What Were The Whales Of The Mesozoic?

[Shamalama]

I'm well aware of the toothy predators of the Mesozoic such as the Mosasaurs, Pliosaurs and Plesiosaurs but were there any large plankton feeders which would be analogous to the Whales of today? It seems that all the predators ate were fish and ammonites and sharks didn't get as big as during the Tertiary.

[Auspex]

Well, the planktonic resources were certainly there...

How about, instead of one big organism, we consider thousands of little ones; small ammonites for instance?

[Shamalama]

Okay, so lots of little preds so that the pred ladder has many rungs instead of just one or two. I can see that and would make sense since there are so many little ammos. Good idea, Auspex!

[Auspex]

Who knows, maybe large-scale seining of krill-sized plankton did not become metabolically profitable until after the demise of the ammonites... Just a thought from way out on the limb.

[Boesse]

There were large filter feeding fish during the mesozoic, such as Leedsichthys. Additionally, many long necked plesiosaurs are hypothesized to actually be bottom feeders, using their long teeth as a sieve for soft bodied invertebrates living in soft, muddy substrates.

Additionally, there is one plesiosaur with hundreds of very tiny, elongate teeth that probably functioned in a similar manner as baleen.

Bobby

[Guest N.AL.hunter]

http://striweb.si.edu/publications/PDFs/19...CollinJanis.pdf

[Auspex]

Thanks, Del; that is a very well reasoned paper.

I can't vet it for accuracy, but it is a study in coherent deductive reasoning.

[Ramo]

I've often wondered if Ptychodus sharks might have been filter feeders. I know that everyone says they fed on clams, oysters, etc. But of all the teeth I have found, and many more I have seen photographed, I see very few with very much wear at all. I also know that they got big, and had big mouths. Has anyone ever considered this feeding method for these sharks?

Ramo

[siteseer]

I've often wondered if Ptychodus sharks might have been filter feeders. I know that everyone says they fed on clams, oysters, etc. But of all the teeth I have found, and many more I have seen photographed, I see very few with very much wear at all. I also know that they got big, and had big mouths. Has anyone ever considered this feeding method for these sharks?

Ramo

I have a severely worn P. whipplei tooth with a wear facet consistent with an almost occluding tooth repeatedly hitting it on one side. I bought it years ago, and in fact recall buying it because I had not seen a Ptychodus with such a prominent wear facet.

One thing to consider is that by the Late Cretaceous all the modern shark orders had appeared, groups with efficient tooth replacement systems and it seems the Ptychodus group did too. Even a mollusk-eating shark did not retain teeth long enough for them to develop visible wear. Perhaps only the occasional individual with a slower-than-normal metabolism is responsible for the faceted teeth. It is rare to see wear facets on any Mesozoic-Cenozoic fossil shark teeth, though I have seen a few (two different Parotodus and the occasional C. megalodon). Some Paleozoic teeth look like they tried to chew through a bucket of bolts.

The teeth of Ptychodus are too well adapted for shell-crushing - simliar to the shape of some rays and the only modern shell-crushing shark, Mustelus (rounded cusp) - to propose another possible diet for them.

[Phoenixflood]

I've often wondered if Ptychodus sharks might have been filter feeders. I know that everyone says they fed on clams, oysters, etc. But of all the teeth I have found, and many more I have seen photographed, I see very few with very much wear at all. I also know that they got big, and had big mouths. Has anyone ever considered this feeding method for these sharks?

Ramo

That is a question that is worth some thought over. My mind drifts to sharks today that have similair teeth like the Port Jackson shark (Heterodontus portusjacksoni). The feed on mollusks, echinoderms and crustaceans but could they also filter feed???

My favorite of the ealry whales are the archaeocetes.

[Ramo]

Siteseer, You make good points, and I'm sure you are more than likely correct. (there have been enough people studying these sharks, and where I find these teeth there are usually tons of mollusks fossils) But it seems weird that during all the years these sharks had to adapt, there are no filter feeders (that I know of), and in the relatively short time whales have had to adapt, they allready have filter feeders.

(I guess us mammals are just smarter)

Ramo

[siteseer]

There were large filter feeding fish during the mesozoic, such as Leedsichthys. Additionally, many long necked plesiosaurs are hypothesized to actually be bottom feeders, using their long teeth as a sieve for soft bodied invertebrates living in soft, muddy substrates.

Additionally, there is one plesiosaur with hundreds of very tiny, elongate teeth that probably functioned in a similar manner as baleen.

Bobby

There was also at least one pterosaur that apparently filter-fed similar to a flamingo.

Megachasmid sharks have been questionably extended back into the Cretaceous (teeth with a similar morphology as the megamouth) but it appears that plankton-eating didn't become popular for large vertebrates until the Oligocene (cetothere whales and the basking shark became common then). Whale shark relatives appeared in the Paleocene but it's difficult/impossible to say when their teeth (and basking shark teeth or megamouth-like teeth for that matter) stopped being functional and their filter-feeding took over but the transition appears to have ended by the Late Miocene (when their teeth became virtually identical to modern forms).

[Ramo]

"There was also at least one pterosaur that apparently filter-fed similar to a flamingo."

I wonder if they were pink, due to their diet, like flamingos?

