Anatomical vestiges

Anatomical vestiges - Anatomical vestiges Confirmation:...

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Anatomical vestiges Confirmation: Figure 2.1.2. Various organisms displaying vestigial characters . From top to bottom: A. Apterocyclus honolulensis , a flightless weevil. The black wing covers cannot open, as they are fused, yet underneath are perfectly formed beetle wings. B. The vestigial flower of Taraxacum officinale , the common dandelion. C. A vestigial pollen grain from the dandelion. There are many examples of rudimentary and nonfunctional vestigial characters carried by organisms, and these can very often be explained in terms of evolutionary histories. For example,
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from independent phylogenetic evidence, snakes are known to be the descendants of four-legged reptiles. Most pythons (which are legless snakes) carry vestigial pelvises hidden beneath their skin (Cohn 2001 ; Cohn and Tickle 1999 ). The vestigial pelvis in pythons is not attached to vertebrae (as is the normal case in most vertebrates), and it simply floats in the abdominal cavity. Some lizards carry rudimentary, vestigial legs underneath their skin, undetectable from the outside (Raynaud and Kan 1992) . Many cave dwelling animals, such as the fish Astyanax mexicanus (the Mexican tetra) and the salamander species Typhlotriton spelaeus and Proteus anguinus , are blind yet have rudimentary, vestigial eyes (Besharse and Brandon 1976 ; Durand et al . 1993 ; Jeffery 2001 ; Kos et al . 2001 ). The eyes of the Mexican tetra have a lens, a degenerate retina, a degenerate optic nerve, and a sclera, even though the tetra cannot see (Jeffery 2001 ). The blind salamanders have eyes with retinas and lenses, yet the eyelids grow over the eye, sealing them from outside light (Durand et al . 1993 ; Kos et al . 2001 ). Dandelions reproduce without fertilization (a condition known as apomixis ), yet they retain flowers and produce pollen (both are sexual organs normally used for sexual fertilization) (Mes et al . 2002 ). Flowers and pollen are thus useless characters for dandelions in terms of sexual
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This note was uploaded on 11/14/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Anatomical vestiges - Anatomical vestiges Confirmation:...

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