Non-retroviral integrated RNA viral sequences (NIRVs) potentially encoding ∼280 amino acid homologs to filovirus VP35 proteins are present across the Myotis genus of bats. These are estimated to have been maintained for ∼18 million years， indicating their co-option. To address the reasons for co-option， 16 Myotis VP35s were characterized in comparison to VP35s from the extant filoviruses Ebola virus and Marburg virus， in which VP35s play critical roles in immune evasion and RNA synthesis. The Myotis VP35s demonstrated a conserved suppression of innate immune signaling， albeit with reduced potency， in either human or Myotis cells. Their attenuation reflects a lack of dsRNA binding that in the filoviral VP35s correlates with potent suppression of interferon responses. Despite divergent function， evolution has preserved in Myotis the structure of the filoviral VP35s， indicating that this structure is critical for co-opted function， possibly as a regulator of innate immune signaling.