Examples of Pre-Mammal Parallel Evolution?

[Kitsune]

The Tasmanian or Marsupial Wolf resembles the Placental Wolf
I am wondering if there are any good examples of this "Pre-Mammal"
ie: Is this a common theme?

[Alyrium Denryle]

The Tasmanian or Marsupial Wolf resembles the Placental Wolf
I am wondering if there are any good examples of this "Pre-Mammal"
ie: Is this a common theme?

Yes. It is called Convergent Evolution, where two unrelated organisms look similar because they share the same, or a similar niche. It happens all the time, and even confused the hell out of systematists and taxonomists until we gained the ability to discern relationships between organisms with molecular techniques.

[Anguirus]

Abso-fraggin'-lutely. Hell, just think about all the worm-shaped animals in the world. Some are flatworms, some are nematodes, some are annelids, some are arthropod larvae, some are cephalochordates (within spitting distance of vertebrates). It's just a damn useful, efficient shape.

Of course, the classic example of convergent evolution is the eye. It's thought to have evolved independently something like 20-30 times, and simple physics dictates that they all look relatively similar despite being such a complex structure. An octopus' eye looks a hell of a lot like a vertebrate eye, doesn't it? Well, they evolved completely independently, and you wouldn't find any anatomical difference until you dissected it and found that the "wiring" of nerves and blood vessels is different.

[Aranfan]

The Tasmanian or Marsupial Wolf resembles the Placental Wolf
I am wondering if there are any good examples of this "Pre-Mammal"
ie: Is this a common theme?

Yes. It is called Convergent Evolution, where two unrelated organisms look similar because they share the same, or a similar niche. It happens all the time, and even confused the hell out of systematists and taxonomists until we gained the ability to discern relationships between organisms with molecular techniques.

Didn't the Eye evolve on its own in like 25 or so different places? Must be a damn useful organ the eye.

[Executor32]

Another good example would be the similarities in form between fish, cetaceans, and ichthyosaurs.

[Junghalli]

Abso-fraggin'-lutely. Hell, just think about all the worm-shaped animals in the world. Some are flatworms, some are nematodes, some are annelids, some are arthropod larvae, some are cephalochordates (within spitting distance of vertebrates). It's just a damn useful, efficient shape.

Don't forget snakes, which also have the same basic shape and means of locomotion. Spitting distance of vertebrates, snakes are vertebrates.

An octopus' eye looks a hell of a lot like a vertebrate eye, doesn't it? Well, they evolved completely independently, and you wouldn't find any anatomical difference until you dissected it and found that the "wiring" of nerves and blood vessels is different.

Interestingly I've heard the cephalopod eye is actually rather better designed than the vertebrate eye, lacking the blind spot we have in the center of our vision.

[Kitsune]

Are there any good primate analogs?

[Modax]

Okay, so say that Carbon-based life evolved on an alien planet, basically similar to Earth in environment, chemical make-up, etc.
Would you expect convergent evolution to produce types of animals that look vaguely familiar to us? This is a tricky question, I know, because the diversity of life of earth means 'familiar' is pretty meaningless. Just look at the kinds of creatures they find at the bottom of the sea, or cambrian fossils for that matter. But this is an issue that pretty much all of SF has to tackle. How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

[Kitsune]

Okay, so say that Carbon-based life evolved on an alien planet, basically similar to Earth in environment, chemical make-up, etc.
Would you expect convergent evolution to produce types of animals that look vaguely familiar to us? This is a tricky question, I know, because the diversity of life of earth means 'familiar' is pretty meaningless. Just look at the kinds of creatures they find at the bottom of the sea, or cambrian fossils for that matter. But this is an issue that pretty much all of SF has to tackle. How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

The other question is does a "Sentient' being even have to be humanoid?

[Junghalli]

Are there any good primate analogs?

I can't really think of any myself.

Okay, so say that Carbon-based life evolved on an alien planet, basically similar to Earth in environment, chemical make-up, etc.
Would you expect convergent evolution to produce types of animals that look vaguely familiar to us?

In the sense that I'd expect things like the wing, the leg, the tree trunk, and the leaf to reoccur on planet after planet because they're fairly straightforward and sensible ways of doing things, yes. But I wouldn't expect precise analogs to Earth mammals, birds etc. like you sometimes see in pop sci fi.

How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

The odds are probably decent as long as you assume a similar evolutionary history. A tetrapod with arboreal ancestors that moved down to the ground in the past.

[Lord of the Abyss]

Snakes, and limbless lizards like glass snakes and others come to mind. So do velociraptor-style dinosaurs and terror birds ( some species even had wings that evolved into clawed limbs ).

