# Mapping the Platypus Genome



## j d worthington (May 8, 2008)

I've always found them to be utterly fascinating little creatures; this information (some of which is quite new to me, though I don't know if that will be the case with others) makes them even more so. So, for those interested:

World's Strangest Creature? Part Mammal, Part Reptile - Yahoo! News

Title, "World's Strangest Creature? Part Mammal, Part Reptile", from LiveScience, by Jeanna Bryner, Wed., May 7, 2008....


----------



## The Procrastinator (May 8, 2008)

The monotremes are certainly incredible beasties, and damn cute with it. I always find it awesome to think of the amount of time they have survived unchanged. I guess if it ain't broke, don't fix it.

And if you're in Oz, either resident or on hols, be careful what you do with your rubbish - you wouldn't want it ending up in a river and choking one of these little darlings!


----------



## Quokka (May 8, 2008)

I thought the mention of the X and Y chromosomes was interesting. I remember reading something about how what would later become the ear may have evolved from structures used for breathing, long before hearing was involved and here we have evidence that the X and Y chromosomes haven't always evolved along the lines of sex chromosomes.

Plus they have the coolest name for their young with both platypus and echidna baby's being puggles .


----------



## Vladd67 (May 8, 2008)

Here is another article on the same theme
Platypus Looks Strange on the Inside, Too | Vladd’s view of the World


----------



## JDP (May 8, 2008)

I was interested to learn that male Platypi have venomous spurs. I didn't know that. I didn't know the young were called puggles either. Brilliant!


----------



## BookStop (May 8, 2008)

Complicated little critters, ain't they?


----------



## gully_foyle (May 8, 2008)

We have one in our local river that I have been fortunate enough to see once. It aint the cleanest river either. Echidna's don't seem that unusual up against hedgehogs and porcupines. But Platypi are just plain bizarre. It's like god let his 5 year old nephew have a stab at designing a critter.


----------



## The Ace (May 8, 2008)

Errrrrr no, the reptilian lower jaw consisted of a number of bones, the dentary being the one that carried the teeth.  In mammals, the dentary has become the mandible, complete with attachment points, and the three remaining bones on each side have migrated and reduced in size to become the familiar hammer, anvil and stirrup of the inner ear.


----------



## Nik (May 8, 2008)

My Spouse asserts that the shift away from mammalian egg-laying should be considered the *final* nail in coffin of 'Intelligent Design'.


----------



## Quokka (May 8, 2008)

The Ace said:


> Errrrrr no, the reptilian lower jaw consisted of a number of bones, the dentary being the one that carried the teeth.  In mammals, the dentary has become the mandible, complete with attachment points, and the three remaining bones on each side have migrated and reduced in size to become the familiar hammer, anvil and stirrup of the inner ear.



No idea how this would fit in or if it was more than just a passing theory but this would have been a lot earlier.

Did our ancestors breathe through their ears?


----------



## Delvo (May 8, 2008)

The Ace said:


> Errrrrr no, the reptilian lower jaw consisted of a number of bones... the three remaining bones on each side have migrated and reduced in size to become the familiar hammer, anvil and stirrup of the inner ear.


The reference to "breathing" still works in reference to an earlier time than that. The ancestors of the reptile-like critters you're talking about were fish, who used those bones to prop open their gills. Some fish still have that feature today; they're called gill struts. The jaws or at least lower jaw are also believed to have been the original gill-strut derivative. Although most critters with jaws have only one set because only the first gill strut pair separated from the others, someone around here posted an article not long ago about a type of moray in which the second has done so as well so they have a second set of jaws in the back of the mouth. And if I'm not mistaken, we can also count the hyoid bone (located in the throat, and the only other bone in humans that floats freely in soft flesh instead of articulating with any other bone) as another gill-strut derivative.


----------



## Delvo (May 8, 2008)

Quokka said:


> I thought the mention of the X and Y chromosomes was interesting... evidence that the X and Y chromosomes haven't always evolved along the lines of sex chromosomes.


Genes don't dictate sex in any living vertebrates but mammals, birds, and a very few kinds of fish; reptiles, amphibians, and nearly all fish have sex determined by some other trigger, such as what the ambient temperature was at the time the embryo enters a certain critical stage of development. (You can't do that if you're keeping the embryo warm all the time, so birds and mammals needed another method, and monotremes' body temperatures are not as consistent as ours, although they are more consistent than reptiles'.) And birds (and those few fish) use a different system from ours that had to develop independently: W and Z chromosomes, with the males being the ones that have two of the same kind and the females having one of each. So evolutionary biologists have long figured that a sex chromosome, in those critters that have them at all, was originally simply a regular ordinary chromosome that at some point got a gene that said "ignore temperature, pheromones, and any other external cues; I'll just make this one this sex no matter what".

