Comparative gross anatomy of ratites

Abstract

The 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.

Gross morphology of rhea oropharyngeal cavity

“…This study confirmed the basic observation by previous authors (Faraggiana 1933, Cho et al 1984, Fowler 1991, Bezuidenhout 1999, Rodrigues 2012) that the rhea tongue is dark coloured small, triangular or V-shaped, and has a flat rigid appearance. Although flat, the surface of the rhea tongue has a spotted appearance.…”

Comparative digesta retention patterns in ratites

“…In the model of continental vicariance, Rheas are nested within the group consisting of Kiwis, Cassowaries, and Emus as a sister group to Tinamous (figure 3B in Mitchell et al 2014). This would mean that their ''intermediate'' gastrointestinal anatomy and physiology evolved recently from among ancestors that otherwise gave rise to birds of comparatively simple gastrointestinal tracts (Emus and Cassowaries: Cho et al 1984;Tinamous: Chikilian and De Speroni 1996;Kiwis: Potter et al 2006) and digestive physiology (this study for Emus), and as a sister group to the only extant flighted ratites. In contrast, the phylogeny based on mitochondrial sequences suggests that after the divergence of Ostriches from the ancestral ratite lineage, Rheas diverged next, with a common ancestor for all remaining ratite taxa (figure 3C in Mitchell et al 2014).…”

Gross anatomical features of the tongue, lingual skeleton and laryngeal mound of Rhea americana (Palaeognathae, Aves): morpho-functional considerations

“…These studies vary from gross morphological descriptions of the tongue of Rhea pennata (Orbigny, 1834) (Cho et al 1984), Casuarius casuarius (Linnaeus, 1758) (Gadow 1879;Pycraft 1900), S. camelus and D. novaehollandiae (Faraggiana 1933;Cho et al 1984;Bonga Tomlinson 2000) to macroscopic and microscopic studies of the tongue of S. camelus (Porchescu 2007;Jackowiak and Ludwig 2008;Tivane 2008;Guimarães et al 2009) and detailed studies (including light and scanning electron microscopy) of the tongue of D. novaehollandiae Soley 2009a, b, 2010b). In contrast, only minimal information on the morphology and function of the tongue (Owen 1835;Faraggiana 1933;Feder 1972;Bonga Tomlinson 2000;Gussekloo and Bout 2005;Santos et al 2011) and laryngeal mound (Owen 1835;Faraggiana 1933;Bonga Tomlinson 2000;Gussekloo and Bout 2005) of Rhea americana (Linnaeus, 1758) has been published.…”