The Repto is mentioned twice in How to Speak Dragonese.
Reptos have been neither seen nor discussed, so nothing is known about them.
Reptos are mentioned as food dishes served to the Fat Consul.
|“||He was eating a light snack of double reptoburger with tomato-and-dormouse relish and popdragons on the side.||”|
|— How to Speak Dragonese|
It is possible that Reptos were not meant to be a specific dragon species at all, but rather referring to a burger made out of Reptiles (which dragons are considered in the Books).