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Since the gizzard is for mechanical digestion, shouldn't that happen before the stomach digests the food with acids? (to make the morsels smaller)

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The gizzard appears to be a structure that bird inherited from a distant ancestor, as the structure is found in dinosaurs (which birds are derived from) and crocodilians. https://en.wikipedia.org/wiki/Gastrolith

As to why, the bird gizzard is not in a better position, (like say the grasshopper gizzard which is located in front of its stomach), the best reply I think off is evolution is blind. The innovations that appear, are random and further constrained by the features that the animal already has.

It is probably the same reason why rabbit eat their own poop to better digest their food, even though cows have evolved a four chamber stomach to handle the same problem of digesting grass. Or why no animal has evolved a second set limbs to fly even though it would be super useful to keep arms to catch prey and not sacrifice said arms to be made into wings.

In a sense these questions of why didn't evolution design it better is evidence that the concept of intelligent design is rubbish. Designs in animals (and bacteria) can be really really dumb.

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    $\begingroup$ "...found in dinosaurs (which birds are derived from)" This is incorrect. Birds are dinosaurs. $\endgroup$ – user24284 Jan 1 '17 at 9:07
  • $\begingroup$ Birds are a derived species of theropod. And theropod are only one of two members of Saurischia. And there is deep divide between Saurischia and Ornithischia. Secondly Birds are a derived species....while they have many features of theropods... the evolution of flight has cause birds to gain many features not shared by most member of theropods. Birds have no teeth, reduced jaws, no grasping fore limbs,a truncated tail, a bird hip, an arrangement found in Ornithischia. Birds are a derived species, avian dinosaurs. $\endgroup$ – JayCkat Jan 1 '17 at 15:00

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