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Osteology and relationships of the southern freshwater lower euteleostean fishes

2011; Pensoft Publishers; Volume: 87; Issue: 1 Linguagem: Inglês

10.1002/zoos.201000020

1860-0743

R. M. McDowall, Christopher P. Burridge,

Fish biology, ecology, and behavior

Temperate lands of the Southern Hemisphere have freshwater fish faunas that are dominated by a series of lower euteleostean genera that seem to fall into three clusters: 1) Retropinna, Stokellia and Prototroctes, forming a family Retropinnidae; 2) Aplochiton, Lovettia, Galaxias, Neochanna, Brachygalaxias, Paragalaxias and Galaxiella included in either a single family Galaxiidae or split between Galaxiidae and Aplochitonidae (the latter including Lovettia); and 3) Lepidogalaxias. Although the generic classification seems relatively well-settled, the familial allocations and phylogenetic relationships among these three groups of genera have been much discussed in recent decades, dating back into the 1960s. There is wide agreement that Retropinna, Stokellia, and Prototroctes are closely related to each other; that the other genera apart from Lepidogalaxias are also closely related to each other and well separated from the retropinnids; but what Lepidogalaxias is related to has been a subject of considerable debate and highly divergent phylogenetic hypotheses for many years. Our study presents extensive morphological information, mostly osteological, that seeks to clarify all of these relationships. Using the Northern Hemisphere Osmeridae as the principal outgroup, our data support the historical relationships discussed above, for all but Lepidogalaxias, though we also suggest that Aplochiton and Lovettia are quite deeply separated from the galaxiid genera. Our conclusions relating to Lepidogalaxias are highly equivocal, given the large numbers of autapomorphic characters in the analysis and the lack of convincing synapomorphies shared by that genus and other southern lower euteleosteans, we conclude that Lepidogalaxias is deeply separated from the other southern genera. Incorporating additional molecular information, we conclude that Lepidogalaxias is possibly the sister group of all other euteleostean fishes, a conclusion that also emerges more explicitly from other, recent molecular studies of this highly controversial taxon. It has so many distinctive morphological characters that it seems difficult, if not impossible, to identify its relationships from osteology alone, though the extent of autapomorphy may result in part from our use of Osmeridae as the principal outgroup. Further studies comparing Lepidogalaxias with other outgroups, or perhaps the use of other types of morphological characters, may reveal more of its relationships. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)