I'm going to jump right in with explanations. Each star, up to a max. of 8, is given to some of the fossils you will encounter.

_-Shells-_
-Colorful
-Ribbed
-Spiny
-Lefty
-Unusual Pattern
-Vertical Pattern
-Rare Color
- Tiny OR Large

_-Trilobites-_
-Stubby Lil' Guy OR Long As Heck
-Large OR Tiny
-Curly Antenna OR Straight Antenna
-Fore Facing Horns OR Back Facing Horns
-Eyestalks
-Colorful
-Unusual Pattern
-Rare Color

_-Crinoids-_
-Unusual Pattern
-Colorful
-Rare Color
-Feathered
-Striped Arms
-Wavy Arms
-Bigg Arms OR Weeny Arms
-Large OR Tiny

Example: A trilobite can never be both Long As Heck or Stubby, but can be Large and Stubby. An 8x star Trilobite can only have these traits and no others, so you don't need to worry about Pyritized, Agatized, or Opalized traits (they just look cool as heck).

Now that we understand what we need, the next question is : How do we get there?
2 things really: The Fossil Combiner and Persistence
As far as I've tested, it's either near impossible or just genuniely impossible to pull an 8x Fossil right out of a box (The highest I've pulled being a 5x Star). With the Fossil Combiner you have some control over that factor (notice how I underlined some). I cannot verify if this is true, but from my experience, you cannot combine a 7x Star with a 2x Star and expect to get an 8x Star. You're more likely to pull a 4x Star or a 5x Star. For my first 7x Star fossil, I used 2 6x Star Fossils, however, my 8x Star was formed with a 7x Star and a 6x Star. I think using a 5x Star with a 7x Star to get an 8x Star is pushing it, but I won't say it's not impossible.

I feel like I shouldn't have to explain this, but just to clarify, combining 2 7x Star Fossils together with the same traits will not net you that missing 8th trait. If, for example, both shell fossils are missing the Lefty trait, the Fossil Combiner will not pre-generate that for you. Neither will combining 2 4x Star Fossils, with a total of 8 unique traits, net you an 8x Star Fossil (You'll most likely get a 5x star, maybe a 6x Star).

Quick disclaimer: Even if the 2 7x star fossils you use to combine would get you 8 unique traits, it is not guaranteed you will get an 8x Star (bull, I know). So, what worked with me was some Oedipus magic (using your children to make children!). If the original parent fossils do not make an 8x Star, try using the child of that combination (trust me, it's not illegal). Just make sure that the child retains the missing trait in either parent or else the next combination is pointless.

In short, not really.

The highest I pulled was a 3x Star, and even then, a 3x Star was rare to pull. So, if you can't seem to pull the fossil you want out of a box, you could just try the tumbler and try to get a 3x Star you want, but you may get a Mineralized (Pyritized, Opalized, you get it) Fossil before you get the fossil you want, for some reason the rates on pulling a Mineralized Fossil from the tumbler are pretty high. If you're still trying to complete all the Fossil Finder quests, the tumbler can be pretty useful but it does cost 8c per spin for all fossils (even though you can resell the fossil you got, you still lose 5c).

TL;DR - Not for the 8x Star Hunt, but not a bad idea for the Fossil Finder quests

This is the end of the guide, but if you have any questions or corrections, just let me know in the comments and I'll try and reply as soon as I can.