Tyranosaurus and chickens--missing link

[Martin]

early Cretaceous, ancestor of T. Rex, with fossil feathers

 

http://pharyngula.org/index/weblog/comments/why_it_looks_like_a_big_chicken/

 

theory is that in the process of getting larger Tyrannosaurids lost their

feathers because they didnt need so much insulation(being bigger)

anyway at one point the really had them

[john5746]

Hmmm...

 

Makes me wonder, will global warming bring about another dinosaur age?

[Sorcerer]

Perhaps in flightless birds, if the theory is correct. However, wouldn't you expect smaller dinosaurs from the time to have feathers if this was the case? I think there are plenty of smaller dinosaur (impression) fossils that dont have feathers. The fossilised archaeopteryx (sp?) did though.

[LucidDreamer]

So what's the consensus on this one Martin? Are feathers a common morphological feature that has arisen more than once or was feathers a feature from an early ancestor to both birds and this tyrannosaurid? Of course those fossil imprints look a little like compressed conifer leaves to me.

[Mokele]

However, wouldn't you expect smaller dinosaurs from the time to have feathers if this was the case? I think there are plenty of smaller dinosaur (impression) fossils that dont have feathers. The fossilised archaeopteryx (sp?) did though.

 

The fossil Archaeopteryx..es (whatever the plural of that is; Archaeopteryi?) were preserved in an excedingly fine-grained sand which was capable of holding such detail. In fact, the fossils were found in a quarry being mined for the sandstone for just that purpose: the sandstone was so fine that it could be etched in detail to make very fine quality printing plates. This type of sandstone is called "lithographic sandstone" and if you ever see really, really old biology pics called "lithographs", it's because this stone was used to make them. In fact, the species name of Archaeopteryx is "lithographica".

 

Iirc, this same type of sandstone also preserves pterosaur fossils with wing membranes and ichthyosaurs with body outlines, and the Chinese fossil beds that have proven so rich have similarly fine-grained sandstone. So the lack of feathers on some dino fossils doesn't necessarily mean they weren't there, only that the situation of their preservation may have precluded preservation of such details.

 

Mokele

[Sorcerer]

yes, but arent there small dinosaurs found in these beds with no feathers??

 

I actually think they look like proto-feathers though, makes sense, but then it begs the question, at what time did scales evolve into plumage, if it wasn't for streamlined flight, what was it for?

 

Could you link me to a phylogenic tree for dinosaurs.... so I can see which branches the feathered specimen is under. I know there are two types of dinosaur, based on their hips, are the larger slower (whatever, long time since I did geo) hipped dinosaurs feathered too? Are their ancestors?

[Mokele]

yes, but arent there small dinosaurs found in these beds with no feathers??

 

Um, maybe? I don't know the exact composition of the beds and what's been found in them. However, that doesn't prove anything general; perhaps the featherless ones are a sister taxon to the taxon that evolved feathers, much like how some lizards have lost their legs (including one group that became snakes), but both legged and legless lizards (and snakes) still exist and co-exist.

 

but then it begs the question, at what time did scales evolve into plumage, if it wasn't for streamlined flight, what was it for?

 

There's no real consensus on the first part of what you asked, but for the second, there's many possibilities, like insulation, better camoflage (they could grow one color protofeathers one season, then shed them and grow in another for another season as the optimum camoflage patterns change), or display.

 

Could you link me to a phylogenic tree for dinosaurs.... so I can see which branches the feathered specimen is under.

 

Well, the phylogeny is continually under dispute, but here's a pretty inclusive one, though it may not be up to the moment accurate:

 

Dinosaur cladogram

 

Oh, and the art on that site is pretty kick @$$ too, FYI...

 

I know there are two types of dinosaur, based on their hips, are the larger slower (whatever, long time since I did geo) hipped dinosaurs feathered too? Are their ancestors?

 

Yes, the saurischians (theropods and sauropods) and the ornithischians (everything else). Both had small, fast bipedal animals in their lineage, but the only feathers found have so far been on theropods. Of course, absences may just be because of preservation imperfections.

 

However, if I recall correctly, we have some skin impressions from a few hadrosaurs, sauropods and even a large theropod that show a rough, pebbled, sorta-scaley hide. Think of the pebbled-looking skin you see on the front legs of tortoises, and you're in the ballpark. So it seems as if feathers might have been confined to small theropods, but the record is too spotty to be sure.

 

Mokele

[Sorcerer]

And bird evolved from theropods?? From the names I wouldve thought they evolved from ornithischians...... or does this just mean bird like?

 

EDIT:

nm found it...... they do come from theropods and ornithischians means bird necked. A little confused though, I only ever learnt Kingdom Phylum Class Order Family Genus Species..... there seems to be several extra here and it doesn't even have the genus and species, what are the others??

