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Dietmar Andres's (1976) dissertation on pterobranchs and primitive graptolites: Graptolithen aus ordovizischen Geschieben und die fruhe Stammesgeschichte der Graptolithen |
ENGLISH SUMMARY The results confirm KOZLOWSKI's statement of near phylogenetic relationship of the recent pterobranch Rhabdopleura and the graptolites: 1. Sutures of periderm of some primitive Ordovician graptolites and of the recent pterobranch Rhabdopleura are similar. The similarities extend to structures lacking obvious adaptative features. 2. Like Rhabdopleura the graptolites possessed one pair of arms. 3. The described primitve graptolites are probably little modified descendants of Cambrian graptolites. 4. The ancestors of the described primitive graptolites were sessile and creeping. 5. The described primitive graptolites display features implying a nearer phylogenetic relationship with Rhabdopleura than all more modern graptolites. Rhabdopleura is a "living fossil",; similar forms must have existed already in the Cambrian and should have been the ancestors of primitive graptolites. 6. Suggestions regarding cortex-formation: The observed ribbon-like cortex elements conform to movements of the cortex secreting cephalic shields of the graptolite individuals creeping outside their tubes. The ribbon like cortex elements are thinner and less regular arranged than the fuselli. The increase in thickness of the cortex is due to a similar process as has been observed in Cephalodiscus. To build the cortex no soft tissue existed on the outside of the fuselli. Hence cortex formation does not imply a principal difference between graptolites and pterobranchs. |
This dissertation was published independently as: Andres, D. 1977. Graptolithen aus ordovizischen Gechieben und die fruhe Stammesgeschicht der Graptolithen - Palaontologische Zeitschrift (51, 1/2, 52-93). . |
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