NUMBER 378 31

Anostomids have further expanded the attach- the modifications in the two taxa. A preopercle ment area for the adductor musculature via a with an enclosed laterosensory canal that extends lateral shelf on the preopercle's ventral arm. That as a continuous ossification to the level of the process forms part of the floor of the bony trough quadrate's articular facet is typical for characi- whose lateral wall is the posterolateral process of forms (e.g., the curimatid, Potamorhina latior, Fig- the quadrate. The preopercular shelf continues ure 27). The Anostomidae and Prochilodontidae, posteriorly beyond the terminus of the quadrate in contradistinction, have the anterior portion of in the form of a gradually diminishing ridge. the preopercular laterosensory canal enclosed by Although not unique to anostomids, a well-de- two or three discrete ossified tubes aligned along veloped lateral preopercular shelf is considered the ventral surface of the quadrate (Figures 28, derived within characiforms. A comparable pre- 29). These separate ossifications were termed the opercular elaboration also occurs in a subunit of subpreopercles by Roberts (1973:218), whereas the Distichodontidae (Vari, 1979:293). The dis- Winterbottom (1980:37) considered them to be tichodontid subunit that has the preopercular part of the preopercle. The homology of these expansion is evidently most closely related to ossified tubes in the two families is questionable. other members of that family, which lack a lat- Even if homologous, the overall most parsimoni- erally elaborated preopercle. The Distichodonti- ous hypothesis of relationships that includes the dae, in turn, shares a variety of derived characters two families indicates that the separate ossifica- with the Citharinidae in which the preopercular tions in anostomids and prochilodontids represent shelf is also absent. Thus, the presence of the independently achieved adaptations to functional preopercular shelf in some distichodontids is evi- requirements that can only be speculated upon. dently an independent acquisition relative to the At least for the Prochilodontidae, Winterbottom's process in anostomids. terminology is preferred, because it is considered Anostomids and prochilodontids may share more reflective of the probable homology of the two other derived suspensorium characters. Sev- elements. The autogenous ossifications in that eral questions exist, however, on the homology of family occur in the region plesiomorphously oc-

SPO

OP

SOP INT PRE

FIGURE 29.—, USNM 103847: A, suspensorium, left side, lateral view; B, quadrate, left side, ventral view. 32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY cupied by the anterior portions of the preopercle either scenario the autogenous preopercular (Figure 28). An anterior subdivision of the preo- laterosensory canal ossifications are homoplasies percle in prochilodontids is necessary for vertical in prochilodontids and anostomids. motion of the quadrate on the preopercle. Such The highly modified genus Gnathodolus differs mobility would be impossible or greatly restricted from other anostomids in its lack of the separate if prochilodontids retained the primitive rigid anterior preopercular ossifications (Winterbot- preopercle that extends along the anteroventral tom, 1980, fig. 41). The absence of the ossifica- surface of the quadrate. A hypothesis that the tions in that genus is most parsimoniously consid- separate ossifications arose via a fragmentation of ered a secondary loss in light of the phylogenetic the attenuate anterior portions of the preopercle distribution of the ossifications and our present is, thus, the simplest. The alternate assumption, information on relationships within the Anostom- inherent in Robert's terminology, that the tubes inae (Winterbottom, 1980). are nonhomologous with portions of the preoper- Most anostomids have the horizontal portion cle, would necessitate the loss of the anteriormost of the quadrate posteriorly bifurcate, as among section of the preopercle ventral to the quadrate prochilodontids (Figures 28B, 29B). However, in followed by the development of two or three new, anostomids the relationships of the quadrate's autogenous elements. medial process with the preopercle differ from the The quadrate-preopercle joint in anostomids is prochilodontid condition, thereby, casting doubt immobile. Thus, the anterior subdivision of the on the homology of the modifications in the two preopercle in that family cannot be ascribed to families. The quadrate's medial process in pro- the same underlying functional explanation ad- chilodontids runs internal to the preopercle with vanced for prochilodontids, moreso because the the longitudinal midline of the resulting quadrate phylogenetic reconstruction indicates that the notch aligned with the anteroposterior axis of the modifications are homoplasious. The anostomid ventral portion of the preopercle. In conjunction suspensorium (Figure 29) has undergone a pro- with other previously discussed suspensorium nounced anterior elongation with a consequent modifications, this restructuring of the quadrate wide separation of the anterior terminus of the permits vertical mobility of that bone on the quadrate and, thereby, the lower jaw from the preopercle. In anostomids, in contrast, the distinct main body of the preopercle. Under such circum- posterior notch in the preopercle, when present, stances the maintenance of continuity between is largely a consequence of the posterior expansion the laterosensory system of the preopercle and of the bone's lateral portion rather than the com- lower jaw necessitates a pronounced lengthening mon posterior development of its medial and of the preopercular laterosensory canal along the lateral processes. The midline of the notch defined ventral margin of the quadrate. If that extension by the medial and lateral processes of the anos- took place via a progressive ossification of the tomid quadrate's posterior region is not aligned anterior portion of the preopercular sensory with the longitudinal axis of the preopercle but, canal, then the extremely attenuate ossified tube rather, lateral to it. Consequently, the medial that results might subsequently subdivide. Alter- quadrate process does not extend internal to the natively, the laterosensory system might extend preopercle, but, rather, often inserts into a notch forward as an unossified canal, which is subse- in that bone to form an immobile joint. In light quently partially strengthened by autogenous os- of these differences, the equivalence of the poste- sifications that developed anterior to the preoper- rior quadrate bifurcation in prochilodontids and cle per se. Data relevant to a selection between anostomids is questionable, moreso since the most these alternative possibilities is not available at parsimonious hypothesis of relationships of the this time. The most parsimonious hypothesis of involved families indicates that these are homo- relationships for anostomids, prochilodontids, plasies. and their close relatives indicates that under A final suspensorium character of note involves NUMBER 378 33 the hyomandibula in anostomids and chilodon- the hyomandibula in anostomids. tids. In both families, that bone has a variously The synapomorphous form of the second in- developed process that extends over the postero- fraorbital of prochilodontids is the only phyloge- dorsal portion of the metapterygoid. The posses- netically significant character within the cir- sion of such a process is evidently derived within cumorbital series at the family level of the four- characiforms and is not known in prochilodontids family group. All prochilodontids examined have and curimatids. It is found, evidently as an in- the ventral margin of the bone anteroventrally dependent acquisition, in some serrasalmines (Co- expanded into a distinct triangular process. The lossoma), parodontids (Parodon, Saccodon), hemio- anterior border of that process, the ventral margin dontids (Bivibranchia), and characids (Acestrorhyn- of the enlarged first infraorbital and the antero- chus). ventral edge of the second infraorbital delimit a Gregory and Conrad (1938), followed by Gery triangular notch that borders the posterior mar- (1961), apparently misinterpreted the identity of gin of the large fleshy lips (Roberts, 1973:229). certain elements in the anostomid suspensorium. No similar alteration of the second infraorbital Comparisons of the illustration of the osteology was found in the characiform outgroups exam- of an unspecified Leporinus species in Gregory and ined in the present study. Conrad's figure 28 with Figure 29 of this study Gregory and Conrad (1938:348) reported that shows their metapterygoid is actually a portion a supraorbital is absent in the anostomid genus of the hyomandibula. The entopterygoid (= me- Leporinus, an erroroneous observation corrected sopterygoid) of those authors should be more by Gery (1961:103). Gery's illustrations of the properly identified as the metapterygoid. The circumorbital series and the dermal ossifications unlabelled ectopterygoid and palatine are illus- anterior to the orbit (1960, fig. 2; 1961, figs.12 , trated so as to appear as portions of the quadrate 15) utilized osteological terminology inconsistent and lateral ethmoid, respectively. Gery's more with that of previous and subsequent authors. detailed illustrations of Leporinus' head osteology The ossification he labels as the lachrymal is the (1961, figs. 12, 14) have similar problems. The bone that Weitzman (1962:28) termed the element labelled as the palatine in his drawing of antorbital. No other author dealing with chara- L. friderici is actually a composite of that element ciforms has identified the antorbital as the lach- and the mesopterygoid. This error results in the rymal and such a homology appears to be erro- remaining elements in the series being sequen- neous. The lachrymal of teleosts has traditionally tially misidentified. His entopterygoid (= meso- been equated with the anteriormost (first) infraor- pterygoid) should be identified as the metapter- bital, whereas Gery (1960, fig. 2; 1961, figs. 12, ygoid. The element labelled by Gery as the me- 15) labelled the anteriormost infraorbital as the tapterygoid is actually the anteroventral section jugal in his figures. The use of jugal for a subunit of the hyomandibula. Gery illustrates a joint of the infraorbital series in ostariophysan fishes between a posterodorsal, triangular hyomandi- apparently follows Gregory and Conrad (1938). bula, and a vertically oriented metapterygoid. Those authors, however, used jugal and infraor- That line of demarcation actually represents the bital 2 interchangeably, whereas Gery applied location of a distinct ridge along the lateral sur- the term to the first infraorbital. face of the hyomandibula, rather than a point of contact between two bones. The actual hyoman- dibula of Leporinus is equivalent to the hyoman- PECTORAL GIRDLE dibula plus metapterygoid of Gery's illustration. The common name for chilodontids, headstan- As a consequence of these misinterpretations, ders, refers to their oblique, head-down swimming Gery's osteological description of various portions orientation (Gery, 1977b:212-213). This highly of the suspensorium (1961:104) is misleading, unusual swimming position and the resultant particularly the comments on the relative size of atypical forces that act on the body perhaps 34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

-POST two primary processes (Weitzman, 1962, fig.19) . The dorsal process of the posttemporal extends dorsomedially along the posterior edge of the EXT parietal, to which it is tightly attached. A second smaller, strut-like process extends from the ven- tromedial surface of the posttemporal to contact the rear of the neurocranium. The laterosensory canal segment in the post temporal's ventral por- tion communicates anteriorly with the sensory canal of the extrascapular and posteroventrally with that in the dorsal portion of the supracleith- rum. The typical characiform extrascapular is triangular with a tripartite laterosensory system that contacts the canals of the pterotic anteriorly, PCL-2 posttemporal posteriorly and parietal dorsally. The chilodontid posttemporal is greatly altered relative to the hypothesized plesiomorphous mor-

