The diverse orderCarnivora includes over 260 placental mammals. While the Giant Panda is an herbivore, nearly all others eat meat as their primary diet item: some (like the cat family) almost exclusively, others (like the bears and foxes) are more omnivorous. Members of Carnivora have a characteristic skull shape, and their dentition includes prominent canines and carnassials.
Older classification schemes divided the order into two suborders, Fissipedia, which included the families of primarily land carnivores, and suborder Pinnipedia, which included the true seals, eared seals, and walrus.
Newer classification schemes, which have been able to integrate the findings from molecular techniques for discovering genetic relationships, generally divide the Carnivora into suborders Feliformia and Caniformia, which includes the pinnipeds.
Recent molecular studies suggest that the endemic Carnivora of Madagascar, including three genera classed with the Viverridae and four genera of "mongooses" classed with the Herpestidae, are all descended from a single ancestor, and form a single sister taxon to the Herpestidae.
According to morphological and molecular evidence, the available phylogeny of the order Carnivora consists of two groups, the Feliformia (cats, mongooses, civets, and hyenas) and the Caniformia (wolves, bears, raccoons, mustelids, and pinnipeds) [23,24].
It is difficult to determine when the alteration of Tas1r2 occurred and whether it preceded or followed the cat ancestor's change in diet to exclude plants.
Clearly, because dogs have a human-like T1R2 structure (see Figure 1) and an avidity for sweet carbohydrates [25], the changes in the cat Tas1r2 must have occurred after the divergence of the Feliformia and the Caniformia.
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