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lightknight7777 t1_ja4ed7f wrote

Reply to comment by DrInsomnia in For birds all sex is anal sex. by Whats-Upvote

It's the tissue from all 3 tracks. In no way can you just claim It's the anus or the vagina or the urinary tract. It is distinct from any of the three it is a merging of. A cloaca is not an anus.

That's why there's a distinct term from anus for it.

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DrInsomnia t1_ja4ifqr wrote

There's a distinct term for it because it serves more than one function. But it developmentally starts as the anal opening, and continues to serve as the anus in an adult. This is really all semantics, but from a developmental biology standpoint it is an anus that has acquired other functionality.

Edit to add, from the Wiki link: "In deuterostomes, the original dent becomes the anus, while the gut eventually tunnels through the embryo until it reaches the other side, forming an opening that becomes the mouth."

Vertebrates are deuterostomes. In bird development, that original "anus" becomes the cloaca.

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lightknight7777 t1_ja4iida wrote

That doesn't make it an anus. It's not.

Semantics is what words mean. Of course it's semantics.

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DrInsomnia t1_ja4j8ck wrote

Yes. And a cloaca is an anus that has taken on additional functionality in some groups. In fact, in mammals the original mammalian ancestor likely had a cloaca, which split into separate openings (in some derived groups). But embryologically it all starts with the anus.

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