rlQuote: have you got any good explanations of how aquatic critters like dolphins 'evolved' sophisticated sonar 'a little bit at a time' , ( and they didn't have very long to get it done either) ?
As the southern Tethyan sea began opening, the entire S Asia area was like a big swampy foreland. Lots of hillocks at sea level and islands connected by shallow embayments. Think of an area as long as the Arabia through SE ASian subcontinent , except its dotted with an expanse of tidal marshes like the mississippi delta. About 56 million years ago, small artiodactyl animals like ambulocetus and pakicetus began differentiating small changes that showed an adaptation to these marshy forelands. Fossil eveidence from the entire S Asian area, especially around the Sunderbaans and bangladesh then clear over to and reemerging at the W inDian and Pakistan coastall areas (remember, India was still being "delivered" 50 + my ago )
Pakicetus and a number of these early fossil "pre-whales" had gradually exibited identifiable evolutionary changes, seen clearly in fossils up the geologic column. Changes such as:
1The sinus and nares began to migrate from the snout tip eventually to wander to the top of the head. (This took about 35 million years, I suppose thats fast, but its clearly evidenced, so its not much under debate)
2feet structures clearly diverge from the "split hooved " animals and began to modify through time as they started out as "river edge loungers" to become more active water habitues. The fossils show animals with body structures not unlike otters, but with legs and feet modifying into flippers rather than webbed paws
3The outer ear and immediate internal structures (stapes etc ) began to be minimized and the jaw and hyoid became more of a hearing tool (Think about it, the original animals could hear well
in air but later became structurally modified to hear better in water
As the entire continent of Asia swung away from its adjoining pre-Tethian land areas, this whole S continent became more open sea and shorefront property (VERY GRADUALLY- about 6 cm a year or about 5 inches)
As the paleo-"cetids" began hearing in water better, they gradually developed so und emitting structures around a hyoid that became modified to develop along with the changing breathing channels. The Nasal structures were gradually migrating to the top of the head and the sound emitting followed by virtue of skull modifications.
The whales and porpoises then (about 30 my ago) began to diverge into 2 major groups, both having rudimentary echlocation systems that further developed so that by about 18 my ago,The porpoises and whales seemed pretty much equipped like modern ones.
The fossil and DNA records of cetacean development through time is one of the best records weve got. There are literally thousands of key stage specimens of fossils that show evolutionary trends
It seemed that the sequence was quite logical. First the pre-whales had their legs and feet modified to more constant life around water then their hearing modified to be better equipped to hear underwater, and, as their lives in water became more " forced full time", their echolocation by active pinging gradually developed along with the breathing apparatus. Remember, this is all a consequence of the rapidly changing environment as an entire plate area began "swinging" apart and leaving an open ocean area behind
I dont know why youre so incredulous RL, as a parallel the newest "Little Lucy" shows an intermediate hyoid bone that while "monkey like" in its structure, showed that it evidences that it is being modified as , perhaps screams and grunts would give way to actual verbalization.
Also, the DNA records from modern whales and specific artiodactyls indicate and ancestral "common ancestor" relationship.
Theres tons of stuff on the web about whales and porpoises and evolution of structures in this divergant group that had its ancestor as a small hoofed animal that had the blind fortune to live in an area like the Mississippi delta. (hoofies are a real pain in the ass when you get your legs sucked in the muck so why not evolve so you can make a better living at the environment at hand)
Were you to concern yourself about echolocation of bats, youd have a much better case in incredulity. Bat fossil records are very sparse. Apparently the number of bat fossils are quite limited.