Why are there no two-legged predators?

[NothingNow]

I may be wrong, but didn't all dinosaurs evolve from bipedal or semi-bipedal archosaur ancestors, with reversion to a full quadrapedal stance in the large herbivores a secondary adaptation? However, this raises the question? Were there any predatory dinosaurs that were not bipeds? Why not? If quadrapedalism provided a better frame for predation because of balance, tripping, etc., why didn't some of the readadpted quadrapeds become predators in the Mesozoic?

IIRC Semi-bipedal, at least for Saurischians.
I think that the ability to use the hands for grasping and/or as weapons has a certain advantage for a predator, plus looking at the spines of Dinosaurs, the bipedal stance allows for higher speeds.

 

[eschaton]

Interestingly, there is evidence that Neanderthals consumed far more meat, as percentage of their total dietary intake, than homo sapiens did or does. While the almost certainly still took the opportunity to eat berries and roots, their diets were probably more similar to carnivores such as bears. So perhaps there were bipedal carnivores after all.

1. Remember, Neanderthals lived in very cold environments - not exactly the steppe tundra, but the boreal forest immediately to the south. Modern humans who lived in those climates didn't eat many plants either.

2. Actually, except for the polar bear, most bears get 90% of their diet from plant matter.

 

[eschaton]

I may be wrong, but didn't all dinosaurs evolve from bipedal or semi-bipedal archosaur ancestors, with reversion to a full quadrapedal stance in the large herbivores a secondary adaptation?

Yes, seems to have happened at least four times independently, with Sauropods, the common ancestor of Stegosaurs/Ankylosaurs, Ceratopsians, and Hadrosaurs.

Were there any predatory dinosaurs that were not bipeds?

No

Why not? If quadrapedalism provided a better frame for predation because of balance, tripping, etc., why didn't some of the readadpted quadrapeds become predators in the Mesozoic?

If you're asking why theropods didn't become quadrupeds, I already answered that - they couldn't turn their palms to face the ground.

If your asking why the "herbivorous" dinosaurs didn't evolve carnivory - well, some of them probably were somewhat omnivorous actually. But the strict hunter niches were already occupied by theropods, and barring mass extinctions, something like a total trophic switch from herbivory to carnivory is uncommon (the reverse is actually very common - there were probably four or five groups of at least partially herbivorous theropods).

Is it possible that bipedal theropods with forearms freed from locomotive needs and able to evolve into full-time grasping/slashing claws or wings outweigh the balance/tripping issues?

You shouldn't overvalue arms just because they're so central to us. I'm not aware of a single large carnivorous theropod which could even bring its hands to its mouth for example. Now, some taxa did have heavily muscled arms, like Allosaurus, and probably did use their arms to hold onto struggling prey while their head did the dirty work. But others, like Carnotaurus, basically lacked functional forearms entirely, and did just fine.

As for smaller species, for the most part they probably folded their long arms tightly when they ran, like birds, and you should remember that even larger "raptors" probably had feathers all the way down their fingers (a birds primary feathers actually *begin* at the wrist).

You're right insofar as once the arms were freed of locomotion, they could do any number of things, and were by default used to grasp. But this is just a classic example of a trait being re-adapted by natural selection. The grasping hand was an effect of being bipedal basically, not the cause.

 

[robertp6165]

Interestingly, there is evidence that Neanderthals consumed far more meat, as percentage of their total dietary intake, than homo sapiens did or does. While the almost certainly still took the opportunity to eat berries and roots, their diets were probably more similar to carnivores such as bears. So perhaps there were bipedal carnivores after all.

Benjamin

1. Remember, Neanderthals lived in very cold environments - not exactly the steppe tundra, but the boreal forest immediately to the south. Modern humans who lived in those climates didn't eat many plants either.

Actually, the evidence that the Neanderthal diet was more "meat heavy" than that of homo sapiens is pretty flimsy. These claims are based on isotope studies, which cannot detect plant-based components of an individual's diet...they can only distinguish between different types of proteins (i.e. tell you which type of meat the person is eating). Recent studies using other methods have found that Neanderthals made extensive use of plant resources whenever they had access to them, just like homo sapiens did in the same environments.

 

[Basileus Giorgios]

Back to the main "why not Mammalian biped predators" question, the answer is simply that unlike the theropod dinosaurs, which evolved from a small, partially bipedal ancestor than probably looked like a long legged crocodile, the mammal predators all evolved from a tree dwelling carnivore called Miacis, which was a quadruped. Since this time, 60 million years ago, there has been no evolutionary need to the carnivora to adopt bipedalism.

As an aside, does anyone else have the book "After Man" by Dougal Dixon? In it, it proposes bipedal predatory baboon descendants dominating Africa, large bipedal bats that walk on their arms in a Hawaii type island, and a new group of cats called the strigers than have evolved a very monkey like way of living in order to prey exclusively on primates.

