Table 1. Skull measurements of Obdurodon and Ornithorhynchus.

Data are means ± SD. n, number of specimens.

Measurements	Obdurodon	Ornithorhynchus	n
GLS	131.20	92.80 ± 8.31	32
Angle (a)	87.06	69.15 ± 3.43	25
Angle (b)	80.59	93.33 ± 3.55	25
Infraorbital foramen	3.47	3.13 ± 0.38	32
Braincase	35.86	32.18 ± 2.19	32
Zygomatic breadth	50.63	42.20 ± 3.98	32
Occipital breadth	27.45	23.76 ± 2.36	32
Orbit	11.85	9.17 ± 0.84	32
Geometric mean	25.41	21.02 ± 1.87	32