What is "sylviornithidae"

Sylviornithidae is an extinct family of flightless birds. Tradiationally assumed to be within Galliformes, recent phylogenetic studies showcase that they rest outside of the galliform crown-group, making them the most recently lived non-galliform Pangalliformes. For the longest time it has been used as a monotypic family for Sylviornis, but recent studies showcase that Megavitiornis was part of this clade as well.