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Author Topic: Dinosaurs and other prehistoric creatures  (Read 196431 times)

Xenodog
Mar 17, 2014, 02:04:57 PM
Reply #960 on: Mar 17, 2014, 02:04:57 PM
Q
Forget Nanotyrannus, here's a real pygmy tyrannosaur, lol. A tyrannosaurid that could be bullied by a troodontid; blasphemy I tells ya.

The more robust tyrannosaurid would still be the top dog; it'd be like a leopard vs a cheetah.


maledoro
Mar 19, 2014, 09:31:22 PM
Reply #961 on: Mar 19, 2014, 09:31:22 PM
Q
Forget Nanotyrannus, here's a real pygmy tyrannosaur, lol. A tyrannosaurid that could be bullied by a troodontid; blasphemy I tells ya.

The more robust tyrannosaurid would still be the top dog; it'd be like a leopard vs a cheetah.
But leopards and cheetahs are not dogs. N'yuk, n'yuk, n'yuk...
:D



Vertigo
Mar 20, 2014, 09:47:06 PM
Reply #963 on: Mar 20, 2014, 09:47:06 PM
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It's somehow not surprising that Maastrichtian North America's oviraptorosaur would be one of the largest ever discovered. USA, 66-72,000,000 BC: when evolution went nuts.

Curious how we're suddenly finding so many new dinosaur genera from that time and place though, given that it's been heavily excavated for well over a century. Off the top of my head, that's Acheroraptor, Nanuqsaurus and Anzu, just in the last four months.
Finally puts paid to that old 'theory' about dinosaur diversity declining around the end of the Cretaceous.

:edit: The journal publication for Anzu has another of those handy time-referencing cladograms, for the Oviraptorosauria, if anyone's interested.


« Last Edit: Mar 20, 2014, 10:09:03 PM by Vertigo »

DoomRulz
Mar 21, 2014, 02:00:25 PM
Reply #964 on: Mar 21, 2014, 02:00:25 PM
Q
Speaking of dino diversity; is it my imagination or does North America seem to really favour giant dinosaur discoveries the most, aside from the exceptions in South America?


Vertigo
Mar 21, 2014, 03:39:23 PM
Reply #965 on: Mar 21, 2014, 03:39:23 PM
Q
There's a definite bias that way. Most dinosaur groups in the region got an exceptional dollop of giantism around the end of the Cretaceous though.


judge death
Mar 21, 2014, 06:31:10 PM
Reply #966 on: Mar 21, 2014, 06:31:10 PM
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There's a definite bias that way. Most dinosaur groups in the region got an exceptional dollop of giantism around the end of the Cretaceous though.
Are there any theories on why they became so huge around the Cretaceous era?
What I knew from before is that the air and oxygen were thicker and made it possible to become bigger but that is an old theory which is too simple to be true in my opinion.

The journal you posted were very interesting to read and seems to counteract some info I got that at the end of creta era the variety of dino species were decreasing and dying out but according to that journal it seems to have been the opposite and not the empty and dying world some documentaries show it like.


Vertigo
Mar 21, 2014, 11:30:41 PM
Reply #967 on: Mar 21, 2014, 11:30:41 PM
Q
Increased oxygen density is certainly a leading theory for insect giantism in certain periods of the Palaeozoic, but the principal behind it wouldn't apply to vertebrates (we discussed it a few pages ago).
I suppose you could speculate that higher oxygen intake could have given dinosaurs more energy, and that they might have used the energy to carry greater bulk around with them, but aside from the concern over whether that would be physically plausible, the oxygen content during the Mesozoic is actually uncertain. Some estimates put it lower than today's.

My personal theory is that dinosaur giantism stems from the need for the herbivores to develop giant stomachs. This gave them greater capacity and efficiency in fermenting plant matter. There are two reasons why this was so important. One, the Mesozoic was dominated by extremely tough plant material that most of today's animals struggle to digest, if they can at all - conifers, cycads, ginkgos, horsetails, ferns. Two, many dinosaurs lacked cheeks or grinding dental batteries, so their stomachs (and swallowed gizzard stones) would do a lot of the work that mammalian grazers' mouths perform.
A giant stomach needs giant legs to carry it, giant muscles to propel that bulk away from predators or onto a mate, a giant mouth to shovel down food quickly enough, a giant neck to reach the ground, and a giant tail to balance the neck.
And of course, predators evolve to match their herbivorous prey, which is why the allosauroids appeared when sauropods started to dominate.

There are other theories, and probably more than one of them are true.

The herbivores and their predators could have been locked in an evolutionary arms race, each undergoing natural selection for increased size as a tool for defence / predation. I'm sure this must have been going on, but doesn't explain the situation in itself - why aren't mammals prone to giantism for the same reason?
Temperatures dropped during the late Jurassic, concurrent with the appearance of colossal sauropods and allosaurs; it's possible (just) that this may be a thermoregulatory development. Larger animals retain body heat more easily, and as we've never found evidence of protofeathers in either group, temperature may have been very important for them. (Personally, I suspect it's only a matter of time until we find feathery baby sauropods and non-coelurosaurian theropods.)
Another theory is that dinosaur populations could survive with few adults compared with mammals, because they didn't need to put as much effort into raising their young. With less adults, there could have been more food to go around, allowing them to sustain larger sizes. Maybe.
Sexual selection has also been proposed... larger dinosaurs won intraspecific contests, or were more attractive to mates.
There's also an old theory that animal groups will simply tend towards giantism if they have the physical tools and requirements for it. But it was proposed by the bloke who put Elasmosaurus' head on the end of its tail, so might be best not to put much stock in that one.

There are other theories I can't think of from the top of my head, and there would certainly have been other factors involved.



Requiem28
Mar 23, 2014, 01:55:59 AM
Reply #969 on: Mar 23, 2014, 01:55:59 AM
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His son is my teacher!

But some of us already know this!




maledoro
Mar 25, 2014, 01:03:26 AM
Reply #972 on: Mar 25, 2014, 01:03:26 AM
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Sam Neill's.


judge death
Apr 03, 2014, 04:28:56 PM
Reply #973 on: Apr 03, 2014, 04:28:56 PM
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Have now these books on the way:
Prehistoric: The Visual History Of Life On Earth book
Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages 2007
encyclopedia of dinosaurs & prehistoric life 2009
THE ILLUSTRATED ENCYCLOPEDIA OF DINOSAURS AND PREHISTORIC ANIMALS

A fast question:
Is looking into the family trees of many dinosaurs but cant find one which shows them all on the same page so to speak, but just shows cuts from it.
Example: Trying to see from which animals the Allosaurinae family tree came from and how they evolved later and if they are related to the tyrannosaurus family tree in any way.
Do you know a good site where I can see the whole family trees for all dinos? :)



 

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