Macroevolutionary trends in Palaeozoic actinopterygians

Henderson, Struan A. C. (2024). Macroevolutionary trends in Palaeozoic actinopterygians. University of Birmingham. Ph.D.

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Abstract

The Actinopterygii (ray-finned fishes) are a highly successful group of bony fish that dominate modern-day aquatic vertebrate faunas. Though ubiquitous today, actinopterygians were a minor component of fish faunas during the Devonian ‘Age of Fishes’, when they were overshadowed by agnathans, placoderms and sarcopterygians. The Devonian to Carboniferous transition saw a major shift, with extinctions of placoderms and sarcopterygians paving the way for the diversification of actinopterygians and their establishment as the primary group of fishes by the end of the Permian. The mechanisms of this rise and lasting dominance through the Palaeozoic are poorly understood, however, a suite of compounding factors obscure early actinopterygian spatiotemporal diversity trends, character evolution and relationships. This thesis presents a comprehensive database of Palaeozoic actinopterygian occurrences, identifying major sampling and taxonomic biases influencing face-value trends in diversity. Trends generally track sampling, and there is overwhelming geographic bias towards Europe and North America. Biases are so prolific that sampling standardisation methods fail to recover biologically meaningful palaeodiversity trends beyond a genuine increase following the end-Devonian mass extinction. A small number of poorly defined, widespread genera mask significant taxonomic and morphological diversity. Description of two Carboniferous actinopterygians using CT scanning reveals hidden morphologies and highlights the relative oversight of Carboniferous actinopterygians: a specimen known for over 100 years from the most heavily sampled region of the Palaeozoic record is recognised as a new taxon. This oversight also contributes to phylogenetic uncertainty, as absence of distinct groups in phylogenetic analyses potentially obfuscates character evolution in the stem-actinopterygians seeding the crown and early, stem-members of extant clades. Despite the seemingly large scale of the problems facing understanding of early actinopterygian evolution, the means of addressing them is clear: taxonomic revision of key genera; expansion of phylogenetic datasets; increased sampling of underrepresented regions; and focus on localised diversity patterns.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):