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Re: living fossils



>I don't feel Ornithorhynchus qualifies as a living fossil: there are fossil
>platypuses, but they're not particularly ancient.  I am fond of Peripatus
>and its table manners, but I don't think it counts either (fossil
>onychophorans are not so very similar to modern ones).
>
>As reards genuine living fossils, I'm quite fond of Limulus, ginkoes and
>crinoids.
>                                                                Bill Adlam

Although Orhithorhynchus has no fossil record, its immediate ancestor
(Obduradon) has Miocene records in northern and central Australia as well
as Paleocene records in Patagonia. Doesn't 60 million years count for a
living fossil? Sounds like age envy.

Obduradon is larger than Orhithorhynchus, but still a bona fide, card
carrying platypus. The more obscure Steropodon from Lightning Ridge is 110
million years old, a monotreme on the platypus side of things, but I am not
sure that we can  confidently call it platypus.

If you cant call platypuses living fossils, then monotremes must surely
qualify as a group and, because some people have been nominating crocodiles
as living fossils, I can't see why a less inclusive group such as
monotremes can't be nominated for the same position.

As for my vote for living fossil? I thought the term living fossil was
extinct! If not, it ought to be. So my vote for living fossil is the
anthrocentric, nintenth century pseuo-intelectual concept; the living
fossil!

However, there is one animal I am aware of that unambiguously qualifies for
the title 'living fossil'. Thalassina is a type of crustacean that lives in
mudflats in northern Australia. Being a crustacean, it grows by shedding or
molting, and it buries these cast-off shells at the bottom of its hole. In
some areas the CaCO3 content of the water is so high that the cast-off
shells fossilise very quickly, possibly before the animal that produced
them has died. Thus you have a genuine living fossil.

Cheers, Paul