Comparative Vertebrate Anatomy Lecture Notes PDF

**Comparative Vertebrate Anatomy** - Is the study of structural similarities and differences among vertebrates. - Examines the structure, function, and evolution of vertebrate organisms - Explores the relationships between their adaptations and environments. **Importance:** Is...

**Comparative Vertebrate Anatomy** - Is the study of structural similarities and differences among vertebrates. - Examines the structure, function, and evolution of vertebrate organisms - Explores the relationships between their adaptations and environments. **Importance:** Is a key tool for understanding evolutionary relationships, as it helps determine whether organisms share common ancestors. **Historical Development:** - **Greek Origins:** **Aristotle** and other philosophers laid the foundation for comparative anatomy. - **Renaissance Period:** Naturalists developed early texts on anatomy. - **19th Century:** Theories of evolution became central to comparative anatomy. **Fields Involved:** **Homology vs. Analogy:** - **Homology:** Traits inherited from a common ancestor, with different function. - **Analogy:** Similar functions in unrelated species, due to convergent evolution, not shared ancestry. **Taxonomy:** Science of classifying organisms. - Based on **evolutionary relationships**, using the **Linnaean system**. - Organisms **[sharing more homologies are considered more closely related.]** **Taxonomic Hierarchy:**  **International Commission on Zoological Nomenclature** **ICZN Principles:** 1. **Principle of Binomial Nomenclature** - Scientific name of a species is a combination of two names. Names of the species is composed of generic name and specific name. 2. **Principle of Priority** - The correct formal scientific name is the oldest available valid name 3. **Principle of Coordination** - When a new zoological name is published, it automatically establishes all corresponding names in relevant ranks 4. **Principle of First Reviser** - Applied in case of conflicts between published names. When a conflict arises between two simultaneously published divergent names, first subsequent author can decide which name has precedence. 5. **Principle of Harmony** - The name of each taxon must be unique and must not replicate or duplicate of any other family, group, or species 6. **Principle of Typification** - Each nominal taxon in the family group, genus group, or species group must have a prefixed name-bearing type. Helps determine what name it applies to. **Binomial Nomenclature** - Scientific names (genus, species, and subspecies) should be in italics. - Genus names start with a capital letter; species names start with a lowercase letter. - The genus name is followed by the species name. - In case of different names for the same genus or species, the earliest published name is accepted. **Evolution:** Long-term adaptation that leads to changes in an organism\'s structure and behavior. **Evolutionary Biology**: Studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. **Misconceptions about Evolution:** - Evolution is NOT about organisms constantly improving or climbing a \"ladder of progress.\" - Evolution does NOT happen by chance - Organisms do NOT \"try\" to adapt; adaptations occur naturally over time. - Natural selection does NOT give organisms what they \"need\"; rather, it favors traits that enhance survival. **Principles of Evolutionary Biology:** - **Relatedness:** All organisms are connected through common descent. - **Variation:** Differences among organisms arise from mutations, genetic recombination, or environmental influences. - **Fitness:** Survival and reproduction depend on traits that enhance an organism's ability to pass on its genes. - **Selection:** Environmental pressures favor organisms with beneficial traits. - **Genetic Drift:** Random changes in allele frequencies, especially in small populations. **Key Figures in Evolutionary Thought** - **Carolus Linnaeus:** Developed a system for classifying plants and animals based on similarities. - **Book:** Systema Naturae. - **Georges Buffon:** Proposed ideas about organismal relationships and evolution. - **Book:** Histoire Naturelle - **Georges Cuvier:** [Father of paleontology], utilizd comparative anatomy as tools - Suggested the idea on **series of catastrophe (extinction) and repopulation** events. - **Jean Baptiste Lamarck:** Founded Lamarckism, the idea that acquired traits are inheritable. - **Charles Lyell:** Argued for gradual changes in Earth's crust through uniformitarian principles. - **Uniformitarian**: Forces molding the planet today have operated continuously throughout history. **Darwin's Four Postulates** 1. **Variability:** Individuals within species vary. 2. **Heritability:** Variations can be passed to offspring. 