Crash Course in Evolution and What It Is

[Vene]

To some extent, it still depends on who you ask, but the only way to make the reptiles monophyletic is to include birds.

[Lithp]

Wouldn't you also have to include mammals? Monophyletic is "all descendents of a common ancestor," correct? And aren't mammals descended from reptiles?

[Vene]

If we look at the phylogeny we see we don't need to include mammals.

[Lithp]

I don't follow. Clearly mammals aren't closely related to birds, dinosaurs, & "modern reptiles," but there are also a number of much older animals, in the Carboniferous & Permian eras, that are classified as reptiles.

[Vene]

Lithp, synapsida is mammals, and anapdsia and diapsida are reptiles. You can easily make mammals monophyletic while keeping them separate from reptiles and have reptiles also be a monophyletic group.

[Lithp]

So, what about this? If the page is to be believed, its ancestors include synapsida & diapsida, & it is still considered a reptile.

[Jack Mann]

For its ancestors to include both synapsida and diapsida, it would require interbreeding between wildly different species.  Rather, it shares a common ancestor with both synapsida and diapsida.

However, it's true that it probably shouldn't be considered a reptile unless mammals are.  Really, what we consider "reptiles" should probably be split into several different groups (testudines, squamates [possibly further split into squamates and sphenodonts], crocodilians, and dinosaurs [including birds]).

[Lithp]

No, I meant to say that its successors include those groups, sorry, I was rushing around with chemistry, & I'm already something like 3 hours late for bed.

[Vene]

Lithp, here's a phylogeny of that organism:

http://sysbio.oxfordjournals.org/content/54/4/530.full

Paleothyris acadiana is still on a completely different lineage than synapsida.

[Lithp]

Then I guess this:

Paleothyris is at the base of a large clade, the Protosynapsida, defined as Paleothyris, Passer, their last common ancestor and all of its decendants. Casineria and the microsaurs are outgroups. The Protosynapsida includes the Synapsida and the Diapsida.

...must be incorrect. All I know is that I keep hearing that mammals evolved from reptiles in the Permian Era. Hence, the conclusion I keep coming to is that either all of those things are wrong, or mammals are descended from animals classed as reptiles.

I wish I had a scanner so I could show you exactly what I'm looking at, but I don't.

[Jack Mann]

Mammals evolved from a common ancestor to reptiles, one which resembled modern reptiles more than modern mammals.  Because of earlier scientific understanding, they were classified as reptiles, leading to a paraphyletic designation (that is, the descendants of a reptile should likewise be called reptiles).  The common ancestor should be called something other than reptile under monophyletic definitions.  I also think that reptilia should be split up.  Right now, reptiles basically consist of everything in amniota left over after mammals and birds are taken out.  The wastebin of amniotes.

[D Laurier]

Tending to agree that "reptiles" is a bogus class. More a "wastebin" than a meaningfull grouping.

[Vene]

Tending to agree that "reptiles" is a bogus class. More a "wastebin" than a meaningfull grouping.

If you want to see a real wastebin look up protista.

[D Laurier]

Tending to agree that "reptiles" is a bogus class. More a "wastebin" than a meaningfull grouping.

If you want to see a real wastebin look up protista.

No thankyou. I'm gonna take your word for it.
I'll just pour myself another margarita instead. It's less frustrating.

[Lithp]

Protists are a fucking mess.