My How Much I've Learned

After 4 years of intensive study, including many sleepless nights and GPA of 3.6in my final year, I apparently can't tell the difference between an early jawless fish and a turtle. I was at the warehouse that containes many of the University's not yet studied specimens and was showed a pile of red Australian limestone sitting outside, weathering out. There were several chunks left around that were not in the pile of rocks to keep, so I was allowed to take one home. Finding one with a pit of thin flat bone with a dimpled texture sticking out I assumed that it was a turtle and that the limestone was from a Plio- or Pleistocene limestone deposit like at Riversleigh Australia. Apparently it's devonian and the bone I picked up was an armoured jawless fish similar to Bothriolepis.
Fish:


Turtle: