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149580.  Tue Feb 20, 2007 4:47 pm Reply with quote

...but no nipples. The milk comes out through the skin. I'd be very surprised if the male had functioning glands, though, as it's the female that incubates the foetal young when they emerge.

149590.  Tue Feb 20, 2007 5:00 pm Reply with quote

It's the hormonal changes of pregnancy that enable the development of mammary glands (as distinct from mammary tissue), and hormonal changes that occur immediately after giving birth that trigger lactation, so I also doubt whether a male platypus actually lactates.

149635.  Tue Feb 20, 2007 6:16 pm Reply with quote

Oh,dear, my memory is letting me down after 37 years........anyway I can't find a reference anywhere to male platypus lactation, so I humbly withdraw the suggestion.

But I don't think you can work out anything from the endocrine arrangements in Eutheria (true mammals), as the platypus is an egg-laying Monotreme, one step away from a reptile. It therefore won't have placental lactogen, but it might have prolactin, as even the fishes do, though of course they use it for something else.

149721.  Wed Feb 21, 2007 4:43 am Reply with quote

Just the fact that it produces milk puts it a great deal closer to the eutherian mammals than it does to the reptiles, and therefore is likely to have other similar arrangements, hormonal or otherwise. Warm-bloodedness, fur, and (apparently) lots of DNA similarities to other placental mammals make it far closer than to the reptiles.

But yes, the exact arrangement of the proto/meta/eu -theria is still the subject of a lot of debate.

Attenborough's Life of Mammals has a long sequence from inside a nesting platypus burrow. I'll have a look...

149796.  Wed Feb 21, 2007 7:56 am Reply with quote

On the subject of male lactation - according to Wikipedia, which gives a reference source, it does occur in one species, the dayak fruit bat (It occurs in other species as well,but this is pathological).

154158.  Tue Mar 06, 2007 8:19 am Reply with quote

Why is the duck billed platypus called Ornithorhynchus anatinus in Latin. Does it have any ornithological links?

154160.  Tue Mar 06, 2007 8:26 am Reply with quote

It lays eggs, maybe that's it?

154178.  Tue Mar 06, 2007 9:00 am Reply with quote

Ornithorhynchus is Greek derived, and means bird-billed. Anatinus is Latin for "pertaining to a duck".

515449.  Mon Mar 02, 2009 4:59 pm Reply with quote

Yes, it is true, unlike what I was taught in school (that the DB Platypus was the only poisonous mammal), there are several species of shrew that have venom. "The poisonous saliva is secreted from submaxillary glands, through a duct which opens at the base of the lower incisors, where the saliva flows along the groove formed by the two incisors, and into the prey."

876835.  Wed Jan 11, 2012 10:43 am Reply with quote

Gray wrote:
Just the fact that it produces milk puts it a great deal closer to the eutherian mammals than it does to the reptiles, and therefore is likely to have other similar arrangements, hormonal or otherwise. Warm-bloodedness, fur, and (apparently) lots of DNA similarities to other placental mammals make it far closer than to the reptiles.

The production of milk antedates mammals. From this 2007 paper by Capuco and Akers:

Paper by Capuco and Akers wrote:
Lactation appears to be an ancient reproductive feature that pre-dates the origin of mammals. A cogent theory for the evolution of the mammary gland and lactation has been provided by Olav Oftedal. The features of current mammals were gradually accrued through radiations of synapsid ancestors, and the mammary gland is hypothesized to have evolved from apocrine-like glands associated with hair follicles (Figure ​(Figure1).1). Oftedal suggests that these glands evolved from providing primarily moisture and antimicrobials to parchment-shelled eggs to the role of supplying nutrients for offspring. Fossil evidence indicates that some of the therapsids and the mammalia-formes, which were present during the Triassic period more than 200 million years ago, produced a nutrient-rich milk-like secretion.

The reference to Olav Oftedal’s work is to this 2002 paper, whose abstract reads:

Paper by Olav Oftedal wrote:
Lactation appears to be an ancient reproductive trait that predates the origin of mammals. The synapsid branch of the amniote tree that separated from other taxa in the Pennsylvanian (>310 million years ago) evolved a glandular rather than scaled integument. Repeated radiations of synapsids produced a gradual accrual of mammalian features. The mammary gland apparently derives from an ancestral apocrine-like gland that was associated with hair follicles. This association is retained by monotreme mammary glands and is evident as vestigial mammary hair during early ontogenetic development of marsupials. The dense cluster of mammo-pilo-sebaceous units that open onto a nipple-less mammary patch in monotremes may reflect a structure that evolved to provide moisture and other constituents to permeable eggs. Mammary patch secretions were coopted to provide nutrients to hatchlings, but some constituents including lactose may have been secreted by ancestral apocrine-like glands in early synapsids. Advanced Triassic therapsids, such as cynodonts, almost certainly secreted complex, nutrient-rich milk, allowing a progressive decline in egg size and an increasingly altricial state of the young at hatching. This is indicated by the very small body size, presence of epipubic bones, and limited tooth replacement in advanced cynodonts and early mammaliaforms. Nipples that arose from the mammary patch rendered mammary hairs obsolete, while placental structures have allowed lactation to be truncated in living eutherians.

In general, presenting a dichotomous distinction between ‘reptiles’ and ‘mammals’ based on traits like vivipary, lactation, endothermy, or pelage grossly over-simplifies matters, as there are exceptions to each of those. As lactation has been shown to have occured in creatures other than mammals, the same can also be said for hair follicles and warm-bloodedness. Pterosaurs (which were not dinosaurs!) had hair-like follicles, for example. So did the (largely) unrelated therapsids, such as cynodonts.

For that matter, being ‘warm-blooded’ (endothermy) is not as clear-cut as one might think. Even such lowly creatures as tuna, sharks, and sphinx moths raise their body temperatures above ambient without requiring basking in the sun, which gives them an edge in the power curve: it’s like they have builtin motors.

However, these creatures achieve warm-bloodedness differently than (most) mammals and (some) dinosaurs do, which is via internal respiration. The moths shiver their muscles to boost their temperature before and during flight. The various warm-blooded fishes have a more elaborate mechansim for achieving warm-bloodedness. It is somewhat interesting that warm-bloodedness occurs in both ray-finned fishes like tuna and cartilaginous fishes like sharks, as these two groups are not thought to be particularly interrelated.

But more specifically, the type of warm-bloodedness that even today occurs in avian dinosaurs is distinct from the mammalian sort, and may not share with mammals a common warm-blooded ancestor. (Then again, they just might, which could rope in the pterosaurs, too.) Many palaeozoologists believe that other groups of dinosaurs beyond the strictly avian ones were also endotherms to some extent or another, although it is unclear how well this matches mammalian endothermy. It is also strongly suspected that the pterosaurs were endotherms.

And as I believe was previously covered on QI, the Naked Mole Rat is an African mammal that is not warm-blooded, so one cannot even say that all mammals are warm-blooded. The Naked Mole Rat can’t internally regulate its body temperate at all, but even other species of Mole Rat are weak endotherms, unable to control their body temperatures with typical mammalian precision.

Lastly, there are not just two extant monotreme species, the platypus and the echidna. Although there is just one platypus, there are several echidna species. Historically, there were two echidnas, but upon reevaluation biologists now account for two extant genera and four living species of echidna, with three species occupying one genus and the fourth placed in another genus.

876838.  Wed Jan 11, 2012 10:52 am Reply with quote

That's really interesting, tchrist, thanks.

877315.  Fri Jan 13, 2012 9:58 am Reply with quote

Originally there were two species of echidna. The long beaked echidna found on the island of New Guinea and the short beaked echidna found on Australia, Tasmania and the south of New Guinea.

The long beaked echidna is now reconised as three distinct species one of which is named after Sir David Attenborough.

The other species may or may not constitute two or three species. New Guinea/Tasmania separated from Australia c10,000 years ago. (Some scientists recognising two/three sub-species). The Tasmanian residents are larger in size than their mainland relatives.

The platypus also lives in Tasmania and is much larger than its mainland cousin. The platypus tends to decrease in size the further north it lives.

877807.  Sun Jan 15, 2012 1:12 pm Reply with quote

Because the platypus both lays eggs and produces milk, it is one of the few animals that can make its own custard.

965958.  Thu Jan 24, 2013 8:14 am Reply with quote

Venomous mammals:

Nine species of venomous mammals in six genera are venomous, although the delivery system of lorises is so weird that there is an argument about whether it is counted.

American short tailed shrew
European water shrew and Mediterranean water shrew
Canarian shrew

Hispaniolan solenodon and Cuban solenodon


slow loris and pygmy slow loris

I bet platypuses are the most painful!

966995.  Sun Jan 27, 2013 10:50 am Reply with quote

Overheard by an Australian river...

I'm also venomous but am I called "the venomous platypus"?

No. That's why humans are arseholes.


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