Interrelationships of basal teleosts with emphasis on the Osteoglossomorpha.

Abstract

The objective of this research was to survey evidence pertaining to the cladistic relationships of basal teleosts. Recent teleosts include four groups, the Elopomorpha, Osteoglossomorpha, Clupeomorpha, and Euteleostei. Patterson & Rosen (1977) proposed that Clupeomorpha and Euteleostei are sister groups forming the Clupeocephala; Clupeocephala and Elopomorpha are sister groups forming the Elopocephala; and Elopocephala and Osteoglossomorpha are sister groups forming the extant Teleostei. Arratia (1991, 1993) questioned the monophyly of the Elopocephala. She proposed that the Elopomorpha, not the Osteoglossomorpha, is the most primitive clade among extant teleosts. The method of determining relative relationships in present analyses is shared derived character states based on the principle of parsimony (Hennig 1966). Detailed comparative studies include both Recent and fossil fishes. Primitive species of each lineage are used because they have less modified characters (Fink & Fink 1981). The phylogenetic analyses were carried out by PAUP3.1 (Swofford & Begle 1993). All characters are usually unordered and initially equally weighted. Strict consensus was used to summarize the information common to all the equally parsimonious trees. A posteriori successive weighting was applied for the analysis of the relationships of euteleosts. On the basis of the detailed morphological comparative study of the fossil and extant representatives, it was concluded that: (1) Osteoglossomorphs compose a monophyletic group. They are distinguished from other groups of teleosts by the absence of a supraorbital, the absence of an autopalatine, a discrete association between the sternohyoid and the second gill-arch, a full neural spine on the first preural centrum, and intestine passing to the left of the stomach. The osteoglossomorphs consists of three subgroups: the Osteoglossoidei (Osteoglossidae + Pantodontidae), the Notopteroidei (Mormyridae + Notopteridae), and the Hiodontidae. The former two sister groups, closer than either is to the Hiodontidae. (2) The Elopomorpha is the sister group of all other extant teleostean groups. The Osteoglossomorpha is the sister group of the Clupeocephala (sensu Patterson & Rosen 1977), characters shared by them are as follows: absence of ethmoid commissural sensory canal, absence of the deep subtemporal fossa bridged by prootic-intercalar, absence of process basalis of metapterygoid, lateral opening of the foramen of the mandibular sensory canal, absence of dorsal process on the 4th epibranchial bone, and absence of gular plate under branchial hyoid. (3) The Euteleostei is not a monophyletic group--the Ostariophysi is the sister group of the Clupeomorpha. Characters uniting ostariophysans and clupeomorphs include supratemporal sensory canal penetrating parietals, basihyal tooth plate absent, six or fewer branchiostegals, and hypural 2 fused to U$\sb1$ but hypural 1 still autogenous. Other euteleosts are grouped as ((((Argentinoidei + Osmeroidei) + Neoteleostei) + Salmonidae) + Esocoidei). (Abstract shortened by UMI.)