Hi all. Been a while since the last time I was here. How are you doing? Well, I'm currently wondering about swimming animals. See, when I see (in videos or real life) animals swimming, Chordata animals especially (fish up to mammals), their methods of swimming seems to differ depending on the animals. However, as far as I've observed and remembered, ectothermic (or should I say poikilothermic?) Chordata such as fish and reptiles tend to swim in sideways waving (sinestral-dextral, left to right), though in case of legged reptiles, this is also the way they walk. In contrast, aquatic mammals (endothermic Chordata) such as dolphins tend to swim in vertical waving (dorsal-ventral, up to down), and as far as I know I've yet to see humans who swim with sideways waving either. Well, admittedly, considering the morphological differences between fish and dolphins, their different methods of swimming may be because of that, since fish are often flat sideways (that is, shorter left-to-right/sinestral-dextral body size) while dolphins are not, and humans are flat back-to-front (dorsal-ventral) and generally swim the same way as dolphins. However, reptiles, like humans, have a shorter dorsal-ventral body distance, and yet they tend to swim like fish. Why is this so? As disclaimer, I haven't really taken note of swimming birds' swimming methods (I tried checking on penguins on Youtube, but their main bodies rarely exhibit any significant waving movement while their flippers fo all the work), and I understand that some fish are more tubular in appearance, not to mention some vertically-flat fish (such as rays) who swim totally differently from their kin. PS: Sorry if I sound a little too smarty with all those latin words ^_^". It's just that I'm trying not to confuse the notion between up/down, front/back and up/down due to involving humans in this question. PS2: And thanks in advance for any replies. Please Register or Log in to view the hidden image!