On electroreception, poisonous ankle spurs, and lots of REM sleep

i-2585accccda3911b8e580dfc271c3203-monotremes 5-9-2007.jpg

Here is another thrown-together collection of things relating to SVPCA... well, I photographed the Short-billed echidna Tachyglossus aculeatus and Platypus Ornithorhynchus anatinus in the Zoology Museum at Glasgow (during SVPCA); the photo of the echidna checking out the camera came from elsewhere. Monotremes have been in the news recently, what with the alleged recent rediscovery of the poorly known Attenborough's echidna Zaglossus attenboroughi Flannery & Groves, 1998 (photo below). I think this is the second taxon named after Sir David: the other is the controversial basal plesiosaur Attenborosaurus Bakker, 1998.

Monotremes are just fantastic, and here are some of the highlights (you'll be familiar with all of them if you class yourself as a high-calibre zoology nerd). Fossil monotremes (like Steropodon from Lower Cretaceous Australia) show that the group has been around for a long time, and essentially doing the same thing for its entire duration: that is, fossil taxa were apparently amphibious or semi-fossorial predators of streams and forest floors (insert comment about spec-world monotremes). Particularly big echidnas - three or four or more times the size of the living taxa - were present in the Pleistocene; true platypuses (or platypodes or whatever) have been around since the Palaeocene (first debuting in South America) and, by the Miocene, species similar to the extant one were around. The best known of these, Obdurodon dicksoni, had horny bill plates like Ornithorhynchus, but also still had teeth (Musser & Archer 1998).

i-43fcc4dfcea197924a4177cc80afb59f-zaglossus_attenboroughi.jpg

As early as 1927, it was suggested that the platypus must have some sort of special 'extra' sense that enabled it to catch prey while hunting with its eyes and nostrils closed. We now know that the platypus bill is innervated by about 100,000 mechanoreceptors and electroreceptors: they are literally able to feel the electrical impulses made by the muscles of their prey. Echidnas also have electroreceptors: 2000 in the long-billed echidnas Zaglossus and only 400 in Tachyglossus (Pettigrew 1999). Echidnas can apparently still detect electrical fields, but their ability to do so is poor compared to the platypus, and it is thought that their electroreceptive abilities are relictual and on the way out. Less well known is that work on the platypus eye suggests that platypuses previously had reasonably good vision, and may originally have used their eyes as well as their bill sense when hunting underwater (Pettigrew et al. 1998).

Then there are the poisonous crural spurs present on the ankles of male platypuses (echidnas have spurs too, but they're blunt and not attached to a poison gland). Poison production peaks to combine with spermatogenesis during August, and at this time males are particularly aggressive, often fighting. One successful envenomation is enough to kill a dog, and people who have been spurred (either accidentally or - in the case of Peter Temple-Smith - deliberately) have reported excruciating pain (Griffiths 1988). Well, duh. The presence of crural spurs in assorted Cretaceous fossil mammals has led some experts to speculate that venomosity was primitive for mammals (Hurum et al. 2006) - how incredibly cool.

The platypus apparently dreams more than any other mammal, and engages in lots of REM sleep. Echidnas do this too, despite early reports to the contrary (Siegel et al. 1998). Platypuses are hard to kill, and euthanized babies (collected for an experiment during the early 1900s) took a disturbing amount of time to drown. Platypuses maintain a low body temperature of about 32º C, even when foraging in water of just 5º C. Platypuses can growl. And... I have lots more to say, but have now written way too much, and am now running late. Great.

Refs - -

Griffiths, M. 1988. The platypus. Scientific American 258 (5), 60-67.

Hurum, J. H., Luo, Z.-X. & Kielan-Jaworowska, Z. 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51, 1-11.

Musser, A. M. & Archer, M. 1998. New information about the skull and dentary of the Miocene platypus Obdurodon dicksoni, and a discussion of ornithorhynchid relationships. Philosophical Transactions of the Royal Society of London B 353, 1063-1079.

Pettigrew, J. D. 1999. Electroreception in monotremes. The Journal of Experimental Biology 202, 1447-1454.

- ., Manger, P. R. & Fine, S. L. B. 1998. The sensory world of the platypus. Philosophical Transactions of the Royal Society of London B 353, 1199-1210

Siegel, J. M., Manger, P. R., Nienhuis, R., Fahringer, H. M. & Pettigrew, J. D. 1998. Monotremes and the evolution of rapid eye movement sleep. Philosophical Transactions of the Royal Society of London B 353, 1147-1157.

