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Possibility of fully armless bipedal Mammals?
Topic Started: Aug 3 2017, 09:59 AM (1,701 Views)
Dazzle Aug 3 2017, 09:59 AM Post #1
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In Dougal Dixon's After Man book, one concept I'm surprised never got as popular(er, became a trope like Flightless Bats, Whale Birds, ect) is the Wakka
http://vignette2.wikia.nocookie.net/speculativeevolution/images/9/9c/Wakka.png/revision/latest?cb=20130327230925

The book implies that South America once again became an isolated continent 25 million years from now. Given how strange island fauna can get, could something like the Wakka ever evolve? A fully bipedal therapod-like mammal with no arms.

It just seems too strange, well, most things in After Man are too strange to be true. At least in the way they are presented.
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Archeoraptor Aug 6 2017, 01:22 PM Post #31
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1. Many pterosaurs had long tails and they flew

basal pterosaurs were not that good fliers
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IIGSY Aug 6 2017, 01:28 PM Post #32
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Aug 6 2017, 01:20 PM
Mammals are generally quadrupedal; dinosaurs as a[n overly] general rule were bipedal. Something like a theropod, ornithopod, or the ancestral dinosaur needs a long tail, because it provides balance when moving bipedally. Without it their horizonal biped stance wouldn't work at all. Something quadrupedal like a ceratopsid or a brachiosaur (which, unlike diplodocids, couldn't rear)? They have noticeably quite short tails. It's not worth the energy investment for a quadruped. This can also apply to a more upright stance, because the center of balance shifts.

On flying animals, a long tail is indeed rather inefficient, it's gonna create drag. That's why only short-tailed pterodactyloid pterosaurs got very large. Perhaps it's why the birds with their pygostyle outcompeted things like microraptorians.
Hadrosaurs where quadrupeds and had long tails.

And why would diplodocids need long tails?
Edited by IIGSY, Aug 6 2017, 06:48 PM.
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LittleLazyLass Aug 6 2017, 01:42 PM Post #33
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 They were falculatively quadrupedal, practicing both quadrupedal and bipedal movement, so the tail was necessary.
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Dragonthunders Aug 6 2017, 01:42 PM Post #34
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 They were also facultative bipeds

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kusanagi Aug 6 2017, 01:47 PM Post #35
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Aug 6 2017, 01:20 PM
Mammals are generally quadrupedal; dinosaurs as a[n overly] general rule were bipedal. Something like a theropod, ornithopod, or the ancestral dinosaur needs a long tail, because it provides balance when moving bipedally. Without it their horizonal biped stance wouldn't work at all. Something quadrupedal like a ceratopsid or a brachiosaur (which, unlike diplodocids, couldn't rear)? They have noticeably quite short tails. It's not worth the energy investment for a quadruped. This can also apply to a more upright stance, because the center of balance shifts.

On flying animals, a long tail is indeed rather inefficient, it's gonna create drag. That's why only short-tailed pterodactyloid pterosaurs got very large. Perhaps it's why the birds with their pygostyle outcompeted things like microraptorians.
I am not sure as whatever their posture in life heterodontosaurs and plateosaurs were built for quadropedalism with a bounding motion. Then observe that silesaurs were obligate quadropeds and the sister taxon to Dinosauria proper. I would rather say that dinosaurs were labile as regards bipedalism-quadropedalism from the start whilst noticing a stemward trend to bounding in lagerpetonids (Prorotodactylus trackmakers) and Scleromochlus. Bipedal hopping gaits in mammals arise from quadropedal hopping gaits, bipedal hoppers switch to striding, and a more bounding gait switches to walking and running at large body sizes.
Edited by kusanagi, Aug 7 2017, 07:43 PM.
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kusanagi Aug 6 2017, 01:47 PM Post #36
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Aug 6 2017, 01:22 PM
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Aug 6 2017, 12:53 PM
1. Many pterosaurs had long tails and they flew

