Analysis for origin and phylogeny of the Ammonoidea based on comparative morphologic and antmical data

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1. Comparative atomical studyTanabe and Sasaki described the anatomical features of a phosphatised siphuncular tissue in a Permian ammonoid from Nevada (USA). This is a first reliable report of ammonoid soft tissue structures (Tanabe et al., 2000). Furthermore, Tanabe and Landman (2002) described the anatomical characteristics of the jaws of Cretaceous Ammonoidea based on well-preserved material from Hokkaido and US Western Interior Province.2. Comparative embryological studyTanabe and co-workers described the ornamentation on the embryonic and early postembryonic shells of exceptionally well preserved Carboniferous goniaitites from Nevada and discussed its implications for embryology and systematics (Tanabe et al., 2001).3. Systematic studyShigeta and co-workers suggested that the Ceratitina have their origin to the Permian Prolecanitida on the basis of comparative SEM observations of early internal shell features of material from Russia and US mid-continent (Shigeta et al., 2001). Tanabe and co-workers have examined the intra- and interspecific variation of early internal shell features of some Cretaceous ammonoids and revealed that the states for qualitative characters appear to be stable within each species, indicating that they can be utilized for higher-level phylogenetic systematics (Tanabe et al. in press).