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I'm in the process of designing a creature loosely resembling a theropod dinosaur that sports a number of horns/tusks on its head and face, and I'm wondering if anyone can help me evaluate its feasibility. I'm not terribly concerned with the practicality/ functionality of the horns/ tusks themselves or their arrangement. They're strictly ornamental and probably stupid from an evolutionary perspective, but I'm pretty resigned to that fact.

Scan of a drawing showing a person riding this beast

What I am concerned with is whether or not they might compromise the creature's ability to lift/ hold up its own head (is the neck thick and muscular enough?) or balance. (Would a longer tail or a tail with a source of extra weight at the end help any?) Are there any compromises I might be able make if they do prove unfeasible in these regards? I've come up with tentative estimates of the horns'/ tusks' weights based on what info I've been able to garner about deer antlers and black rhino horns. I'm estimating the two large horns at 2-3 pounds each, the vertical horn jutting up between these two at 1.5-2 pounds, the snout and chin horns at 0.75 to 1 pounds each, and the tusks (which are made of the same material as the horns) at 1.5 to 2 pounds each.

Here is an updated version of the creature design featuring a thoracic hump as per one of the suggestions I've received. revised animal design

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Your creature is fine, there are theropods with crests and other crap on their head, and your theropod is short necked and stocky so ballance should be fine. Air sacs make the front of the animal a lot lighter than it looks. Also you should straighten that top line on the hips (it should not curve down much), otherwise you are cutting away about half the muscle mass of the hind legs.

Your rider however is all wrong.

If you look at ostrich riders they need to be seated directly over where the feet touch the ground in a standing position. More importantly the rider needs to stay upright not lean forward. If anything they may want to lean back and swing their legs forward. Posture wise it is more like sitting on a motorcycle than a horse, this is becasue a theropod is going to be a lot wider than a horse. So you should mover your rider back over the hips in a more seated position.

Alternatively they could sit behind the hips and lay forward, but they will have to stay in that position.

Now yes an ostrich is smaller than your theropod but the balance issue is the same.

standing

enter image description here

here is an allosaurus for body comparison. I also recommend http://www.skeletaldrawing.com/

enter image description here

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  • $\begingroup$ So if I were to have my riders leg's out in front of the theropod's (in order to avoid chaffing for instance from her legs rubbing against the dinosaur's as it walks), I could accomplish this by putting her upper body in a reclining position that places weight behind the hips in order to help compensate for the weight of the legs placed in front? $\endgroup$ – Joseph Rouleau Nov 24 '17 at 16:51
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    $\begingroup$ I am having trouble visualizing what you describe. You basically want him seated in a more chair like posture, with their butt as far back as possible and their thighs almost horizontal. Just like the bottom ostrich rider. The top of a theropods hips are wide and somewhat flat and really would not move, so with a saddle it should not be bad. this image has the right sitting position even if the anatomy is odd. img00.deviantart.net/8cc2/i/2014/099/1/5/… You may even want to do somthing like a camel saddle. $\endgroup$ – John Nov 24 '17 at 20:29
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To be frank, I'm not so worried about the horns on your creature; the rider on the back is a far bigger problem.

The real issue you have with this creature is centre of gravity. The legs are too far back to balance the creature correctly, unless it has a very heavy tail. Most of the body (where the bulk of the weight will be) sits forward of the legs, as does the rider. This creature looks to me like he'll tip forward constantly.

The smaller front 'paws' are about right, as is the hip placement, but I'm thinking the best way to solve this is to give it a longer, stronger hamstring / quadriceps configuration in the first joint of the leg, that largely brings the leg forward, then have the calf go straight down from there so that the foot (which probably needs to be larger) is sitting close to the centre of the body (the head and tail would then counterbalance each other). This means that the calf of the leg could come down at (say) 40% distance between hips and shoulders, then the foot could be (say) 20% of the same length. That should make it far more likely that such a creature could support a rider, who'd be sitting on the back roughly above the foot.

That said, I'd strongly consider making your dinosaur stand more upright if supporting a rider, as the configuration I'm describing above would put a lot of stress on the leg and foot bones because there's a lot of off axis joints that would leave the animal's most powerful leg muscles working more as shock absorbers than power transfer conduits.

