Whale Evolution & "Macro Evolution"

The information quoted below follows the evolution of the whale. It has examples on transitional species and is a good documented case of intermediate species. This is a documented case with evidence from the fossil records of one animal evolving into a new one. Simplifying what is presented, the animals shown takes us from a land dwelling animal, to an animal that lives on land and in sea, to a an animal that lives only in the sea. We see the animals shape change, it lose its legs, develop fins, grow larger, and become adapted to life in the sea.
If any one has any questions please feel free to ask.


Whale Evolution

Sinonyx
Sinonyx, a wolf-sized hyena-like, land-dwelling mammal with hoofs from the order Condylarthra, which gave rise to artiodactyls ( even-toed hoofed mammals), perissodactyls ( odd-toed hoofed mammals), proboscideans (Trunk-nosed mammals), from the late Paleocene, about 60 million years ago. The characters that link Sinonyx to the whales, thus indicating that they are relatives, include an elongated muzzle, an enlarged jugular foramen (a natural opening or perforation through a bone or a membranous structure), and a short basicranium (underside of the skull). (Zhou and others 1995). The tooth count was the primitive mammalian number (44); there were different types of teeth like mammals today. The molars were very narrow shearing teeth, especially in the lower jaw, but possessed multiple cusps. The elongation of the muzzle is often associated with hunting fish - all fish-hunting whales, as well as dolphins, have elongated muzzles. These features were atypical of mesonychids, indicating that Sinonyx was already developing the adaptations that later became the basis of the whales' specialized way of life. Length 1.5 meters/ 5 feet.

Pakicetus
The next fossil in the sequence, Pakicetus, is the oldest cetacean (marine mammal), and the first known archaeocete (ancient whale). It is from the early Eocene of Pakistan, about 52 million years ago (Gingerich and others 1983). Although it is known only from fragmentary skull remains, those remains are very diagnostic, and they are definitely intermediate between Sinonyxand later whales. This is especially the case for the teeth. The upper and lower molars, which have multiple cusps, are still similar to those of Sinonyx, but the premolars have become simple triangular teeth composed of a single cusp serrated on its front and back edges. The teeth of later whales show even more simplification into simple serrated triangles, like those of carnivorous sharks, indicating that Pakicetus's teeth were adapted to hunting fish.

A well-preserved cranium shows that Pakicetus was definitely a cetacean with a narrow braincase, a high, narrow sagittal crest, and prominent lambdoidal crests. Gingerich and others (1983) reconstructed a composite skull that was about 35 centimeters long. Pakicetus did not hear well underwater. Its skull had neither dense tympanic bullae nor sinuses isolating the left auditory area from the right one - an adaptation of later whales that allows directional hearing under water and prevents transmission of sounds through the skull (Gingerich and others 1983). All living whales have foam-filled sinuses along with dense tympanic bullae that create an impedance contrast so they can separate sounds arriving from different directions. There is also no evidence in Pakicetus of vascularization of the middle ear, which is necessary to regulate the pressure within the middle ear during diving (Gingerich and others 1983). Therefore, Pakicetus was probably incapable of achieving dives of any significant depth. This paleontological assessment of the ecological niche of Pakicetus is entirely consistent with the geochemical and paleoenvironmental evidence. When it came to hearing, Pakicetus was more terrestrial than aquatic, but the shape of its skull was definitely cetacean, and its teeth were between the ancestral and modern states. Length 1.5 meters/ 5 feet

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Basilosaurus
The particularly well-known fossil whale Basilosaurus represents the next evolutionary grade in whale evolution (Gingerich 1994). It lived during the late Eocene and latest part of the middle Eocene (35-45 million years ago). Basilosaurus was a long, thin, serpentine animal that was originally thought to have been the remains of a sea serpent (hence it is name, which actually means "king lizard"). Its extreme body length (about 15 meters) appears to be due to a feature unique among whales; its 67 vertebrae are so long compared to other whales of the time and to modern whales that it probably represents a specialization that sets it apart from the lineage that gave rise to modern whales.

What makes Basilosaurus a particularly interesting whale, however, is the distinctive anatomy of its hind limbs (Gingerich and others 1990). It had a nearly complete pelvic girdle and set of hindlimb bones. The limbs were too small for effective propulsion, less than 60 cm long on this 15-meter-long animal, and the pelvic girdle was completely isolated from the spine so that weight-bearing was impossible. Reconstructions of the animal have placed its legs external to the body - a configuration that would represent an important intermediate form in whale evolution.

Although no tail fluke has ever been found (since tail flukes contain no bones and are unlikely to fossilize), Gingerich and others (1990) noted that Basilosaurus's vertebral column shares characteristics of whales that do have tail flukes. The tail and cervical vertebrae are shorter than those of the thoracic and lumbar regions, and Gingerich and others (1990) take these vertebral proportions as evidence that Basilosaurus probably also had a tail fluke.

Further evidence that Basilosaurus spent most of its time in the water comes from another important change in the skull. This animal had a large single nostril that had migrated a short distance back to a point corresponding to the back third of the dental array. The movement from the forward extreme of the snout to the a position nearer the top of the head is characteristic of only those mammals that live in marine or aquatic environments. Length 15 meters/ 50 feet.

Dorudon
Dorudon was a contemporary of Basilosaurus in the late Eocene (about 40 million years ago) and probably represents the group most likely to be ancestral to modern whales (Gingerich 1994). Dorudon lacked the elongated vertebrae of Basilosaurus and was much smaller (about 4-5 meters in length). Dorudon’s dentition was similar to Basilosaurus’s; its cranium, compared to the skulls of Basilosaurus and the previous whales, was somewhat vaulted (Kellogg 1936). Dorudon also did not yet have the skull anatomy that indicates the presence of the apparatus necessary for echolocation (Barnes 1984). Length 5 meters/ 16 feet.
Basilosaurus and Dorudon were fully aquatic whales (like Basilosaurus, Dorudon had very small hind limbs that may have projected slightly beyond the body wall). They were no longer tied to the land; in fact, they would not have been able to move around on land at all. Their size and their lack of limbs that could support their weight made them obligate aquatic mammals, a trend that is elaborated and reinforced by subsequent whale taxa.

Peace
Mick
*hugs*
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Link:http://www.smithlifescience.com/WhaleEvolution.htm

I'll admit that this is post of mine from a thread on a different forum.