. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 148 Bulletin Muscinn of Coniixirative Zoology, Vol. 150, No. 3. Figure 36. Evolution of the caudal skeleton in the advanced neoteleosts. The arrows connecting the different types indicate possible structural changes, not phyletic lineages. The epurals are stippled, the second preural neural spine crest is black. The primitive configuration of the caudal skeleton is exhibited in the Myctophiformes. In the Paracan- thopterygii the most anterior epural fuses with the second preural neural spine crest. Further specializat
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 148 Bulletin Muscinn of Coniixirative Zoology, Vol. 150, No. 3. Figure 36. Evolution of the caudal skeleton in the advanced neoteleosts. The arrows connecting the different types indicate possible structural changes, not phyletic lineages. The epurals are stippled, the second preural neural spine crest is black. The primitive configuration of the caudal skeleton is exhibited in the Myctophiformes. In the Paracan- thopterygii the most anterior epural fuses with the second preural neural spine crest. Further specializations involve the fusions of the hypurals into platelike elements. In the Acanthopterygii fusions occur of two preural vertebrae, of which one has a complete neural spine and the other a reduced or no neural spine crest. The result of this vertebral fusion is a caudal skeleton configuration which is convergent to that of the Paracanthopterygii. Among more specialized Acan- thopterygii fusions occur of the hypurals to form hypural plates. The Paracanthopterygii i,s at best an ill- defined group. The pharyngeal jaw ap- paratus does not furnish any phylogenet- ic information because in percopsiforms the retractor dorsalis muscle still has two heads, as in mvctophiforms, in which the lateral head inserts on the fourth pharyn- gohranchial. The lateral jaw nniscles of paracanthopterygians furnish conflicting evidence. In primiti\e paracanthopteryg- ians (percopsids and gadids) the maxilla is associated with two muscles, the A, and A^f3. More advanced paracanthopteryg- ians resemble the Mvctophidae in ha\- ing only A,/3 inserted on the maxilla. The paracanthopterygians were first defined as a superorder (Rosen and Patterson, 1969) on the basis of the structural spe- cialization in the caudal skeleton. In all adult paracanthopterygians the caudal skeleton is characterized by the presence of a full neural spine on the second preur- al centrum, and two epurals (Fig. 36). Such a structural
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