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Luck of the neornithines.
Trying to connect several recent threads (my source for data is Chiappe,
L.M. 1995 The first 85 million years of Avian evolution. _Nature_
No non-neornithine fossils have been found after the Cretaceous. Chiappe
believes enantiornithines probably became extinct _before_ the K/T and
notes that indeed the last record of several lineages (of
non-neornithines) was before the Maastrichtian.
In contradiction to Feduccia's sole-shorebird-survivor-cracking-crabs
followed by post K/T neornithine radiation, Chiappe notes "There is
compelling evidence documenting the presence of several lineages of modern
birds at the end of the Cretaceous. Taxa closely related to extant
anseriforms, gaviiforms, charadriiforms and procellariiforms have been
found in Campanian and Maastrichtian rocks..."
Taken together this evidence suggests not a winner-take-all roll of the
dice at the K/T, but a gradual replacement of one clade by another! To
argue against this one would have to argue not against the
conclusion, but against the evidence which leads to the conclusion.
I am certainly not competent to do this but it would seem to me that the
fossils, as the ultimate arbiter of such disputes, have arbitrated this
How would one species be replaced by another. Of course it wouldn't have
to be competition, but it may have been. And, to explore the idea
of neornithines possessing winning adaptations it is relevant to note--as
Chiappe does--that neornithines and enantiornithines were quite different
from each other. Among these differences was probably the faster growth
rate (I'm not sure if this is argued--Chiappe is pretty
categorical about it), and the advanced development of hindlimb kinematics
in the neornithines. In terms of agility in flight, the latter
characteristic may have been very important.
So this was a very big deal--for the first time in the world's history all
the birds had beaks and advanced flight characteristics. The neornithines
seem to have completely usurped other species. In addition, the fossil
record appears to exonerate the K/T "event" completely from having any
role in this.