Eyes and the emergence of predators

I'm sure most of you are familiar with the idea that the first real animal predators – i.e. animals that actively seek out and eat other organisms for food – evolved pretty much in association with the appearance of eyes, in the shallow Cambrian seas, about 500 million years ago.

I just had a thought about that: if there was a strong link between the evolution of eyes and of predators, which suggests that the world's animals were sort of waiting to be able to see before they started hunting, why is it then that so many predators that have evolved since primarily use other senses, such as smell and hearing, to locate their prey? Why go back?

Don't get me wrong, I'm not suggesting something is odd or amiss here – just that it is a curious thought. Evolutionary reversals are not uncommon. Since vertebrates managed to crawl onto land and become adapted to terrestrial life, several groups have gone back to the sea, including plesiosaurs, placodonts, nodosaurs, ichthyosaurs, mosasaurs, cetaceans (whales, dolphins, and porpoises) and pinnipeds (basically seals); crocodiles evolved to become semi-aquatic. Since birds evolved flight, several groups have lost that ability: ratites (ostriches, emus, etc.), penguins and the ancient terror birds. One could probably write a dozen books on just the topic of reversals in evolution.

A simple answer to the question earlier could be that, while many predators today use their smell or hearing to locate prey at a distance, they still rely on eyesight when they are close enough. I recall reading that sharks, having exremely poor vision, use their insanely acute sense of smell to detect a wounded animal maybe miles away, and, when they come within a metre or so of the prey, they use their eyes, but when coming even closer, they cannot see (for their big snout being in the way, I guess) and then use their special sense that can feel electric impulses from the animal's muscles, to direct where they close their jaws.

This makes some sense (pun not intended, but I like it!), especially for land- and water-based predators, since vision is physically limited by trees, bushes, hills, or simply the natural murkiness of water. Scent particles and noise, on the other hand, won't be as restricted. But, sight is probably the most convenient way of homing in on prey when you have it within visible range, so I wouldn't be surprised if most predators shift to sight-dominated pursuit when they are close enough to their prey.

And, maybe that explains why the evolution of eyes sparked the emergence of predators...