Vision & olfaction in otters and humans

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NOCTURNAL FORAGING ECOLOGY AND ACTIVITY BUDGET OF THE SEA OTTER (ENHYDRA
LUTRIS) IN ELKHORN SLOUGH, CALIFORNIA
SM Wilkin 2003 SFSU thesis

... Improved night vision equipment has made observation of nocturnal
behavior possible for the first time ...
I quantified the nocturnal foraging behavior of sea otters in Elkhorn Slough
by direct observation using night vision goggles.
- Duration of successful nocturnal dives (ie, resulting in prey capture)
were not different from diurnal dive durations (nocturnal 44.64", diurnal
45.46").
- Foraging success was greater at night : 1.41 dives were required to obtain
prey items (diurnal success rate 1.63/prey item).
- Prey species composition differed ... more crabs consumed at night.
- They spent 22 % of the time foraging (16 % estimated from diurnal scan
samples) ...
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Human ancestors dove during midday, but used dark-adaptation at depth (See Gislen & Schagatay, accomodative focusing), probably with bright-surface reflex exhalation (photic sneeze). Sharks have excellent dark adaptation, their lucida tapetum can change from mirror to black via pigment change (cf squid camouflage), something humans lack.
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Carnivore olfactory bulb size: allometry, phylogeny and ecology
JL Gittleman DOI 10.1111/j.1469-7998.1991.tb03815.x
Journal of Zoology 225: 253*272

Olfactory bulb size was measured in 146 species of Carnivora in order to
examine whether recently observed functional patterns for overall brain size
were similar for component parts of the brain. Comparative measures were
analysed in relation to various allometric characters (body, brain and skull
size), phylogeny, behaviour and ecology. Olfactory bulbs are significantly
and positively correlated with all allometric variables, but indices of
skull size correlate slightly more closely than other variables. This
probably relates to functional aspects of skull size, facial proportions,
and anterior elements of the brain. Phylogenetic associations were examined
by two comparative methods: the method of independent contrasts and
phylogenetic autoregression. Both revealed similar phylogenetic correlation
at generic and familial levels. Using calculated values from either method,
relative olfactory bulb size only correlates with zonation among seven
behavioural and ecological variables; aquatic otters have smaller bulb sizes
than carnivores of other zonal types. This agrees with discussion about the
diminution of olfactory communication in aquatic environments. Also,
olfactory bulb size correlates with home range size, which is consistent
with a recent model on the use of olfaction for foraging in designated home
ranges. Generally, comparative differences in olfactory bulb size in
carnivores do not associate with functional variables found in other
comparative studies. Nevertheless, future analyses of specific brain
components in mammals may be more useful than overall brain size for testing
evolutionary hypotheses of mammalian brain size.
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Otters & humans lost some olfaction / sense of smell, improved vision.

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The ayeaye lemur of Madagascar have an unexpected large brain. It isn't aquatic but uses echolocation.
JA Kaufman cs 2005 Anat Rec A Discov Mol Cell Evol Biol 287:1026-37
Anatomical analysis of an aye-aye brain (Daubentonia madagascariensis,
primates: Prosimii)

 

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Bone size & density in terrestrial mustelids vs aquatic otters

Functional correlates of differences in bone density among terrestrial and
aquatic genera in the family Mustelidae (Mammalia)
FE Fish & BR Stein Zoomorphology 110:339-345 doi 10.1007/BF01668024

... the costs of maintaining an increased skeletal mass increases according
to locomotor function as follows :
- swimmers,
- sedentary forms,
- slow runners,
- fast runners,
- flyers.
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Archaic coastal humans had larger and denser bones than apes or modern humans, indicating slow dive-foraging (in parallel with sea otters, manatees, walruses) and contraindicating significant running or flying, per cost of bone maintenance. Merely eating seafood (gotten via boats rather than sustained slow diving) does not produce pachyosteosclerosis (large dense bones).

 

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From Marc Verhaegen at AAT forum:

"There are apparently still a lot of misunderstandings of AAT.

(1)
AAT (semi-aquatic ancestors at some time) is based on features of *living*
humans (olfactory reduction, skull-spine-legs on 1 line, fur loss, SC fat
etc.) but this doesn't say much on when & where it happened (only that is
was not so long ago: otherwise our semi-aq.features had disappeared more
completely).

(2)
Fossil+archeol.data can give information on the fossils themselves, but the
exact genetic relation to living humans is uncertain (except when DNA can be
extracted from the fossils).
IOW, the fossils have to be studied on their own.
This is not so difficult in the case of fossil Homo.
Pleistocene Homo colonised different continents & islands - when you
disperse between Boxgrove & Flores you have to cross at least a few coasts -
and pachyosteosclerotic skulls are only seen in spp that regularly dive.
OTOH no pachyostotic species frequently runs.
How much time exactly the different Homo fossils at some time spent
beachcombing/wading/diving etc is still uncertain, but no animal with an
external nose is fully aquatic, and OTOH the pachyostosis suggests they at
some time spent a lot of time, probably daily, in the water.
This does not exclude that many or even most Homo fossils can be found
inland.

When we combine these data on living humans (1) & on fossil Homo (2), it's
obvious that our ancestors at some time during the Pleistocene were
littoral.
How & how much time our ancestors spent in the water at some time is another
debate, of course, but that they were littoral during some period(s) is
beyond doubt.

BTW, all this says nothing on apiths. They were confined to Africa & were
not coastal AFAWK. They too have to be studied on their own.
As long a people keep confusing different things (eg, using Laetoli in
trying to say something on AAT), they'll never understand."

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Agree, but note that both sea otters and blue whales have noses which are (unexpectedly?) similar externally to human noses, as compared to freshwater kin.