thorn in the books is about the same size as saphire, but had less time to grow
heres my theory
thorn was morzans dragon and he survived.
zar'roc is red and so is thorn. we dont know what colour or what name morzans dragon had
maybe this also gives strength to murtagh with a stronger dragon

well first of all he said that the red egg hatched for him in the ancient language. also if that was true thorn would be a lot bigger than saphira. that would also be way to many dragons/riders survivng their partner dying. also thorn was smaller than saphira just had large legs

but if he was the same size as saphira except long legs he still had less time to grow so something is going on here
maybe its galbotorixs power,
brom surviveid
murtagh just said he hatched for him, someone could use a spell to make him go into an egg to survive morzan dying and if needed galbotorix could get him out.
kinda like a re-hatch

Umm, ppl? Rhunon (the elf smith) made the swords for the Riders when they were finished with their training. She also made them in the color of the Riders dragons. That means that Morzans dragon was red. Galby's original sword will be a different color than Shruikan. And as for how Thorn grew so fast, isn't it true that guys grow faster and taller than girls? So he probably has twice her growth rate. It was a good theory, but if you look closely at evidence in the books you can find these things in there. Oh, and Saphira's egg was about as long as Eragon's arm, or at least around that length, so I don't imagine that even Galby would be strong enough to force a dragon to regress back into a hatchling. And Brom himself said that during the fighting at Doru Araeba, that Galbatorix managed to scavenge three eggs. I used the word scavenged because Thorn and the next dragon would have been better off smashed instead of forced into Galby's service. I didn't use Saphira there because she escaped Galby's clutches.

i doubt it

didnt brom(book or movie i 4got) say that if the dragon's rider died, the dragon would die 2. therefore, thorn cant be morzans dragon.

ya if it was it would be much bigger than saphira not to mention murtagh told eragon that thorn hatched for him.

and anyway the reason he had larger legs was cause he was a male 0_0

ok that didnt make much sence...

thats what it says in the book

im pretty sure...males legs tend to be bigger i guess...and he was younger so his frame is smaller

it's definaely not morzan's dragon 'cause (like someone else said,) murtagh said hat it hatched for him. and don't anybody start saying that with galby's magical powers he turned him back into an egg cause i don't believe that!

YEah, if that happened, Galby could be able to turn Saphira into an egg and Eragon would be hopeless at defeating the Empire.

thorn grew so fast because he was there with the most powerful man in alagaesia, galby. dont u think tht he would maybe know something tht would be able to make a dragon or any thing for tht mater, grow fast? plus like others have said, he is a male, and in most cases males tend to grow faster than females.

ADDING INTO ANOTHER THEIORIE:

if murtagh is morzans son it would be likely tht they would both be red.
just like if brom was eragon'f father, they were both blue.

its a family trait like hair color or something i guess.