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Author Topic: Dinosaurs and other prehistoric creatures  (Read 196405 times)

DoomRulz
Feb 14, 2014, 07:47:29 PM
Reply #915 on: Feb 14, 2014, 07:47:29 PM
Q
When you say tyrannosauroid, does that term refer to basal specimens, or something in-between basal and true?

If it was contemporaneous with Acrocanthosaurus, then there's no way it could have been the apex predator. Unless it's name was Saurophaganax, which was long gone by then, it couldn't have been. These mystery teeth are definitely tyrannosauroid in design?


Vertigo
Feb 14, 2014, 09:28:04 PM
Reply #916 on: Feb 14, 2014, 09:28:04 PM
Q
Well, Tyrannosauroidea is the superfamily name within Coelurosauria, so technically it encompasses everything from Proceratosaurus to Tyrannosaurus. The group only has two subdivisions, Proceratosauridae and Tyrannosauridae, but has a large nexus of animals which don't fit into either of those (they're more basal than tyrannosaurids, and typically more derived than proceratosaurids). There's a lot of uncertainty around the early members of the family, some researchers don't consider proceratosaurids to be a valid group at all.

Personally though, if I'm talking about a 'tyrannosauroid', I'm generally talking about something from the family that's more basal than a tyrannosaurid. There's a pretty clear divide - the earlier members of the group are mostly small, three-fingered sprinters, whereas pretty much all the tyrannosaurids are huge and bulky with two functional fingers.


Tooth fossils can be very misleading, as tooth shape can be similar through convergent evolution rather than a taxonomic relationship (I'm guessing you know that already). It's also incredibly rare for a tooth find to later be associated with a full animal (which gives you some idea of what a vast number of species there must have been). With that said, in this case, the teeth show a number of evolved traits also seen in Xiongguanlong's, and also occurred contemporaneously, so it'd be one hell of a coincidence if they weren't closely related.


Anyway, in my opinion the 20Ma gap between Siats and Lythronax is caused by the incomplete fossil record rather than a lack of the niche being filled. There should be a series of 500-1500kg tyrannosauroids with diminishing arms, heavier builds and deepening skulls lurking somewhere in the deposits of that period.


DoomRulz
Feb 15, 2014, 02:15:11 PM
Reply #917 on: Feb 15, 2014, 02:15:11 PM
Q
Well, Tyrannosauroidea is the superfamily name within Coelurosauria, so technically it encompasses everything from Proceratosaurus to Tyrannosaurus. The group only has two subdivisions, Proceratosauridae and Tyrannosauridae, but has a large nexus of animals which don't fit into either of those (they're more basal than tyrannosaurids, and typically more derived than proceratosaurids). There's a lot of uncertainty around the early members of the family, some researchers don't consider proceratosaurids to be a valid group at all.

Then where would they fit in, in the minds of those researchers? Super-Coelurosauria? :P

Personally though, if I'm talking about a 'tyrannosauroid', I'm generally talking about something from the family that's more basal than a tyrannosaurid. There's a pretty clear divide - the earlier members of the group are mostly small, three-fingered sprinters, whereas pretty much all the tyrannosaurids are huge and bulky with two functional fingers.

More basal than a tyrannosaurid to me sounds like it would be proceratosaurid.

Tooth fossils can be very misleading, as tooth shape can be similar through convergent evolution rather than a taxonomic relationship (I'm guessing you know that already). It's also incredibly rare for a tooth find to later be associated with a full animal (which gives you some idea of what a vast number of species there must have been). With that said, in this case, the teeth show a number of evolved traits also seen in Xiongguanlong's, and also occurred contemporaneously, so it'd be one hell of a coincidence if they weren't closely related.

For my own sake, because my knowledge of scientific terminology is limited, convergent evolution means the evolution of two animals that evolved similar features (e.g. dolphin and a shark, in terms of body design) but aren't actually related, right?

Anyway, in my opinion the 20Ma gap between Siats and Lythronax is caused by the incomplete fossil record rather than a lack of the niche being filled. There should be a series of 500-1500kg tyrannosauroids with diminishing arms, heavier builds and deepening skulls lurking somewhere in the deposits of that period.

