It was a mammal -- there was a fairly large mammalian class on Zarathustra -- but beyond that he was stumped. It wasn't a primate, in the Terran sense. It wasn't like anything Terran, or anything else on Zarathustra. Being a biped put it in a class by itself for this planet. It was just a Little Fuzzy, and that was the best he could do.
That sort of nomenclature was the best anybody could do on a Class-III planet. On a Class-IV planet, say Loki, or Shesha, or Thor, naming animals was a cinch. You pointed to something and asked a native, and he'd gargle a mouthful of syllables at you, which might only mean, "Whaddaya wanna know for?" and you took it down in phonetic alphabet and the whatzit had a name. But on Zarathustra, there were no natives to ask. So this was a Little Fuzzy.
The three volumes of the Fuzzy series, in order, are:
Little Fuzzy (available as a free read at Project Gutenberg)
Fuzzies and Other People
(first two volumes were also published in a single binding as The Fuzzy Papers before the third volume was found; see below)
The Fuzzy books are a part of a much larger future history created by Piper, as are most of his other novels and short stories.
Note: Piper committed suicide in 1964 with only the first two volumes in the series in print; it was known that he'd written a third volume ... the original manuscript had been submitted to and read by Frederick Pohl, but it disappeared after that. The carbon was eventually found in 1982 and this long-awaited third volume was finally published in 1983: the full tale is here, but there are spoilers in the tellings). In the interim other authors had been commissioned to write concluding novels (I recommend you not bother with those. They were not good)