Redescription, taxonomy and phylogenetic relationships of Boavus Marsh, 1871 (Serpentes: Booidea) from the early–middle Eocene of the USA

The extinct fossil snake Boavus occurs in early–middle Eocene localities in the United States. Four species are currently recognized, but until now, no formal phylogenetic analyses have been conducted to test its relationships within snakes. Here, we provide an osteological redescription and systematic revision of the genus, accompanied by phylogenetic analyses using multiple methods. Based on new morphological information obtained through first-hand observation and published descriptions, differences between Boavus occidentalis, B. agilis and B. affinis can be ascribed to normal intracolumnar vertebral variation, making the latter two junior synonyms of the first species. Our phylogenetic analyses retrieved Boavus within crown-Booidea as an early booid but outside of Boidae. A morphological and molecular analysis of booids, with dense taxon sampling including fossil and living forms, results in a new booid phylogeny. Boavus, along with other fossil booids from Europe (Eoconstrictor, Messelophis, Rieppelophis, Rageryx), suggests that crown-Booidea likely diverged earlier than estimated by some molecular studies (∼45.4 Ma).