The standards also vary by field. It's not unusual for supervisors to be the last author on any paper that a group publishes, even if they had basically no inpu

The standards also vary by field. It's not unusual for supervisors to be the last author on any paper that a group publishes, even if they had basically no input into it directly. I've been listed on papers just because I designed and built the equipment that happened to be used for the experiments, even though I didn't do anything but a quick review of the actual paper. For most papers, unless there's an indication otherwise, it's generally only safe to assume the first author listed that actually did the bulk of the work and write-up, and the others are there mainly for having some potentially quite indirect contribution.