Fossil gap analysis supports early Tertiary origin of trophically diverse avian orders

Abstract

Recent molecular studies have cited the general incompleteness of the fossil record to support claims that most extant avian orders diverged in the mid-Cretaceous, some 40 m.y. before their first fossil appearances in the early Cenozoic. To evaluate these assertions, I used gap analysis to estimate confidence intervals for the beginnings of the observed stratigraphic ranges for the related extant avian orders Strigiformes (owls), Caprimulgiformes (goatsuckers), and Apodiformes (swifts, hummingbirds), and for the origin of the common ancestor to this larger megaclade. Ninety-five percent confidence intervals for the origins of these groups extend no more than 2 m.y. before the Cretaceous-Tertiary (K-T) boundary and are contained within the Paleocene for strigiforms, apodiforms, and the common ancestor to the megaclade. The confidence level that these orders diverged from a common ancestor after the K-T boundary exceeds 99%. Thus, the quality of the fossil record is consistent with the classical view that trophically diverse extant bird orders arose and diversified rapidly following the widespread extinction of other terrestrial groups at the K-T boundary.