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Andrew Simpson | 1 May 2005 04:12
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re: bipedal crocodylomorphs


> 
> Snyder 1954 did something like this with lizards
> (testing only quads vs.
> the 19 sometimes bipeds) and made a list of the
> differences (DML
> archives also have this list as it's been often
> repeated).
> 

Are you refurring to modern lizards when you say 19
bipeds? If not are there any modern lizards who are
actually considered bipeds despite occasional moments
onto two feet? 
I am interested in the origin of bipedism but have not
done much study in this area. I've always assumed that
there have only been two original forays onto two feet
proper. Predino reptiles and Man. 

Andrew

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sean newell | 1 May 2005 02:51
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Jurassic Park Dinosaurs

Hey All. just wondering if what dinosaurs are going to be in Jurassic Park 
4. are there any new ones?

Peace

Sean
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David Peters | 1 May 2005 01:33
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re: bipedal crocodylomorphs

John Hutchinson wrote:

Does anyone one [know] where the bipedalism idea first comes from, and
what papers
have dealt with it in the most detail?

>>>>

The notion of bipedalism among various diapsids is over 100 years old
and I'm not sure who first coined the idea ? but if you're looking for
analogs and evidence, IMHO, the worst way to answer this question is to
go searching among synapsids (sorry Jaime). They're different in every
way.

Rather, seek those answers among the diapsid taxa that you know are
bipedal and then work backward phylogenetically  to the quads. Between
them try you'll be able to determine what marks them as different
morphologically.

Snyder 1954 did something like this with lizards (testing only quads vs.
the 19 sometimes bipeds) and made a list of the differences (DML
archives also have this list as it's been often repeated).

Do the same with Eoraptor, Sharovipteryx and Scleromochlus, three (how
could they be anything other than) bipedal diapsids. And maybe
Pseudhesperosuchus just for grins.

When you do, I think you'll find the same answer that Snyder found 50
years ago.
(Continue reading)

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Jaime A. Headden | 1 May 2005 06:22
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re: bipedal crocodylomorphs

David Peters (davidrpeters <at> earthlink.net) wrote:

<The notion of bipedalism among various diapsids is over 100 years old and I'm
not sure who first coined the idea ? but if you're looking for analogs and
evidence, IMHO, the worst way to answer this question is to go searching among
synapsids (sorry Jaime). They're different in every way.>

  Eh, I have no problem with people disagreeing with me, but "different in
everyway" is not precisely true. One quadrupedal tetrapod and another show
similar constraints towards bringing the limbs beneath the body, as in
archosauromorphs and many different groups of "basal" sauropsids and synapsids.
The hypothesis is that these animals should show similar features if they
developed their vertical limbs in a similar manner and thus should also show
similar limbs if they developed bipedalism in the same manner. 

  So far, the constraints on long ilia with bipeds do not all correllate one
one one with one another, since there are many quadrupeds among tetrapods (all
of them, bar a few descendant groups), and not all of them have long ilia. So
one then looks at those species with long ilia and what else they have in
common. Excluding synapsids is yet another unparsimonious a priori descision
that affects the outcome. Despite hominoid spinal orientation, the relationship
of the femur and the ilia/subiliac pelvic bones have retained their
plesiomorphic relationship: ischia ventral and posterior to femur, pubes
ventral and anterior to femur, and ilia anterior and dorsal (cranial) to femur.
Thus, I disgree that excluding synapsids helps answer the hypothetical raised
above. Given the limb organization of dicynodonts and, say, pareiasaurs, and
their similarities from "rootward" parareptiles versus "crownward" ones
relative to them (i.e., procolophonids are to pareiasaurs as cistecephalids are
to kannemeyeriids, sprawling versus semi-upright), these distinctions in
synapsids are paralleled (and thus informative) in sauropsids.
(Continue reading)

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W. M. Svensen | 1 May 2005 07:59
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Re: Jurassic Park Dinosaurs


>Hey All. just wondering if what dinosaurs are going to be in Jurassic 
>Park 4. are there any new ones?

As far as I can tell, there's not enough information available at this point for anyone beyond the writers to
say. And if the rumors I'm hearing about it being put on hold indefinitely or even getting nine grams are
true, we may never know.

(After Jurassic Park 3, I can't say that I find those rumors very distressing.)

W. M. Svensen
http://www.gondolend.net
http://www.gondolend.net/Svensen
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Mickey Rowe | 1 May 2005 09:01
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Dinosaur List Administrative Message

This file was last touched February 18th, 2004.

