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On this parallel earth all vertebrates received the ability to efficiently produce super strong materials from readily available minerals/nutrients in the mid Triassic.

The specifics of these composite organic metamaterials aren't super important just that:

  • The metamaterials are of comparable density to bone, but with over 60 times the compressive strength of even the strongest bone and vastly more tensile and shear strength. This also makes these materials stronger than anything humans can currently synthesize in large quantities, by a fair margin.
  • The metamaterials can be up to as hard as diamond.

Let's also assume that when creatures received this ability, they very rapidly developed the ability to produce these composite materials in as many different ways as as they can produce bone and keratin (to ensure they actually fully utilize the potential of these materials).

When it comes to the super strength aspect of this question, assume the autotrophs at the base of food chain started producing over an order of magnitude more caloric energy in the mid Triassic as well. Additionally these autotrophs and the animals that eat them have developed new stores of chemical energy that can function as well as fats and carbohydrates, but have energy densities on par with natural gas.

Given many dinosaurs in evolutionary history seem to have reached about the maximum size that their biology allowed, this seems like an area where one should be able to make quite decent predictions about speculative evolution.

The mid Triassic is being chosen as the starting point for this speculative evolution question, because dinosaurs were already widespread.

So with these advantages how large and fearsome would dinosaurs become?

Answers should take into consideration that other than the specific traits mentioned above, these creatures are still evolving from actual dinosaurs. With their initial biology varying only in the aforementioned ways.

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Using basic square/cube law, a dinosaur with 60x the bone strength could get 60^1/3 times as big (assuming the muscle strength is similarly increased). The cube root of 60 is about 3.9, so they could get a little less than four times as long/tall and still move around as well the original "real world" scale dinosaur.

Of course, unless you have something like 4x the available oxygen in the air, your 4x scale dinosaur won't last long before it suffocates; it'll weigh 60x as much, but have only about 15x as much lung area to absorb oxygen.

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  • $\begingroup$ I mean if there's selective pressures on the dinosaur like there were on birds, there's no reason they wouldn't just adapt to: have more efficient lungs: breath faster, have more red blood cells, etc. $\endgroup$ – Vakus Drake Sep 9 at 19:30
  • $\begingroup$ @VakusDrake Birds with superchargers are the rare species that fly genuinely high. Higher hematocrit won't fix limitations on how fast oxygen can diffuse in from air in the lungs, or CO2 out. This limitation applies to breathing faster, too (not to mention air velocity in a windpipe several meters long). A "more efficient" lung would have more area per volume -- but the smaller alveoli would be harder/slower to ventilate; the size we have is about as good as they'll get. $\endgroup$ – Zeiss Ikon Sep 9 at 19:35
  • $\begingroup$ I'm not an expert in lung biology, but I don't think suffocation is certain. Rather than just scaling up everything in the lung uniformly, you could have a lung cavity that's scaled up, but filled with alveoli that are on the same scale as the original. These would fill the larger volume while having a larger surface area than scaled-up alveoli, potentially allowing enough surface area for gas exchange. These dinosaurs can get a lot bigger on a macro scale, but the microanatomy doesn't have to. $\endgroup$ – Nuclear Wang Sep 9 at 19:35
  • $\begingroup$ The ratio of area to volume is determined by the alveoli size; keep them the same, you get the same ratio the real world had. $\endgroup$ – Zeiss Ikon Sep 9 at 19:36
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    $\begingroup$ @ZeissIkon "Birds with superchargers are the rare species that fly genuinely high." My point is that there could be selection pressures for dinosaurs to get more efficient lungs just like there was selection pressures for birds that flew at high altitudes. $\endgroup$ – Vakus Drake Sep 9 at 19:41
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Bone strength and food was not a limiting factor for dinosaur size. Most limiting factors are:

  • Breath - it is not about liters of oxigen per second, but about difference in parcial pressure of O2 and CO2 (not absolute values, but difference!). Large dinosaur has long long blood vessels, and a long time for gases to come throu body. Each cell this flow is passing by reduces O2 and increases CO2. It means that larger body requers larger difference in between O2 and CO2 at start to allow all body cells to breath. Or high blood flow and thus higher metabolism, but this leads to next limitation. This one limitation factor is exactly why all current land animals have sizes they have now and we have no megafauna any more.
  • Thermal regulation - living tissue is mostly just a water. And water has some definite termal conductivity. It means that dinosaur's inner body parts can't be deeper than some threshold from surface of dinosaur, or they just cook alive. This threshold depends on metabolism and some thermoregulation mechanisms (if we cut out elephant ears - it would die from overheating), but can't be deeper than about 2-3 meters for air-cooled (i.e. all landbase) animals with metabolism, that alow chasing and hunting (that leads us for next limitation).
  • Movement speed - when we increase size, mass increases as a cube, but strengh of bones and musles icreases as a square. It means that dinosaur becomes "relativly weaker" and slower - it has less force for more mass. If we increase musles over-proportinally, breath of this mussles becomes an issue (longer path for gases!) and also thermoregulation (more power - more heat). Why cheetah (a cat of large dog size!) can't run 120 km/h for long? Exactly becase of this: his blood stream can't provide enough oxigen for his mussles, and it does it run on inner energy reserves of his musles. Extreemly large dinos would have mass thousand times more than cheetah, and for them even 10 km/h would be an unreachable speed (like it was for some bigest dinosaur we know)

All this limitation lead to some unusial behaviors of dinos. Large one were extreamly slow: both raptors and preys. Hunting of megabests were like a pavers race (its a hyperbole , of cause. T-rex was able to bearly catch human, but compared to his size it would look like A380 landing).

So what dinos would do with that kind of metamaterial - they would not increase size much (only percents), but would develop sharper and deadler teeth (herbiovores would be able to eat tree trunks!) and claws, and strong bullet(cannon)proof bodyarmor.

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