Walker quaternary dating
Solid lines show geological ranges of taxa with first and last occurrences shown by squares. (2006) described the earliest penguin fossils and analyzed complete mitochondrial genomes from an albatross, a petrel, and a loon. Dashed lines show postulated phylogeny compiled from the literature (Slack et al. The penguin fossils were from a Paleocene (early Tertiary) formation just above a well-known Cretaceous/Tertiary boundary site. Single origin of a pan-Pacific bird group and upstream colonization of Australia. Fossil Evidence for the Extant Avian Radiation in the Cretaceous -- Clarke et al. (2005) provide apparent evidence that cousins of living birds coexisted with dinosaurs more than 65 million years ago. How are birds currently distributed throughout the planet and what factors have contributed to this distribution?
Birds occupy all continents and habitats but, of course, some continents & some habitats have more species than others.
This explosive, punctuated model, following a major extinction event, reflects the standard pattern of vertebrate evolution, especially documented following the Permian extinctions.
Yellow areas indicate the subclass Ornithurae; blue areas indicate the subclass Sauriurae (From: Feduccia 2003).
These taxa are extinct today, but by the close of the Cretaceous, representatives of several modern bird taxa were sharing the skies with these extinct birds.
A birdwatcher 65 million years ago could have seen relatives of today's loons, geese and ducks, albatrosses and petrels, and gulls and shorebirds, and possibly other familiar birds as well.