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RE: Giant plankton-eating fish of the Mesozoic

GUY LEAHY <xrciseguy@q.com> wrote:

> Another potential impact on marine Cretaceous ecosystems is
> these giant plankivorous fish would have represented an important
> food resource for mosasaurs, and the extinction of
> _Bonnerichthys_ and relatives at the K/Pg boundary could
> have contributed to mosasaur extinction, at least to the
> more hypercarnivorous taxa...

There were also some fairly large cartilaginous fish about at the time (Late 
Cretaceous), including possible filter-feeders.  Shark teeth of Late Cretaceous 
age from the Western Interior Sea were assigned by Kenshu Shimada (2007; JVP 
27:512â516) to the Megachasmidae, a family of large filter-feeding sharks that 
survive to this day (_Megachasma pelagios_, or 'megamouth' shark).  Shimada 
(2007) suggested that his LK species (_Megachasma comanchensis_) might have 
been likewise planktivorous, based on striking similarities in the dentition 
between the Cretaceous and extant species.  Interestingly, the 
_Rhinconichthys_/_Bonnerichthys_ Science paper downplays the importance of 
these putative megachasmid teeth - even though K. Shimada is one of the 
co-authors of the Science paper!

There is also a possible planktivorous shark (though perhaps not neoselachian) 
from the Late Triassic of Europe, known from teeth and gill-rakers 
(_Pseudocetorhinus pickfordi_, a possible synechodontiform).  Planktivorous 
pachycormids might have supplanted these forms in the early Jurassic.  
Nevertheless, there is enough fossil evidence to suggest that pachycormids 
might not have had a monopoly on the large-planktivore guild in the Mesozoic.