In the Oligocene deposits of South Carolina found a nearly complete skeleton of a large Dolphin Ankylorhiza tiedemani, reported in Current Biology. The structure of its limbs suggests that the toothed whales (which include dolphins) and baleen whales (these include, for example, the blue whale) has developed some adaptation to aquatic way of life converged in similar conditions, but independently from each other. Among these adaptations include shortened humerus, absence of a tubercle on the radius and narrow tail end. And judging by the skull and teeth of this Dolphin, it hunted large prey and have occupied an ecological niche similar to the one that now belongs to the killer whales.
Under some assumptions, the ancestors of cetaceans was similar to a water Olenka, who when threatened by predators dives. However, these ungulates — they were like water Olenyok or not — were not adapted to spending time in the water. For about 50 million years cetaceans have acquired a number of adaptations to the new environment: the hind limbs they have reduced; the tail became a fin and the main body of the movement; the front legs are also turned into fins, but the tail; the spine longer able to bend much, and vertebrae in this short. In addition, changed and inner ear, and the integument, and even the brain.
Modern cetaceans are divided into two main groups: toothed and baleen whales. As the taxa they arise 34-36 million years ago. Basilosauridae, from which, apparently, happened baleen whales, moving through the curves of the entire spine, not his tail. Humerus the longest and the many features of anatomy, is typical of the living cetaceans, they have not yet been. Accordingly, the toothed and baleen whales, a number of adaptations to swimming could occur independently, and their set does not have to match.
Understand more about how and what has changed in the appearance of toothed and baleen whales, helped study almost complete skeleton of a Dolphin Ankylorhiza tiedemani age of 24.7 to 23.5 million years old, found in South Carolina. It was conducted by the American paleontologists headed by Robert Bassnectar (Robert Boessenecker) from the Paleontological Museum, University of California. Earlier representatives of this species found only rostrum — anterior part of the maxilla. Now it became clearer what the length had a pet (4.8 meters), as was the structure of its teeth (unlike modern toothed whales, this Dolphin’s teeth had two roots), and some other details.