On the Origin of Feces

[tyrannosaurus vex]

Disappointment Ahead: This is not actually about poop.

I believe Evolution is true. But... I have a question.

Say there's a dinosaur. And millions of years later, his descendants are birds. Okay, fair enough. I can understand why a species might evolve the ability of flight. But why start down that path if it takes millions of years to get there? What practical advantage is a dinosaur with a few sparse feathers? What advantage in natural selection does an animal have that, for example, has evolved feathers but not flight? Do its genes just say "well, that's okay, we're going for flight and we'll get there eventually, for now all we have are feathers..." ?

[Mesozoic Mister Nigel]

I think it's more a matter of "this tree-dwelling creature's fluffy protective covering that resembles scales has an interesting side-effect of slowing them down when they fall out of trees, if they spread their forelegs out. Oh look, that means that the ones with long forelegs and better fluff-scales are more likely to survive and breed. etc"

[Requia ☣]

Feathers are good for insulation.  Birds got feathers, mammals got fur, same purpose originally, but feathers turned out to be useful for the flying thing later on.

[Rumckle]

Feathers may also have been useful for attracting mates.

[Golden Applesauce]

Evolution is all step-wise - cumulative small changes that have beneficial or at least neutral effects.  AFAIK polymers don't have the ability to form long term plans.

A leading hypothesis concerning the development of feathers is that they provided insulation.  Feathers trap a layer of air near the skin of the animal, keeping it warmer.  (This is part of how oil spills fuck up birds - the oil penetrates into the zones where air would be and destroys that insulating property.)

After you get feathers, ideas are that wings and proto-wings helped animals that jump a lot.  For example, a predator that leaps onto its prey could "steer" a little if bit its forelimbs could provide small amounts of drag and/or lift where necessary.  For that, you really need a bipedal predator - cats jump, but their forelimbs are tied up in walking.  You need a creature that has powerful hind legs for leaping and for speed, low body weight, and arms that aren't particularly crucial for anything else: a raptor-like dinosaur.

Remember that insect flight had occurred long before feathered flight - so animals that hunt insects could greatly increase their food supply if they could catch flying insects.  Jumping is like artificial height here - if you can jump an extra foot you can reach higher flying insects as if you were a foot taller, but you don't have to feed a a larger body that actually is a foot taller.

More info:
http://en.wikipedia.org/wiki/Origin_of_avian_flight
(also look at the "Flying and gliding animals" and "Insect Flight" links.)

[Kai]

Disappointment Ahead: This is not actually about poop.

I believe Evolution is true. But... I have a question.

Say there's a dinosaur. And millions of years later, his descendants are birds. Okay, fair enough. I can understand why a species might evolve the ability of flight. But why start down that path if it takes millions of years to get there? What practical advantage is a dinosaur with a few sparse feathers? What advantage in natural selection does an animal have that, for example, has evolved feathers but not flight? Do its genes just say "well, that's okay, we're going for flight and we'll get there eventually, for now all we have are feathers..." ?

Okay, before addressing your question, I have a few points. Semantics, mostly, but in science it's important to be precise with words.

1. Better to say that you accept the theory of evolution, rather than believe. Accepting as an explanation means it's easier to change in the light of new evidence.

2. "Dinosaurs" is not a natural grouping of organisms. Its a common term, like daddy longlegs, which could talk about any number of things. Better to talk about Avemetatarsalis, or a particular group of Theropods from which the Class Aves branches.

3. Since we can't know descendent-ancestor relationships, and we can't test them, it is better not to use words like "descended from". It gets put to use in the popular parlance but it's scientifically untestable. Better to say that Class Aves is within the clade Avialae, which is the sister taxon to the Deinonychosauria, both of which are considered to be in the Clade Umaniraptora. Notice that while we can say all the Umaniraptora share a common ancestor, we can't say that a particular species in the fossil record is the ancestor.


Okay, to your question: Why do flightless Theropods have feathers?

Now, we can address this at two levels, the proximate and the ultimate level.

At the proximate level, this question means, what is the mechanism for feathers? What causes feathers to occur? What are feathers derived from? These sorts of things. Proximate questions (even if they are worded as why) really have to do with HOW, the direct mechanism. This might be developmental or physiological as well as plainly morphological.

At the ultimate level, this question means, why do they have feathers, what is the thing being selected upon, what are the evolutionary benefits of feathers. Ultimate questions address why at the level of survival of individuals and lineages to reproduce.

