Viral fossils are the subject of an emerging field of Evolutionary Biology dubbed Paleovirology, the study of ancient viruses. Viral fossil or Paleovirus is an informal term for regions of genomes that originate from ancient germline integration of viral genetic material. The scientific term for such regions is endogenous viral element or EVE . EVEs that originate from the integration of retroviruses are known as endogenous retroviruses, or ERVs, and most viral fossils are ERVs. They may be traced to millions of years back, hence the terminology, although strictly speaking, it is impossible to detect an ancient virus in fossils. The most surprising viral fossils originate from non-retroviral DNA and RNA viruses.
Types of Viral fossil 
Although there is no formal classification system for EVEs, they are categorised according to the taxonomy of their viral origin. Indeed, all known viral genome types and replication strategies, as defined by the Baltimore classification, have been found in the genomic fossil record. Acronyms have been designated to describe different types of viral fossil.
EVE: endogenous viral element .
NIRV: Non-retroviral Integrated RNA Virus
ERV: Endogenous Retrovirus
HERV: Human Endogenous Retrovirus
DNA viruses 
RNA viruses 
Viral fossils originating from non-retroviral RNA viruses have been termed Non-retroviral Integrated RNA Viruses or NIRVs. Unlike other types of viral fossils, NIRV formation requires borrowing the integration machinery that is coded by the host genome or by a co-infecting retrovirus.
Successful attempts to "resurrect" extinct viruses from the DNA fossils have been reported.
See also 
- "Ancient "Fossil" Virus Shows Infection to Be Millions of Years Old", by Katherine Harmon, Scientific American, September 29, 2010
- Katzourakis, Aris; Gifford, Robert J. (18 November 2010). "Endogenous Viral Elements in Animal Genomes". PLoS Genetics 6 (11): e1001191. doi:10.1371/journal.pgen.1001191. PMC 2987831. PMID 21124940.
- Weiss, RA (2006 Oct 3). "The discovery of endogenous retroviruses.". Retrovirology 3: 67. doi:10.1186/1742-4690-3-67. PMC 1617120. PMID 17018135.
- Emerman M., Malik H.S. "Paleovirology — Modern Consequences of Ancient Viruses". PLoS Biology, 8(2)2010 doi:10.1371/journal.pbio.1000301
- Taylor, D. J.; J. Bruenn (2009). "The evolution of novel fungal genes from non-retroviral RNA viruses". BMC Biology 7. doi:10.1186/1741-7007-7-88.
- Koonin, E. (2010). "Taming of the shrewd: novel eukaryotic genes from RNA viruses". BMC Biology 8. doi:10.1186/1741-7007-8-2.
- "How to Resurrect an Extinct Retrovirus", Scientific American, November 2, 2006