A pseudo-penis is a term used of any structure found on an animal that while superficially appearing to be a penis

Penis

The penis is a biological feature of male animals including both vertebrates and invertebrates...

, is derived from a different developmental path.

Mammals

In mammals, all intact developmentally typical males have a penis, but the clitoris

Clitoris

The clitoris is a sexual organ that is present only in female mammals. In humans, the visible button-like portion is located near the anterior junction of the labia minora, above the opening of the urethra and vagina. Unlike the penis, which is homologous to the clitoris, the clitoris does not...

 in the females of the following species is sufficiently enlarged that it is usually termed a pseudo-penis: spotted hyena

Spotted Hyena

The spotted hyena also known as laughing hyena, is a carnivorous mammal of the family Hyaenidae, of which it is the largest extant member. Though the species' prehistoric range included Eurasia extending from Atlantic Europe to China, it now only occurs in all of Africa south of the Sahara save...

, squirrel monkey

Squirrel monkey

The squirrel monkeys are the New World monkeys of the genus Saimiri. They are the only genus in the subfamily Saimirinae.Squirrel monkeys live in the tropical forests of Central and South America in the canopy layer. Most species have parapatric or allopatric ranges in the Amazon, while S...

, lemur

Lemur

Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species...

, juvenile fossa

Fossa (animal)

The fossa is a cat-like, carnivorous mammal that is endemic to Madagascar. It is a member of the Eupleridae, a family of carnivorans closely related to the mongoose family . Its classification has been controversial because its physical traits resemble those of cats, yet other traits suggest a...

 and binturong

Binturong

The Binturong , also known as the Asian Bearcat, the Palawan Bearcat, or simply the Bearcat, is a species of the family Viverridae, which includes the civets and genets. It is the only member of its genus...

. The enlarged clitoris in the fossa is supported by an os clitoridis, a bone similar to the os penis found in most mammals. However, the fossa's os clitoridis and pseudo-penis shrink as the juvenile female grows, unlike that of other pseudo-penis species. The labia of the spider monkey

Spider monkey

Spider monkeys of the genus Ateles are New World monkeys in the subfamily Atelinae, family Atelidae. Like other atelines, they are found in tropical forests of Central and South America, from southern Mexico to Brazil...

 are elongated and may be similarly confused during display. Elongated labia

Elongated labia

Elongated labia is an possibly genetic feature of certain Khoisan groups, whose female members develop relatively elongated labia minora, hanging up to four inches outside their vulva when they are standing in an upright position...

 are also observed in humans.

The mammalian pseudo-penis appears to be simply for display, although the hyena is an exception: the female hyena additionally uses her pseudo-penis for urination, copulation, and childbirth. In addition, this makes it difficult for males to mate without the full cooperation of females, which helps the female-dominated society of spotted hyenas to eliminate forced sex

Rape

Rape is a type of sexual assault usually involving sexual intercourse, which is initiated by one or more persons against another person without that person's consent. The act may be carried out by physical force, coercion, abuse of authority or with a person who is incapable of valid consent. The...

.

Birds

A notable example of a bird with a pseudo-penis is the Red-billed Buffalo Weaver, which can still mate even if its pseudo-penis is disabled.
Only 3% of bird species have a phallus

Phallus

A phallus is an erect penis, a penis-shaped object such as a dildo, or a mimetic image of an erect penis. Any object that symbolically resembles a penis may also be referred to as a phallus; however, such objects are more often referred to as being phallic...

: the common urogenital arrangement for both males and females is the cloaca

Cloaca

In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

, through which all elimination and reproduction (via juxtaposed cloacas) occurs, but certain bird species, particularly ratites, screamer

Screamer

The screamers are a small family of birds, the Anhimidae. For a long time they were thought to be related to the Galliformes because of similar bills, but they are truly related to ducks , most closely to the Magpie Goose...

s, waterfowl

Waterfowl

Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....

, and
cracids

Cracidae

The chachalacas, guans and curassows are birds in the family Cracidae.These are species of tropical and subtropical Central and South America. One species, the Plain Chachalaca, just reaches southernmost Texas in the USA...

 (a family of arboreal galliformes

Galliformes

Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...

) exhibit a phallus

Phallus

A phallus is an erect penis, a penis-shaped object such as a dildo, or a mimetic image of an erect penis. Any object that symbolically resembles a penis may also be referred to as a phallus; however, such objects are more often referred to as being phallic...

 in the male, a structure derived from the internal cloacal wall which is generally associated with sperm competition

Sperm competition

Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...

. Popularised species include the Ruddy duck

Ruddy Duck

The Ruddy Duck is a small stiff-tailed duck.Their breeding habitat is marshy lakes and ponds throughout much of North America, and in South America in the Andes. They nest in dense marsh vegetation near water. The female builds her nest out of grass, locating it in tall vegetation to hide it from...

 and the Argentine lake duck. The corkscrew-shaped phallus of the latter can approach 16 inches in length.