Review of ichthyodectiform and other Mesozoic teleost fishes, and the theory and practice of classifying fossils. Bulletin of the AMNH ; v. 158, article 2

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New York : American Museum of Natural History
"The ichthyodectiform fishes are a nominal order of Mesozoic teleosts that have been assigned to three of the four extant teleostean cohorts in one or another recent work, and whose monophyly and composition have not previously been established. From a detailed anatomical survey, it is concluded that the Ichthyodectiformes is monophyletic, and is characterized by an endoskeletal ethmo-palatine bone (a new term) in the floor of the nasal capsule, and by uroneurals that cover the lateral faces of the preural centra. Ichthyodectiform subgroups are the Allothrissopoidei (new name, Allothrissops, Upper Jurassic, only) and Ichthyodectoidei, the latter containing the Ichthyodectidae (nine nominal genera, Upper Jurassic-Upper Cretaceous) and Saurodontidae (two genera, Cretaceous). The Crossognathidae (two genera, Cretaceous) share the ichthyodectiform uroneural character, but show no other ichthyodectiform features, and have certain synapomorphies with higher teleosts. They are placed as Teleostei incertae sedis. A new scheme of teleostean interrelationships is proposed, in which the Euteleostei and Clupeomorpha are sister-groups, these two combined (Clupeocephala, new usage) are the sister-group of the Elopomorpha, and those two combined (Elopocephala, new usage) are the sister-group of the Osteoglossomorpha. Ichthyodectiforms cannot be assigned to any of these teleostean subgroups. This outline of teleostean relationships is extended by specifying a sequence of derived character states shared by extant Teleostei and the Jurassic forms Tharsis dubius, Leptolepis coryphaenoides, Proleptolepis spp., Pholidolepis dorsetensis, and Pholidophorus bechei. From these character states a corresponding phyletic sequence is inferred such that each named taxon is the sister-group of all those preceding it. Within this scheme, the ichthyodectiforms are the sister-group of Tharsis and extant teleosts. Ichthyodectiform relationships therefore lie between members of the Leptolepididae, as that group is currently defined, making it polyphyletic. Various other Mesozoic teleosts are reviewed, and their relationships specified in this scheme as precisely as the available information permits. One 'leptolepid,' Leptolepides, is the sister-group of extant clupeocephalans. Another, 'Leptolepis' bahiaensis, is a clupeocephalan incertae sedis. 'Leptolepis' macrophthalmus and 'L.' talbragarensis are Teleostei incertae sedis, with relationships in the region of Tharsis and the ichthyodectiforms. The nominal genus Anaethalion contains one Lower Cretaceous elopomorph, 'A.' vidali, and an unnamed Jurassic elopomorph, whereas the remaining species are Elopocephala incertae sedis. The Jurassic 'leptolepid' Ascalabos and the Upper Jurassic and Lower Cretaceous form genus Pachythrissops are Teleostei incertae sedis, in the same way as 'Leptolepis' macrophthalmus. With these and other relationships proposed in a cladogram (fig. 54), possible methods of classifying such extended sister-group systems, including series of fossils in which each is the sister of a group containing extant taxa of high tank, are discussed. To avoid naming taxa of high rank for single paleospecies, and to avoid frequent changes in the names and ranks of extant taxa, a new convention for dealing with fossils is proposed. We recommend that those fossil taxa whose relationships can be inferred be incorporated in the hierarchy of extant taxa simply by listing them in sequence, within the extant taxon of lowest rank to which they belong. A particular list of sequenced fossils is established according to the convention that each listed fossil group is the plesiomorph sister-group of everything beneath it in the taxon. These listed fossil taxa may have names indicative of any rank, whatever rank may have existed by previous convention, but sequenced fossil taxa are always distinguished by the prefix plesion (new term). Within a monophyletic group of extinct species, however, usual sister-group ranking procedures are followed. The use of plesions is a convention or compromise which makes it unnecessary to rank extinct taxa formally in the same hierarchy as extant taxa. Many of the fossils we have investigated are too poorly known for their relationships to be specified unambiguously. These fossil taxa are incertae sedis, at a specified level in the hierarchy. We recommend that the term incertae sedis be restricted to fossils, and discuss the implications of that recommendation"--P. 85.
p. 83-172 : ill. ; 26 cm.
Includes bibliographical references (p. [167]-172).