The Final Outpost

tbh a lot of this is setting it up to look like we might be getting a spuristo-alstalto hybrid of some sort, or a spuristo's equivalent of a glacia and transira

I'm afraid the explanation's much more mundane than that - to be able to breed with the Alsaltos, they need to have all the matching set of genes. So since the Transira Alsaltos, Klara Alsaltos and Glacia Alsaltos all have "Body", "Tails", "Ice" and "Fire" genes, the Silenta Spuristos also need to have that set.