The Origin and Evolution of Vertebrates Lecture 21 PDF

The Origin and Evolution of Vertebrates Lecture 21 Chapter 34 Last class Most forms of animal life are Invertebrates Animals are classified into major groups by developmental patterns and derived features of each lineage Left off at chordates are deutero...

The Origin and Evolution of Vertebrates Lecture 21 Chapter 34 Last class Most forms of animal life are Invertebrates Animals are classified into major groups by developmental patterns and derived features of each lineage Left off at chordates are deuterostomes... Objective: Identify the major lineages of chordates and describe the unique derived features that distinguish each group. Chordates are a group within deuterostomes Derived traits include: Notochord Dorsal Hollow Nerve Cord Pharyngeal Slits Post-anal Tail Chordates are a group within deuterostomes. Four derived traits include: 1. Notochord. \ Structure: A flexible, rod-like structure made of cells derived from the mesoderm, surrounded by a sheath. Location: Runs along the dorsal side, below the nerve cord and above the digestive tract. Function: Provides structural support and serves as an axis for muscle attachment. Development in Vertebrates: replaced by the vertebral column (spine) in adults Chordates are a group within deuterostomes. Four derived traits include: 2. Dorsal Hollow Nerve Cord. \ Structure: A tube-like, hollow structure running along the back (dorsal side) of chordates. Development: Forms from an infolding of ectoderm that rolls into a neural tube. Location: Positioned above the notochord. Function in Vertebrates: Develops into the brain and spinal cord, forming the central nervous system. Chordates are a group within deuterostomes. Four derived traits include:. 3. Pharyngeal Slits or Clefts \ Structure: Openings or grooves in the pharynx, the region just behind the mouth. Development: Form during embryonic development of endoderm, but mesoderm and ectoderm contribute to structure Function: gills for respiration in aquatic species, contribute to structures like the ear and throat in terrestrial chordates Chordates are a group within deuterostomes. Four derived traits include: 4. post-anal tail. Structure: An extension of the body \ beyond the anus, composed of muscles and skeletal elements. Location: Positioned at the rear of the body, posterior to the anus. Function: Provides propulsion in aquatic species and balance, signaling, or other roles in terrestrial species. Development in Vertebrates: May be reduced or vestigial in some adults (e.g., "tail bone in humans) Lancelets and tunicates are chordates that lack a backbone Vertebrates have a backbone (and more features) Derived traits of vertebrates Vertebral Column (Spine): A backbone made of vertebrae that surrounds and protects the spinal cord (takes over role of notochord). Endoskeleton: An internal skeleton made of bone or cartilage. Cranium (Skull): A protective structure for the brain. Complex Nervous System: Includes a well-developed brain and spinal cord. Closed Circulatory System: Blood circulates through vessels, usually with a heart. Neural Crest: A group of cells unique to vertebrates that contribute to the development of various structures, including parts of the nervous system, skull, and heart.  Overview of vertebrate evolution and key characteristics Vertebrates: hagfishes and lampreys Lack jaws Rudimentary backbone of cartilage not bone! Chordates > Vertebrates > Chondrichthyes (sharks, rays and relatives) Evolution of jaws and mineralized (bony) skeleton Gnathostomes have jaws that likely evolved from modified gill-supporting skeletal rods Chordates > Vertebrates > Chondrichthyes (sharks, rays and relatives) Cartilaginous Skeleton: Skeleton made of cartilage, with some areas calcified (e.g., jaws, vertebrae). Paired Fins: Pectoral and pelvic fins for stability and mobility; males have claspers for sperm transfer. Electroreception: Specialized sensory organs called ampullae of Lorenzini detect weak Placoid Scales: Tooth-like scales reduce water electrical fields generated by other organisms. These resistance and provide protection. organs, located on the head and around the snout, help locate prey, navigate, and sense environmental Gill Slits: Five to seven slits on the sides of the changes, even in murky water or complete darkness. head for respiration.  Osteichthyans (bony fish) include Ray-finned fishes and lobed finned fishes Osteichthyans Bony Skeleton: Skeleton made of bone. Swim Bladder: Most have a swim bladder for buoyancy, some have lungs. Scales: Covered in cycloid or ctenoid scales for protection and reduced drag. Operculum: Bony gill cover for protection and respiration. Paired Fins: Pectoral and pelvic fins for movement and balance. Osteichthyans (bony fish) include the three lineages : Actinopterygii (ray-finned fish) Actinistia (coelacanths) (lobed-finned fish) Dipnoi (lungfish) (lobed-finned fish)  Actinopterygii (ray-finned fish) Ray-finned fish have: fins supported by thin, flexible rays a swim bladder for buoyancy a streamlined bony skeleton Actinistia (coelacanths) and Dipnoi (lungfish) are lobed-finned fish. Lobe-finned fish have: fleshy, lobed fins with a central bone structure at base, muscle extends into fin may have lungs (ie. lungfish) in addition to gills, possess a more robust, bony skeletal structure Tetrapods are Gnathostomes that have four limbs. Other derived traits of tetrapods include: Limbs with Digits: Limbs evolved into strong, weight-bearing structures with distinct digits (fingers or toes), replacing the lobed fins. Lungs: Adaptation for breathing air with well-developed lungs; most tetrapods are adapted for terrestrial life, although some (like amphibians) still rely on gills during part of their life cycle. Neck: The development of a neck, allowing for independent head movement, is a key feature that differentiates tetrapods from fish. Strong, Modified Skeleton: The evolution of a stronger, modified skeleton, including adaptations like a robust pelvic and pectoral girdle, to support life on land. Tetrapods > Amphibians Moist Skin: Thin, permeable skin for gas exchange and moisture retention. Metamorphic life cycle: from aquatic larvae (with gills) to terrestrial or semi-aquatic adults (with lungs). Ectothermy: Cold-blooded, relying on external heat sources for temperature regulation. Simple Lungs: Lungs for air breathing; some retain gills or use skin for respiration.  