 

Animalia

Vertebrata

Tetrapoda

Sauropsida

Archosauromorpha

Ornithodira

Dinosauria

Theropoda

Tetanurae

Coelurosauria

Avialae

 

from

http://dinosauricon.com/genera/archaeopteryx.html

[Auburngirl05]

EDIT:

nm found it...... they do come from theropods and ornithischians means bird necked. from

http://dinosauricon.com/genera/archaeopteryx.html

"Ornithischian" means bird-hipped, the shape of the pelvis and arrangement of the pubic bone/ilium/ischium are "bird-style", as opposed to theropods, it's a case of convergent evolution, kind of ironic that birds ended up stemming from the theropod line, which had drastically different hip structure to start out with.

[Mokele]

A little confused though, I only ever learnt Kingdom Phylum Class Order Family Genus Species..... there seems to be several extra here and it doesn't even have the genus and species, what are the others??

 

Well, all the others we added as "in betweens" for the sake of making talking about animal groups more preciese. Some, like "tetrapoda" are part of the new emphasis on cladistic classification (which, as I understand it, is a bit of a controversy).

 

 

And yeah, I've always found it ironic the the "bird hips" never became birds, but the "lizard hips" did. Heh.

 

Mokele

[Martin]

So what's the consensus on this one Martin? Are feathers a common morphological feature that has arisen more than once or was feathers a feature from an early ancestor to both birds and this tyrannosaurid? Of course those fossil imprints look a little like compressed conifer leaves to me.

 

LucidDreamer, sorry for not replying! I only just now noticed you had asked me a question----lost track of this thread for a while. I dont know!!!

I really dont know what the consensus among the experts is, or whether there even is a consensus!

 

this board has a great collection of people savy about bio

Skye, Mokele, Sorcerer, a lady from Yorktown Virginia, and many others but I cant remember all the names. I will leave the guessing to them.

 

 

If i had to guess I would guess that feathers are insulation that evolved just once in dinosaurs

 

and I would guess that a certain bunch of little insect-eating dinosaurs discovered that if they evolved their feathers to be longer and broader and flatter----on their forelegs especially---that it would help them in jumping and gliding

 

I would guess that they got food by jumping up into the air, or from one tree branch to another, and that aerodynamics first served to STABILIZE AND GUIDE their jumps. so that would provide an evolutionary pressure to improve the design of feathers. then once feathers were really good aerodynamically they could move in the direction of actually flying

 

and then they were birds

 

 

however this scenario is not based on knowledge and does not represent any consensus that I know of. thanks for asking tho. it is a challenging question how feathers and flight could co-evolve.

[Sorcerer]

"Ornithischian" means bird-hipped, the shape of the pelvis and arrangement of the pubic bone/ilium/ischium are "bird-style", as opposed to theropods, it's a case of convergent evolution, kind of ironic that birds ended up stemming from the theropod line, which had drastically different hip structure to start out with.

 

Oops I meant ornithodira:

Ornithodira Gauthier, 1986 "bird necks" == {Neornithes + Pterodactylus + Lagosuchus + Herrerasaurus + Triceratops + Saltasaurus}

 

Its a problem that happens when you speed read.....for instance two words beggining with a capital N and then Z will read as New Zealand to me.... and they can be paragraphs ahead.... I don't even know why I do it, I was never taught it or anything.

[LucidDreamer]

If i had to guess I would guess that feathers are insulation that evolved just once in dinosaurs

 

and I would guess that a certain bunch of little insect-eating dinosaurs discovered that if they evolved their feathers to be longer and broader and flatter----on their forelegs especially---that it would help them in jumping and gliding

 

I would guess that they got food by jumping up into the air' date=' or from one tree branch to another, and that aerodynamics first served to STABILIZE AND GUIDE their jumps. so that would provide an evolutionary pressure to improve the design of feathers. then once feathers were really good aerodynamically they could move in the direction of actually flying

 

and then they were birds

 

 

however this scenario is not based on knowledge and does not represent any consensus that I know of. thanks for asking tho. it is a challenging question how feathers and flight could co-evolve.[/quote']

I would agree with your hypothesis on the path to flight for the birds. I think that is probably the path that all flying creatures took. Though I suppose that they didn't necessarily have to be carnivores. I guess one of the most interesting questions is whether feathers evolved before these creatures started gliding or afterwards.

[Mokele]

I think that is probably the path that all flying creatures took.

 

Actually, not necessarily. In insects, it's thought that wings first evolved as thermoregulatory organs, and then became aerodynamicly efficient for drifting on the breeze (I'm not really sure if that counts cas "gliding" because it doesn't involve laminar flow and the usual concept of lift, but rather relies on turbulence and boundary layer effects and vorticies).