3. **Overproduction:** More offspring are produced than can survive. 4. **Natural Selection:** Individuals with favorable traits survive and reproduce more. **Natural Selection Key Components: (ICE AGE)** - **[I]**nherited variation exists within the population - **[C]**ompetition results from an overproduction of offspring - **[E]**nvironmental pressures lead to differential reproduction - **[A]**daptations that benefit survival are selected for - **[G]**enotype frequency changes across generations - **[E]**volution occurs within the population **Transformation vs. Descent with Modification**  Theories of Evolution \| BioNinja  Theories of Evolution \| BioNinja **MacroEvolution vs MicroEvolution:**  **Speciation:** The process by which new species form, often due to reproductive isolation. **[Anagenesis]** **[Cladogenesis]**  - **Anagenesis:** Evolution within a lineage, without branching. - Known as **[Phyletic Evolution]** - **Cladogenesis:** Splitting of a lineage into two species, with branching **Types of Speciation:**  1. **Allopatric:** Geographic isolation causes species divergence. 2. **Parapatric:** Two groups of a species live next to each other but in slightly different environments. 3. **Sympatric:** Divergence without geographic separation but evolve differently until they can no longer interbreed. 4. **Peripatric:** Small isolated populations evolve into new species. 5. **Artificial Speciation:** Human-driven through selective breeding. **Adaptation:** The process of organisms adjusting to their environment to survive: - **Behavioral:** Actions that enhance survival (e.g., hibernation). - **Structural:** Physical traits aiding survival (e.g., penguin blubber). - **Physiological:** Internal adaptations (e.g., venom in snakes). **Habitat**: The place where an organism lives, providing its basic needs (food, water, shelter). - Changes in the habitat can cause adaptations, leading to evolution **Systematics, Phylogeny, and Cladistics** **Systematics:** The study of biodiversity and phylogenetic relationships among organisms. **Cladistics:** A method of analyzing evolutionary relationships based on shared, derived traits. **Phylogeny:** The evolutionary history and relationships of species. Phylogenetics \| BioNinja - **Cladograms:** Diagrams representing species\' relationships through branching. - **Phylogenetic Trees:** Diagrams showing evolutionary relationships, including time scales. **Parts of a Phylogenetic Tree:**  - **Node:** The point of divergence. - **Branch:** Evolutionary lineage. - **Clade:** A common ancestor and all its descendants. **Synapomorphy**: A trait present in the immediate ancestor but not in the earliest ancestor. **Symplesiomorphy**: A trait present in both the immediate and earlier ancestors (ancestral/primitive traits). **Autapomorphy**: A unique, derived trait found in a single taxon. **Grouping Types:** A diagram of paraphysical lines Description automatically generated - **Monophyletic Group:** Includes a common ancestor and all its descendants. - **Paraphyletic Group:** Includes a common ancestor but not all descendants. - **Polyphyletic Group:** Includes species without a common ancestor. **Outgroup Comparison:** A method of determining whether traits are primitive (shared with outgroup) or derived (unique to the ingroup).  **Origin of Chordates** - **Chordates** are a large phylum of animals that include vertebrates, sea squirts, and lancelets. - Share characteristics like **notochord**, d**orsally situated central nervous system**, and **gill slits** during some stage of their development. - **Evolution Timeline**: Evolved during the **Cambrian period** from a **deuterostome ancestor** (related to **echinoderms** and **hemichordates**). **Theories of Chordate Origin:** 1. **Echinoderm Origin**: - Proposed by **Johannes Muller (1860)**. - Suggested that **[echinoderm larvae]** gave rise to chordates through a process called **neoteny** (retention of juvenile features into adulthood). - **Echinoderms** are deuterostomes with mesodermal skeletal elements made from **CaCO3**. - Fossil: **Calcichordate**. 