Vertebrates 1

Vertebrates 1 - Vertebrates 1: Chordates, vertebrates and...

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Unformatted text preview: Vertebrates 1: Chordates, vertebrates and tetrapods Represented in early fossil record Chordate Roots 530 MYA Chordate-like fossils from China are ancestral “missing links” between invertebrates & vertebrates Haikouella FIGURE 34.8 Similar to lancelets but appeared to have a larger brain and eyes. No cranium FIGURE 34.1 Present but rare in Burgess Shale. Segmented body & tentacles 1.5 inches long Piakaia Chordate Phylogeny Brain and cranium evolve first in the vertebrate lineage The vertebral column follows The jaws, ossified skeleton, and paired appendages evolve later Phylogeny consistent with the early Cambrian fossils in Chinese strata Figure 34.2 Phylum Chordata Vertebrates , animals with backbones, are members of the phylum Chordata Chordates are bilaterally symmetrical and members of the Deuterostomia Deuterostomia includes echinoderms Chordata includes two subphyla of invertebrates, cephalochordates and urochordates , that are more closely related to vertebrates than invertebrates Chordate characteristics Four key features of chordate anatomy Figure 34.3 – Notochord – Dorsal, hollow nerve cord – Pharyngeal slits – Muscular, post-anal tail Notochord The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord It provides skeletal support throughout most of the length of a chordate In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord Dorsal, Hollow Nerve Cord The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord The nerve cord develops into the central nervous system: the brain and the spinal cord Pharyngeal Slits or Clefts In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body Functions of pharyngeal slits : – Suspension-feeding structures in many invertebrate chordates – Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods) – Develop into parts of the ear, head, and neck in tetrapods Muscular, Post-Anal Tail Chordates have a tail posterior to the anus In many species, the tail is greatly reduced during embryonic development The tail contains skeletal elements and muscles It provides propelling force in many aquatic species Subphylum Cephalochordata Figure 34.4 2 cm Lancelet Branchiostoma floridae Subphylum Urochordata Also known as Tunicata , tunicates or sea squirts Two siphons Filter-feeding Figure 34.5 Tunicates, Adult Animals without Backbones A Vertebrate-Like Larva The tadpole larva swims until it attaches to a surface by its head and undergoes metamorphosis , during which most chordate characteristics (nervous system & notochord) disappear Figure 34.4c Hox Genes & Brain Evolution Craniates are chordates that have a head Distinct skull contains a brain at the anterior end of the dorsal nerve cord, eyes and other sensory organs Enables chordates to coordinate more complex...
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Vertebrates 1 - Vertebrates 1: Chordates, vertebrates and...

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