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On Sat, Apr 9, 2011 at 10:42 PM, Don Ohmes <email@example.com> wrote:
> Don't know, but it sounds like the Rhyncophthirina might spend a lot of time
> reminiscing about the good old days.
> Is the allometry of skin thickness in extant animals known well enough to
> speculate about details of the mouth parts required to parasitize a
I also wondered if Rhyncophthirina parasitized sauropods (and/or other
kinds of thick-skinned, non-avian dinosaur) during the Cretaceous.
But as far as we know, all non-avian dinosaurs went extinct at (or
close to) the K-Pg boundary. The Rhyncophthirina lice needed hosts to
carry them across into the Cenozoic. What were the Rhyncophthirina
parasitizing in the early Cenozoic, before elephants and warthogs were
invented? Whatever it was, those hosts would needed to have survived
the K-Pg extinction.
The alternative hypothesis is that, like their Anoplura cousins (=
sucking lice), the Rhyncophthirina were parasitizing small, furry
mammals in the Cretaceous, and these were the hosts that carried the
Rhyncophthirina lice across the K-Pg boundary. In other words, the
adaptations that Rhyncophthirina have for parasitizing large,
thick-skinned mammals with little or no hair, are secondary. The
problem with this hypothesis is that the blood-sucking mouthparts of
the Anoplura are thought to have evolved from something similar to the
blood-feeding Rhyncophthirina-like arrangement (mandibles at the end
of a long proboscis-like snout). So presumably Rhyncophthirina-style
mouthparts go back to the Cretaceous too, and pre-date the Anoplura.
> Certainly cowhide is thicker than rabbit-skin, but as a function of volume,
> I intuitively expect cowhide to be relatively thinner...
Probably not from the viewpoint of the louse. Unless the louse was
*much* bigger too. Modern Rhyncophthirina lice (_Haematomyzus_) are
actually very small.