aLog-likelihood values, DInL, with standard deviations, s, relative to the best tree and estimated bootstrap probabilities, pBoot (Kishino 1989, 1990),for different positions of the spiny dogfish in the piscine ML tree. The trees were reconstructed by exhaustive search based on an alignment of 2687aa. The analyses were performed using the PROTML program (Adachi and Hasegawa 1996a) applying the mtREV-22 model of aa evolution(Adachi and Hasegawa 1996b). The best topology is consistent with that shown in Fig. 1, but the position of the dogfish relative to the teleosts andthe coelacanth was not conclusively established. According to current phylogenetic theory cartilaginous fishes are basal to the split betweenActinopterygii and Sarcopterygii (topology 6). That topology and topology 7 (spiny dogfish basal to the bony fishes in the presently reconstructedtree) were statistically rejectable as being about 3 SD worse than the best tree.