. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 98 Bulletin Museum of Comptinitire ZooIo<i,y, Vol. 750, No. 3 anterior dorsal fin-spine pectoral fin-spine posterior dorsal fin-spine. intermediate spines anal fin-spine lOn Figure 2. Climatius reticulatus, a Lower Devonian acanthodian fish. (From Moy-Thomas and Miles |1971|, courtesy of W. B. Saunders Publishing Co.) based on an analysis of the distribution of various characters (hsted in the cap- tion). This figure indicates that the acti- nopterygians share a common ancestor with a group consisting of tlie coela
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 98 Bulletin Museum of Comptinitire ZooIo<i,y, Vol. 750, No. 3 anterior dorsal fin-spine pectoral fin-spine posterior dorsal fin-spine. intermediate spines anal fin-spine lOn Figure 2. Climatius reticulatus, a Lower Devonian acanthodian fish. (From Moy-Thomas and Miles |1971|, courtesy of W. B. Saunders Publishing Co.) based on an analysis of the distribution of various characters (hsted in the cap- tion). This figure indicates that the acti- nopterygians share a common ancestor with a group consisting of tlie coela- canths (Actinistia), lungfishes, and tetra- pods, and that these two groups together share a common ancestor with the acan- thodian fishes. The Acanthodii, often very inappro- priately called "spiny sharks," first ap- pear in the fossil record in the Lower Si- lurian. They are the most primitive members of the teleostome fishes (Fig. 1) and are characterized by pectoral fin spines, strong spines anterior to the dor- sal and anal fins, and the presence of nu- merous small bony plates which form a protective cover over the branchial cham- ber (Fig. 2). Primitively the acanthodian fishes possess two dorsal fins which have internal unsegmented stiffening rays (Moy-Thomas and Miles, 1971). These fishes have rather large eyes relative to their head size and are generally as- sumed to have fed in the midwater or on the surface. The Actinistia or coelacanths (Fig. 3) are first known from the Middle Devo- nian and are represented today by the single genus, Latimeria, discovered in 1938 off East London, South Africa. The coelacanths have two dorsal fins, two ex- ternal nostrils, and an intracranial joint— a division between the anterior and pos- terior portions of the cranium allowing the anterior (ethmosphenoid) portion to be elevated during feeding (see Lauder, 1980a; Thomson, 1966, 1967). The caudal fin of coelacanths has a characteristic di- phycercal or "tassel sh
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