Are there any dinosaurs left in the ocean?

Answer 1

That depends on what you mean:

If you meant "Are there remains of creatures predating recorded history located beneath present-day bodies of water" the answer is yes. While paleontological digs are generally done in more easily accessed locations then the deep ocean floor, many digs done along the faces of cliffs or bluffs near the ocean and it is reasonable to assume that such fossil evidence as exists onshore in such locales would also be present in strata of the same age offshore, should such strata have survived erosion during the interim from deposition to modern day.

If you meant "Are there remains of creatures predating recorded history located beneath the present day sites where ancient bodies of water used to exist" the answer is absolutely and undeniably yes. In fact, nearly all fossil deposits are of such a nature (there are exceptions, but they are very rare. One example of such an exception would be fossil deposits in volcanic ash, though this deposit would also have had to occur many miles inland, in a high desert that has not undergone flooding or glacial activity since to truly qualify as a deposit not meeting this question's criteria). This is because the remains of a creature generally need to be sealed in a sedimentary deposit to be fossilized in the first place, and they generally need to be fossilized to be preserved for durations longer than that of human existence. Sedimentation occurs when the remains of a creature ends up in a river which transports it to a lake, ocean, or delta and deposits it on the calm floor of such an area. Other sediments carried by the river, such as sand grains and mountain soils, are then deposited on top of the remains over a long period of time, sealing what's left beneath mud which later becomes rock. (This is an instance of sedimentation, not the definition). Another method of preservation besides sedimentation would by entrapment in a glacier. This is common only for fossils of the last Ice Age, as glaciers from previous Ice ages generally no longer exist (though there may be such deposits from very, very long ago beneath the ice sheet of Antartica, which is believed to have migrated from the equator to the south pole during the course of the Mesozoic Era). Both glacial and sedimentary deposition are water dependent (ice being crystallized water), so it is easy to see why almost all fossil deposit occur in the manner you may have meant to describe.

If you meant "Are there species of organisms, found underwater today, that could reasonably be expected to be capable of reproduction with a member of the population from which modern populations are descended; that is to say, are there aquatic 'living fossils'?" the answer would be yes, horseshoe crabs and nautiluses being examples.

If you meant "Are there individual aquatic organisms whose curent age surpasses all of recorded history" the answer is maybe. Certainly there are terrestrial trees and some bushes that are known to have been at least as old as 10,000 years, but such an individual's continued existence in an environment as hostile as the ocean floor or , worse, open water is rather unlikely. Additionally no such organism has yet been found. However, there is a fungus that has been genetically identified as a single individual which does predate recorded history, and if the anthropocentric nature of Biology continues to wane, coral reefs may soon be considered single organisms, which would make the existence of an aquatic being older than our history much more likely. Even if such a policy change does not occur, the only environment less well studied than our own oceans is that of deep space, and I do not think any person would be justified in ruling out the existence of such an organism until much more research is done.

If you meant "Is there a fish/mesosaur/other animal predating human history alive today?" Then an underwater specimen would be nearly the only possible answer, the surface of the planet being far too well explored. However, the answer would still be almost certainly no, as an individual organism with moving parts, like arms or legs, wears out after only so long and dies. Furthermore, more animals have nerve cells that cannot replace themselves indefinitely, though some exceptions (like hydras and starfish) exist. While a good deal of aquatic animals show "negligible senescence" (such as whales, some rockfish, and some turtles) out to 200 years, it is known that these animals do experience senescence, just at a much slower rate. It is therefore exceedingly unlikely that any such animal experiences senescence at such a rate that it would live longer than our 10,000 years of history. In order to survive that long, an animal would need to be truly immune to the effects of senescence. For animals that fit this limiter, see the website in the Related Links.

Answer 2

No. Dinosaurs were purely terrestrial life forms. They were accompanied by marine reptiles such as icthyosaurs and plesiosaurs, but both of these groups are extinct.