Attachment Scars Research Articles

Late Jurassic and early Cretaceous Ostreidae in Arctic seas of Siberia

Four arctic species of Liostrea related to the European L. delta (Smith) form a distinct evolving lineage in the Anabar-Khatanga basin during Late Jurassic Early Cretaceous time These are, in ascending order: Liostrea ex. gr. delta (Early Kimmeridgian), L. plastics (Trautschold) (Kimmeridgian), L. praeanabarensis n. sp. (described) (Volgian), and L. anabarensis Bodyl. (Early Cretaceous). Their morphology is reviewed. The lineage is characterized by small, oval to falcate shells with strong posterior curvature, convex left valves, and flat to slightly concave right valves. Widely, subevenly spaced concentric lamellae cover the surface. Some species develop small dorsoposterior auricles. Population analysis of two species demonstrates considerable variability in valve outline and development of the attachment scar and auricle.. Chronologically successive species show up to 10 percent morphologic overlap, demonstrating their genetic relationship. Principal evolutionary trends in progressively Younger species...

SIGNIFICANCE OF THE LATERAL FURROWS ON THE ROSTRUM FOR THE DEVELOPMENT OF BELEMNITE TAXONOMY

Belemnite rostra bear longitudinal furrows of various kinds, ranging considerably in strength. The present systematic classification of belemnites is based on characters other than the generally indistinct marginal or lateral furrows which, nevertheless, are important because they probably are attachment scars for the fins. One reason for their neglect by taxonomists in belemnite classification is that they are not useful for differentiation of genera, but tend to remain fairly constant within the subfamily. A study of several thousand specimens shows that Cylindroteuthis and Pachyteuthis, represented by 13 species, have a similar pattern of lateral grooves and belong in the same subfamily (Cylindroteuthinae). A different pattern common to Aulacoteuthis and Oxyteuthis shows that these genera were correctly united by Stolley in a different subfamily (Oxyteuthinae). Attention to details of the lateral grooves will also permit working out the phylogeny of major stocks, such as the descent of Belemnitellinae ...