2. **Hemichordate Origin**: - Proposed by **Romer (1959)**. - Suggested **ancestral deuterostomes** were [**sedentary tentacle feeders**,] with ciliated, mucous-laden tentacles to trap plankton. - Modern example: **Acorn worm**. - Fossil: **Hemichordate**. 3. **Urochordate Origin**: - Proposed by **W. Garstang (1928)** and later supported by **N.J. Berrill (1955)**. - Suggested chordates **evolved from [sessile filter-feeding urochordates]** by the larval stage evolving into adults (via **neoteny**) and **losing their sedentary adult stage**. - Modern examples: **Tunicate adult** and **Tunicate larva**. 4. **Cephalochordate Origin**: - Proposed by **Chamberlain (1900)**. - Cephalochordates, such as **Amphioxus**, possess all the chordate characters in a typical state. - Fossil: **Pikaia gracilens**. 5. **Combined Theory**: - Proposed by **E.J.W. Barrington (1965)**. - Common **ancestor of echinoderms and chordates** was a **[sessile ciliary arm feeder]** living in a plankton-rich Cambrian environment, evolving into a free-swimming form in times of food scarcity. - Fossils: **Yuknessia**, **Pikaia gracilens**. **Key Characteristics of Chordates:** - **Dorsal hollow nerve cord** - **Notochord** - **Pharyngeal pouches** - **Tail** **Embryology** - The branch of biology that studies prenatal development, including **gametes (sex cells), fertilization,** and the **development of embryos and fetuses**. **Theories of Embryological Development:** 1. **Ernst Haeckel**: Proposed "**Ontogeny recapitulates phylogeny**," suggesting that the [stages an animal embryo] undergoes during development are a [**chronological replay** of its species\' evolutionary past]. 2. **Gavin de Beers**: Recapitulation isn't the only relationship between embryos and ancestors. - Embryonic structures may or may not be present from ancestors or descendants. - Embryonic structures can be **vestigial (lost)** or retained into adulthood. - Developmental stages may be repeated in earlier stages but not in later stages. - The developmental sequence may or may not be altered in descendants. **Stages of Embryo Formation** 1. **Gametogenesis:** Formation of sex cells (gametes) 2. **Fertilization:** Formation of zygote with sex cells 3. **Cleavage:** Rapid cell division 4. **Blastulation:** Morula develops to blastula 5. **Gastrulatioon:** Formation of three-layered structure 6. **Neurulation:** Ectoderm forms neural tube, becomes CNS 7. **Organogenesis: G**erm layer differentiates into organs. **Gametogenesis:** the process of gamete formation - Occurs in primary reproductive organs, **Gonads** - **Male gonads** are the **[testes]**. - **Female gonads** are the **[ovaries]**. - **Gametes** are an organism\'s reproductive cells, also known as **sex cells**. - **Spermatogenesis**: The formation of sperm. - **Leydig cells** produce testosterone in the presence of **luteinizing hormone (LH)**. - **Sertoli cells** act as \"**nurse\" cells** in the seminiferous tubules, aiding spermatogenesis. - **Spermiogenesis**: The **final stage of spermatogenesis** where spermatids **mature into [spermatozoa]**. - **Oogenesis:** The formation of ova (eggs). - **Corpus Luteum**: endocrine structure that releases hormones to **thicken** the [uterine lining] (**endometrium**). **Fertilization:** is fusion of **haploid gametes**, egg and sperm, to form the **diploid zygote**. **Cleavage:** known as **cellulation** - **Formation of [blastomeres] into [blastula]**. - The process by which the **zygote undergoes repeated mitotic cell division.** - **MORULA** - is a mass of 16 totipotent cells in a spherical shape - **BLASTULA** - spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). **Cleavage in Embryos:** - **Animal Pole**: Region in the developing embryo with **small cells that [divide rapidly].