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The diagram you produced on Page 4 of Cladistics:. OG E B A D C. -- black eye. -- long wing. -- wide neck. -- long leg -- dark body. -- large eye. -- thick leg -- wide body.

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-- wide wing -- long stinger

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The diagram you produced on Page 4 of Cladistics:

OG E B A D C

-- black eye

-- long wing

-- wide neck

-- long leg

-- dark body

-- large eye

-- thick leg

-- wide body

The differences in the in-group are explained in 10 steps!

Comma separation at one step might be clearer!

-- wide wing

-- long stinger

Your cladogram probably uses numbered traits…

I’m doing it this way for a reason…


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This diagram is based on the same clade critter data…

But is not the result of cladistic analysis:

OG E B A D C

25 Steps!!

<-- black eye

<-- long leg

<-- dark body

<-- wide neck

<-- thick leg

<-- wide body

<-- long wing

<-- large eye

<-- wide wing

<-- long stinger

What concept was used to make this diagram?

Scientists reject this diagram because of parsimony…why?


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This is likely your cladogram from Page 4 of Cladistics

OG E B A D C

-- black eye

-- long wing

-- wide neck

-- long leg

-- dark body

-- large eye

-- thick leg

-- wide body

-- wide wing

-- long stinger


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F

What do we do with the newly-discovered Clade Critter (page 5)?

OG E B A D C

-- black eye

-- long wing

-- wide neck

-- long leg

-- dark body

-- large eye

-- thick leg

-- wide body

-- wide wing

-- long stinger


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F

There are two possible explanations--which is most parsimonious?

OG F B A D C

-- dark

bodyR

-- black eye

dark --

body

-- long wing

Two

Forward

Evolutions

-- wide neck

-- dark bodyR

-- long leg

-- dark body

-- large eye

A homoplasy of

parallelism or…

convergence

-- thick leg

-- wide body

A single evolution

But two reversals

-- dark body

-- wide wing

-- long stinger

Is it easier to evolve or to lose the characteristic?


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Reversal Homoplasy

The Case of Tetrapods


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Tetrapod limbs are complex

Ball joint at girdle (pectoral or pelvic)

Proximal segment has one heavy bone

Hinge joint at elbow or knee

Distal segment has two bones for rotation of hand/foot

Small cuboidal bones at wrist and ankle for flexibility of hand/foot position

Long metacarpal/metatarsals for palm/instep

Phalanges for the digits (fingers/toes)


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Tetrapod limbs are stereotypical

The complex structures are shared among these tetrapods:

Fishes (some are more plesiomorphic)

Amphibians

Reptiles

Birds

Mammals

Conclusion: rather than evolving complex limb form and function separately and identically among all these groups of species (i.e., many homoplasies), the tetrapod leg design evolved just once in a common ancestor (i.e., more parsimonious)


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  • Forward evolution of a leg requires modification of:

    • Bones

    • Muscles

    • Connectives

    • Vascular Paths

    • Neural Paths

Reversal of a complex trait is comparatively parsimonious

Reversal could be just ONE point mutation in ONE gene that normally puts limb development into motion.

Without the first step, the rest does not happen.


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Tetrapod evolution has been reversed multiple times!

Thus, it must be easily done… i.e. is parsimonious

Legless amphibians: caecilians

Legless lizards: glass lizards

Ajolote: mole lizards

Snakes

So some gene functioning early in tetrapod development can mutate (become defective), rendering some ancestral species (and its descendants) legless.

All the rest of the tetrapod genes that had evolved to make the limbs, are made useless by this one mutation.


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Caecilians:

terrestrial amphibians

http://www.wildherps.com/images/herps/standard/017614_caecilian.jpg

http://www.wildherps.com/images/herps/standard/017612_caecilian.jpg

http://scienceblogs.com/zooillogix/caecilian.bmp


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A photo of parent Caecilian with offspring

R635RmqosDI/AAAAAAAANYc/jwcNDv1suD4/flesh+eating+amphibian+caecilians%5B2%5D


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http://www.unexplained-mysteries.com/gallery/albums/userpics/22445/normal_ajolote.jpg

This ajolote is a snake that reversed the reversal blocking only pectoral limbs (note: belly scale pattern and limb location)

Or it is a lizard that has reversed only its pelvic limbs


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There are also partial losses: the Boa has vestigial pelvic limbs

http://www.edwardtbabinski.us/images/spurs1.jpg

Of course the alternative interpretation is a partial reversal of loss


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There are several clear examples of reversals of reversals:

http://dakotabirding.com/Snake_wlegs.jpg

This snake has reversed the reversal blocking pectoral limbs


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This is another verified reversal of a reversal:

http://www.telegraph.co.uk/earth/wildlife/6187320/Snake-with-foot-found-in-China.html

This snake has reversed the reversal blocking pelvic limbs


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Of course humans will make false claims!

This claim of pectoral limbs is clearly false:

http://robandjan.files.wordpress.com/2008/08/snake1.jpg

This snake is in the act of swallowing a frog, NOT sprouting legs!


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F

There are two possible explanations--which is most parsimonious?

OG F B A D C

-- dark

bodyR

-- black eye

dark --

body

-- long wing

Two

Forward

Evolutions

-- wide neck

-- dark bodyR

-- long leg

-- dark body

-- large eye

A homoplasy of

parallelism or…

convergence

-- heavy leg

-- wide body

A single evolution

But two reversals

-- dark body

-- wide wing

-- long tail

Is dark body a complex characteristic?

Maybe one enzyme!


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