Which came first, aquatic or terrestrial mammals?
343898
The most recent common ancestor of mammals and the bird/reptile clade was probably a terrestrial creature.  The most recent common ancestor of all live mammals was also terrestrial.  The animals along that direct line of descent were also all probably terrestrial.\n\nCastorocauda was a semi-aquatic animal that evolved along a side branch of that line.  Semi-aquatic mammals have evolved many times among modern mammals.  Examples are beaver, otter, platypus, star-nosed mole, hippo, muskrat, water vole, yapok, desman, nutria, and others.  These can all be traced to terrestrial ancestors.\n\nModern marine mammmals can also all be traced to terrestrial ancestors.  \n\nThe closest living relatives to whales and dolphins are the hippos.  They evolved from a terrestrial even-toed ungulate.\n\nThe closest living relatives to the manatees and dugongs are the elephants and hyraxes.  They evolved from a terrestrial afrotherian.\n\nThe closest living relative to the seals, sea lions, and walrus are raccoons, weasels, skunks, badgers, red pandas, and their relatives.  They evolved from a terrestrial caniform carnivoran.
403629
The Dolphin as a spices is billions of years old. So to answer your question they evolved from sea dinosaurs.
434454
Claim: Hymens are an aquatic trait. \n\nFact: Besides humans, hymens are found in lemurs (fellow primates, you'll note), guinea pigs, mole rats, hyenas, horses, llamas, and fin whales. Except for fin whales, none of these mammals are aquatic.  Also, AATers suggest that the reason for a hymen in humans was to seal off the female reproductive organs from waterborne parasites and such; but since the hymen is generally absent from the time of first intercourse (and very often before) this protection wouldn't be available for much of the female's lifespan.\n\nSo if by fihes you mean fin whales yes they do :D\n\nEDIT\nSo you know AAT stands for Aquatic Ape Theory
995613
Well, Studies have shown that life started with a single cell organism. This was figured by the adaptation that they grew to multiple cells which were mammals. So the correct answer would be "The chicken came before the egg.
258814
since we all evolved form one celled organisms, which started in water, then we do come from fish. the "land egg" got us out of the water.
855593
I would look here for your answer and/or a link that could get you your answer http://en.wikipedia.org/wiki/Vertebrate\n\nGood Luck!!!
897506
Terrestrial tetrapods have no spiral valve, more veination, large intestines, while fish may have spiral valves and no large intestines.
25919
Mammals such as your cat and us evolved from early amniotes called Therapsids, as the Professor stated. Therapsids were sometimes called "Mammal-like reptiles" but in fact, all the "modern reptiles" (lizards, snakes, crocs, turtles) evolved from another "branch" of early amniotes. The things that all amniotes have in common either 1) were inherited from a common ancestor or 2) evolved independently and achieved similar aspect. Most of the times you can tell when this is the case because such features look superficially similar, but not so much under closer examination. For example, vertical pupils are characteristic of many nocturnal animals that are very dissimilar, such as cats, alligators, or some frogs; these were acquired independently and these animals regulate their eyes somewhat differently. However, all vertebrates have one pair of eyes; this is an inherited shared trait.
712762
Land animals are awesome, but we seem to know more about them than marine animals. Marine animals are so amazing, so fascinating, so mysterious. Underwater wildlife is so beautiful. If I were you, I'd go with marine animals. They are so breathtaking. I love whales. I really want to go whale watching. It's so amazing that I want to cry because of the beauty.....I love marine wildlife. If you major in marine biology, just think of the amazing opportunities you'll get....all the marine wildlife to see, to discover....go for it.
103909
>>>>>> Only vertebrates have teeth.\n\nThat isn't true. Lampreys have teeth and are not vertebrates. The radulae of many molluscs also have teeth.\n\nThe rest of your answer was spot on though.
1111879
It's known as "fossil fuel" because it was created ages ago. The "fossil" part is not dinosaurs or mammoths, etc. Liquid petroleum came most likely from prehistoric small marine animals and algae that became buried in marine sediments. Terrestrial plants buried in freshwater swamps usually became coal. Larger animals are usually eaten by scavengers or decomposed by fungi and bacteria and play little or no role in the production of petrochemicals. Some oil deposits were ancient long before dinosaurs were around.
862177
.  Animals which have a simple evolutionary history are usually soft bodied, and soft bodies animal do not leave good fossils.  It is easy to find analogs for evolutionary steps toward certain animals, the whale for example,  but finding an clear-cut sequence of fossils is difficult.\n.  But, looking at analogs, consider the weasel, the otter, the seal, the manatee and the whale.  The difference between any two steps in this sequence is fairly small, but the difference from one end to the other seems quite large.\n.  There are enough fossils whose ages may be determined that, studied as a group, studied as a group, they demonstrate an increase in complexity of organisms over time and indicate familial relationships.  Bony headed fishes, known only from fossils, were the ancestors of fish like the coelacanth.  Fishes like the collegian were ancestral to both modern fishes and the fish which pulled themselves up from the water on strong, bony fins.\n.  The horse has some obvious ancestors, but the the fossil record of those ancestor becomes weaker as you go back in time.  The fossil record  between shrew like mammals and those creatures which had some horse like characteristics has big gaps in it..
45666
Terrestrial:Small,mostly composed of soild matter.\nJovian:Large,mostly comprised of gases
1042549
because they have gills that extract oxygen from the water, much like land animals have lungs that extract oxygen from the air.
1120467
As pointed out whales are mammals, they give birth to live young and nurse them with mammary glands. Whales have flippers that evolved from hands and actually have the digital structure pretty much intact, some even have the remains of pelvises and non-functioning hind limbs, clear evidence of their terrestrial origin.\n\nIf your really interested talkorigins.org has a really interesting article on the subject, it's heady, but a good read.
1010312
yes.\n\nthey are mammals and do not breathe underwater.\n\nthey take in air at the surface, so it does not matter what type of water they live in.
1003505
the earliest known form of life is cyanobacteria which grew in bluish green pod like colonies approximately 3.4 billion years ago.