For example, how do we know velociraptors we’re family and pack oriented? How do we know some were passive, and some were very aggressive predators? How do we know what foods they ate?
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There are clues left behind in the fossils, for example we know Allosaurus was incredibly aggressive. I challenge anyone to point to a specimen of allosaurus that’s more than 50% complete without a traumatic injury. Whatever it was these animals were doing, they were getting themselves injured at an insane rate, and continuing to hunt/fight even when seriously wounded.
Similarly there are coprolites (fossilized poop) and also fossilized stomach contents to give information on what the animals were eating. For example we know that Baryonyx was dining on a combination of terrestrial and aquatic prey, as our first specimen had both fish scales and the bones of a young dinosaur in its stomach.
But the most common way of determining how dinosaurs lived, is through morphology (study of the animal’s body/proportions/functions) and supplementing this with comparing it to modern animals with similar features. For example we can tell a lot about what an animal ate, and how it used its jaws by comparing them to animals today with similar teeth.
-For example hadrosaurs had a line of [grinding molars along the back of their jaws](https://discovery.sndimg.com/content/dam/images/discovery/fullset/2021/2/23/GettyImages-926845916.png.rend.hgtvcom.616.616.suffix/1614148110544.png), this suggests they were chewing vegetation similarly to a modern cow. We combine this data was the multitude of specimens that had fossilized plant material in their guts, which allow us to determine exactly what kinds of plants they preferred.
-Tyrannosaurus had [enormous teeth](https://www.countryclubdentistry.com/x/lc-content/uploads/2015/09/t-rex-teeth2.jpg), that weren’t very sharp, but were essentially like railroad spikes, or ‘lethal bananas’, robust and strong, capable of withstanding colossal forces, like a crocodile on steroids. This suggests that they used sheer bite force to crush armored prey. And indeed that’s what we find. We have evidence of Tyrannosaurs having bitten clean through a Triceratops’ horns or simply crushing the skull with a single bite, indicating that they were not shy about engaging with prey head on.
-Allosaurus on the other hand had [relatively small but wickedly sharp serrated teeth](https://cdn.shopify.com/s/files/1/1534/3595/products/S037_ALLOSAURUS_FRAGILIS_SKULL_2015-600x600_600x.jpg?v=1583454114), the skull itself was comprised of a series of arches that allowed them to absorb a lot of stress. Also the jaws show adaptation for opening [very *very* wide](https://www.asiaone.com/sites/default/files/original_images/Nov2015/Allosaurus_reuters.jpg). This indicates they worked similarly to a modern monitor lizard (like the komodo dragon), [which have similar teeth](https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/KomodoDragon_Skull.jpg/1200px-KomodoDragon_Skull.jpg). The animal didn’t have a very high bite force, but instead used its neck to pull, tearing flesh with the serrated teeth, almost like a saw. All the while the skull would resist the forces produced by the struggling prey. This also gives an implication to what kind of prey Allosaurus was going after. The insane gape and strategy of using blood loss to kill, suggests that it was hunting very large animals, much larger than itself. A wide gape allows the animal to engage with a much larger animal, and blood loss is the most efficient way to kill something you can’t overpower (Komodo dragons do the same today). Unlike Tyrannosaurus that was hunting prey around its own size, Allosaurus ate sauropods (long-neck boys), even a young sauropod was many times larger than an Allosaurus.
However none of this is certain, what we have are a series of very educated guesses that are always evolving over time, as new information comes into play. Sometimes theories that have stayed in place for decades can get overturned by new information.
For example, it turns out that Velociraptors were almost certainly not pack-hunting animals. It’s possible they banded together to hunt in a sort of mob-mentality, similarly to modern crocodiles, however there exists no evidence that a wolf-like pack structure existed, and plenty of evidence to contradict this. The most powerful evidence comes in analyzing the oxygen isotopes in the bones. This can give a clue as to what the animals were eating. It turns out that young dromeosaurs (the family that includes velociraptor) ate a very different diet than the adults. You’d expect if the animals were pack hunters like wolves, that the young would be eating whatever the adults were. This was not the case.
Now there could be data unearthed to re-support the pack hunting hypothesis, or we could be looking at the data wrong. Perhaps the adults caught and fed the juveniles smaller prey until they were capable of joining the pack in a hunt. Or perhaps young dromeosaurs hunted for themselves until they came of age and assembled a pack as adults.
Everything with dinosaurs is fickle and subject to change, but there’s a lot that can be learned just from the evidence left behind by the fossils.
Hope that clears some things up. Cheers!
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