(These are notes I was making while going through the description, so they aren't very organized.)
Right, there aren't any subtropical biomes here. Perhaps that will be rectified later.
Spearfishing: herons use bait to hunt, as well as fake safe spots.
Hang on, these got to Fermi? Land of the Fermisaurs?!
The underside spikes make mating difficult, true, but protective spines make mating tricky for spiny mammals, and hyenas have quite a difficult time giving birth. "Limited advantage" would probably not be sufficient reason to get rid of the spikes, unless it had some disadvantage as well. If it needed to lie flat on its nest and cling to the bark to avoid getting hurt in storms, it would be be able to lie flatter without the spikes on its underside. If female Seashrogs would preferentially mate with male Seashrogs with smaller underside-spikes (especially likely as they mate belly-to-belly) it's plausible the males' underside spikes would become tiny, and females' spikes would become smaller as a side effect of selection.
"Making noise similar to those of squeaky toys". That's hilarious. I'm just imagining these guys get the reputation of being super-dangerous and untouchable, so some tiny, delicious creature squeaks like one of these just to trick predators.
Not all mammals (and surely shrews) are prone to scurvy. Did it lose Vitamin C production?
"he leftovers are dried out in the sun and stored inside the nest." Do any animals specifically dry out food? If not, that might need to be tweaked.
"relatively the same" You mean "relatively unchanged".
You should elaborate on "basic language". Do you mean that as in "knows lots of tricks" or "communicates simple desires via a lexicogram computer" or "can use a lexicogram computer to accurately report a sequence of events that happened hours ago"?
It's interesting to see the Mangots, Gumjorns, and Hockels spreading more.