The unique chordate body plan evolved within the deuterostome animals sometime before the Cambrian (Valentine, Jablonski, and Erwin 1999; Blair and Hedges 2005). Nerve cords in hemichordates and chordates evolved … 1. Base of Chordates Phase 3: Origin of … Myomeres/segmentation Distinctly "Craniate-looking" circulation Base of Cephalochordates and Craniates Early Chordate Evolution. They may have evolved from some freshwater forms as Chamberlain (1900) pointed out that all modern chordates … Chordate - Chordate - Evolution and paleontology: Many scientists maintain that chordates originated sometime earlier than 590 million years ago; that is, they predate the fossil record. ORIGIN OF CHORDATES (Suneel Singh) SUMMARY Chordates evolved sometime during Cambrian period, 500 million years ago during Cambrian explosion, almost at the same time when invertebrates were beginning to evolve. ECHINODERM -HEMICHORDATE THEORY-ORIGIN OF CHORDATES: This theory infers origin of chordates, hemichordates and echinoderms from a common ancestor. THE ORIGIN OF CHORDATA. 3. 1. Introduction. Download Citation | On May 1, 2001, Noriyuki Satoh and others published Origin and evolution of chordates | Find, read and cite all the research you need on ResearchGate. Chordates are animals characterized by the possession of a notochord, a dorsal neural tube, somites, pharyngeal gills, an endostyle, and a postanal tail. The following special pages in this volume are of memoirs for an international workshop on “Origin and Evolution of Chordates” organized by … Chordates have also been … As a result of further investigations, the … Such early representatives were soft-bodied and therefore left a poor fossil record. This theory is based on the following evidences. Preface. COELENTERATE THEORY-ORIGIN OF CHORDATES : According to this theory chordates were developed from … This book discusses the origin and evolution of chordates. Three schemes for evolution of the chordate and hemichordate nerve cords. This is the Garstang’s theory. The ‘Hydroskelett-Theory’ (Gutmann 1972) was the first coherent model for chordate evolution, based on the principles of engineering and constructional morphology. Chordates traditionally include vertebrates, lancelets (cephalochordates), and tunicates, but tunicates do not exhibit a chordate … Then, chordates were thought to have evolved from an ancestral chordate tadpole larva that underwent paedomorphosis and now retains adult characteristics with the larval tail . The oldest known fossil chordate … HYPOTHESES ON THE ORIGIN AND EARLY EVOLUTION OF CHORDATES 101 erous conodonts were clearly active swimmers and ap-pear to have a short non-metameric region at their fore a) EMBRYOLOGICAL EVIDENCE -ORIGIN OF CHORDATES: Both echinoderms and chordates have enterocoelic coelome, mesoderm and deuterostomous mouth. Since Charles Darwin proposed the evolution of animals by means of natural selection [], the origin and evolution of chordates from common ancestor(s) of deuterostomes have been investigated and discussed for more than 150 years [2–20].Chordates consist of three distinct animal groups: cephalochordates, urochordates (tunicates) and vertebrates. (a) The ancestor of chordates and ambulacrarians had a nerve net. Before focusing on the origin of the Craniata, let me mention the most accepted theory to explain the origin of chordates, which resulted in Craniata and vertebrates. The origin of … Many biology theories were put forward to explain the Origin of Chordates.