Could there have been intelligent life on earth?

Although this thread has turned into a debate about whether there could've existed an animal more intelligent than humans, it's worth pointing out that there are some astonishingly intelligent non-human animals still alive today.
The only key behavioural traits that set humans apart from other animals are religion and representative art (though neanderthals and even earlier human species (might have had these traits too, which could explain where they evolved - e.g. Homo habilis).

Lots of other animals have complex tool-use and problem-solving abilities (all primates, cetaceans, cephalopods and most birds), semantic language (look up vervet monkey alarm calls) other forms of art (look up bower-birds) and even levels of self wareness and awareness of other individuals (macaques 'gossip' about other troop members; magpies, dolphins, whales and great apes recognise themselves in reflections).

Even looking up how insects make decisions, the 'waggle dance' of bees or how leaf-cutter ants build fungus farms is sure to convince you that intelligence isn't restricted to ourselves. Some insects have ridiculously complex communication and, even if 'understanding' these displays is purely a reflexive response that took millions of years to evolve, it still requires a basic capability to be able to receive the information, process it and use it based on something the animal has previously learned to make a decision on how to behave in response. That's common to all animals with any kind of nervous system (likely millions and millions of species) so there does exist at least a basic level of intelligence throughout most of the animal kingdom.