Thread: Dinosaurs

Good day everyone!

I feel that there are simply not enough threads on one of the most entertaining subjects in biology. Dinosaurs! To counteract this disappointingly dinosaur-less trend, we're going to have a discussion about dinosaurs. No need to adhere to any sort of subsubject of dinosaurs if you want, just state an interesting fact you know of, a question you may have, discuss the evolution of birds, or just tell us about your favourite dinosaur!

So, in order to get a discussion going, I propose that some theropods were warm blooded, perhaps all of them. The reason lying with the evolution of feathers. Many smaller theropods have been shown to have a coat of down feathers, velociraptor to name one. These downy feathers would have functioned as a layer of insulation for those chillier days, and possibly may have had a function in mating, since the plumage of feathers so often is an indicator of health and good genes to members of the opposite sex in modern birds.

What do you think?

I haven't reviewed the literature on this for ten years or more, but I understand the consensus is pretty much that many dinosaurs were warm blooded. This is based upon the feather evidence, microstructures of bones and estimations of probable metabolism and energy expenditure.

I think it makes sense and the picture of the lumbering, inept, slothful beast is best consigned to the junk pile of misinterpretation. Increasingly I think of birds as dinosaurs, to the extent that when I wake up in the morning I think to myself, "the dinosaurs are noisy this morning" rather than "the birds are noisy this morning".

Here is an interesting abstract:

Fricke,H.C. Rogers,R.R. "Multiple taxon–multiple locality approach to providing oxygen isotope evidence for warm-blooded theropod dinosaurs." Geology, 28, 2000.

Oxygen isotope ratios of fossil remains of coexisting taxa from several different localities can be used to help investigate dinosaur thermoregulation. Focusing on the Late Cretaceous, oxygen isotope ratios of crocodile tooth enamel from four separate localities exhibit less of a decrease with latitude than do ratios of tooth enamel from coexisting theropod dinosaurs. A shallower latitudinal gradient for crocodiles is consistent with how oxygen isotope ratios should vary for heterothermic animals having body temperatures coupled with their environments (“cold blooded”), while a steeper gradient for theropods is consistent with how these ratios should vary for homeothermic animals having constant body temperatures independent of their environments (“warm blooded”). This inferred homoethermy in theropods is likely due to higher rates of metabolic heat production relative to crocodiles and is not an artifact of body size.



In the book "In Search of the Causes of Evolution: From Field Observations to Mechanisms", the authors observe that 'At last count there are almost 700 valid generic names of dinosaurs, almost half of which have been created since 1993..." The huge diversity of dinosaur types, locally, globally and temporally, is not adequatley appreciated by most people.

I also think of birds as dinosaurs. I think it's just a really beautiful evolutionary lineage. If you take a second to really look at birds, you can definitely see the similar morphology and habits.

Ophiolite, I like your "the dinosaurs are noisy this morning." Personally I sometimes refer to (small) birds as 'little flying dinosaurs.' Given a typical (though inaccurate) man-eating, Jurassic Park-type view of dinosaurs, it's kind of scary when put that way, and amusing.

Much of the Age of Dinoasaurs was also a period of global warming, with temperatures more than 5C higher than present day. CO2 levels were high, and oxygen was higher than present. Dinosaurs lived in what is now Antarctica.

It has been suggested that these factors helped dinosaurs reach the massive sizes that many achieved.

I didn't know about the feathers being downy - that's interesting!

But couldn't this insulation benefit a cold-blooded dinosaur also? Perhaps I'm naive to think a warm-blooded animal would need the insulation less.

***

How about these downy feathers begin around the hind legs and crotch, so our reptile can set on (her) eggs like a mother hen? Naturally the (sexual characteristic feathers) could evolve wildly through sexual selection, and thereby blunder into some unexpected utility (wings). Can anyone imagine early archaeopteryx showing off its plumage one day and accidentally falling from a tree?

Describing birds as dinosaurs has always seemed a bit weird to me - even though I understand the cladistic reasons behind it. It's a little bit like describing humans as a clade of lobe-finned fish - technically true but not very helpful.

Originally Posted by skeptic

Dinosaurs lived in what is now Antarctica.

Definitely. Yet, we must consider that Antarctica was once a lot more northerly until after it broke off from India and Australia. If only we could get some paleontologists to do a dig in Antarctica, they would no doubt find many new species.

Originally Posted by Zwirko

Describing birds as dinosaurs has always seemed a bit weird to me - even though I understand the cladistic reasons behind it. It's a little bit like describing humans as a clade of lobe-finned fish - technically true but not very helpful.

It seems a bit weird when you think of a bird as a dinosaur at first, but after you take a look at the phylogeny, it fits perfectly, and it then becomes awkward to not think of them as dinosaurs.

I think I disagree with your lobe-finned fish analogy. While we can be categorized in a clade with lobe-finned fish as the most distant common ancestor, we cannot be categorized as a clade of lobe-finned fish. An interesting thought though, it took me a while to figure out what it was that I disagreed with.

Originally Posted by Pong

I didn't know about the feathers being downy - that's interesting!

But couldn't this insulation benefit a cold-blooded dinosaur also? Perhaps I'm naive to think a warm-blooded animal would need the insulation less.