So, using strong inference, I'm going to lay it out for you. Strong inference is the best method for addressing scientific questions, in which one produces multiple hypotheses and designs one or more crucial experiments to eliminate all but one of those hypotheses. By parsimony, that will be the most likely answer.

So, at the proximate level I can lay out various hypotheses about how feathers develop, what tissues feathers develop from. If I watch, for example, the development of birds, I can see that the cells that grow into feathers are homologous to the cells that develop into scales in other Diapsids (ex. snakes, turtles, crocodilians). So, we can conduct observational experiments with various epidermal tissues to show that scales and feathers show a common embryological origin. So, at the proximate level, feather cells and scale cells are derived from the same tissue. Feathers might even be a modified scale, though I don't know off the top of my head any way of testing that.

So, why DO flightless Theropods have feathers? Obviously we can't just go find living specimens and conduct experiments upon them, so we have to settle for living and non living models.


I'll post part two of this tomorrow. With all of this, I'm trying to show you how this doesn't have to be a just so story, you can really answer these questions with satisfaction.

[Mesozoic Mister Nigel]

AWESOME, Kai! I'm looking forward to part two.

[Triple Zero]

AWESOME, Kai! I'm looking forward to part two.

This!

It's almost making up for the thread not really being about poop.

[LMNO]

But why start down that path if it takes millions of years to get there? What practical advantage is a dinosaur with a few sparse feathers? What advantage in natural selection does an animal have that, for example, has evolved feathers but not flight?

Because the LORD YOUR GOD wanted it to be that way.
    \

[Pterodactyl Handler]

Feathers are completely inferior to fleshy, wretched wings.

[LMNO]

[Kai]

In testing evolutionary hypothesis, all of them really come down to five reasons.

1. Predators/Parasites/Pathogens
2. Nutrition
3. Fecundity
4. Abiotic Factors
5. Competition

And when I say all I mean every trait with selection pressures, those pressures come down to one of the five above reasons. And so, ultimate level hypotheses always address at least one of those reasons.

So, here are my example hypotheses for "Why do flightless theropods have feathers".

1. Flightless theropods have feathers to thermoregulate body temperature and increase survival. (Abiotic factors)
2. Flightless theropods have feathers as a mating display which increases mating success (Fecundity).
3. Flightless theropods have feathers for territorial displays to reduce competition and increase survival (competition).
4. Flightless theropods have feathers as a protection against pathogens and parasites, increasing overall survival (predators/parasites/pathogens).

Of course, the problem we run into now is that the original flightless theropods have been extinct for millions of years now. We can use models to test abiotic factors such as thermoregulation (you can probably dream up an experiment gluing feathers to surfaces under different conditions etc), but for the others we really need a live model. There is a saying in biology, that for every question there is a perfect model to test that question upon (known as Krough's Law or Principle after August Krough).

How about....ostriches and their kin? They're large flightless birds, relatively easy to raise in captivity, and apparently they're running wild and escaped in the American Southwest. This seems to me to be the perfect living model to test the above hypotheses upon, at least initially.

The underlying issue for the reason for feathers comes down to adaptation and exaptation. Adaptation is a novel trait that comes about due to selection pressures. Exaptation, on the other hand, is when an adapted trait is later coopted for a new use, and receives further adaptation due to this use. The same issue of which came first is central to the origin of flight in insects as well as birds. Did wings/feathers/lobes originate to provide some sort of gliding support and then over time they were selected to become full wings, OR were feathers and wing lobes originally for some other purpose, and they later became exapted for flight?

Maybe there will be a part three later.

[Telarus]

I read an article saying that much of the recent fossil finds from the China desert show that a majority of the late "dinosaurs" were feathered and much of our past conception was flawed (look back @ any dino book for kids written pre 1970, you don't even get coloration changes, which were the big thing around when Jurassic Park was written).

[Kai]

I read an article saying that much of the recent fossil finds from the China desert show that a majority of the late "dinosaurs" were feathered and much of our past conception was flawed (look back @ any dino book for kids written pre 1970, you don't even get coloration changes, which were the big thing around when Jurassic Park was written).

Yeah, most of our knowledge of feathered theropods (specifically Umaniraptors) comes from fossil finds in China. And it's not like we're talking a single fossil here. There are tones of feathered Umaniraptor fossils.

[Kai]

I feel an In Those Days coming on.....