Which type of armor did the legions under Caesar and Augustus use?

This question came via a comment on an earlier podcast.

'Which type of armour did the legions under Caesar and Augustus use? I understand the lorica segmentata was adopted later, but was it used during Octavian's era? 

Additionally, I've found references to three types of scuta (shields): the curved oval used by late Republican soldiers, a slightly curved rectangular version, and the iconic rectangular scutum seen in reliefs of Trajan and Aurelius. Could you clarify which types of shields were used during Augustus' later reign and the periods of Germanicus and Vespasian?'

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