Why does the Obscurus not appear in the textbook?

Question

In the film version of Fantastic Beasts and Where to Find Them, the main story revolves around a creature called an Obscurus. Now without giving too much of the story away, Mr. Scamander has particular interest in this creature. He goes to great lengths to try to protect the one he has located and contained in his briefcase.

However, in his textbook of the same name, the Obscurus is not one of the entries. Although the in-universe publisher is "Obscurus Books".

Is there any reason why the creature was omitted? Did Newt give any in-universe explanation or has JK Rowling commented on the matter out-of-universe?

Answer 1

Word of God answer from Rowling: "An Obscurus isn't a creature"

Rowling responded to a fan's speculation on twitter, saying that Obscurus would not be featured in the updated edition of Fantastic Beasts and Where to Find Them, because it "isn't a creature".

Scholastic: The new edition of Fantastic Beasts and Where To Find Them will feature a foreword by Newt & six new beasts!
Ruby: Let me guess: Swooping Evil, Thunderbird, Wampus, Pukwudgie, Horned Serpent and Obscurus
J.K. Rowling: An Obscurus isn't a creature...

Answer 2

Well, first of all, quite a number of creatures are omitted from the version of Fantastic Beasts published by J.K. Rowling. No thunderbird, no swooping evil, and so forth. I suppose one could argue that they were redacted, but Rowling has mentioned (on Pottermore) various other creatures that would seem to meet the criteria for “beasts” as laid out in Fantastic Beasts and Where to Find Them, yet are not mentioned.

Perhaps the textbook that we have is not the Fantastic Beasts that people really use in HP. Perhaps, for example, it was redacted for publication for the non-magical community.

But more relevant to this particular case, the evidence suggests that Newt does not consider the Obscurus a "creature" or “beast”:

MADAM YA ZHOU: You know which of your creatures was responsible, Mr. Scamander?

NEWT: No creature did this . . . Don’t pretend! You must know what that was; look at the marks . . .

ANGLE ON SENATOR SHAW’S FACE.

ANGLE ON NEWT.

NEWT: That was an Obscurus.

_{Fantastic Beasts and Where to Find Them}

Since the Obscurus is a manifestation of the subconscious of a witch or wizard, and can indeed be spoken with and reasoned with to some extent (as we see at the end of the movie), it seems possible that Newt considers it more being than beast.

Answer 3

It’s a parasitic Dark force, not a creature.

When Newt and Tina explain to Jacob what an Obscurus is, they explain that it’s an uncontrollable dark force created when a young wizard tries to suppress their magic powers.

“NEWT
I met one in Sudan three months ago. There used to be more of them but they still exist. Before wizards went underground, when we were still being hunted by Muggles, young wizards and witches sometimes tried to suppress their magic to avoid persecution. Instead of learning to harness or to control their powers, they developed what was called an Obscurus.

TINA
(off JACOB’S confusion)
It’s an unstable, uncontrollable dark force that busts out and – and attacks . . . and then vanishes . . .”
_{^{- Fantastic Beasts and Where to Find Them (The Original Screenplay)}}

Newt further describes it as a parasitical magical force.

“GRAVES
So it’s useless without the host?

NEWT
‘Useless? Useless?’ That is a parasitical magical force that killed a child. What on earth would you use it for?”
_{^{- Fantastic Beasts and Where to Find Them (The Original Screenplay)}}

The Obscurus isn’t in “Fantastic Beasts and Where to Find Them” because as Newt, the book’s author, explains, it’s not a creature, it’s a parasitical magical force.

Answer 4

In the book Fantastic Beasts, Newt outlines that there are three categories of magical entities: beings, beasts and spirits. Dementors for example are spirits and I’m guessing an Obscurus is as well which would explain its absence from the book and be in accordance with Rowling’s and Newt’s assertion that it's not a beast.