>I take it that by the "oldest," you mean the longest-lived.
The genus goes back at least to the late Cretaceous. We have 2
species in the NZ cretaceous. Another seems to g right through from
the early Paleocene to early Miocene or later; that's a LONG-lived
species; it's exceedingly common in some late Oligocene localities.
None of these reach much more than 14cm in length.
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Regards
Andrew