It's like a dog had extensive cosmetic surgery to look like a lizard. Also - they laid eggs.

Inostrancevia | Dinosaur Revolution Wiki | Fandom

Like mammals, Inostrancevia was likely warm-blooded and covered in fur, with limbs that were in an almost fully erect posture and heterodont dentition. However, Inostrancevia differed from modern mammals, as it still had very primitive jawbones, laid eggs, and couldn't lactate.