Only Female Niironox can get pregnant.

She typically is pregnant for a full year while her pups develop. She carries usually between 1-3 pups at a time. The most a female can have is 6, but that's extremely rare.
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A Niironoxes uterus is similar to canines. But unlike canines, she has to be pregnant longer.

Niironox pups develop slowly, but are born the same way dogs birth their puppies.

I won't go into that level of detail. It's pretty straightforward.
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Niironox are born with their bulbs covered by a thick layer of skin, to hide their tail lights.

They don't start growing quills and plating until they reach puberty (same as us - usually twelve to fourteen years old)

But their tail lights come out when they reach two years old. When they are weaned from their Mothers and gain their teeth.

(cont...)

(I'm writing this at nearly 4am, if it doesn't make a lot of sense, that's why)
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A Niironoxes teats are only visible when she becomes pregnant and become more visible closer to birth.

Once she stops nursing, it takes about 6 months for her body to return to normal. Until then, she'll look similar to the girl in the top left.
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Don't think she's alone in this, the Father will become extremely protective of her and his pups. And very aggressive towards outsiders.

If he chooses to stay around. Most males do, but some will abandon their mates.

Just the same for females, she might give birth and after, abandon her mate and pups.

It all depends on the Niironox and its behaviour. Usually though, they can't ignore their protective instincts.

More on Instincts later. That's all for now.

Interesting!
I'm ngl, the little bellies (or uhh, I guess big xD) on the pregnant Niironox are actually kinda cute!

I honestly have to say, I like the fact you made these guys mammals, it's something you don't see everyday when it comes to dragons, and makes them more unique, at least to me it does--

I really adore this species 'XD

I love their snoots
And I agree with Lilly, it's so cool and unique that they're mammals!