Theropod From Triassic Sweden Show Dinosaurs Were Colossal Sizes Early In Its Evolution

First of all, the original article is in Swedish, and the details are acquired using google translate so what I'm about to write might not be 100% accurate, but the general gist of it shouldn't be too far off, especially the data.

So according to folks who translated the original article, the first footprints of a large theropod dinosaur had been discovered as far back as 2015. The footprint was around 80 cm from around 203 million years ago. This would put it in the late Triassic Norian. Dinosaurs have only existed for around 40 million years during that time and didn't completely dominate the planet until after the Triassic/Jurassic extinction that killed off many other reptiles. They had to compete with a lot of carnivores and herbivores. The biggest Rauisuchians (this is the name of a group of carnivores distantly related to dinosaurs and not the name of any specific animal) is estimated to be 8-10 meters (its fossils are incomplete). The biggest carnivorous dinosaur at the time was thought to be around 6 meters. Or so we thought.

Now we have more than just footprints. Scientists have found the bones, more footprints, and even fossilized poo from a very large carnivorous dinosaur from around the same age. No numbers were given, but it's believed to be similar in size to Allosaurus. Allosaurus was around 8-10 meters on average. This is simultaneously a huge shock and also predictable. Why?

Where there are big carnivores, there are even bigger herbivores. We've had the thigh bone of a huge unknown herbivore for a few years now. It's nicknamed Highland Giant. This thigh bone is around the same size as the biggest T. rex, but it's likely from a herbivore similar to sauropodomorphs like Plateosaurus. These aren't professional estimates, but my own speculation. With a femur that big, we could be looking at an 18-ish meter herbivore that's easily over 10 tons. The Highland Giant is obviously no match for the Sauropods of the Jurassic and Cretaceous, but even at around 18 meters, it is colossal! Before this discovery, we thought the biggest herbivores were only around 10 meters (Lessemsaurus) and this is twice the size of that. A big herbivore would require a big predator to hunt it.

Don't get me wrong, I'm not suggesting this new giant predator to be hunting a fully grown Highland Giant. Assuming they had a very wide range and encountered each other, animals aren't stupid. There is no way an 8-10 meter carnivore tackling a full-grown healthy adult Highland Giant. They will still be hunting young animals, sick animals, and old animals. The Highland Giant probably grew that big because once it reaches full size, nothing would dare to attack it. Packing hunting is also out of the question since we have no real evidence of such behavior from this new carnivore. Even pack hunters don't gang up on large healthy adults. Growing big is a viable evolutionary tactic to stay alive. But what if these 2 animals aren't within each other's range? What if they had their own local large-bodied carnivore/herbivore to deal with? Did dinosaurs reach colossal sizes much earlier than we thought?

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