Complex sentence: Like modern elephants, Columbian mammoths were probably social and lived in matriarchal (female-led) family groups; most of their other social behaviour was also similar to that of modern elephants.
Split into simpler sentences: Like modern elephants, Columbian mammoths were likely very social and lived in matriarchal (female led) family groups. It is therefore probable that most of their other social behaviour was similar to that of modern elephants.