[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Unorthodoxies in Reptilian Phylogeny [Romer 1971]
If Diadectomorpha is the sister group to Amniota, which genus in both
are sister taxa (or closest to the node)?
Newtonmas present for you: I'll explain the terms that you somehow never
looked up during the last five or more years.
Cladogenesis: one population splits into two clades, which are by
definition sister taxa.
--B and `--C are sister taxa.
are sister taxa.
B and C, without their stems (--), are strictly speaking not sister
taxa, though this simplification is usually harmless.
A and B are _not_ sister taxa, and neither (and for the exact same
reason) are A and C.
--Amniota and `--Diadectomorpha are sister-groups. Period. No member of
Amniota is the sister-group of any member of Diadectomorpha; these two
taxa are clades, so any part of Amniota can only be the sister taxon of
another part of Amniota.
"Which ones are closest to the node?" Do you mean which diadectomorph is
the sister-group to all other diadectomorphs as a whole, and which
amniote is the sister-group to all other amniotes as a whole? The answer
to the former is *Limnoscelis*, as I showed in the tree; the answer to
the other is that Theropsida and Sauropsida are sister-groups and
Amniota has a node-based definition.
(All of "Limnoscel(id)idae" was recently sunk into *Limnoscelis*, and
even into *L. paludis* if I recall correctly.)
(Disclaimer: I have so far acted as if Diadectomorpha had a branch-based
definition. I don't know if it has any definition. A branch-based one
would fit historical and current usage best, however.)
Why are Solenodonsaurus and Procolophon not considered close to this
group (see below)?
I simply forgot about *Solenodonsaurus*. It's either the sister-group of
(Amniota + Diadectomorpha) or the sister-group of the whole
(Seymouriamorpha + (Lepospondyli + (Amniota + Diadectomorpha))) clade
according to recent analyses; unfortunately all specimens are badly
preserved (I happened to see the best one in Berlin) and therefore
difficult to interpret. For instance, there are two possibilities for
where the dorsal midline of the skull is.
*Procolophon* is an ordinary amniote. More precisely, an unremarkable
sauropsid (except for its adaptations to herbivory). Even more
precisely, it's a deeply, deeply nested procolophonoid; more
plesiomorphic ones like *Owenetta* look like standard basal amniotes. I
don't understand why you bring it up. Is it the herbivory by
labiolingually broad teeth, shared with Diadectidae, but even more so
between the latter and *Trilophosaurus*?
If Westlothiana is the basalmost lepospondyl, which genera are its
closest sister taxa?
By "basalmost" I mean that the entire rest of Lepospondyli, quite
possibly including Lissamphibia, _as a whole_ is its sister-group.
Every taxon has _one_ sister taxon, except if it forms part of a hard
polytomy ( = a case where a population _really_ split into three or more
clades simultaneously -- soft polytomies are gaps in our knowledge where
we haven't figured out the exact sequence of dichotomies yet, hard ones
are what the real ones are called).
Why not Paleothyris?
Because it's a standard-issue sauropsid, close to Diapsida. Shares
nothing with *Westlothiana* except plesiomorphies.
If Macrocnemus is an archosaurosaurormorph, which taxon is its
closest sister taxon?
Why not Jesairosaurus?
I didn't say it's not. Nobody knows. There is as yet no phylogenetic
analysis which includes all relevant taxa.