evolution

Evolution of cephalopods

Modern cephalopods (squids, cuttlefishes and octopuses) are thought to have evolved during the Devonic (400 to 345 million years), arising from the Bactritids (Ward, 1983 Fig. 1), a simple and uniform group in structure (Teichert, 1988). The reduction and eventual complete loss of the chambered shell was an evolutionary answer to the increasing need of mobility and deeper swimming to avoid vertebrate predators and competitors (Packard, 1972). However, the current forms arose among the periods Upper Triasic and Lower Jurassic (195 million years) (Ward, 1983 Fig. 1). Octopods appeared from a branch of an ancestral stock at the same time that the Teuthoidea and Sepioidea (Ward, 1983 Fig. 1). The monophyly of the octopods has been confirmed by molecular and morphological methods (Young et al., 1998) and the cirrate octopods probably comprise the oldest evolutionary lineage of octopods (Voss, 1988). The sister group of octopods is Vampyromorpha (Young & Vecchione, 1996; Carlini & Graves, 1999). The Naef’ s Protoctopus is considered to be near base in the octopods, which gave origin to two evolutionary lines, one of the Incirrina and another of the Cirrina (Voss, 1988). The Naef’ s Protopolypus, has been proposed as ancestor to the Incirrina, had biserial suckers, derived from uniserial Protoctopus (Voss, 1988). Proteroctopus ribeti (Fischer & Riou, 1982) of the Middle Jurassic (160 MY) of The-Voulte-south-Rhone (France) and Paleoctopus newboldi (Woodward, 1896) of the Upper Cretaceous (80 MY) of Sahel Alma (Lebanon) are the well-known fossils of octopods (Voss, 1988a). Engeser (1988) suggested, on the basis of cirri absence in the fossil that can belong to the basal group of the incirrate octopods, and that the separation of the incirrate and cirrate happened in the late cretaceous. The ink sack has been defined as an apomorphy of the incirrate octopods (Voight, 1997), which was already present in P. newboldi, bringing near more east fossil to the incirrate. However, loss of an ink sac is almost an adaptation to depth and the use of this character has produced an artificial classification with no evolutionar significance (Allcock & Piertney, 2002).

Fig. 1 Evolution of cephalopods (Ward 1983).

Nautilus and Achantoteuthis

Photos by L-F Opazo and CM Ibáñez

PHYLOGENY OF CEPHALOPODA

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References

  1. Allcock, A.L. & Piertney, S.B. 2002. Evolutionary relationships of southern ocean Octopodidae (Cephalopoda: Octopoda) and a new diagnosis of Pareledone. Marine Biology, 140, 129-135.
  2. Carlini, D.B. & Graves, J.E. 1999. Phylogenetic analysis of cytochrome C oxidase I sequences to determine higher-level relationships within coleoid cephalopods. Bulletin of Marine Science, 64, 57-76.
  3. Engeser, T.S. 1988. Fossil “Octopods”- A critical review. The Mollusca 12, Paleontology and Neontology of Cephalopods (ed. by M.R. Clarke & E.R. Trueman), pp. 81-87. Academic Press, London.
  4. Packard, A. 1972. Cephalopods and fish: the limits of convergence. Biologial Review, 47 (2), 241-307.
  5. Teichert, C. 1988. Main features of Cephalopod evolution. The Mollusca 12, Paleontology and Neontology of Cephalopods (ed. by M.R. Clarke & E.R. Trueman), pp. 11-79. Academic Press, London.
  6. Voight, J.R. 1997. Cladistic analysis of the octopods based on anatomical characters. Journal of Molluscan Studies, 63, 311-325.
  7. Voss, G.L. 1988a. Evolution and phylogenetics relationship of deep-sea octopods (Cirrata and Incirrata), The Mollusca 12, Paleontology and Neontology of Cephalopods (ed. by M.R. Clarke & E.R. Trueman), pp. 253-276. Academic Press, London.
  8. Ward, P.D. 1983. The extinction of the Ammonites. Scientific American, 249 (4), 114-124.
  9. Young, R.E. & Vecchione M. 1996. Analysis of morphology to determine primary sister-taxon relationships within coleoid cephalopods. American Malacological Bulletin, 12 (1-2), 91-112.
  10. Young, R.E., Vecchione, M. & Donovan, D.T. 1998. The evolution of coleoid cephalopods and their present biodiversity and ecology. South African Journal of Marine Science, 20, 393-420.