A thicker atmosphere would provide more static lift, but flapping wings in thicker atmosphere would require larger muscles and use more energy. There are schola

A thicker atmosphere would provide more static lift, but flapping wings in thicker atmosphere would require larger muscles and use more energy. There are scholarly writings out there on this topic, but I'm not familiar enough with any of them to have an opinion. I know there's a school that argues pterosaurs couldn't fly today solely due to lower atmospheric density, and a school that argues they could. I think the lower oxygen levels would still be the primary barrier due to energy requirements.