What is the first bilateral animal?
The first bilateral animal fossil is Vernanimalcula ("Small Spring Beast"), a simple metazoan that lived 580 and 600 million years ago during the edition period. Vernanimalcula was discovered in 2005 in a phosphatic fossil deposit in the Chinese province of Guizhou, which was called Doushantuo formation. Phosphatic fossils are extremely detailed, with microscopic function, allowing analyzes impossible with other fossil types. A minority of scientists argues that Vernanimalcula is a tafonomic artifact caused by the intrusion of phosphate into an inorganic or unicellular spherical object, but most consider it a true fossil of bilateral animal.
Most animals are bilateral, which means they are symmetrical around the central axis. Exceptions include mushrooms that have no symmetry, Cnidarians (jellyfish and relatives) that have radial symmetry, and several echinoderms (star and relatives) with pentaradial symmetry, but it evolved from bilateral ancestors. The restThey are bilateral.
Vernanimalcula is small (0.1 - 0.2 mm) fossil in the shape of an oval. It has a mouth, intestines and several surface pits that can be sensory organs. If it is a real animal and not a taphomic artifact, Vernanimalcula would have several hundred cells. It could have been eutelic, like many modern microfaunas, which means that every adult had the same number of cells and only increased as the cells spread. Vernanimalcula is considered tribroblastic, which means, like most modern animals, its body consisted of three layers, ectoderm, mesoderm and endoderm.
The discovery of early bilateral animals, such as Vernanimalcula , taught some interesting facts about the development of bilateral animals in general. First, Vernanimalcula is Coelomat, which means it has a cavity of the body. This is proof that Coelomats was the first mThe legs and akoelomates (as non -atures) have evolved from coelomates rather than vice versa.
There are some indirect evidence of triboblastic bilateral animals 600 million years ago, in the form of trace fossils from India and a decrease in microbial towers called Stromatolites billion years ago, indicating the possible presence of grazing organisms, which can be bilateral animals.