Hi,

I'm searching for (realistic) smaller mammals for poser like:

hedgehogs

rabbits

hares

small rodents

weasels

otters

...

also very much appreciated would be a realistic wolf and / or fox.

Are there any such things out there?

If you search for "Animals" at DAZ and limit it to Poser results you'll see a whole bunch of various animals, most of them being Poser 7 era. 

The search at Rendo doesn't have an animals category and searching for that term doesn't filter real well.  There is a Forest Bundle available which used to be sold at Content Paradise. But that's back in the Poser 6/7 era as well.

Whether or not they are realistic enough for your needs is the question. Standards have changed a lot since those days.

DAZ3D would be the place to check for more realistic animals compatible with Poser.  When Content Paradise was open, they had a variety of animals, but in my opinion, they were subpar.  Some of those are now legacy content in Poser.

Renderosity does have an animals category.

Try here https://www.renderosity.com/marketplace/departments/359578/wild?sb=newest&page=1&results_per_page=120

or here https://www.renderosity.com/marketplace/departments/359577/domestic?sb=newest&page=1&results_per_page=120

A lot of these are the ones hborre mentioned from Content Paradise but there are some from elsewhere

Thank you...

the content paradise animals are.... really not up to standart, I'm afraid. I searched through DAZ and will again, but it's also not  a real good choice over there. Bigger animals no problem (but there Hivewire has filled the gap very well in regards of felines, horses and deer; still hoping for more choice for the dog though) but smaller beats - meh. The Noggins rat is still serving well enough, and I have a range of Lynes, but thewse are very basic.

Do you need to pose them? Fab.com (was Sketchfab) has a lot of 3D models some of which are high quality, just not as Poser characters/props. Usually can be used as fbx. Quality varies but some look good. https://www.fab.com/category/3d-model/characters-creatures--animals  Prices tend to be high though.