Vertebrates evolution

• Hox genes are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis
• Craniates wirh backbones - have two or more gene duplication events, including the Dlx family of transcription factors
• Neural crest cells are a bilateral border of cells in craniates
• Myxini- Hagfishes, a basal group of craniates, have a skull made of cartilage
• Detromyzontida - Lampreys represent the most basal lineage of vertebrates, with 35 species inhabiting marine and freshwater.
• Conodonts, with cone teeth, are considered early vertebrates and lived in during the late Cambrian to Triassic periods
• Chordates share common characteristics:

  • All chordates have a notochord ●composed of large fluid-filled cells encased in fairly stiff, fibrous tissue
  • Dorsal hollow nerve cord
  • Pharyngeal slits or clefts
  • Muscular post-anal tail
• Cephalochordates, like lancelets, are the most basal (earliest diverging) group of living chordates
• Urochordates, commonly called tunicates or sea squirts, are sessile animals
• Craniates- chordates with a head or brain, and possesses two or more hox gene
• Somites: are segnmmetal axial structure.
• Myllokunmingia Fengjia: is among the oldest possible craniates, found in the lower Cambrian Chengjiang (518 million years ago)
• Aquatic environment: 395 ma

  Transitional period: 340 ma

  Terrestrial environment: 315 ma
• Chordates: Bilateral symmetry, segmented body, notochord, notochordal placode. Belong to clade of animals known as deuterostomia.
• Notochord is composed of large fluid-filled cells enclosed in fairly stiff, fubrous tissue.
• Deuterostomes have anus first, mouth second.
• Protostome has mouth first, anus second.
• Dorsal hollow nerve cord: contains the spinal cord and nerves that carry sensory information to the brain
• Pharyngeal slits or clefts are the openings between the pharynx and the nasal cavity
• Muscular, post-anal tail: tail that extends posterior to the anus.
• Craniates derived characters: neural crest( Bilateral bonds of cells)
• Origin if craniates: 3 cm long Haikoulla ( discovered in 1999: china)
• Vertebrates with additional innovations emerged during Ordovician, Sulirian, and Devonian Period.
• Majority of early vertebrates lived in shallow marine environments.
• The first vertebrate fossils were found in the Cambrian period.
• Lampreys are parasitic jawless fishes that attach themselves to other animals using suction cups on their mouths.