Innovation and Speciation: whale changes (Evolution)

by David Turell , Sunday, May 28, 2023, 17:19 (335 days ago) @ David Turell

More specific alterations that are required:

https://evolutionnews.org/2023/05/from-bears-to-whales-a-difficult-transition-2/

"So cetaceans have nostrils on the tops of their heads, called “blowholes” because at the surface they blow moisture-laden air out of them. Blowholes are unusual not just because of their anatomical location. They are very unlike the nostrils of other mammals. The blowhole of a cetacean is surrounded by thick muscular “lips” that keep the hole tightly closed except when the animal makes a deliberate effort to open it at the surface. Total submersion thus takes less effort for cetaceans than for animals that must actively exclude water from their air passages.

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"Bones cannot protect the lungs of an animal at such high pressures, so cetacean lungs collapse during deep dives. To make this possible, their rib cages have many “floating ribs” that are not attached to the breastbone. Cetaceans also have diaphragms that are oriented nearly parallel to the spine rather than perpendicular to it (as in humans). Anesthesiologists...point out that “the large area of contact between lung and diaphragm in cetaceans allows for the diaphragm to smoothly collapse the lung along the lungs’ shortest dimension” (belly to back).

"There’s another reason why cetaceans’ lungs must collapse during deep dives. Air contains nitrogen, which under high pressure can be absorbed from the lungs into the blood. When pressure is reduced the nitrogen can bubble out of the blood, causing potentially fatal decompression sickness (“the bends”). By collapsing their lungs and expelling the air, cetaceans avoid this problem.

"But collapsing a lung introduces a different problem: how to re-inflate it quickly at the surface. To insure that tissues in their collapsed air sacs do not stick to each other, the lungs of deep-diving mammals contain special “surfactants” with anti-adhesive properties.

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"Flukes are shaped like airplane wings, with a streamlined foil profile, rounded leading edge, and long tapered trailing edge. Biologists who analyzed flukes in 2007 concluded that they are “generally comparable or better for lift generation than engineered foils.

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"...the testicles are inside the body. In most mammals (even sea lions) the testicles are outside the body, because sperm production normally requires a temperature several degrees below normal body temperature. In cetaceans, the testicles are cooled below body temperature by countercurrent heat exchangers. Veins carry cool blood from the dorsal fin and flukes to the testicles, where it flows through a network of veins that pass between arteries carrying warm blood in the opposite direction. The arterial blood is thereby cooled before it reaches the testicles.

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"Female cetaceans have specialized nipples for suckling their young underwater. The mother’s nipples are recessed in two slits. According to Slijper, “while suckling their young, cetaceans move very slowly; the calf follows behind and approaches the nipple from the back. The cow then turns a little to the side, so that the calf has easier access to the nipple, which has meanwhile emerged from its slit. Since the calf lacks proper lips, it has to seize the nipple between the tongue and the tip of its palate.

"Then the mother forcefully squirts milk into the calf’s mouth. Even after the calf lets go, milk can often be seen squirting from the nipple. Young calves cannot stay underwater as long as adults; they have to surface frequently to breathe. So the milk is three to four times as concentrated as the milk of cows and goats; it has the consistency of condensed milk or liquid yogurt. The calf thereby receives much more nourishment in a much shorter time.

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"Even if the transition were perfectly documented with intermediate forms, however, it would not answer the “how” questions. How did the features needed for a fully aquatic lifestyle originate? How would the hind limbs of a sea lion turn into a fluke (which is very different)? How would a male’s testicles become simultaneously internalized and surrounded by countercurrent heat exchange systems? How would a female develop specialized nursing organs to inject milk forcibly into her calf? Indeed, why would any of these changes occur? Sea lions are already well adapted to their amphibious lives."

Comment: Many of these changes are irreducibly complex: note internal testes must be cooled so the internalization must have had simultaneous development of a circulatory cooling system. Not by chance.