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RE: marine reptile McMenu

Jonas Weselake-George wrote:

> Tim, does the molecular evidence suggest that lower taxonomic levels of
> Krill strated radiating at this time?

Here's what Jarman (2000) has to say...

"Early events in the speciation history of krill (Malacostraca: Euphausiacea), 
an abundant group of extant pelagic
crustaceans, were studied with slowly evolving nuclear DNA sequences (large 
subunit ribosomal DNA, 28s rDNA).
Krill have no fossil record, so very little is known about their palaeobiology. 
The timing of past speciation events
in krill was estimated by comparing change in their 28s rDNA to change in the 
28s rDNA of their close relatives
that do have a fossil record. Relationships between krill genera were also 
studied by phylogenetic analysis of partial
28s rDNA sequences. The analyses estimated the time that the last common 
ancestor of the krill family Euphausiidae
lived to be the lower Cretaceous about 130 million years ago (Mya). Two 
lineages of krill survived the end Cretaceous
extinctions 65 Mya and the modern genera of krill were established before the 
end of the Palaeogene 23 Mya."

> So, does anyone know of any study looking at overall changes in feeding
> apparatuses among marine predators throughout the Mesozoic? If there are any
> recognisable trends it would be quite interesting.

I don't know of any such study.   (That's not to say there hasn't been any; I'm 
not particularly au fait when it comes to the ecology of sea reptiles.)  

The elasmobranch portion of such a study would be especially tricky, given that 
(as cartilaginous fish) most specimens don't preserve the jaws, or any of the 
body, and are known only from teeth.



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