cursorial (capable of running) mesonychid Pachyaena. Archaeocete femora are generally much shorter. The femoral head is spherical and, at maximum, has a width of , similar to Indocetus but much larger than mesonychids and Rodhocetus. The trochanteric fossa, supporting the lateral rotator group at the hip, is quite deep, but other than this, the femur does not seem to have supported particularly strong extensor or flexor muscles. The femoral condyles of Ambulocetus are quite long compared to those of other archaeocetes and mesonychids, suggesting the knee was capable of hyperflexion (bending). The tibia is overall similar to those of mesonychids. The feet are huge, probably longer than the femur. The toes are also relatively long, with the fourth digit measuring in length. The fifth digit is slightly shorter and much less robust than the fourth. The phalanges of the toes are short, and end with a convex hoof. Like seals, the phalanges of both the hands and feet are flattened, which may have streamlined them to allow for webbed feet. Palaeobiology Diet The robustness of the cheek teeth, as well as the cusp arrangement, suggests they were involved in crushing, and the fact that both the premolars and molars were involved in crushing indicates Ambulocetus required a large area for crushing, such as when biting into large prey items. Similarly, the broad and powerful snout makes it unlikely it was pursuing small, quick prey items (which would have required a narrow snout like dolphins or gharials). The snout was also long, which may have precluded the ability to crush bone because it would have had reduced structural integrity at the tip. The anatomy of the cheek teeth resembles those of Mesozoic marine reptiles which fed on armoured fish, large fish, reptiles, and ammonites, and the teeth may have been used to grip onto prey firmly. Therefore, Thewissen suggested Ambulocetus was most likely an ambush predator, the jaw adapted to handle struggling prey. The unusually deep pterygoids potentially functioned to dissipate force while the prey was struggling. The eyes of Ambulocetus were placed on the top of the head, similar to crocodiles and other animals that prefer to keep most of their body submerged with the eyes peeking out of the water. The nasal canal has bony walls extending into the throat, much like in crocodiles where they keep the nasal airways open while the animal is killing prey either by