ancient krogan art likely depicting kakliosaur.
Kakliosaur are a species of domesticated riding beasts from the planet Tuchanka. They were domesticated and used as war-mounts by the krogan, but went extinct during the rachni wars.
It is quite possible that the Kakliosaur were resurrected during the time of the reapers invasion of the galaxy. It seems Commander Shepard is capable of finding a Kakliosaur skull encased in amber, salarian scientists was able to clone these creatures because of the durable DNA. Once resurrected they Joined the krogan in battle.