There had to have been. Either that, or something changed with the prey items of that period. A tiddler like Lythronax isn't going to just knock off a heavyweight like Acrocanthosaurus.


Vertigo
Feb 18, 2014, 01:05:30 AM
Reply #918 on: Feb 18, 2014, 01:05:30 AM
Q
Then where would they fit in, in the minds of those researchers? Super-Coelurosauria? :P
...
More basal than a tyrannosaurid to me sounds like it would be proceratosaurid.

Well, you asked. It will get geeky.
The argument is whether or not Proceratosaurus and its closest relatives form a divergent group within Tyrannosauroidea, sistered to other discovered tyrannosauroids, or if they're ancestral to these later members of the group (including tyrannosaurids), which would lump them in with the rest of the superfamily.
Important to note, there are at least six genera which aren't members of either subdivision, including Dryptosaurus and Appalachiosaurus which were the dominant predators in eastern North America near the end of the dinosaur era, contemporaneously with tyrannosaurids in the west (kept apart by the Western Interior Seaway).


Quote
For my own sake, because my knowledge of scientific terminology is limited, convergent evolution means the evolution of two animals that evolved similar features (e.g. dolphin and a shark, in terms of body design) but aren't actually related, right?

Exactly.


Sabby
Feb 18, 2014, 01:20:45 AM
Reply #919 on: Feb 18, 2014, 01:20:45 AM
Q
I'm an arachnophobic, but I find insects wnd arachnids in general to be fascinating. What are some interesting prehistoric bugs?


Vertigo
Feb 18, 2014, 02:17:57 AM
Reply #920 on: Feb 18, 2014, 02:17:57 AM
Q
Well, the Carboniferous saw a profusion of giant insects (probably due to increased oxygen levels, we had a little discussion about this earlier), so it's a good place to start.

The go-to giant creepy prehistoric bugs are Meganeura and Arthropleura. Meganeura's a gargantuan carnivorous dragonfly, with a wingspan over 60cm. Arthropleura is rather nightmarish - a proto-centipede which could rear up to look you in the eye. Thankfully, it didn't appear to have jaws capable of large-scale predation.





Extending the term 'bug' out to cover all arthropods, the most iconic has to be the trilobite. Not particularly big, not doing anything particularly bodacious, but extraordinarily ancient, long-lasting and generally cool-looking.
They're some of the first complex animals to evolve, 521 million years ago, and immediately dominated their environments throughout the Cambrian and Ordivician. They weathered a number of mass extinctions, gradually whittled away a bit further each time, and it took the apocalyptic Permian extinction of 250 million years ago to finally wipe them out (the worst extinction event in history, obliterating most life on the planet). In total, they were around for 270 million years - longer than mammals, archosaurs or any land-based vertebrate order alive today.




There's a slightly more comprehensive list of creepy old bugs here.


Sabby
Feb 18, 2014, 03:14:52 AM
Reply #921 on: Feb 18, 2014, 03:14:52 AM
Q
I'm curious as to why there are no spiders on that list :/


DoomRulz
Feb 18, 2014, 03:44:48 AM
Reply #922 on: Feb 18, 2014, 03:44:48 AM
Q
Then where would they fit in, in the minds of those researchers? Super-Coelurosauria? :P
...
More basal than a tyrannosaurid to me sounds like it would be proceratosaurid.

Well, you asked. It will get geeky.
The argument is whether or not Proceratosaurus and its closest relatives form a divergent group within Tyrannosauroidea, sistered to other discovered tyrannosauroids, or if they're ancestral to these later members of the group (including tyrannosaurids), which would lump them in with the rest of the superfamily.
Important to note, there are at least six genera which aren't members of either subdivision, including Dryptosaurus and Appalachiosaurus which were the dominant predators in eastern North America near the end of the dinosaur era, contemporaneously with tyrannosaurids in the west (kept apart by the Western Interior Seaway).

Wouldn't a relation to the superfamily or being ancestral be dependent on whether they show traits shared amongst tyrannosaurids, i.e. shortened snouts, stronger jaw muscles, smaller front limbs, etc...?