Okay, so say that Carbon-based life evolved on an alien planet, basically similar to Earth in environment, chemical make-up, etc.
Would you expect convergent evolution to produce types of animals that look vaguely familiar to us? This is a tricky question, I know, because the diversity of life of earth means 'familiar' is pretty meaningless. Just look at the kinds of creatures they find at the bottom of the sea, or cambrian fossils for that matter. But this is an issue that pretty much all of SF has to tackle. How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

"Vaguely humanoid" is kind of, well, vague, but if the creature in question comes from a four limbed ancestry, then bipedalism is a likely attribute of tool users. But as we see looking at Earth life, other limb numbers are quite viable; for that reason alone I'd expect even "vaguely humanoid" to be rare. Unless mantis-shaped qualifies.

[Elfdart]

Are there any good primate analogs?

Sloths and opossums have prehensile hands and feet and spend most of their time in trees. Squirrels and raccoons, too.

[Anguirus]

Interestingly I've heard the cephalopod eye is actually rather better designed than the vertebrate eye, lacking the blind spot we have in the center of our vision.

Absolutely. God is a squid.

"Vaguely humanoid" is kind of, well, vague, but if the creature in question comes from a four limbed ancestry, then bipedalism is a likely attribute of tool users. But as we see looking at Earth life, other limb numbers are quite viable; for that reason alone I'd expect even "vaguely humanoid" to be rare. Unless mantis-shaped qualifies.

There are a lot of very logical qualities that led to our explosive intellectual and evolutionary success. For instance, we (including certain apes) are about the only animals that can accurately project an object (i.e. throwing). This is the result of our binocular vision, shoulder and arm structure, prehensile fingers, reasonably sized brain, etc. We needed all that just to hit game with a rock...which gave us a reason to design better rocks that went farther, an action which our vision, coordination, etc. made physically possible...

The basic human form is terrific for manipulation, sensing, long-distance locomotion, climbing (more of an ape thing, we traded it for roaming ability). Hence, I can accept a certain amount of humanoid alienism in a setting before my SOD is seriously violated. Though it helps to also have non-humanoids. And no magic space clouds.

(An example of a feature "better" than standard human...having different breathing and speaking holes. A more logical back structure for a biped. Examples that might be "worse"...fewer fingers/less efficient manipulators, weaker legs, shorter lifespan, smaller brains due to harsher mechanical limitations. Heck, maybe some atrophying limbs that are mostly getting in the way.)

[defanatic]

How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

You might see similar structures, like an alien eye, legs, fins and what have you.
..

[GrandMasterTerwynn]

Okay, so say that Carbon-based life evolved on an alien planet, basically similar to Earth in environment, chemical make-up, etc.
Would you expect convergent evolution to produce types of animals that look vaguely familiar to us? This is a tricky question, I know, because the diversity of life of earth means 'familiar' is pretty meaningless. Just look at the kinds of creatures they find at the bottom of the sea, or cambrian fossils for that matter. But this is an issue that pretty much all of SF has to tackle. How likely do you think it is that a vaguely humanoid body plan has/will evolve on an alien world?

First, let's start with the components that are likely to share in common with us.

A) Eyes? Yep. The laws of physics tends to dictate that electromagnetic sensing devices can only have a certain form. The details will come down to how the eyes are implemented, but we'll be able to tell that they have them.

B) Ears? Yes, the same laws of physics apply to ears that apply to eyes.

C) Orifices? Presumably they will have some hole that serves as an intake for oxygen, water, and food (since they will need large quantities of all three to survive and maintain the sort of activity level that a large brain demands.) Orifices to expel waste or reproductive material with are nice, but not strictly necessary.

D) Appendages? Well, they'll need some to ambulate with, and some to manipulate with. The number and layout tend to be a happy accident of evolution, more than anything else.

So we'll be able to look at an alien, and we'll be able to guess what bits of the alien do what. But will it look humanoid? Let's examine this further:

Layout: Principal sensory organs will tend to be located close to wherever the alien keeps its brain. Again, this is the laws of physics talking . . . a signal traveling along a short nerve fiber will reach the brain faster than those traveling along a really long nerve fiber. So it will have a face. Where you put the face is related to where the brain evolved. This face will also tend to have a limited number of eyes and ears. Audiovisual processing is expensive, which is why everything on this planet that makes significant use of eyes only have two of them. (Box jellies have more than two, but they also have a distributed network of low-level neural processing, rather than a discrete brain.)