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Just a quick comment: Attenborosaurus conybeari is not so much controversial as poorly described. The taxon was set up by Bob Bakker in 1993, and has a very limited description: "Differs from all other long-necked plesiosaurs in having a more elongated, evenly tapered snout with a much reduced tooth count and massive tooth crowns. Among the Liassic genera closest to Archaeonectrus, but differs in having a much more massive muzzle and much thicker teeth"

The problem with this taxon is that the holotype of "Plesiosaurus" conybeari was in the Bristol Museum, and was one of a number of important specimens destroyed by bombing during WWII. It is known from casts, but this obviously limits the amount of reliable information we can obtain. Some isolated elements from Bornholm in Demark have been ascribed to this taxon (REES & BONDE 1999, MILAN & BONDE 2001) , but I have doubts as to whether or not these bits and pieces can be reliably be assigned to the genus.

[From Darren: thanks Richard. By 'controversial' I meant that it jumps around in phylogenies a bit.]

> Echidnas do this too, despite early reports to the contrary
> (Siegel et al. 1998).

There sinks the hypothesis that echidnas had such a huge neocortex because they had no REM sleep and were therefore unable to get rid of old informations. I had championed this once, but I have to admit defeat now.

This leaves the Question - why the huge neocortex? Most other ant- and termite eating mammals like anteaters and pangolins are small-brained (I don't know about the aardvark) and seem to get along well enough with it. Breaking into an ant- or termite nest needs big claws and lots of muscle, but it isn't much of an intellectual challenge. Most other australian animals have smaller brains than animals that hold the same niche in other continents - obviously because Australia, a dry continent without much vulcanism, is a low-energy environment. So why is it the other way around with anteaters, pangolins and echidnas?

(insert comment about spec-world monotremes)

Just look the other way for a few million years while they have no competition in one particular niche, and what happens? Tsk, tsk...

true platypuses (or platypodes or whatever)

Platypuzzesses is the correct plural, quoth the Ozgod.

have been around since the Palaeocene (first debuting in South America)

Monotrematum has even been used as a calibration point in molecular divergence date estimates based on this assumption. But where does it come from? Monotrematum is known from two isolated teeth. No echidna with teeth is known. So how can anyone tell if M. is a crown-group monotreme, let alone on the platypus side?!?

Is it known if electroreception works in soil or if it requires an outright body of water?

By David Marjanović (not verified) on 05 Sep 2007 #permalink

Yay! Monotremes!

Cool stuff, thanks for putting this up.

Echidnas can apparently still detect electrical fields, but their ability to do so is poor compared to the platypus, and it is thought that their electroreceptive abilities are relictual and on the way out.

(emphasis added)

Um... has somebody measured the selection gradient on monotreme electroreception? Just because some phenotypic trait is relatively reduced in one group compared to a relative does not imply that the phenotype in question is inevitably going away. What's the cost to echidnas of growing and maintaining that set of neurons?

"The platypus apparently dreams more than any other mammal . . . ." What about, one wonders?

Good to see longer posts again, Darren, but guard against them eating in to your working (earning) time!

I enjoyed your talk at The Conference that Dare Not Speak its Name about bringing Cryptozoology in from the cold. I've long thought that many of your pieces in the previous and current incarnations of Tet Zoo merit hard covers (from a stable like, say, Collins), but assumed you would have already thought of this (being a published author already), so never bothered to mention it. Could have kicked myself when you mentioned Karl Shuker's suggestion of this at Woolsery coming as a surprise.

By P Terry Hunt (not verified) on 05 Sep 2007 #permalink

Attenborosaurus, eh? I've heard the name, but have never gazed upon its "formal" description. Bakker has an irritating but sort of charming air of informality about him, which makes him great for talking to a lay audience but irritating when you're reading one of his peer-reviewed papers. The description for Attenborosaurus isn't as limited as it is vague.

Basal mammalian poison spurs? This is why I read TetZoo.

How could we all have lost something so intrinsically useful? There are so many people I would have spurred by now... I wonder if that could be why we lost them: they made it too easy to do in rivals, irrespective of fitness. But that doesn't explain how we got them in the first place, or why they are retained anywhere. What ancillary conditions change poison spurs from an advantage to a liability?

