Chordates

DEUTEROSTOMES

  • Definition: Deuterostomes are a group of animals that include echinoderms and chordates, characterized by the development of the blastopore into the anus during embryonic development, and display radial, regulative cleavage.

ECHINODERMATA

  • Common Name: "Spiny skin"

  • Examples: Sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers.

  • Habitat: All members are marine organisms.

ECHINODERMATA SYMPOMORPHIES

  • Pentaradial Symmetry: Symmetrical arrangement of body parts around a central axis, typically five-pointed.

  • Water Vascular System: Unique hydraulic system used for locomotion, feeding, and gas exchange.

  • Tube Feet: Extensions used for grip and locomotion, operating through the water vascular system.

  • Endoskeleton of Calcium Carbonate: Internal skeletal structure that provides support and protection.

TRUE/FALSE: ECHINODERMS STATEMENTS

  1. False: Echinoderms are not bilaterally symmetrical; rather, they exhibit pentaradial symmetry as adults.

  2. False: Movement is primarily facilitated by tube feet, not the calcareous endoskeleton.

  3. False: Not all echinoderms produce dangerous spines; some are harmless.

  4. True: Echinoderms are believed to have evolved from bilaterally symmetrical ancestors.

  5. False: Echinoderms undergo radial regulative cleavage, not mosaic cleavage.

CHORDATA

  • This phylum is highly diverse, containing organisms that exhibit a series of fundamental characteristics during some point of their life cycle:

    1. Pharyngeal Gill Slits: Openings that lead from the throat to the outside, useful in feeding and respiration.

    2. Dorsal Hollow Nerve Cord: A cord of nervous tissue along the dorsal side, integral to the central nervous system.

    3. Notochord: A supportive rod that runs alongside the dorsal hollow nerve cord, composed of collagen in early species, which becomes vertebrae in later forms.

    4. Post-Anal Tail: An extension of the body past the anus, present at some stage of development.

VERTEBRATES

  • Sub-Phyla of Chordata:

    • Cephalochordata (Lancelets): Small, fish-like, marine animals primarily engaged in filter feeding through gill slits.

    • Urochordata (Tunicates): Marine organisms that are mostly sessile as adults; they retain pharyngeal gill slits for feeding and gas exchange.

    • Vertebrata: Include hagfish, lampreys, sharks, ray-finned fish, lobe-finned fish, amphibians, reptiles, birds, and mammals.

LOSS OF PHARYNGEAL SLITS

  • Some outgroups of Chordata, such as hemichordates (acorn worms) and xenoturbellida (Xenoturbella), did not retain pharyngeal slits, indicating a branch in evolutionary history.

AMNIOTIC EGG

  • Structure: Comprises three inner membranes:

    • Surrounds the embryo.

    • Yolk Sac: Derived from mother, providing nutrients.

    • Allantois: Responsible for waste disposal.

  • Albumen: Acts as a cushion for the embryo, providing both water and mechanical support.

  • Advantages:

    • Provides structural support and protection.

    • Nutritional support through the yolk.

    • Prevents water loss which enables reproduction away from water.

    • Membranes allow for efficient gas exchange.

CRANIUM & VERTEBRAE

  • Vertebrae: A column formed of cartilaginous or bony structures providing protection for the spinal cord along the dorsal side of species.

  • Cranium: A protective encasement for the brain, made of bone, cartilage, or fibrous material.

FUR & MILK IN MAMMALS

  • Fur: Body covering composed of the protein keratin, serving to retain body heat.

  • Milk: Nutrient-rich food for young, produced by mammary glands.

JAWS

  • Definition: Mouth parts that open and close to facilitate feeding, often equipped with teeth.

  • Evolution: Jaws likely formed from mutations in developmental regulatory genes affecting gill arches:

    • Jawless vertebrate origins with gill arches.

    • Intermediate forms evolve into gnathostomes (jawed fish).

LOBED-LIMBS AND LIMBS

  • Requires appendages allowing movement on land; lobed limbs serve as a precursor to full evolution of true limbs.

  • Significant fossils include:

    • Eusthenopteron (~385 mya): Displays lobe-like fins.

    • Tiktaalik (~375 mya): Transition species.

    • Acanthostega (~365 mya): Early limbed organisms.

LUNGS

  • Function: Enables gas exchange in terrestrial environments;

  • In Internal lungs, membranes remain moist promoting efficient gas exchange.

  • Lungs evolved from the swim bladder, which benefits aquatic species by preventing sinking.

SCALES

  • Composed of keratin; serve as a protective outer layer, which can also evolve into other structures like feathers.

CHORDATA IDENTIFYING CHARACTERISTICS

  • 1. Amniotic Egg

  • 2. Cranium & Vertebrae

  • 3. Dorsal Nerve Cord, Notochord, Post-Anal Tail

  • 4. Fur & Milk

  • 5. Jaws

  • 6. Limbs

  • 7. Lobed Limbs

  • 8. Lungs

  • 9. Scales

CEPHALOCHORDATA (LANCELETS)

  • Composition: Consists of about 22 species, entirely marine and small in size.

  • Feeding: Filter feed utilizing gill slits and live in sandy substrates.

UROCHORDATA (TUNICATES/SEA SQUIRTS)

  • Composition: Approximately 2000 species, all of marine origin.

  • Characteristics: Some adults are sessile, while pharyngeal gill slits are present in both larvae and sexually mature forms.

HAGFISH & LAMPREYS

  • Key Features: These are jawless vertebrates that possess a cranium.

  • Primitive Classification: They belong to the most primitive group of vertebrates, characterized by a cartilaginous skeleton and an eel-like appearance.

REPTILES

  • Majority are ectothermic, with the exception of birds (endothermic) and include all species evolved to live on land.

  • Egg composition: Hard egg shell for protection.

MAMMALS

  • Defining characteristics include fur/hair and the ability to nourish offspring with milk, produced in mammary glands.

TYPES OF MAMMALS

  1. Monotremes: Egg-laying mammals (e.g., platypus and echidna). Only five known species. Milk is secreted without nipples, located in Australia and New Guinea.

  2. Marsupials: Give birth to underdeveloped young that complete their development in a pouch post-birth.

  3. Placental Mammals: Give birth to fully developed young through a complex structure known as the placenta, which is a modified amniotic egg allowing for efficient nutrient and waste exchange.

PRIMATES

  • Characteristics: Derived features such as grasping hands, flattened nails, and complex social behaviors leading to extensive parental care.

CATEGORIZATION OF PRIMATES

  • Anthropoids (e.g., New World monkeys, Old World monkeys, gibbons, and great apes including humans):

    • Hominins: Bipedal primates that include Homo sapiens and numerous extinct species, showing evolutionary trajectory over millions of years.

    • Examples include Ardipithecus, Australopithecus, and various species of early Homo.

OUT-OF-AFRICA HYPOTHESIS

  • Theory: Proposes that modern humans evolved in Africa and migrated, leading to the global distribution observed today.

  • Observations: Genetic diversity decreases with distance from Africa, indicating historical migratory patterns and fossil records getting younger as distance increases.

TIMELINE OF MIGRATION OUT OF AFRICA

  • Human origins traced back to 300,000+ years ago in Africa.

  • Migration timelines and patterns highlight the age and geographical dispersion of H. sapiens across various continents.