Temporal patterns in disparity and diversity of the Jurassic ammonoids of southern Germany

S. Koenemann,M. S. Simon,D. Korn

doi:10.5194/fr-14-77-2011

Abstract

A morphometric analysis of the characteristic whorl cross-sections of 1,200 Jurassic ammonoid species from southern Germany enabled us to characterise their morphospace. The successive Jurassic ammonoid faunas of southern Germany show characteristic patterns in morphospace occupation. While Early and Middle Jurassic ammonoids occupy limited areas of the morphospace range, the Late Jurassic ammonoids cover the entire spectrum. The ammonoids are characterised by an overall increase of both taxonomic diversity and morphological disparity in the course of the Jurassic. Strong fluctuations occur until the middle Late Jurassic, followed by a diversity decrease in the early Kimmeridgian and a disparity reduction in the early Tithonian. While diversity and disparity show similar progression during most of the Early Jurassic, they diverge subsequently and show only poor correlation until the end of the Jurassic. Particularly in the Middle Jurassic diversity and sea level changes correlate strongly. Neither temporal patterns in diversity nor disparity support the hypothesis of a mass extinction event in the early Toarcian. Significant changes in diversity and disparity in the early Callovian support a putative migration event of Boreal ammonoids into the Tethyan realm. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201000016" target="_blank">10.1002/mmng.201000016</a>

Highlights

Morphology represents an important tool in descriptive and analytical biology and in palaeontology
Whereas early studies concentrated on qualitative description of morphological characters, there was a transition in the early 20th century leading to analytical approaches with quantitative elements (Thompson 1917; see Bookstein 1998)
In our study we focus upon fluctuations of Jurassic ammonoid morphospace occupation within a geographically defined area (Fig. 1) and the possible causes of these changes

Summary

Introduction

Morphology represents an important tool in descriptive and analytical biology and in palaeontology. Whereas early studies concentrated on qualitative description of morphological characters, there was a transition in the early 20th century leading to analytical approaches with quantitative elements (Thompson 1917; see Bookstein 1998). This new exploratory focus called morphometrics contained measurement data (metric values, angles etc.) and was introduced ‘. Due to the lack of information about morphological characters of a given shape as a whole, a second transition was necessary that focused on shape and occurred in the late 20th century The establishment of this ‘geometric morphometrics’, allowed the description of the entire shape of an organism or any part of its skeleton or shell and its geometrical features. With the aid of these methods it is possible to outline a morphospace containing a broad spectrum of morphological information representing the entire shape

Methods

Findings

Discussion

Conclusion