The most primitive ancestor of the class may be it or its close relative, Saccorhytus. Saccorhytus Chinese called the crisscross cyst, was a small animal that lived in the Ediacaran ocean 540 million years ago. This is the earliest known hindomour, and its body length is only about 1 mm. It does not have an anus, the residue of the food it eats after digestion still has to be discharged from its mouth, and its way of digesting and digesting food is somewhat similar to that of jellyfish, but it is indeed the earliest hindquarter.
The reason is that the four pairs of conical holes in its body prove that it is a posterior mouth animal. It looks a bit like an embryo, like the early forms of our human development in the mother's womb. We humans are also part of the post-mouth animals. So what is a posterior mouth animal? Posterior-mouthed animals are those that have an responsible for eating and an anus responsible for excretion.
Biological classification of our human beings:
Neobial total domain - Eukaryote domain - Single flagellate - Animal general domain - Animal kingdom - True prozoozoic sub-boundary - Bilateral symmetrical organisms - Posterior mouth animal general phyla - Chordate phylum - Vertebrate subphylum - Submaxillary gate - Telebony fish high order - Meatfin fish general order - Lungfish tetrapods - Tetrapods - Tetrapods - Reptiles - Amnioids - Arch order - Theropods - Cannithopods - Suborder Cannithopods - Mammals - Mammals - Euphrasans - Northern Mammals - Primates - Primates - Homo sapiens - Homo sapiens.
Students who like to eat bony fish, that is to eat cousins Oh, the big rebellion ah (sharks eat casually, they are cartilaginous fish, our enemies, of course, the national second-level protected animal great white shark or do not eat, otherwise you will have to sit in jail Oh! ）