You can use a stegosaurus to gather woods, using the heavy plates mode. They don't have weight reduction, however, they have a lot of weight. Moreover it gathers so much wood! It's amazing, I have a stego named Stella and every tree give me almost 100 woods and she can hold between 800 to 700 woods inside it's inventory.
Even though Casteroids are better at collecting wood, mammoths can carry so much more, and have higher weight reduction. They also move faster and have a larger attack range. When gathering wood on a mammoth, I personally have found that it’s stomp, or left trigger (Xbox) attack gathers more than its main attack
Although they don't have weight reduction Theris are extremely fast gatherers. I gather wood with my Theri and have a beaver following so that when my Theri gets encumbered I just throw it all on the beaver.