Bowdler-Hicks, Alison
(1996)
The evolution, taxonomy and stratigraphical significance of selected Caradoc trinucleid trilobite lineages.
MSc(R) thesis, University of Glasgow.
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Abstract
A new more workable classification of Caradoc cryptolithine trinucleid trilobites is proposed. The classification uses the position of the E2 arc pits in relation to the distinct radial alignment of pits within arcs In to Ei. Most Harnagian species hitherto classified into three genera and five species, namely Salterolithus caractaci caractaci, Salterolithus caractaci paucus, Salterolithus praecursor, Smeathenia smeathenensis and Broeggerolithus harnagensis, show a pronounced lack of E2 pit alignment with inner arcs. These are now grouped in two species of one genus, Salterolithus caractaci and Salterolithus harnagensis. The early species show environment sensitive morphotypes in large populations of great diversity. All younger species show distinct radial alignment of E2 pits with the inner arcs. Whilst all these younger species remain within the genus Broeggerolithus some have been reclassified to sub species or synonymised as a more population and not typological approach to classification has been adopted. The species Broeggerolithus broeggeri, B. ulrichi, B. soudleyensis, and B. globiceps are now subspecies of Broeggerolithus broeggeri. Broeggerolithus longiceps, B. melmerbiensis, B. aff. discors are synonymised with B. nicholsoni. The type species for Salterolithus and Broeggerolithus remain unchanged.
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