PCL-3 phology described above. The bone is reduced ventrally, with the ventromedial posttemporal sc process and the laterosensory canal segment ab- COR sent. The dorsal, relatively unaltered, portion of the bone is elongate, tapers dorsally and attaches FIGURE 30.—Caenotropus maculosus, USNM 231545, pectoral girdle, left side, lateral view (radials and pectoral fin rays firmly to the posterior margin of the parietal removed). (Figure 31). The reduction of the posttemporal's

account for most of the numerous unique pectoral girdle modifications in the family. Examination of the overall form of the girdle shows that the proportions of the major elements differ markedly from those encountered in other characiforms. Unlike many characiforms, chilodontids have a cleithrum with a distinct posterior development of the lamina above the pectoral fin base (Figure 30). More notable is the ventral expansion of the supracleithrum's main shaft over the cleithrum's lateral surface. Consequently, the supraclei- thrum's length is well over half of the girdle's PTE total vertical span. The increased overlap of the SPH cleithrum on the supracleithrum increases the internal rigidity of the pectoral girdle, with the flexibility of that complex on the neurocranium reduced by alterations of the supracleithrum, SAP posttemporal, and pterotic. With few exceptions, SCL characiforms have the pectoral girdle attached to the neurocranium via a relatively complex post- FIGURE 31.—Caenotropus maculosus, USNM 231545, dorsal temporal. In the typical condition the posttem- portion of pectoral girdle and posteroventral portion of poral's main body is triangular and gives rise to neurocranium, left side, lateral view. NUMBER 378 35 laterosensory canal segment and the supraclei- or even contacts, the medial surface of the supra- thrum's dorsal expansion result in direct contact cleithrum. Chilodus and Caenotropus have that pter- of the extrascapular and supracleithral laterosen- otic process posterolaterally expanded into an sory canal segments. A reduced posttemporal sen- obliquely aligned, flattened plate. That plate con- sory canal typically occurs in various smaller tacts the medial surface of, and corresponds in characiforms that have an overall reduction in form to, an associated anterior process of the head ossification. In those taxa, however, this supracleithrum (Figure 31). This articulation, to- reduction results in a gap in the laterosensory gether with the above-described dorsal joint be- canal system rather than direct communication tween the pterotic and dorsal tip of the supra- between the canals of the supracleithrum and cleithrum, renders the pectoral girdle immobile extrascapular as in chilodontids. The plesiomor- relative to the neurocranium. Although a contact phously present ventromedial posttemporal proc- of the supracleithrum with the posteroventral ess is also absent in some parodontids and in process of the pterotic occurs in various characi- various less well-ossified characiforms assigned to forms, such as articulation via a distinct distally a number of different families. The information widened posteroventral pterotic process has been of this study and other data indicates that it is encountered in only one group of nonchilodontid most parsimonious to consider the chilodontid characiforms. The African family Citharinidae posttemporal reduction as nonhomologous with has the posteroventral portion of the pterotic those in the outgroups. The chilodontid extra- flared outwards into a slightly bi-pronged plate scapular is less elaborate than that common to that contacts the medial surface of the supra- most characiforms. The anterior laterosensory cleithrum's dorsal portion. Comparison of these canal is absent as a distinct process, being repre- functional complexes in chilodontids and cithar- sented only by an anterior opening midway along inids reveals that the pterotic expansion in the the margin of the remaining ossified tube. Citharinidae differs in overall form from the dis- The marked reduction in the relative size and tally ovoid supporting process of the Chilodonti- complexity of the chilodontid posttemporal elim- dae. The citharinid supracleithrum also lacks the inates that element as the primary junction of the well-developed anterior process that articulates pectoral girdle and neurocranium. Rather, in with the pterotic in chilodontids. Citharinids, chilodontids the primary dorsal articulation be- furthermore, do not possess the other distinctive tween the pectoral girdle and the neurocranium pectoral girdle modifications of chilodontids and is achieved via the insertion of the dorsal tip of the Citharinidae shares uniquely derived char- the supracleithrum into a distinct pocket in the acters with, and is evidently most closely related posteroventral corner of the pterotic (Figure 31). to, the Old World Distichodontidae (Vari, The expanded dorsal portion of the supraclei- 1979:324). These factors support a hypothesis of thrum is overlain dorsolaterally by the reduced the independent acquisition of the more ventral extrascapular and is bordered dorsally by the of the pterotic-supracleithral contacts in the Chil- remaining dorsomedial portion of the posttem- odontidae and Citharinidae. poral. No comparable direct pterotic-supraclei- Three postcleithra along the posterior margin thral contact has been found in the other chara- of the pectoral girdle are typical for characiforms. ciforms examined, nor has a similar association The dorsalmost (postcleithrum 1) is a flattened, of the supracleithrum with the posttemporal and round ossification located at the posterior margin extrascapular been encountered in the order. of the contact area of the supracleithrum and Chilodontids also have a second area of pter- cleithrum. Postcleithrum 2 is usually a flattened, otic-supracleithral articulation. The posteroven- ovoid bone at the rear of the cleithrum's posterior tral corner of the characiform pterotic typically lamina. The straight or slightly curved, rod-like bears a distinct process that ranges in form from postcleithrum 3 attaches to the medial surface of a short spur to a distinct spine that approaches, postcleithrum 2 and extends ventral of the latter 36 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY element. Postcleithra of this type are common to ture that communicates with the sensory canal of most curimatids, prochilodontids and anostom- the supracleithrum. The anostomid extrascapular ids. Chilodontids, however, have that system has an additional posterodorsal sensory canal seg- modified both at the familial and intrafamilial ment opening onto the posterior or posterodorsal levels. In all members of that family, postclei- margin of the bone. The resultant quadripartite thrum 1 is lacking (Figure 30). Although the system is not encountered in the other families absence of the element is considered derived, its under discussion. Gregory and Conrad (1938, fig. lack is not unique to this family within the Char- 28) mistakenly illustrate the extrascapular (their aciformes. No postcleithra are present in the gas- scalebone) of Leporinus as carrying a tripartite teropelecins of the family Characidae (Weitzman, laterosensory canal; an error repeated by Gery 1954:226). Postcleithrum 1 is also missing in the (1961, figs. 12, 16) in his discussion of Leporinus African hepsetid characoid Hepsetus (Roberts, friderici. However, all specimens of L. friderici and 1969:426), the distichodontids Nannocharax and other Leporinus species examined have the quad- Hemigrammocharax (Vari, 1979:311) and the New ripartite extrascapular laterosensory canal system World anostomid genera Synaptolaemus and Sartor herein considered typical for anostomids. (Winterbottom, 1980:46) among others. Nonethe- less, the results of this study and our present understanding of phylogenetic relationships in NEUROCRANIUM the order indicate that the losses in those taxa are Pronounced differences in aspects of neuro- homoplasious relative to the absence of the ele- cranial morphology occur in each of these fami- ment in chilodontids. Within the Chilodontidae, lies. Many, including subtle differences or contin- two different conditions of the third postclei- uous variation in the form or proportions of var- thrum exist. The bone is altered into a highly ious bones, are difficult to quantify and/or polar- curved, anteromedially shifted ossification in ize. The characters noted in the following discus- Caenotropus (Figure 30), but is totally lacking in sion, consequently, tend to be discrete apomor- Chilodus. The utility of these postcleithral adap- phies, many of which were previously noted in tations in phylogenetic reconstruction is reduced association with changes in other body systems, by the existence of two equally parsimonious with which they are functionally associated. Such explanations for the distribution of these charac- previously discussed characters are only cited in ters. First, the curved third postcleithrum actually passing in this section. represents a synapomorphy for all chilodontids, The mesethmoid is very broad in curimatids, with the bone having been subsequently lost is with the large associated cartilagenous ethmoid Chilodus. Second, the form of the bone in Caenotro- block particularly distinctive. That cartilage mass pus and the absence of the ossification in Chilodus fills the space between the mesethmoid dorsally each represent synapomorphies for their respec- and the vomer ventrally and has posteriorly di- tive genera independently modified from the gen- eralized characiform type of third postcleithrum. rected lateral processes that contact the corre- Present data do not permit a decision as to which sponding anterior projections of the lateral eth- of these explanations is preferable. moid. This cartilage mass undergoes a progressive laminar ossification of its exposed surfaces, but The numerous pectoral girdle modifications in the major portion remains as an unossified block the Chilodontidae contrast with the relatively even in adults. Such a large cartilagenous eth- invariant forms of that system, at least at the moid block has also been found only in the family level, in the Curimatidae, Prochilodonti- African Citharinidae among characiforms exam- dae, and Anostomidae. The single exception in- ined in the present study. The similarities in the volves the anostomid extrascapula. The extra- ethmoid region morphology may be a reflection scapular laterosensory system of characiforms is of their common microphagous feeding habits, typically tripartite with a single posterior aper- but these similarities are homoplasious under our NUMBER 378 37 present concepts of characiform phylogeny. These toral girdle in the Chilodontidae are two adap- concepts indicate that the Citharinidae and Cur- tations of the pterotic, which serve to reduce the imatidae are not each others closest relatives (see mobility of the pectoral girdle relative to the "Phylogenetic Reconstruction" and Vari, 1979). neurocranium. These were discussed at length in The mesethmoid in the Chilodontidae, in con- the section on the pectoral girdle (p. 34). tradistinction to that in curimatids, is laterally Variation exists within the Characiformes both compressed and anteroventrally developed into a in the number of posttemporal fossae and in the distinctly angled process that extends between bones that border some of the apertures. The vast the medial margins of the premaxillae (Figure majority of characiforms are characterized by a 32). The ventral expansion of the mesethmoid dorsal and posterodorsal pair of fossae on either results in the total separation of the premaxillae side of the neurocranium. Curimatids possess and, more interestingly, in the mesethmoid con- those apertures and an additional third small tributing to an appreciable portion of the margin round fossa entirely within the epioccipital. This of the upper jaw (sec "Teeth and Jaws"). As type of third posttemporal fossa also occurs in the noted on page 10, this ethmoid region morphol- Hemiodontidae (Roberts, 1974:416, fig. 5) and ogy is evidently synapomorphous for the members Parodontidae (Roberts, 1974:425, fig. 59). A more of the Chilodontidae. extensive, vertically ovate third posttemporal The Curimatidae has reduced the flexibility of fossa bordered by both the epioccipital and ex- the suspensorium on the neurocranium via a occipital is found in the Old World characiform distinct direct articulation between the lateral families Citharinidae and Distichodontidae ethmoid and palatine (Figure 25). The typical (Vari, 1979, fig. 15) arid the Neotropical characid characiform lateral ethmoid has a discrete narrow tribe Cynodontini (Vari, 1979:289). edge along the entire lower margin of its ventral The presence of an epioccipital or epioccipital- wing. In curimatids, there is instead a distinct exoccipital posttemporal fossa is apparently de- longitudinal expansion of the ventral midsection rived within the Ostariophysi with the epioccipi- of the wing into a cartilage-capped articular facet, tal portions of each aperture presumably homol- which contacts a similar palatine process. As ogous. Comparable apertures have not been re- discussed in the description of the suspensorium, ported or discovered in characiforms outside of this is evidently a synapomorphy for all curima- these groups or in other otophysans. The posses- tids. sion of such openings would, thus, appear to be Associated with the overall changes of the pec- apomorphous within the order. The available

