This is rather interesting - a specimen of the bird Archeorhynchus spathula (STM7-11) from the Lower Cretaceous Jiufotang Formation (northeastern China) has been shown to have probable evidence of preserved lungs
Wang, X., O’Connor, J. K., Maina, J. N., Pan, Y., Wang, M., Wang, Y., Zheng, X., & Zhou, Z. (2018). Archaeorhynchus preserving significant soft tissue including probable fossilized lungs. Proceedings of the National Academy of Sciences, 201805803.
Wang etal 2018 Archaeorhynchus lungs.pdf