THE ORDERS OF TELEOSTOMOUS FISHES. A PRELIMINARY REVIEW OF THE BROADER FEATURES OF THEIR EVOLUTION AND TAXONOMY. BY WILLIAM K. GREGORY. In the course of their teaching work at Columbia Professors Osborn and Dean have realized the need of students for a brief general review of the evolution of the Vertebrata, in so far as this may be inferred from the hard parts of existing and fossil forms. The preparation of such a work was undertaken in 1902 by Pro- fessor Osborn with the assistance of Dr. J. H. McGregor, and in 1904the present writer was commissioned to work up the material for the section on the Ganoids and Bony Fishes. The following preliminary review of these forms is published with the hope of eliciting the suggestions and criticisms of ichthyologists. It is largely based upon the well-known writings of Smith Woodward, Boulenger, Gill, Jordan and Evermann, and Jordan, to whom most of the statements of fact should be credited, and it is dso intended in the main to reflect the views of those authorities. But many other sources are drawn upon; the method of present- ation is not the conventional one, and the classification adopted (after considerable reflection) is believed to reconcile the marked differences in method in the American and English systems. The writer is under obligations to Dr. 0. P. Hay for certain valuable suggestions and criticisms and to Professors Henry Fairfield Osborn and Bashford Dean, his esteemed preceptors, for the general methods of analysis. The student seeking a general knowledge of the teeming hosts and almost endless structural modifications of the teleostomous fishes is at present confronted by two very distinct ,systems of classification: the American system, as exemplified in the latest classification adopted by President Jordan,' and the new IAGiridc to thStiidy 0) Fishes, 2 vols., 4t0, New York 1905. 437 438 WILLIAM K. GREGORY English method of Dr. G. A. Boulenger.’ The discovery of the reasons for this divergence in method, of the common grounds upon which both systems rest, and of a means of harmonizing these differences in a new or compromise classification, may be facilitated by a glance at the recent history of the taxonomy of fishes, and by a brief reference to some of the principal functions of “natural ” classifications in general. First, as to the history of systematic ichthyology. In England Gunther’s classification was long held as orthodox. It represented more especially the combined labors of Cuvier, J. Miiller, Agassiz, and Gunther himself, and was essentially pre- evolutionary in method. The larger groupings were fairly natural, but many of the smaller ones were really heterogeneous, and held together by homoplastic characters. The chief criteria of classification were external characters. In America Cope and Gill approached the subject from the standpoint of evolution. Cope3 in 1871 sketched out the broad lines of a new classification based on a careful study of a large osteological collection. This classification was founded to a large extent upon internal, skeletal characters. AS compared with previous systems it was also founded on a larger number and range of characters and was thus less subject to thedeceptive effects of characters resulting from convergent or parallel evolution. Gill4 had already recognized the naturalness of the assem- blages called by him Nematognathi, Eventognathi. In 1872 Gill published his “ Arrangement of the Families of Fishes” which was revised and extended in his memoir6 of 1893. 1 Tcleostei (Systematic Part), The Cambridge Natiwal History, vol. “Fishes, Ascidians,” etc., 1904, pp. 539-127. 2 An Iqiirodztctioiz to the Study of Fishes, avo, Edinburgh. 1880, pp. xii-xvi. 3 I’ Observations on the Systematic Relations of the Fishes, ” Proc. Anrer. Assoc. Adv. ‘Sci., 20th meeting, IndianapoBs, 1871, pp. 317-343. 4 “Catalogue of the Fishes of the Eastern Coast of North America,’! Proc. Acad. Nut. Sci., Phila., 186;, pp. 1-63. 5 “ Arrangement of the Families of Fishes, or Classes Pisces. Marsip- braiicliai, and Lepiocardii,” Swtithsonian 1Wisc. Coll., NO 247, 1872, pp. i-xlvi, 1-49. 6 “Families and Subfamilies of Fishes,’’ MWZ.Nut. Acad. Sci., Vol. VI, pp. 125-1.38. THE ORDERS OF TELEOSTOMOUS FISHES- 439 In this classification which has been the basis of all subsequent work of the American school, precision, classicism, and a strict adherence to the canons of nbmenclature reinforced a keen analysis and a judicious weighing of taxonomic values. The attempt was made to readjust these values so that they might express more nearly the various degrees of affinity, and to intro- duce more uniformity in the value assigned to the same taxo- nomic grade in different groups of vertebrates. Many currently recognized families were variously divided, the component parts being’ elevated to the rank of separate families, while many groups were labeled ‘‘of uncertain position.” The dictum that “ analysis must precede synthesis ” was consistently followed, and a great increase in the number of ordinal, subordinal, and family divisions was deemed preferable to the