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Rather than sending the whole long administrative message each month
I'm going to give you only the table of contents and the two sections
that I expect to be the most popular.  If you wish to see the entire
document you can visit it at any time at:
(Continue reading)

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Thomas R. Holtz, Jr. | 1 May 2005 13:45
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RE: bipedal crocodylomorphs

> From: owner-dinosaur <at> usc.edu [mailto:owner-dinosaur <at> usc.edu]On Behalf Of
> David Peters
>
> >>>>
>
> The notion of bipedalism among various diapsids is over 100 years old
> and I'm not sure who first coined the idea ? but if you're looking for
> analogs and evidence, IMHO, the worst way to answer this question is to
> go searching among synapsids (sorry Jaime). They're different in every
> way.
>
> Rather, seek those answers among the diapsid taxa that you know are
> bipedal and then work backward phylogenetically  to the quads. Between
> them try you'll be able to determine what marks them as different
> morphologically.
>
[snip]

> A modern look at the subject would be refreshing, since it is my
> impression that the earliest notions were just that, notions, without
> much substance other than relative limb length and the authority of the
> author. I mean, really, what did they have to work with back then?

Part of the problem here is the consideration of bipedality and quadrupedality as mutually exclusive
conditions. Instead, they are
part of a continuum. MANY lizard species, for instance, are bipedal during their rapid phase of
locomotion. This is not just true of
big charismatic ones (basilisks, frilled lizards, etc.): this is true of a vast range of forms. Indeed,
this may be the ancestral
condition for Diapsida: sprawling quadrupedality at low speeds, sprawling bipedality at high speeds.
(Continue reading)

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David Peters | 1 May 2005 13:57
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Re: bipedal crocodylomorphs


"Jaime A. Headden" wrote:

> David Peters (davidrpeters <at> earthlink.net) wrote:
>
> <The notion of bipedalism among various diapsids is over 100 years old and I'm
> not sure who first coined the idea ? but if you're looking for analogs and
> evidence, IMHO, the worst way to answer this question is to go searching among
> synapsids (sorry Jaime). They're different in every way.>
>
>   Eh, I have no problem with people disagreeing with me, but "different in
> everyway" is not precisely true. One quadrupedal tetrapod and another show
> similar constraints towards bringing the limbs beneath the body, as in
> archosauromorphs and many different groups of "basal" sauropsids and synapsids.

DP: When you say "bringing the limbs beneath the body" that can mean two different things. If you bring the
knees beneath the hips and the feet follow, that's one style. If you keep the knees sprawling and also bring
the feet beneath the
hips, that's another style.

>
> The hypothesis is that these animals should show similar features if they
> developed their vertical limbs in a similar manner and thus should also show
> similar limbs if they developed bipedalism in the same manner.
>
>   So far, the constraints on long ilia with bipeds do not all correllate one
> one one with one another, since there are many quadrupeds among tetrapods (all
> of them, bar a few descendant groups), and not all of them have long ilia. So
> one then looks at those species with long ilia and what else they have in
> common. Excluding synapsids is yet another unparsimonious a priori descision
(Continue reading)

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David Marjanovic | 1 May 2005 17:21
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Re: bipedal crocodylomorphs

> DP: When you say "bringing the limbs beneath the body" that can mean two 
> different things. If you bring the knees beneath the hips and the feet 
> follow, that's one style. If you keep the knees sprawling and also bring 
> the feet beneath the hips, that's another style.

Does the former style even exist?

>> The hypothesis is that these animals should show similar features if they
>> developed their vertical limbs in a similar manner and thus should also 
>> show
>> similar limbs if they developed bipedalism in the same manner.

It also greatly depends on their starting points. Look at any mammalian 
pelvis (xenarthrans excepted -- they use the ischia as postacetabular alae 
of the ilia). It's ridiculous. The ilia aren't parallel to the vertebral 
column, but oblique. They don't even touch the vertebrae medially to the hip 
joints, only far farther cranially. As a result, only 1, 2 or 3 sacral 
vertebrae are actually connected to the pelvis! This is because a size 
squeeze stands at the origin of Mammaliomorpha ( = Mammalia, Tritylodontidae 
and the like). Mouse-sized animals don't need robust connections between 
pelvis and vertebral column, so the number of sacrals and the sutures 
between ilia and sacrum got _reduced_. As a result, in the mounted elephant 
skeleton in the university here only 2 or so sacrals touch the ilia, which 
are oriented transversely instead of longitudinally. In the giraffe skeleton 
that number is 3 or 4 or something.
        As a result, I'd say our ilia don't have postacetabular alae. They 
consist mostly of preacetabular alae which lie _dorsally_ to the hip joints.

> DP: alligators: bipedal ancestors.
(Continue reading)

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Christopher Collinson | 1 May 2005 19:51

Re: bipedal crocodylomorphs

> chamaleons and drepanosaurids: bipedal at times on branches, at least
> hypothetically in the latter case.

>They don't move much in this stance, though.

Its misleading to use these as examples of  bipedality because, at most, all
they can take is a tripodal stance. Chameleons have a prehensile tail and
drepanosaurids have that tail claw, so presumably it was also anchored to a
branch at all times. Also its not as though they take any steps while in
this posture (at least chameleons don't and its presumably the same for
drepanosaurids as well), its stand up grab a branch with your hands and then
let go with your feet. All the while the tail remains tightly coiled around
a branch, only when the feet have a firm grip on the next branch is the tail
relaxed.
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Gmane