Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 78, 1950
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Discussion

No Triassic Cidaridae are known from Australia. The oldest Cidarid from that region is “Cidaris” comptoni Glauert (1923), from the Cretaceous of Western Australia. This species, whatever its real generic position may be, is certainly unrelated to Dicyclocidaris, as the structure of the two forms is not at all comparable.

Of the three subfamilies of Cidaridae recognized by Mortensen (1928), two, namely the Stereocidarinae and Diplocidarinae, are unknown prior to the Jurassic. The remaining subfamily, the Streptocidarinae, ranges from Lower Carboniferous to the Lias in Europe and North America. The special feature of the Streptocidarinae is the imbrication of some of the plates. The material of Dicyclocidaris so far obtained is insufficiently complete to determine the presence or absence of this condition. What does appear to be highly significant, however, is the fact that the ambulacral margins of the interambulacral plates are denticulate. This is one of the diagnostic characters of

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Fig. 1—Dicyclocidaris denticulata, holotype specimen. OR, tubercle of the outer scrobicular ring; IR, tubercle of the inner scrobicular ring. Positive impression taken from original negative external mould. Lower border proximad.
Fig. 2—D. denticulata, cotype specimen, showing the inner scrobicular ring relatively further within the margin; abbreviations as for Fig. 1. Positive impression taken from original negative external mould.

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Miocidaris, a genus of Streptocidarinae typical of the Triassic of Europe and North America. There is also a further important parallel between Dicyclocidaris and Miocidaris. With only one exception, the Cidarids did not develop crenulated tubercles until the Jurassic. The exception is Miocidaris, which already had the crenulation developed in the Triassic. To this we must now add Dicyclocidaris. The evidence would thus point rather strongly in favour of grouping Dicyclocidaris with Miocidaris in the Streptocidarinae.

The two genera are mutually distinguishable by the fact that the scrobicular tubercles are monocyclic in Miocidaris, dicyclic in Dicyclocidaris. Dr Th. Mortensen, of the Copenhagen University Museum, who has examined photomicrographs of the interambulacral casts, makes the following interesting comment on the possible meaning of the inner ring of tubercles, so foreign to the usual conception of Cidarids (private communication, 28/3/48): “I cannot help thinking of Porocidaris, with a circle of pores inside the scrobicular ring. Just as these pores in Porocidaris are no true pores, I think the inner series of tubercles in your Cidarid are no true tubercles, viz. not spinebearing, as are the scrobicular tubercles, but only a peculiar structure within the areole. From my knowledge of the Cidarids I should think it impossible that there could have been a circle of spines inside the normal circle of scrobicular spines, these latter lying always directly as a cover of the muscle of the primary spine. I think you have here a new genus forming a close analogy to Porocidaris.”

If the foregoing discussion is a correct interpretation of the fossils, then it seems that the following conclusion may legitimately be made. As early as the Triassic the echinoid fauna of the New Zealand region contained an element which, although at the equivalent evolutionary stage to that occurring contemporaneously in Europe and North America, nevertheless showed a distinctive Zealanic character of at least generic value. Whether this Zealanic character. could more correctly be described as Australasian cannot be determined until something is known of the Triassic Cidaridae of Australia.