-- wide wing -- long stinger The diagram you produced on Page 4 of Cladistics: -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck-- long wing OG E B A D C Your cladogram uses numbered traits… I am doing it this way for a reason… Comma separation at one step might be clearer! The differences in the in-group are explained in 10 steps!

<-- wide wing <-- long stinger <-- thick leg <-- wide body <-- large eye <-- long leg <-- dark body <-- black eye <-- wide neck <-- long wing OG E B A D C This diagram is based on the same clade critter data… But is not the result of cladistic analysis: What concept was used to make this diagram? Scientists reject this diagram because of parsimony…why? 25 Steps!!

-- wide wing -- long stinger This is likely your cladogram from Page 4 of Cladistics -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck-- long wing OG E B A D C

-- wide wing -- long stinger What do we do with the newly-discovered Clade Critter (page 5)? -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck-- long wing OG E B A D C F

-- wide wing -- long stinger There are two possible explanations— which is most parsimonious? -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck -- long wing OG F E B A D C F dark -- body A single evolution But two reversals -- dark body -- dark body R -- dark body R Two Forward Evolutions Is it easier to evolve or to lose a characteristic? A homoplasy of parallelism or… convergence

Reversal Homoplasy The Case of Tetrapods

Vertebrate Clade Homeothermy (a homoplasy) Homeotherms are polyphyletic Reptiles are?

Adopted Text: Freeman Biological Science Pearson Figure 25.4 Tulerpeton (  362 mya) Acanthostega (  365 mya) Tiktaalik (  375 mya) Eusthenopteron (  385 mya) Fin rays Humerus Distal elements Ulna and radius Time

Adopted Text: Freeman Biological Science Pearson Figure 25.9 TurtleHumanHorse Bird BatSeal Humerus Radius and ulna Carpals Metacarpals Phalanges Tetrapod Limb: Homologous Structures crawl type run arm-fly hand-fly swim

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)

Tetrapod limbs are stereotypical The complex structures are shared among these tetrapods: 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)

Reversal of a complex trait is comparatively parsimonious Forward evolution of a leg requires modification of: Bones Muscles Connectives Vascular Paths Neural Paths 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.

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 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. The useless genes are still present, however! And this can be evidenced and documented.

Caecilians: Tetrapod leg reversed in terrestrial amphibians ard/017614_caecilian.jpg ard/017612_caecilian.jpg

A photo of parent Caecilian with offspring R635RmqosDI/AAAAAAAANYc/jwcNDv1suD4/flesh+eating+amphibian+caecilians%5B2%5D

This ajolote is a snake that reversed the reversal restoring pectoral limbs (note: belly scale pattern and limb location) mysteries.com/gallery/albums/userpics/22445/normal_ajolote.jpg

There are also partial losses: the Boa has vestigial pelvic limbs Of course the alternative interpretation is a partial reversal of loss

There are several clear examples of reversals of reversals: This snake has reversed the reversal, restoring pectoral limbs

This is another verified reversal of a reversal: This snake has reversed the reversal, restoring a pelvic limb

Of course humans will make false claims! This claim of pectoral limbs is clearly false: This snake is in the act of swallowing a frog, NOT sprouting legs!

-- wide wing -- long stinger There are two possible explanations— which is most parsimonious? -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck -- long wing OG F E B A D C F dark -- body A single evolution But two reversals -- dark body -- dark body R -- dark body R Two Forward Evolutions A homoplasy of parallelism or… convergence Is dark body a complex characteristic? Maybe one enzyme!

-- wide wing -- long stinger There are two possible explanations— which is most parsimonious? -- thick leg -- wide body -- large eye -- long leg -- dark body -- black eye -- wide neck -- long wing OG F E B A D C F dark -- body Two Forward Evolutions A homoplasy of parallelism or… convergence Maybe one enzyme! And one fewer step!

Make sure your homework cladogram (Page 6) is solved: 1.applying the homoplasy to the simplest character 2.uses the fewest steps, and 3.uses a forward and a reverse rather than two forward evolutionary steps!! In other words, is the MOST PARSIMONIOUS!