Cladistically (phylogenetically), vertebrates – chordates with the notochord replaced by a vertebral column during development – are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull. However, while lampreys are vertebrates, hagfish are not. At some time in their life, chordates all possess a stiff rod, called a "notochord". These fish are also characterised by the absence of paired fins. Here are various groups of vertebrates in the order in which they evolved. There are a few groups of chordates that do not possess a backbone (these organisms are not vertebrates and are instead referred to as invertebrate chordates). The vertebrate ancestor no doubt had more arches than this, as some of their chordate relatives have more than 50 pairs of gills. jawless fishes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals Vertebrate chordates all possess a cranium (braincase) that protects the brain. Vertebrates are a well-known group of animals that includes mammals, birds, reptiles, amphibians, and fish.The defining characteristic of vertebrates is their backbone, an anatomical feature that first appeared in the fossil record about 500 million years ago during the Ordovician period. The bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. Some taxicologists are … Animal Kingdom Chordates Tunicates Lancelets Vertebrates Jawless fish Cartilaginous fish Bony fish Amphibians Reptiles Birds Mammals Invertebrates Gills Gill filament Figure 3 Gas exchange occurs in the gill filaments. On the other hand, fossils of early chordates are very rare, since invertebrate chordates have no bones or teeth, and only one has been reported for the rest of the Cambrian. This is a superclass of around 100 species of jawless fish. While there is a fossil record for these ancient relatives of ours, there are, amazingly, also examples of invertebrate chordates still alive today. Bodies completely covered with bony armor plates 4. Jawless fishes—the hagfishes and lampreys—have a distinct cranium and complex sense organs including eyes, distinguishing them from the invertebrate chordates. In addition to the lack of jaws agnathas can also be categorized by their lack of fins, the presence of a dorsal notochord. fish The vertebrates have a nebulous starting point. Agnatha (Ancient Greek ἀ-γνάθος "no jaws") is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species.The group is sister to all vertebrates with jaws, known as gnathostomes. Jawless Fishes Jawless fishes are craniates that represent an ancient vertebrate lineage that arose over one half-billion years ago. Small jawless fish 2. Agnatha which means "without jaws" are a superclass which is made up of an assortment of fish that are jawless. Early examples include Haikouichthys. Fishes were the earliest vertebrates, with jawless species being the earliest and jawed species evolving later. They are active feeders, rather than sessile, suspension feeders. Bony skeleton, including vertebrae 3. Jawless fishes—the hagfishes and lampreys—have a distinct cranium and complex sense organs including eyes, distinguishing them from the invertebrate chordates. Ate sea-floor invertebrates 5. 1) invertebrate chordates; tunicates & lancelets (lack backbone or cartilage) 2) vertebrate chordates; jaw less fish,cartilaginous fishes,bony fish, amphibians, reptiles, birds & mammals; all have cranium, … Members of the agnatha class are probably the earliest vertebrates. Invertebrate ancestor Vertebrae Jaws and paired appendages Lungs Four limbs Amniotic egg y toads anders s s Birds ls -shes and ians Endothermy Nonvertebrate chordates Jawless fishes Cartilaginous fishes Bony fishes Amphibians Reptiles Birds Mammals