** - **Vegetal Pole**: Region with **large cells containing [yolk]**, which **[divide slowly]**. **Types of Cleavage:** Image result for holoblastic cleavage 1. **Meroblastic Cleavage**: The cleavage furrow is restricted to cytoplasm, at the animal pole. (**Birds and Fishes**) 2. **Holoblastic Cleavage**: The cleavage furrow bisects the entire egg. (**Amphibians and Mammals**) **Egg Classification Based on Yolk Amount:** - **Alecithal**: No yolk (Eutherian mammals). - **Microlecithal**: Small or negligible amount of yolk (Amphioxus, Tunicates). - **Mesolecithal**: Moderate amount of yolk (Dipnoi, Petromyzon). - **Macrolecithal/Polylecithal**: High amount of yolk (Reptiles, Birds). **Yolk Distribution:** The main results of fertilization 1. Restoration of the diploid number of chromosomes 2. Determination of the sex 3. - **Isolecithal/Homolecithal**: Yolk is uniformly distributed throughout the egg (Echinoderms, Amphioxus, Mammals). - **Telolecithal**: Moderate or large amounts of yolk concentrated in the vegetal pole. **Cleavage in Specific Species:** 1. **Amphibians**: **Mesolecithal** and **holoblastic**. - Unequal-sized blastomeres, with larger ones at the **vegetal pole** (nourishment) and smaller ones at the **animal pole** (developing embryo). - **Blastocoel** forms towards the animal pole. 2. **Birds (Aves)**: **Macrolecithal** and **meroblastic** (partial cleavage). - **Vegetal pole**: large yolk mass, cleavage furrow cannot penetrate it. - Animal pole: small **blastoderm**, narrow **blastocoel**. 3. **Mammals**: **Microlecithal** and **holoblastic**. - Unequal-sized blastomeres. **Gastrulation:** Process in which the single-layered blastula is **reorganized into a multilayered structure** called **gastrula**.  - Gastrulation results in: - Formation of the **three embryonic germ layers**. - Formation of the embryonic gut (**archenteron**). - Appearance of the major **body axes**. **Three Germ Layers:** 1. **Ectoderm**: Forms [skin, brain, nervous system], [teeth] and [ENT], 2. **Mesoderm**: Forms [muscles, skeletal system, circulatory system], and [kidney], [urogenital ducts]. 3. **Endoderm**: [Gut lining], [cavities and Foregut, Midgut, Hindgut organs.] **Mesenchymal Stem Cell:** Multipotent stromal cells that can differentiate into a variety of cell types. - Unspecialized pack of tissue of a developing embryo and its cells enter the formation of specialized tissues.  **Types of Embryos:** - **Diploblastic**: two embryonic cell layers (no mesoderm). - **Triploblastic**: three embryonic cell layers. **Blastopore:** First opening that forms during embryonic development - In **protostomes**, becomes **[mouth]**. - In **deuterostomes** (echinoderms & chordates), becomes **[anus]**. **Neurulation: Folding process** in vertebrate embryos, transforming the **neural plate into the neural tube**. - The embryo at this stage is termed the **neurula.** **Organogenesis** Development of organs from the three germ layers: - **Endoderm**: Forms internal linings, digestive, and respiratory systems. - **Mesoderm**: Forms muscles, skeleton, blood vessels, and more. - **Ectoderm**: Forms skin and the nervous system. - Migration of primordial germ cells (Mesenchyme). **Extraembryonic Membranes** - Assist in the development of the embryo, originating from the embryo but not part of it. - Perform roles in nutrition, gas exchange, & waste removal.  - **Amnion**: Protects the embryo in a sac filled with amniotic fluid. - **Amniotes**: develop within an amniotic sac - **Anamniotes**: **do not** develop an amniotic sac - **Yolk Sac**: Source of food for the developing embryo. - **Chorion**: Participates in gas exchange. - **Allantois**: Stores metabolic wastes and also participates in gas exchange. **Extraembryonic Membranes in Different Vertebrates:** 1. **Fish**: - Only the **yolk sac** forms. - Respiration and excretion occur through direct contact with the environment. 2. **Reptiles and Birds**: - **Amnion**: Protects the embryo. - **Yolk Sac**: Source of food. - **Chorion**: Gas exchange. - **Allantois**: Stores wastes (mainly **uric acid**) and also aids in gas exchange. 