5-Chordate_and_Vertebrate_Phylogeny_2023W1-POST__1_

Lesson Outline

• Introduction to Phylogeny

• Chordate Characteristics

• Chordate Phylogeny

• Vertebrate Phylogeny and Evolution

• References:

  • (7th Edition) Chapter 2: p. 48-79

  • Chapter 3: p. 86-89, 94-126

  • Chapter 7: p. 242-250

  • (6th Edition) Chapter 2: p. 48-74

  • Chapter 3: p. 86-89, 94-127

  • Chapter 7: p. 241-249

  • (5th Edition) Chapter 2: p. 47-73

  • Chapter 3: p. 84-87, 92-102

  • Chapter 7: p. 235-243

Learning Outcomes (Lecture 5)

• Determine classification of unknown organisms as chordates.

• Classify an unknown vertebrate based on morphological and physiological features.

• Explain how key vertebrate characters (e.g., cranium, jaws, paired fins) shaped the lifestyle and diversity of vertebrate taxa.

Chordate Phylogeny

• Chordates belong to the Phylum Chordata.

• Chordates are classified as deuterostomes.

• Phylum Chordata includes three subphyla:

  • Cephalochordata

  • Urochordata

  • Vertebrata

Chordate Characteristics

• All chordates exhibit a common body plan with the following five characteristics present at various developmental stages:

  1. Dorsal hollow nerve cord

  2. Notochord

  3. Pharyngeal slits

  4. Post-anal tail

  5. Endostyle (homologous to the thyroid gland in vertebrates)

Dorsal Hollow Nerve Cord

• Likely a synapomorphy for chordates.

• A hollow structure dorsal to the digestive tract, arising from ectoderm during embryonic development.

• Central nervous system formation, including brain and spinal cord.

Notochord

• A rod with a core of cells and fluid, surrounded by a fibrous sheath.

• Provides structural support; capable of bending without compressing.

• Functionally replaced by vertebral column in many vertebrates during development.

Pharyngeal Slits

• Openings in the pharynx, significant during development in all chordates.

• Synapomorphy for deuterostomes—often covered in terrestrial vertebrates prior to birth or hatching.

Post-anal Tail

• A synapomorphy that is a posterior extension of the body beyond the anus.

• Contains myomeres, contributing to muscle segmentation.

Endostyle

• A groove in the pharynx that produces mucus and processes iodine.

• Homologous to the thyroid gland in vertebrates.

Chordate Problem Examples

1. Differentiate between notochord and dorsal hollow nerve cord; identify true statements regarding their differences.

2. Phylogenetic tree analysis to locate various chordate synapomorphies.

Urochordata and Metamorphosis

• Urochordata includes species like sea squirts.

• Metamorphosis from a larval stage (with noticeable chordate characters) to a sessile adult.

Hemichordates and Echinoderms

• Hemichordates are classified as "half chordates" due to shared characteristics like pharyngeal slits.

• Molecular evidence supports grouping them with echinoderms under the concept of Ambulacraria.

Vertebrate Phylogeny and Evolution

• Major groups: Agnatha, Gnathostomata, Tetrapoda, Amniota.

• Key Features:

  • Evolution of the vertebral column differentiates ancestral vertebrates from other chordates.

  • Development of a cranium benefits early vertebrates by enhancing protection and feeding efficiency.

  • Muscular pharyngeal pump evolution improves feeding methods significantly.

Types of Vertebrates

• Agnathans (jawless vertebrates, e.g., hagfish, lampreys).

• Gnathostomes (jawed vertebrates; includes cartilaginous and bony fish).

Important Terminology

• Protostomes, Deuterostomes, Echinoderms, Chordata, Urochordata, Cephalochordata, Vertebrata.

• Specific groups within vertebrates such as: Myxinoidea, Petromyzontida, Chondrichthyes, Osteichthyes, Amphibia, Testudines, Lepidosauria, Archosauria, Aves, Mammalia, Monotremata, Metatheria, Eutheria.

Summary of Phylogenetic Relationships

• Overview of vertebrate classification.

• Discussion on the evolution of characters and the implications on vertebrate lifestyle and diversity.