Although it is not known with certainty what caused their extinction, a great deal is known about the anatomy of the dinosaurs, given the preservation of skeletal elements in the fossil record. Currently, a number of vertebrate species face extinction primarily due to habitat loss and pollution.
According to the International Union for the Conservation of Nature, more than 6, vertebrate species are classified as threatened.
Amphibians and mammals are the classes with the greatest percentage of threatened species, with 29 percent of all amphibians and 21 percent of all mammals classified as threatened.
Attempts are being made around the world to prevent the extinction of threatened species. For example, the Biodiversity Action Plan is an international program, ratified by countries, which is designed to protect species and habitats. Figure 1. However, a few vertebrates have secondarily lost their vertebrae and, instead, retain the notochord into adulthood e. Vertebral column : A fossilized skeleton of the dinosaur Diplodocus carnegii shows an extreme example of the backbone that characterizes vertebrates.
Vertebrates are also the only members of Chordata to possess a brain. In chordates, the central nervous system is based on a hollow nerve tube that runs dorsal to the notochord along the length of the animal.
In vertebrates, the anterior end of the nerve tube expands and differentiates into three brain vesicles. Vertebrates are the largest group of chordates, with more than 62, living species. Vertebrates are grouped based on anatomical and physiological traits. Tetrapods can be further divided into two groups: amphibians and amniotes.
Amniotes are animals whose eggs are adapted for terrestrial living; this group includes mammals, reptiles, and birds. Amniotic embryos, developing in either an externally-shelled egg or an egg carried by the female, are provided with a water-retaining environment and are protected by amniotic membranes. Privacy Policy. Skip to main content. Search for:. Characteristics of Chordata Animals in the phylum Chordata share four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
Learning Objectives Identify the key features of the chordates. Key Takeaways Key Points These characteristics are only present during embryonic development in some chordates.
The notochord provides skeletal support, gives the phylum its name, and develops into the vertebral column in vertebrates. The dorsal hollow nerve cord develops into the central nervous system: the brain and spine.
Pharyngeal slits are openings in the pharynx that develop into gill arches in bony fish and into the jaw and inner ear in terrestrial animals. The post-anal tail is a skeletal extension of the posterior end of the body, being absent in humans and apes, although present during embryonic development. Key Terms notochord : a flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine nerve cord : a dorsal tubular cord of nervous tissue above the notochord of a chordate pharyngeal slit : filter-feeding organs found in non-vertebrate chordates lancelets and tunicates and hemichordates living in aquatic environments.
Chordates and the Evolution of Vertebrates Chordata contains two subphylums of invertebrates: Urochordata tunicates and Cephalochordata lancelets. Learning Objectives Describe the features and phylogenetic history of lancelets and urochordata. Key Takeaways Key Points Urochordata tunicates and Cephalochordata lancelets are invertebrates because they lack a backone. Larval tunicates Urochordata posses all four structures that classify chordates, but adult tunicates retain only pharyngeal slits.
Larval tunicates swim for a few days after hatching, then attach to a marine surface and undergo metamorphosis into the sessile adult form. Lancelets Cephalochordata are marine organisms that possess all features of chordates; they are named Cephalochordata because the notochord extends into the head. Lancelets may be the closest-living relatives to vertebrates.
The Evolution of Craniata and Vertebrata Both genomic and fossil evidence suggests that vertebrates evolved from craniates, which evolved from invertebrate chordates.
Learning Objectives Explain how genomics informs scientists about chordate evolution. Key Takeaways Key Points The clade Craniata includes animals that have a cranium: a bony, cartilaginous, or fibrous structure that surrounds the brain, jaw, and facial bones.
Members of Craniata include the vertebrates and hagfish. Genomic evidence suggests that vertebrates diverged from cephalochordates lancelets , which had previously diverged from urochordates tunicates.
Fossil evidence suggests that most vertebrate diversity originated in the Cambrian explosion million years ago. Two whole- genome duplications occurred in early vertebrate history.
Key Terms cranium : the part of the skull enclosing the brain, the braincase genomics : the study of the complete genome of an organism Cambrian explosion : the relatively rapid appearance over a period of many millions of years , around million years ago, of most major animal phyla as demonstrated in the fossil record. Characteristics of Vertebrates Vertebrata is a subphlyum of Chordata that is further defined by their bony backbone. Learning Objectives Identify the defining characteristics of vertebrates.
Key Takeaways Key Points As chordates, vertebrates have the same common features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Vertebrates are further differentiated from chordates by their vertebral column, which forms when their notochord develops into the column of bony vertebrae separated by discs. Vertebrates are the only chordates that have a brain as part of their central nervous system.
Key Terms vertebral column : the series of vertebrae that protect the spinal cord; the spinal column chordate : a member of the phylum Chordata; numerous animals having a notochord at some stage of their development; in vertebrates this develops into the spine notochord : a flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine.
Licenses and Attributions. CC licensed content, Shared previously. Evidence suggests that the entire vertebrate genome underwent two duplications, leaving evolution extra copies of each gene to play with. These two whole genome duplications are thought to have driven vertebrate innovation -- the introduction of genetic characteristics unique to vertebrates.
The development of new characteristics relied heavily on new types of gene regulation, which allowed vertebrates to turn specific genes on and off. However, scientists had never connected the dots from genome duplication to these newfound regulatory controls.
By comparing the lancelet to vertebrates, such as the zebrafish, the study authors drew these connections. The researchers found that the lancelet genome contains far fewer regulatory regions than vertebrate genomes, though both contain about the same number of genes. Vertebrate genome duplication may have cleared space for these additions, as genes were lost in the process and left gaps between those left behind.
The remaining genes became subject to tight control over time, and as duplicate genes diverged in function, the scientists hypothesize that different tissues may have started to evolve. The results also revealed a regulatory mechanism in lancelets formerly thought to be unique to vertebrates.
Chemical structures known as methyl groups appear in abundance on vertebrate genomes and regulate the genes they're attached to.
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