3. **Mammals**: - **Monotremes**: Produce [shelled eggs] (echidna, platypus). - **Marsupials (Metatherians)**: Pouched mammals (no true placenta). Yolk sac provides rudimentary connection to the mother\'s blood. - **Eutherians**: [Placental mammals] with a placenta that facilitates nutrient transfer, gas exchange, hormone secretion, and fetal protection. **Vertebrate Integumentary System** **Integument (Skin):** The outer covering of vertebrates, including mucous membranes. - **Function**: Forms the interface between organisms and the external environment. - **Other functions include**: - **Protective barrier**: - Protects against mechanical, chemical, bacterial, and UV damage, as well as thermal damage and desiccation. - **Cutaneous receptors**: For sensation. - **Temperature regulation**: Helps maintain homeostasis. - **Excretion**: Through sweat. - **Vitamin D synthesis**: From sunlight exposure. - **Embryonic Origin and Development** - **Epidermis**: Derived from **ectoderm**. - **Dermis and Hypodermis**: Derived from **mesoderm**. **Structure of Skin** 1. **Epidermis**: **Stratified** **squamous/transitional epithelium** ([keratinized]). - Contains pigment cells and protect immune systems - Layers: - **Stratum Corneum**: Outermost layer; composed of dead keratinocytes; provides a barrier against environmental threats and water loss. - **Stratum Lucidum**: Present only in thick skin (palms, soles); thin, transparent layer; reduces friction. - **Stratum Granulosum**: Keratinocytes begin keratinization; contains keratohyalin granules; contributes to waterproofing. - **Stratum Spinosum**: Several layers of spiny keratinocytes; strengthens skin via desmosomes; contains Langerhans cells for immune defense. - **Stratum Basale**: Deepest layer; contains mitotically active basal cells; melanocytes and Merkel cells present for pigmentation and sensory functions. - **Epidermal Cells**: - **Keratinocytes**: 90% epidermal cells; produce **keratin**. - **Melanocytes**: 8% of epidermal cells; produce **melanin**. - **Langerhans Cells**: Trap antigens in the skin. - **Merkel Cells**: Make contact with sensory neurons (tactile function). 2. **Dermis**: Contains blood vessels, nerves, hair follicles, smooth muscles, glands, and lymphatic tissue. - Composed of **areolar connective tissue** (collagen, elastin, reticular fibers). - Provides tensile strength and physiological support for the epidermis. 3. **Hypodermis**: Not part of the skin; lies below the dermis. - Made up of fat, connective tissue, and larger blood vessels - Functions: - Attaches skin to underlying bones and muscles. - Supplies blood vessels and nerves to the skin. - Composed of **loose connective tissue** and **elastin**. - Providing padding and **insulation** for the body and **attaches skin to underlying bone and muscle**. **Chromatophores** - Provide concealing coloration. - Color depends on combinations of chromatophores and the degree of pigment dispersion. - **Metachrosis**: Ability of some vertebrates to change color, controlled by the **endocrine** and **nervous system**. **Types of Chromatophores:** 1. **Melanophores**: Produce **yellow, brown, or black**. - **Function**: Protect chromosomes in the **stratum basale** from UV rays. - **Freckles and moles**: Concentration of melanin in one spot. 2. **Lipophores**: Contain **carotenoids** (yellow, orange, red). - **Xanthophores**: Produce yellow pigments. - **Erythrophores**: Produce red pigments. 3. **Iridophores/Guanophores**: Cause iridescence in vertebrates (fishes). - Contain **guanin (purine) crystals**. **Glandular Epithelium:** Type of epithelial tissue involved in **producing and releasing secretory products** (sweat, saliva, breast milk, digestive enzymes, etc.). - **Exocrine glands**: Secrete substances **onto epithelial surfaces via [ducts]**. **Classification of Unicellular Exocrine Glands:** 1. **Club Cells**: Elongated binucleated cells in amphibians; secrete mucus, may stimulate alarm or fear. 2. **Granular Cells**: Found in lampreys and fishes; secrete mucus in skin. 3. **Goblet Cells**: Narrow at the apical end, wide at the base (found in bony fishes); secrete mucus. 4. **Sacciform Cells**: Secrete toxic products to repel enemies. **Types of Multicellular Glands** 1. **Tubular Glands**: - **Simple Tubular**: Short blind tubes in the dermis, extend to the surface (e.g., thumb pads in anurans). - **Simple Coiled**: Long, narrow tube with coiled distal end, located in the dermis; openings referred to as **pores** (e.g., sweat glands). - **Simple Branched**: Divides into branches at the distal ends (e.g., axillary sweat glands). - **Compound Tubular**: Consists of multiple simple tubular glands (e.g., mammary glands). 