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Ornithorhynchus anatinus, the platypus. (A) Lateral view of the skull in a juvenile. (B) Lateral view of the skull in adult. (C) The three teeth (a small pre-molar and two molars) on the upper left maxilla of a juvenile. (D) The three opposite teeth on the lower left jaw. Bars: A and B, 1 cm; C and D, 1 mm.
