Critical Reasoning

Hi All,

Boa constrictors have tiny hind leg bones buried in muscles toward their tail ends. These vestigial legs are a clue that snakes descendants from lizards over 100 million years ago and walked the earth on their hind legs. A recently discovered fossil of boa constrictor has very fragile hind legs with half formed hind leg bones that could not have supported the animal's weight on land

Which of the following statement, if also true, would most strongly support the conclusion that the fragile hind leg bones are remnants of legs that boa constrictor once had?

A)No other snakes comparable to boa constrictor in size and weight have remnants of hind leg bones
B)No fossil of ancient boa constrictor with intact hind legs capable of supporting the animal's weight have ever been discovered.
C)It has not yet been conclusively proved that these vestigial legs of boas are non-functional.
D)Older boa constrictor fossils confirmed that ancient boas had full hind leg bones.
E)Animals with hind legs would typically also have pelvises and these would be evident in their fossils.


OA: D

Source: CracktheVerbal CR Book.

There is no explanation given. I am not able to get OA.
Could you pls explain me.

Thanks in advance.

Regards,
Uva.

This argument, in essence, is saying that boa constrictors are descended from lizards, and that the ancient boa constrictors had functional legs. So a very old boa constrictor ancestor would have fully formed legs. A less ancient ancestor, like the recently discovered fossil described in the argument, would still have legs, but those legs would be less functional. And the final evolutionary step would be our modern boa constrictor, which doesn't have functional legs at all, but rather, vestigial leg bones.

Boiled way down it would like this:

Very old: functional legs ----> Not as old: less functional legs ------> contemporary: legs not functional at all

The only part we're missing direct evidence of: the very old constrictors that have fully functional legs. Well, if we found older constrictor fossils with full hind leg bones, that would be powerful evidence that constrictors used to walk.