basal pterosaurs were not that good fliers
Dimorphodon no, bur Rhamphorhynchus and Campylognathus? They seem pretty airborne to me.
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Scrublord Aug 8 2017, 08:37 PM Post #37
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Even so, you'll notice that long-tailed pterosaurs never grew above a certain size (about 6 feet in wingspan), whereas tailless ones grew much larger.
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kusanagi Aug 8 2017, 08:52 PM Post #38
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Scrublord
Aug 8 2017, 08:37 PM
Even so, you'll notice that long-tailed pterosaurs never grew above a certain size (about 6 feet in wingspan), whereas tailless ones grew much larger.
It doesn't mean they were poor fliers. Even Dimorphodon's aspect ratio might not make it srmiflightless, as appealing as that idea might be, because Mimiopterus vesper bats have merely switched to a fluttering flight behaviour. Of course there is a big difference of size and ecology but the aspect ratio might not be as bad for Dimorphodon as some people assume. Erect hindlimbs may be primitive or perhaps not - is it primitive in azdarchids?

I wonder if having a flying bird as big as Aepyornis is simply a matter of habitually adopting quadropedal takeoff as ducks and Balaeniceps will do, situationally - is there a reason birds don't do it more often?
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Zoologist Aug 8 2017, 09:01 PM Post #39
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I actually read an article a few months back (tried to find it again and I couldn't, unfortunately) that analyzed Mesozoic mammal locomotion, and it came to the conclusion that ancestrally mammals, or near-mammals, were burrowers, which favors strong forelimbs. This meant according to the article that it is much more difficult for mammals to become bipeds compared to archosaurs, which had different ancestral niches.
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IIGSY Aug 8 2017, 09:09 PM Post #40
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Aug 8 2017, 09:01 PM
I actually read an article a few months back (tried to find it again and I couldn't, unfortunately) that analyzed Mesozoic mammal locomotion, and it came to the conclusion that ancestrally mammals, or near-mammals, were burrowers, which favors strong forelimbs. This meant according to the article that it is much more difficult for mammals to become bipeds compared to archosaurs, which had different ancestral niches.
What was the ancestral archosaur like? And the ancestral lepidosaur for that matter?
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Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

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ÐK Aug 8 2017, 10:28 PM Post #41
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Aug 6 2017, 12:34 PM
So why did birds and mammals loose it?
The loss of the caudofemoralis goes further back in maniraptorans than just birds. Maniraptorans as a whole show signs of reduction of the CFL, and it's especially obvious in dromaeosaurids, troodontids and primitive avialans, where the tail is all but reduced to a just a bony rod with hardly any prominent musculature surrounding it, and the development of hip and knee driven locomotion was already underway.

Why this shift happened doesn't seem to be very clear. It could perhaps relate to early flighty adaptations in ancestral maniraptorans, or perhaps their much smaller body sizes promoted such a method of locomotion.


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Aug 6 2017, 12:53 PM
Archeoraptor
Aug 6 2017, 12:52 PM
birds-long tail bad for flying as you see msot bird,except mesozoic groups had short tails
1. Many pterosaurs had long tails and they flew
Little
Aug 6 2017, 01:20 PM
On flying animals, a long tail is indeed rather inefficient, it's gonna create drag. That's why only short-tailed pterodactyloid pterosaurs got very large. Perhaps it's why the birds with their pygostyle outcompeted things like microraptorians.
Scrublord
Aug 8 2017, 08:37 PM
Even so, you'll notice that long-tailed pterosaurs never grew above a certain size (about 6 feet in wingspan), whereas tailless ones grew much larger.
I wouldn't consider the long tail of non-pterodactyloids as the primary factor for their relatively smaller wingspans. Remember, all the stupidly humongous pterodactyloids are incredibly pneumatic, and their skeletons are blown up to massive linear dimensions, to a degree the non-pterodactyloids never achieved. Consider ctenochasmatoids and kin, which had pneumaticity more comparable to non-pterodactyloids than the pteranodonts or azhdarchoids and only ever achieved similarly sized wingspans.

