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

Abstract

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 gizzardbased herbivory. Abstract. -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.

Comparative digesta retention patterns in ratites

“…In particular, rather than relying on fecal collection from enclosure floors (even though covered by carpets), the use of a harness system as described by Bennett et al (2012) would have been preferable. Note that effects of differences in particle size reduction, which may occur on natural foods due to the scaling with body mass (Fritz et al 2011), did not affect the results of the present study because a common diet was used that had been finely ground before pelleting. The marker excretion curves obtained in the present study can be linked to concepts of guts as chemical reactors (Penry andJumars 1987, Caton andHume 2000).…”

“…A morphophysiological adaptation common to herbivorous and granivorous birds is the use of a muscular gizzard filled with grit for the reduction of ingesta particle size (e.g., Moore 1999, Fritz et al 2011. How the flow of digesta through the gizzard is regulated is still poorly understood, in particular whether a sorting mechanism exists that allows smaller particles to pass quickly while retaining larger ones (reviewed in Fritz et al 2012).…”

Full Issue

“…Note that effects of differences in particle size reduction, which may occur on natural foods due to the scaling with body mass (Fritz et al 2011), did not affect the results of the present study because a common diet was used that had been finely ground before pelleting. The marker excretion curves obtained in the present study can be linked to concepts of guts as chemical reactors (Penry andJumars 1987, Caton andHume 2000).…”

Methane emission by adult ostriches (Struthio camelus)

“…However, given that ostriches achieve a high degree of particle size reduction in their gizzard (Fritz et al, 2011) and showed mean faecal particle sizes of 0.7-1.5 mm when fed a diet of fresh lucerne (Fritz et al, 2012), this effect might not be particularly pronounced.…”

“…When compared to herbivorous mammals of similar body mass (BM), ostriches are characterised by a similar gut capacity, food intake, food particle size reduction (via gizzard grinding), digesta passage times and food digestibility (Fritz et al, 2011(Fritz et al, , 2012Frei et al, 2015). Ostriches are kept as farm animals in many countries worldwide, nowadays mostly for earning profit from selling their meat (Cooper, 2007).…”