By Nathan Myers (not verified) on 05 Sep 2007 #permalink

Nice article; sorry it made you late, though.

Is it possible that the large brains of modern monotremes is a relic of a common ancestor? (and they simply haven't had much in the way of negative selection pressure to get rid of the large brains)

I heard on one tv program about venom, that platypi venom is not affected by morphine.

again, thank you for giving attention to the Monotrema.

have nice days & be well.

By Anthony Docimo (not verified) on 05 Sep 2007 #permalink

This leaves the Question - why the huge neocortex?

That's what's called a "good question". We don't even know why we have such a big one. There's a girl in Germany whose, I think, right hemisphere is missing. It was taken out due to cancer or something. Tomography images are published: one side of the skull is empty, filled just by cerebrospinal fluid. Now, apart from a few oddities, said girl is normal, plus bilingual in German and Turkish. We have no idea what a bloated brain is good for.

BTW, ours isn't that big either. It's at the upper end of what's expected for a mammal of our size -- not beyond.

In any case, the speculation that the purpose of dreaming is forgetting was rather silly anyway. "The closer you get to humans, the worse the science gets."

By David Marjanović (not verified) on 05 Sep 2007 #permalink

Brains are quite an expensive luxury. We turn off all the bits we're not using, at any given time. (That might be much of the appeal of video games, as the better you get, the less of your brain is powered up.) I don't believe in brains hanging around unused, teenagers and Republicans notwithstanding. A critter with a big brain is using it for something. Maybe it only used sometimes, and maybe only to display perfect timing in a mating dance, but it's certainly used.

By Nathan Myers (not verified) on 05 Sep 2007 #permalink

Well, I thought the Crick and Mitchison dream theory was pretty nifty, and is not done justice by such tags as 'reverse learning' or 'the purpose of dreaming is forgetting'. If you read up on neural network modelling of pattern recognition you get an idea of just how much training on positive and negative examples it takes to get a reasonable level of accuracy with new stimuli; also the 'parasitic modes' C&M talked about are a real issue for models, and also make intuitive sense as a source of tics, compulsions and obsessions as well as bad dreams. You may be right, David, but so far all the science we have is done by humans.

Attenborough also has a less direct connection with another fossil reptile; as recounted in 'Life on Air', in the 1960s he filmed a 'Yurlunggur' (rainbow serpent) ceremony in Arnhem Land (Northern Territory, Australia) and was subsequently given the eponymous once-used didgeridoo. I used the same name for a genus of madtsoiid snake in '92 after finding it in an anthropology book. What I didn't know (but DA did) was that the name itself is considered secret, not to be spoken among the uninitiated. Some years later I got cut off rather abruptly and without explanation during a phone interview on ABC Radio's Darwin station, just after I'd mentioned 'Yurlunggur' - I suppose the announcer was worried about scandalising the more traditional listeners, but it was still a bit rude. How's one supposed to respect traditional 'secret' knowledge if you can read it in a library book, OR if it actually remains a secret?

Back to monotremes... I've been bitten by venomous elapid snakes numerous times and it doesn't bother me too much (as long as they're non-lethal), but the idea of handling a platypus is quite scary. The size of that spur!

By John Scanlon, FCD (not verified) on 05 Sep 2007 #permalink

Is anything known about what the platypus venom is derived from? When you've got venomous teeth, you can figure the venom developed from saliva, but what would you have around your ankles that would be adaptable for poison purposes? Really, really bad foot odor? :-)

Cool post.

Thanks for another informative and entertaining post. The picture of the echidna with the camera is the cutest thing I've seen in ages - where'd it come from?

About those teeth...

Haven't they been identified with triconodont teeth, thus making monotremes highly derived triconodonts? If so, this would make the triconodonts the longest lived tetrapod line in the history of the world.

> How could we all have lost something so intrinsically useful?
> What ancillary conditions change poison spurs from an
> advantage to a liability?

Nathan,
If you have a parasagittal gait, you are in danger of stinging yourself, see also here:
Kielan - Jaworowska/Hurum: http://www.app.pan.pl/acta51/app51-393.pdf

Haven't they been identified with triconodont teeth, thus making monotremes highly derived triconodonts?

No.

By David Marjanović (not verified) on 06 Sep 2007 #permalink

> Is it possible that the large brains of modern monotremes is a
> relic of a common ancestor?

