Data from: Gizzard vs. teeth, it’s a tie: food-processing efficiency in herbivorous birds and mammals and implications for dinosaur feeding strategies

Particle size reduction is a primary means of improving efficiency in
herbivores. The mode of food particle size reduction is one of the main
differences between herbivorous birds (gizzard) and mammals (teeth). For a
quantitative comparison of the efficiency of food comminution, we
investigated mean fecal particle sizes (MPS) in 14 herbivorous bird
species and compared these with a data set of 111 non-ruminant herbivorous
mammal species. In general MPS increased with body mass, but there was no
significant difference between birds and mammals, suggesting a comparable
efficiency of food processing by gizzards and chewing teeth. The results
lead to the intriguing question of why gizzard systems have evolved
comparatively rarely among amniote herbivores. Advantages linked to one of
the two food comminution systems must, however, be sought in different
effects other than size reduction itself. In paleoecological scenarios,
the evolution of "dental batteries," for example in ornithopod
dinosaurs, should be considered an advantage compared to absence of
mastication, but not compared to gizzard-based herbivory.