Oh boy... this old chestnut. There have been no gravity changes. Gravity is a function of mass, and the mass of the Earth has been pretty well constant for the last 4 billion or so years. And neither are all animals smaller now than they were. Horses were the size of smallish dogs 50 million years ago. Humans are much taller than their ancestors. Blue whales are easily the biggest animals that have ever lived (fragmentary bits of super-dinosaurs notwithstanding). So while there were some animals bigger in the past, there are plenty that were smaller.
The reason a lot of these extinct fishes seem so large is because we don't often see really big fish. Partly, that's because fishing pressure has reduced their populations so the big individuals just aren't around anymore because they are caught and eaten too soon to get that big. In other cases (e.g. oarfish) we simply don't see them except when corpses wash up on beaches. While everyone here knows about the really big sharks, there are quite a few huge bony fish too. Here are a few:
Oarfish, up to 11 metres (~36 feet)
Atlantic blue marlin, up to 5 metres (~16.5 feet)
Atlantic halibut, up to 3.2 meters (~11 feet)
Pacific bluefin tuna, up to 3 meters (~10 feet)
Giant grouper, up to 2.7 meters (~8.5 feet)
Atlantic cod, up to 2 meters (~6.5 feet)
Cheers,
Neale
Man that thing must have been huge!!!!
Its head was 30cm long! Wonder why theyve gotten smaller...
look at ALL animals from those times, their relatives are no MUCH smaller than what they were.
There are many reasons that they think they got smaller such as gravity strength changes, etc
/www.sheppeyfossils.com/pages/Brychetus.htm
