Ah yes. "Speculation" yet another of the magic words Creationist toss around as if they poof away the evidence in a cloud of smoke.
Tell you what, take these three observations and actually address them without using magic words and we can have a serious discussion.
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If cetaceans evolved from terrestrial mammals we would expect to find certain things in addition to the characteristics that undeniably make them mammals.
From physiology we see that unlike fish and marine reptiles (see the ichthyosaur body plan), which move side to side, whales should move up and down just like their terrestrial counterparts do. Indeed, that is what we observe. A potential falsification would be if they undulated side to side and their flukes were shaped and positioned like those of Ichthyosaurs.
Based on the fact that we've observed atavistic legs on whales, we would expect from genetics and embryology to see that they retain anatomical or molecular vestiges for hind leg development. We observe both.
Embryonic dolphins develop limb buds that are absorbed back into the body as the fetus grows. (see photo at bottom of page)
Cetacean Palaeobiology
Cetaceans also have the gene package for limb development. In legged vertebrates, Sonic Hedgehog and Hand2 work together to develop them, but in cetaceans that gene package is non-functioning so the limb buds never develop unless there is a problem and atavistic hand limbs actually grow.
Developmental basis for hind-limb loss in dolphins and origin of the cetacean bodyplan
Press release here:
05 » How ancient whales lost their legs, got sleek and conquered the oceans » University of Florida
>> In all limbed vertebrates, Sonic hedgehog is required for normal limbs to develop beyond the knee and elbow joints. Because ancient whales’ hind limbs remained perfectly formed all the way to the toes even as they became smaller suggests that Sonic hedgehog was still functioning to pattern the limb skeleton.
The new research shows that, near the end of 15 million years, with the hind limbs of ancient whales nonfunctional and all but gone, lack of Sonic hedgehog clearly comes into play. While the animals still may have developed embryonic hind limb buds, as happens in today’s spotted dolphins, they didn’t have the Sonic hedgehog required to grow a complete or even partial limb, although it is active elsewhere in the embryo.
The team also showed why Sonic hedgehog became inactive and all traces of hind limbs vanished at the end of this stage of whale evolution, said Cohn. A gene called Hand2, which normally functions as a switch to turn on Sonic hedgehog, was shown to be inactive in the hind limb buds of dolphins. Without it, limb development grinds to a halt. <<
The ancestor of the whale thought to be Pakicetus Inachus. Based on the following.
Arrangement of cusp on molar teeth. Pre molars are simple triangular teeth composed of single cusp serrated in the front and back edges. Teeth were adapted to hunting fish.
Positioning and folding of the ear bones within the skull.
Shape of the skull is cetacean. High narrow sagittal crest, and prominent lambdoidal crest.
Characteristics of the inner ear found only in cetaceans.
Auditory bulla formed from the ectotympanic bone used for underwater hearing.
Based on fragments, it was described as having a semi aquatic life style and illustrated on the front cover of the prestigious journal ‘Science’ as an aquatic mammal absent of hind legs.
Reality.
When found in 1983 by PD Gingerich it was immediately declared to be a primitive whale based on fragments of one skull. Nothing below the skull was found at that moment to support the idea that it was a sea creature. The assumptions were based totally on skull fragments.
When additional fossils were found Pakicetus has a four footed skeletal structure similar to that of wolves or mesonychids.
The first finding was not a complete skull, but the posterior portion of the cranium, two fragments of the lower jaw, isolated upper and lower cheek teeth.
The ear of Pakicetus is that of a land mammal, there is no evidence that it can hear under water, or any evidence of vascularization of the middle ear to maintain pressure during diving.
Teeth resembling those of mesonychids.
Cetaceans all exhibit large mandibular foremen, the lower jaw holds a fat pack that extends toward the ear, both associated with underwater hearing. Pakicetus has a small mandibular foramen, and lacks the fat pack.
Ear bone is not like a whale, which has a finger like projection [sigmoid process], but which is plate like, as found in land fossils.
