Do the Dementor and the Obscurus have something in common?

Question

Both feed on human emotion, both are highly deadly, and both do not appear in Fantastic Beasts and Where to Find Them.

Do the Dementor and the Obscurus have something in common? More than meets the eye? Say origin story?

Answer 1

Rowling has said that she "loves the thought".

At first I thought the Obscurus was a baby dementor in its amniotic sac.

J.K. Rowling: I love that thought!
_(Twitter)

This might imply that there is some connection between the two. Rowling usually only expresses her approval of theories that fit her world, while scorning the ones that don't.

Rowling has said that Obscuruses don't appear in the Fantastic Beasts textbook because they "aren't creatures". The exact nature of Dementors are unknown, but Rowling often refers to them as "creatures".

Answer 2

Seems doubtful

Although it's certainly not impossible, one of the problems with any kind of relation between the two is that an Obscurus isn't really a creature; it's described as a manifestation of magical energy, rather than a being in its own right:

An Obscurus is the repressed energy of a child who is forced to hide his or her magical talent. This energy can manifest itself as an entity on its own that can erupt in violent, devastating fury.

^{Fantastic Beasts and Where to Find Them: Magical Movie Handbook "Beasts" The Obscurus}

Newt: 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}

In contrast, we're pretty sure that dementors are creatures; they're certainly capable of independent reasoning, communication, and something that resembles "breeding", which is more than we get from an obscurus. Although their origins are quite mysterious, and I don't want to wholly discount the possibility, it does seem as though they're separate concepts that just happen to be related to the darker aspects of human nature.

Answer 3

Description of a Dementor:

'Dementors are among the foulest creatures that walk this earth. They infest the darkest, filthiest places, they glory in decay and despair, they drain peace, hope and happiness out of the air around them. Even Muggles feel their presence, though they can’t see them. Get too near a Dementor and every good feeling, every happy memory, will be sucked out of you. If it can, the Dementor will feed on you long enough to reduce you to something like itself – soulless and evil. You’ll be left with nothing but the worst experiences of your life.’

-Remus Lupin on Dementors, Harry Potter and the Prisoner of Azkaban

JK Rowling told the Canadian Press in 2000 that "These evil creatures don't, by the way, breed but grow like a fungus where there is decay."

(Source: https://www.quora.com/Where-do-Dementors-come-from-Are-there-Dementor-babies)

Description of an Obscurus:

An Obscurus was the manifestation of the repressed energy of a magical child (known as an Obscurial). Described as a "dark" and "parasitic" force, an Obscurus was created when the child in question was forced to repress their talent through physical or psychological abuse. This energy could manifest itself as a separate entity that can erupt in violent, destructive fury.

(Source: http://harrypotter.wikia.com/wiki/Obscurus)

Though they don't have much in common, there are a few similarities that we can spot, mainly in the description of a Dementor:

"Grow like a fungus where there is decay."

And the description of an Obscurus:

Described as a "dark" and "parasitic" force.

They're both dark and foul creatures that have a similar description in how they look (I.e. Dark and parasitic,) and how they act (I.e. Feeding on human emotions,) but overall they don't have enough in common for any sort of backstory. Though, as ibid said above J.K. Rowling liked the thought of Obscurials being young Dementors:

At first I thought the Obscurus was a baby dementor in its amniotic sac.

J.K. Rowling: I love that thought!

However, as J.K. Rowling did not actually confirm this theory, this cannot be used as canon evidence.