Is it homogeneous or did they converge? Did we both evolve from warm-blooded reptiles that are extinct maybe?
Welcome to Biology.SE.
Did you say warm-blooded?
warm-blood is very unclear. The correct terms are endo-, exo-, poikilo- and homeo- therm. In short…
Source of heat
- endo = inside
- exo = outside
Variation in inside temperature
- Poikilo = varies
- homeo = does not vary
Any combination of these two axes exist. For example: If the temperature in the environment never varies you can be homeotherm without needing to be endotherm. A fun example also are the large dinosaurs that are thought to be homeotherms because their metabolism produce some heat and they are so large that they remain warm thanks to this heat source. However, they were probably not able to regulate actively their temperature. Therefore, I would tend to qualify dinosaurs as homeo-exo-therm but I wouldn't be surprised if someone prefers to call large dinosaur homeo-endo-therm individuals. Hope that makes sense to you.
By warm-blooded I will assume you meant endotherm.
MRCA of mammals and birds (and other things)
The Most Recent Common Ancestor (MRCA) lived 301.7 millions years ago (see on tolweb and on OneZoom). This MRCA was exotherm. In consequence, birds and mammals endothermy are an example of convergent evolution (even if they are not using exactly the same mechanisms).
References to go further into the evolution of endothermy in birds and mammals