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Secondarily flightless birds or Cretaceous non-avian theropods?



Kavanau, J. L. 2009. Secondarily flightless birds or Cretaceous
non-avian theropods? Medical Hypotheses, in press.
doi:10.1016/j.mehy.2009.09.015

Summary:
Recent studies by Varricchio et al. reveal that males cared for the
eggs of troodontids and oviraptorids, so-called “non-avian theropods”
of the Cretaceous, just as do those of most Paleognathic birds
(ratites and tinamous) today. Further, the clutches of both groups
have large relative volumes, and consist of many eggs of relatively
large size. By comparison, clutch care by most extant birds is
biparental and the clutches are of small relative volume, and consist
of but few small eggs. Varricchio et al. propose that troodontids and
oviraptorids were pre-avian and that paternal egg care preceded the
origin of birds. On the contrary, unmentioned by them is that abundant
paleontological evidence has led several workers to conclude that
troodontids and oviraptorids were secondary flightless birds. This
evidence ranges from bird-like bodies and bone designs, adapted for
climbing, perching, gliding, and ultimately flight, to relatively
large, highly developed brains, poor sense of smell, and their feeding
habits. Because ratites also are secondarily flightless and tinamous
are reluctant, clumsy fliers, the new evidence strengthens the view
that troodontids and oviraptorids were secondarily flightless.

Although secondary flightlessness apparently favors paternal care of
clutches of large, abundant eggs, such care is not likely to have been
primitive. There are a suite of previously unknown independent
findings that point to the evolution of, first, maternal, followed by
biparental egg care in earliest ancestors of birds. This follows from
the discovery of remarkable relict avian reproductive behaviors
preserved by virtue of the highly conservative nature of vertebrate
brain evolution. These behaviors can be elicited readily by exposing
breeding birds to appropriate conditions, both environmental and with
respect to their eggs and chicks. They give significant new clues for
a coherent theory of avian origin and early evolution.

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Only two pages, nothing earth-shaking here.

Cheers,
Nick Gardner