FIGURE 1. Map locality, 1) state of Baja California Sur, Mexico; 2) Oligocene outcrops of San Juan Member, El Cien Formation; 3) El Saladito and mesa El Tosoro fossilferous localities, north to San Juan de la Costa village.
FIGURE 2. General stratigraphy and observations at mesa El Tesoro; 1) view of the strata over the mined phosphatic Humboldt bed; 2-3) position of the gray phosphatic sandstone over the Humboldt bed; 4) fossils Tlaxcallicetus cf. guaycurae in situ in the gray phosphatic sandstone and 5) ventral view, left ear region of Tlaxcallicetus sp., field observation at mesa El Tesoro.
FIGURE 9. Detailed features of Tlaxcallicetus guaycurae (MU EcSj5/06/31), (1) pitted edge in the glenoid fossa that suggest a fibrocartilaginous joint; (2) inflated and rounded squamosal prominence; (3) external occipital sulcus on the posterior middle part of the supraoccipital.
FIGURE 10. Ear region and left periotic comparison between Tlaxcallicetus species, ventral view. Tlaxcallicetus sp. (MU EcSj5/18/95) (1-2), Tlaxcallicetus guaycurae (MU EcSj5/06/31) (3-4), and specimen found at mesa El Tesoro, Tlaxcallicetus sp., field observation (5-6).
FIGURE 22. Philogenetic position of Tlaxcallicetus. 1) Under equal weights, consensus tree recovered from 260 parsimonious trees (1327 steps, consistency index CI= 0.246, retention index RI= 0.686, rescaled consistency index RCI= 0.168756, tree total length 1474). 2) Under implied weights: k = 6, consensus tree from 3 parsimonious trees (85.63773 steps, CI= 0.271, RI= 0.724, RCI= 0.196204, tree total length 1338. Black squares mark unequivocal characters that support the different groups (see legend). Support branch belongs only to those clades with 50% or more consistency. Dashed lines suggest a probable inclusion of taxa in clade.