Figure 6. Molecular time-scale for decapodiform cephalopods indicating a in A redescription of the fossil coleoid cephalopod genus Palaeololigo Naef, 1921 (Decapodiformes: Palaeololiginidae) and its relationship to Recent squids

Figure 6. Molecular time-scale for decapodiform cephalopods indicating a potential position for the Palaeololiginidae and Chtenopteryx on two alternative decapodiform phylogenies (modified from Strugnell et al. [2006]). The topologies result from two alternative Bayesian analyses using: (A) all three codon positions of three nuclear genes (octopine dehydrogenase, rhodopsin, pax-6) partitioned by codon; and (B) only first and second codon positions of the same three nuclear genes. The divergence dates of Palaeololiginidae from Bathyteuthis and Chtenopteryx and also Chtenopteryx from Bathyteuthis are hypothetical. A simplified possible scenario of morphological character loss is depicted. Notes: Ɨ indicates the presence of suckers on the buccal lappets; • indicates the presence of accessory nidamental glands (which is present in Chtenopteryx, but apparently lost in Bathyteuthis); indicates the presence of fused axons in the giant nerve fibre system; ▲ indicates the "juvenile" characters for Oegopsida detailed by Naef (1923), namely the form of gladius with a long narrow rachis, subterminal position of the fins, and also quadriserial suckers on the arms, which Naef (1923) believed to the ancestral form for all Oegopsida; "open" shapes (O, O, Δ, Z)