TY - JOUR
T1 - The Upper Cambrian trilobite Olenus at Andrarum, Sweden
T2 - A case of iterative evolution?
AU - Lauridsen, Bodil Wesenberg
AU - Nielsen, Arne Thorshøj
PY - 2005/9
Y1 - 2005/9
N2 - The morphological changes in four species-level lineages of the Late Cambrian trilobite Olenus from the Alum Shale at Andrarum, south-east Scania, Sweden, have been analysed with the aim of re-examining the classical study of iterative evolution by Kaufmann (1933a). New material comprising 647 pygidia was collected for a restudy of Olenus, and for comparison the skeletal development of 918 cephala and 568 pygidia from the associated Homagnostus obesus were included. The re-examination shows that (1) only pygidia of the O. transversus - O. truncatus - O. wahlenbergi lineage display a statistically significant directional change towards a narrower shape; (2) all other lineages, including the agnostids, show net morphological stasis; (3) hence iterative directional evolution cannot be confirmed. Based on morphological investigations it is tempting to conclude that the lineage O. transvenus - O. truncatus - O. wahlenbergi represents just one species displaying gradual morphological changes. Whether this is an evolutionary or an ecophenotypic phenomenon remains uncertain. The vertical distributions of olenids and agnostids are compared by using vanadium/(vanadium + nickel) ratios from the Olenus Zone of the nearby Gislövshammar-2 drill-core. It appears that incursions of olenids were linked to increases in bottom-water oxygen levels and that Homagnostus obesus was tolerant of lower dysoxia than olenids.
AB - The morphological changes in four species-level lineages of the Late Cambrian trilobite Olenus from the Alum Shale at Andrarum, south-east Scania, Sweden, have been analysed with the aim of re-examining the classical study of iterative evolution by Kaufmann (1933a). New material comprising 647 pygidia was collected for a restudy of Olenus, and for comparison the skeletal development of 918 cephala and 568 pygidia from the associated Homagnostus obesus were included. The re-examination shows that (1) only pygidia of the O. transversus - O. truncatus - O. wahlenbergi lineage display a statistically significant directional change towards a narrower shape; (2) all other lineages, including the agnostids, show net morphological stasis; (3) hence iterative directional evolution cannot be confirmed. Based on morphological investigations it is tempting to conclude that the lineage O. transvenus - O. truncatus - O. wahlenbergi represents just one species displaying gradual morphological changes. Whether this is an evolutionary or an ecophenotypic phenomenon remains uncertain. The vertical distributions of olenids and agnostids are compared by using vanadium/(vanadium + nickel) ratios from the Olenus Zone of the nearby Gislövshammar-2 drill-core. It appears that incursions of olenids were linked to increases in bottom-water oxygen levels and that Homagnostus obesus was tolerant of lower dysoxia than olenids.
KW - Agnostids
KW - Evolution
KW - Olenids
KW - Palaeoecology
KW - Trilobites
KW - Upper Cambrian
UR - http://www.scopus.com/inward/record.url?scp=28244444831&partnerID=8YFLogxK
U2 - 10.1111/j.1475-4983.2005.00499.x
DO - 10.1111/j.1475-4983.2005.00499.x
M3 - Article
AN - SCOPUS:28244444831
SN - 0031-0239
VL - 48
SP - 1041
EP - 1056
JO - Palaeontology
JF - Palaeontology
IS - 5
ER -