It is agreed that there is a higher taxon that is monophyletic comprising all remaining fishes, supported by morphological evidence, but there is need for convincing molecular evidence that is in agreement to support this conclusion of its monophyly. There is, however, some disagreement on the boundaries of the Teleostei when fossil taxa such as Pycnodontiformes, Aspidorhynchiformes, Pachycormiformes, Pholidophoriformes, and Leptolepidiformes and others are considered (hence arguments of teleost monophyly must be carefully framed). A summary of some earlier work on teleost monophyly and boundaries is given in Nelson (1994) and de Pinna (1996a), and a summary of recent works can be found in Arratia (1997, 1999, 2004). At least 27 anatomical synapomorphies were found by de Pinna (1996a) to support monophyly of the group when defined as the most inclusive group of actinopterygians not including Amia and relatives (the Halecomorphi) and Lepisosteus and relatives (the Ginglymodi). G. Arratia has added immensely to our understanding of the basal members and their phy-logeny (e.g., Arratia, 1997, 1999, 2004), but, as she makes clear, we require a much better understanding of characters and their homology before we can erect a sound classification.
Patterson and Rosen (1977) defined the teleosts as a group of halecostomes with the ural neural arches elongated as uroneurals, basibranchial toothplates unpaired, and premaxilla mobile. In addition, the teleost urohyal is distinctive, being formed as an unpaired ossification of the tendon of the sternohy-oideus muscle (Arratia and Schultze, 1990). Given the comblike cladogram presented in Arratia and Schultze (1987), with amiiforms and pachycormids progressing toward the teleost level, it is difficult to establish any one place in the transition as the place where teleosts begin; it depends on what characters are employed to define them. Arratia and Schultze (1987) include the pachy-cormids in the teleosts, whereas, in the strictest sense, it is used by some for groups above the level of Pholidophorus.
In the following classification, I will give several groups of primitive fossil teleosts first. These are followed by the four lineages, including all living teleosts (collectively termed the Teleocephala by de Pinna, 1996a), given as subdivisions, the Osteoglossomorpha, Elopomorpha, Ostarioclupeomorpha
(= Otocephala), and Euteleostei. These taxa are sequenced according to the sister-group relationships postulated by Patterson and Rosen (1977) (with redefinition of their Euteleostei), with the Elopomorpha, Ostarioclupeomorpha, and Euteleostei composing the Elopocephala, and the Ostarioclupeomorpha and Euteleostei composing the Clupeocephala. Arratia (1991) challenged the view that osteoglossomorphs are more primitive than elopomorphs on the grounds that the caudal skeleton of Elops is more primitive than that of the osteoglossomorphs. Subsequent detailed work of Arratia (1997, 1999, 2004, and others) further supported the view that elopomorphs are the living sister group of all other living teleosts. However, this in turn has been challenged by Patterson (1998) (but see the rebuttal by Arratia, 1998) and particularly by the works of Filleul (2000), Inoue and Miya (2001), Inoue et al. (2003), and Wang et al. (2003). There are challenges in the two main hypotheses presented, and while I favor the arguments presented by the works of G. Arratia, I have not changed the classification pending better resolution of remaining questions.
Teleosts probably arose in the middle or late Triassic, about 220-200 million years ago. They have a rich fossil record (e.g., Patterson, 1993; Arratia, 1997, 1999, 2004). Several early fossil groups of uncertain relationships and not otherwise mentioned are given in Nelson (1994:89) and the above works of G. Arratia.
Teleosts are the most species-rich and diversified group of all the vertebrates. They dominate in the world's rivers, lakes, and oceans. About 26,840 extant species, about 96% of all extant fishes, placed in 40 orders, 448 families, and 4,278 genera.
fOrder PHOLIDOPHORIFORMES. Position uncertain. Probably not monophyletic, possibly polyphyletic (e.g., Arratia, 2004, and reference to her 2000 study). Some members of this group may have shared a common ancestry with the leptolepidiforms in the Triassic and, independently, the elopo-morph and osteoglossomorph teleostean lines in the Triassic or Jurassic. All major teleostean lines radiate in the Cretaceous.
Families perhaps belonging here include Archaeomaenidae, Ichthyokentemidae, Oligopleuridae, Pholidophoridae (i.e., Eurycormus), and Pleuropholidae.
fOrder LEPTOLEPIDIFORMES. Position uncertain. Family LEPTOLEPIDIDAE. Probably marine, Triassic to Cretaceous.
This family is probably polyphyletic (e.g., Maisey, 1991:272-73).
fOrder TSELFATIIFORMES. Position uncertain. Body deep; mouth bordered by premaxilla and maxilla; dorsal fin extending along most of back; pectoral fins inserted high on body; pelvics absent or present with six or seven rays; caudal fin deeply forked with 18 principal rays; palate toothed; most fin rays unsegmented. Cretaceous.
Much work on this group has been conducted by L. Taverne (e.g., Taverne, 2000). Taverne and Gayet (2004) found evidence placing this assemblage in the Clupeocephala. It is maintained in its position here pending a cladistic analysis with better understanding of the characters involved. The orthography of the ordinal name has been corrected from that used in Nelson (1994) by adding "iformes' to the stem of the type genus, Tselfatia.. This error originated in Nelson (1976) in spelling the subordinal name "Tselfatoidei" rather than Tselfatioidei.
Plethodidae (= Bananogmiidae)—e.g., Plethodus.
Protobramidae—e.g., Abisaadichthys, Eusebichthys, and Protobrama.
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