What really confuzzles me is that they identified two platypus chromosomes as X and Y anyway while identifying 10 OTHER "sex chromosomes". What else did they use to define what makes an X/Y an X/Y, how in the world can a system with TEN different sex chromosomes work, and why would that one function have almost a fifth of their chromosomes involved in it?



JDP said:


> I was interested to learn that male Platypi have venomous spurs.


I saw a TV show about a guy who got stung by one of those a few years ago. It turned out that the venom doesn't threaten the victim's life or health. It just goes for the peripheral nerves and causes really really intense pain... constantly without any breaks or pauses... for months or years.



Nik said:


> My Spouse asserts that the shift away from mammalian egg-laying should be considered the *final* nail in coffin of 'Intelligent Design'.


I'm tempted to start talking about how it was actually a good thing but I suspect this was a dry joke... 

* * *

One thing I don't like about the way this got reported is that they made it sound as if either mammals evolved from reptiles or the platypus resulted from crossbreeding between mammals and reptiles. It's not exactly an uncommon convention; our earliest and most reptile-like synapsid ancestors are still often referred to as "mammal-like reptiles" even by pro comparative anatomists who know better, like it's an informal nickname like referring to crocadilians as "crocs" or _Velociraptor_ as "raptor". And it's true that, way back then, they did have some reptile-like traits: egg-laying, splayed-out limbs, apparently cold-bloodedness, and fusion of what are now the "ear bones" to the lower jaw. But they had already separated from the ancestors of reptiles and had some distinct traits different from them and in common with us, such as the synapsid skull structure instead of diapsid, and apparently a soft, moist, porous skin like mammals and amphibians have (because only the diapsids ever invented terrestrial scales, which aren't the same thing as fish scales). And they developed some other mammalian traits so rapidly that even the most reptile-like among them were almost never without them, such as putting two or more different kinds of teeth in the same mouth, separating the "ear bones" from the lower jaw, standing up higher off the ground, and perhaps some early versions of temperature control like the sail on the _Dimetrodon_'s back.

In short, our ancestors and reptiles' ancestors separated from each other long before the three groups of mammals separated from each other, long before even the dinosaurs were around, with no crossbreeding since then, but you'd never know it from the way these articles described the monotremes.


----------



## Ursa major (May 8, 2008)

Delvo said:


> What really confuzzles me is that they identified two platypus chromosomes as X and Y anyway while identifying 10 OTHER "sex chromosomes". What else did they use to define what makes an X/Y an X/Y, how in the world can a system with TEN different sex chromosomes work, and why would that one function have almost a fifth of their chromosomes involved in it?


 
I'm confuzzled as well (as would be the Platypus, if it could read).

Perhaps someone who has access to the relevant issue of Nature can enlighten all of us.


----------



## The Procrastinator (May 9, 2008)

Can't de-confuzzle you bout that but I would just like to throw in (apropos Delvos' discussion of genes dictating sex) that kangaroos have the capacity to choose the sex of their young'uns - younger females will almost always give birth to females  -they save the males for their old age. Not to be satisfied with that, they can also keep an embryo in "suspended animation", delaying the birth process until a good season comes along. And they can produce two "recipes" of milk while lactating, one for an older joey who is still feeding but has emerged from the pouch, and a different one for a tiny hairless young'un just starting out.

I have also noticed that plants here do not always flower according to season, but may flower according to rainfall...


----------



## Dave (May 9, 2008)

At least you have explained to me why my wife's hearing should be affected by the fact that she has a jaw click. 

As for 'Intelligent Design', isn't that just proof that God is male? If women were in charge of design we would all be Seahorses.


----------



## Dave (May 9, 2008)

Delvo said:


> One thing I don't like about the way this got reported is that they made it sound as if either mammals evolved from reptiles or the platypus resulted from crossbreeding between mammals and reptiles.


What people always forget is that the vast majority of species that have once existed did not survive, probably close to 100%. Even the fossil record only records a little more, and then only the most successful that survived for a long period. All the missing links and steps inbetween are lost, and piecing together a tree of evolution is bound to be difficult and liable to frequent mistakes. It's just a shorthand to say something is a half-way cross between such and such, when in reality it is a very distant cousin.

Also, the way Evolution is taught in Primary school, or at least how it was to me, (and that is the most Science many people get) was that there was the Age of Reptiles, then the Age of Birds, then the Age of Mammals; as if there was indeed some great design involved. In reality, proto-mammals and proto-birds were all living alongside Dinosaurs; who have more in common with birds than the reptile species that have survived to the present-time. The ancestors of Platypus and the ancestors of other mammals had probably already divulged when they were still small creatures hiding at the feet of the reptiles.


----------

