#tetrapod

Tyrannoroter heberti lived in a lush tropical coal forest covering what is now Nova Scotia, Canada during the late Carboniferous, about 307 million years ago.

It was a member of the pantylid family in the recumbirostran lineage, a group of tetrapods whose evolutionary relationships are still a little uncertain. Traditionally they were classified as lepospondyl "amphibians", but more recently some studies have found them to be either very early sauropsids or convergently reptile-like stem-amniotes.

Known only from a partial skull and jaw, based on the proportions of its pantylid relatives Tyrannoroter was probably around 30cm long (~1') and would have resembled a squat lizard with a large blunt triangular head.

It would have had small bony scales within its skin, with interlocking polygonal "armor" on the underside of its jaw and chest, and irregular pebbly scales on other parts of its body. It may also have had claws on its toes, and potentially was capable of burrowing using a combination of its stout limbs and its shovel-like snout.

The roof of its mouth and the inside of its jaw were covered in extensive "batteries" of blunt teeth that show evidence of shearing and grinding motions – suggesting it may have been primarily processing tough plant matter, and making it one of the earliest known herbivorous tetrapods.

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Macroevolution Through Evograms

The origin of tetrapods

The word “tetrapod” means “four feet” and includes all species alive today that have four feet — but this group also includes many animals that don’t have four feet. That’s because the group includes all the organisms (living and extinct) that descended from the last common ancestor of amphibians, reptiles, and mammals. So, for example, the ichthyosaur, an extinct swimming reptile, is a tetrapod even though it did not use its limbs to walk on land. So is the snake, even though it has no limbs. And birds and humans are tetrapods even though they only walk on two legs. All these animals are tetrapods because they descend from the tetrapod ancestor described above, even if they have secondarily lost their “four feet.” Tetrapods evolved from a finned organism that lived in the water. However, this ancestor was not like most of the fish we are familiar with today. Most animals we call fishes today are ray-finned fishes, the group nearest the root of this evogram. Ray-finned fishes comprise some 25,000 living species, far more than all the other vertebrates combined. They have fin rays — that is, a system of often branching bony rays (called lepidotrichia) that emanate from the base of the fin. In contrast, the other animals in the evogram — coelacanths, lungfishes, all the other extinct animals, plus tetrapods (represented by Charles Darwin) — have what we call “fleshy fins” or “lobe fins.” That is, their limbs are covered by muscle and skin. Some, such as coelacanths, retain lepidotrichia at the ends of these fleshy limbs, but in most fleshy-finned animals these have been lost...