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This includes a conservative estimate that modern sea and shorebird lineages diverged at least by the Late Cretaceous about 74 million years ago. It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Additional fossils and molecular data are still required to help understand the role of biotic interactions in the evolution of Late Cretaceous birds and thus to test that the mechanisms of microevolution are sufficient to explain macroevolution.
Prominent and well-known Cretaceous bird taxa included the Enantiornithes, a fairly diverse group of birds, mostly flying forms; Hesperornithiformes, toothed birds (see drawing below) which were mostly flightless swimmers; and Ichthyornithiformes, toothed flying birds that probably fed on fish. The fossil record also indicates that some groups once occurred in areas well outside their present range (e.g., parrots in Wyoming), while others have apparently always been limited to certain areas: The past history of bird distribution can, to varying degrees, be inferred based on present distribution & the geological history of changes in climate, sea level, and the location of land masses. The distribution of some groups of birds may have been influenced by continental drift (Cracraft 1974). The most plausible hypothesis requires at least three losses of flight and explains the many morphological and behavioral similarities among ratites by parallel or convergent evolution. Credibility intervals (95%) are indicated by grey bars at numbered internal nodes. Periods when Antarctica was ice-covered (black continuous bars) are indicated by shaded grey rectangles. Finally, this phylogeny demands fundamental reconsideration of proposals that relate ratite evolution to continental drift. Ocean temperature is based on high-resolution deep-sea oxygen isotope records. Origin and expansion of penguins -- Classic problems in historical biogeography are where did penguins originate, and why are such mobile birds restricted to the Southern Hemisphere?