Early evolution of modern birds is fuzzy, so a fossil foot showing unexpected diversity in penguins shortly after the dinosaurs went extinct is big news
Hanneke Meijer is a bird paleontologist. She blogs on Lost Worlds Revisited, part of the science blog network
Wednesday 5 April 2017 08.00 BST Last modified on Wednesday 5 April 2017 10.06 BST
The theory that birds descended from bipedal dinosaurs, Coelurosaurs to be exact, is now well-established within the palaeontological community. With that one out of the way, bird palaeontologists can focus on more pressing issues, such as the origin and evolution of Neornithes, the group of birds that comprises all living birds. Several groups of extinct birds are known to have existed alongside the dinosaurs, such as the aquatic diving birds Hesperornithiformes, the large, toothed Ichthyornithiformes, and the “opposite birds” Enanthiornithidae, named after the distinct anatomy of their shoulder girdle. None of them gave rise to the birds we see in our backyard today.
The early evolution of modern birds is fuzzy, to say the least. Models based on molecular clocks place the origin of Neornithes as far back as the Early Cretaceous, whereas others suggest that modern birds did not diversify until the Late Cretaceous (see Brocklehurst et al., 2012 for a discussion). The sparse fossil record of Mesozoic Neornithes does little to clear things up.
Modern birds can be split into two major groups; the Palaeognaths (meaning “old jaws”) include the flightless ostriches and kiwis, whereas the Neognaths (“new jaws) contains all other birds. The earliest group of birds to split off within the Neognaths was that of the Galloanserae, the group containing the Anseriformes (ducks and allies) and the Galliformes (pheasants, grouse and allies). The earliest Neognath may be the galliform Austinornis lentus, dated to about 85 million years ago (Clarke, 2004), although some doubt about its presumed identity as a galliform remains. The description of Vegavis iaai as a Late Cretaceous (68-66 million years) member of the duck lineage suggests that Neognaths had already split into modern groups before the end of the Mesozoic era. However, whether the radiation of the remaining Neognaths occurred before or after the Cretaceous – Paleogene extinction remains a topic of discussion.