Parallel to whale evolution: bone density increase in human ancestors and whale ancestors.
Whales originated from aquatic artiodactyls in the Eocene epoch of India
This undated handout artist rendering provided by Northeastern ... - Yahoo! News Photos
[50 million years ago, coastal India, artiodactyles are the taxonomic group including ancestors of deer, cows, pigs, hippos, whales in parallel convergence but not genetically related to elephants, manatees, tapirs, rhinos]
JGM Thewissen, LN Cooper, MT Clementz & BN Tiwari 2007 Nature 450:1190-4
Whales originated from aquatic artiodactyls in the Eocene epoch of India : Abstract : Nature
Although the first ten million years of whale evolution are documented by a remarkable series of fossil skeletons, the link to the ancestor of cetaceans has been missing. It was known that whales are related to even-toed ungulates, but until now no artiodactyls were morphologically close to early whales. Here we show that the Eocene South Asian raoellid artiodactyls are the sister group to whales. Indohyus is similar to whales, and unlike other artiodactyls, in the structure of its ears & premolars, in the density of its limb bones & in the stable-oxygen-isotope composition of its teeth. We also show that a major dietary change occurred during the transition from artiodactyls to whales and that raoellids were aquatic waders. This indicates that aquatic life in this lineage occurred before the origin of the order Cetacea.
Re: Whale evo
Whales may have evolved from raccoon-sized creature - Yahoo! News
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Whales may be related to deer-like beast - Yahoo! News
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(MV: dense limbed quadrupedal wader in shallow waters)
my interpretation:
I tend to agree, the dense-limbed version of mouse deer - raccoon form/niche sounds right, though loss of fur coat and replacement with subcutaneous fat (pig-like) probably occurred early, since it was shallow dwelling not deep diving. Note the exposed teeth, like some small tropical deer, and recall the large missing canines in beluga whales which recently disappeared, and the smaller ivory canine teeth of large deer. Manatees are specialized to eat sea grass, this animal probably did not.
50ma ancestor of whales, deer, pigs, hippos probably looked and lived somewhat similarly, 5 toes, canines, semi-aquatic, probably rolled around in mud during drought, omnivorous-herbivore large rat, probably occasionally scavenged as well, as do pigs, which eat fish, crayfish, molluscs. I doubt it was specialized herbivore, but able to live on plants generally including creek, marsh and littoral plants.
no backfloating. no vertical floating/wading. some slight aquarboreal abilities (not as well as tropical fishing cat or grey fox) possibly mangroves.
Possibly tropical uplifting Himalayan rivers were too cool for crocs (only smaller fish eating gharials) so river-sea didn't have large fast predators, allowing these and manatee ancestors to develop more
aquatic traits around Indian coasts and in rivers.
Some physiological/niche parallels to babirusa, tapir, capybara, SE Asian mouse deer.
At some point, switching to aquatic sleeping and superb echolocation required aquatic-only specialization, splitting from hippos, pigs and semi-aquatic deer ancestors.
DDeden
