In this lesson we take you back to the beginning of the Phanerozoic Eon to learn what it truly means to have backbone, as we encounter the key anatomical features of vertebrates and their closest chordate relatives. We’ll also introduce the language of evolution – phylogenetics – as we examine some of the contenders for the title of ‘The Earliest Vertebrate’, and give you a crash course in sedimentology, so you can begin to piece together the spectacular environments that were home to our early aquatic ancestors. Just a quick note before you get started: 'Palaios' is the Greek word for 'ancient', so palaeontology or paleontology is the study of ancient life. Both spellings are correct, with palaeontology used in Britain, and paleontology more common in the US.