Why were they so big?

>>>>What pussels me is the size of the creature. 3 meter.

>>>>Today,fish that live part of their life on land or just incidently

>>>> crawl on land are much smaller.

Such fish are much smaller today because humans have exterminated all the larger species. Australia alone was once home to a 2 metre lungfish and a 3 meter freshwater eel, both of which could presumably travel over land.

The fact is that the average size of freshwater fish species has shrunk dramatically in the last 100,o00 years, not just those that moved on land. And of course the average size of mammals species, of frog species and of reptile species has also shrunk.

This has nothing to do with environment or evolution, it is simply selective extermination by a novel species: us. Rest assured that if humans didn't exist these giant fish would still be with us.

>>>>When animals evolve into big forms it has usually to do with

>>>>predator/prey interaction.

When animals evolve into big forms it very rarely has anything to do with predator prey interactions. In fact exactly the opposite is true.

Animals in environments with no predators are almost universally larger than similar species elsewhere, and animals that are hunted regularly are almost invariably smaller than similar species, or even populations of the same species, that are hunted less frequently or effectively.

Consider, for example, where the world's largest pigeon, the dodo, lived. And the world's largest eagle? And where does the world's largest bear live? And where did the world's largest bison live? And the world's largest lizard? The world's largest tortoise? I could extend this list almost forever. Name any group of animals and by far the largest individuals will live (or have lived) in environments where they are/were not hunted. Once again the fact that many of these species were exterminated by humans or animals we imported highlights the reason for the size change.

In actual fact animals get big for two main reasons: food storage and intraspecies competition. A large animal has relatively less surface area and more internal storage space, so all things being equal larger animals can withstand hibernation, drought and so forth better than smaller animals. The other reason animals get big is so they can fight each other. This is particularly driven by males fighting over mates. Linked to that is the fact that large animals can support larger gonads, and so can produce more young.

Playing off against those pressures to get ever larger are the need to be able to move and the need to be able to evade predators. When a population is freed from the constraints of predator evasion it almost invariably grows larger.

So the fact that these fish were so large could be evidence that they were able to evade predators without resorting to stealth or speed.

Honestly I have no idea...

but what you said about the size and complixity of internal organs does seem to make sense, I mean the first computers were the size of a large room, and now we have them in everything, and they can be very small, maybe nature was similiar in its evolution. and that is why everything has gotten smaller, I mean think of how much larger the earth and more abundant the resources must seem to ants.

The smaller we are then the more of us will fit.

Why couldn't this apply to the first pioneers? These pioneers were not exclusively terrestrial, but spent much time in the water, where they may have been some good reason to remain large.

where u found that information anyway size dosent matter in evolution it depends on its adaptabiliyty to its environment