biostudies-literatureLytras SMedical Research CouncilMedical Research Council of the United Kingdomveab012https://www.ebi.ac.uk/biostudies/studies/S-EPMC7955980biostudies-literatureUnknown7(1)Hepadnaviruses (family <i>Hepadnaviviridae</i>) are reverse-transcribing animal viruses that infect vertebrates. DNA sequences derived from ancient hepadnaviruses have been identified in the germline genome of numerous vertebrate species, and these 'endogenous hepatitis B viruses' (eHBVs) reveal aspects of the long-term coevolutionary relationship between hepadnaviruses and their vertebrate hosts. Here, we use a novel, data-oriented approach to recover and analyse the complete repertoire of eHBV elements in published animal genomes. We show that germline incorporation of hepadnaviruses is exclusive to a single vertebrate group (Sauria) and that the eHBVs contained in saurian genomes represent a far greater diversity of hepadnaviruses than previously recognized. Through in-depth characterizVirus evolutionAncient evolution of hepadnaviral paleoviruses and their impact on host genomes.PMC7955980ANID/FONDECYT1180705MC_UU_12014/12ANID/FONDAP/152000022294377Lytras SArriagada GGifford RJfalseAncient evolution of hepadnaviral paleoviruses and their impact on host genomes.Hepadnaviruses (family <i>Hepadnaviviridae</i>) are reverse-transcribing animal viruses that infect vertebrates. DNA sequences derived from ancient hepadnaviruses have been identified in the germline genome of numerous vertebrate species, and these 'endogenous hepatitis B viruses' (eHBVs) reveal aspects of the long-term coevolutionary relationship between hepadnaviruses and their vertebrate hosts. Here, we use a novel, data-oriented approach to recover and analyse the complete repertoire of eHBV elements in published animal genomes. We show that germline incorporation of hepadnaviruses is exclusive to a single vertebrate group (Sauria) and that the eHBVs contained in saurian genomes represent a far greater diversity of hepadnaviruses than previously recognized. Through in-depth characteriz2021-01-01T00:00:00Z2021 Jan2026-05-07T03:18:43.779Z2025-04-03T21:34:20.674ZS-EPMC79559803374754410.1093/ve/veab012