If this common ancestor was indeed aquatic or semi-aquatic, this would make a lot of sence; living in the three-dimensional environment of a water collumn and having a sence of electroception would probably be a catalyst for large brain size (mormyrids are an example).

> (and they simply haven't had much in the way of negative selection
> pressure to get rid of the large brains)

But wouldn't the supposed low-energy character of Australia's terrestrial ecosystems be such a negative selective pressure? Or the need for hefty fossorial legs and claws and massive muscles to power them - a must for breaking into ant or termite burrows, and probably competing with the brain for energy resources?

Alan Kellogg wrote:
If so, this would make the triconodonts the longest lived tetrapod line in the history of the world.

Aren't all extant tetrapod lines equally old? Or, if you mean, "longest-lived since branching from a line leading to another extant group", then the longest-lived ones have to be the amphibian and amniote lines.

Just a little fuzzy on the metric here....

By Mike Keesey (not verified) on 06 Sep 2007 #permalink

More about brains: I don't get citing people who survive with less brain than the rest of us as evidence of much. My neighbor's cat gets along without claws, but it lives in a rather less challenging environment than its ancestors.

To understand a big brain, we don't need to discover a way to use it all the time, we only need to discover a single moment in the animal's life in which it is essential to successful reproduction. One activity very demanding of neural volume is control of submillisecond timing; in humans, that means throwing rocks and, equally, dancing. Has anybody studied mate selection in these creatures?

By Nathan Myers (not verified) on 06 Sep 2007 #permalink

Or the need for hefty fossorial legs and claws and massive muscles to power them - a must for breaking into ant or termite burrows, and probably competing with the brain for energy resources?

Building big muscles and bones during development probably takes lots of energy, sure. But maintenance once you've got them is really low. Compared to kidney, liver, and of course brain, muscle tissue has a very low resting metabolic rate. Bone maintenance is even less demanding.

Having said that, brain is so expensive that I'd be surprised if these guys were really not using all that fatty tissue. How neurologically demanding is electroreception, or adding any sensory mode?

Apparently echidnas are remarkably good at finding their way through mazes and similar tests, so not only do they have big brains, they use them too.
The suggestion about mate selection is interesting. It has always seemed likely to me that our large brains are largely due to intra-species competition/arms race. I mean how smart do you really need to be to dig out a tuber or even to kill a mammoth? However outwitting a rival requires being smarter than he/she is.

By Tommy Tyrberg (not verified) on 06 Sep 2007 #permalink

"About those teeth...

Haven't they been identified with triconodont teeth"

Three problems here. (i) A roughly "triconodont" form of premolar seems to be plesiomorphic (is it un-p.c. to say "primitive"?) for mammals, going back to such Triassic pre-mammals as the Trithelodonts. Lots of Mesozoic mammals had 'em; it's not clear they are very closely related to each other.
(ii) By the time you get to critters confidently assigned to the Monotremata (or even to some stem group: has anybody introduced "Monotrematomorphoformes" for the last common ancestor of all the fragments Tom Rich has found and all its descendents?), the teeth are so derived (= weird) that it's hard to say WHAT they evolved from.
(iii) People who seem to know what they are talking about seem to think the Monotreme molar might have evolved from something Tribosphenic (or nearly: Aegialodon-grade). There are some Mesozoic Gondwanan forms with teeth that look startlingly like placental or marsupial teeth, but are WAY too early. (The unpronounceable Ausktribonyctes, for example,, uunless the name is unmemorizable as well....) So there is a widely held view that tribosphenic molars were evolved independently by two Mesozoic lineages, the Boreosphenidans (marsupials, placentals, and their closer relatives) and Australosphenidans in Gondwana. And that Monotremes might be more closely related to the Australosphenida than to any of the "triconodont" types.
I suspect there are more Mesozoic mammalian surprises to come, though, and this year's orthodoxy might become next years bad joke.
...And, come to think of it, don't the Echidna's toes in the skeletal picture at the top look a lot like those in the reconstructed skeleton of Fruitafossor?

[from Darren: on the very last point, apparently Bakker was going around for a while referring to Fruitafossor as 'the Morrison echidna'.]

By Allen Hazen (not verified) on 07 Sep 2007 #permalink

Allen, that's Ausktribosphenos nyktos: 'Australian Kretaceous tribosphenic mammal of-the-night', from the fabulous intertidal Flat Rocks site. And yeah, I agree that more Gondwanan Mesozoic mammaliaform diversity is going to keep trickling out and whatever theories are being argued about now may turn out to be not imaginative enough.

