DUNN: DEVELOPMENTAL OSTEOLOGY 



49 



ities include upper jaw bones (Berry, 1 964a), head spines (Ken- 

 dall, 1979; Washington, 1981; Yuschak, 1982; Washington and 

 Richardson, MS), gill arches (Leiby, 1979b; Yuschak, 1982; 

 PotthofTet al., 1984), and lateral skull bones (Leiby, 1979b). 



Patterns of chondrification may also be of value in inferring 

 phylogenetic relationships. Washington and Richardson (MS) 

 noted that while chondrification of skeletal bones in most scor- 

 paeniform fishes is a relatively brief process, occurring in pre- 

 flexion and early flexion larvae, chondrification was prolonged 

 (occurring through most larval development) in hexagrammids 

 and in three genera of cottids. These authors also considered a 

 unique pattern of ossification of cartilaginous rings in the regions 

 of the parietal and frontal spines as a synapomorphic character 

 uniting three genera of cottids. 



Vertebral column and associated bones. — Vertebral centra, neural 

 and haemal spines, apophyses, and ribs all undergo variable 

 changes in configuration with growth. A number of workers have 

 documented the development of the vertebral column and as- 

 sociated bones in a variety of taxa, but attempts have not been 

 made to analyze the phylogenetic significance of the ontogeny 

 of these structures. The sequence and direction of ossification 

 of vertebral centra is known to vary among taxa (e.g., Moser 

 and Ahlstrom, 1970; Mook, 1977; Potthoff" et al., 1984), but 

 this character has yet to be analyzed among groups of fishes. 



Among those elements of the vertebral column which have 

 been studied in various taxa, Potthoff"and Kelley (1982) noted 

 that the neural and haemal arches in Xiphias first develop dis- 

 tally opened, whereas in other perciforms studied, split arches 

 were observed in small larvae on the anterior two centra only. 

 Washington and Richardson (MS), in their study of cottid larvae 

 and scorpaeniform outgroups, noted in various taxa the reduc- 

 tion or absence of the first neural spine, presence or absence of 

 autogenous neural arches on centrum one, shape of anterior 

 neural arches, and whether or not the first neural arch was 

 distally fused or open. Potthoff" and Kelley (1982) cited the 

 unique position and development of ribs in Xiphias compared 

 to other perciforms studied, and Washington and Richardson 

 (MS) examined the location, number, and position of ribs in 

 cottids and perciform outgroups. 



Fins and their supports— Y>OTsaX and anal fins— The sequence 

 of formation of dorsal and anal fins as well as the order of 

 development of their constituent spines and/or rays varies among 

 taxa (Dunn, 1983b). This succession of formation may be rel- 

 atively constant among related groups or it may vary, but the 

 phylogenetic significance of these events, if any, has yet to be 

 analyzed. Additionally, numerous taxa of larvae possess tran- 

 sient, often bizzare, structures, such as elongate dorsal spines 

 or rays or anal rays (e.g., Kendall, 1979; Moser, 1981). These 

 structures are of taxonomic value and may contain phylogenetic 

 information, but the homologies of these structures, if any, are 

 not known (Govoni, this volume). 



PotthoflTet al. (1984) indicated that the second dorsal and 

 anal fins are the first to develop in most perciform fishes. How- 

 ever, in generally more advanced species, dorsal fin rays (or 

 spines) develop first anteriorly and second dorsal and anal fin 

 ray development starts after the first dorsal fin is either partially 

 or fully developed. Fahay and Markle (this volume) described 

 the sequence of fin formation in gadiform fishes. Usually the 

 vertical fins ossify at nearly the same time, but two or more 

 centers of ossification are present in those genera (e.g., Molva. 



Merluccius) with a single long dorsal fin (or a short first dorsal 

 fin preceding a longer second dorsal fin). 



The ontogeny of pterygiophores has received considerable 

 attention from Potthofl"and colleagues (e.g., PotthofT. 1975, 1980; 

 Potthoff'et al., 1980, 1984). The developmental pattern of fin 

 pterygiophores may suggest phylogenetic relationships. PotthofT 

 and Kelley (1982) noted that the first dorsal pterygiophore in 

 Xiphias arose from either one or two pieces of cartilage, as is 

 the case in Morone (Fritzsche and Johnson, 1 980), but not in 

 scombrids. Washington and Richardson (MS) observed the on- 

 togenetic migration of dorsal fin pterygiophores, relative to neu- 

 ral arch position, in three cottid genera. Proximal and distal 

 radials may fuse during ontogeny (Yuschak, 1982) and the pres- 

 ence or absence of medial radials may characterize certain groups 

 of fishes (PotthofT and Kelley, 1982). 



Pectoral and pelvic fins and their supports.— 'Wilh some excep- 

 tions, pectoral fins develop rays later in the larval period than 

 median fins (Dunn, 1983b). Transient, elongate spines and 

 rays also develop in the pectoral fins of some taxa (Moser and 

 Ahlstrom, 1974; Moser, 1981); such structures may be of taxo- 

 nomic value, but their phylogenetic significance, if any, and their 

 homologies are not known. Relatively few descriptions have 

 been published on the development of the pectoral fin (e.g., 

 Houdeand PotthofT, 1976; Potthoff", 1980; Potthoff"and Kelley, 

 1982; Yuschak, 1982; Potthofl["et al., 1984), and few systematic 

 inferences have been drawn. PotthofTet al. (1984) noted, in 

 Anisotremus virginicus. the ontogenetic fusion of the supratem- 

 poral-intertemporal, the elongation of the anterior coraco-scap- 

 ular cartilage, and the reduction in length of the posterior pro- 

 cess. Washington and Richardson (MS) examined the orientation 

 of the cleithrum, as well as its outer lip, the length of the scapula- 

 coracoid complex, the base of the cleithrum, and the cleithral 

 extension over the pelvic bone (among other characters of the 

 pectoral girdle) in their analyses of cottids and their allies. 



The ontogeny of the pelvic fin and its supporting structures 

 also has been little investigated (PotthofT, 1980; PotthoflTet al., 

 1980; Fritzsche and Johnson, 1980) and infrequently used in 

 systematic studies. Dunn and Matarese (this volume) indicated 

 that in gadid larvae the length of the posterior-lateral process 

 of the basipterygia differed among subfamilies and tended to be 

 reduced or wanting in those genera presently considered ad- 

 vanced. 



Caudal fin.— The development of the caudal fin in teleosts, a 

 subject Dr. Ahlstrom was extremely interested in (e.g., Ahlstrom 

 and Moser, 1976), seems to have received more study than other 

 bony structures. However, few workers have attempted to in- 

 terpret the phylogenetic significance of the development of this 

 fin (Dunn, 1983b). 



The fusion of bones, reduction in size of structures, or'loss 

 of elements by absorption can frequently be observed in the 

 development of the caudal fin in some fishes. Additionally, based 

 on ontogenetic evidence, the structure of this fin may differ from 

 that commonly accepted based on adult specimens (Dunn, 

 1983b). 



Ontogenetic changes in the caudal fin and associated bones 

 which have been used to infer phylogenetic relationships include 

 the reduction through fusion of ural centra (Moser and Ahl- 

 strom, 1 970; and others), discreet or fused hypural bones (Wash- 

 ington and Richardson, MS; Dunn and Matarese, this volume), 

 absence of the parhypural in certain taxa which normally possess 

 one (Washington and Richardson, MS), characteristics (e.g.. 



