A systematic revision of the Harpetidae (Trilobita) and a critique of cladistic biogeographic methodology
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2002
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University of Melbourne
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School of Botany
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PhD thesis
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Thesis (PhD)-- University of Melbourne, School of Botany, 2002
Includes bibliographical references (leaves 195-224)
Thesis (PhD)-- University of Melbourne, School of Botany, 2002
Includes bibliographical references (leaves 195-224)
Abstract
The ten genera of Harpetidae (Bohemoharpes, Brachyhipposiderus, Dolichoharpes, Dubhglasina, Eoharpes, Harpes, Kielania, Lioharpes, Scotoharpes and gen. nov.) are reviewed. The monophyly of the Harpetidae is corroborated, and all ingroup genera can be defended as monophyletic groups except for the non-monophyletic Scotoharpes group. Emended diagnoses are provided for all the genera within the family. The three subfamilies Dolichoharpinae, Eoharpetinae and Harpetinae are placed in synonymy within the Harpetidae. The genera Australoharpes and Sinoharpes are placed in synonymy with Dubhglasina. Thorslundops and Wegelinia are placed in synonymy with Hibbertia, and the subgenus Lioharpes (Fritchaspis) placed in synonymy with Lioharpes. Four new species of Kielania (Kielania spp. 1-4) and a new genus (gen. nov.) and two new species (gen. nov. spp. 1-2) are described for the first time.
Using these eight harpetid genera (Bohemoharpes, Dubhglasina, Eoharpes, Harpes, Hibbertia, Kielania, Lioharpes and Scotoharpes), the cladistic methods of standard parsimony and three-item analysis are compared. The methodological integrity of these methods is thoroughly examined and their inner workings exposed. Many cladists today use these programs without investigating how the black box of algorithms functions or the implications of the process they apply to the input data. Three-item analysis emerges as the more rigorous method, satisfying the discovery paradigm.
Several cladograms based on three-item analysis that specify monophyletic taxa from the Siluro- Ordovician are transformed to taxon-area cladograms and combined to uncover geographic congruence. Cladistic biogeography uncovers geographic congruence using cladistic-based methodologies. The agreement of several taxon-area cladograms rarely yields a fully resolved result. Areas may overlap, taxa may not be evenly distributed and thus, ambiguity may be prevalent in the data. Ambiguity is incongruence and may be resolved by reducing paralogy and resolving potential information. During the last 20 years, several new approaches in cladistic biogeography (i.e. Brooks Parsimony Analysis, Assumption 0) have interpreted ambiguity as congruence. These methods are problematic because they are generational. Methods constructed under the generation paradigm are qualifiers for flawed concepts and immunize such concepts from falsifying evidence. A critique of modified Brooks Parsimony Analysis (BPA) reveals that taking an a priori evolutionary stance in biogeography leads to flaws in implementation.
Area cladistics adopts paralogy-free sub-tree analysis, using Assumption 2, to discover the relative positions of continents through time. Geographic congruence is best explained by allopatry (geographic isolation). Vicariance, dispersal and combinations of both are recognized causes for allopatric speciation. Area cladistics highlights the concept that all these events occur in response to geological changes (e.g. continental drift) either directly, by geographic boundaries, or indirectly, at the level of ocean currents. Examples from the literature and from the harpetid genus Hibbertia all agree with the geological process. The examples include Ordovician-Silurian and Lower Devonian trilobites to yield a general areagram, which is a representational branching diagram that depicts the relationships of areas.
Finding one common biogeographic pattern from several unrelated groups is a qualitative approach to interpret the positions of continental margins through time. Area cladistics is not a substitute for palaeomaps that are derived from palaeomagnetic data, but general areagrams add to the body of knowledge and yield more precise interpretations of the Earth's past.
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Trilobites, Cladistic analysis, Biogeography -- Methodology.