Complex sentence: There were 25 caudal vertebrae preserved, with 22 still being accounted for; the last several caudal vertebrae, which have been lost, were partially fused into a pygostyle-like structure.
Split into simpler sentences: There were 25 caudal vertebrae preserved, with 22 still being accounted for. The last several caudal vertebrae, which have been lost, were partially fused into a pygostyle-like structure.