FIG. 22. Astrapotherium magnum A in Cranial Morphology And Phylogenetic Relationships Of Trigonostylops Wortmani, An Eocene South American Native Ungulate

FIG. 22. Astrapotherium magnum A, AMNH VP-9278 and B, YPM PU 15261, rostral end of palate in ventral and dorsal aspects. Long tongue of bone in center of each view is composed of fused palatal processes of right and left premaxillae. In all examined astrapotheriid specimens preserving premaxillae, these elements are completely edentulous (in B, projections on rostral margin represent broken edge of premaxillae). In B, ventral and dorsal surfaces of premaxilla are flat without grooves; sutures are fused or hidden by matrix, and left premaxilla has been medially crushed onto right premaxilla. Key: 1, interpremaxillary suture (partly obliterated in YPM PU 15261); 2,?grooves, exposed by breakage (in AMNH VP-9278 only); 3, medial (internal) maxillopremaxillary sutures; 4,?foramen exposed in latter suture; 5, floor of nasal cavity; 6, terminal part of maxilla bearing canine tusk. Incisive foramen not securely identified (see text). In figure 42, compare lengthy lateral maxillopremaxillary suture in Mesotherium with its absence in Astrapotherium (C157, facial process of maxilla).