AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2827, pp. 1-57, figs. 1-45 August 13, 1985 An Essay on Euteleostean Classification DONN E. ROSEN' ABSTRACT The anatomy of the occipital region and rostral letic and raises questions about the monophyly of cartilage in euteleostean fishes is reviewed in some the fishes formerly grouped in the Osmeroidei. detail. These data, in combination with other an- Evidence is presented on how the occipital region atomical features taken from the literature, have might be used in acanthomorph systematics, and led to a reassessment of interrelationships within includes reasons for rejecting the concept of the the Euteleostei. This review supports the notions Paracanthopterygii, as this group was formerly that the Salmoniformes, Aulopiformes, Mycto- constituted. phiformes, and Beryciformes are nonmonophy- INTRODUCTION The earliest general classification of fishes dan (1923), A. Smith-Woodward (1932), in which it is possible to pick out many of Norman (1934), Berg (1940) and its various the main components of the Euteleostei is translations, reprinted editions and slightly that ofJohannes Muller (1844), in which the modified versions, and lastly Greenwood et teleosts as a whole were presented as a ver- al. (1966), McAllister (1968), and J. Nelson tebrate subclass, and their components as or- (1984)] went through an evolution from the ders. These orders of Muller's bore names early nonsubordinated, ordinal classifica- that may seem strange and unfamiliar to to- tions of Muller (1844), Agassiz (1858), Gill day's student, but the etymological charac- (1872), Boulenger (1904), and Regan (1909, teristics of many of them were preserved for 1929), to the complex subordinated, hierar- some time, a few even to the present. chical system of Goodrich (1909). It was Some of these names and their cross- Goodrich (1909) who introduced the use of equivalents in different classifications were uniform group endings, a practice that was reviewed and explained in detail by Myers adopted by Berg (1940) and his successors, (1958) and now it remains only to emphasize to ease recognition of the hierarchical posi- that these many different classifications tion of a group in the general classification. [Muller (1844), Agassiz (1858), Gunther During all ofthis history some ofthe fishes (1859-1870), Gill (1872), Boulenger (1904), now assigned to the Euteleostei were distrib- Regan (1909, 1929), Goodrich (1909), Jor- uted throughout most of the higher taxa rec- 1 Curator, Department of Ichthyology, American Museum of Natural History. Copyright © American Museum of Natural History 1985 ISSN 0003-0082 / Price $5.25 2 AMERICAN MUSEUM NOVITATES NO. 2827 MULLER 1844 REGAN 1906 1929 FIG. 1. Branching diagrams representing the degree of resolution of teleostean classifications from 1844 (Muller) to 1909 (Goodrich) and 1929 (Regan). 1985 ROSEN: EUTELEOSTEANS 3 ognized by earlier authors. For example, in ment is a sign ofhealth and vigor in the field MiUller's (1844) classification of fishlike ver- that should serve as an example for other tebrates, the subclass Teleostei included six vertebrate systematists, some of whom have orders, each of which included taxa now en- abandoned the search for hierarchical order compassed by the Euteleostei. Thus, his in favor ofgeneral ecological research or lab- Acanthopteri included "perciform" fishes; the oratory studies of the behavior of selected Anacanthini, the codfishes, cusk eels, and species. flatfishes; Pharyngognathi, the labrids, and This paper is premised on certain new ob- their immediate allies; the Phystomi, the oto- servations and interpretations of teleostean physan Ostariophysi, percopsiforms, myc- anatomy and the cladistic notions derived tophids, salmonids, galaxiids, synbranchid from them. One of these notions, in agree- eels, pikes, and mudminnows; the Plectog- ment with Fink and Weitzman (1982) and nathi, members of the modem Tetraodon- Fink (1984), is that the Salmoniformes ofRo- tiformes; and the Lophobranchii, the pipe- sen (1974) is not monophyletic. The second fishes, and seahorses. The Physostomi of is that the Aulopiformes of Rosen (1973) is Muller also included some osteoglosso- also not monophyletic. A third is that Poly- morphs and the former is understood to be mixia and the acanthomorph neoteleosteans more or less equivalent to the Malacopteryg- are defined, in part, by the absence of a re- ii, Isospondyli, and Clupeiformes in classi- sidual neural arch between the first vertebra fications as recent as Berg's (1940). The three and the occiput that is primitively present in latter "groups" were unnatural assemblages most halecostomes, many primitive eute- of primitive teleosts, which included