By "diversification" I take it they are referring to ancestry.
|Modern birds occupy a wide diversity of |
niches and exhibit a variety of behaviors. The
broad structure of our phylogeny suggested diversification
along general ecological divisions,
such as water birds, shorebirds, and land birds.
As I have said, the ancestry of birds was into a few major branches with subbranches off those major branches.
The authors of this study confirm this, presenting the major branches as "water birds, shorebirds, and land birds".
And the authors confirm the subbranching when they say:
They are confirming exactly what I have proposed.
|adaptations to these environments clearly arose multiple times,|