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Re: Synapsids weren't reptiles?



Comments inserted:

> > I am looking at an article in the March 2008 issue of
> New Scientist.   It's
> > a discussion about missing links or something; I seem
> to be missing the
> > first page.
> >
> > It says that synapsids "were once" called
> mammal-like reptiles, bot no more,
> > "because synapsids are not reptiles -- the two
> groups evolved in parallel
> > from a common ancestor".
> >
> > What was the common ancestor - an amphibian?

Keep in mind tetrapods like Icthyostega were not amphibians under the current 
definition, and reptiles did not evolve from amphibians.
Calling Icthyostega an amphibian is about as valid as calling something like 
Coelophysis or Gallimimus an Ostrich.
- Similar body forms/ lifestyles, one preceeds the other, and there is a close 
evolutionary relationship, but one is clearly not the other.

The common ancestor was a tertapod - probably living at least a partially 
aquatic/amphibious lifestyle, but it was not an Amphibian (although don't some 
still argue that temnospondylii are predecessors to salamanders?, if so, would 
that make amphibians paraphyletic?)
> 
> No, an amniote. The first amniote, which was neither
> synapsid nor
> sauropsid, but was immediately ancestral to synapsids and
> sauropsids.
> (The authors are probably using "reptile" to
> refer to some group
> within _Sauropsida_, although arguably the term
> "reptile" should just
> be abandoned.)
Why should reptile be abandoned? what is wrong with using it synonymously with 
sauropsid? is it because some use it paraphyletically by excluding the bird 
node?
Should the term "fish" be abandoned? After all cladistically - we are 
lobe-finned fish. Unless you define fish paraphyletically, it becomes quite 
correct to call whales and doplhins "fish". Yet people still know what you are 
talking about when you say "fish"- so it is still usefull, and thus shouldn't 
be abandoned.
I'm ok with para-phyletic groups that exclude a node, as long as the exclusion 
is explicitely noted within the group definition, and it doesn't confuse 
evolutionary relationships.
However, I would not be ok with excluding the tetrapod node from fish, and then 
including the cetecean+piniped+Icthyosaur, etc nodes. - I can accept 
paraphyletic groups as usefull clasification if they exclude a node, and don't 
re-include select groups from an excluded node.

How else do we talk about studying lobe finned fish today (lungfish, 
ceolocanths) without considering whales, birds, humans, snakes, etc? 

Synapsids clearly weren't reptiles- they likely had no scales, didn't excrete 
uric acid, didn't have beta keratin, etc.
So even though I am fine with paraphyletic groups in some cases, I'm not ok 
with calling all amniotes, excluding the mammal crown, reptiles.
> 
> "Synapsida" is generally used to refer to the
> mammalian total group
> nowadays (i.e., everything sharing closer ancestry with
> mammals than
> with any extant non-mammal). Other names for this group are
> "Theropsida" and "pan-Mammalia".
> 
> A preferable term for the paraphyletic group that used to
> be termed
> "synapsids", "mammal-like reptiles",
> etc. is "stem-mammals" (i.e., the
> mammalian stem group: the total group minus the crown
> group).
So, would a preferable term, in your opinion, for the older more traditional 
definition of reptiles(which does not include birds), be stem-birds - i.e. the 
sauropsid stem group minus the crown bird group?