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RE: Leaellynasaura, Tails, and Integument
Of the various complete dromaeosaur tails known to date, curvature in them is
shallower than is know in less "confined" tails, such as those of
similarly-preserved ornithomimosaurs. Alternately, curvature appears to be
unknown in hadrosauroid tails where a lattive is present, and the tail of
*Homalocephale* shows no curvature with a dense sheath of ossified "tendons"
surrounded the vertebrae and haemal arches.
Some people have suggested that the caudal rods in dromaeosaur tails did not
inhibit that much curvature; that it (in extension) would be possible to bend a
tail much like a standard "unenclosed" tail. No one, that I know of at least,
has done a curvature analysis on the tail by excluding the rods, or even to
assert if this would tell us anything. If the bone's inflexibility does not
inhibit standard curvature, how do we test this? Do we artificially remove the
rods from dromaeosaur tails (digitally, perhaps?) and test their flexibility
through manipulation? Is the shape of the prezygapophyses substantially
different if you lose the rods? Testing the flexibility of the rods alone as
bone or half-tendon/half-bone, or some composition inbetween, might help
determine restrictions on tail flexibility.
But then there's the other issue: unlike mammals and birds with ossified
tendon sheets, ossified tendon lattices in iguanodontian ornithischians form an
actual lattice crossing as much as 8-10 vertebrae in the dorsal, sacral, and
caudal regions. If the ossified features in dromaeosaur tails are seemingly
uninhibiting or not as inhibiting as thought (for reasons that haven't been
quantified in print), the tendon lattice in iguanodontians is less secure:
presumably, these tendons were bound to their corresponding vertebrae, but are
they bound to each vertebrae between the two ends, and are they bound to the
tendons that they cross passing at the other angle?
To both of these groups, I would ask: If such a system is not very
inflexible, what is the functional use of a system of ossified tendons (noting
that tendons ossify in mammals when put under high strain, to reduce said
strain) when locking the vertebrae may be more plausible (as in
hyposphene/hypantrum articulations) and conservative of a system? What use then
also is a system where the tail of a dromaeosaur is so inflexible, or the tail
of a hadrosaur so stiff?
Jaime A. Headden
The Bite Stuff (site v2)
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
> Date: Tue, 13 Jul 2010 01:11:55 +0200
> From: email@example.com
> To: firstname.lastname@example.org
> Subject: Re: Leaellynasaura, Tails, and Integument
> quote from a manuscript of mine:
>>>Norell & Makovicky (1999: fig. 21) figure an S-curved,
>>>articulated tail of Velociraptor mongoliensis in dorsal view.
>>>Tracing the path of the tail axis of the Velociraptor specimen
>>>in Rhinoceros 4.0® allows measuring the angle across the
>>>first bend as 98° for the first ten caudals, which translates
>>>to nearly 10° per intervertebral joint.
> That specimen shows extremely elongated zygs. So much for lateral
> stiffening...... OK, compared to crocodiles and especially monitors,
> this IS limited mobility.
> Norell, M.A. & Makovicky, P.J. 1999: Important features of the
> dromaeosaurid skeleton II: information from newly collected specimens
> of Velociraptor mongoliensis. American Museum Novitates 3282, 1–45.
> On Tue, Jul 13, 2010 at 12:29 AM, Dann Pigdon wrote:
>> On Tue, Jul 13th, 2010 at 4:39 AM, Jocelyn Falconnet wrote:
>>> "Dorsoventral and cranial expansion of
>>> postzygapophyses (up to 44% of vertebral body length) on vertebrae in
>>> the terminal half of the tail of L. amicagraphica suggests an
>>> alternative to ossified tendons to provide caudal axial rigidity."
>>> As far as I understand, the caudal vertebrae of *Leaellynasaura*
>>> exhibits several anatomical features seemingly related to the
>>> stiffening of the tail, analogous to the adaptations seen in the
>>> classical theropod and ornithischian examples. Pretty interesting
>>> example of convergent evolution and functional evolution.
>> My question is: would such a stiffening system restrict lateral movement of
>> the tail? If the stiffening
>> was mainly to hold the tail erect, then perhaps it only had to prevent it
>> from bending in the sagittal
>> plane. That might leave enough lateral flexibility to curl the tail about
>> the body - or at least to allow
>> the animal to turn around inside a burrow.
>> Then again, if the stiffening was mainly present in the terminal half of the
>> tail, might the base of
>> the tail be flexible enough for a cute little Leaellynasaura to tuck it's
>> sleepy head and neck under it
>> in a suitably adorable fashion?
>> Dann Pigdon
>> Spatial Data Analyst Australian Dinosaurs
>> Melbourne, Australia http://home.alphalink.com.au/~dannj
The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with