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What Sex is That Rex?

CFLarsen

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What Sex is That Rex?

Tyrannosaurus rex meet Tyrannosaurus regina. For the first time, paleontologists have identified a T. rex as female by discovering a type of bone tissue that appears to be related to egg-laying. The trademark may help scientists distinguish the sex of other bird-like dinosaurs, but its delicate and transient nature could preclude wide use.

Most direct indicators of sex—reproductive organs, for example—don't fossilize. In a few cases, paleontologists have discovered eggs inside a skeleton (Science, 15 April, p. 375) allowing them to know for sure they found a female.

Now a team led by Mary Schweitzer of North Carolina State University in Raleigh has found in a dinosaur fossil the remains of tissue associated with egg-laying. Schweitzer and her colleagues were studying the 70 million-year-old bones of a remarkably well-preserved Tyrannosaurus (Science, 25 March, p. 1852) when Schweitzer noticed a type of bone tissue she had never seen before—at least not in a dinosaur. Located inside a leg bone, the brownish tissue was very fibrous and disorganized. "It's completely distinctive," Schweitzer says.

...

To compare the Tyrannosaurus fossil with living birds that were at least somewhat comparable in size to the dinosaur, the team cut up the legs of a pregnant ostrich and an emu that had died before laying all its eggs. Like the Tyrannosaurus tissue, the medullary bone of these so-called ratites was relatively thinner than in chickens; that makes sense because birds with larger bones are inherently stronger, so calcium loss is less of a threat.

The potential payoff of identifying sexes in dinosaurs is great, says Anusuya Chinsamy-Turan of the University of Cape Town South Africa: one could better study population dynamics, for example.

Source
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Compare that to Kent Hovind's and Ken Ham's crude "analysis" of dinosaurs. Those buggers ain't got nothing on real science... ;)
 

For the first time, paleontologists have identified a T. rex as female by discovering a type of bone tissue that appears to be related to egg-laying.
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Why didn't they just check if it had a dick or not?
 
They had a nice segment on this on NPR yesterday. It's not a definitive determination of sex, as this condition (the calcium forming tissues) only occurs when the female is in egg-production mode.
Still, it may allow other comparisons that were not previously possible.
 
Just a thought. In mammals, XY is male while XX is female. In birds it's the other way round. Is anything known about when this split might have occurred? It seems quite a fundamental difference, so is presumably primitive.

Rolfe.
 
Rolfe said:
Just a thought. In mammals, XY is male while XX is female. In birds it's the other way round. Is anything known about when this split might have occurred? It seems quite a fundamental difference, so is presumably primitive.

Rolfe.
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There's an argument based on analysis of platypus sex chromosomes that the seperation of avian ZZ/ZW and mammalian XX/XY occured about 210 MYA.

Platypuses have 10 (count 'em) sex chromosomes and the X chromosome at one end is homologous to a human X while there is one near the other end of the chain that is homologous to a bird's Z chromosome.

The relevant article is Grutzner et al "In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes" Nature 432, 913 - 917, December 16th 2004
 
Wow.

That's the kind of stuff you file away in your brain and marvel over.


What makes it really amazing is the fact that we have the knowledge and ability to check that information against creatures living today.


Wow.



Boo
 
Re: Re: What Sex is That Rex?

Iconoclast said:
Why didn't they just check if it had a dick or not?
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You could read the quote:

Most direct indicators of sex—reproductive organs, for example—don't fossilize.
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:p
 
Iconoclast said:
It's also a reproductive organ?
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.........perhaps you might want to check if there are any children in the neighborhood looking like you.... ;)
 
Camillus said:
There's an argument based on analysis of platypus sex chromosomes that the seperation of avian ZZ/ZW and mammalian XX/XY occured about 210 MYA.

Platypuses have 10 (count 'em) sex chromosomes and the X chromosome at one end is homologous to a human X while there is one near the other end of the chain that is homologous to a bird's Z chromosome.