numer- leosts, and in neoscopelids but not mycto- ous taxa later treated by Greenwood et al. phids among the Myctophiformes, as rede- (1967) as euteleosteans in another unnatural fined by Rosen (1973) to include the assemblage that Greenwood et al. (1966) had myctophids and neoscopelids.2 A fourth is previously termed the Protacanthopterygii. Progress has been slow, teleost classifications 2 This and other characters conflict with four shared, going through a long period when all teleosts derived features for myctophids and neoscopelids given were assembled into one ofthree main kinds: by Stiassny (Ms), but are consistent with the presence of lower, intermediate, or higher even as re- a subocular shelf, and single, medial, rostral cartilage in cently as Gosline (1971). most polymixiids and acanthomorphs (absent in neo- The first comprehensive modem attempt scopelids), and three or fewer predorsal bones in myc- at detailed hierarchical synthesis since Good- tophids, polymixiids, and acanthomorphs (four in neo- rich (1909) was that of Greenwood et al. scopelids). One of Stiassny's characters linking the two (1966), closely followed by that ofMcAllister families is the cone-shaped ventrally directed parapoph- (1968). This history is best appreciated by yses for Baudelot's ligament that will, I believe, prove a of dia- to be the primitive state of a similar structure in Poly- examining sprinkling branching mixia and other acanthomorphs (fig. 18). Another of grams extracted from the main components Stiassny's reasons for linking myctophids and neosco- of each of the systems proposed since 1844 pelids is described by Lauder (1983). In Lauder's paper, (figs. 1 and 2). he stated that "all myctophiforms (including neoscope- It might be guessed that many major taxo- lids; Rosen, 1973) possess a unique attachment of the nomic problems have remained unsolved branchial skeleton to the urohyal." In myctophids, how- once an interest in cladistic methods ofanal- ever, the third hypobranchials have long anteroventral ysis and classification was adopted by the ich- tips that clasp the urohyal laterally, whereas in neosco- thyological community and most of these pelids, the anteroventral tips ofthe third hypobranchials problems might be expected to be within the extend forward above the urohyal to the dorsal edge as the of all where they are attached by ligament. The latter condition Euteleostei, largest recognized is similar to that for primitive acanthomorphs (e.g., Poly- teleostean assemblages. I do not regard these mixia) except that in the latter, the ligaments from the problems as close to solution since there ex- third hypobranchials extend forward to contact the dor- ists, still, significant disagreement amongst sal edge of the urohyal more anteriorly. In any event, I ichthyologists on the interpretation of char- see no character here that clearly aligns myctophids with acter information and the delimitation of neoscopelids. This leaves two ligament characters of natural groups (Fink, 1984). This disagree- Stiassny's to align those taxa, as compared with the eight 4 AMERICAN MUSEUM NOVITATES NO. 2827 that the Neoteleostei is characterized by a Certain subsidiary notions also emerge as tripartite occipital condyle (the basioccipital consequences of this work, (1) that the "os- and two exoccipital condyles), as described meroids" and the Salmonidae might not be and illustrated by Rosen and Patterson (1969), monophyletic groups. Pefiaz (1983, p. 370) and which unites stomiiforms with them, as recently attempted an ontogenetic diagnosis elaborated by Fink and Weitzman (1982) and ofthe Salmonidae, but pointed out that some Fink (1984). A fifth is that, in disagreement of the diagnostic features may also be found with Fink and Weitzman (1982), the presence in other fish groups, (2) that Aulopus, and ofa well-defined triplejoint that incorporates perhaps some closely allied forms excluding two large exoccipital condyles is not evidence Chlorophthalmus, mightjointly form the sis- for linking the Salmonidae with the neote- ter group to the Ctenosquamata based, in part, leosts since this type of joint has a limited on the anatomy of the rostral cartilage, and distribution only in Recent salmonines and (3) that within the groups that remain, the is, therefore, probably convergent. A sixth is old Paracanthopterygii toadfishes and their that neoteleosts primitively show a cervical immediate allies might be more closely linked gap between the occiput and first vertebra. A to cods and theirs than the cods are to cusk seventh is that the Acanthomorpha are de- eels and brotulas based on both neurocranial, fined by complete closure of the cervical gap vertebral, and gill arch evidence.3 via two prezygapophyseal