 

[GodRaimundo]

KANGAROO: "Excuse me, but does anyone have some Grey Poupon?"

Sigged!

 

[Eigenwelt]

Bipedal locomotion takes far more processing power than quadripedal due to balance issues. Look up the difficulties with ASIMOV and you'll see what I mean. (Every dinosaur and reptile capable of bipedal locomotion has a tail to help with balance.)

For a mammalian predator to justify the extra resources needed to run a brain capable of bipedal locomotion you need those now free front limbs to seriously contribute to the caloric intake. All the existing apex predators (ursine, feline, canine) have no need to make that trade off because they're already at the top of their respective food chain. Their exisiting advantages of weight, strength, speed, etc. are enough to secure their survival and procreation.

Human beings aren't as big, or as strong, or as fast... they need an advantage and that advantage is tools. Tools manipulated by developed forelimbs with opposable thumbs.

The omnivore nature of humanity doesn't preclude it from being a predator, it's an integral part of how it is a predator. All large predators spend more time resting than we do. Hunt, eat, sleep. We don't have that ability. We have to make the tools which allow us to hunt. That takes time. We're slower which means it takes longer to cover the same hunting terrain. The ability to forage and consume other food sources to suppliment our hunting is what allows us to be hunters.

 

[The Kiat]

well humans are bipedal apex predators

Technically, we're opertunistic scavengers... but thing of it is, scavangers have to have much patience, and apes are not known for having it. Thus, we accelerate death.

 

[eschaton]

As an aside, does anyone else have the book "After Man" by Dougal Dixon? In it, it proposes bipedal predatory baboon descendants dominating Africa, large bipedal bats that walk on their arms in a Hawaii type island, and a new group of cats called the strigers than have evolved a very monkey like way of living in order to prey exclusively on primates.

It was fun when I was young, but now that I know a bit more about evolutionary biology, it's fairly ridiculous in parts. There are several groups of people online who've done better work than he did. Admittedly, it was heads above The Future Is Wild though.

 

[Valdemar II]

Technically, we're opertunistic scavengers... but thing of it is, scavangers have to have much patience, and apes are not known for having it. Thus, we accelerate death.

We're predators, the fact that we're omnivous doesn't change that. While we original may have started as scarvenges at the time of Homo Erectus we were primary predatorial omnivours. If you look at a human we're clearly meant to be predators primary pack hunters (slow but steady we can out tire almost any prey), but we can also hunt solitary in area with low competion.

 

[Flocculencio]

Are we really preditors in the classic sense? Don't we raise most of our meat from birth and send it through a factroy-like slaughter process? We don't even need legs for that.

I mean I guess you could argue that hunting deer or other wild game is a different story, but with the use of firearms, once again, legs and mobility really don't factor into human carnivorism these days, even if you were to use a bow.

But regardless, we do have them... Although I think the original intent of this thread is to think about the bipedal dinosaur preditors that actually chased down and kill its prey, and compare them to existing fauna today.

All those details are merely incidental recent developments, though. They've had a huge impact but humans have only been pastoralists for the past few thousand years.

Essentially we're mammilian velociraptors- we use teamwork and tools coupled with our massive endurance to take much larger prey than many mammals our size. Remember- humans do have a lot more endurance than many animal species- we're specialised for long distance chases. Whack a spear into a bison and track it til it falls.

Also we have dogs.

 

[Hawkeye]

Essentially we're mammilian velociraptors- we use teamwork and tools coupled with our massive endurance to take much larger prey than many mammals our size. Remember- humans do have a lot more endurance than many animal species- we're specialised for long distance chases. Whack a spear into a bison and track it til it falls.

Or chase it down until it dies of a heat stroke and then chuck rocks at it. But then again, I guess I'm old fashioned.

 

[The Kiat]

We're predators, the fact that we're omnivous doesn't change that. While we original may have started as scarvenges at the time of Homo Erectus we were primary predatorial omnivours. If you look at a human we're clearly meant to be predators primary pack hunters (slow but steady we can out tire almost any prey), but we can also hunt solitary in area with low competion.

And that last steak you ate.. did you go out and kill the cattle/bison/whatever yourself and cook the meat shortly there after? If you did, then good for you. If not, then we are scavengers. A predator kills their prey, while scavengers tend to eat anything that's not nailed down. Our genus has always eaten animals that have been dead for quite some time. And a scavenger has to be smarter than a predator, because they must figure out how to get the most from the least. A lion only needs to know how to ambush and run down their prey. If that was all we evolved to be, then we wouldn't be having this conversation since humans never would have started agriculture and settled down. Now you might argue the case of pastorialism, but most of those societies are nomadic or semi-nomadic, again not a good combination for advance societies. Civilizations tend to have literature, while nomads do not. A real pain to carry all those books around. We're far more like bears than lions. Yes, we will hunt and kill when the chance arises (hense the opertunistic part), but that is not how we get most of our meat.

