Interesting research paper on BP vision. Constrictor snakes is an ancient design that successfully evolved in many regions, and BPs in particular have ‘heat pits’ tied into their vision so they can in effect see heat.
The Boidae, the boas and the pythons, are of great
interest for several reasons. First, they are considered to be
primitive snakes, known from the uppermost or Maastrichtianphase of the Late Cretaceous, approximately 65 million years ago…
Some of the more obvious primitive characteristics of the Boidae include vestiges of the pelvic girdle and hind limbs, coronoid bones in the lower jaw, teeth on the premaxilla and retention of both the left and right common carotids (Carroll, 1988). Second, and not unrelated to the first, it is generally accepted that the boid pattern of retinal photoreceptors is ancestral to the patterns of the more advanced snakes (Crescitelli, 1972). Finally, most of the boas and all of the pythons have specialized labial thermoreceptors which play an important role in the behavior of the snake. The input from these thermoreceptors appears to be integrated with retinal information in the optic tectum.