What is unusual about the method of reproduction in monotremes mammals?

The most unusual aspect of monotreme reproduction is that they lay eggs, unlike other mammals which give birth to live young. This is a primitive trait that sets them apart from other mammals and is a key characteristic of this unique group.

Here's a breakdown of what makes their reproduction unusual:

* Laying eggs: This is the most obvious and unusual feature. The eggs are leathery, similar to reptile eggs, and are incubated by the mother.

* Having a pouch: While they lay eggs, monotremes also have a pouch, similar to marsupials, where they nurture their young after hatching.

* Lactation: Like all mammals, monotremes produce milk to nourish their young. However, they don't have teats like other mammals; instead, they have specialized milk patches where their offspring lick milk.

These unique reproductive traits make monotremes fascinating and highlight their evolutionary history as a group that branched off from other mammals very early on.