Ontogenetic Trajectories

During ontogeny, a remarkable migration of the specimens across the morphospace can be observed, reflecting the transformation of the conch morphology from widely umbilicate to more involute, etc. The position of the centroids for distinct

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Fig. 3.13 Principal components analysis of manticoceratid ammonoids, shown are PC1 (x axis) and PC2 (y axis). A - Morphospace of the complete data set; the specimens of Manticoceras from Coumiac are highlighted (circles). B - The migration of ontogenetic stages across the morphospace; light grey for juvenile specimens, dark grey for adult specimens. C - The migration of the centroid of the specimens from Coumiac across the morphospace. D-I - Morphospace occupation of different growth stages (relevant growth stages are shown as circles; other growth stages are shown as dots) of Manticoceras from Coumiac: D - specimens >40mm dm, E - specimens from 20-40mm dm, F - specimens from 10-20mm dm, G - specimens from 6-10mm dm, H - specimens from 3-6mm dm, I -specimens < 3mm dm.

growth intervals display a slightly discontinuous morphological change with a more rapid character unfolding in juveniles.

For a closer view, the samples from Coumiac, Oberscheld, and Büdesheim were separately analyzed (Fig. 3.14). This shows that the Coumiac sample displays a rapid early ontogenetic modification of conch morphology, but a stagnation in stages larger than 20 mm conch diameter. The centroids of the samples 20-40 mm and > 40 mm differ only slightly. A similar picture can be seen in the material from Oberscheld.

♦ specimen UMDK 275 O specimen UMDK 219 O specimen UMDK 218 • specimen UMDK 276
♦ specimen MB.C.3791 O specimen MB.C.3790 O specimen MB.C.3789 • specimen MB.C.3792

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Fig. 3.14 Principal components analysis of manticoceratid ammonoids and the migration of ontogenetic stages across the morphospace, shown are PC1 (x axis) and PC2 (y axis). Young specimens are on the right and older specimens on the left. A - Manticoceras from Coumiac; B - manticoceratids from the eastern Rhenish Mountains; C - manticoceratids from Büdesheim; D - manticoceratids from the Timan, South Urals, and Altay Mountains.

The Büdesheim material differs markedly from the other two. The earliest juvenile morphospace of the Coumiac and Oberscheld material is not occupied by the specimens from Büdesheim, and the later ontogeny is strongly accelerated. Specimens of the 6-10 mm size range are morphologically similar to those from Coumiac and Oberscheld, but the specimens from Büdesheim (Fig. 3.14C) reach a conch geometry at 10-20 mm conch diameter that is only characteristic for specimens larger than 40 mm in the other two samples (Fig. 3.14A, B, D).

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