Skull shape and size changes in different subpopulations of the California Sea Lion (Zalophus californianus) in Mexico.

This article focuses on the morphological divergence of skulls between two geographically separated subpopulations of California sea lions (Zalophus californianus) in Mexico: one on the Pacific coast of the Baja California peninsula (PC) and the other in the Gulf of California (GC). Using artificial neural networks and 2D geometric morphometrics on adult male skulls, the study found no significant differences in skull size but identified significant shape differences across dorsal, ventral, and lateral views. Specifically, sea lions from the GC subpopulation exhibit wider, lower skulls with a more voluminous nuchal crest and narrower rostrum compared to those from the PC subpopulation. These morphological distinctions align with previous genetic studies, suggesting that the two subpopulations are undergoing evolutionary divergence potentially driven by geographic isolation and differing environmental pressures.