DECEMBER 2002
SVP Talks From Oklahoma Meeting
Here are notes on some of the interesting talks that were presented in early
October.
Elephant bird embryo - Amy Balanoff and Tim Rowe report exciting CT scan of the
egg of an extinct elephant bird, Aepyornis allowed them to see the bones of the
embryo and reconstruct them with rapid prototyping. In this way they can study
the copies of the bones outside the shell without damaging the egg or the
embryo. This is very exciting because of the implications for this procedure and
method. They can see amazing detail in the skull including things like the path
of arteries into the braincase. The postcranial skeleton was not as developed
due to the early age of the embryo but should be helpful in determining the
growth pattern of the elephant bird.
Mososaur soft tissue – N. Geist et al report on a Kansas mososaur specimen of
Platecarpus found with extensive preservation of soft tissue including
integument. There are two large stains which may have been indications of
internal organs, possible the liver and kidney. Analysis of the stains showed
high concentrations of high molecular weight organic compounds and iron not
found in the nearby matrix.
Paul Sereno – Abelisaurid Theropods from Africa: Phylogenetic and Biogeographic
Implications. There were two new abelisaurids that he found in Niger.
Jack Horner and Glenn Storrs – Keratinous Covered Dinosaur Skulls. The skulls of
horned dinosaurs like Triceratops are known to have groves along its surface
believed to have been for blood vessels to the epidermal layer. They believe
that the keratinous sheath may have covered the whole skull top and bottom.
Lawrence Witmer, Chatterjee et al– Anatomy of the Brain and Vestibular Area of
two Pterosaurs: Implications for Flight, Head Posture, Behavior. Acid prepped
skulls of a more basal Rhamphorhyncus from Solnhofen and a Cretaceous Anhanguera
were compared. Pterosaurs had relatively smaller brains per body size than birds
probably because of birds evolution from larger brained dinosaurs. The large
semicircular canals indicate a well refined organ of equilibrium. However, the
orientation of the vestibular apparatus relative to the long axis of the skull
was different indicating very different head postures. Rhamphorhyncus had a
horizontal orientation while that of Anhanguera was strongly angled down. These
should affect feeding and aerodynamic effects.
Gary Bir and Robert Bakker – Dinosaur Social Life: Evidence from Shed Tooth
Demography. Using crocs as a model they determined that in the Late Jurassic
Como Bluff area baby croc teeth were only found in sheltered areas where they
were protected by parents. The larger teeth of juveniles and adults were found
in open water sites. Few teeth from large adults are found because few live that
long. They found that this trend was true for theropod dinosaurs in Como also
with hatchling teeth found in association with those of older juveniles and
adults. They also determined that they had a 100 times better chance of reaching
adulthood than crocs.
David Krause et al – Claw Geometry is an Indicator of the Terrestrial Habits of
Pterosaurs. They studied the claws of 100 pterosaurs and related them to the
claws of birds to determine that pterosaurs were predominantly non-arboreal and
walked bipedally, using their hand claws for food manipulation. The mean foot
claw measurements were the same as those for walking birds while the hand claws
were like the claws of perching birds.
Frank Sanders and Ken Carpenter – Mechanics of Stegosaur Tails as Weapons. A
mathematical model was made based on the tailbones of a stegosaur, their maximum
articulation angles, their degrees of freedom, and inferred muscle mass. A model
was made of metal bones with springs as muscles and they calculated the range of
movement (13 degrees from the median) and the maximum force generated (enough to
easily pierce the skin of an Allosaurus). There is a damaged Allosaur tail
vertebra and a stegosaur with a broken spike that might have become embedded in
an attacking allosaur.
Scale to Feather Transition Explained
The University of California has shown experimental steps in the origin and
development of feathers using molecular biology. A Nature article by C. Chuong
et al try to tackle the problem of the first feather because of all the new
Chinese feathered bird specimens being reported. Are they feathers,
protofeathers or something else entirely? A common belief is that the scales
elongated into rachides that then became notched to form barbs. But there was no
real evidence to back that theory up. Here it is reported that the barbs form
first and then fuse into the rachia. Unstructured feathers or downy feathers are
made up of just the barbs and barbules with no rachis. These downy feathers were
studied on chickens. This study is a good example of the popular new combined
study of evolutionary biology and developmental biology called “Evo-Devo”. They
studied the growth of new downy feathers after plucking them out of chickens and
adjusting the expression levels of the genes (including the popular sonic
hedgehog gene) involved. The result was many abnormal feathers with rachides and
barbs. Each of the three genes studied caused different changes in the
organization of the new feathers. The authors still feel that the transition of
down to flight feathers was probably a very long process that may have taken 50
MY to be refined. However, now they have a better feel for how it could have
happened. This study should also shed some light on the development of other
epithelial organs like hairs, lungs, and many more.
Why Sharks Have Hammerheads
An article by Adam Summers in the November Natural History explains theories
about the hammerhead shark. Common theories are that it improves sensory
perception or that it improves hydrodynamics (the use to hammer prey is
discounted as the delicate eyes are at the hammering ends). The wide head spread
the gel filled electroreceptors used to detect prey. In tests they were able to
sense prey from a greater distance than sharks with regular heads. The wide head
also seems to stabilize them during turns allowing them to turn faster as well.
They also have found that the heads seem to be getting smaller as they evolve.
Karen Nordquist, ESCONI Paleontology Study Group
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