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
Specimens of Archaeopteryx Justice in Karlsruhe, which upheld the Superior District Court's decision in 2003, bringing a 14-year lawsuit to a close and earning the sixth "Archaeopteryx" specimen its name of Solnhofen. The Solnhofen specimen represents the largest "Archaeopteryx" individual known. It is represented by a nearly-complete skeleton on a plate sized 39 x 52 cm. There is no counterslab associated with this specimen. The skeleton shows a death posture typical of theropods and especially similar to that of the Eichstätt specimen. The animal's carcass was likely deposited and buried completely articulated. Despite the specimen's skeletal completion, plumage traces are very faint and