trying to understand the "Tronco" in a marriage record

example: Tronco
Nicolas Lozano
Jose santos Lozano 1. Timotea Lozano
Proquinta Lozano 2. Telisfora Reinaga
Maria Trinidad Alvarez 3. Lorenzo Galaviz
Jose Guadalupe Duran 4. Maria Galaviz

how do I read this I guess im confused in why certain names are on that list and others are not. example: Maria Trinidad Alvarez is Jose Guadalupe Duran mother why is his dad not on the list.