Figure 8
From: The brown adipocyte differentiation pathway in birds: An evolutionary road not taken
Partial cladogram of the vertebrates. Taxa in which UCP1 are known to be present are indicated by a red dot. Those in which UCP1 is known to be absent are indicated by a black dot. The question mark indicates the span within the evolutionary history of the amniotes during which UCP1 and the capacity to produce functional brown fat was lost.