Origin of birds mitochondrial uncoupling protein, UCP1, which is thermogenic. In mammals, UCP1 functions within brown adipose tissue to protect newborns against hypothermia. In modern birds, skeletal muscle serves a similar function and is presumed to have done so in their ancestors. In this view, bipedality and other avian skeletal alterations were side effects of muscle hyperplasia, with further evolutionary modifications of the forelimbs, including adaptations for flight or swimming, and vestigiality, being secondary consequences of two-leggedness. "Archaeopteryx" has historically been considered the first bird, or "Urvogel". Although newer fossil discoveries filled the gap between theropods and "Archaeopteryx", as well as the gap
Archaeopteryx be black throughout, with heavier pigmentation in the distal tip. The feather studied was most probably a dorsal covert, which would have partly covered the primary feathers on the wings. The study does not mean that "Archaeopteryx" was entirely black, but suggests that it had some black colouration which included the coverts. Carney pointed out that this is consistent with what we know of modern flight characteristics, in that black melanosomes have structural properties that strengthen feathers for flight. In a 2013 study published in the "Journal of Analytical Atomic Spectrometry", new analyses of "Archaeopteryx"'s feathers revealed that the animal