Tom Holtz recently (IHHO in his humble opinion) listed ideas on hot to confirm a theropods arboreality. These are good ideas. One I think once done and shown theropods could have climbed trees would then require even more tests and ideas and so on and so on because of the terrestriality bias. What needs to be done is to stop Pigeon hole nature into arboreality, but nature will prove us wrong.
There has been a recent study on island endemic lizards (I didn’t copy the article but I know the series that it was in. I wish I had copied it.) showed that terrestrial and arboreal lizards of the same genus (?, or was it species?) did not show any skeletal differences. If it was found in a quarry it would have been interpreted as being terrestrial. Komodo monitors will climb trees until it reaches a length of 6 feet. They also show arboreality in their skeletons. Bears climb, a certain goat can climb trees, dogs, squirrels, etc, but their skeletons don’t show this. What about the pelycosaurs _Varanosaurus_ and _Aerosaurus_? They are about the size of a small Komodo monitor, could they climb trees?
With theropods there is a terrestrial bias, and placing a theropod in a tree gets laughed at. I’ll admit that I was one who laughed at the idea. Greg Paul had put on _Ornitholestes_ in a tree and I thought yea right. But maybe he’s right. I’ll have to look at it more closely. What about dromaeosaurids? Could they have climbed trees? This is something I’m working on and a few others. Will that be accepted? Probably not. A _Deinonychus_ is bigger than a Komodo monitor but would have been lighter. Why must theropods be put through a more rigorous testing than other animals? Terrestrial bias is why.
There are some animals that arboreality is not questioned. _Kuehneosaurus, Icarosaurus, Coelurosauravus_ with there long ribs are believed to have been gliders so it had to climb trees to have something to glide from. No big tests needed.
There is a preconceived notion on what an early bird would look like. But when one is found in the Late Triassic it is considered to be a composite because it doesn’t fit that preconceived notion. I’ve talked to Sanker and the person who excavated _Protavis_. I believe them that it is just one genus in the block. I bet even if a totally intact, articulated specimen, it will still be thought of as a composite animal.
The opposite is true for _Rahonavis_. It is a long tailed bird that is older than Archaeopteryx. Some believe that this is a composite animal. With the bird_Vorona_ and a theropod. There are three reasons why this is wrong. 1). The _Vorona_ is two big for _Rahonavis_ arms. 2). There is a sauropod skeleton in between the two and most importantly _Vorona_ is from a lower bedding plain. There were long tailed birds in the Mesozoic, but since they do not fit the idea of a bird, then it is considered to be a composite. Just because the animal doesn’t fit a preconceived notion doesn’t mean it is a composite. Trees are a niche that was filled and it should be considered.
What about burrowing animals? We know _Thrinaxodon_ and _Cistecephalus_ were burrowers because they were found in burrows. Bakker says Drinker was found in a burrow, but does anyone believe him? Not many, because he’s Bakker. There are some things that Bakker says that I disagree with, but this I think he may be right. Also _Protoceratops_ is now considered by a few to have been a burrower. Just because Bakker says it doesn’t mean that we should just dismiss it.
So there were niches during the Mesozoic that was filled, in trees and in the ground, that needs to be thought about and not forgotten. Just because an animal doesn’t fit a preconceived notion, it doesn’t mean that it is a composite. We need to have a more open mind for what animals could have done.