Another possible explanation for the survival of neornithine birds across the K-T boundary occurs in the
recent NAPC abstracts. Here's the URL for the abstract, by Judd Case.
Dr. Case notes that the Antarctic record of Maastrichtian birds appears to consist exclusively of
neornithines, in contrast to other sites in Gondwana, where enantiornithines occur. I'm speculating
wildly here, but perhaps the geographic distance of Antarctica from the K-T impact site provided enough of a
"buffer" to muffle the full effects of the impact, allowing some neornithine lineages to survive the K-T event.
These survivors could then disperse to other areas where the impact effects were more severe. This could
provide a possible selection mechanism for the survival of neornithines vs. enantiornithines across the K-T
boundary. Neornithines survived because they happened to live in Antarctica, while no enantiornithines survived
because they didn't. The neornithines could have been in the right place at the right time,
an explanation Steven Jay Gould might find intriguing... ;-)