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Re: diminutive dinosaurs



--- Adam S Smith <sea_saur@yahoo.co.uk> wrote:
>  The person asking the question was, I
> > think, more interested if any
> > dinosaurs might have been diminutive for other
> > reasons. 
> 
> I was indeed. Perhaps if I take theropods out of the
> equation, then we don't have a problem. 

Well, there a plenty of nonvolant theropods (many of them are even avian).
 
> It seems biologically
> possible for, say, a minute sauropod to occupy a small
> lizards niche, given enough time to evolve.
> Furthermore, A sauropod in a lizard niche would
> naturally become lizard-like, and would taxonomically
> be distinct from sauropods sensu stricto, in the same
> way that the Aves are taxonomically distinct (but see
> ongoing discussion!) from non-avian theropods.

Or in the same sense that *any* clade is "distinct" from any paraphyletic group
that includes the clade's immediate ancestors, but not the clade itself.

If a lineage of sauropods were to somehow evolve into lizard-like forms, it
would be gradual, and there would be no special point at which they were no
longer sauropods. (Heh ... come the think of it, the name would be far more
apt! Real sauropods have extremely unlizardlike feet....)

> A problem with a crown-group definition of birds (and
> crown-groups as a whole) is that it is forever-
> changing and ultimately doomed.

Not if you are specific, e.g., "extant at time of publication".

The utility of crown clades is, I think, that they denote the clade for which
soft tissue, behavior, complete DNA sequences, etc. are known.

Incidentally, if you are using the crown clade definition of _Aves_
(=_Neornithes_), then _Liaoxiornis_ would be a pretty tiny non-avian dinosaur.

=====
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