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  • $\begingroup$ Thanks! I'll tweak the design accordingly. Do you think scaling up the creature a bit would lessen the impact the rider's position would have on its ability to balance or just make things more problematic from a speed and weight bearing perspective? $\endgroup$ – Joseph Rouleau Nov 24 '17 at 1:59
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    $\begingroup$ Actually, scaling up isn't a bad idea for 2 reasons; first is that the rider is relatively smaller, meaning that balance and load bearing are a little easier, and secondly because a larger creature will have stronger bones and muscles to support its own weight, therefore will handle the rider in addition more easily. The chief concern about scaling up is that it can lead to some minor speed reductions and some major agility / dexterity reductions. If you're just running straight line, not a problem but ducking and weaving would be more of an issue. $\endgroup$ – Tim B II Nov 24 '17 at 2:03
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    $\begingroup$ Alright cool, thanks! I take it then that so long as I'm not scaling it up by some absurd amount, the square-cube law's not going to cause me too much trouble. I'm a little unclear on one point, though. Would you say this creature is unfeasibly front heavy if we exclude the additional frontward weight of the rider or set the rider squarely above the hips, and if so (last question- I promise), which method of adding more weight to the tail do you think would be more effective, adding a club-like weight at the tip or bulking up and/or lengthening the entire tail? $\endgroup$ – Joseph Rouleau Nov 24 '17 at 7:52
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    $\begingroup$ So the chest area just below the neck is a touch bulky, unless you're planning for an animal to use its pectorals to grab at prey with its front arms. As for the tail, if you're staying true to the therapods, don't put a club thing on the end of the tail, just make the part that attaches to the body (just behind the legs) a little bulkier would be my guess, although it looks perfect the way it is. And you're right, if you're only scaling up by around 10-30%, shouldn't be a problem. :) $\endgroup$ – Tim B II Nov 24 '17 at 8:01
  • $\begingroup$ Humans walk upright, whiles gorillas and chimpanzees can't manage for more than short periods. It has something to do with spinal development, which one reason why babies only start walking at about one year. Also, kangaroos balance on their tails somehow to help them stay upright - You might be able to incorporate those ideas. $\endgroup$ – Rissiepit Nov 24 '17 at 9:26
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I suggest the rider would be better placed directly over the animal’s hind legs or perhaps just slightly in front of them. When the animal is walking or stationary it would have its head and upper body raised and its tail lowered so the rider will be on a slope and much closer to the animal’s body (any saddle or stirrup’s used need to accommodate this).

When the animal runs it would lower its head and raise its tail as a counter balance. At this point the rider probably needs to be more upright and over the hind legs to avoid unbalancing the creature. Another option would be riding as a horse jockey does, with the legs well up to avoid getting in the way of the animal’s leg movement.

If you want the rider to be a little further forward, it would always be possible to counter balance that by adding a little weight behind the rear legs, sword, shield, extended saddle packs etc, but obviously don’t overdo it. A larger animal would make the whole thing easier, provided it was trained not to eat the rider ;o)

Another option on a bigger animal would be two riders - one forward and one aft of the rear legs.

T. Rex running

(https://phys.org/news/2017-07-tyrannosaurus-rex-couldnt.html)

I think the rider needs to sit between where the animals feet are...