[Phoenixflood]

Here are some links I found on a new whale found in India.

http://adsabs.harvard.edu/abs/1998PNAS...9515464B

http://www.pnas.org/content/95/26/15464.full.pdf

[Boesse]

Hey Folks, some points -

1)But it seems weird that during all the years these sharks had to adapt, there are no filter feeders (that I know of), and in the relatively short time whales have had to adapt, they already have filter feeders.

--> There are several extant filter feeding elasmobranchs, including Basking sharks (Eocene to modern), Megamouth Sharks (Cretaceous to modern), Whale sharks (at least Miocene to recent), and Manta Rays (at least Pliocene to recent). Siteseer, you can correct me on the ages here... (actually, it looks like you already answered a few of these above).

Additionally, sharks have evolved very slowly, and many lineages haven't really changed significantly since the Paleogene.

2) Megachasmid sharks have been questionably extended back into the Cretaceous (teeth with a similar morphology as the megamouth) but it appears that plankton-eating didn't become popular for large vertebrates until the Oligocene (cetothere whales and the basking shark became common then). Whale shark relatives appeared in the Paleocene but it's difficult/impossible to say when their teeth (and basking shark teeth or megamouth-like teeth for that matter) stopped being functional and their filter-feeding took over but the transition appears to have ended by the Late Miocene (when their teeth became virtually identical to modern forms).

--> Aetiocetids started filter feeding presumably by the early Oligocene, and there is a late eocene mysticete with possible baleen from Antarctica (Llanocetus). Thought I'd mention that Basking sharks already had elongate, large gill rakers by the Oligocene.

3) There was also at least one pterosaur that apparently filter-fed similar to a flamingo.

--> Pterodaustro, right? There's also a filter feeding adaptation in Ornithomimid dinosaurs.

4) (there have been enough people studying these sharks, and where I find these teeth there are usually tons of mollusks fossils)

--> This might be due to sedimentary transport processes treating teeth, shells, and pebbles as hydraulically equivalent entities, and concentrating them into distinct horizons.

Bobby

[siteseer]

Hey Folks, some points -

--> There are several extant filter feeding elasmobranchs, including Basking sharks (Eocene to modern), Megamouth Sharks (Cretaceous to modern), Whale sharks (at least Miocene to recent), and Manta Rays (at least Pliocene to recent). Siteseer, you can correct me on the ages here... (actually, it looks like you already answered a few of these above).

Additionally, sharks have evolved very slowly, and many lineages haven't really changed significantly since the Paleogene.

Bobby

Yeah, the megamouth shark lineage is still hazy even only as far back as the Early Miocene. Teeth identical to the modern species are known from the Middle and Late Miocene. Teeth from the Late Oligocene and Early Miocene of California and Oregon that resemble megamouth teeth may or may not belong to an ancestor (consensus seems to be leaning toward the former or at least a close relative). The Late Cretaceous occurrence (Shimada, 2007) is based on four teeth. Their identification as "megamouth" has already been rejected (de Schutter, 2009) - considered more odontaspidid in design.

de Schutter, P. 2009.

The Presence of Megachasma (Chondrichthyes: Lamniformes) in the Neogene of Belgium, First Occurrence in Europe. Geologica Belgica. 12 (3-4): 179-203.

Shimada, K. 2007

Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology. 27 (2): 512-516.

[Shamalama]

Great article on exactly what I was asking! Thanks for posting that N.Al.Hunter.

I like all the other angles that have been brought up including the sharks. What it's looking like to me is that up until the end of the Cretaceous there were no major, large filter feeders analogous to modern whales simply due to the fact that the predators were more numerous and larger in size. Think about it... it would be very hard for an animal to evolve to a large size and feed primarily on plankton if the existing predators were feeding on them. Whales evolved with, in my opinion, minimal predator pressure other than sharks. Even while the whales were getting bigger, the sharks were matching their size with the apex being Megalodon. Thus you had something of an ecological balance.

I know it's impossible to tell if ammonites were filter feeders, but maybe there were soft bodied organisms they fed on that did the filtering.

[ashcraft]

I don't know much about filter feeders, but I think that I read that whales evolved during a spike in plankton. There used to be many more species of whales that filter fed and fed on fish etc that also were more abundant during this time. Megalodon evolved to feed upon this new whale protein source. When the ocean currents changed, fewer nutrients were brought up from the bottom, and the amount of plankton declined (mineral nutrients, not sunllight, are the limiting growth factor in water environments), leading to the decline of many whale species.

Brent Ashcraft

[Tr-J-K]

Another thing to consider is that of course the fossil record is terribly incomplete. Most of the marine deposits that we have now represent shallow seas or coastal regions, not deep sea environments. What was swimming in the deep oceans of the Cretaceous? Kinda hard to say for sure, since a lot of that seabed is still at the bottom of the ocean. In the Pacific, the oceanic crust in fact dates to the Jurassic. In the Atlantic, you'll have Cretaceous crust...so we can't really know what was at out in the middle of the ocean with any great certainty.

[Shamalama]

Tr-J-K... Are you suggesting we arrange for an excavation on the floor of the pacific to answer this question? If so, I'm in.... but we will need a huge cofferdam to keep the excavation area clear of water.

[Tr-J-K]

Tr-J-K... Are you suggesting we arrange for an excavation on the floor of the pacific to answer this question? If so, I'm in.... but we will need a huge cofferdam to keep the excavation area clear of water.

I'll contact the Navy!