Egg squashed by short river creature (5)
I believe the answer is:
rhino
This could be a double definition.
'egg squashed by short river' is the first definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe there's a link between them I don't understand?
'creature' is the second definition.
(short for rhinoceros)
Can you help me to learn more?
(Other definitions for rhino that I've seen before include "Massive mammal with one or two horns on its nose, in short" , "When provoked, one may charge" , "big game" , "Hi, Ron! (anag)" , "African/Asian ungulate" .)