A rare occurrence of serrate conodont elements of Panderodus Ethington in the Middle Ordovician ‘Täljsten’ interval at Kinnekulle, south Sweden

Abstract

The stratigraphically rare occurrence of serrate Panderodus in latest Ordovician and Silurian conodont faunas has commonly led to suggestions that these are ecophenotypic varieties of non-serrate species of the genus. Following the discovery of a serrate Panderodus morphotype in the Middle Ordovician ‘Täljsten’ interval at Kinnekulle, Sweden, it is suggested that such morphotypes should be treated as separate taxa. The stratigraphical occurrence of Panderodus serratus haellekisensis n. ssp. represents the earliest known species of this genus in Baltoscandia, and suggests that the serrate morphology may actually be a primitive feature. The elements encountered are minute and the characteristic panderodontoid groove is underdeveloped; a combination of characters that may be interpreted as a juvenile growth stage. Conversely, this morphology could be viewed as a primitive feature, considering the fact that serrate Panderodus specimens tend to also be small in the Silurian. As these elements are restricted to one single bed in the ‘Täljsten’ interval – a unit of grey limestone formed during a period of environmentally ‘anomalous’ conditions – the occurrence of P. s. haellekisensis may be interpreted as a temporary but unsuccessful immigration attempt. Its centre of origin, however, remains ambiguous.