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
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.
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