[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: 11th specimen of Archaeopteryx
Scott Hartman wrote:
> I must have a different copy of their paper than you do, as they
> explicitly conclude "Our findings suggest early birds foraged
> predominantly on the ground, rather than supporting previous
> suggestions of arboreal claw adaptations, which appear to have evolved
> later in the lineage."
> Which is of course my point.
Here is precisely the point I have been trying to make. Thank you for
clarifying it. We have the same paper, but there is a distinction or
meaning to that you have not acknowledged.
The second sentence of Glen and Bennett (2007) points out that there is a
'false dichotomy' in the understanding of paleontologists between birds
that live in trees vs. those that live on the ground. The authors' big
contribution was to more quantitatively define this habitat preference
along a continuum.
One large percentage of living birds forage almost exclusively on the
ground. These are called 'dedicated ground foragers" by Glen and Bennett.
There is another percentage that forage predominantly on the ground. These
are called "predominant ground foragers'. Another group forage in trees
and are called 'predominantly arboreal foragers'.
Please acknowledge the following point: all three of these foraging groups
include members that roost or nest in trees.
Arboreal claw adaptations correlate with tree foragers, not tree roosters.
Furthermore, please consult their figure 2C. The spread of values for
Archaeopteryx includes two or three specimens that overlap the
predominantly ground foraging group, and two that are solidly in the
dedicated ground foraging group.
My point is finer than you seem to believe. I agree that the preponderance
of evidence places Archaeopteryx and Microraptor as ground foragers. I am
discussing the possibility that, like other ground foraging basal
paravians like pheasants, grouse, turkeys, and tinamous, they roosted in
trees. That is not an arboreal animal, it is a dedicated ground foraging
The large ratites have no members that roost in trees, so far as I know,
but their body sizes are exclusively larger than the animals we are
discussing here, making direct comparison difficult. Moreover, one taxon
that is sometimes suggested as having been ancestral to ratites, the
lithorithids, apparently do have perching adaptations, possibly making
ratite earthboundness a derived character.
Lastly, on Hopson, please consult his figure 7, 8, or 9, where you can
clearly see that the spread for Archaeopteryx lands in the overlap - below
a few arboreal birds and above most but not all ground birds.