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On 4/9/2011 10:56 PM, Tim Williams wrote:
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.
Is host preference always hard-line?
The source of first resort, Wikipedia, mentions Ischnocera and Amblycera
in addition to Rhync. and Anoplura -- and states that Ischnocera and
Amblycer are chewing lice that parasitize both birds and mammals. This
implies (if correct) that closely related chewing lice can inhabit a
wide range of taxa.
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.
Seems very plausible as well. Even so, they (Ryhnc.) would be
interesting relative to what a non-avian dino-louse might look like.
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.
But as you say, may have disappeared in the interim and then re-evolved...