The relevant article is Grutzner et al "In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes" Nature 432, 913 - 917, December 16th 2004
Click to expand...
Wow, that one's advanced a long way since the Paleolithic (when I were an undergraduate!) Fascinating stuff, but I still bet it all tastes like chicken.... :D

Rolfe.
 
Re: Re: What Sex is That Rex?

Iconoclast said:
Why didn't they just check if it had a dick or not?
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A very insightful question.

Humans are unusual among mammals in that they lack a baculum, or penis bone, as the base of the self same organ. Other mammals have quite prominent ones, supposedly walrus bacula were used by eskimos as war clubs.

Dinosaurs almost certainly copulated by the mail climbing on top of the female in a three point stance. I have no idea how stegosaurs managed, don't ask. Then the beasts would probably wrap the bases of their tails together and proceed with business.

With all the distance involved, you would think a great big dinosaurian penis would be rather useful. After all, Armadillos, faced with the similar problem of all the armor getting in the way during intimate moments, have evolved a spectacularly huge penis, about a third of the male's length.

Who knows. As it turns out, to the infinite chagrin of anyone who wants to know just how "big" T rex was, the archosaurian equivalent of a phallus appears to lack a baculum. Curse the luck!

Most reptile males have something approximating a penis (though that's a dangerous statement to make in a day and age when tentacle rape was invented), though most birds lack it. "Primitive" birds, like ratites, do have the "penis", so I would expect one in dinosaurs as well. Just not one that would fossilize.


Edit:

Just in case you were wondering, based on identification by the traditional osteogendermorphy (I invented that word BTW) of the base of the tail, the female rex was about 15% bigger than the male.
 
"...supposedly walrus bacula were used by eskimos as war clubs." Neutrino-Cannon

Supposedly?? This is not the sort of issue which normally engenders supposition. One expects certainty. Particularly from the Walrus.
 
While recently in New York, I came upon a bone shop that was, indeed, selling bacula.

I was going to buy one for the GF back home... and then realized just how wierd that would be.

So I got her a pretty ammonite instead.

Anyhow, I'm not done derailing this thread just yet. I have (something similar to) proof that the eskimoes were armed with the most freudian weapons of all time!
 
Re: Re: Re: What Sex is That Rex?

neutrino_cannon said:
Humans are unusual among mammals in that they lack a baculum, or penis bone, as the base of the self same organ. Other mammals have quite prominent ones, ....
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My limited experience of non-human mammals doesn't really back this up. The only domestic mammal that has an os penis as far as I know is the dog. Cat, horse, bull, sheep, pig, or even come to that the rabbit and the rest of the "small furries", no such thing. A big variety of shapes and sizes, but only the dog has a bone.

I'm sure you're right and a goodly number of other mammals are also in that category, but based on the sample I know about, I'm querying the idea that man is "unusual".

Rolfe.
 
Hmmm... indeed. I was so impressed by the selection of bacula from the various groups that I assumed it was the norm. Lessee, It's obviously present in pinnipeds and canids (as well as basal carnivores like racoons if the bones in the shop were labled correctly), but appearantly not in cats.

Rodents have got it, so do edentata (is that group now considered polyphyletic? I never see it refered to in modern literature) which are pretty close to basal mammals, so I would figure that the basal condition in eutherians is to have a baculum.

I have no idea about the rest of the mammals, and I'm certainly not in the position to do a survey of all living mammals, so I'll just go with the wikipedia article which states that:


The baculum (also penis bone, penile bone or os penis) is a bone found in the penis of most mammals.
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But then again, why would they know?
 
Re: Re: Re: Re: What Sex is That Rex?

Rolfe said:
My limited experience of non-human mammals doesn't really back this up. The only domestic mammal that has an os penis as far as I know is the dog. Cat, horse, bull, sheep, pig, or even come to that the rabbit and the rest of the "small furries", no such thing. A big variety of shapes and sizes, but only the dog has a bone.

Rolfe.
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Lagomorphs don't have an os penis but all rodents (as far as I know) do. I'm certain that guinea pigs, rats, mice and hamsters have got them.
 
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