16
J.T. Eastman and A. Clarke
despite their evolutionary pelagization most species remain benthic or
demersal [1].
When Did the Radiation Take Place?
Cladistic analysis of the notothenioids suggests that the suborder is
monophyletic, though at present the topology of the split between
Harpagiferidae and Artedidraconidae is not resolved (Fig. I). Recent
molecular evidence from sequence analysis of 12S and 16S ribosomal
RNA genes from 18 species spread across 5 families has broadly
supported the analyses based on morphological data. It has, however,
suggested that the most speciose family, Nototheniidae, may be
paraphyletic [8].
The notothenioid diversification appears to have been protracted
throughout much of the Tertiary, with the initial divergence of some of the
basal families having taken place during the early fragmentation of
Gondwana. At this time stocks appear to have become established in
brackish water on isolated continental blocks (Pseudaphritis in Australia,
and Eleginops in South America).
Possible notothenioid
outgroups
Notothenioids
Fig. 1. Notothenioid phylogeny of Lecointre et al. [65] with familial nomenclature of
Balushkin [25]. Rb, hemoglobin, AFGPs, antifreeze glycopeptides