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  • $\begingroup$ When an animal runs, it needs to be imbalanced. Think of a human running. They lean forward so far that they would fall over if they weren't moving. Look at actual pictures of T. Rex and other theropod dinosaurs. Their legs are too far back for them to be balanced. That's because their legs are positioned for maximum speed when running. When they were standing still, they probably rested on their tails, and when they were walking, I'd guess they carried their upper bodies more upright to balance. $\endgroup$ – Peter Shor Nov 24 '17 at 16:08
  • $\begingroup$ Would a stationary posture like this be correct do you think? It looks like the tail and torso are almost parallel, but the head is still raised above the level of the tail's tip. (Peter Shor- looks like you answered my question before I even finished posting it. thanks!) ithttps://i.amz.mshcdn.com/KRKNTQ76_G3yqAN88aZAjczt634=/950x534/filters:quality(90)/https%3A%2F%2Fblueprint-api-production.s3.amazonaws.com%2Fuploads%2Fcard%2Fimage%2F187610%2F5fa6db5a4d78458aba3dab8dc0a46fd9.jpg $\endgroup$ – Joseph Rouleau Nov 24 '17 at 16:09
  • $\begingroup$ That looks imbalanced to me. But I'm not an expert. $\endgroup$ – Peter Shor Nov 24 '17 at 16:13
  • $\begingroup$ @PeterShor let me add a photo $\endgroup$ – Slarty Nov 24 '17 at 16:37
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    $\begingroup$ Looking at kangaroos standing, walking, and running, it's possible that dinosaurs positioned their feet under their center of balance by bending their knees or tilting their legs. But unfortunately, it looks like the standard reconstruction of T. Rex standing doesn't worry about the center of balance. $\endgroup$ – Peter Shor Nov 24 '17 at 16:39
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If the head is heavy, your creature would likely need big neck muscles and corresponding spinal processes on its backbone to support the weight. It isn't so much the actual carrying around of the head/horns which is the problem - it is the muscle power needed to raise and lower the head when the creature wants to eat something on the ground, or have a drink of water.

The hump of a bison is a good example of an animal with this muscle mass and enlarged spinal processes on the thoracic vertebrae.

Here is a modern bison, showing the skeleton inside the hump: American bison

And this is a prehistoric bison, with enormous horns: Bison latifrons had huge horns

All this weight at the front (head, neck muscles, thoracic hump) will indeed need some sort of counterweight. Probably in the hip region or the root of the tail, rather than by giving the creature an ankylosaurus-style tail club. Massive great leg bones and muscular legs would be a start - and would also make it a more powerful runner or kicker. If you don't mind it having a slightly waddling run - so it gallops like a crocodile, rather than like an ostrich - then the tail muscles would be providing energy for walking/running, and you could justify a thick heavy base to the tail.

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  • $\begingroup$ Do you think the thoracic hump would have to be as large and conspicuous as the bison's or might a head/neck/upper spine arrangement resembling an elk's be sufficient? I read that an elk's antlers can weigh up to 40 lbs and I estimated the total of weight of my creatures' horns at about 10-14 lbs, so i'm hoping i can get away with a subtler hump and longer neck for aesthetic reasons. I do kind of suspect that the rear-facing antlers might enable the elk to more easily lift and lower its head by acting as a counterweight though, perhaps ruling out this possibility for my animal. $\endgroup$ – Joseph Rouleau Dec 1 '17 at 22:25
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    $\begingroup$ @JosephRouleau. Not sure if you mean elk=moose, or elk=wapiti. But yes, if the load is less, the bones and attached muscles can be smaller, so the hump can be smaller. On the other hand, a shoulder hump might be something useful for your rider to hang onto when riding bareback! :-) Looking up horn weights or whole skull weights for Dinka cattle, Watusi cattle, British longhorns, or Texas longhorn cattle might be useful to you. They are all horn sheath over a bone core, which sounds more like your theropod horns than antlers are (e.g. they don't shed them). $\endgroup$ – DrBob Dec 2 '17 at 13:46
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    $\begingroup$ @JosephRouleau Forgot to say... ornamental horns are not evolutionarily stupid. If the purpose of the ornament is to attract the opposite sex, then it makes plenty of sense - the dinos with the most impressive horns get all the girls (or boys in a polyandrous species). If both sexes have horns-as-weapons, then that implies the need to fight your own kind over food or water in times of scarcity. e.g. reindeer, oryx. In cattle,cows' horns stick out to the side, to jab a rival in the ribs, or swipe at a predator while turning on the spot. Bulls' horns face forwards, to fight other bulls head on. $\endgroup$ – DrBob Dec 2 '17 at 13:54
  • $\begingroup$ Oh, I was thinking wapiti, (just for the sake of elucidation). I'll give those weights a look. Thanks! $\endgroup$ – Joseph Rouleau Dec 2 '17 at 15:41

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