25 1 Vertebrate Origins KEY CONCEPT All vertebrates

25. 1 Vertebrate Origins KEY CONCEPT All vertebrates share common characteristics.

25. 1 Vertebrate Origins The phylum Chordata contains all vertebrates and some invertebrates. • Chordates share four features at some stage of development. – notochord – hollow nerve cord tail – pharyngeal slits hollow nerve cord – tail notochord pharyngeal slits

25. 1 Vertebrate Origins • Most chordates lose some or all of these characteristics in adulthood. hollow nerve cord tail notochord pharyngeal slits

25. 1 Vertebrate Origins All vertebrates share common features. • An endoskeleton allows vertebrates to grow to large sizes. – internal – made of bone or cartilage

25. 1 Vertebrate Origins • An endoskeleton can be divided into four parts. – – braincase (cranium) vertebrae bones gill arches (in fish and some amphibians) braincase vertebrae bones

25. 1 Vertebrate Origins • There are seven classes of vertebrates. – Agnatha are jawless fish. – Cartilaginous and bony fish are characterized by the presence of jaws. – Amphibians are characterized by the presence of four limbs. – Reptiles, birds, and mammals are characterized by the presence of an amnion. – Birds are characterized by the presence of feathers. – Mammals are characterized by the presence of hair.

25. 1 Vertebrate Origins JAWS Jaws helped vertebrates to become successful predators. VERTEBRAE Vertebrates have a segmented backbone. Amphibia Mammalia birds mammals Aves amphibians Osteichthyes bony fish Chondrichthyes cartilaginous fish lamprey Agnatha FOUR LIMBS Four limbs let animals move from the water to life on land. FEATHERS Feathers insulate birds from the cold and allow for flight. HAIR Hair helps mammals to maintain constant body temperatures by roviding insulation from the cold.

25. 1 Vertebrate Origins Fossil evidence sheds light on the origins of vertebrates. • Tunicates may be the closest relatives to vertebrates. • The first recognizable vertebrates were jawless fish. • Two groups of jawless fish still exist today. – lampreys – hagfish