Location of the ureteral openings in the cloacas of tinamous, some ratite birds, and crocodilians: A primitive character

Abstract

Cloacas of 67 avian species, of both sexes, from various habitats and differing dietary habits, were examined macro- and microscopically to investigate possible variation in the location of the ureteral openings. Differing from most birds studied, in adult male Rhea americana and several tinamous species the ureters were found to open into the coprodeum. In these species the urodeum receives only the vas deferens or oviduct. Similarly, in crocodiles Caiman crocodilus yacare, but not in lizards Tropidurus montanus and snakes Crotalus durissus terrificus, the ureters empty into the coprodeum. This similarity between ancient birds (ratites and tinamous) and crocodiles may indicate a primitive character linking reptiles and birds. This unusual position of the ureteral orifice can represent an adaptation to facilitate urine collection into the coprodeum and large intestine. Another possibility is that this variation in ureter position is a male reproductive strategy to avoid the mixture of urine and semen in the cloaca. There were no evident correlations between the location of the ureteral openings and the birds' habitat, diet, or histology of the coprodeal mucosa. The occurrence of a phallus in eight species of birds was detected, as well as a peculiar vascularization related to the coprodeal epithelium of anseriformes. Together, these data add to the scarce information about the morphophysiology of the avian cloaca, and also contribute to clarify avian phylogenetic linkages.

Morphogenesis and Patterning of the Phallus and Cloaca in the American Alligator, <b><i>Alligator mississippiensis</i></b>

“…By stage 19, the Wolffian duct opens into the proctodeum adjacent to the uroproctodeal fold. These findings are consistent with previous reports that the genital ducts of crocodilians empty caudally into the proctodeum and not the urodeum, a trait that is unique among reptiles [Gadow, 1887;Forbes, 1940;King, 1979;Ferguson, 1985;Kuchel and Franklin, 2000;Oliveira et al, 2004;Cabrera et al, 2007;Cabrera and García, 2010].…”

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

“…In the domestic fowl, with a body mass several times that of the Black Coucal, the deferent duct papillae are short wart-like structures, 1-2 mm in length (Lake 1981;Waibl and Sinowatz 1999). A comparable length (2-3 mm) is found in the Mallard (Anas platyrhynchos; Oliveira et al 2004). In the much larger domestic turkey, the length of the deferent duct papillae does not seem to exceed 5 mm (cf.…”

The socio-sexual behaviour of extant archosaurs: implications for understanding dinosaur behaviour

“…It should be noted that there are other features that could conceivably be included in the above list, one of which is the location of the ureter openings in the archosaurian cloacal cavity. Oliveira et al (2004) noted that the paleognatha R. americana and several tinamou species had ureters that opened into the coprodeum with the urodeum only receiving the vas deferens or oviduct. An identical layout was noted for the crocodilian Caiman yacare though this was not observed in any of the squamates studied.…”