The reasons why the giant panda does not belong to Genus Ursus:

For over a century the precise taxonomic classification of the giant panda was constantly under debate by biologists. At last, modern molecular studies have in recent years provided important insights that the giant panda belongs to Genus Ailuropodidae, not Genus Ursus nor the racoon family (the Procyonidae).

• Diet characteristics:
  99% of the primary food source the giant panda feeds on is bamboo, a diet that's high in specialization.
• Notable behavior differences between the two:
  Bears in high elevations or in temperate zone hibernate in winter, whereas the giant panda is active all year round, the reason being that it's primary diet – the bamboo, does not contain the necessary nutrients required for hibernation.
• Notable differences in the number of chromosomes between the two:
  Brown bears of the Ursinae family have 37 pairs of chromosomes, all of which are acrocentric, whereas the giant panda has just 21 pairs, mostly metacentric. This is a clear evidence that the panda's metacentric chromosomes are bear's acrocentric chromosomes attached together, a result of chromosomal fusion in an ancestor (now extinct). The red panda has 22 pairs of chromosomes.