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From the movie Tremors, behold the graboid:

It followed me home mommy, can I keep it?

These are vicious, SUV to bus sized sandworms that have acquired a taste for human flesh. They are known to "swim" through the earth really fast too.

I know some characteristics the graboids have in the movies are unrealistic (their speed comes to mind). What I am interested in knowing is: how would a realistic graboid species look like? And how could such a species (the realistic, not the movie one) have evolved?

This question is part of the Anatomically Correct Series.

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    $\begingroup$ May i suggest you change the title to "Anatomically Correct Giant Earth Worm (Graboid)" or some such thing? Because outside of the context of the movie no one knows what a Graboid is. $\endgroup$ – AndreiROM Jul 29 '16 at 14:10
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    $\begingroup$ @AndreiROM done, with an extra "carnivore" on top of that. Nice name for a band, by the way. $\endgroup$ – Renan Jul 29 '16 at 14:14
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    $\begingroup$ I vote to never have to answer this question. I say we just find ourselves unable to decide which of Bert's explosives to bring back, so just set one, and let nature (and/or Bert) take its course. $\endgroup$ – Cort Ammon Jul 30 '16 at 2:13
  • $\begingroup$ I feel as if the square-cube law applies here. A creature of that size is already in danger of basicallly having it's body to heavy to sustain. It could only manage that size with large thick bones, which would make it hard to 'slither' to support movement. It's going to be a struggle keeping the body oxygenated above ground, if buried it would tend to sufficate due to lower oxygen and additional weight crushing it. Only viable version I could see would either be limited to swamp like lands where water and soil mix & water provides boyance & oxygen through gills or much smaller. $\endgroup$ – dsollen Aug 2 '16 at 23:51
  • $\begingroup$ I just like when one pops its head into the bunker. Most awesome part of a Sci-fi movie ever. $\endgroup$ – Xandar The Zenon Aug 15 '16 at 14:25
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We do not see the Graboid, the graboid does not see us

The graboid is a highly evolved megafaunua. Similar to the giant sloth and the cave bear, the Graboid does indeed have a miniature equivelant; The star nosed mole. The star nosed mole is the fasted eating mammal on earth, able to find, identify, eat, chew and swallow down its food in an average of just 227 milliseconds – less than quarter of a second. By comparison, it takes people 650 milliseconds to brake after seeing a traffic light turn red.

Evolving to hunt down other megafauna the mole grows the extreme sizes and since it is now hunting more dangerous animals with better weapons, its super nose evolves harder, claw-like weapons.

Finally, the speed. Most moles clock in at an impressive speed of 5 mph for short distances through their pre-dug tunnels. But since we fail to see graboids digging, it may be safe to assume that they just travel through their tunnels. Since the full size off Graboids is never truly revealed- we only see their super specialized noses- we cannot guess just how fast the star nosed graboid would be, but we can assume that it would be much faster than humans.

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  • $\begingroup$ I think you've misunderstood the digging speed of moles - that should be feet per hour, not miles per hour, and that is for loose soil $\endgroup$ – pluckedkiwi Jul 29 '16 at 16:51
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    $\begingroup$ @pluckedkiwi no, I know what I said and I meant it $\endgroup$ – TrEs-2b Jul 29 '16 at 17:06
  • $\begingroup$ how exactly does it dig? $\endgroup$ – άλεξ μιζέρια Jul 29 '16 at 17:24
  • $\begingroup$ @άλεξμιζέρια same way moles do, with their claws, the nose is meant for eating, not digging $\endgroup$ – TrEs-2b Jul 29 '16 at 17:34
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    $\begingroup$ @pluckedkiwi Looking at the edit history you can clearly see that I editted after I commented, I had read my information wrong and I editted to fix it $\endgroup$ – TrEs-2b Jul 29 '16 at 18:07
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They are descended from placoderms. Having an animal that size burrowing requires handwaving no matter what so let's focus on the anatomy.

Hard bony plates on the head, check

Bony plates instead of teeth, check.

Smooth skin or superficial scales on the rest of the body, allowing for the evolution of spines, check.

The potential for a single pair of limbs in certain life stages, check

Internal postcranial skeleton to support body, check

The potential for huge sizes, the largest is 8 meters long, check

Bonus several freshwater species are or are nearly blind and are bottom dwelling.

So you have a burrowing placoderm that evolved for terrestrial soil.

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Well there are creatures which swim through loose, dry sand so maybe the graboid can do that. However, the real world ones are all small. Here's a video explaining how the sand swimmer snake does it by being long, skinny and smooth.

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