Subclass NEOPTERYGII
Fin rays equal in number to their supports in dorsal and anal fins; premaxilla with internal process lining the anterior part of nasal pit; symplectic developed as an outgrowth of hyomandibular cartilage. In addition, the spermatozoa of neopterygians has lost a plesiomorphic feature of vertebrates—the acrosome (several species, however, have acrosome-like structures) (Jamieson, 1991).
It is generally agreed that the neopterygian fishes are a monophyletic group. However, there is much uncertainty about the relationships of the basal taxa, and much more work will be required before even a reasonable phylogenetic hypothesis of relationships of the basal groups can be put forth. The fossil record extends as far back as the Late Permian with Acentrophorus.
An overview of the classification adopted here is as follows (the Halecostomi and Halecomorphi are not named in the main classification):
Class Actinopterygii Subclass Cladistia Subclass Chondrostei Subclass Neopterygii
Halecostomi (halecostomes)—for such extinct taxa as Macrosemiiformes, Semionotiformes, and Pycnodontiformes and the following coordinate taxa. In some earlier works this was viewed as sister to the Ginglymodi (for Lepisosteidae) (as adopted in Nelson, 1984). Arratia (2004) reviewed the early fossil taxa.
Halecomorphi (halecomorphs)—for Amiiformes and related fossil taxa and the remainder. This assumes that Amiiformes and some other groups are sister to the teleosts, whereas some evidence exists supporting the older view that Amiiformes and Lepisosteiformes form a monophyletic group, the holosteans. Grande and Bemis (1998) and Arratia (2004) discussed the membership. See below for mention of disagreement as to whether the Osteoglossomorpha or the Elopomorpha are the most primitive extant taxa.
Division Teleostei
Subdivision Osteoglossomorpha Elopocephalans
Subdivision Elopomorpha Clupeocephalans
Subdivision Ostarioclupeomorpha (= Otocephala) Subdivision Euteleostei
The view expressed in the present classification that chondrosteans and neopterygians are coordinate taxa is regarded as a working hypothesis. However, the conclusions, with respect to extant groups, that amiiforms and the teleosts are sister groups with lepisosteids being their primitive sister group requires further testing in the face of some molecular data supporting that, among living neopterygians, amiids and lepisosteids may form a clade separate from teleosts (comprising the one-time recognized Holostei).
Arratia (2004) gave an insightful evaluation of our understanding of hale-comorph and teleost phylogeny. This work nicely shows what we know and what remains uncertain. Arratia (2001) introduced the term Teleostomorpha for the taxon including the Teleostei (with Pholidophorus as the primitive sister taxa) and stem-based fossils and used the term Teleocephala of de Pinna (1996a) for the included taxon covering everything sister to the Ichthyodeciformes. She further explored this concept of relationships in Arratia (2004). These taxa are not formally introduced into classification here pending more work on the basal groups involved.
There are many neopterygian taxa of uncertain position. For example, Nursall and Capasso (2004) described a fascinating fossil from the upper Middle Cretaceous of Lebanon (Gebrayelichthys uyenois, the Archangelfish). It is a highly compressed fish placed in its own family, Gebrayelichthyidae.
The next orders given below up to Teleostei were generally regarded as the holosteans, of which the last, the Pachycormiformes, is the hypothesized sister group to the teleosts (see Arratia, 2001, for other possible candidate groups— Amiiformes, Lepisosteiformes, Dapedium, Pycnodontiformes, Pachycormiformes, and Aspidorhynchiformes). These following orders are not placed in higher categories to indicate any particular hypothesized phylogenetic position. Rather, the subclass Neopterygii is recognized with one division—the monophyletic Teleostei—with several orders sequenced before it.
fOrder MACROSEMIIFORMES. One family, Macrosemiidae, Jurassic and Lower Cretaceous, known from Europe and Mexico (González-Rodríguez et al., 2004; González-Rodríguez and Reynoso, 2004).
fOrder SEMIONOTIFORMES. Extant gar and the fossil Semionotidae are often recognized in the same order, either under the ordinal name Lepisosteiformes or Semionotiformes (e.g., Nelson, 1976, 1994). In contrast, I placed them in separate orders in Nelson (1984) and do so now following the scholarly and highly detailed work of Grande and Bemis (1998). Their ongoing studies may yet result in further changes.
tFamily DAPEDIIDAE. Position uncertain.
Body deep; dorsal and anal fins long; gular present. Upper Triassic to Lower Jurassic; in marine and freshwater deposits; North America, Europe, and India. E.g., Dapedium.
tFamily SEMIONOTIDAE (Lepidotidae). Dorsal ridge scales present; epiotic with a large posteriorly directed process; mouth small; body fusiform; dorsal and anal fins short. Triassic to Cretaceous.
Genera include Lepidotes Paralepidotus, and Semionotus (e.g., Tintori, 1996). Among the many genera excluded is Acentrophorus, known from the Late Permian, and not assigned here to any higher taxon.
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