I’m a huge believer in identifying the need for a proper tool for any specific task.
The nature of flora and fauna calls for organic modeling. Plain Rhino can do this to some extent and in small infrequent doses, but IMO it’s an inefficient exercise to get to that final result.
Can an OBJ/STL mesh head be purchased and imported? Yes. But what happens when specific features need to be changed or altered? (cheeks, nose, eyes) I’ll admit I’ve not explored Rhino’s mesh tools to tell if it’s possible to massage an imported mesh that way, but I can’t imagine it’s simple. Same can be asked about a polysurface head done purely in Rhino nurbs. Can changes be made easily to one region without worrying about its edge tearing away from an adjacent polysurface?
An organic modeling plug-in like Clayoo or TSplines allows immediate and direct manipulation of surfaces. The surface is continuous and not made up of a patchwork. Therefore, no tearing issues. Once the organic model is manipulated to satisfaction, a copy can be converted to nurbs polysurfaces as needed. All future changes in features are simply made in the organic model (direct manipulation) and one-click-converted to a watertight Rhino polysurface.
If creating organic objects will be a frequent requirement, I’d suggest investing the time to learn the organic modeling plug-in. If it’s a one-time requirement, acquire a mesh or look into a figure-creating software like Poser. You should probably also seek a program called “Marvelous Designer”
I tackled human head modeling within a year of picking up T-Splines. This model done using only two isometric photos of the subject.