Unreal is very particular about how it arranges vertices and triangles. It will split vertices along all kinds of material attribute seams.
You cannot use the default unreal import path if you can’t deal with this.
I’m assuming that you’re blending between these to create a person-to-wolf morphing animation?
If so, you could perhaps create a morph target that takes the first mesh to the second mesh. You can then animate this morph target between 0 and 1, and then swap out to the new mesh when the morph is done. If you try to skinned animate at the same time, that might not work as well, though.