The smallest species of chameleon is found only on an island in Madagascar. This island has unique geological and climatic conditions that are essential for the chameleon to survive. The chameleon was recently declared an endangered species. Years from now, why won't this chameleon's remains make for a good index fossil?

Index fossils pertain only to prehistoric creatures that lived before modern times.

Because it's the smallest of all chameleons, the fossils will be nearly impossible to see.

The large number of fossils discovered will exceed the maximum number required for an index fossil.

The fossil's location isn't widespread because it is found in only one isolated region of the world.

The fossil's location isn't widespread because it is found in only one isolated region of the world.

And index fossil is the fossil of an organism that has ideally 2 characteristics.

1. The time period in which the organism existed as a species is fairly limited.

2. The species was wide spread over the world.

The reason for the above two characteristics is that the presence of an index fossil is extremely useful in determining the date of a rock layer and therefore the date of other fossils in that same rock layer.

With that in mind, let's look at the options and pick the best one.

Index fossils pertain only to prehistoric creatures that lived before modern times.

* Nope. The age doesn't matter. If it's old enough to be fossilized, it's old enough to study. So this is a bad choice.

Because it's the smallest of all chameleons, the fossils will be nearly impossible to see.

* Radiolarians are a popular index fossil for dating marine sediments. Since they're only about 0.1 mm to 0.2 mm in size, the chameleon is quite massive compared to a radiolaria. So this is a bad choice.

The large number of fossils discovered will exceed the maximum number required for an index fossil.

* If there were a large number of fossils, that would make it easier to use as an index fossil. So this is a bad choice.

The fossil's location isn't widespread because it is found in only one isolated region of the world.

* Exactly. The usefulness of an index fossil is in determining the date of other fossil deposits. And since this chameleon is only present in a single region, it would be quite useless in dating fossils elsewhere in the world. So this is the correct choice.

Index fossils are fossils that are indicators of specific geological time. In order for a fossil to be an index fossil, it needs to belong to a species that is widespread and abundant. Therefore, in the case of this species of chameleon, this species has a really narrow range and its numbers are small, so in the future, it wouldn't be a good indicator of the fauna of this geological era.