2. **Saccular (Alveolar) Glands**: - **Simple Saccular**: Single bulb or acinus at the end of the duct (e.g., mucus and poison glands in amphibians). - **Simple Branched**: Multiple acini along a single excretory duct (e.g., Meibomian glands). - **Compound Saccular**: Consists of several simple saccular glands (**lobules**) (e.g., mammary glands). **Classification of Exocrine Gland Based on Secretion** A group of cartoon objects Description automatically generated with medium confidence 1. **Merocrine Secretion-** Secretion via exocytosis; cell stays intact. (e.g., sweat glands) 2. **Apocrine Secretion-** part of the cell breaks off with secretion. (e.g., mammary glands) 3. **Holocrine Secretion-** Entire cell disintegrates to release secretion. (e.g., sebaceous glands) **Types of Exocrine Glands by Secretion:** 1. **Mucous Glands**: Secrete mucus (e.g., unicellular glands in aquatic vertebrates). 2. **Serous Glands (Sudoriferous Glands)**: Secrete watery substances (e.g., sweat glands). 3. **Sebaceous Glands**: Secrete oily substances (e.g., **uropygial glands** in birds, **ceruminous glands**, and **Meibomian glands** in humans). **Scales** 1. **Epidermal Scales**: - Formed in the **stratum germinativum**. - Found in terrestrial tetrapods. - Shed and replaced periodically (**ecdysis**). - Examples: **Scutes** of turtles and snakes. 2. **Dermal Scales**: - Derived from **dermal bone**. - **Dermatome origin**. - Examples: Found in fishes. **Types of Dermal Scales in Fish:** 1. **Cosmoid**: Small, thick scales with cosmine and enamel layers; found in lobe-finned fish (*Latimeria*). 2. **Placoid**: Basal plate embedded in dermis with a spine projecting through the epidermis; dentine and enamel layers; found in sharks. 3. **Rhomboid/Ganoid**: Rhomboidal in shape, composed of bones, with **ganoin** on the surface. 4. **Ctenoid and Cycloid**: Bony layers with concentric ridges (growth increments); allow flexibility. **Integument of Fishes** - **Non-keratinized skin**, covered with a **mucus cuticle**. - Functions: - Prevent bacterial penetration. - Contribute to laminar water flow across the surface. - Make fish slippery to predators. - Contain toxic or repellent chemicals. **Epidermis of Fishes:** - Alive and active at the surface, with no keratinized cells. - Mitosis occurs beyond the basal layer. - Contains **epidermal cells** and **unicellular glands** (contribute to the mucus cuticle). **Integument of Amphibians** - Specialized for **cutaneous respiration** (gas exchange through the skin). - **Epidermis** has four layers: 1. Stratum basale. 2. Stratum spinosum. 3. Stratum granulosum. 4. Stratum corneum (allows **cutaneous respiration**). - **Dermis**: Contains fibrous connective tissue, **mucus**, **poison glands**, and **chromatophores**. **Integument of Reptiles** - Adapted to terrestrial environments. - Extensive **keratinization**, with fewer skin glands. - **Epidermis**: - Stratum basale. - Stratum granulosum. - Stratum corneum (outermost layer). - **Dermis**: Composed of fibrous connective tissue; **dermal bones** found in crocodiles, lizards, and extinct reptiles. **Molting (Ecdysis):** - **Periodic shedding** of the skin, often complete in snakes and some lizards. - Affected by health, temperature, humidity, and environmental factors. **Skin Glands in Reptiles:** - Restricted to certain body areas, important for reproduction and protection. - **Fermoral Glands**: Found in lizards, along the hind limbs. - **Scent Glands**: Open into the cloaca in crocodiles and some turtles. **Integument of Birds (Aves)** - Skin covered by **feathers**, adapted for movement. - **Feathers**: Epidermal growths that form a distinctive outer covering, or plumage - **Epidermis**: Composed of **stratum basale** and a **transitional layer to the stratum corneum**. - **Dermis**: Richly supplied with blood vessels, sensory nerves, and smooth muscles. - **Brood Patch**: Highly vascularized dermis in the breast area during the brooding season. **Skin Glands in Birds:** - **Uropygial Gland**: Secretes oil for preening, makes feathers water-repellent. - **Salt Glands**: Excretes excess salt. **Integument of Mammals** - Multilayered system of keratinized skin, hair, and glands - Others include - **Hair**: Primary epidermal appendage. - **Horns**: Permanent, keratin-covered projections surrounding live bone. - **Antlers**: Composed of bone, cartilage, fibrous tissue, skin, nerves, and blood vessels. - **Hooves**: Keratinized coverings on the toes of ungulate mammals.