Intraspecific variation of phragmocone chamber volumes throughout ontogeny in the modern nautilidNautilusand the Jurassic ammoniteNormannites (original) (raw)
Related papers
The Evolution and Development of Cephalopod Chambers and Their Shape
PloS one, 2016
The Ammonoidea is a group of extinct cephalopods ideal to study evolution through deep time. The evolution of the planispiral shell and complexly folded septa in ammonoids has been thought to have increased the functional surface area of the chambers permitting enhanced metabolic functions such as: chamber emptying, rate of mineralization and increased growth rates throughout ontogeny. Using nano-computed tomography and synchrotron radiation based micro-computed tomography, we present the first study of ontogenetic changes in surface area to volume ratios in the phragmocone chambers of several phylogenetically distant ammonoids and extant cephalopods. Contrary to the initial hypothesis, ammonoids do not possess a persistently high relative chamber surface area. Instead, the functional surface area of the chambers is higher in earliest ontogeny when compared to Spirula spirula. The higher the functional surface area the quicker the potential emptying rate of the chamber; quicker cham...
Changing morphospace occupation of the Ammonoidea from the Devonian to the Jurassic
Measurements taken from over 5,900 ammonoid species were used to calculate three cardinal conch parameters, the conch width index (CWI), umbilical width index (UWI) and the whorl expansion rate (WER). These three parameters are very descriptive in terms of the conch morphology of an ammonoid: the CWI affects the hydrodynamic properties of the conch, the UWI the shape of the whorl cross section, and the WER the length of the body chamber and the degree of coiling of the conch. A principal components analysis was performed on the conch parameters of all of the ammonoids and a two-dimensional empirical morphospace was plotted based on the first two principal components. The PCA was broken down into the five major geological periods. The morphospace analysis reveals some interesting changes to the ammonoid conch morphs over time. The morphological range quickly fills out in the Devonian, the Carboniferous is heavily represented by globular conch morphs, and despite the Permian–Triassic ...
The authors propose new methods for the measurement of ammonoid conchs and their parameters. The new empirical measurements pertain to the surface area of the opening of the conch and the perimeter length of the conch opening. Estimated heights of the buccal mass and hyponome are also used based on their ratios with the aperture height obtained from Nautilus pompilius. The new measurements are: Conch Opening Surface Area (COSA), Conch Opening Perimeter Length (COPL), Buccal Mass Height (BMH), Buccal Mass Area (BMA), Hyponome Height (HypH), and Hyponome Area (HypA). The new parameters are: Conch Opening Perimeter Length Index (COPLI), Conch Opening Surface Area Index (COSAI), and Buccal Mass Area Index (BMAI). The aforementioned measurements and parameters have been obtained from over 60 ammonoid species from the Devonian through to the Jurassic representing a wide range of morphotypes. The authors suggest that these new methods will help to reveal more information about the palaeobi...