My assertion is that a biologically active Mars is not an "extraordinary claim." Not at all. Prior to 1965 (so long ago as to be in the Dark Ages!) biology on Mars -- of some sort -- was presumed to exist because there was nothing known to preclude it. That presumption changed, pretty much instantly, when lunar-like craters were discovered by Mariner 4. (In fact, they had been seen telescopically well before 1965, but that's another issue.)

Still, there was nothing to preclude the presence of biology on Mars -- except for those lunar-like visuals (reinforced by the Moon landing simultaneously with the Mariner 6 and 7 flybys in 1969.) Biology on Mars was only "extraordinary" because there was no life on the Moon, and at the time, thanks to those Mariner images, Mars was presumed to be "like" the Moon, although little knowledge of the planet had actually changed substantially. Conditions on the surface of Mars were long known to be unfavorable for most terrestrial life -- too cold, poisonous atmosphere, low pressure, etc -- but that never precluded some kinds of terrestrial life, and cannot by definition be a barrier to Martian life.

As time has gone by, nothing has been adduced to preclude Martian biology, and significant evidence is developed that supports a biological interpretation, yet consensus insists that biology on Mars is an "extraordinary" claim, when it should be nothing of the kind.

In my view, the "extraordinary claim" is that Mars is biologically sterile. Nothing supports that claim at all.