A new research has identified a sperm-resembling creature called monosiga as the closest living surrogate to the ancestor of all animals.
The study determined that Earth may have given rise to two distinct groups of animals: bilaterians - animals with bilateral symmetry, like humans - and non-bilaterians, which include corals, jelly fish, hydra, unusual, often poisonous, creatures known as cubozoans, and other organisms.
Free-living, unicellular organisms called choanoflagellates, however, could be on every person’s family tree, so long as it was a gigantic one.
“It is clear that the choanoflagellates - living representative is monosiga - are the best candidate for the nearest relative of animals,” research co-author Rob DeSalle told Discovery News.
“So, a choanoflagellate-like organism could be looked at as a probable common ancestor for animals,” added DeSalle, curator at the Sackler Institute for Comparative Genomics at the American Museum of Natural History.
He and his colleagues compiled data from multiple gene sequences derived from many sources to find over 9,400 variable characters that contain parsimony information, which collectively refers to the shared, derived traits that help biologists infer species relationships on the tree of life.
They determined that so-called “simple” and “lower” tier animals, such as corals and jellyfish, evolved in parallel to “higher” animals, like seemingly more complex insects and even humans.
On the tree of life, monosiga then currently holds the root position for the latter group.
The new research completely shakes up the non-bilaterian animal ordering as well.
Previously, it was thought that either super simple-structured or comb jellies were at the root of the non-bilaterian animal tree. Instead, complete outsiders - placozoans - have been placed in that basal position.
First discovered gliding along glass in laboratory aquariums just over 100 years ago, placozoans are animals that lack a nervous system and possess four types of body cells.
“Placozoa, because of their simple body plans and their position in our tree, are a good candidate for the common ancestor of non-bilaterian animals,” DeSalle explained.