Showing papers by "Per Ahlberg published in 1998"

Faunal dynamics and microevolutionary investigations in the Upper Cambrian Olenus Zone at Andrarum, Skåne, Sweden

Abstract: The Upper Cambrian Homagnostus obesus/Olenus Biozone is well exposed in the old quarries at Andrarum, and is typically represented by unfossiliferous black shales with fossiliferous carbonate concretions. Near the north end of the “Great Quarry”, however, the shales themselves are replete with fossils, and in these a 1.8 m section has been logged to establish how trilobite populations fluctuated through time. Successive bedding planes were examined, at 1-cm intervals where possible, and for each surface trilobite exuviae, with rare complete specimens, were counted within a 5×5 cm quadrat. Olenus and Homagnostus are very common, but their abundance fluctuates dramatically; they co-occur in the upper part of the sequence but are otherwise almost mutually exclusive. This suggests that they had different ecological requirements. The rare Glyptagnostus and the bradoriid “ostracode” Cyclotron are confined to particular levels; the latter genus is found where no other fossils are present and may have be...