Amnoites are tetrapods that have a terrestrial adapted egg The amnion is a protective membrane that surrounds the embryo, filled with fluid to cushion and prevent desiccation. In contrast to amphibians, the amniotic eggs of reptiles and some mammals have a shell, and protective membranes (amnion, chorion, allantois) that physiologically support the growing embryo. Amniotes also acquired rib cages (supports ventilation of lungs). Reptiles are amniotes with these characteristics: Scaly Skin: Waterproof, keratinized skin covered with scales that prevent water loss and enable survival in dry environments. Reproduction: involves internal fertilization, with fertilization occurring inside the female’s body and a shelled egg being deposited on land Ectothermy: Reptiles rely on external heat sources to regulate their body temperature (except birds, they are endothermic). Efficient Lungs: Well-developed lungs for air breathing, adapted to terrestrial life. Clawed Limbs: Limbs are often adapted for walking, climbing, or swimming, with claws for traction  Mammals are amniotes that have hair and produce milk other characteristics of Mammals include: Hair/Fur: Provides insulation and helps regulate body temperature. Mammary Glands: Female mammals produce milk to nourish their young. Endothermy (Warm-Blooded): Ability to regulate body temperature internally. Live Birth: Most mammals give birth to live young (with the exception of monotremes, which lay eggs). Three Middle Ear Bones: Ossicles (malleus, incus, and stapes) for enhanced hearing. Mammals are amniotes that have hair and produce milk other characteristics of Mammals include: Specialized Teeth: Differentiated teeth (incisors, canines, molars) for various functions. Vertebral Column: A well-developed backbone that supports the body and houses the spinal cord. Advanced Brain: A larger, more complex brain, especially the neocortex for higher-order functions. Advanced Kidneys: Efficient kidneys for water conservation and excretion of urea. Fat Layer: Subcutaneous fat that provides insulation and energy storage. Extended Prenatal Care: Longer gestation periods and extensive parental care after birth. Monotremes are mammals that lay eggs A characteristic of ancestral amniotes (retained in most reptiles) Have hair but no nipples, milk is secreted from a gland on the abdomen of the mother- young suck milk from fur. Marsupials are mammals that do not lay eggs, they give birth to live young and have nipples. Animals in this group also have: Placenta, that supports the developing embryo, but it is simpler and less developed than the next group of animals we will talk about Pouch or external development: After birth, the underdeveloped young continue their development in a pouch (in species like kangaroos and koalas) or attached to the mother's abdomen, where they nurse and grow.  Eutherians are Long Gestation: Extended pregnancy allows for more Placental Mammals developed offspring at birth. Orca: 17 months gestation Placenta: A complex structure that enables nutrient, gas, and waste exchange between mother and embryo. Live Birth: Eutherians give birth to relatively developed young after longer gestation. Elephant: 22 months gestation No Pouch: Offspring are not carried in a pouch but are nurtured post-birth. Advanced Organ Systems: Eutherians have more specialized and efficient organ systems for survival in diverse environments. Primates are Eutherians with these derived features: Grasping Hands/Feet: Opposable thumbs/toes for gripping. Forward-Facing Eyes: Binocular vision for depth perception. Large Brain: Enhanced cognitive abilities. Flat Nails: Instead of claws, for better grasping. Flexible Limbs: Wide range of motion for climbing. Social Behavior: Complex group dynamics. Extended Parental Care: Longer care and dependency of offspring.  Bipedalism: Walking upright on two Humans are primates with: legs. Larger Brain: Particularly a large neocortex, which is involved in complex thought, reasoning, and problem-solving. Language: Ability to use complex language for communication. Tool Use: Advanced use of tools and technology for survival and manipulation of the environment. Reduced Jaw and Teeth Size: Smaller teeth and jaw compared to other primates, reflecting a shift in diet and use of tools for food preparation. Larger, More Complex Social Structures: Highly developed social and cultural behaviors, including artistic expression In Summary Deeper nodes in the animal tree of life define animals by embryonic development and each lineage acquired novel derived characters throughout evolution Not all chordates are vertebrates The evolution of skulls and backbone, jaws and calcified bones, lobed fins, limbs with digits and amniotic eggs are all key evolutionary events that explain the evolution of different animal lineages To Read for Next Class Chapter 53 Population Ecology Chapter 54 Community Ecology