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342 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
laterally and slightly dorsally is evidence for raptorial adaptations
early in theropods."
2. WHAT CAN CLAWS TELL Us?—Kenneth Parkes precipitated
some lively discussion by saying, "I'd like to get back to
the previously suggested rejection of trees as a source of gravity.
I was very impressed at the Archaeopteryx conference with
a paper that John will remember, where direct comparisons
were made of the claw morphology of bark-climbing and nonbark-
climbing organisms—lizards, squirrels, and birds
[Yalden, 1985]. He found that the morphology of the claws of
the bark-climbing animals differed from the ground-dwelling
forms but were exactly like those of Archaeopteryx. After that
paper, I recall you John [Ostrom] saying, 'I am convinced.' So
if Archaeopteryx did not go up trees, why did it have treeclimbing
claws?" Paul quickly reminded us of the potential
flaw in arguments that place Archaeopteryx in trees by saying,
"There's an alternate hypothesis to trees; there is a scmb cover
problem with that hypothesis in that there were no trees. Arid
islands with a scmb cover—zero trees."
Paul Buhler, however, pointed out, "The problem is that you
can have desert and an inland sea and still have a nice forest
not too far away. In the Solenhofen near Eichstatt they have
found dragonflies and other aquatic insects. That means that
not too far away there must have been a forest present which
was denser than the one documented in the fossil record. So
you cannot tmst the fossil record in the immediate vicinity of
the specimen to reflect the ecological situation of the entire
surrounding area."
"The claws of Archaeopteryx are indeed, in superficial form,
similar to something like a woodpecker," added Stefan Peters,
"but they are not strong enough. There are claws in animals
that do not climb at all; for instance, in some cuckoos you will
find claws that look like the claws of climbers. It may be a
climber has to have claws similar to this or that, but you cannot
reverse this argument. You cannot say, 'If I find an animal with
such claws, it must have been a climber.' Lions, for example,
have very similar claws but do not climb very often. We published
a paper on this; I am not very convinced by this argument.
As far as I can see, the claws [of Archaeopteryx] are the
only argument which remains for the arboreal theory."
3. WHAT ARE THE LIMITATIONS OF THE CURSORIAL THEO­
RY?—After discussing the above evidence, which lends some
support for the notion that the flight of birds arose from an arboreal
ancestor, discussion of evidence in support of the "cursorial
theory" was inevitable. Buhler initially asked, "What
benefit can you get by mnning along and getting away from the
earth [using wings]? There is a problem—the most probable
situation is that the animal is a prey which is mnning away. In
that case, by jumping from the ground the animal will be giving
up its energy transformation system. That means it will be
getting slower by gliding or flying, and I cannot think of any
possibility where mnning and jumping into the air will be advantageous."
To address the question about possible advantages of leaving
the ground through flight, Ted Goslow asked, "Our work on
the organization/action of the supracoracoideus in birds has led
us to wonder if just the act of getting out of the way, or of taking
off quickly, could be reason enough. Could early flight
have been an erratic behavior to evade predation by jumping
from the ground or from a tree for that matter? Does this make
any sense?" Storrs Olson responded by saying, "In the case of
flying from trees where you are going into a different medium
and you are experiencing an optical change it does, but not in a
terrestrial situation."
"Among students of mammalian locomotion," noted Goslow,
"the question of why saltation [richochetal locomotion] as
a form of locomotion would ever evolve is often asked. Is not
one possible selective advantage thought to be predator evasion
through erratic movements?"
Virginia Naples indicated that two points need to be considered
in any discussion of leaping and its relationship to early
flight. "If an animal is mnning and intends to jump and remain
in the air for any length of time, that animal must get high
enough to complete a downstroke, an upstroke, and a second
downstroke in order to stay in the air. Secondly, I am concerned
that if you are leaping into the air to escape a predator or
startle a predator, you are only going to be successful if you
also change direction. That requires a tremendous level of
[neural] sophistication in terms of maneuverability in flight,
and I do not know if these early forms were capable of this."
"We have a modern analog," said Sankar Chatterjee, "the
kangaroo. They jump, they leap, but they never use their forelimbs
in any way suggesting flight. It doesn't matter how far or
how long they jump—they never use their forelimbs."
"This brings up another point," said Storrs Olson, "although
I do not know how related the origin of flight is to the evolution
of bipedality, but when you have bipedal, terrestrial animals,
the tendency is always to shorten the forelimbs. You have kangaroos,
kangaroo rats, and humans. When animals come down
from the trees and assume a terrestrial position, the forelimbs
are shortened. This is directly against everything that happens
with birds where you have elongation of the forelimbs."
John Ostrom recalled that in 1974, "I wondered why Archaeopteryx
had hands that were designed like 'flyswatters.' I
thought maybe the primaries could be used as flyswatters [Ostrom,
1974]. Critics at the time did not like this, and I do not
blame them; now I have a better understanding of powered
flight. A former student, Rick Vazquez, described how the
hand of a bird is supinated upon the trochlea carpalis and how
this supination acts to streamline the upstroke [Vazquez, 1992].
I illustrated this morning in my presentation how this ability
was already present in dromeosaurs, such as Deinonychus and
Velociraptor. There is something in the gene pool which allows
for this. In modem birds, for example the starling, a wingbeat
cycle occurs in just 70 milliseconds. In these small birds at
least, the wing must supinate many times per second and it
does so automatically. Archaeopteryx had this same ability. It