Re: quick ?: dinos and birds

[forelf@internet19.fr (Francoise Forel)]

> Landry:
> 
> Birds are not the closest extant relatives to dinosaurs; they -are-
dinosaurs,
> in fact, they are advanced maniraptoran theropods and probably the sister
> group to dromaeosaurids.  
> 
> Dinosaurs were at one time suspected to be diphyletic (that is, having
evolved
> from two separate ancestors and grouped together without including the
groups'
> common ancestors), but recent research has proven that dinosaurs really
are
> monophyletic after all.  Dinosaurs are united by a suite of characters,
which
> includes specializations in the limbs, three or more sacral vertebrae,
and a
> perforate acetabulum (the lattermost feature having been subsequently
lost in
> advanced avians).  
>

Dinosaurs were sometimes thought to have evolved from three or even more
ancestors, I think.
Thye idea that dinosaurs are monophyletic isn't  that recent. The first
person who formulated it was Owen (1842). Seeley (1888, I think) convinced
everyone that dinosaurs were diphyletic. Bakker and Galton (1974) first
argued for monophyletic dinos after that. I don't think 1974 research
should be called recent, with all the new discoveries that have occured
since then.
 
> Since birds are dinosaurs, the closest extant relatives must therefore be
> crocodylians, the only living archosaurs aside from birds.  As both
dinosaurs
> and lepidosaurs (lizards and the like) are reptiles (in the modern sense),
> they are related to some extent, but not closely.  Crocodylians are more
> closely related to birds than they are to lepidosaurs! 
> 
> Well, I hope that helps clear things up.
> 
> Rachel Clark
> 
> "You will respect my authori-TAY!" 
> 

Felix Landry
e-mail: forelf@internet19.fr