According to a morphological analysis by Thewissen et al., pakicetids display no aquatic skeletal adaptation; instead they display adaptations for running and jumping.

Great variations in aquatic adaptations exist among them, with some probably able to support their weight on land, whereas others could not.

They don't show any aquatic adaptations.

He noted that several related forms without aquatic adaptations have similar cervical ribs, which provide a passive support system for the elongated neck.

Several animal groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water.

Apsaravis, however, was found in a sand dune environment, and it has no obviously aquatic anatomical adaptations, giving clear evidence that not all early members of Ornithurae were shorebirds.

Skin of the Cretaceous mosasaur Plotosaurus: implications for aquatic adaptations in giant marine reptiles.

They then erected two subfamilies for the rest of the protocetids based on their degree of aquatic adaptation:

Ceratopteris was long placed in the monogeneric family Parkeriaceae, thought to be unique because of its aquatic adaptations.

It had aquatic adaptations including flattened tail bones and remnants of soft tissue between the toes of the back feet, suggesting that they were webbed.