Pakicetus Inachus is suspected to have evolved into Ambulocetus
Evolutionist support.
In 1992 Hans Thewissen and Taseer Hussain found Ambulocetus digging in the hills of Islamabad Pakistan. It was deemed that Ambulocetus was unlike modern cetaceans because it was able to walk on land, probably in way similar to modern sea lions, weighing about 650 lbs., and in the water it combined aspects of the locomotion of modern seals, otters, and cetaceans. This represents a critical intermediate between land mammals and marine cetaceans.
Had a robust radius and ulna [the two bones in the upper forearm]. They reported that the structure of the forearm would have allowed powerful elbow extension by triceps, and that, unlike modern cetaceans, elbow, wrist, and digital joints were flexible and synovial. The hand was long and broad, with five digits. The femur was short and stout, and the feet were enormous. The toes were terminated by short phalanx carrying a convex hoof. They suggested that unlike modern cetaceans, Ambulocetus had a long tail, and that it probably did not possess a fluke.
Identified as a cetacean with functioning legs, and a skeleton that allowed a degree of terrestrial walking.
Skull was cetacean, long muzzle, teeth similar, reduced zygomatic arch, and tympanic bulla.
Lower jaw has a large cavity, which in modern tooth whales housing external pad of fat which channels the sound from the lower jaw to the ear.
Due to the structure of the nasal cavities, had the ability to swallow under water.
Reality
First constructed in 1992 from a few skeletal fragments which consisted of part of the skull and jaw, a number or vertebrae, some ribs, nearly complete foot and hand limb. One tail vertebrae was found 5 meters away.
In 1996 the information was changed based on what was alleged to be the remainder of the beast. Becomes questionable since when something dies its bones should be found close together. Why two different times, makes it questionable.
The snout was not preserved.
Ambulocetus has eye raised on top of head similar to alligators.
Ambulocetus is thought to have evolved into Rodhocetus.
Evolutionary support
Has four legs, a fluke and flippers. Would swim using it fluke similar to a whale. Beginning of the type of locomotion seen in modern whales.
Reality.
There is discrepancy between the reconstructive description of Rodhocetus and the fossil evidence. The reconstruction had a whale fluke but there was no fossil evidence to confirm this.
When PD Gingerich was asked about the fluke discrepancy he said, “Well we don’t have the tail for Rodhocetus so we don’t know for sure it had a ball vertebrae indicating a fluke so I speculated it had a fluke.”
Also the flippers were drawn on.
When asked about the flippers, Gingerich said, “Since then we found the forelimbs, the hands and the arms of Rodhocetus and we understand that it does not have the kind of hands that can be spread out like a whale, and if you don’t have flippers I don’t think you can have a fluke and really power swimming, I doubt that Rodhocetus had a fluke tail.”
But it is still drawn with a fluke and flippers.
Probability
If a mesonychid evolved into a whale too many extreme changes in anatomy would have to take place by chance.
Front legs of the mesonychid would have to change into pectoral fins.
The back legs of the mesonychid would have to disappear.
The nostrils of the mesonychid would have to move to the top of his head and form a blow hole.
The mesonychid would have to develop a dorsal fin by accident.
The bony tail of the mesonychid would have to change into a cartilaginous fluke.
The hair of the mesonychid would have to disappear and be replaced by blubber.
The body of the mesonychid would have to increase by 80000 lbs.
The external ears of the mesonychid would have to disappear and change for high pressure diving, all by chance.
This would require a vast amount of new genetic information. For just one protein of 100 amino acids it would require 300 new letters to the genetic code in the proper sequence.
Equivalent to blindfolded illiterate toddler typing several paragraphs of meaningful literature, without mistakes.
Anatomical similarities do not always indicate common descent. For example the mole has a bird like sternum and wrist bones, but it would be absurd to conclude that birds evolved from moles. Common sense states that no fossil can be considered evidence for evolution. When a bone is found in the dirt, one thing is known for sure, it died. Everything else is speculation written into the interpretation of the evidence.