METH

METH

FIGURE 32.—Caenotropus maculosus, USNM 231545: A, anterior portion of neurocranium, left side, lateral view (large stippling represents cartilage); B, anterior portion of neurocranium and upper jaw, dorsal view. 38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY information does not, however, permit a polarity determination on the presumed transition series between the epioccipital limited and epioccipital- exoccipital bordered forms of third posttemporal fossae. The exact phylogenetic relationships of the two other characiform families with the curimatid form of epioccipital fossa have not been rigorously examined. Hemiodontids (sensu Roberts, 1974) have a median orbital ossification, the rhino- sphenoid, unique to a subunit of the Characi- formes among fishes. The possession of that ele- ment is, thus, considered a synapomorphy uniting the components of that assemblage. That char- acter and others unite the Hemiodontidae most closely to characiforms other than curimatids, which lack the bone. The phylogenetic relation- ships of the Parodontidae are enigmatic. Roberts (1974:429) noted various characters common to the Parodontidae and Hemiodontidae. However, he felt that traditional concepts of a close rela- tionship of the two families were not well corra- FIGURE 33.—Scaphium and rear of neurocranium, left side, borated. In the absence of a tested hypothesis of lateral view: A, Leporinus reinhardti, AMNH 4O1O4SD; B, the relationships of parodontids to a group of Psectrogaster amazonica, AMNH 40088SD. (Scale = 5.0 mm.) noncurimatid characiforms, I can only note that the series of characters that unite curimatids with teromedial margins of the exoccipitals diverge prochilodontids, anostomids, and chilodontids, laterally to form a median arch. The resultant which lack the opening, would indicate that the opening encompasses the lateral borders of the common possession of a epioccipital posttemporal foramen magnum dorsally, and the cavum sinus fossa in curimatids and parodontids is homopla- imparis ventrally. A horizontal sheet of bone sious. extends from the medial surface of the main body Curimatids and prochilodontids share a dis- of each exoccipital to meet its counterpart at the tinctive modification of the basic characiform midline. The shelf formed by those processes bauplan of the neurocranium's posterior region. serves both as the floor of the forman mangum The most widespread and hypothesized plesio- and roof of the cavum sinus imparis. In lateral morphous characiform condition of the portions view (Figure 33A), the posterior margin of the of the exoccipitals proximal to the foramen mag- exoccipital proximal to the foramen magnum is num is illustrated in Figures 33A and 34. The distinctly concave. Viewed from the rear (Figure exoccipitals are complex, paired elements in con- 34) the region of concavity is seen as a bony pillar tact medially. Each exoccipital articulates ven- bounded by the lateral occipital foramen and trally with the median basioccipital and along its foramen magnum, with an indentation, the fossa dorsal border contacts the unpaired supraoccipi- for the scaphium, present on its posterior surface. tal. The dorsal portions of the exoccipitals meet The concave medial lip of this scaphial fossa medially along a vertical joint that extends ven- corresponds in shape to, and closely approxi- trally from the articulation of the exoccipitals mates, the anterior margin of the first Weberian with the supraoccipital to the foramen magnum. ossicle, the scaphium, to which it is ligamentously Ventral to that area of midline contact, the pos- connected. In the majority of characiforms out- NUMBER 378 39

LOC

CSI

BOC FlCURE 34.- -Leporinus reinhardti, AMNH 40104SD, region of foramen magnum, posterior view. side of curimatids and prochilodontids, the fossa amen and communicates anteriorly with the neu- ranges from a negligible depression in some an- rocranium's interior. This expanded fossa for the ostomids (Figure 34) to a distinct cul-de-sac in scaphium subdivides the primitively single verti- characids such as Brycon (Weitzman, 1962, fig. 5). cal pillar bounded by the foramen magnum and A foramen, the lateral occipital fenestra, is typi- lateral occipital foramen into two parts (Figure cally found along the midlateral surface of the 35). The medial portion that borders the foramen exoccipital. That aperture's degree of develop- magnum and cavum sinus imparis is deeply in- ment differs within the order, ranging from a dented to accommodate the anterior margin of barely apparent foramen to a large opening oc- the scaphium to which it is ligamentously at- cupying most of the surface of the exoccipital tached. A marked outwards shift of the primi- lateral to the foramen magnum. The lateral oc- tively lateral edge of the fossa results from the cipital fenestra typically has a nearly vertical expansion of that aperture. Thus, the associated orientation and serves, at least in part, as a pas- portion of the exoccipital's lateral surface is now sage for nerves. more obliquely aligned than in the hypothesized Curimatids and prochilodontids share a dis- primitive condition. With this change in inclina- tinctive restructuring of the portion of the exoc- tion the opening of the lateral occipital fossa faces cipital bounded by the lateral occipital foramen more posterolaterally in curimatids and prochil- and the foramen magnum. In both families the odontids than in other characiforms. plesiomorphous cul-de-sac fossa for the scaphium The rear margin of the exoccipital lateral to is greatly expanded laterally and anteriorly (Fig- the enlarged fossa for the scaphium is also poste- ure 35). As a consequence the slightly or moder- riorly expanded. This expansion results in a single ately developed scaphial fossa common to most inclusive opening leading to the foramen mag- characiforms is altered in curimatids and pro- num, cavum sinus imparis, and the paired sca- chilodontids into a large foramen that is contin- phial fossae. The foramen magnum and sinus uous anterolaterally with the lateral occipital for- cavum imparis apertures are consequently in- 40 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

LOC

BOC FIGURE 35.—Psectrogaster amazomca, AMNH 40088SD, region of foramen magnum, posterior view. eluded in the neurocranium rather than located men. In gasteropelecins the foramen's lateral along its posterior margin as in the primitive opening is shifted ventrally to a deep fossa barely condition. The posterior extension of the lateral posterodorsal to the lagenar capsule. With this margin of the exoccipital also results in the pos- repositioning, the foramen's opening is now di- terior portion of that element overlapping the rected ventrolaterally, whereas a lateral orienta- scaphium's anterior section to the level of the tion is common to the majority of characiforms, attachment point of the interosseus ligament (Fig- and a slightly dorsolateral alignment is shared by ure 33B). curimatids and prochilodontids. The ventral po- Examination of a wide variety of other chara- sition and ventrolateral orientation of the fora- ciforms and Ostariophysans has revealed only a men in gasteropelecins, contrary to the more single group, the Gasteropelecinae, with compa- dorsal location and slightly dorsolateral align- rable exoccipital modifications (Weitzman, ment of the aperture in prochilodontids and cur- 1954:218, figs. 5, 10). The gasteropelecin exoccip- imatids, is not, in itself, evidence of the nonho- ital, as that in curimatids and prochilodontids, mology of the other shared exoccipital modifica- has the deep foramen form of fossa for the sca- tions. The variation in lateral occipital foramen phium. This results in the inclusion of the fora- position might rather represent different apomor- men magnum, cavum sinus imparis, and paired phous adaptations of a shared derived ancestral scaphial fossae in a large common opening and condition common to curimatids, prochilodon- the anterior overlap of the scaphium by the ex- tids, and gasteropelecins. occipital's margin. The only significant difference A hypothesis of the homoplasy of the exoccip- between the gasteropelecin exoccipital and that ital alterations must, therefore, depend on a phy- common to curimatids and prochilodontids oc- logenetic reconstruction of greater generality curs in the position of the lateral occipital fora- within characiforms. The results of this study NUMBER 378 41 indicate that the phylogenetic relationships of extends obliquely posterodorsally to attach to the curimatids and prochilodontids lie with characi- medial surface of the second rib, and terminates forms other than gasteropelecins (see "Phylo- posteriorly on the anterior border of the third rib genetic Reconstruction"). The question of the (Figure 36). A second, shorter ligament, dorsal possible relatives of gasteropelecines within char- and parallel to the first, extends between the first aciforms has not been critically analyzed, using and second ribs. Anostomids have a greater num- more recently formalized systematic procedures. ber of ribs incorporated into the system, although Nonetheless, Weitzman's conclusion (1954:231) the individual intercostal ligaments are not as that "the Gasteropelecinae probably arose from developed as in chilodontids. The ventral liga- some generalized characid somewhat like As- ment in anostomids commences on the posterior tyanax, Brycon, and Bryconamericus" is consistent margin of the first full pleural rib, attaches to the with our present knowledge of character polarities medial margins of the second and third ribs,an d and phylogenetic relationships within the Char- terminates posterodorsally on the anterior border aciformes. Although we are presently unable to of the fourth rib. A second, more dorsal, ligament rigorously test a hypothesis of the probable hom- extends between the first and third ribs, with an oplasy of the exoccipital modifications of gaster- attachment to the inner surface of the second rib. opelecins on the one hand and those in the assem- The described pattern is the simplest within the blage consisting of curimatids and prochilodon- family, with the number of ribs and intercostal tids on the other, the available data, nonetheless, ligaments in the system further increased in some indicates that these seemingly equivalent char- anostomids. The ligaments' exact function is un- acters represent convergencies. A final neurocranial character of note is the size of the lagenar capsule of curimatids. In the Gurimatidae, the capsule is significantly ex- panded into a large bulbous chamber. The apo- morphous enlargement is notable both relative to the condition in the other three families under consideration and the various characiform out- groups examined.

VERTEBRAL COLUMN AND RIBS A variety of derived characters that involve the anteriormost pleural ribs and the associated ver- tebrae occur in anostomids and chilodontids. One of the more distinctive characters common to these families are the two or more discrete, well- developed intercostal ligaments that join the mid- sections of three or more of the anteriormost full UG pleural ribs. These intercostal ligaments presum- ably are thickened sections of the broad connec- PR tive tissue sheet that typically joins the medial margins of the pleural ribs. The intercostal liga- ments in chilodontids are thicker than those in anostomids and span a maximum of three ribs. FIGURE 36.—Chiloduspunctatus, USNM 231542, fifth to eighth The ventral ligament in chilodontids arises from vertebrae, dorsal portions of anteriormost full pleural ribs the posterior margin of the first full pleural rib, and intercostal ligaments, left side, lateral view. 42 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

