Update 03/2010: Orangutan orphans in water
Face always kept above water surface with throat air sac inflated while nose breathing.
Orangutan protects human from crocodile:
You can protect orangutans from extinction:
"Swimming" orangutan, note the throat-neck, likely the bare skin is slightly swollen due to laryngeal air sacs inflated, used when vertical floating or surface sculling with head above water.
Orangutan attempts to hunt fish with spear (likely bamboo, note the nodes [click to enlarge photo]). See here for article on fishing macaque monkeys fishing monkeys
Naturalists were shocked to see the apes go across a river to gain access to some of their favourite fruits at a conservation refuge on Kaja island in Borneo.
Orangutans at Runga river pallas island orphan orangutan sanctuary seen entering water for sweet corn cobs, splashing. No crocs in that area. Probably not swimming. link
The more stories and "almost swimming' photos, the more doubt arises.
Wading? Yes. Vertical floating? Possible, but probably only if learned in
shallow wetland first. Swimming horizontally? No, no clear evidence of that. Can't blame the folks there for making a fuss about it though, the forest is being destroyed so quickly for oil palm plantations and lumber.
The bottom photo is of two siamang gibbons (lesser apes) which frequently call loudly with inflated air sacs. I hypothesize that ancient hominoids lived in tidal rainforests (estuarboreal), and enlarged throat air sacs were selected (like in frogs) for better vertical flotation and vocalization. Human ancestors remained at the tidal shores but moved from these dense mangroves (per MV) to open shores diving/backfloating at lagoon reefs for shellfish etc. while the ape ancestors followed rivers inland to more arboreal and less aquatic habitat. Humans today do not normally have laryngeal air sacs, however trumpet blowers and glass blowers sometimes develop laryngocoels which are pathological laryngeal air sacs.
The morphology of all extant apes (except the small gibbons) and the skeletal fossils of Lucy & Selam (Australopithecus afarensis) possessing hyoid bones indicate enlarged laryngeal air sacs, while those of Homo neandertalensis and ancient Homo sapiens do not.
Background: Laryngocoele/laryngocele/laryngeal air sac
A laryngocele is usually a cystic dilatation of the laryngeal saccule. The etiology behind its occurrence is still unclear, but congenital and acquired factors have been implicated in its development [1,2]. Laryngoceles appear to be an atavistic remnant from the higher apes (DD: correction, higher apes are not our ancestors, hominoids are ancestral to both Homo and extant apes), particularly those who use their arms with the thoracic cage fixed whilst swinging through the trees (DD: addendum, vertical climbing/floating/wading with arms holding vegetation). ... the laryngocele could have been caused by prolonged and repeated valsalva... the increased air pressure in the larynx may make an already existing laryngocele manifest .
Congenitally, the laryngeal saccule is a remnant corresponding to the lateral laryngeal air sacs of the higher anthropoid apes, which may on occasion, manifest suddenly in response to pressure caused by coughing, straining at stool, or trumpet playing (i.e. valsalva maneuvers [used in diving to equalize middle ear pressure]). An acquired laryngocele may develop when the laryngeal ventricle becomes functionally obstructed as a result of an increase in intraglottic pressure, e.g. excessive coughing, playing a wind instrument or obstruction of appendicular ostium [1,2].
Three types of laryngoceles are described. An internal laryngocele is confined to the interior of the larynx and extends posterosuperiorly into the false vocal cord and the aryepiglottic fold; this type appears on laryngoscopy as a smooth swelling of the supraglottis. An external laryngocele extends superiorly to appear laterally in the neck through the opening in the thyrohyoid membrane for the superior laryngeal nerve and vessels; these clinically present as a swelling in the neck at the level of the hyoid bone anterior to the sternocleidomastoid muscle. The simultaneous existence of both features is termed a combined laryngocele [1-4].
The simple laryngocele is an uncomplicated air-filled dilatation of the appendix of the laryngeal ventricle.
Laryngeal air sac in whales, function: Full size right whales forage at the water surface, swim slower than human sport swimmers, and are the fattest whales (float at the surface when dead, which is why whalers called them "right whales"). Pygmy right whales are far less fatty due to their small size and metabolism, so their laryngeal air sac adds buoyancy when foraging on krill copepods near the surface. Apes in shallow water generally seek surface Aquatic Herbaceous Vegetation (AHV) (see the gorilla videos) and only seek bottom foods (water bugs under rocks/leaves) while wading in ankle-deep water. Human ancestors at seashores were tide-affected, and foraged for food from the shallows to perhaps 30+m deep. Because they were enveloped in a thin layer of buoyant thermoinsulative skin fat, denser bones were selected for, bringing the body to neutral buoyancy in seawater (similar to sea otters and walruses).
update: bowhead whales also surface feed and have lar. air sacs, AFAICT no other whales have lar. air sacs and do not typically feed at the surface.
So, bowhead whales, pygmy right whales and apes forage near the water surface and possess laryngeal air sacs; while (ancestral) humans, sea otters, blue whales forage near the sea bottom and lack laryngeal air sacs.
Air sac size quite small (though this is a small whale), compare to 1 liter air sac in orangs or 20-50 liter pharyngeal air sac in walrus. Why did Homo lose the laryngeal air sac? Switch to humming type speech and backfloating and addition of subcutaneous fat layer and stop climbing?
(Stranded) Pygmy right whale dissection, showing lungs and laryngeal air sac at left.
Gorilla foraging in wetland with partly inflated laryngeal air sac:
Note gorilla posture, red scalp, air sac, water just below shoulders.
upright posture - moroto/proconsul aquarboreal climbing/slow brachiating/wading/floating/walking/hanging
red scalp - post-hylobatid hominoid canopy woven nesting mimicry of raptor, grabbing hook-like hand, cooing infant (became hooting in large arboreals), human preemies have lanugo from eyebrows to scalp, which when pulled forward in surprise (eyebrow flash/frown) (or sun avoidance without protruding brows) becomes danger sign to raptor from above, evolutionarily later lost when brain-skull-protruding jaws enlarged.
air sac - visible in photo to the right of the sunlit hair, to left of throat, it is convex ( rather than concave )
due to partly inflated air sac. Human throat would show concave except at adams apple.
water - high enough to give flotation (of face) an advantage