Is it homogeneous or did they converge? Did we both evolve from warm-blooded reptiles that are extinct maybe?

  • $\begingroup$ The previous answer is good. Here is a shorter one: no. Their common ancestor was most likely "cold blooded" and similar to a crocodile or some sort of crocodilian . $\endgroup$
    – user26942
    Commented Oct 11, 2016 at 1:04
  • $\begingroup$ I think the OP meant "homologous" rather than "homogeneous" ... $\endgroup$
    – Ben Bolker
    Commented Feb 12, 2018 at 21:52

1 Answer 1


Welcome to Biology.SE.

Did you say warm-blooded?

The term 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

  • 1
    $\begingroup$ According to this, mammals and birds share common cold blooded ancestor. And also comment that reptiles are "Imperfectly warm blooded" $\endgroup$
    – Dexter
    Commented Nov 13, 2015 at 14:42
  • $\begingroup$ I added some info for the large dinosaurs. I wouldn't trust too much a paper that uses the terms "cold-blood" and "warm-blood". But anyway, we agree that the MRCA was exotherm I guess. $\endgroup$
    – Remi.b
    Commented Nov 13, 2015 at 14:46
  • $\begingroup$ It does not appear borken to me. But I might have modified it right at the moment of yuor comment 2 days ago! $\endgroup$
    – Remi.b
    Commented Nov 16, 2015 at 21:14

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