certain, but the interconnected anterior pleural elongate medial surface of the parapophyses ar- rib complex in these fishes may be associated with ticulates with a vertically elongate fossa. That their oblique, head-down swimming position. articular surface incorporates ventrally the ple- The oblique body orientation during locomo- siomorphous small fossa on the lateral face of the tion is most pronounced in the Chilodontidae centrum and a vertically elongate flange on the (Gery, 1977b:212-213), which have the thickest lateral surface of the neural arch and spine (Fig- intercostal ligaments. The first three full pleural ure 37). Such lateral elaborations of the neural ribs spanned by these heavy bands in chilodontids arch and spine are unknown elsewhere in the have their proximal portions and the parapo- order. This degree of dorsal development of the physes, neural spines, and arches of the associated components of this complex is greatest on the vertebrae extensively restructured. Among char- second full pleural rib and associated portions of aciforms the typical moderately developed para- the sixth vertebrae. This development is also ap- pophyses on the first three full pleural ribs insert parent, though not as pronounced, on the first into circular or ovoid articular fossae limited to and third full pleural ribs. The consolidation that the respective centrum's lateral surface (Weitz- results from these adaptations eliminates the mo- man, 1962, fig. 12). However, the chilodontids tion of the dorsal portions of the ribs relative to Caenotropus and Chilodus, have the proximal por- the vertebral column, particularly given the more tions of the first three full pleural ribs expanded distal interconnections of these ribs via the afore- dorsally, which results in the proximal portions mentioned intercostal ligaments. of the ribs having a triangular form with maxi- mum vertical development in the region adjoin- MYOLOGY ing the parapophyses (Figure 37). The parapo- physes are also expanded vertically relative to the Considerable variation exists in the morphol- ossification in other characiforms. The dorsally ogy of the jaws, suspensorium, gill arches, and the parts of the neurocranium associated with those systems among curimatids, prochilodontids, an- ostomids, and chilodontids. Congruent with the osteological changes are a series of adaptations of NS the associated musculature. Two myological apomorphies have already been described in the discussions of the gill arches PR and epibranchial organs. The first is the distinc- tive vertical muscle band that extends along the anterior and posterior surfaces of the chilodontid epibranchial organ's dorsal portions (see "Epi- branchial Organs"). The other is the greatly PR thickened obliquues dorsalis associated with the highly modified fourth gill arch in the Anostom- idae and Chilodontidae (see "Gill Arches"). The form of the adductor mandibulae is hy- pothesized to be synapomorphous for the four- family unit. In his discussion of the cheek mus- culature in Leporinus, Alexander (1964:183-184) CEN noted the presence of a discrete medial portion of FIGURE 37.—Chilodus punctatus, USNM 231542, sixth verte- the adductor mandibulae, which he suggested bra, parapophyses, and dorsal portion of pleural ribs, ante- was the A3 section of that muscle. That homology rior view. is reasonable within the context of our present NUMBER 378 43

AAP DO

LIG

LAP PMX

HYO

FIGURE 38.—Leporinus striatus, USNM 231948, cheek and suspensorium musculature, left side, lateral view. understanding of characiform myology. A dis- as a discrete muscle band margined medially by tinct A3 portion of the adductor mandibulae that a tendinous sheet, which coalesces anteriorly with arises from the lateral surface of at least the the tendon of A2. A comparable situation exists mesopterygoid and metapterygoid is common to in serrasalmins. Thus, the A3 of these taxa differs curimatids, chilodontids, prochilodontids, and in origin and mode of insertion relative to the anostomids, with further pronounced apomor- condition of the A3 form in the Curimatidae, phous changes unique to each of the latter two Prochilodontidae, Anostomidae, and Chilodonti- families (Figures 38, 39). In its simplest condition, dae. Consequently the characteristic morphology as m curimatids and chilodontids, the A3 is of the A3 section of the adductor mandibulae is formed by a series of anterolaterally slanting fi- hypothesized to be a synapomorphy for the latter bers that have an origin on the dorsolateral sur- four-family clade. face of the mesopterygoid and metapterygoid. Two sets of apomorphous modifications of the These muscle slips attach laterally to the tendi- cheek musculature are characteristic for the spe- nous band located along the medial surface of the cies of anostomids on one hand and those of A2 portion of the adductor mandibulae. No com- prochilodontids on the other. One character in parable form of A3 has been encountered in the the Anostomidae is particularly noteworthy. The broad, but by no means exhaustive, outgroup anostomids available for myological study comparisons carried out among other characi- (Abramites, Anostomus, Leporellus, Leporinus, Rhy- form taxa, nor has it been reported in the litera- tiodus, and Schizodon) have a triangular muscle in ture. The A3 reported in citharinids and disticho- the posterodorsal portion of the orbital chamber dontids (Vari, 1979:316) differs in several fea- (Figure 38). The V-shaped ventral portion of the tures. That muscle arises from the anteromedial muscle is capped by an aponeurotic sheet that surface of the hyomandibula and extends forward attaches onto a discrete process on the anterodor- 44 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

AAP DO

PMX

LAP MX

DEN

FIGURE 39.—Prochilodus rubrotaeniatus, USNM 225419, cheek and suspensorium musculature, left side, lateral view. sal margin of the hyomandibula. The muscle fans rectly to the maxilla (Figure 38). A second section out dorsally with an origin on the anteroventral of the Ai, medial to the above, arises from the face of the sphenotic and orbital surface of the entire ventral surface of the trough formed by the frontal. The phylogenetic derivation of the mus- lateral shelf of the quadrate and preopercle. Com- cle is uncertain, but the levator arcus palatini is mencing posteriorly at the terminus of the quad- the most likely source. That homology hypothesis rate, the muscle extends anteriorly with a tendi- is advanced primarily on the evidently common nous band along its dorsomedial margin. That function of the two muscles and their general connective tissue sheet progressively thickens an- proximity. Furthermore, in some characiforms teriorly to form a distinct tendon, which attaches the medial portion of the levator arcus palatini to the maxilla. The A2 portion of the adductor overlaps the anterior margin of the hyomandi- mandibulae is significantly more highly devel- bula; the medial portion also has a limited medial oped transversely in anostomids (Figure 38) than origin along the anteroventral face of the sphen- in chilodontids, curimatids, and prochilodontids otic spine comparable to, though not as extensive (Figure 39). In those families, the posterior por- as, that of the discrete triangular muscle in an- tion of the A2 section of the adductor mandibulae ostomids. Outgroup comparisons have failed to lies lateral to the levator arcus palatini with an reveal another characiform group with a similar origin solely from the angle of the preopercle. discrete muscle. Such a form of the muscle is also common to The adductor mandibulae of anostomids is numerous generalized characiforms and evidently unusually altered. The Ai section of the muscle is primitive in the order. In the Anostomidae, by subdivided into two portions. The first section is contrast, the posterior portion of A2 has an addi- located along the anteroventral portion of the tional medial section that extends internally to cheek and extends anterodorsally to attach di- the ventral portion of the levator arcus palatini NUMBER 378 45 and has an apomorphous partial origin from a distinctly concave region of the anteroventral portion of the hyomandibula. The junction between the posteriorly separated HI lateral and medial sections of A2 in anostomids is demarcated by a tendinous band, which progres- sively thickens anteriorly to form a distinct ten- don that extends forward to an insertion on the lower jaw. A considerable portion of the median margin of that tendon serves as the insertion site for the A3 portion of the adductor mandibulae. That muscle section is greatly developed relative to the condition in curimatids, prochilodontids, and chilodontids, with this expansion particularly pronounced in the region of the ventral wing of the lateral ethmoid (Figure 38). This dorsally bulging muscle section attaches to the medial and dorsal surfaces of the ligament and joins ante- riorly with the medial surface of the dorsally expanded anterior portion of A2. The dorsal con- FIGURE 40.—Prochilodus rubrotaeniatus, USNM 225419, mus- tact between these two muscle sections results in culature of the ventral surface of the head, ventral view the common tendon on the A2 and A3 running (branchiostegal rays of right side removed). internal to the muscle masses that attach to the lower jaw, rather than along their dorsal margin. area of origin along the horizontal arm of the Such a morphology of the musculature is consid- preopercle and ventral section of the vertical limb ered derived in light of the absence of comparable of that element. The A2 is consequently reduced adaptations in outgroups examined in the present to a relatively small, horizontally aligned band study. The Aw portion of the adductor mandi- with a limited origin on the vertical arm of the bulae, present in most characiforms, was not preopercle in the region ventral to the insertion found as a separate muscle in anostomids; an of the levator arcus palatini. The muscle section apomorphous absence previously noted by Alex- becomes increasingly attenuate anteriorly, giving ander (1964:183). rise to a tendinous band. The relatively large A3 Not unexpectedly, the highly unusual suctorial attaches to the medial margin of that tendon, mouth of prochilodontids is reflected in the myol- which then passes forward to the lower jaw. This ogy of the cheek region (Figure 39). The most reversal of the usual proportions of the Ai and A2 distinctive character of the prochilodontid adduc- sections of the adductor mandibulae is distinctive tor mandibulae is the great expansion posteriorly for prochilodontids among characiforms exam- of the muscle's Ai section. As a consequence the ined. Ai arises from across the entire horizontal arm of A myological synapomorphy for the four-fam- the quadrate and preopercle with a partial origin ily clade occurs in the musculature of the ventral on the ventral portion of its vertical arm. Ante- surface of the head. Characiforms typically have riorly the muscle has a broad direct insertion on a hyohyoidei abductores with a relatively broad the angulo-articular's posterior margin and an insertion on the dorsal surface of the branchio- insertion on the maxilla via the primordial liga- stegal rays. The anterior portion of the muscle ment. The posterior expansion of the Ai has progressively tapers anteriorly, with a discrete excluded the A2 from most of its plesiomorphous origin from the anteroventral margin of the uro- 46 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY hyal and the anteromedial surface of the hyoid CURIMATIDAE RIOCHIIJOOONTIDAE ANOSTOMIDAE CMLOOONTIOAE arch. The posteroventral portion of the urohyal is covered by the sternohyoideus, which is readily 74 99 visible in ventral view and only partially over- lapped, primarily anteriorly, by the hyohyoidei adductores. In the Curimatidae, Prochilodonti- dae, Anostomidae, and Chilodontidae, in con- -58 trast, the hyohyoidei abductores has a broad insertion across the entire ventral surface and lateral margins of the ventrolateral wings of the urohyal, contrary to the narrow attachment to the anteriormost portion of the bone found in other characiforms (Figure 40). This broad at- tachment results in both the near total ventral FIGURE 41.—Cladogram of the most parsimonious hypothe- overlap of the sternohyoideus by the hyohyoidei sis of relationships of the families Curimatidae, Prochilodon- abductores and drastic restriction of the aperture tidae, Anostomidae, and Chilodontidae (numbered synapo- of the gill slits. A reduction in the gill slit aperture morphies correspond to those of the text). also occurs in parodontids and some distichodon- tids and characids. In none of the examined outgroups is the constriction of the gill openings four-family assemblage and those that involve a arrived at in a manner comparable to that in subunit of that lineage and a characiform out- these four families. The mode in which the con- group. In conjunction with the phylogenetic re- striction is achieved in the Curimatidae, Prochil- construction, that discussion provides the basis odontidae, Anostomidae, and Chilodontidae is for the evaluation of previous classificatory consequently considered a shared derived char- schemes as reflectors of the phylogenetic history acter for the assemblage. of the four-family assemblage and its subunits. Figure 41 presents the most parsimonious phy- Phylogenetic Reconstruction logenetic hypothesis that incorporates the previ- Synapomorphies within the osteological and ously discussed synapomorphies. The apomor- myological systems described in the previous sec- phous characters defining the various suprafam- tion provide information relevant to a hypothesis ilial assemblages and families are numbered se- of familial and suprafamilial relationships among quentially within . That procedure simpli- the Curimatidae, Prochilodontidae, Anostomi- fies the visualization of character distribution and dae, and Chilodontidae. These same systems also familial relationships. The numbering of the demonstrate synapomorphies for the members of characters in the following text corresponds to the each family. The following discussion first details numbered synapomorphies of the cladogram in the synapomorphies for the four-family unit, fol- Figure 41. lowed by those derived characters that distinguish clades of decreasing universality within that as- THE FOUR-FAMILY ASSEMBLAGE semblage. Subsequent to the reconstruction of the The hypothesized monophyly of the assem- most parsimonious hypothesis of phylogenetic re- blage formed by the families Curimatidae, Pro- lationships among these families, there is a dis- chilodontidae, Anostomidae, and Chilodontidae cussion of those derived characters that have a is supported by the following synapomorphies for phylogenetic distribution incongruent with the the four-family unit. arrived at hypothesis of relationships. The discus- sion deals both with homoplasies internal to the 1. The elimination of the direct contact between NUMBER 378 47