I'm curious as to why there are no spiders on that list :/

Spiders aren't insects.


Omegamorph
Feb 18, 2014, 01:19:22 PM
Reply #923 on: Feb 18, 2014, 01:19:22 PM
Q
And the list has Chilopoda and Eurypterida... both Arthropoda but not Insecta. Should have had a different title.


Vertigo
Feb 18, 2014, 03:15:05 PM
Reply #924 on: Feb 18, 2014, 03:15:05 PM
Q
Then where would they fit in, in the minds of those researchers? Super-Coelurosauria? :P
...
More basal than a tyrannosaurid to me sounds like it would be proceratosaurid.

Well, you asked. It will get geeky.
The argument is whether or not Proceratosaurus and its closest relatives form a divergent group within Tyrannosauroidea, sistered to other discovered tyrannosauroids, or if they're ancestral to these later members of the group (including tyrannosaurids), which would lump them in with the rest of the superfamily.
Important to note, there are at least six genera which aren't members of either subdivision, including Dryptosaurus and Appalachiosaurus which were the dominant predators in eastern North America near the end of the dinosaur era, contemporaneously with tyrannosaurids in the west (kept apart by the Western Interior Seaway).

Wouldn't a relation to the superfamily or being ancestral be dependent on whether they show traits shared amongst tyrannosaurids, i.e. shortened snouts, stronger jaw muscles, smaller front limbs, etc...?

They're within the superfamily either way. Proceratosaurus has been shuffled around numerous groups over the years (as its name suggests), but today the majority consensus is that it and the other proceratosaurids are tyrannosauroids.

The difficulty in determining whether proceratosaurids were directly ancestral to tyrannosaurids, is the fragmentary nature of the record. The only reasonably well-known Jurassic tyrannosauroids are proceratosaurids, but they show quite a few highly individual traits - most obviously, head crests.


:edit: I've had a nagging feeling all day that I know at least one researcher who doesn't consider Proceratosaurus itself a tyrannosauroid, and I've just realised it's Gregory Paul, who thinks it's closer-related to Ornitholestes. With Tyrannosauroidea lurking so close to the base of Coelurosauria, the distinction at the top can be very blurry. With that said, Paul's classification for Proceratosaurus (and Ornitholestes) is in "maniraptoran miscellanea". ¬_¬
Doesn't help that Proceratosaurus is known only from a skull, and even then, one missing its top.

So there we have it, a third option. Proceratosauridae not being a valid group because of Proceratosaurus not being a proceratosaurid.


DoomRulz
Feb 18, 2014, 04:06:16 PM
Reply #925 on: Feb 18, 2014, 04:06:16 PM
Q
I would take that with a grain of salt until someone like Holtz or Currie come out and say it. Paul isn't a certified palaeontologist.

The idea of proceratosauridae not being directly related to tyrannosauroid but rather an offshoot of coelurosauria makes sense on one level I think because from a skeletal structure, share more in common with them than say Guanlong with tyrannosaurid.



DoomRulz
Mar 07, 2014, 06:54:04 PM
Reply #927 on: Mar 07, 2014, 06:54:04 PM
Q
And here comes the cloning talk...


Greedo
Mar 07, 2014, 06:58:51 PM
Reply #928 on: Mar 07, 2014, 06:58:51 PM
Q
Loads of people are now saying its a hoax...

I dont know what to make of this tbh, they proberly saying it because they dont want to believe and if its real they will be scared, thats how it goes...



Vertigo
Mar 07, 2014, 10:30:32 PM
Reply #929 on: Mar 07, 2014, 10:30:32 PM
Q
In related news, the heating in my house failed at the same time as the Berlin museum. The ensuing cold made my genitals shrink by so many orders of magnitude that they could only be described as a set of subatomic particles. Being subject to quantum physics in this state, they now allow me to travel through time, at will. Using my time travelling schlong, I travelled back to the time when some arsehole thought up that story, and have returned to my present quantum state to inform you that the story is bullshit.


 

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