Monday, January 30, 2006

Monotremes are not that confusing

Pegasus Discovered!:
“Mammals” that lay eggs, secrete venom from ankle spurs, have no nipples, and have a cloaca. A bizarre mix of avian and mammalian features to be sure,
This from the creationist buffoons at Dembski's blog.

The cloaca is something birds have, but they have it because their reptilian ancestors have a cloaca also. It is entirely unsurprising that a basal mammal would share a character with the reptilian ancestors of mammals, birds and reptiles. The eggs are very unlike bird eggs, but bear a striking resemblance to reptile eggs.

Venom is not characteristic of birds, so I'm not sure how that snuck in.

And those nipples. Instead of discrete mammary glands, the monotremes have a patch of skin with modified sweat glands. Young platypuses hatch out of their eggs and use the hair (hair!) over that patch of skin as a straw.

So let's review. We have a mammal that has various characters part way along the transition from reptile to mammal. This is what you would predict if mammals share a reptilian ancestor.

The Dembskiites decided that these reptilian features looked a little avian. The problem is that they aren't, and the only reason it looks at all avian is that birds share a reptilian ancestor, also.

It's not like this is the first time we've done this little merry-go-round. Take the quiz.