the fourth and fifth upper pharyngeal tooth tidae as a convergence is, thus, the simplest ex- plates. planation. Comparable parsimony arguments ap- 2. The absence of dentition of the fourth upper ply to other characters homoplasiously present pharyngeal tooth plate. within the four-family assemblage and in one or 3. The A3 portion of the adductor mandibulae more characiform outgroups. The overall distri- with an extensive origin along the lateral sur- bution of such homoplasious characters does not face of the mesopterygoid and metapterygoid form any other pattern consistent with an alter- and a broad insertion on the tendon of A2. nate concept of relationships as, or more paris- 4. The longitudinally expanded attachment of monious than, that advanced herein. the hyohyoidei abductores on the urohyal. Although this hypothesis of relationships is the CURIMATIDAE AND PROCHILODONTIDAE CLADE least robust in the phytogeny when evaluated in The less inclusive familial and suprafamilial terms of the number of synapomorphies, it is not clades among the Curimatidae, Prochilodontidae, challenged by any equally parsimonious alterna- Anostomidae, and Chilodontidae are defined by tive hypothesis derivable from the characters ex- numerous advanced characters. Synapomorphies amined. The convergencies shared by the various of the Curimatidae and Prochilodontidae pri- subunits of this assemblage with diverse characi- marily are associated with the food gathering and form outgroups typically involve a single family manipulating systems, with a lesser number being and an outgroup rather than a monophyletic two exoccipital modifications. In summary these family unit and the outgroup. Thus, hypotheses shared derived characters are as follows. of the homoplasious nature of those characters are supported both by the synapomorphies for 5. The reorientation of the dorsal process of the the four-taxon unit and the shared derived char- fourth epibranchial anteriorly with its con- acters that unite each pair of family level sister sequent extension over the dorsal surface of groups. The homoplasious nature of the occur- the fourth infrapharyngobranchial. rence of such characters in and outside of the 6. The anterodorsal expansion of the cartilagi- four-taxon unit under consideration is also indi- nous fifth epibranchial, its attachment to the cated by the available data on the phylogenetic posterodorsal margin of the fourth epibran- placement of the characiform outgroups that chial, and the resultant encirclement of the share the convergent characters. A supramaxilla, fifth efferent branchial artery. for example, is evidently limited to the Chilodon- 7. The large sac-like, muscular epibranchial or- tidae and the characid Chalceus among characi- gan that extends dorsal to the medial ele- forms and is considered an independently ac- ments of the dorsal portion of the gill arches. quired apomorphy in each of the two lineages. 8. The conversion of the plesiomorphously flat That hypothesis is in agreement with a parsimony fourth upper pharyngeal tooth plate into a evaluation, based both on the synapomorphies curved ossification wrapped around the for the four-family unit and the more numerous fourth infrapharyngobranchial. shared derived characters that unite chilodontids 9. The reduction or loss of dentition on the fifth with anostomids that lack a supramaxilla. Addi- upper pharyngeal tooth plate. tional support for a hypothesis of the homopla- 10. The reduction or loss of an ossified first bas- sious distribution of the ossification comes from ibranchial. the various shared derived characters (e.g., com- 11. The absence of dentition on the fifth cerato- mon possession of a rhinosphenoid) that join branchial. Chalceus to the Characidae, in which a supramax- 12. The anteromedially directed process on the illa otherwise is absent. Considering the presence fourth ceratobranchial's ventral surface. of a supramaxilla in Chalceus and the Chilodon- 13. The distinct, posteroventrally aligned flange 48 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

on the lateral surface of the opercle or a 17. The third posttemporal fossa bordered solely further derived condition of that process. by the epioccipital. 14. The increase in the depth and width of the 18. The anteroventral process on the third hy- fossa for the scaphium that results in inter- pobranchial that extends parallel to the ven- connections of the fossa with the lateral oc- tral aorta. cipital foramen laterally and the interior of 19. The absence of an ossified first basibranchial. the cranium anteriorly. 20. The posteroventral expansion of the fifth up- 15. The posterior development of the lateral per pharyngeal tooth plate into a curved, margin of the exoccipital lateral to the fora- convoluted process. men magnum, thereby forming a common 21. The secondary posterodorsal, cartilage- aperture for the foramen magnum, cavum capped process on the palatine. sinus imparis, and paired fossae for the sca- 22. The cartilage-capped articular process along phium and a cover laterally for the antero- the ventral edge of the lateral ethmoid's ven- lateral surface of the scaphium. tral wing. 23. The horizontal shelf on medial surface of the The phylogenetic hypothesis based on the metapterygoid. above characters (i.e., the close relationships of 24. The large cartilagenous ethmoid block and the Curimatidae and Prochilodontidae) is in widened mesethmoid. agreement, in whole or in part, with some previ- 25. The enlarged lagenar capsule. ous classificatory schemes, but noteably different from those of Boulenger (1904) and Roberts The absence of dentary and premaxillary den- (1973) (see "Comparisons with Previous Classifi- tition is the only externally apparent discrete cations"). Examination of the characters that tra- synapomorphy for the members of the Curima- ditionally distinguish these families shows that tidae. Most members of the family, nonetheless, they are largely external synapomorphies for the share a distinctive bauplan that permits their members of the Prochilodontidae, particularly identification at the family level without the ne- those in mouth form, rather than any discrete cessity for examination of the jaws. Some curi- external features of curimatids. Indeed, only the matids, however, differ dramatically from the first listed shared derived character for the mem- typical curimatid body plan and are not readily bers of the latter family (see below), the toothless recognized as members of the family. Curimata jaws, is apparent in external examination. Two ocellata is distinctly fusiform and can be rather subunits of the assemblage characterized by char- easily confused with some hemiodontids, which it acters 5 to 15 are, in turn, definable by a series of closely parallels in body form and pigmentation synapomorphies unique to the members of each pattern (Gery, 1977b, fig. 3). Alternatively, some family. curimatid species are extremely deep-bodied with large individuals of Curimata abramoides (in which the body depth exceeds 50% of standard length) FAMILY CURIMATIDAE representing the extreme in that direction (Kner, The Curimatidae is the least derived taxon 1859, pi. 2). among the four families under consideration in The intrafamilial of the Curimati- terms of the overall number of synapomorphies dae is highly confused, with many of the nominal found during the present study. The shared de- genera consisting of evidently unnatural group- rived characters congruent with the hypothesis ings of species. The number of recognizable forms that the Curimatidae forms a monophyletic lin- among the described species is uncertain. Studies eage are the following. to date (e.g., Vari, 1982b) have shown that about twenty of the ten dozen presently recognized 16. The lack of dentary and premaxillary denti- species are invalid, but also that numerous pre- tion. viously unrecognized distinct species exist. NUMBER 378 49

