Giant plankton-eating fish of the Mesozoic

[Tim Williams <tijawi@yahoo.com>]

Not directly dinosaur-related, but interesting nonetheless because of the 
impact on marine Mesozoic ecosystems.  A new paper in Science provides a reason 
for why there are no unambiguous plankton-eating reptiles in the Mesozoic: they 
were muscled out by big fishies.  The following paper describes two new genera 
of planktivorous fishes (_Rhinconichthys_ and _Bonnerichthys_), part of a 
radiation of planktivorous stem teleosts (Pachycormidae) that continued to the 
end of the Cretaceous.


Although certain plesiosaurs have been described as "filter-feeders" (e.g., 
_Aristonectes_, _Kaiwhekea_), with the small teeth and wide jaws used to strain 
out small prey, it's my understanding that this is not true "filter-feeding" (= 
suspension feeding).  Instead, these plesiosaurs might have had a feeding 
strategy more like the crab-eater seal, which has sieve-like teeth for trapping 
krill.


Friedman, M., Shimada, K., Martin, L.D., Everhart, M.J., Liston, J., Maltese, 
A., and Triebold, M. 100-Million-Year Dynasty of Giant Planktivorous Bony 
Fishes in the Mesozoic Seas.  DOI: 10.1126/science.1184743 Science 327, 990 
(2010).

"Large-bodied suspension feeders (planktivores), which include the most massive 
animals to have ever lived, are conspicuously absent from Mesozoic marine 
environments.  The only clear representatives of this trophic guild in the 
Mesozoic have been an enigmatic and apparently short-lived Jurassic group of 
extinct pachycormid fishes.  Here, we report several new examples of these 
giant bony fishes from Asia, Europe, and North America.  These fossils provide 
the first detailed anatomical information on this poorly understood clade and 
extend its range from the lower Middle Jurassic to the end of the Cretaceous, 
showing that this group persisted for more than 100 million years.  Modern 
large-bodied, planktivorous vertebrates diversified after the extinction of 
pachycormids at the Cretaceous-Paleogene boundary, which is consistent with an 
opportunistic refilling of vacated ecospace."