Vertebrates and invertebrates are two main divisions inside the kingdom Animalia, differentiated generally by the existence or absence of a spine. Este estado hipotético se ha denominado blastaea, y se cree que es el reflejo del estado de blástula que se develop en el desarrollo de todos los animales. Por tanto, esta teoría considera que los an

Some palaeontologists have advised that animals appeared Considerably previously than the Cambrian explosion, perhaps as early as 1 billion years ago.[102] Early fossils that might stand for animals surface as an example from the 665-million-year-outdated rocks of the Trezona Formation of South Australia. These fossils are interpreted as most proba