Neat review, but I'd query some of the inferences regarding theropod anatomy.
Firstly, there's the transformation of the forelimbs into wings. The authors make the point that cranial kinesis in birds "enhances dexterity and precision of the bill - faculties that became all the more important as the ancestors of birds sacrificed hands capable of fine manipulation in favour of wings as avian flight arose". This is a rather old view, that theropods gave up their grasping abilities as the forelimb became a wing. However, the evidence suggests that theropods didn't have much in the way of grasping abilities in the first place. In general, given their constrained mobility and limited reach (even in long-armed theropods), it's no surprise that in certain lineages the forelimbs became dedicated to functions such as display or flight (or both). (It's also no surprise that in many theropod lineages the forelimbs were drastically reduced and almost disappeared altogether.)
Secondly, the size of the sternal keel and its proposed role in take-off from the ground. According to Field &c, the more extensive sternal keel of Euornithes is related to an increased need for ground-level take-offs. Thus, the well-developed keel is associated here with the more terrestrial or semiaquatic lifestyles of euornithine birds; this contrasts with enantiornithines, which tended to be more arboreal (though not all, e.g., _Elsornis_). But in modern birds the take-off is initiated by the hindlimbs, regardless of whether the bird is in a tree or on the ground. The ability to take-off from the ground likely goes back to flying terrestrial theropods like _Microraptor_ and _Archaeopteryx_, with the launch similarly hindlimb-driven.
Also, the Avisauridae (a Late Cretaceous enantiornithine clade), evolved a well-developed sternal keel convergent with euornithines (as noted by Field &c); but avisaurids have a highly specialized perching pes, which suggests a highly arboreal lifestyle. So the proposed link between a well-developed sternal keel and a more terrestrial lifestyle doesn't hold. The well-developed keel has probably more to do with more advanced flight abilities rather than a terrestrial versus arboreal ecology.