is an analysis of the evolutionary mechanism leading to 

 it. This presents a strikingly clear case of intraordinal 

 evolution primarily through the processes of reduction, 

 simplification, and loss of elements, especially of the 

 bony parts. Reductive tendencies in the evolution of 

 vertebrates, including many groups of fishes, are not un- 

 common (Myers 1958), and the reductions that have 

 taken place in plectognaths are of especial interest only 

 because of the extreme exaggeration of the tendency 

 in this order. The reductive trend in the evolution of 

 plectognaths obviously is not absolute, and certain 

 morphological units in circumscribed groups show an 

 opposite tendency, e.g., the stomach and complex mus- 

 culature of tetraodontoids, the pectoral girdle of ostra- 

 coids, the scales in nearly all groups except a few tetra- 

 odontids, etc. 



The main point, however, is that the generalized mem- 

 bers of the order, the triacanthoids, possess only slightly 

 less than the percoid complement of bones, but many 

 bones have become reduced or simplified, fused with 

 others, or entirely lost in what appear to be clear 

 evolutionary lines derived from these basal plectog- 

 naths. This is especially evident in the: branchial ap- 

 paratus; caudal, dorsal, and anal fin supporting struc- 

 tures; dorsal fin spines; pelvic fin and girdle; jaws and 

 teeth; and myodome. 



The plectognaths are also of biological interest because 

 of their supposed position at one of the major end lines of 

 modern teleost radiation and because of their great 

 diversification in structure, size, behavior, way of life, 

 and habitat (Tyler 1965c). They range from 22 mm and 

 30 g to 2 m and 1,000 kg in adult length and weight, from 

 relatively normal shapes to strangely specialized forms 

 with long tubular snouts or aborted caudal regions, from 

 scaleless to heavily armored, from nearly toothless to 



equipped with massive crushing beaks, from drably 

 colored to gaudy, from palatable to poisonous flesh, etc., 

 and with comparable contrariety in behavior, habits, and 

 habitats. They include the spikefishes, triplespines, trig- 

 gerfishes, filefishes, boxfishes, trunkfishes, pursefishes, 

 pufferfishes, porcupinefishes, and giant ocean sun- 

 fishes. 



The plectognaths are of some commercial interest 

 directly, for the dried skins or encasements of the weirder 

 forms are sold as curios, while a few species are sold for hu- 

 man consumption, such as tetraodontids, called sea squabs 

 on the east coast of the United States and fugu in Japan, but 

 of greater worth indirectly — the young of many plectog- 

 nath species are important forage for such popular large 

 oceanic fishes as dolphins, tunas, and billfishes. 



The Plectognathi are thought to have been derived 

 from a percoid ancestry related to the same line which 

 gave rise to the acanthuroids (the surgeonfishes and their 

 allies) in the late Cretaceous, but the evidence of this 

 hypothesized relationship is not yet conclusive (Tyler 

 1968, 1970c). The osteology of the fossil and Recent 

 acanthuroids is not well known, but with the osteologj' of 

 the plectognaths being made better known here, it will be 

 easier to search among the acanthuroids for a group 

 which shows a preplectognath type of organization and 

 which may be related to the speculated ancestral stock 

 common to the two groups. 



Because the plectognaths are often of exotic form and 

 occur in European waters, even though their center of 

 diversification is the Indo-Pacific, a few species were 

 described by early naturalists from Aristotle and Pliny to 

 Linnaeus. But some species still remain to be described, 

 many others are inadequately known, and much con- 

 fusion remains about the systematics of the group, even 

 at the familial level. 



Methods 



The majority of the specimens of the Recent species 

 studied for this monograph were prepared by potassium 

 hydroxide clearing, alizarin staining, and glycerin preser- 

 vation, prior to the advent of techniques using trypsin. A 

 few specimens were prepared by maceration as dry or 

 alcohol wet whole skeletons, or parts thereof, while 

 limited dissections were made on alcohol - preserved 

 whole materials. For fossil species, only superficial sur- 

 face preparation with chipping and weak acid washes 

 was employed. 



A list of the species examined, along with the num- 

 bers of specimens and their sizes, general localities, and 

 catalogue (or other identifying) numbers of their reposi- 

 tories, appears toward the end of this work. 



Length of specimens is always standard length (SL), 

 unless otherwise noted, taken from the anteriormost 

 middle point of the upper jaw (often from the tip of the 

 exposed upper teeth) to the middle of the line of flexure 

 at the caudal fin base, and measured and recorded with a 

 needlepoint dial caliper to the nearest 10th of a millimeter 

 (mm), but with lengths given here of over 100 mm 



rounded off to the nearest mm (0.5 and above to the next 

 highest integer). 



The survey of the osteology of the order was hindered 

 by the poor showing of internal features in several fossil 

 forms, by the relative unavailability of specimens for 

 clearing and staining of about one-fifth of the described 

 species currently considered valid, by a lack of time and 

 purpose to describe and illustrate each available species 

 (especially in genera with large numbers of osteologically 

 similar forms), and by the demands of space conser- 

 vation and publication costs. It is felt, however, that the 

 species selected for osteological inclusion (167 studied, 

 and 115 illustrated, for one skeletal region or another, of 

 the approximately 320 Recent species, and nearly all of 

 the fossil forms) adequately cover the anatomical diver- 

 sity of the group, and almost always cover the entire 

 range of external and osteological differences of the more 

 highly modified as well as more normal represen- 

 tatives of each family. I find it difficult to believe that 

 there is a missing link or living relic among those Recent 

 and fossil plectognaths not examined for this work which 



