Blow Holes

[Hypno-Toad]

How could blow holes evolve in whales, porpoises and dolphins? I can see how other features came about from limbs changing shape to become more paddle-like. But the blow hole seems like such a departure from terrestrial mammal physique. Is it a relocated nasal passage?

[CalMeacham]

Whale evolution: The blowhole

From Milan Klima, Development of the Cetacean Nasal Skull 1999 Springer
The fact that the cetacean nose moved, in the course of evolution, from the tip of the rostrum up to the vertex of the head, is among the most perfect of adaptations to aquatic life. In this and many other special adaptations of their morphology and physiology, cetaceans surpass most primarily aquatic animals even though they themselves have developed from land mammals that breathe with lungs, and have only secondarily conquered the aquatic environment. To a certain extent, cetaceans can be considered to be the most successful group of aquatic animals of all time.

Conclusive paleontological evidence shows the way in which the nasal openings were moved in the course of phylogeny (see Kellogg 1928; Slijper 1962; Gaskin 1976; Oelschlager 1978, 1987, 1990; Moore 1981). That this evolutionary process is repeated in a way during ontogeny became obvious through external observations on embryos and fetuses (Kukenthal 1893). At the earliest embryonic stages the nasal openings are still situated at the rostra tip like those of land mammals; they are gradually shifted more and more towards the vertex of the head at the older stages. At the same time, a long rost rum with narrow jaws develops. Until recently, practically nothing was known about the morphogenetic processes concealed in this metamorphosis, about what cranial structures take part in it, and about the exact way in which the cetacean skull becomes transformed during embryogeny.

So, yes.

[markn_1]

Yep.

Whale evolution: The blowhole

Conclusive paleontological evidence shows the way in which the nasal openings were moved in the course of phylogeny (see Kellogg 1928; Slijper 1962; Gaskin 1976; Oelschlager 1978, 1987, 1990; Moore 1981). That this evolutionary process is repeated in a way during ontogeny became obvious through external observations on embryos and fetuses (Kukenthal 1893). At the earliest embryonic stages the nasal openings are still situated at the rostra tip like those of land mammals; they are gradually shifted more and more towards the vertex of the head at the older stages.

ETA Aagh! Ninjaed with the same reference.

[Hypno-Toad]

Cool.

[MEBuckner]

Here’s a diagram of the internal anatomy of a dolphin’s head. You can see that the blowhole is in the same relative position with respect to the mouth (maxilla and mandible), brain, and so on as in any other mammal; it’s just that the proportions have been stretched a bit.

Note that the dolphin’s “forehead” does not correspond to its brain (as our foreheads do with our brains). It would be quite hard to see how a mammal’s nose could gradually evolve to be on the other side of its brain, but that isn’t what happened. The “forehead” is actually where the “melon” is. The “melon” (which is located between the mouth and the blowhole) is an organ unique to the toothed whales, and is basically a mass of fatty tissue, which seems to have something to do with echolocation.

[bump]

Like **CalMeacham’s **link points out, it started as nostrils on the end of the nose and gradually evolved to be up and over the head.

Here’s a link with some fossil skull diagrams showing how it happened. (Fig. 20)

From Land to Water: the Origin of Whales, Dolphins, and Porpoises -...

[markn_1]

@MEBuckner

Here’s a diagram of the internal anatomy of a dolphin’s head.

The dolphin’s head contains a structure called “monkey lips”???
No matter what happens the rest of the day, that will undoubtedly be the best thing I learned today.

[crowmanyclouds]

@MEBuckner

Here’s a diagram of the internal anatomy of a dolphin’s head. {…}

It’s hard, as a layman, not to think that it isn’t that the ‘nose’ moved up on it’s own but instead it was the melon that pushed the ‘nose’ up.

CMC fnord!

[Senegoid]

As I heard it described once, the entire “melon” is just the whale’s or dolphin’s upper lip!

– Senegoid
Former dolphin research lab assistant, trainer,
former member IMATA (Int’l Marine Animal Trainers’ Ass’n)
Charter member, Society of Marine Mammology