- Startpagina tijdschrift
- volume 15 (2012)
- number 4 - Proceedings of the XIth International S...
- Intraspecific variation in the genus Stelidioseris (family Actinastraeidae, suborder Archeocaeniina, order Scleractinia; Jurassic-Cretaceous)
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Intraspecific variation in the genus Stelidioseris (family Actinastraeidae, suborder Archeocaeniina, order Scleractinia; Jurassic-Cretaceous)
Abstract
The genus Stelidioseris (= Actinastrea s.l.) is one of the most common genera in the Late Jurassic and Early Cretaceous and has a high number of species. Species separation is generally based on calicular dimensions, septal symmetry, and septal number. To obtain better insight into intraspecific variation and results for species separation, systematic measurements of the corals were taken and statistically analysed. As a preliminary study, ten type specimens were selected for analysis. In thin sections a large number of calices (up to 200) were measured, including their diameter, distance and the thickness of the wall and coenosteum. For all values, the arithmetic mean, standard deviation and the coefficient of variation were calculated. In Stelidioseris, the calicular diameter is the character with the lowest variation. The distance of the calicular centres, the thickness of the wall, and the number of calices per a given area show a much higher variation and are therefore less suitable for distinguishing samples within a population or species of different faunas. It was found that about 70% of all values of the lumen diameter fall in the first interval (range of the arithmetic mean ± standard deviation). Hence, the first interval is a good representation for most types of measured values in fossil corals. The results are compared to traditional methods by remeasuring published material. It is concluded that the application of systematic measuring should be extended to other species rich coral genera.
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Over : Hannes LÖSER
Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Blvd. Luis Donaldo Col. Los Arcos, Colosio S/N y Madrid, 83250 Hermosillo, Sonora, México; loeser@paleotax.de