By nature’s arrangement, fruits and flowers are considered the food of insects and birds; grass and other legless living entities are meant to be the food of four-legged animals like cows and buffalo; animals that cannot use their front legs as hands are meant to be the food of animals like tigers, which have claws; and four-legged animals like deer and goats, as well as food grains, are meant to be the food of human beings.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
अन्नं चराणामचरा ह्यपदः पादचारिणाम् । अहस्ता हस्तयुक्तानां द्विपदां च चतुष्पदः
annaṃ carāṇāmacarā hyapadaḥ pādacāriṇām | ahastā hastayuktānāṃ dvipadāṃ ca catuṣpadaḥ
SB 6.4.9