[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



No quantitative data, David. There are other interesting things about
the theory of the slashing dromeosaur ungual:

-In sabertooths, for stabbing large prey they need enlarged neck
musculature, as indicated by the enlarged mastoids processes, and
perhaps the prominent nuchal crests. I cannot see such enlarged
attachment areas of muscular insertion in the hindlimb of
Deinonychus, overall of the origin of the musculature for the digital
flexors in the tibiotarsus or tarsometatarsus. I acknowledge there is
a well-developed cnemial crest, but not better developed than in most
other theropods. Thus, if musculature for stabbing in sabertooths is
so hypertrophied for just stabbing, one can suppose that Deinonychus
should have even more hypertrophied musculature for slashing, that
requires more strenght than stabbing.

-Among human blade weapons, I do not know of slashing weapons where at
the same time the flesh of the enemy/prey is hitted by an edge and a
long point at its extreme (although most blade weapons are made to
kill other humans, not elephants).

-the transversal compression of the ungual, being there a ventral edge
or not, can be alternatively related to increase resistance in the
direction in which the point of  the ungual enters, which is not
latero-medial (it would give the claw greater resistance to the
shearing forces acting on the base of the ungual).

-Large prey killing would require Deinonychus to jump over its prey
and perhaps climb on it. The criticism to the arboreal paravian
theory, that deinonychosaurs do not present special climbing devices,
may apply to it climbing prey (although prey's hide is softer than
tree bark, so it is more easy to sunk the claws there). For example,
perhaps the relative robustness of Smilodon when compared to the lion
may enable the sabertooth to climb its large prey – somewhat
off-topic, most cats climb well, but lions seem to be much large for
the general cursorial construction of cats to permit them to support
their weight; cursorial adaptation likely do not permit them to exert
the forces that climbers of comparable size, but not cursorial, such
as black bears and gorillas, can exert-. The forelimbs of Deinonychus,
even possessing large unguals, are too slim to suggest this
leopard-sized animal (Ostrom 69') could climb or support itself so
easily to the prey. With its short metatarsus (Ostrom 76'), its
ability as a leaper would also not be so good.

-In Ostrom's 1969 work, fig. 74, digit II ungual is well removed from
the ground when the metatarsus form a less than 90 ° angles with the
soil behind the ground-foot contact. This occurs on early phases of
the step. However, at later stages of hindlimb retraction (near the
end of the step), the metatarsus will form an angle greater than 90°
with the soil behind the ground-foot contact. Here it seems that the
claw cannot be maintained so far from the ground at retraction.

-Greater range of extension in digit II is seemingly common in other
dinosaurs. For digits II-IV to be approximately subequal in lenght (as
in Deinonychus), digits with more interphalangeal articulations (as
digit IV) would theoretically be more flexible and capable of more
extension and flexion than digits with less interphalangeal
articulations (as digit II) if all interphalangeal joint permitted the
same movement range, so that more lateral digits would be more
"extendable" and "flexable". This can be compensed if the
interphalangeal joints of the digits with less phalanges (digit II)
permit greater freedom of movements, and would not necessarily imply
an hyperextended position.

-Ungual phalanx of digit II is larger than those of digits III and IV
in most birds, perhaps related to the fact that to have digits II-IV
of similar lenght, the less numerous phalanges of digit II have to be
more elongated. This being said, I recognize the digit II ungual in
dromaeosaurs is elongated with respect to the two phalanges basal to
it, and the whole feet, in relation to what is seen in other
dinosaurs.

Again bothering everybody with weird applications of the EPB, but many
birds hit with their limbs when attacked (yesterday I saw a hen with
chicken flying half a meter from the ground against a boy and throwing
kicks in the air towards him – the boy fled), what is better
accomplished by cassowaries (with large digit II ungual) and
ostriches, which are said to have killed dogs. Seriemas and secretary
bird seem to use the digit II claw to kill small prey, of course they
are not entirely comparable, and perhaps rather derived, although I
heard of chicken killing snakes with both feet and bill. So, with use
of the EPB, may we think of a defensive, intraspecific fighting, or
not-so bigger than itself prey predation function for the ungual in
paravians?