Here's an apparently simple morphological question: why doesn't 'dinosaur' end with -us?
Compare:
dinosaur
brachiosaurus, stegasaurus, apatosaurus, tyrannosaurus [rex]
Etymonline isn't too helpful in this case:
http://etymonline.com/index.php?term=dinosaurI can assume that "dinosaur" is just a change (it's the exception), with a loss of that final syllable.
But I also wonder: -r was a common nominative masculine singular ending in Latin, so that could explain it too. Then why the -us vs Ø?
When I started thinking about the meaning, something very interesting occurred to me:
-us seems to refer to specific species of dinosaur.
Ø is used more with generic, maybe casual usage.
So "tyrannosaurus" is a specific species (because it's the scientific name?), while a Tyrannosaur is any large flesh-eating lizard creature-- the class of all dinosaurs that resemble T-Rex's.
Likewise, a "dinosaurus" feels like a very specific kind of creature (whatever kind that might be).
This seems to hold for new coinings as well:
"Herbasaur" is a perfectly valid (hypothetical) name for a dinosaur that only eats plants.
"Herbasaurus" is a perfectly valid (hypothetical) name for a certain species of dinosaur that happens to eat only plants.
Does anyone else share my intuition on this one? Am I imagining things?
And do you have any general insight into the distribution of that -us?