 

I guess one of the most interesting questions is whether feathers evolved before these creatures started gliding or afterwards.

 

Well, the phylogeny that seems most reasonable to me says a bit of both: there were proto-feathers long before flight, and around about gliding simple feathers came about, then advanced feathers (like modern ones) later. Of course, a lot of it is hypothetical, and there's still the issue of which preceded which.

 

Mokele

[LucidDreamer]

opps, I forgot about insects, but I think they pretty much followed the same path though. Instead of gliding from tree to tree they glided from plant to plant. Its interesting that both feathers and insect wings are thought to have evolved from thermoregulation devices. Is there some subtle significance to that?

 

Mokele, have we found other fossils of proto-feathers besides just this tyrannosaurid? If we have and we can confirm their that they are indeed proto-feathers than I imagine proto-feathers probably evolved before any kind of gliding and then they were adapted after gliding began.

[Ophiolite]

opps, I forgot about insects, but I think they pretty much followed the same path though. Instead of gliding from tree to tree they glided from plant to plant. Its interesting that both feathers and insect wings are thought to have evolved from thermoregulation devices. Is there some subtle significance to that?

On the other hand that's not true for bats (is it? You could lose a lot of heat through those mebraneous wings, but if you were that small why would you want to?), or the gliding mammals.

 

Mokele, have we found other fossils of proto-feathers besides just this tyrannosaurid? If we have and we can confirm their that they are indeed proto-feathers than I imagine proto-feathers probably evolved before any kind of gliding and then they were adapted after gliding began.

I thinks its the only one so far:

http://www.nurseminerva.co.uk/adapt/feathers.htm

[coquina]

What about the concept that feathered flight was a favorable adaptation which enabled the creatures that had it to escape predation more effectively?

 

Doesn't it follow that as small fast preditors evolved, those creatures that could hop from a low tree limb to a higher one out of reach of the nasty little ba$tards would survive to reproduce more often? Having gotten up in a tree, the ones that were able to glide the fartherest from the pack baying at the trunk of the tree in frustration would again be the most likely to escape.

 

and I would guess that a certain bunch of little insect-eating dinosaurs discovered that if they evolved their feathers to be longer and broader and flatter----on their forelegs especially---that it would help them in jumping and gliding

 

Martin - I'd like to gently chide you on the above statement. It implies that the dinosaurs chose to evolve feathers fit for flight. My college bio prof would have rapped my knuckles if I'd made a statement like that.

It would be more proper to state that the beasts who randomly evolved the better shaped feathers caught more insects and survived to reproduce more often. (I expect you know better - I hear the folks on educational TV making the same sort of statements. It's just that evolution is misunderstood by so many, I think we need to try to write as accurately as we can about it.)

[LucidDreamer]

What about the concept that feathered flight was a favorable adaptation which enabled the creatures that had it to escape predation more effectively?

A slight twist on the subject that's just as plausable' date=' but it all boils down to the same thing. Gliding creatures evolved from leaping creatures, and flying creatures evolved from gliding creatures.

 

 

Martin - I'd like to gently chide you on the above statement..

Ya, I talk about evolution that way too sometimes. I forget that there are people out there who are not familiar with evolutionary theory.

[AzurePhoenix]

Another basic theory is that afte evolving for whatever purpose (i personally fly with the thermo-regulation jazz) feathers attained even more prominant use stemming from their purposes for display... i think its obvious that dinos were very visual creatures (look at the crests on ceratopsians, horns on therapods and pachycephalosaurs, and the varying patterns of plates employed by stegosaur, or the crests evolved by hadrosaurs.)

 

Such visual devices, though perfectly capable of serving those groups purposes, were biologically expensive to grow and develop, whereas feathers can be embellished and unique-ified just as well, for a fraction of the cost. This need for a unique visual identifier may hve helped to develop the structures needed to get past fluffy down (just speculation, on my part) and towards asymetrical flight feathers

 

In addition, coelusaurs were the most bird-like of the saurischians, and probaby gave rise to birds. What many paleontoligist have determined is that the flapping motions performed by fying birds are almost identicle to the "mantis-strike" grasping movement supposedly employed by such smal coelurasaurs as troodontids and dromaeosaurs.

 

It'd be easy to imagine small arboreal dinos leaping through the jungle canopy and reaching a point where natural selection leads to combination of these two separately evolved features, and bippity-boppity-boo, gliding... a few thousand years and natural selection favors better flappers, and in no time - Yay!!! Birdies!!!

[AzurePhoenix]

just remembered, anyone see or read about the recently varified Microraptor gui fossils? All four limbs feathered for advanced gliding (possibly powered flight) plus a specially feathered tail... Sweet Stuff!!