TAILIEUCHUNG - THE LATE JURASSICAMMONITE FAUNA OF NEW ZEALAND_2

Frontispiece: The shorelines of Kawhia Harbour, a large embayrnent on the north-westem coastline of the North Island of New Zealand, have been the prime sources of Late Jurassic ammonites since the first collections by Hochstener in 1859. The illustrations show representative views ofthe south side of the harbour. | PART 6. PALAEOECOLOGY FAUNAL SPECTRA The post-mortem drift of empty shells as observed in modern Nautilus . Kennedy Cobban 1976 Saunders Landman 1987 Ward 1987 1988 has at least theoretically the potential of distorting the relative proportions of ammonite taxa at specific stratigraphic horizons. However it is currently thought that in practice the effect of post-mortem drift is minimal and that therefore the faunal spectra derived from study of ammonite assemblages can provide a reasonably representative sample of ammonite populations and habitats through space and time Westermann 1990 1996b Cecca 1992 . A number of authors . Ziegler 1967 Kennedy . Cobban 1976 Westermann 1990 1996b Cecca 1992 Fernandez-Lopez Melendez 1996 have drawn attention to the ecological differences between the two major groups of ammonites the streamlined smooth-shelled Leiostraca of the early ammonite literature including notably the phylloceratids and lytoceratids and the strongly ornamented Trachyostraca. Modem opinion envisages the Leiostraca as having been pelagic types capable of living offshore and also of populating deep-shelf habitats 250300 m depth Westermann 1990 1996b see also Cecca et al 1990 Mouterde Elmi 1991 . However as noted by Kennedy Cobban 1976 p. 34 the local abundance of Lejostraca in clearly shallow-water deposits indicates that they were not entừely confined to deep-water situations. By contrast the Trachyostraca are generally considered to have inhabited neritic shallow-water environments ca. 30-100 m depth Westermann 1992 . Following Ziegler 1967 the Late Jurassic ammonite assemblages of New Zealand can be represented by means of spectra illustrating the proportions of Leiostraca and Trachyostraca Fig. 58 . Ziegler 1967 fig. 12 proposed that the dominance of Leiostraca in relation to Trachyosttaca at a specific stratigraphic level was indicative of deep water conditions ca. 300-400 mdepth . However as cautioned by Kennedy Cobban 1976 p. 34 off-shore rather .

• Nông nghiệp
• Murihiku Terrane
• Puaroan stage
• Heterian stage
• Nomenclature
• successions of New Zealand
• Measurement of specimens