Question

Name three characters that vertebrates share with other chordates as well as three characters that evolved as novelties in the ancestors of vertebrates. Discuss the embryonic origin of these vertebrate specific characters and explain which changes in life style they made possible.

Answer 1

Phylum chordata possess 4 unique characteristics:

1. Dorsal hollow nerve cord which is formed from a dorsal ectoderm tube. It forms the central nervous system (CNS)
2. Notochord is located between nerve cord and gut. It is a simple endoskeleton in chordates.
3. Pharyngeal Slits : In early chordates it is used for filter feeding later it is modified for gas exchange.
4. Postanal Tail : It s a skeletal extension of the posterior end of the body and it extends beyond the anus.It contain muscles and skeletal elements.

As chordates, vertebrates also posses these 4 unique characteristics during embryonic stage and later these characteristics will undergo development. But the three basic characteristics that vertebrates share with other chordates are dorsal hollow nerve cord, notochord and pharyngeal slits.

If we come with the evolution of vertebrate from early chordates . Then we have the

• Notochord which develops into a vertebral column (with a bony vertebrae separated by discs) in vertebrates.
• Dorsal hollow nerve cord develops into CNS containing brain (which is enclosed by skull) and spinal cord.
• Pharyngeal Slits developed as gills in bony fishes and jaws and inner ear for terrestrial animals.
• The post-anal tail which is present in the embryonic stage is absent in humans and apes during further development.

Phylum chordata has three subphylums

• Urochordata

• Cephalochordata

• Craniata

Both genomic and fossil evidence suggests that vertebrates evolved from craniates. Vertebrates posses the characteristic triat from the craniates that they have a cranium (made up of bone and cartilage) to surround brain, jaw and facial bones.

Other additional characteristics vertebrate includes are

• a closed circulatory system containing heart , arteries, capillaries and veins.
• Red blood cells for oxyen transport
• Respiratory system including lungs or gills.