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Re: more about "feather" find
> yet evolved in mammals? what was the size smallest
> discernible detail on the impression that is used to
> conclude *Estemmenosuchus* had naked skin
We do not need discernible detail. Absence of integument traces in rocks
derived from fine-grained lacustrine sediment usually mean that the carcass was
nude at the point of embedding. This can be due to taphonomy (waterlogged
carcasses shed integument before disarticulating; see some Archie specimens) or
Basically: if you can discern different internal organs but no "keratin halo"
in a number of fossils, would that not suggest haitlessness?
We know that, as far as can be told, all birds were feathered. So, the limit of
embedding conditions for feather traces to remain would be the detection limit
for this type of integument. Ditto mammalian hair. Bristles, like here, would
leave traces even under worse conditions.