The taxonomic limits of the Curimatidae of 31. The reduction in the overall relative size of this study differ from those utilized by the vast the retroarticular and its shift onto the me- majority of prior researchers. Traditionally, curi- dial surface of the angulo-articular. matids and Anodus have been associated on the 32. The transverse compression of the fifth upper basis of their edentulous jaws. Some authors orig- pharyngeal tooth plate and the mobility of inally described various curimatid species in An- that element with respect to the fourth epi- odus (e.g., Anodus latior Spix, in Spix and Agassiz, branchial. 1829) or used Anodus as a genus in curimatids 33. The transverse expansion of the basihyal's (e.g., Eigenmann and Allen, 1942:300). Other anterior portion. researchers (e.g., Eigenmann and Eigenmann, 34. The ventrally notched interhyal and the 1889; Fernandez-Yepez, 1948) have reserved An- sesamoid ossification in the ligament that odus for a limited number of fusiform species joins the interhyal to the posterior ceratohyal. known from the Orinoco and Amazon river ba- 35. The transverse broadening of the branchio- sins. Those authors, nonetheless, either associated stegal rays. the genus in some unspecified manner with curi- 36. The transverse widening of the urohyal's ven- matids (Eigenmann and Eigenmann, 1889) or tral wings. explicitly placed it in the Curimatidae, as the 37. The ontogenetic expansion of the opercular subfamily that formed the sister lineage to curi- flange into a broad, flat, thickened region on matids (sensu stricto) (Fernandez-Yepez, 1948: the opercle's lateral surface. 19). However, the phylogenetic affiliations of An- 38. The tripartite ectopterygoid that is mobile odus appear to lie with the Hemiodontidae rather relative to the quadrate and preopercle. than the Curimatidae (sensu stricto), a hypothesis 39. The posteriorly notched quadrate that is ver- first advanced by Roberts (1974) and confirmed tically mobile on the preopercle and the lat- by this study. That larger assemblage, in turn, eral shelf on the quadrate. shows various synapomorphies with some, but 40. The subdivision of the anterior portion of the not all characids, to which it is apparently more preopercular laterosensory canal into two or closely related. more ossified tubes. 41. The form of the second infraorbital. FAMILY PROCHILODONTIDAE 42. The posterior extension of the Ai portion of the adductor mandibulae. The family Prochilodontidae is a very distinc- 43. The reduction of the A2 portion of the ad- tive assemblage having the following numerous ductor mandibulae. shared derived characters. Prochilodontids are most readily recognizable 26. The increased number of functional and re- externally by their enlarged fleshy lips, which placement tooth rows and teeth per row. evert into a suctorial oral disk. That mouth form 27. The highly developed fleshy lips that form a is unique to the family among characiforms and suctorial oral disk. the listed synapomorphies for the members of the 28. The bulbous form of the premaxilla. family are all associated with oral apparatus mod- 29. The bulbous form of the maxilla, the numer- ifications. Three genera (Ichthyoclephas, Prochilodus, ous maxillary fenestrae, and the posterome- and Semaprochilodus) with some 30 to 40 nominal dial bony maxillary process that serves for species, presently are recognized, although an the attachment of the maxillo-mandibular understanding of the actual number of valid spe- ligament. cies must await a thorough revision of the family. 30. The foreshortened dentary and the ex- Many of the species are economically important panded, laterally rotated dentary replace- and undertake large-scale, long-distance, - ment tooth trench with a large medial fenes- ing-associated migrations. Roberts (1973) has de- tra. scribed the osteological variation in the Prochil- 50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY odontidae and provided a partial synopsis of the 58. The presence of two or more intercostal lig- available life history information for the family. aments that join the three or more of the anteriormost full pleural ribs. ANOSTOMIDAE AND CHILODONTIDAE CLADE The two subunits of the assemblage defined by The Anostomidae and Chilodontidae have characters 44 to 58 are, in turn, distinguished by been the subject of divergent opinions concerning their less inclusive sets of shared derived charac- their interrelationships and the appropriate ways ters. These clades are (1) the morphologically to reflect those concepts taxonomically. Some of diverse, speciose family Anostomidae; and (2) the the adaptations common to the two families are Chilodontidae, a small group both in terms of quite unusual, particularly the various restructur- genera and species, that is, characterized by nu- ings of the branchial apparatus. Those gill arch merous synapomorphies and relatively little in- modifications and the synapomorphies in other trafamilial variation. body systems are as follows. FAMILY ANOSTOMIDAE 44. The longitudinal foreshortening of the man- dible. The family Anostomidae is largely character- 45. The pronounced enlargement of the upper ized by branchial apparatus and suspensorium and lower pharyngeal dentition. modifications that reflect the unique overall form 46. The presence of two or more cusps on all of those systems in the family. The synapomor- pharyngeal teeth. phies for the species of anostomids are as follows. 47. The shift in the alignment of the fourth upper 59. The expansion of the ascending process of pharyngeal tooth plate that results in its the premaxillary resulting in a heavy trian- contact with the fourth epibranchial rather gular bone. than the fifth upper pharyngeal tooth plate. 60. The pronounced expansion of the dentary 48. The vertical thickening of the fifth upper replacement tooth trench, and the distinct pharyngeal tooth plate. fenestra along the ventral portion of the 49. The transverse expansion of the posterior trench. region of the third infrapharyngobranchial. 61. The enlargement of the dentary and premax- 50. The thickening and posterodorsal reorienta- illary teeth. tion of the dorsal process of the fourth epi- 62. The expansion of the third epibranchial's branchial. medial portion to form a curved process that 51. The vertical expansion of the anterior process extends medially over the fourth infraphar- of the fourth epibranchial. yngobranchial's dorsal surface. 52. The highly developed obliquues dorsalis as- 63. The very well-developed cord-like ligament sociated with the fourth infrapharyngobran- that runs between the lateral surface of the chial. ectopterygoid and the ventral wing of the 53. The longitudinal foreshortening of the hyoid lateral ethmoid. arch. 64. The distinct process on the posterolateral 54. The oblique angle of the articulation be- surface of the ectopterygoid. tween the anterior and posterior ceratohyals. 65. The expansion of the preopercle's lateral sur- 55. The distinct cord-like ligament that joins the face to form a shelf for the origin of the lateral surface of the ectopterygoid and ven- adductor mandibulae. tral wing of the lateral ethmoid. 66. The enclosure of the anterior portion of the 56. The prominent lateral shelf on the quadrate. preopercular laterosensory canal by two or 57. The hyomandibular process that extends three autogenous ossified tubes. over the metapterygoid's posterodorsal re- 67. The quadripartite laterosensory canal system gion. in the extrascapular. NUMBER 378 51

68. The two or more intercostal ligaments that 74. The reduction in the relative size of the pre- unite four or more of the anteriormost full m axilla. pleural ribs. 75. The expansion in the relative size and thick- 69. The triangular, autogenous section of the ness of the maxilla. levator arcus palatini that arises from the 76. The ossified supramaxilla located along the posterodorsal portion of the orbital cavity posterodorsal margin of the maxilla. and inserts on the anterodorsal margin of the 77. The anteroventral expansion of the meseth- hyomandibula. moid into an angled process that extends 70. The subdivision of the Ai portion of the between the premaxillae. adductor mandibulae. 78. The three or more cusps on all pharyngeal 71. The expansion of the posterior part of the A2 teeth. portion of the adductor mandibulae medial 79. The posteroventral expansion of ceratobran- of the levator arcus palatini and its partial chial four into a broad, curved surface. origin on the hyomandibula. 80. The expansion of the anterior portions of 72. The dorsal expansion anteriorly of the A3 ceratobranchial five into a cup-shaped plate. and A2 portions of the adductor mandibulae 81. The rotation anteriorly of the tooth-bearing that results in the contact of these muscles portion of ceratobranchial five. with each other dorsal to the tendon that 82. The ridges on the dorsal surfaces of cerato- attaches to the main body of A2. branchials 1, 2, and 3. 73. The absence of the Aw portion of the adduc- 83. The reorientation posteriorly of the fifth up- tor mandibulae. per pharyngeal tooth plate. Anostomids are a distinctive group of some 84. The pronounced transverse expansion of the ten genera, a number of which are monotypic, third infrapharyngobranchial's posterior por- but with Leporinus containing some 70 nominal tion. species. Phylogenetic relationships within the 85. The ridges on the ventral surfaces of epibran- subfamily Anostominae, which is characterized chials 1, 2, and 3. by some very unusual jaw adaptations, were an- 86. The posterior rotation of the ventral portion alyzed by Winterbottom (1980), who also revised of the fourth epibranchial. the contained species. Most of the remaining 87. The lateral and dorsal expansion of the car- genera, particularly Leporinus, are poorly under- tilaginous fifth epibranchial to form the ma- stood phylogenetically and taxonomically. jor part of the anterior wall of the epibran- chial organ. 88. The shell-shaped connective tissue sheet that FAMILY CHILODONTIDAE extends dorsal to the fifth ceratobranchial The members of the Chilodontidae have in and forms the posterior wall of the epibran- common a profusion of synapomorphous modifi- chial organ. cations not encountered elsewhere in the families 89. The distinct ridges on the soft tissue layer analyzed or often in any other fishes. Many of that covers the adjoining surfaces of the these characters are associated with the form of fourth and fifth ceratobranchials. the epibranchial organ, which is not approxi- 90. The distinct band-like muscle on the anterior mated in outgroups reported on in the literature and posterior surfaces of the epibranchial or examined during this study. A second system organ. that shows marked modifications is the pectoral 91. The laterally thickened anterior and poste- girdle; perhaps as a consequence of the unusual rior ceratohyals with pronounced ridges head-down body orientation utilized by chilodon- along their lateral surfaces. tids while swimming. The various synapomor- 92. The complex, thickened interhyal with the phies for members of the family are as follows. ligament that extends to the metapterygoid 52 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

