No giant fire-breathing lizards with a nuclear-fission metabolism? No archaic, unimaginably tenacious life-forms with fivefold symmetry belonging to no known phylum, or protean entities reshaping themselves at a cellular level to avoid detection while they assimilate their hosts? Thawing out long-frozen monsters is not what it used to be. And I grant that the name 'pandoravirus' has its ominous elements but the researchers missed a chance by not calling it Kaijūvirus.
discovered Mimivirus. Well, identified it; Mimivirus had been noticed infecting an amoeba in 1992 but labelled as a bacterium on account of being so feckin' large, i.e. visible in a light microscope, and larger than many bacteria.
In accordance with the phenomenon of morphogenetic resonance, other giant virus species started springing into existence wherever people looked for them, including Mamavirus and Megavirus, and (as nomenclature creativity began to falter) CroV the Cafeteria roenbergensis virus. All boasting about a thousand genes spread across million-basepair genomes. Not the usual minimal replication toolkit, designed to function in a bacterial cell or the nucleus of a eukaryote where the replication / transcription machinery is already in place waiting to be hijacked, but rather enough for independent transcription and tRNA-ing and ribosoming in viral assembly factories in the host cell's cytoplasm. Inevitably they have parasitical viruses of their own -- a fractal viral ecosystem -- which piggyback on the giant-virus factories.
Also too, these new Nucleocytoplasmic large DNA viruses are all related -- their replication proteins are more similar among themselves than they are to the eukaryote and prokaryote equivalents. They inherited them from a common ancestor rather than acquiring them from their hosts in independent gene-transfer episodes in the course of the last few billion years. Perhaps they all started as a cellular entity that downsized itself; if so, this happened about the same era that bacteria and eukaryotes and archaea were diverging. Or you might prefer the egg-came-first theory that megaviruses became the first eukaryotes (starting out as an infection within another prokaryote, but staying in place rather than killing the host, absorbing the host's DNA, and becoming a nucleus).
There appears to be a tradition (or an old charter or something) that any paper on Supersized Virology should include one Jean-Michel Claverie among the co-authors.
Anyway, all these megaviruses replicate within a geometrical icosohedral capsid, like a flu virus although orders of magnitude larger. Until J.-M. Claverie looked in a pool behind an Australian university and found the first Pandoravirus, which has a 2.5-million-basepair genome. Also a nicely-rounded bottle-shaped capsid as if trying to look organic. "Don't be scared of us, we're not all harsh and robotic like Mimivirus, we're organic, trust us." FALSE SENSE OF SECURITY sez I.
No great surprise, then, that the genetic constitution and replication proteins of the Pandoravirus species look nothing like the mechanics of the Megaviruses. Wherever they came from, it was an independent path of evolution. So where does the 34-millennia-old Siberian virus fit into the picture? Apparently it has a flask-shaped capsid like Pandoravirus, BUT its genome fits comfortably into the Megavirus family.
Evolution is just messing with us now.