First of all, I am only asking this question about true dinosaurs. I am aware of, but not asking about: Pelycosaurs, which lived before the dinosaurs; or Crocodilians, which lived before, with, and after them, etc…. It seems that every purely carnivorous dinosaur fossil we have found has been a two-legged Therapod. We have found bipedal herbivorous dinosaurs, but no quadrupedal carnosaurs. Is there a theory as to a reason behind this? Were Therapods simply first and “guarded their niche” successfully, or is there a good reason why a quadrupedal carnosaur wouldn’t be successful. Or, is it simply that we haven’t found their fossils yet?
If looking on scientific guesses and bases… Then I have come to the conclusion that, the bacteria from which the living beings dinosaurs evolved were not supposed to have four functional legs. But the bacteria that arrived with a deadly and powerful meteorite , which also extinguished the dinosaurs brought something else on Earth that helped the life to evolve on the kind of level we know it today.
One reason may be speed. It appears that the most primitive dinosaurs were bipedal. If so, then a transition from bipedalism to quadrupedalism may have been done to allow a particular species to gain bulk, since 4 legs can support more weight than two. An increase in bulk would also result in a decrease in speed. Since a slow predator is one that will starve, those species that have transitioned from bipedalism to quadrupedalism most likely do it because large size protects them from predators. That means herbivores are more likely to evolve from bipedalism to quadrupedalism among dinosaurs. One may then point out that T. rex is large. Yes, but T. rex is also likely to be a savenger because of its bulk. Further, even T. rex is dwarfed by the sauropods.
Because they always used two hands for their silverware.http://zoocrewkids.blogspot.com/
Plenty were four legged, you’re looking at anything that does not eat plants.
Not everything was a raptor, t-rex or ovi whatsis.
They speculate that we’ve only found a mere 10% of the dinosaur species so far. That leaves 90% undiscovered.
I doubt dinosaurian carnivores were bipedal simply because theropods “guarded their niche.” Had quadrapedalism been more advantageous, it would’ve been selected for. The bipedal stance may have prevailed because it conferred greater height, necessary for dealing with sauropods (which tended to predominate in many mesozoic environments) and for spotting other types of prey before the predator was spotted. (We know that dinosaurs had VERY acute vision, and it certainly paid to be able to see over obstacles, which a biped could do better than a quadruped.) Speed wasn’t necessarily a reason since some quadrupeds like cheetahs are fast. Not that theropods weren’t fast–it is very silly to depict T. rex as a slow scavenger, especially in light of its big cnemial crests, for massive leg musculature.