On the sucsess of marine vectors of terrestial clades

[Zor]

From the Triasic period onward a fairly common trend is evident, in which marine vectors of land based creatures (Manatees, Whales, Sea turtles, Mosasaurs, Plesiosaurs, Ichthyosaurs, Marine Crocodiles in the Jurassic period) have evolved and thrived. Now the question here is simple, why is this the case? Said creatures should be at a disadvantage for having to return to the surface to breathe in comparison to things which can extract air from the water. So why has let thes creatures compete with fish and such for so long?

Zor

[Serafina]

Simple: They brought other advantages.

Besides, having to breathe air is not that much of an disadvantage. Sure, it limits your possible depth, but most fish stay at more or less the same depth anyway.

[Surlethe]

Simple: They brought other advantages.

Would you mind elaborating, please? We tend to frown on one- or two-line posts.

[Serafina]

Simple: They brought other advantages.

Would you mind elaborating, please? We tend to frown on one- or two-line posts.

Such as yours? .

Seriously, it hard to determine without knowing what other species lived at the time they "started" to live in the water.
Nonetheless, it is a valid point.

But here is a possible szenario:

As species similar to todays walruss/seal/otter has some advantages compared to fish:
-safe nesting grounds: Their children are safer on land than in the water (of course, depending on the enviorment).
-higher-level social structure: Lots of whales have more complicated social behaviour than fish.
-brain size/intelligence: whales are very intelligent. walruss/seal/otter are more intelligent than (most?) fish.
-being endothermic species: This is VERY usefull - whales can travel all around the world and easily survive cold AND warm water.
Once they spend a lot of time in the water AND are sucessfull, they will adapt to be better swimmers, divers etc. And eventually, they will spend ALL their time in the water, and be a nicely adapted species.

There may be other factors, but i am no biologist.

Besides, evolution is not all about competition. A species that finds a biological niche and has no predators hunting it will survive.

[Edi]

Simple: They brought other advantages.

Would you mind elaborating, please? We tend to frown on one- or two-line posts.

Probably not as many predators to hunt them initially. That's a pretty big one. See your own post in the other thread about present day animals not being static. Walruses and such are borderland species in the sense that they live on the border of two pretty distinct environments and then it's just a matter of migrating completely into one of the two, which happens gradually. Whale evolution and transitional forms have been fairly well understood for some years and there is absolutely no reason why the same factors would not have been the case for things such as plesiosaurs.

[Akhlut]

Survival of young, especially with mammals, and probably with marine reptiles like icthyosaurs which were almost certainly entirely aquatic and therefore, had to be viviparous or ovoviviparous. This allows the young to develop to a point where they can survive fairly easily on their own, whereas most fish expend tremendous numbers of young just to see a few survive.

Further, marine mammals provision of milk for their young allows the young to grow more easily, as they don't have to fend for their own food.

[Solauren]

Doesn't most plant life, at least the small, easy to suck up stuff exist near the surface of the ocean anyway?

And the small fish that eats that?

Seems to me they don't have to breath water to get to that.

Plus, you know, there's that whole "as a result of breathing air, I'm one of the biggest things on the planet, please, pick a fight with me you skinny little sharks" advantage.

[Zor]

Plus, you know, there's that whole "as a result of breathing air, I'm one of the biggest things on the planet, please, pick a fight with me you skinny little sharks" advantage.

Well things like Whale Sharks, leedsichthys and Megalodons have proven that fish can get damn big.

Zor

[EarthScorpion]

Well, it's also the fact that land-living supercharges, so to speak, the creature. Mammals, for example, have a four chamber heart, in which the blood is oxygenated in a separate pumping cycle to the circulation around the rest of the body, so it can be sent around at higher pressure (because the main cycle doesn't have to risk tearing the fragile blood vessels that allow diffusion from the lungs/gills), and thus allows more sustained periods of activity. By contrast, fish only have a two chamber heart, which goes heart-gills-body-heart, which is less ... I don't think efficient is quite the right word. Powerful, maybe.

[Alyrium Denryle]

There three primary reasons

1) They were avoiding competition from other land animals
2) They were filling un-occupied niches.
3) They are doing so gradually.

To use an example: There were very few waters-edge ambush predators until crocodilians came along. They literally had no competition, and because they laid eggs on land were less sensitive to environmental fluctuations than their amphibian counterparts that did exist.

[TheLostVikings]

Well, it's also the fact that land-living supercharges, so to speak, the creature. Mammals, for example, have a four chamber heart, in which the blood is oxygenated in a separate pumping cycle to the circulation around the rest of the body, so it can be sent around at higher pressure (because the main cycle doesn't have to risk tearing the fragile blood vessels that allow diffusion from the lungs/gills), and thus allows more sustained periods of activity. By contrast, fish only have a two chamber heart, which goes heart-gills-body-heart, which is less ... I don't think efficient is quite the right word. Powerful, maybe.

Yup. It's also worth mentioning that a human would not be able to function with gills instead of lungs, we would simply not be able to extract enough oxygen from the water to make it worthwhile.

So while having to resurface every few hours to breathe might be an inconvenience, it gives them a tremendous advantage over anything that doesn't breathe air. They simply have a higher-energy fuel in their engines which allows them to out-muscle anything else on their turf.