Thanks again for drawing my attention to this forum.
Speaking of vestigial features, one of my favorite examples with whales and snakes is the manatee / sea cow / dugong.
Unlike whales, which have virtually lost their limbs, the manatee is in the middle of transition between leg and flipper. Not all, but some retain toe nails identical to their elephant cousins, some have completely lost their toenails.
A list of Sirenians, with sketches are at: http://www.savethemanatee.org/sirenian.htm
For instance, West African Manatee has toenails but Amazonian Manatee does not.
Excerpts:
“The nearly complete skeleton of an ancient aquatic mammal with legs has been unearthed in Jamaica. The 50-million-year old skeleton is one of the best examples so far of the evolution from a land animal to an aquatic animal, said Daryl Domning, a paleontologist at Howard University in Washington, D.C., who reported the discovery.”
“The skeleton found in Seven Rivers, Jamaica, is a new genus and species of the order Sirenia, which encompasses the ancestors of modern-day manatees and dugongs. Commonly known as sea cows, sirenians are plant-eating mammals that spend their entire lives in water. They started out as land animals, however.”
http://news.nationalgeographic.com/news/2001/10/1010_jamaicaseacow.html
Hans Thewissen’s team has been doing work on early Sirenian:
Manatee and Elephant Fossils
Seacows (including manatees and dugongs) and elephants are closely related, and their common ancestor lived more than 55 million years ago in Africa or South Asia. They are also related to the Desmostylia, an extinct group of hippo-like mammals that lived on the shores of the Pacific Ocean. Together, Sirenia (seacows), Proboscidea (elephants), and Desmostylia are referred to as tethytheres.
Ongoing research in the Thewissen Lab focuses on the origin and early divergence of the tethytheres. Fossils of anthracobunids are known from Pakistan and India. Fewer than 50 fossils of members of this family have ever been found, and they played a key role in the early evolution of the tethytheres. It is likely that anthracobunids were ancestral to later sirenians, proboscideans, and/or desmostylians.
http://darla.neoucom.edu/DEPTS/ANAT/Thewissen/
LeVar Burton and Sea Cows
LeVar Burton and Veterinarians comparing Sea Cow features with elephants, and give a closeup of the toenails (Click the “Preview This Video” link) for real media segment.
Some further links on sirenians