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Sex and the New Papers II
Some free gems from the Proceedings of the Royal Society B:
Manabu Sakamoto 2010 "Jaw biomechanics and the evolution of biting performance
dinosaurs". Proceedings of the Royal Society B.
Despite the great diversity in theropod craniomandibular morphology, the
presence and distribution
of biting function types across Theropoda has rarely been assessed. A novel
biomechanical profiling using mechanical advantage computed for each biting
position along the
entirety of the tooth row was applied to 41 extinct theropod taxa. Multivariate
ordination on the
polynomial coefficients of the profiles reveals the distribution of theropod
biting performance in
function space. In particular, coelophysoids are found to occupy a unique
region of function space,
while tetanurans have a wide but continuous function space distribution.
Further, the underlying
phylogenetic structure and evolution of biting performance were investigated
comparative methods. There is a strong phylogenetic signal in theropod
indicating that evolution of biting performance does not depart from Brownian
Reconstructions of ancestral function space occupation conform to this pattern,
unexpected major shifts in function space occupation can be observed at the
origins of some
clades. However, uncertainties surround ancestor estimates in some of these
internal nodes, so
inferences on the nature of these evolutionary changes must be viewed with
Elizabeth R.Dumont 2010 "Bone density and the lightweight skeletons of birds"
Proceedings of the
Royal Society B.
The skeletons of birds are universally described as lightweight as a result of
minimizing the energy required for flight. From a functional perspective, the
weight (mass) of an
animal relative to its lift-generating surfaces is a key determinant of the
metabolic cost of flight.
The evolution of birds has been characterized by many weight-saving adaptations
reflected in bone shape, many of which strengthen and stiffen the skeleton.
unstudied in birds, the material properties of bone tissue can also contribute
to bone strength and
stiffness. In this study, I calculated the density of the cranium, humerus and
femur in passerine
birds, rodents and bats by measuring bone mass and volume using helium
displacement. I found
that, on average, these bones are densest in birds, followed closely by bats.
As bone density
increases, so do bone stiffness and strength. Both of these optimization
criteria are used in the
design of strong and stiff, but lightweight, manmade airframes. By analogy,
increased bone density
in birds and bats may reflect adaptations for maximizing bone strength and
minimizing bone mass and volume. These data suggest that both bone shape and
properties of bone tissue have played important roles in the evolution of
flight. They also reconcile
the conundrum of how bird skeletons can appear to be thin and delicate, yet
contribute just as
much to total body mass as do the skeletons of terrestrial mammals.
Spatial Data Analyst Australian Dinosaurs
Melbourne, Australia http://home.alphalink.com.au/~dannj