And while a long tail probably does confer some degree of drag, I imagine it would be a fairly minimal concern considering that long-tailed pterosaurs decked theirs out in elaborate tail vanes and lobes for display. Also consider that while modern birds all have short pygostyles, there are still plenty of them that sport ludicrously long and heavy tail feathers that would effectively defeat the purpose of a short tail if they long, dragging tails were a major hindrance to flight. Even the first short-tailed birds sport extravagantly long feathers on their stubby tails, Confuciusornithiformes and Enantiornithes are well known for theirs.


kusanagi
Aug 6 2017, 01:47 PM
Then observe that silesaurs were obligate quadropeds and the sister taxon to Dinosauria proper.
I wouldn't go so far as to call them obligate quadrupeds, since the skeleton of Silesaurus possess features of the vertebral column that are consistent with the animal being able to stand and run on its hind legs alone. The anatomy of the limbs also suggests this, because while the forelimbs are of such a length that they probably were held down on the ground (even in the absence of any manual bones), the anatomy of the hindlimb still implies that much of its body weight was supported over the pelvis and could carry it on just two legs (along with their relative robustness compared to the very gracile forelimbs). Naturally, these could be considered holdovers from a obligatorily bipedal ancestor, but they would still permit Silesaurus bipedal movement. 'Facultative' biped, or rather, 'facultative quadruped' would be more befitting.


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Aug 8 2017, 09:09 PM
What was the ancestral archosaur like? And the ancestral lepidosaur for that matter?
The ancestral archosaur would be something sprawling/semi-upright, predatory and possibly semi-aquatic reptile, going by the anatomy of primitive phytosaurs, early pseudosuchians, aphanosaurs, and the nearest stemward Archosauriformes (e.g. proterochampsids). On the whole, a fairly unspecialised terrestrial animal, the general anatomy of which you could trace back all the way towards the base of Archosauromorpha.

Now the tail of archosauromorphs has been relatively reduced a few times independently, like in rhynchosaurs or azendohsaurids, and maybe erythrosuchids (a little hard to be sure with those proportions), but the long tail remains in the line leading to Archosauria in a few clades that are considered to be semi-aquatic, or at least capable swimmers (i.e. proterosuchids, proterochampsids, "vancleavians", phytosaurs). Perhaps it's reasonable to infer that the long, well muscled tail of archosaurs came about from their antecedents requiring a muscular sculling organ in the water, that was later adapted to provide the powerful locomotory caudofemoralis in their terrestrial descendants?

As for the ancestral lepidosauromorph, it probably would have just generally resembled modern squamates and tuataras in body form, something kind of like the ancestral archosaurormorph: a sprawling, terrestrial reptile with a generalised lizard-esque body plan.
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IIGSY Aug 8 2017, 10:41 PM Post #42
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ÐK
Aug 8 2017, 10:28 PM
Insect Illuminati Get Shrekt
Aug 8 2017, 09:09 PM
What was the ancestral archosaur like? And the ancestral lepidosaur for that matter?
The ancestral archosaur would be something sprawling/semi-upright, predatory and possibly semi-aquatic reptile, going by the anatomy of primitive phytosaurs, early pseudosuchians, aphanosaurs, and the nearest stemward Archosauriformes (e.g. proterochampsids). On the whole, a fairly unspecialised terrestrial animal, the general anatomy of which you could trace back all the way towards the base of Archosauromorpha.

Now the tail of archosauromorphs has been relatively reduced a few times independently, like in rhynchosaurs or azendohsaurids, and maybe erythrosuchids (a little hard to be sure with those proportions), but the long tail remains in the line leading to Archosauria in a few clades that are considered to be semi-aquatic, or at least capable swimmers (i.e. proterosuchids, proterochampsids, "vancleavians", phytosaurs). Perhaps it's reasonable to infer that the long, well muscled tail of archosaurs came about from their antecedents requiring a muscular sculling organ in the water, that was later adapted to provide the powerful locomotory caudofemoralis in their terrestrial descendants?

