Stumped .. anyone ...

The statement "I don't have as much money as he does" is a idiomatic comparision.

However in the question there is no comparision...its only a assertion saying that "horny jaws function as teeth"

Does this help?

Here's what it is. English is pretty idiomatic about dangling verbs. They are silent a lot, meaning not written out at the end of the sentence. This is an example of that. You will generally not see a do or does left at the end of a sentence on GMAT. Here are a few examples:

I'm prettier than Bianca. (is -- not included)
Jamaal made better chicken than Ezra. (did -- not included)
Mom swims more fluidly than Dad. (does -- not included)

The difference is when there is a pronoun at the end of the sentence, then you will more often see the dangling verb included, i.e.:

I have more money than she does.
We're so much smarter than they are.
Bob googles so much faster than I do.

Note: In these cases, leaving off the dangling verb is also grammatically correct.

You will also note that each one of these examples is about judgment and comparisons. In the example sentence, it is not really a judgment of one thing OVER the other, but rather a simple comparison. Therefore the 'dangling do' is redundant and can be dropped very definitely.

Although the turtle has been toothless for more than 150 million years, in some contemporary turtle species the moderately sharp and jagged edges of their horny jaws function for teeth.
a) their horny jaws function for teeth
b) its horny jaws function for teeth
c) its horny jaws function as do teeth
d) the horny jaws function as teeth do
e) the horny jaws function as teeth

OA:E

correct idiom function as>>Eliminate A,B

Point to be noted:species can be used as both singular/plural

Between C,D,E??
The it is said to work as a possesive poison..this is not clear..please explain in detail

: : : :

the essence of the clause is "the edge of the jaws function as teeth". Here "as" is used to indicate a "state" or "quality" not to indicate comparison.
"as" is used as a preposition not conjunction here.
ie: The computer functions as a calculator.
He did the speech as a comedian.
The girl played the sport as a professional.

1. X functions as Y does
2. X functions as Y

"does in 1 is redundant, because there is no ambiguity.

Ambiguity arises when you got multiple nouns in the main clause. There are many ways to disambiguate

(1) as does X (comparing subject to subject)
(2) as to/for X (comparing objective pronouns)
(3) as in georgia (comparing adverbs or place)
(4) as when blah blah (comparing time)