In today's Science: http://www.sciencemag.org/cgi/content/full/306/5696/653
Zhou, Z., & F. Zhang. 2004. A precocial avian embryo from the lower
Cretaceous of China. Science 306 (5696): 653.
Precocial because it has a full down covering. It's an enantiornithine.
Cheers,
Christopher Taylor