As for the ancestral lepidosauromorph, it probably would have just generally resembled modern squamates and tuataras in body form, something kind of like the ancestral archosaurormorph: a sprawling, terrestrial reptile with a generalised lizard-esque body plan.
So, essential a terrestrial crocodile?



How far back do you have to go before the ancestor of archosaurs to be a generic lizard like animal? Because that was the ancestral form of sauropsids, and of amniotes in general.
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Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


More pictures


Other cool things


All African countries can fit into Brazil
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ÐK Aug 8 2017, 10:51 PM Post #43
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Aug 8 2017, 10:41 PM
So, essential a terrestrial crocodile?
I wouldn't say that, myself. Crocodilians have some fairly specialised anatomy and adaptations that wouldn't be present in the ancestral archosaur, even if their generalised bauplans are superficially similar.

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Aug 8 2017, 10:41 PM
How far back do you have to go before the ancestor of archosaurs to be a generic lizard like animal? Because that was the ancestral form of sauropsids, and of amniotes in general.
For superficial similarity without any obvious specialisations (like the hooke-jaw in proterosuchids and so on), I'd say maybe around the base of Crocopoda, with early allokotosaurs like Pameleria and near-Archosauriformes like Prolacerta. Naturally, they still have features that ally them closer to archosaurs than to lepidosaurs, but in a generalised sense they're fairly generic. From derived archosauromorphs (i.e. Teyujagua) and into Archosauriformes, you start to see more obvious derivations of the skull and other body parts (like osteoderms) that are decidedly less generic looking.
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I'm sorry but in what alternative universe would thousands of zebras be sent back in time by some sort of illegal time travel group to change history and preparing them by making gigantic working animatronic allosaurs?

~Komodo, Zebra's sent back in time (4/1/13)
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kusanagi Aug 8 2017, 10:51 PM Post #44
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Typical total group archosaurs - prolacertiformes, which are at least slightly paraphyletic - resembled large lizards in their ankles and only the most crownwards (Prolacerta) present any real evidence for endothermy. Formerly they were regarded as actual squamate relatives. And ichthyosaurs, sauropterygians, testudines and choristlderes are all potentially further back down the total group at a point where it is hard to tell who is an archosaur relative or a lepidosaur one.
Edited by kusanagi, Aug 8 2017, 11:02 PM.
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IIGSY Aug 8 2017, 11:01 PM Post #45
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ÐK
Aug 8 2017, 10:51 PM
Insect Illuminati Get Shrekt
Aug 8 2017, 10:41 PM
So, essential a terrestrial crocodile?
I wouldn't say that, myself. Crocodilians have some fairly specialised anatomy and adaptations that wouldn't be present in the ancestral archosaur, even if their generalised bauplans are superficially similar.

Insect Illuminati Get Shrekt
Aug 8 2017, 10:41 PM
How far back do you have to go before the ancestor of archosaurs to be a generic lizard like animal? Because that was the ancestral form of sauropsids, and of amniotes in general.
For superficial similarity without any obvious specialisations (like the hooke-jaw in proterosuchids and so on), I'd say maybe around the base of Crocopoda, with early allokotosaurs like Pameleria and near-Archosauriformes like Prolacerta. Naturally, they still have features that ally them closer to archosaurs than to lepidosaurs, but in a generalised sense they're fairly generic. From derived archosauromorphs (i.e. Teyujagua) and into Archosauriformes, you start to see more obvious derivations of the skull and other body parts (like osteoderms) that are decidedly less generic looking.

Interesting. So archosauromorphs and lepidosauromorphs split in the mid permian?
Projects
Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


More pictures


Other cool things


All African countries can fit into Brazil
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