What are some examples of animals that appear to be on the surface very similar, but are, in fact, quite different in at least one distinctive regard?
There are numerous marsupials that, through environmental pressures, appear very similar to placentals that fill equivalent environmental niches. I'm thinking specifically of a wolf-like marsupial.
http://www.ucmp.berkeley.edu/mammal/marsupial/marsupialwolf.gif
Use the past tense, that man!
Dear Faldage: Der Quibblemeister asks is it not
filling a similar niche in predator hierarchy
rather than adjusting to environmental pressure?
Methinks Pfranz is trying to out quibble you, Dr Bill.
- joe [a quibble is worth a thousand facts] sunday
Dear WW: Not a really good example, but the lamprey eel
and the true (Sargasso?) eels look quite similar except for
mouth parts.
Here's a URL with a lot of pictures of fish found in Pennsylvania:
http://216.239.53.104/search?q=cache:qDo3fZN4SbsJ:sites.state.pa.us/PA_Exec/Fish_Boat/pafish/fishhtms/chapindx.htm+picture+lamprey+eel&hl=en&ie=UTF-8Sorry that URL made screen go wide.