***

How about these downy feathers begin around the hind legs and crotch, so our reptile can set on (her) eggs like a mother hen? Naturally the (sexual characteristic feathers) could evolve wildly through sexual selection, and thereby blunder into some unexpected utility (wings). Can anyone imagine early archaeopteryx showing off its plumage one day and accidentally falling from a tree?

A warm blooded animal must maintain a certain core temperature; if it drops a little too low or goes a little too high, the animal will die. Even we have a surprisingly narrow range of temperature tolerance. If our core temp drops by even 4 degrees (I think 4, perhaps more/less), we die. Cold blooded animals actually have a wide range of tolerance. They have an optimal body temp, but they can still function and live at temps much lower. Insulation works to keep warmth in, rather than cold out (since it would also work to keep warmth from the sun out - bad for cold blooded animals), and as such a cold blooded animal would find no real use for it.

One of the possible evolutionary reasons for the advent of veined (wing) feathers would relate to hunting practices. It is possible that in a small, feathered dinosaur, veined feathers along the underside of the arm could have aided in hunting by acting as a net to kind of guide its prey in a straight line. The long outstretched arms of a dinosaur bearing long veined feathers would be able to keep a prey item from darting to either side (when in close proximity, of course). And so, the evolution of flight feathers was set in motion!

On an interesting note relating to Archeopteryx plumage...
http://www.bbc.co.uk/nature/13965976

Insulation would slow the rate at which an exothermic animal would heat up.
I am under the impression that it is fairly easy to evolve an endothermic metabolism, and plenty of animals (even mammals) are only "moderately warm blooded". To clarify, I mean that animals tend to exist on a spectrum of "cold" and "warm bloodedness", and that with changing pressures I think an animal's position could quickly shift along this spectrum.

I think that if it is important enough for the the animal to begin trying to really control its temperature that it would already be on the path to endothermy before insulation begins to evolve.

Here is an article that finds strong evidence suggesting that even the massive sauropods-the dinosaurs I have most often herd suggested that were cold blooded-in fact maintained their body temperatures at around 96-100 F (as opposed to the ~115 F temperatures they'd naturally have due to their massive body sizes).

Originally Posted by Beard Baron

A warm blooded animal must maintain a certain core temperature; if it drops a little too low or goes a little too high, the animal will die. Even we have a surprisingly narrow range of temperature tolerance. If our core temp drops by even 4 degrees (I think 4, perhaps more/less), we die. Cold blooded animals actually have a wide range of tolerance. They have an optimal body temp, but they can still function and live at temps much lower. Insulation works to keep warmth in, rather than cold out (since it would also work to keep warmth from the sun out - bad for cold blooded animals), and as such a cold blooded animal would find no real use for it.

Actually, cold blooded animals can and do generate body warmth internally. This is especially true for cold blooded animals that move fast, expending a lot of energy. If a marlin or a great white shark are caught on a line, and then gutted, the internal organs will be felt to be quite hot. Those animals generate their own internal heat.

it is quite feasible that a dinosaur might generate internal heat, and need this warmth for its functioning, while still being technically cold blooded. For such a cold blooded animal, downy feathers for insulation might be a very important adaptation.

Certainly the dinosaur egg requires a tighter range of temperature than the adult. This is why I suggest the feathers - if downy - likely originated as "setting" feathers.

Such feathers have great potential to adapt further, because they would become objects of mate selection, so easily outgrow their utility. Sexual markings often develop in spite of utility. In this way a dinosaur could adapt showy, ungainly plumage - wings! - that just happen to realize the real utility of flight.

question,
Is there an ideal temperature for cold blooded animals across the board, or does differing species require different heating temps?

over.

As a very, very broad generalisation, the ideal temperature is close to that of human body temperature - 37C. However, it does vary a lot since different species evolve different enzyme systems, and the enzymes all have different optimal temperatures. There are even Antarctic fish that die if their body temperature rises above 0 C.

The stegosaurus had something that resembled a brain near it's ass. Literally a brain in the ass. It's own brain (the one in the HEAD) was connected to the one in the ass by the spinal cord.

Evolutionary effects it could of had was faster sensory output - like a reflex. This tells me the dinosaur was too damn big for it's own good, so it needed another brain at the other end to have better motor skills.

Originally Posted by chma2

The stegosaurus had something that resembled a brain near it's ass. Literally a brain in the ass. It's own brain (the one in the HEAD) was connected to the one in the ass by the spinal cord.

Evolutionary effects it could of had was faster sensory output - like a reflex. This tells me the dinosaur was too damn big for it's own good, so it needed another brain at the other end to have better motor skills.

Actually the walnut size ass brain has been challenged for a number of years now. The enlarged area is argued to have been similar to that of the glycogen bodies found in modern bird genera.

Originally Posted by chma2

The stegosaurus had something that resembled a brain near it's ass. Literally a brain in the ass. It's own brain (the one in the HEAD) was connected to the one in the ass by the spinal cord.

Evolutionary effects it could of had was faster sensory output - like a reflex. This tells me the dinosaur was too damn big for it's own good, so it needed another brain at the other end to have better motor skills.

Stegosaurus would have been a hilarious animal. Its head:body ratio would have been similar to our fist:body ratio. With those short front legs, if it were to attempt running, it would have tripped over its own head!

Come to think of it, Spike, the stegosaurus from The Land Before Time was kind of the idiot of the group, wasn't he? Hilarity!