Pinnae

Some ferns, such as Hen and Chicken Fern produce new plants at the tips of the fronds' pinnae, which are sometimes referred to as bulbils.

The ear ossicles are pachyosteosclerotic (dense and compact) and differently shaped from land mammals (other aquatic mammals, such as sirenians and earless seals, have also lost their pinnae).

The facial region of skull is relatively small, with pinnae very small or lacking, and the vibrissae are well developed.

The pinnae were free on day 36, and eyes opened later, on days 115–121.

This occurs when the pinnae are still, and the animal can enhance the effect by flapping them.