Identification hints: The orders and families are listed in phylogenetic sequence. Therefore, it is helpful to
be able to distinguish a primitive or ancestral fish from an advanced or derived fish to quickly find the
appropriate order. This is not always an easy task but certain characters can be examined to give a general
impression. For example, more ancestral fishes generally have the position of the pelvic fins more abdominal
while advanced fishes usually have them thoracic or jugular (Fig. 17 above). Primitive fishes also tend to
lack true spines (Fig. 15), have the maxilla with teeth and a prominent part of the gape (Fig. 6), and have
non-protrusible mouths (Fig. 5). There are some exceptions to this, however, and these characters should
be used cautiously. An example are the barracudas (family Sphyraenidae) that have true spines and the
premaxilla predominant in the gape but that have abdominal pelvic fins and non-protrusible jaws. Since
barracudas are considered advanced fishes, the primitive characteristics are thought to have evolved
secondarily from more advanced character states.