[Taxacom] Reptilia

[Elise Tancoigne]

Dear Kenneth,

To compare the two sentences "Birds are dinosaurs" and "Birds are 
descendants [of some] dinosaurs"  you have to precise what you mean with 
"Dinosaurs" and "Birds".
I guess there's no problem for the meaning of "birds" ; it appears for 
"dinosaurs", which can have at least two meanings. It comes from the 
fact that in our working area, words remain while their meaning change.

If you use "Dinosauria" to designate the paraphyletic group which 
doesn't include the Birds, then "Birds are descendants [of some] 
dinosaurs" would be more correct.
On the other hand, if you use the word "Dinosauria" for the monophyletic 
group which includes Birds, you may say that "Birds are dinosaurs".

So, the question is not "what are the forbidden/allowed words ?" but 
"what's the consensual meaning of the word I use ?" and "do I recognize 
the theoretical changes it underlies ?"
If I agree with the fact that we are looking for monophyletic groups to 
build phylogenies, then I have to use the names in their new, 
monophyletic, meaning. If I disagree, I will use the word in its 
previous meaning. In this case, as this meaning is not the consensual 
meaning used by the scientific community, I will have to precise it.

Of course, it is also useful to have names for paraphyletic groups, 
particularly in non-phylogenetic contexts. For example, in an ecological 
discussion, I may need the word "dinosaurs" in its old sense, or the 
word "fish". But I will have to precise how I define it, if many 
definitions have existed for it.

(I hope I'm not too disorganized, and understandable : please accept my 
apologies for my english mistakes !)

Elise Tancoigne,
Muséum national d'histoire naturelle
Paris


Kenneth Kinman a écrit :
> Dear All,
>      As David noted, Reptilia is "real".  I have often wondered if such
> taxa would become more acceptable if we stopped calling them
> "paraphyletic" and instead called them truncated clades.  I see no
> problem in separating off Class Aves, as long as I put an {{Aves}}
> marker in Class Reptilia next to its sister group (and the same with
> Class Mammalia).     
>       The study of tetrapod vertebrates has long been separated into
> three (Herpetology, Ornithology, and Mammalogy).  The latter two study
> clades (Aves and Mammalia), while Herpetology studies a truncated clade
> (Tetrapods minus birds and mammals).  Is there any good reason not to
> continue doing so?  Likewise, the study of Ichthyology also studies a
> truncated clade (Vertebrates minus tetrapods).  Seems like a pretty
> useful concept to me, whether you call them paraphyletic taxa or
> truncated clades.  
>          --------Ken Kinman                                   
> P.S.  Why is the phrase "Birds are dinosaurs" any more correct or useful
> than "Birds are dinosaur descendants".   The latter actually seems more
> precise and preferable (except to those who forbid a truncated clade
> like the traditional Dinosauria).
>
> -------------------------------------------------------------      
> David Campbell wrote: 
> "Real" is of course a problematic term. Reptilia is a paraphyletic group
> of organisms with certain similarities that provide or exclude certain
> ecological options, so in one sense it is "real"; however, almost all
> phylogenetic analyses do not support it as monophyletic, and those that
> have can readily be explained as being misled by plesiomorphic or
> convergent features. 
>
>
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