Comparative gross anatomy of ratites

Abstract

AbstractThe four most common ratites kept in captivity, emus, rheas, ostriches, and cassowaries, share similar musculoskeletal features based on their common evolution to a flightless form. However, they differ in body size and coloration, wing size relative to entire body size, extent of leg feathering, and number of toes. During necropsies we observed the differences among the birds, which include the shape of tongue and tonsils, a tracheal cleft found only in emus, varied shapes of the thymus, spleen, bursa of Fabricius, proventriculus, duodenal loop, and ceca, different lengths of colon and ceca relative to the entire intestinal length, and different coloration of the gonads. Several of the structural differences reflect the phylogeny of the ratites. Rheas and ostriches share common features in relatively large wings, kidney‐bean shaped spleen, tan gonads, and long ceca, whereas emus and cassowaries have relatively small wings, short ceca, and similar proventriculi. The anatomical variations may reflect their varied diets in the wild and the different behaviors among the groups such as their characteristic vocalizations. Knowledge of the differences may be useful in formulating proper diets for captive birds and is important for the recognition of clinically normal structures in the ratites.