By John Scanlon, FCD (not verified) on 07 Sep 2007 #permalink

> A roughly "triconodont" form of premolar seems to be
> plesiomorphic (... ) for mammals, going back to such Triassic
> pre-mammals as the Trithelodonts.

This is something of an understatement. Trinaxodon had triconodont dentition, and it wasn't even an eucynodont.

> Lots of Mesozoic mammals had 'em, it's not clear they are very
> closely related to each other.

The Eutriconodonta (those often large - by mesozoic mammalian standards - carnivores and scavengers like Repenomamus or Gobiconodon) may indeed form a clade, but they are closer to us than they are to monotremes.

> The unpronounceable Ausktribonyctes,

Wasn't it Ausktribosphenos (phew...) or Bishops?

Ask, and you get answers. :)

Anyway, I've been thinking about the echidna's large neo cortex and it occured to me. Might the large neo cortex allow an echidna to construct and maintain a mental map of his territory. Much as the large neo cortexes of most primates allow them to construct and maintain mental maps of their territory.

That is, an echidna is able to remember where things are in its territory, and to modify that map when things change. Not how fascinated by that camera the echidna in the one picture is. It is thoroughly investigating the object so it can recognize it again should it come across it later.

Why would it need this ability? Well, because termite tests are few and far between in the echidna territory, and thus knowing where to go to find a meal is important. Then too there is the fact that termite colonies pretty much last only as long as the food supply, so an ability to learn and adapt becomes important

Johannes:
>But wouldn't the supposed low-energy character of Australia's terrestrial ecosystems be such a negative selective pressure? Or the need for hefty fossorial legs and claws and massive muscles to power them - a must for breaking into ant or termite burrows, and probably competing with the brain for energy resources?

Not really - think of orangutangs...they need large brains to remember where the fruiting trees are (since the fruits are far apart and not simaltaneous in a large forest)

By Anthony Docimo (not verified) on 07 Sep 2007 #permalink

Thanks, Anthony.

BTW, orangutang - ending with the letter "g" - is rumored to be the malay word for "man in debt" :-), but I'm not a linguist and don't know if this is true or just an urban legend.

The fact that the camera is hollow might well be sufficient reason for the echidna to be trying to rip it open; just the sort of place that a small colony of ants or termites might be hanging out (I wouldn't try this with my own camera).
I don't think there's any sense in which "termite nests are few and far between in the echidna territory" - termites (i.e. colonies) are in fact the dominant large herbivores over almost all of mainland Australia (i.e. throughout the distribution of Tachyglossus), and often extremely abundant over vast areas. It may be advantageous for echidnas to remember the location of every colony they've ever visited (along with the quality and depth of intervening soils and crevices they can use to escape predators), but not because colonies are rare or likely to have been exhausted; more that each of several hundred colonies will only provide a few mouthfuls every few weeks, so it's important to get around to enough of them at long enough intervals to be worthwhile. But whether that begins to explain a difference in brain size between echidnas and other 'anteaters' I don't know: maybe the average size of colonies is bigger in Africa and South America, such that each animal only needs to know a small number of them.

By John Scanlon, FCD (not verified) on 09 Sep 2007 #permalink

Marjanovic,

You give a whole new meaning to, "Unhelpful".

Well, Kellogg. As far as I know, they have never been identified with triconodont molars, so I don't know where you got that from, which means I don't know what you are talking about, which in turn means that, sorry, I can't help you, beyond literally answering your question. And that I'm able to say in a single word.

A roughly "triconodont" form of premolar seems to be plesiomorphic (is it un-p.c. to say "primitive"?) for mammals

Well, "primitive" implies "progress", and that is not definable, among other problems... think of "plesiomorphic" as "the normal condition", the one that mammals have unless they've modified it. -- But monotreme teeth aren't triconodont ( = three cusps in a straight line), they are more or less tribosphenic ( = several cusps and crests surrounding two basins).

Of course, with a little imagination, you can derive every tooth shape from the triconodont one -- because that's what has ultimately happened.

By the time you get to critters confidently assigned to the Monotremata (or even to some stem group: has anybody introduced "Monotrematomorphoformes" for the last common ancestor of all the fragments Tom Rich has found and all its descendents?),

Australosphenida is probably what you're looking for.