 

[Bill Cameron]

And that last steak you ate.. did you go out and kill the cattle/bison/whatever yourself and cook the meat shortly there after?

Kiat,

Now you're just being silly.

The fact that our species has been raising our meat for several thousand years now doesn't obviate the fact that our species lived as cursorial hunters for hundreds of thousands of years and evolved into that role over an even longer period.


Bill

 

[Valdemar II]

And that last steak you ate.. did you go out and kill the cattle/bison/whatever yourself and cook the meat shortly there after? If you did, then good for you. If not, then we are scavengers. A predator kills their prey, while scavengers tend to eat anything that's not nailed down. Our genus has always eaten animals that have been dead for quite some time. And a scavenger has to be smarter than a predator, because they must figure out how to get the most from the least. A lion only needs to know how to ambush and run down their prey. If that was all we evolved to be, then we wouldn't be having this conversation since humans never would have started agriculture and settled down. Now you might argue the case of pastorialism, but most of those societies are nomadic or semi-nomadic, again not a good combination for advance societies. Civilizations tend to have literature, while nomads do not. A real pain to carry all those books around. We're far more like bears than lions. Yes, we will hunt and kill when the chance arises (hense the opertunistic part), but that is not how we get most of our meat.

So you would say that lions, tigers, icebears, wolves, jaguars, black bears and eagles are scavengers, because the speciments which live in zoos doesn't hunt their food self? A bill said the fact that our lifestyle have change, doesn't change our biological histories, we're build for hunting not scavenging even if we're oppotunistic scavengers (like all the species mentioned above are too).

 

[Flocculencio]

And that last steak you ate.. did you go out and kill the cattle/bison/whatever yourself and cook the meat shortly there after? If you did, then good for you. If not, then we are scavengers. A predator kills their prey, while scavengers tend to eat anything that's not nailed down. Our genus has always eaten animals that have been dead for quite some time. And a scavenger has to be smarter than a predator, because they must figure out how to get the most from the least. A lion only needs to know how to ambush and run down their prey. If that was all we evolved to be, then we wouldn't be having this conversation since humans never would have started agriculture and settled down. Now you might argue the case of pastorialism, but most of those societies are nomadic or semi-nomadic, again not a good combination for advance societies. Civilizations tend to have literature, while nomads do not. A real pain to carry all those books around. We're far more like bears than lions. Yes, we will hunt and kill when the chance arises (hense the opertunistic part), but that is not how we get most of our meat.

Don't be silly. All that is merely a relatively recent development which makes life more convenient for us since we don't have to hunt animals down anymore. This is what those big brains are for, mate. Just because I feed my dog dry food in a bowl doesn't mean that he's not a predator. He's still a pack hunter evolved to work symbiotically with humans.

 

[eschaton]

This conversation has gone on quite an aside, but I think ultimately humans are opportunistic, not hunters. Among "hunter-gatherers" today, depending upon the warmth of the climate the amount of animal matter in the diet ranges from 10% in tropical forest to essentially 100% in the arctic. I've actually read articles suggesting the invention of fire was more important in that it allowed humans to eat a lot of plant matter which was formerly poisonous and/or unpalatable through cooking, and (given fire was invented by Homo ergaster), this, and not increased meat eating, may have contributed the most to the development of the modern human mind.

Edit: My point being, humans were so successful because we can do anything, from being a vegan to eating nothing but meat. This allows us to fill essentially every niche in just about any habitat, provided we have the right cultural toolkit.

 

[Ofaloaf]

As for smaller species, for the most part they probably folded their long arms tightly when they ran, like birds, and you should remember that even larger "raptors" probably had feathers all the way down their fingers (a birds primary feathers actually *begin* at the wrist).

I'm quite fond of the 'cursorial' origin of avian flight, which suggests that feathered dinosaurs originally stuck their feathered wings out parallel to the ground during sprints and other high-speed theactrics, acting as stabilizers for the creatures. So, rather than folding their arms in like a modern bird, surely it's still a possibility that feathered raptors et al stuck their arms outwards, using their arms as proto-wings and stabilizers?

I've also seen speculative depictions of feathered dinosaurs-- I've got one here of Rinchenia mongoliensis in front of me-- still using their hands for grasping. In the case of Rinchenia, so that it can grasp and pick up mussels to crack open, which makes sense enough.

It was fun when I was young, but now that I know a bit more about evolutionary biology, it's fairly ridiculous in parts. There are several groups of people online who've done better work than he did. Admittedly, it was heads above The Future Is Wild though.

I still don't quite understand the reasoning behind the Squibbon.

 

[NothingNow]

I still don't quite understand the reasoning behind the Squibbon.

there is no reasoning behind the Squibbon beyond rule of cool.

 

[Keenir]

But isn't easier for the brain to coordinate two legs instead of four? I consider that as a huge advantage.

it's easier to coordinate. it's harder to balance, and harder to keep from falling.