Other observers have different opinions. Ars Technica reports:
While most NASA scientists chalked it up to a curiosity and nothing more, one California man has decided that this explanation was not enough. On Monday, Rhawn Joseph, a self-described “astrobiologist” filed a writ of mandamus against NASA. In his 11-page brief, he accused NASA of a “dereliction of duty,” and wants to compel the agency to take “100 high-resolution photographs” of the rock in question.
. . .
Joseph further argues that he “immediately recognized” the rock for what NASA officials apparently could not: a “mushroom-like fungus, a composite organism consisting of colonies of lichen and cyanobacteria, and which on Earth is known as Apothecium.”
A copy of Joseph's writ is available here. I recommend it highly. Here is a sample of some of its strongly worded language that also details some of Joseph's efforts before his filing:
[A]lthough the rover Opportunity is equipped with a "microscopic imager” no microscopic investigation was under taken and no microscopic pictures released. Any legitimate scientist would have taken hundreds of close-up and microscopic pictures from every angle. Inexplicably NASA and its rover team not only failed to take close up photos they refused even after John Callas, Steven Squyres, Charles Bolden and other NASA administrators at NASA headquarter [sic] were contacted by this Petitioner and supplied evidence that this was a biological organism which had germinated on that rock and grew into a larger organism after 12 Martian days had passedJoseph has written more on the Mars rock. He has an article on the (peer reviewed?) website, Cosmology.com, where he writes about his investigation of the rock (or fungus) photos. Here is the abstract:
An analysis of photos taken of the Martian surface by the NASA rover Opportunity, 12 Martian days apart and released to the public in January 2014, reveals evidence of biological activity. In photo Sol 3528, a small "bowl-shaped" growth appears on a Martian rock outcropping. When photos were taken of the same outcrop on Sol 3540 (12 Martian days later), the small bowl-shaped structure had become a fully grown bowl-shaped organism resembling Apothecia. What appears to be spore-producing "paraphyses" can be observed on the structure, as is apparent upon magnification and which is typical of Apothecia. Apothecia are composite organisms, a mixture of fungus and cyanobacteria. The lack of any debris field or disturbance of Martian soil or small stones in the immediate vicinity of the structure rules out meteor or a rock which was displaced from another location.It will be fun to see how this lawsuit progresses. I look forward to reading additional motions and papers by Rhawn Joseph.