A review of early gadiform evolution and diversification: first record of a rattail fish skull (Gadiformes, Macrouridae) from the Eocene of Antarctica, with otoliths preserved in situ |
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Authors: | Jürgen Kriwet Thomas Hecht |
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Institution: | 1. Department of Collections, Museum für Naturkunde, Humboldt-Universit?t zu Berlin, Invalidenstr. 43, 10115, Berlin, Germany 2. Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown, South Africa
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Abstract: | Codfishes, the Gadiformes, are quite abundant in modern temperate and polar waters with a fossil record ranging back into
the Palaeogene. The oldest records are from the Danian and Selandian of Europe and South Australia. The bipolar distribution
early in their evolutionary history implies that their origin must have occurred quite early in the Palaeocene, or even in
the Late Cretaceous with subsequent rapid diversification. By the Eocene, gadiforms were highly abundant and widespread. With
the exception of gadiforms, no Eocene Antarctic teleostean group is present in the modern Antarctic fauna. Here, we review
the early evolution and diversification of gadiforms in general and of macrouroids in particular. We also describe the undoubtedly
oldest skeletal macrourid specimen with otoliths preserved in situ. It is the first definitive record of this group from the
Eocene of Antarctica filling a gap in its stratigraphic distribution. The fossil record of gadiforms in general and macrouroids
in particular indicates that the origin of both was in shallow shelf environments but with adaptations to deep-water settings
early in their evolution. While gadoids seemingly originated in the earliest Palaeogene and rapidly experienced a first major
radiation event in the eastern North Atlantic and/or North Sea Basin, macrouroids evolved in the Southern Ocean and migrated
northwards into the South Atlantic before the establishment of the circum-Antarctic current and subsequent isolation of the
Antarctic fish fauna. These two timely and regional separated adaptive radiation events in the Palaeogene gave rise to their
modern taxonomic diversity and global distribution. |
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Keywords: | Seymour Island La Meseta formation Gadiformes Adaptive radiation |
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