Revision and description of the actinopterygian fishes of Devonian Eastern Gondwana
This thesis examines the total diversity of fossil actinopterygian or ray-finned fishes of Devonian Gondwana. The bulk of the material comprises newly prepared specimens from the famous Late Devonian (Frasnian) Gogo Formation of Western Australia, much of which was collected in the 2005 field season...
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| Format: | Thesis |
| Language: | English |
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The Australian National University
2010
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| Online Access: | https://dx.doi.org/10.25911/5d611c4342fe3 https://openresearch-repository.anu.edu.au/handle/1885/150190 |
| Summary: | This thesis examines the total diversity of fossil actinopterygian or ray-finned fishes of Devonian Gondwana. The bulk of the material comprises newly prepared specimens from the famous Late Devonian (Frasnian) Gogo Formation of Western Australia, much of which was collected in the 2005 field season. Also examined are specimens from the Middle Devonian deposits of the Aztec Siltstone, Antarctica; the Bunga Beds of New South Wales and the Mt Howitt fossil sites of Victoria. With the benefit of this new material, I describe new several new genera and species of Devonian actinopterygians and clarify the descriptions of previously described forms. Although still a relatively sparse ichthyofaunal component, the Devonian diversity of the Gondwanan ray-fins was much greater than hithert o recognised, with at least five species present in the Gogo Formation. With an improved understanding of early ray-finned anatomy, characters previously considered primitive or of special diagnostic value are re-evaluated. Newly prepared material from the Aztec Siltstone of Antarctica and the Bunga Beds of New South Wales represent forms similar to Howqualepis rostridens from the Givetian of Victoria. The Antarctic form is named Donnrosenia schaefferi while the Bunga Beds fossil is questionably assigned as a congener of Howqualepis. The similarity of freshwater fossil actinopterygians throughout southeastern Australia and South Victoria Land, Antarctica supports previously described macrovertebrate evidence for a regionally endemic ichthyofauna in the Middle Devonian. Additionally, the pectoral fin of H. rostridens is redescribed and is broader in shape and less extensively unsegmented than previously recognised. Of the five Gogo taxa, the genus Mimia Gardiner and Bartram (1977) is renamed Mimipiscis nom. nov. due to preoccupation. Newly available material of the type species, Mimipiscis toombsi, reveals ontogenetic variability in ornamentation and new data on the parasphenoid and shape of the caudal fin. A second form, Mimipiscis bartrami sp. nov., differs from the type species in details of the body shape, squamation, snout, suboperculum and parasphenoid. Two new genera, Gogosardina and Pickeringia gen. nov. are described. Gogosardina is a highly elongate form with a unique arrangement of postrostrals which form the anterior margin of the pineal opening. Pickeringia gen. nov. possesses a highly distinctive spinose ornamentation over the skull, scales and lepidotrichia and extremely large vestibular fontanelles. Specimens of Gogosardina and M. bartrami sp. nov. are known to possess conodont elements within the body cavity suggesting diet and hunting strategies. A phylogenetic analysis of Devonian ray-fins suggests a limited degree of regional endemism in Eastern Gondwana with unique families present on the Gogo reefs and freshwater habitats in southeastern Australia and Southern Victoria Land, Antarctica. The close similarity of the actinopterygian faunas of Antarctica, New South Wales and Victoria adds to an already large body of evidence suggesting a regionally endemic Gondwanan ichthyofauna in the Middle Devonian. |
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