People who seem to know what they are talking about seem to think the Monotreme molar might have evolved from something Tribosphenic (or nearly: Aegialodon-grade).

That's what they said before Australosphenida was discovered ( = before it was discovered that the monotremes and animals like Ausktribosphenos and Ambondro are closely related). Now everyone agrees it happened, but among animals very, very distantly related to Boreosphenida and Aegialodon.

By David Marjanović (not verified) on 11 Sep 2007 #permalink

A bit scary here, lots of funny words (relictual? Monotrematomorphoformes?) I've never heard of before.

"Poison production peaks to combine with spermatogenesis during August, and at this time males are particularly aggressive, often fighting".

This is interesting, as it may bear relevance to something I just figured out relating to ancient waterside human ancestor diving, and the placement of concentrated apocrine glands in the axillaries and pubic region in direct association with hydrodynamic void-filling (fluffy) secondary hair, where scent is least likely to be washed off during immersion, especially for a backfloating diver.

Do the platypus poison glands share a (derived?) commonality with apocrine glands or anal glands, rather than the more typical salivary venomous glands? Aren't the spurs on the digits closest to the anus? Could they have migrated evolutionarily from there, from a former pair of "stink" glands (cf skunk)? Considering that they are used in intraspecific competition (unlike poisonous snakes competing, which never bite each other), this seems more likely, rather than predator avoidance or predation, and further conferred by the synchrony of spermatogenesis hormonal activation (parallel to apocrine excretion increase during puberty).

Likely the echidna's electroreceptors were retained in marshes around wet soils, somewhat of a parallel to the star-nosed mole which also lives in wet soil, vision, olfaction and auditory sensing is impaired there. (I'm assuming the echidna is not particularly good at hearing, seeing or smelling compared to typical terrestrials. This reduction in olfaction typical of many aquatic mammals correlates to reduced scent gland activation or in this case, an increase in toxicity of gland products).

Dreams = subconscious learning = pattern recognition in 3 dimensions.
A recent psych. study discussed that: Questions could be solved in either a hard method or an easy method, those that took a nap solved them using the easy method, those that stayed awake couldn't figure out the easy method, although they got the right answer. Dreams are more efficient (time-wise) learning.

"It has always seemed likely to me that our large brains are largely due to intra-species competition/arms race".

Yes, likely in some form, in connection with tidal waterside living.

One reason I don't like the "dreaming is for forgetting" hypothesis is what I dream. Whenever I can remember it, it's vaguely based on something that I'm not necessarily supposed to forget (such as rising earlier the next day) and builds it into a completely wacky story.

Another is that the opposite of forgetting sometimes happens in my dreams: reinforcement. I've spoken foreign languages and done simple calculations in a few. I also often try to read, especially scientific articles, but it's very frustrating because the text keeps changing in front of my eyes.

Furthermore, I do forget stuff during the day. This especially concerns having done automatted procedures like locking the door and taking the key with me: I can't remember having done it, yet I have done it.

And then there are people with a photographic memory who seem to forget nothing at all and yet have space for all that information in their brains...

In sum, I like the hypothesis best that says dreams are "thunderstorms in the brain", association and imagination running free and unconstrained. If they have a positive effect, it's the joy of thinking, though my dreams are almost never pleasant (usually they aren't nightmares either, though, just boring and illogical).

By David Marjanović (not verified) on 15 Sep 2007 #permalink

Have I now given you enough detail? If not, please tell me what exactly you want to know.

BTW, where my surname comes from ch would be pronounced as "ts" followed by "ch" as in "Loch". And is there a particular reason for why you address me by surname and surname only? I haven't encountered that outside of 19th-century contexts... I've imitated it above just because I find it funny.

By David Marjanović (not verified) on 20 Sep 2007 #permalink

Speculation (wildest so far) Eureka!

The volar surfaces allow a certain small amount of respiration in humans and other mammals, derived from when pre-mammals ancestors had a body covering of (fingernail-like) scales which in birds became feather quills, replaced in mammals by naked skin with increased hair from the face (manatee whiskers & body hair), the volar surfaces always staying bare of scales and hair and retaining primitive exchange of O2 & CO2 (froglike) via the volar eccrine sweat glands which like the lungs must always remain moist-wet. (THAT was a weird dream indeed! in regards to D. Marjanović's "thunderstorms in the brain" hypothesis)

... or so ...

(I woke up with this thought, decided to publish it at AAT & at Tet Zoo.)