Proving a negative is a fools errand. The fossil record developed thus far doesn't support it. Additionally there is such intelligence as the Octopus which has an evolutionary split much earlier than mammals and birds.

  The last common ancestor of [humans] and octopuses is a flatworm that 
  trawled the sea floor 750 million years ago. This is the most recent 
  creature that we both have a direct line of descent from – it represents 
  the point at which we diverged down separate evolutionary pathways. To 
  illustrate just how early this was, this was 80 million years before any 
  animal showed bilateral symmetry – the familiar body plan with a defined 
  top and bottom, and right and left; 350 million years before tetrapods – 
  the first four legged creatures that gave rise to all birds, reptiles, 
  mammals and amphibians – came into existence; and 500 million years before 
  the emergence of dinosaurs.