premature group- ings of the traditional classification. Attention was in this way directed to the very numerous families and groups which were really of uncertain affinities, but which had always been thrown in with other divisions by the conservatism which resents the introduction of new groups and new names. An important synthetic step was the frequent use of the superfamily. In England and on the Continent the Guntherian system was gradually found inadequate, and the importance of the skeleton in classification became recognized as ichthyology and especially palzichthyology developed. Dr. A. S. Woodward adopted the broad features of Cope’s classification, which he improved in many respects, but the older system still remained in general use. The new and very notable classification of Dr. Boulenger, re- ferred to above, is the first since that of Gunther to gain general acceptance in England. Dr. Boulenger refers 1 to the classifica- tion of Gunther as being to a “great extent based on physiological principles, ” whereas his new classification “aims at being phylogenetic.” It is based upon his studies of the rapidly grow- ing collection of fish skeletons in the British Museum; it reflects also the labors of Cope, Gill, Sagemehl, A. S. Woodward, of Jordan and his co-workers, and thus represents the most com- prehensive analysis of osteological characters which has yet appeared. I op. Cit., p. 542. 440 WILLIAM K. GREGORY Boulenger’s classification is true to British tradition in the fewness of its larger divisions; and many families, suborders, and orders of the American system are not recognized as distinct divisions. Thus the differences between the English and Ameri- can systems are very salient. By the American method as exemplified in Dr. Jordan’s latest work, 18 orders, about 33 sub- orders, and considerably more than 200 families of true Teleosts are recognized; by the English method all are swept into the single “order” Teleostei which is coordinate in value with the orders Crossopterygii, Chondrostei, Holostei, and which is sub- divided into thirteen suborders which for the most part have the value of the orders of the American system. Boulenger’s treatment of the “suborder” Ostariophysi may serve as an in- stance of this extensive synthesizing. Since this assemblage is regarded as a natural one the divisions Heterognathi, Eventog- nathi, Nematognathi are not used, and the Characins, Carps, and Catfishes are all united as families in the suborder Ostario- physi. In Boulenger’s definitions of these families the trench- ant structural differences between them are revealed, but so far as the classification itself indicates they might be no more separated than, say the Tarpons (Elopidae) from the Lady-fishes (Albu- lids), or the Herrings (Clupeidz) from the Salmons (Salmonidae). These differences in method seem to arise from the dual nature and function of a natural classification in the modern sense. A natural classification must necessarily express, first, degrees of homological resemblances and differences and, second, degrees of genetic relationship; but it cannot at the same time express bath with equal accuracy, and its primary purpose is to express degrees of homological resemblances and differences. In comparing the end forms of diverging lines of descent we find that between any two forms degrees of geiietu relationship are solely a function of time and of the rate of reproduction, while degrees of homologous structural relationships are a function of varying rates of evolution. To borrow an illustration from mammalogy, we may suppose that a certain group of pre-Tertiary mammals has given rise to the modern Insecti- vores on the one hand and to the Bats on the other. Between this ancestral group and each of the two modern groups a number THE ORDERS OF TELEOSTOMOUS FISHES 441 of generations has elapsed which we may assume to be roughly equal along both lines of descent. Therefore, in degree of blood kinship to this ancestral group both Bats and Insectivores are about equally far removed. But in homological structural re- semblances the modern Insectivores are much nearer to this group than are the Bats, and hence so far as ciassification is concerned, the ancestral, group and the Insectivores would probably be placed in a single order, while the Bats are set off in another order. Here plainly, degrees of blood relatwnslaip do mt exactly correspoizd 20 degrees of Itontological structural reseinblaiices aizd dio-ererzces, nor to the divisions of classification. In order to make classification correspond even roughly to degrees of blood relationship, i.e. to phylogeny, we must assign varying systematic values to different characters in proportion to their inferred relative phylogenetic age. For example, the notochord and other chordate characters which appear in certain larval Ascidians are regarded as of far greater phylogenetic age than the typical characters of adult Ascidians, and hence these transient characters are given a very high systematic value, so that through them the group is placed within the phylum Chordata.