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RE: Giant plankton-eating fish of the Mesozoic
GUY LEAHY <firstname.lastname@example.org> 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.