Sunday, August 19, 2007

Common Descent 3 by DDeden

Too Deep, Too Often, Too Soon?

At Originally Posted by naiad View Post
Totally OT now, but I am not sure about the role of air in underwater hearing. The most advanced orders of fish, Cypriniformes (carp, minnows, most coarse fish, danios, loaches etc.), Characiformes (tetras), Siluriformes (catfish), and Gymnotiformes (electric eels, knifefish), have a series of bones connecting the air bladder to the inner ear, allowing them to hear a much wider range of sounds than other fish. This must be important, because species which no longer need an air bladder for buoyancy (catfish, loaches), still have a small one for hearing, and in some cases for producing sounds.
DD: Do most of those fish live somewhat amphibiously, compared to pelagic ocean fish? If so, air conduction would be significant, as it is in frogs and seals. AFAIK most ocean pelagic fish have one inner bone connected to the inner ear, while mammals have three. (I'd guess sharks have none). Do you know for certain that these (catfish, loaches) while at depth have air-filled bladders connected to their ears? Can the bladders empty at depth, (or fill with water or oil) and then refill with air at the surface? It is also possible that their ears are functionally deaf at depth but they pick up (hydrosonic) vibrations via their lateral line and/or bones.

I think there's a freshwater fish that squirts water up at flying insects, I would guess that fish has good air-conduction aural capabilities (ear-air-sac), but also good water-conduction aural capabilities.

o0O0o0O0o0O0o `<8{(((>< o0O0o0O0o0O0o Regarding hearing underwater Too Deep, Too Often and Too Soon; although I think that ancestral humans dove at equatorial seashores in warm surface water, I've no doubt they encountered cool to cold water at depth and especially during coastal migrations farther from the equator. Evidence of ear exostosis (bony ear canal rings) has been found in a number of human fossils (Upper Nile River, Peruvian coast, Rome coldwater baths), this occurs due to sustained periodic exposure to cold water in the external ear canal over time. I think exostosis indicates mostly youthful single males habitually competing at greater depths without sufficient surface intervals to warm the ear canal and cerumen, over time this would produce bony accretion around the canal. This may indicate spearfishing more than mollusc hunting, since spearing requires a longer time at depth. However the fact that humans are no where nearly as hydrodynamic mammals like dolphins, sea lions, etc. indicates that spearfishing or "fast" chasing pelagic fish was not as common as "slow" diving for sessile/benthic foods (molluscs, oysters, marine snails, etc.). I'd guess spears were more jabbing-thrusting-prying tools, rather than shooting weapons; useful for crabs, flounder, immobile camoflaged octopi and such. AFAICT, paired archaic divers backfloated/dove in rotation at warm sunlit surface, the middle ear was warm-water filled and the external canal also warm-water filled, the earwax kept this warm water in place during the dive into the colder depths when the MDR was engaged, acting like thermal ear-plugs but not air-holding ear plugs. Although yet unconfirmed, I feel quite certain that simultaneously a similar thermo-retention system was employed in the sinunasal cavity and affiliated middle ears (via the eustacian tubes) by allowing warm surface water (larynx was valved shut) in and then closing the nasal passage via the swollen inferior concha (VR) and/or philtrum closure early during the dive into the cooler depths, preventing the "sinus-ice cream headache" otherwise sure to affect the diver (and which is now often covered by mask or hood) and alleviating the need for continuous equalizing with each elevation/pressure gradient.

So archaic human seashore divers/backfloaters used water-conduction hearing during their dive-foraging cycles, when hearing the dive partner was more significant than hearing prey or predator.

Allowing sun-warmed, UV-sterilized blood-temperature surface saline into the external ear, middle ear & sinonasal cavities just before diving deep meant that cold water at depth would trigger the facial and trigeminal nerves on the face maximizing the MDR, (unlike a full face mask & hood), yet (presumably) avoid the accompanying ice cream headache typical of prolonged cold water immersion of the bare face and forehead. This kept the brain warm at depth (conserving oxygen and energy), while the blood from the extremities moved towards the body core and the rest of the body acclimatised to the chilly temperature. Upon resurfacing, backfloating allowed maximum solar absorption, and blood returned to the small blood vessels of the sunwarmed extremities.

Ear extoses: Diving into the cold w/o retaining the warm Here's an article by DiBartolomeo JR 1979

Exostoses of the external auditory canal

Ann Otol Rhinol Laryngol Suppl 88 (6 Pt 2 Suppl 61) :2-20.

Exostosis of the external ear canal is a disease unique to man. It has been
identified in prehistoric man, affecting the aborigines of the N.American
continent. Aural exostoses are typically firm, sessile, multi-nodular bony
masses which arise from the tympanic ring of the bony portion of the
external auditory canal. These growths develop subsequent to prolonged
irritation of the canal. The large, primitive jaw of prehistoric man placed
great mechanical stress on the tympanic ring. Chronic aural suppuration seen
in the pre-antibiotic era was soon followed by exostoses.

Today, prolonged
contact of the external ear canal with cold sea water is
the most prevalent
cause (aquatic theory). As a result the disease is now
essentially limited
to coastal regions. In this way we have seen exostoses
appear in different
stages of the evolution of man as a result of mechanical,
chemical and now
thermal irritation.

The author is an otolaryngologist in a coastal region.
In examining 11,000 patients during a 10-year period, 70 cases of
symptomatic exostoses of the external auditory canal were identified. The
incidence of exostoses was found to be 6.36 per 1000 patients examined for
otolaryngologic disease. It is a predominantly male disease. The development
of these "irritation nodules" is painless until the tenth year of aquatic
exposure to irritation, when symptoms of obstruction occur. The hearing loss
associated with exostoses is usually a conductive type, secondary to
occlusion of the canal by impacted cerumen or acute external otitis. The
results of studying the thermal characteristics of the body of water used
for such aquatic activities is presented.

DDeden (Thanks MV at AAT)
"Dive well and come up for more"

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