Palaeontology of decabrachiate Cephalopoda - an ultrastructural approach to their morphogeny and phylogeny
Final Report Abstract
Micro- and ultrastructural studies on fossil and recent coleoids revealed many interesting aspects on their shell morphology and therefore shed new light on the morphogeny and phylogeny of the Coleoidea. The non-presence of tabular nacre in the dorsal conotheca of belemnitids as well as the record of suckers in a belemnoid were surprising observations by which the postulated monophyly of the "Neocoleoidea" were strongly questioned. Apart from this, the mosaic of belemnitid and spirulid (and sepiid) characters observed in diplobelids, "Naefia" matsumotoi and Groenlandibelus rosenkrantzi suggests that decabrachians originated directly from Mesozoic belemnoids (instead of Palaeozoic bactritoids). This idea requires a convergent evolution of the spirulid caecum and, indeed, significant differences between the ammonoid and the spirulid type of protoconch doubts the postulated homology between the bactritoid and the spirulid caecum. Molecular divergence estimates confirmed the origin from mid to late Mesozoic belemnoids rather than from Carboniferous bactritoids. True spirulids are characterized by their 2-layered conotheca, their overall protoconch morphology, as well as the presence of rectangular dorsal soft tissue attachment scars. Sepiids are similar to spirulids in many aspects, but the observation of stripe-like dorsal attachment scars typical for belemnitids supports the "belemnoid root-stock theory" and opens the possibility that the "Decabrachia" might represent a paraphyletic taxon. The combined existence of a rudimentary septation in the gladius conus, a rostrum-like structure, and a similar life style indicates a close phylogenetical relationship between belemnoids and teuthids, which might in turn support the paraphyletic nature of the "Decabrachia". The overall conclusions of the present project implicates that first unambiguous members of the Decabrachia appeared during the late Cretaceous when belemnites s.s. disappeared in many parts of the world.
Publications
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(2010). A new diplobelid belemnoid (Coleoidea: Cephalopoda) from the Upper Cretaceous of Hokkaido (Japan). Paleontological Research, 14: 1-10
Fuchs, D. and Niko, S.
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(2010). New evidence of functional suckers in belemnoid coleoids (Cephalopoda) weakens support for the "Neocoleoidea" concept. Journal of Molluscan Studies, 76 (4): 404-406
Fuchs, D., Boletzky, S. v. and Tischlinger, H.
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(2011). Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules. Bioessays
Kröger, B., Vinther J. and Fuchs, D.
