A field guide to mesozoic birds and other winged dinosaurs

Unenlagiines
“Half birds”, a highly specialized group of wading ornithodesmids
adapted to heron-like ambush fishing. They are the only frond-tailed
birds found below the equator, and the only definitive long-tailed birds
from the southern continents. Because flight is only known to have definitively
appeared in ornithothoraces (enantiornitheans & euornitheans),
it is unknown how this group was able to disperse to South America and
Madagascar. The possible primitive unenlagiine Rahonavis ostromi, though
fragmentary, shows well-developed wings and may have had adequate
enough powered flight to “island hop” between the northern and southern
continents, subsequently spawning a secondarily flightless radiation of fishers.
As in modern flightless birds, the feathers of the flightless unenlagiines
probably became long and plumulaceous (downy or open-vaned).
92