and quadrate attaching to the discrete me- and one or more characiform outgroups. The dial process of the interhyal. majority of these incongruities are loss characters, 93. The ventral expansion of the main shaft of while others are sufficiently different in the var- the supracleithrum. ious groups that possess them to cause doubts 94. The elimination of the ventral process and about their homology. laterosensory canal bearing portion of the Characters hypothesized to be homoplasiously posttemporal and the anterior section of the distributed within the four-family unit are as extrascapular. follows. 95. The direct articulation of the dorsal tip of 1. The distinct lateral shelf on the quadrate in the extrascapular with the pterotic. the Prochilodontidae and the unit that consists 96. The expansion of the posteroventral spine of of the Anostomidae and Chilodontidae. the pterotic into a flat articular surface that 2. The autogenous ossified tubes associated with contacts a corresponding supracleithral the anterior section of the preopercular latero- process. sensory canal system in the Prochilodontidae 97. The absence of postcleithrum 1. and Anostomidae. 98. The dorsal expansion of the proximal por- 3. The absence of a dentary replacement tooth tions of the first three full pleural ribs. trench in the Chilodontidae and Curimatidae. 99. The vertical expansion of the parapophyses 4. The longitudinal foreshortening of the lower and articular fossae associated with the first jaw in the Prochilodontidae and the unit that three full pleural ribs. consists of the Chilodontidae and Anostomi- Very few of the shared derived characters com- dae. mon to the members of the family are readily 5. The reduced teeth not in direct contact with visible externally. Consequently, chilodontids do the jaws in the Chilodontidae and Prochilo- not appear as highly derived superficially as do dontidae. members of some of the other families in the suprafamilial lineage under discussion. Though Roberts (1973) also advanced the similarities very distinct anatomically, the group has not in ethmoid (= mesethmoid) form and the enclo- undergone any great intrafamilial differentiation sure of the angular (= retroarticular) by the or phyletic radiation. Two genera and three or dentary as indicators of close anostomid-prochil- four species presently are recognized (Gery, odontid relationships. The homology of these 1977b). characters is difficult to evaluate. If they are homologous apomorphies they would be consid- Discussion ered homoplasies under the results of this study. That decision and the comparable treatment of The advanced hypothesis of relationships is the the five characters listed above are based on most parsimonious derivable, given the available parsimony criteria. Including the two characters information on the polarity and distribution of listed by Roberts, we find that three characters characters in the examined body systems of curi- support a hypothesis of a sister group relationship matids, prochilodontids, anostomids, and chilo- between the Prochilodontidae and the Anostom- dontids. The size and complexity of the Chara- idae (the two characters proposed by Roberts and ciformes and scarcity of specimens of various taxa character 2 above). Two characters (1 and 4 limits the practical outgroup comparisons. Thus, above) are congruent with the concept of the the occurrence of characters may in some cases Prochilodontidae being most closely related to be wider than noted here. the lineage that consists of the Anostomidae and Two types of homoplasies were encountered: the Chilodontidae. One character (number 3 those internal to the four-family clade and con- above) unites the Chilodontidae and Curimati- vergencies between a subsection of that lineage dae. Finally, one character (number 5 above) NUMBER 378 53 unites the Prochilodontidae and Chilodontidae. subunits of the Distichodontidae, the Hemiodon- If we consider the tooth reduction of character 5 tidae (particularly Bivibranchia and Anodus) and to be an intermediate state to the total loss of jaw within the Characidae Acestrorhynchus, Chalceus, dentition in the adults of the Curimatidae, a Cotossoma, Crenuchus, Hydrolycus, Rhaphiodon, and reduction or loss of jaw teeth would rather be a the Gasteropelecinae. The characters involved, synapomorphy for the assemblage formed by the comments on their possible homology, and more Prochilodontidae, Chilodontidae, and Curimati- specific details on their phylogenetic distributions dae. are discussed in the preceeding "Character De- The acceptance of even the most corraborated scription and Analysis". Neither the ingroup of these phylogenetic alignments (that is, uniting homoplasies nor those with characiform out- the Prochilodontidae and the Anostomidae) groups show a repeated pattern of phylogenetic would require the hypothesis that all 11 charac- distribution consistent with an alternative equally ters considered synapomorphous for the Curi- or more parsimonious hypothesis of relationships. matidae and Prochilodontidae arose indepen- The majority of the noted outgroups have only dently in those two lineages and that a similar one shared derived character in common with situation exists with respect to the 13 characters some subunit of the four-family assemblage ana- synapomorphous for the Anostomidae and Chil- lyzed. Hypotheses of relationships based on such odontidae. The selection of a hypothesis of a sister characters are obviously less robust than that group relationship between the Prochilodontidae based on the more numerous characters listed in and Anostomidae would indeed eliminate the the previous section. Only two taxa, the Old three homoplasies noted above but would neces- World characiform family Citharinidae and the sitate a hypothesis that 24 other characters arose Neotropical genus Anodus show any multiple, de- independently; as such, it would be obviously less rived similarities with subunits of the clade con- parsimonious. Comparable arguments are appli- sisting of the Curimatidae, Prochilodontidae, An- cable to the other characters considered homopla- ostomidae, and Chilodontidae. sious in the present study. The loss of dentition on the fourth upper pha- Such criteria are also applicable to the question ryngeal tooth plate is a characteristic of the Cith- of the absence of the first postcleithrum in chilo- arinidae and the entire four-family assemblage. dontids and a subunit of anostomids, and the The Citharinidae has a reduction or loss of lower absence of an ossified first basibranchial in curi- pharyngeal dentition and the presence of an matids and some anostomids. Several characters opercular flange in common with the Curimati- considered synapomorphous for the members of dae plus Prochilodontidae. Both the Citharinidae the Anostomidae are evidently secondarily lost in and the Curimatidae have a third posttemporal Gnathodolus and perhaps its sister genus Sartor,fossa and possess a well-developed cartilagenous which was not available for study (see "Suspen- ethmoid block. An outwardly rotated dentary sorium and Circumorbital Series"). Once again, replacement tooth trench is shared by the Cith- parsimony arguments based on the available data arinidae and the Prochilodontidae. Finally, the on intra-anostomid relationships suggest that the Citharinidae and Chilodontidae have in common absence of those characters within the Anostom- a secondary contact of the supracleithrum with a idae is a secondary loss. posteroventrally expanded process of the pterotic. A variety of other characters were noted which Any hypothesis of a sister group relationship be- evidently occur homoplasiously in the group that tween the Citharinidae and any family or multi- consists of the Curimatidae, Prochilodontidae, familial grouping just listed would require the Anostomidae, and Chilodontidae or subunits of assumption that the various hypothesized syna- that clade and various characiforms outgroups. pomorphies for the Citharinidae and Disticho- These characiform outgroups include the Cith- dontidae (Vari, 1979) are actually homoplasies. arinidae, Parodontidae, and Hepsetidae, various In the majority of cases it would also necessitate 54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY similar assumptions relative to the numerous syn- it is correct to use the various adaptations of the apomorphies for the unit that consists of the third postcleithrum in the Chilodontidae. The Curimatidae, Prochilodontidae, Anostomidae, above characters, the analyses of polarities, and and Chilodontidae or subgroups of that clade. alternate scenarios consistent with their phyloge- Thus, for example, the recognition of the Cith- netic distribution were discussed in greater detail arinidae and Curimatidae as sister groups on the in preceeding sections of this paper. basis of their synapomorphous possession of a third postemporal fossa and a large cartilagenous Comparisons with Previous Classifications ethmoid block would necessitate the assumption that characters 1 through 15 are homoplasies. A number of alternate taxonomic concepts That procedure results in obviously less parsi- have been proposed for the families Curimatidae, monious hypotheses. Prochilodontidae, Anostomidae, and Chilodonti- The second taxon, the genus Anodus, shares the dae. Those treatments typically lack an explicit absence of jaw teeth with the Curimatidae, the statement of the methodology of analysis and the absence of lower pharyngeal teeth with the Cur- phylogenetic assumptions underlying the classi- imatidae and Prochilodontidae, and the absence fication. Rather, each of the previously proposed of teeth on the fourth upper pharyngeal tooth classifications is an amalgam of phenetic and plate with the Curimatidae, Prochilodontidae, quasi-phyletic concepts, with a consequent low Anostomidae, and Chilodontidae. The hypothesis retrievability of the underlying phylogenetic as- of a sister group relationship between Anodus and sumptions. Two exceptions, at least with respect the four-family assemblage is incongruent with to the last factor, were the studies of Eigenmann the various synapomorphies that unite the genus (1917) and Roberts (1973). and the Hemiodontidae (Roberts, 1974). Any The differing classificatory schemes or phylo- hypothesis of a close relationship between Anodus genetic hypotheses fall into five major patterns, and subunits of the four-family clade is in addi- arranged chronologically by first presentation tion incongruent with the various synapomor- (family concepts follow Greenwood et al., 1966). phies for and within that quadri-familial assem- 1. The union of the Curimatidae, Prochilodon- blage. tidae, Chilodontidae, and Parodontidae in one Uncertainties about the homology of the teeth taxon and the separation of the Anostomidae on the prochilodontid suctorial mouth make it in a second taxon of equivalent rank (Giinther, impossible to unambiguously evaluate the proper 1864). phylogenetic level at which it was appropriate to 2. The placement of the Curimatidae and Pro- use the absence of maxillary teeth as a character chilodontidae with the Citharinidae; the An- in the phylogenetic reconstruction. The absence ostomidae with some members of the Chara- of teeth on that bone may be either a synapo- cidae and Lebiasinidae; and the Chilodonti- morphy for the four-family unit or at broader or dae with the Hemiodontidae and Parodonti- narrower levels of taxonomic unversality. The dae (Boulenger, 1904). reduced size of the jaw dentition in chilodontids 3. The incorporation of the Curimatidae, Pro- and prochilodontids may be homologous, perhaps chilodontidae, Anostomidae, and Chilodonti- also representing an intermediate stage in a re- dae into a single taxon (Regan, 1911; Gregory ductional trend, which achieves its terminal con- and Conrad, 1938). dition in the edentulous jaws of curimatids. The 4. The recognition of the Curimatidae, Pro- ambiguity associated with the question of homol- chilodontidae, Anostomidae, Chilodontidae, ogy in the character makes it impossible to deter- Hemiodontidae, and Anodinae as a discrete mine the appropriate level at which to use the lineage (Eigenmann, 1917). morphological information. Similarly, it is not 5. The union of the Curimatidae, Prochilodon- possible to determine at what phylogenetic level tidae and Chilodontidae as a taxon, distinct NUMBER 378 55

