Conch size evolution of Silurian–Devonian tentaculitoids. (1st February 2019)

• Record Type: Journal Article
• Authors: Wei, Fan
• Is Part Of: Lethaia. Volume 52:Number 4(2019)
• Page Start: 454
• Page End: 463
• Publication Date: 2019-02-01
• Subjects: Tentaculitoids -- conch size -- macroevolution -- Devonian -- Silurian; Paleontology -- Periodicals; Geology, Stratigraphic -- Periodicals; 560
• DOI: 10.1111/let.12324
• Languages: English
• ISSNs: 0024-1164

Abstract

Abstract : Conch size changes of tentaculitoids are reported from the Silurian and Devonian strata. The combination of measurements of diameters and apical angles allows the reconstruction of tentaculitoid volumes. The conch wall thickness and number of septa can be investigated through observations of thin sections. Within the examined groups, the average conch volume (including the adult part and the whole conch) of tentaculitids increased from the Llandovery to the Pragian and then decreased until the Frasnian. A similar trend was observed in the Devonian dacryoconarids, which peaked for average conch volume in the Emsian. Sea‐level change was probably the main factor controlling the conch volume of tentaculitids and dacryoconarids. The continuous decrease in the average number of septa and the average volume of tentaculitid and dacryoconarid juvenile part from the Pragian (or the Emsian) to the Frasnian indicates a reduction of juvenile duration and earlier reproductive behaviour. The ratio of adult part to juvenile part volumes increased from the Emsian to the Frasnian in tentaculitids, suggesting that the angle between the conch and the water–sediment interface decreased. The conch volume and thickness of the juvenile part and the adult part in all tentaculitoid groups demonstrated similar trends. The average volume of the initial chamber and the adult part of dacryoconarids changed synchronously, with the peak value in the Emsian. Homoctenids, with the smallest conch and the thinnest wall, probably lived in deeper water than dacryoconarids.