Number of appendages: The more appendages you add to an alien, the more neural tissue you have to devote to controlling them. Animals with lots of appendages on Earth tend to solve the problem by putting the neurological controls in the limbs themselves, reducing the brain's processing requirements. The octopus is a prime example of this. Their brains don't have fine motor control . . . most of that marvelous brain is devoted to processing input from those marvelous eyes. Their brain's involvement in motion seems to be to tell the arms what, in very general terms, ought to be done and let the ganglia in the arms do all the processing on how to go about doing it. So a sapient alien will probably have a relatively small number of limbs. That number, however, isn't guaranteed to be four. For example, discounting their wings, a bird has three limbs . . . two legs and a beak.

Bilateral symmetry: A happy accident of evolution here. It's likely not a requirement for a sapient creature. You could imagine an alien with quadrilateral symmetry, for instance. If you wanted to give it binocular, forward-facing vision, you could postulate that one or two of its quarters are the dominant ones.

So what are the odds that a humanoid body plan will turn up on an alien planet? Remote.

[Surlethe]

Are there any good primate analogs?

I don't know how much water this holds, but I've speculated that the similarities in human and bonobo sexuality is convergent evolution, since bonobos split from chimpanzees more recently than chimps diverged from humans.

Sloths and opossums have prehensile hands and feet and spend most of their time in trees. Squirrels and raccoons, too.

Nitpick: little wikipedia and some guesswork points to rodents diverging from early prosimians and their relatives while they were in trees, and thus probably had opposable thumbs on hands and feet.

[Kitsune]

Creatures like Flying Squirrels long before any of the flying or gliding Mammals of today and not directly related to them

http://news.bbc.co.uk/2/hi/science/nature/6176061.stm

It is an older article but still interesting.

[Aeolus]

Saber teeth is a common example of convergent evolution.

[hongi]

Interestingly I've heard the cephalopod eye is actually rather better designed than the vertebrate eye, lacking the blind spot we have in the center of our vision.

Our eye is wired back to front, which seems pretty inefficient to me. Photons have to pass left to right through the neuronal 'wiring' to meet the photoreceptors at the back, before the signal is sent back right to left. Octopodes don't have any such problem.

[Duckie]

One of the most striking aspects of convergent evolution to me is that New World and Old World vultures are completely unrelated animals.

The bald head, the scavenging, their circling behavior- it's all convergent evolution, because Old World Vultures are related to birds of prey (how worse of a rap than those they get for being uglier); while New World Vultures are of uncertain origin but possibly more related to Storks and Flamingoes (!).

[Darth Yoshi]

Really? I didn't know that New World vultures weren't birds of prey. You learn something new everyday.

[Modax]

Interestingly I've heard the cephalopod eye is actually rather better designed than the vertebrate eye, lacking the blind spot we have in the center of our vision.

Absolutely. God is a squid.

Close, but not quite...God is Cthulhu.

[Duckie]

Really? I didn't know that New World vultures weren't birds of prey. You learn something new everyday.

Technically, according to wikipedia (I know, but I'm not an orinthologist), Birds of Prey are defined via habits, not genetics, so New World Vultures are birds of prey- just ones genetically irrelated to actual eagles, falcons, and old world vultures.

Nobody really knows- I tried looking it up. Some people tried to class them into storks and herons and so forth, but genetic evidence is overturning the entire old taxonomy in every single study of animals*, so they're in a weird flux. They have their own family called Falconiformes, I believe, which is defined as 'It looks like a falcon'**, making it one of those weird families scientists put animals that they don't know where they go [witness Pongo, for 'apes that aren't humanish', before it was reorganized to be more scientific]

*Take a look at any field of animal study and you'll hear "This used to be classed as X, but genetic evidence now shows".
**This description of bird taxonomy is completely inaccurate and probably insulting to orinthologists, but it's the best I'm willing to do without having to look up and get into what exactly a falcon is.

[Ypoknons]

Are there any good primate analogs?

Gorillas have a very prominent sagittal crest. Chimpanzees and australopithecines do not posses these features, however, the it is present in Paranthropines to crack nuts. Now that's not exactly parallel since the reasons the crest is present differ, but its the closest thing I can think of.

[petesampras]

Interestingly I've heard the cephalopod eye is actually rather better designed than the vertebrate eye, lacking the blind spot we have in the center of our vision.

Absolutely. God is a squid.

More importantly a retina which is attached the right way round can be anchored more firmly to the back of the eye, so less vulnerable to blindness from detached retina. However, I have come across an argument in favour of inverted retinas being better able to re-absorb waste fragments from the tips of the retinal cells through the back of the eye. Not being a biologist, I have no idea as to the soundness of that argument.