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Re: disease-carrying varmints biting dinos

David Marjanovic <david.marjanovic@gmx.at> wrote:

> Yay insects biting ammonites.

Yay indeed.  This "insect-borne-diseases-killed-off-the-dinosaurs" is
just "mammals-ate-all-the-dinosaur-eggs" in a new guise.  Simplistic
explanations for a complex extinction event.

> The pentastomids, BTW, are limited to the respiratory tracts of tetrapods. 
> Neontologists have come to consider them internalized fish lice. 
> Paleontologists instead
> point to Early Cambrian fossils that look like pentastomids but had no hosts 
> as far as anyone can see... I wouldn't be surprised if they turned out to be a
> completely different sort of arthropod some day.

Yes as adults, extant pentastomids infect the respiratory tract of
tetrapods, the "main" host.  However, pentastomid larvae can infect
fish, the intermediate host.  The putative pentastomids from the
Cambrian resemble the larvae of extant pentastomids.  It goes without
saying that these Cambrian pentastomid-like creatures (irrespective of
whether they are pentastomids or not) lacked the complex life-cycles
of extant pentastomids. If these Cambrian critters were parasites,
they may have been endoparasites on contemporary basal craniates or
vertebrates.  From a purely paleoecological perspective, it is likely
that as long as there are potential hosts, there will be parasites of
some sort or another.

The precise phylogenetic position of pentastomids is still a hot topic
AFAIK.  According to one molecular-based phylogeny, the clade
comprising pentastomids and fish lice (Branchiura) is basal to the
Hexapoda-Crustacea clade.  Others nest them inside the Crustacea.