from, but equivalent in rank to, that contain- Boulenger's taxonomic scheme (1904) places ing the Anostomidae (Gery, 1977b). subunits of the monophyletic four-family unit in 6. The hypothesis that the Prochilodontidae is three different taxa that each contain other char- not closely related to the Curimatidae but aciform groups. His proposed classification is, rather to the Anostomidae (? and Chilodonti- thus, highly incongruent with the proposed phy- dae) (Roberts, 1973). logenetic history of the clade. Temporarily put- ting aside the works of Regan and of Gregory and The degree to which phylogenetic concepts, if Conrad, we can see that Eigenmann's more ex- any, were incorporated into the majority of the plicit phyletic statement agrees with that pre- above classificatory schemes is uncertain. Thus, sented here in uniting curimatids, prochilodon- it is only possible to note the utility, or lack tids, chilodontids, and anostomids into a single thereof, of the previously suggested taxonomic lineage. Eigenmann did not, however, suggest subdivisions as appropriate indicators of the hy- what were the relationships among these four pothesis of relationships arrived at in this study, families. The limited internal resolution of his given the criterion that all recognized taxa must hypothesis restricts comparisons at lower levels of be monophyletic. Eigenmann's (1917) hypothesis universality. Our present understanding of phy- can reasonably be interpreted as a phyletic con- logenetic relationships within characiforms, indi- cept, although with a limited degree of resolution cates, however, that the Hemiodontidae and An- of relationships within his proposed lineage. Sim- odinae, which he also aligned with those taxa, are ilarly, Roberts (1973) dealt with questions of actually more closely related to other phyletic relationship, although there is some question as subunits of the order. to the exact hypothesis advanced. Gery (1977b), in recognizing an Anostomidae Giinther's (1864) Anostomina group, which for a group that consists of anostomids, and a consisted of what are now considered anostomids, Curimatidae formed by curimatids, chilodontids, is monophyletic according to the findings of this and prochilodontids, nearly approximates study. Prochilodontids, curimatids, and chilodon- Gunther's classification; differing only in separat- tids, together with hemiodontids and parodon- ing the Parodontidae into a separate taxon. Given tids, all were included in his Curimatina. Given the fact that his Curimatidae does not satisfy the the separation of anostomids into a separate primary criterion of this analysis—that it contains group, as the Anostomina, Giinther's Gurimatina all the descendents of its hypothesized common group is nonmonophyletic, in that it does not ancestor—it is considered an invalid indicator of include all descendents of the hypothesized com- the hypothesis of relationships arrived at in this mon ancestor of the lineage. Thus, Giinther's study. classification is not an appropriate vehicle to Returning to the earlier classifications of Regan convey the hypothesis of the relationships arrived (1911) and Gregory and Conrad (1938), we see at herein for the Curimatidae, Prochilodontidae, that their union of what are presently recognized Anostomidae, and Chilodontidae. Furthermore, as the Curimatidae, Anostomidae, Chilodontidae, the Hemiodontidae, placed by Giinther in the and Prochilodontidae into a single taxon accu- Curimatina group, shares various derived char- rately reflects the monophyly of the group other acters, including the presence of a rhinosphenoid than for the inclusion of the genus Anodus, which and tooth form, with subunits of the Characidae, is apparently more closely related to the Hemio- with which it is presumably most closely related. dontidae (Roberts, 1974). These works are the The exact phylogenetic placement of parodontids only previous studies that utilized a classificatory is not resolved, but available data fails to support scheme under which nearly all recognized taxa the hypothesis that they are more closely related constitute monophyletic assemblages under the to the remaining members of Giinther's Curima- results of this study. Gregory and Conrad (1938) tina group than those taxa are to anostomids. were not explicit about their concepts of relation- 56 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY ships within the four-family lineage. Therefore, exists on the identity of the specific group or comparisons cannot be made at lower levels of groups he considered the closest relatives to the universality between their scheme and the hy- prochilodontids. In the abstract to his work pothesis advanced in this study. Other than for (1973:213) he stated that prochilodontids "are the aforementioned inclusion of Anodus in the closely related to Anostomidae and Chilodonti- Curimatinae by Regan, his classification agrees dae," whereas in his discussion of relationships with the phylogenetic hypothesis advanced herein (1973:221) he stated that "the evidence favoring both at the level of the four-family unit and at relationship between Prochilodontidae and An- lower levels of universality. Regan did not com- ostomidae is relatively strong." The latter, more ment on the possible relationships of the four- limited concept of the sister group to prochilo- taxon group to other characiforms, whereas Gre- dontids is that discussed at greatest length in the gory and Conrad made a qualified suggestion paper and, thus, presumably more in keeping that the assemblage formed by these four families with the ideas of the author. Both concepts of was most closely related to the Citharinidae outgroup relationship run counter to the results (sensu Greenwood et al., 1966). The numerous of this study. The hypothesis that prochilodontids synapomorphies for citharinids and distichodon- are phylogenetically aligned with the lineage that tids (Vari, 1979) indicate that Gregory and Con- consists of anostomids and chilodontids would rad's suggestion is incongruent with available necessitate the especially unparsimonious hypoth- data on characiform phylogeny. esis of repeated convergent acquisitions in the Regan united the taxa as a family with three Curimatidae and Prochilodontidae of all eleven subfamilies, whereas Gregory and Conrad consid- of the characters herein considered synapomor- ered them to form a subfamily. More recently phies for the members of the curimatid-prochilo- each of the components has been recognized as a dontid clade. The more restricted hypothesis of full family (Greenwood et al., 1966). It is, of relationships that uses the Anostomidae as the course, presently impossible to be non-arbitrary sister group to the Prochilodontidae would in- in the decision as to which taxonomic level is the volve both those concepts of convergence and the most appropriate for the entire assemblage or its independent acquisition in the Chilodontidae subunits given a possible range between a single and Anostomidae of the numerous derived char- subfamily and four families. Such a decision must acters considered synapomorphies for that bifam- await a phylogenetic hypothesis of this clade's ilial lineage in this study. Thus, both of the two placement within characiforms. The recognition possible sister group concepts mentioned by Rob- of four separate families in this study is in keeping erts are significantly less parsimonious than the with the general practice of most recent works. hypothesis of relationship arrived at in this study. Suprafamilial taxa for more inclusive groupings are not proposed at this time because of our still Resumen preliminary concepts of higher level relationships within the Characiformes. Una hipotesis acerca de las relaciones filoge- It was noted earlier that Roberts' treatment neticas de las familias Curimatidae, Prochilodon- (1973) of the Prochilodontidae was the one work tidae, Anostomidae, y Chilodontidae pertene- to advance phylogenetic concepts for at least cientes al Orden Characiformes es presentada, portions of the four-family assemblage. Roberts, utilizando la metodologia de la sistematica filo- without specific cross-reference, commented that genetica (cladistica) propuesta por Hennig earlier researchers had proposed a close relation- (1950). Numerosos caracteres derivados (apomor- ship between the Curimatidae and Prochilodon- ficos), compartidos por estas cuatro familias, fu- tidae. His primary premise, in contrast, was that eron encontrados en las mandibulas, arcos bran- the relationships of prochilodontids lie with quiales, suspensorium, neurocraneo, columna ver- groups other than curimatids. Some ambiguity tebral, y musculatura de la cabeza. Los resultados NUMBER 378 57 de este estudio indican que los Curimatidae estan matidae, a pesar de la larga tradicion taxonomica mas cercanamente relacionados con los Prochil- la cual asocia estos taxa. En este estudio, la odontidae. La unidad formada por estas dos fam- inclusion de Anodus en la familia Curimatidae ilias es a su vez el grupo hermano (sister group) esta apoyada por varios caracteres derivados com- de la unidad formada por las familias Anostomi- partidos (sinapomorfias). dae y Chilodontidae. Se encontraron tambien Tres formas diferentes de organos epibranqui- una serie de carcateres unicos (autapomorfias), ales (bien desarrollados) han sido determinados que definen a estas familias como unidades mon- en los Characiformes. Los Curimatidae y Pro- ofileticas. chilodontidae tienen un organo epibranquial pa- La hipotesis de relaciones desarrollada en este recido a un gran saco muscular, mientras que los sentido rechaza la sugerencia presentada por de la familia africana Citharinidae son altamente Roberts (1973:221) la cual establece que los Pro- divididos y soportados por una serie de pequenas chilodontidae estan mas cercanamente relacion- osificaciones. El organo epibranquial en Chilo- ados con la familia Anostomidae, que a los Cur- dontidae esta formado por una extension cartila- imatidae. Boulenger (1904) reunio los Curimati- ginosa de quinto epibranquial, una banda de dae y Prochilodontidae con la familia de chara- tejido conectivo asociado al cuarto epibranquial ciformes africanos Citharinidae. Los datos obten- y partes del cuarto y quinto ceratobranquiales. idos en este estudio y el trabajo previo de Vari Las diferencias morfologicas entre estos tres tipos (1979) indican que el criterio de Boulenger crea de paquetes faringeos y los datos disponibles sobre un taxon no-natural. Giinther (1864) y Gery las interrelaciones de los Characiformes indican (1977a) erigieron un taxon para incluir Anostom- que organos epibranquilaes bien desarrollados, idae y otro taxon de rango equivalente para los han evolucionado separadamente, al menos tres Curimatidae, Prochilodontidae, y Chilodontidae. veces, dentro de este Orden. Esta conclusion esta Segun el criterio de este estudio, el ultimo taxon de acuerdo con la hipotesis previa de Nelson propuesto por los citados autores es no-monofile- (1967) quien sugirio que los organos epibranqui- tico y no refleja la historia evolutiva de este grupo ales desarrollados aparecieron independiente- de familias. El concepto de relaciones filogeneti- mente en diferentes grupos de peces. Bertmar, cas llevadas adelante por Eigenmann (1917) esta Kapoor, y Miller (1969) en contraste, considera- de acuerdo con la filogenia hipotetica propuesta ron que estos organos son ancestrales para los en este estudio. Sin embargo, Eigenmann incluye peces teleosteos, cuya ausencia en muchas lineas a los Hemiodontidae en su discusion, grupo que evolutivas seria debido a perdidas secundarias. es excluido en este trabajo. Roberts (1974) sugiere Los resultados de este estudio indican que esta que el genero Anodus (un characiforme sin dientes) ultima hipotesis no es parsimoniosa cuando es no esta cercanamente relacionado con los Curi- aplicada al Orden Characiformes. Literature Cited

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Spell out titles of Review of manuscripts and art by the Press for requirements books, articles, journals, and monographic series. For book and of series format and style, completeness and clarity of copy, and article titles use sentence-style capitalization according to the arrangement of all material, as outlined below, will govern, within rules of the language employed (exception: capitalize all major the judgment of the Press, acceptance or rejection of manu- words in English). For journal and series titles, capitalize the scripts and art. initial word and all subsequent words except articles, conjunc- Copy must be prepared on typewriter or word processor, tions, and prepositions. Transliterate languages that use a non- double-spaced, on one side of standard white bond paper (not Roman alphabet according to the Library of Congress system. erasable), with VU" margins, submitted as ribbon copy (not Underline (for italics) titles of journals and series and titles of carbon or xerox), in loose sheets (not stapled or bound), and books that are not part of a series. Use the parentheses/colon accompanied by original art. Minimum acceptable length is 30 system for volume(number):pagination: "10(2):5-9. " For align- pages. ment and arrangement of elements, follow the format of recent Front matter (preceding the text) should include: title page publications in the series for which the manuscript is intended. with only title and author and no other information; abstract Guidelines for preparing bibliography may be secured from page with author, title, series, etc., following the established Series Section, SI Press. format; table of contents with indents reflecting the hierarchy of Legends for illustrations must be submitted at the end of the heads in the paper; also, foreword and/or preface, if appropri- manuscript, with as many legends typed, double-spaced, to a ate. page as convenient. First page of text should carry the title and author at the top Illustrations must be submitted as original art (not copies) of the page; second page should have only the author's name accompanying, but separate from, the manuscript. Guidelines and professional mailing address, to be used as an unnumbered for preparing art may be secured from Series Section, SI Press. footnote on the first page of printed text. All types of illustrations (photographs, line drawings, maps, etc.) Center heads of whatever level should be typed with initial may be intermixed throughout the printed text. They should be caps of major words, with extra space above and below the termed Figures and should be numbered consecutively as they head, but with no other preparation (such as all caps or under- will appear in the monograph. If several illustrations are treated line, except for the underline necessary for generic and specific as components of a single composite figure, they should be epithets). Run-in paragraph heads should use period/dashes or designated by lowercase italic letters on the illustration; also, in colons as necessary. the legend and in text references the italic letters (underlined in Tabulations within text (lists of data, often in parallel columns) copy) should be used: "Figure 9b. " Illustrations that are in- can be typed on the text page where they occur, but they should tended to follow the printed text may be termed Plates, and any not contain rules or numbered table captions. components should be similarly lettered and referenced: "Plate Formal tables (numbered, with captions, boxheads, stubs, 9b." Keys to any symbols within an illustration should appear rules) should be submitted as carefully typed, double-spaced on the art rather than in the legend. copy separate from the text; they will be typeset unless other- wise requested. If camera-copy use is anticipated, do not draw Some points of style: Do not use periods after such abbre- rules on manuscript copy. viations as "mm, ft, USNM, NNE." Spell out numbers "one" Taxonomic keys in natural history papers should use the through "nine in expository text, but use digits in all other aligned-couplet form for zoology and may use the multi-level cases if possible. Use of the metric system of measurement is indent form for botany. If cross referencing is required between preferable; where use of the English system is unavoidable, key and text, do not include page references within the key, but supply metric equivalents in parentheses. Use the decimal sys- number the keyed-out taxa, using the same numbers with their tem for precise measurements and relationships, common frac- corresponding heads in the text. tions for approximations. Use day/month/year sequence for Synonymy in zoology must use the short form (taxon, author, dates: 9 April 1976." For months in tabular listings or data yearpage), with full reference at the end of the paper under sections, use three-letter abbreviations with no periods: Jan, Literature Cited.' For botany, the long form (taxon, author, Mar. Jun," etc. Omit space between initials of a personal name: abbreviated journal or book title, volume, page, year, with no "J.B. Jones." reference in Literature Cited") is optional. Arrange and paginate sequentially every sheet of manu- Text-reference system (author, yearpage used within the script in the following order: (1) title page, (2) abstract, (3) text, with full citation in Literature Cited" at the end of the text) contents, (4) foreword and/or preface, (5) text, (6) appendixes. must be used in place of bibliographic footnotes in all Contri- (7) notes section, (8) glossary, (9) bibliography, (10) legends, butions Series and is strongly recommended in the Studies (11) tables. Index copv may be submitted at page proof stage, Series: (Jones, 1910:122) or ...Jones (1910:122). If but plans for an index should be indicated when manuscript is bibliographic footnotes are required, use the short form (author, submitted. «•

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