Comparative Vertebrate Anatomy - Evo-Com Lecture Notes PDF

Summary

These lecture notes cover comparative vertebrate anatomy, discussing structural similarities and differences among vertebrates, exploring their evolutionary relationships, and the importance of comparative anatomy in understanding evolution. The notes also include historical context, taxonomy, and key figures in evolutionary thought.

Full Transcript

**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:** ![](media/image2.png) **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** ![](media/image4.png) Theories of Evolution \| BioNinja ![Theories of Evolution \| BioNinja](media/image6.jpeg) Theories of Evolution \| BioNinja **MacroEvolution vs MicroEvolution:** ![](media/image8.png) **Speciation:** The process by which new species form, often due to reproductive isolation. **[Anagenesis]** **[Cladogenesis]** ![](media/image10.png) - **Anagenesis:** Evolution within a lineage, without branching. - Known as **[Phyletic Evolution]** - **Cladogenesis:** Splitting of a lineage into two species, with branching **Types of Speciation:** The 4 Basic Modes of Speciation Show How Species Evolve - Biology Wise 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](media/image12.jpeg) - **Cladograms:** Diagrams representing species\' relationships through branching. - **Phylogenetic Trees:** Diagrams showing evolutionary relationships, including time scales. **Parts of a Phylogenetic Tree:** Phylogeny - Congenital Heart Disease & the NKX2-5 gene - **Node:** The point of divergence. - **Branch:** Evolutionary lineage. - **Clade:** A common ancestor and all its descendants. ![](media/image14.png) **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:** - **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). ![Reading trees: A quick review](media/image16.png) **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). ![](media/image19.png)**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 the active cytoplasm, usually at the animal pole. 2. **Holoblastic Cleavage**: The cleavage furrow bisects the entire egg. **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). ![](media/image21.jpeg)**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**. ![Animal Development II: Gastrulation & Organogenesis \| Organismal Biology](media/image23.png) - 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. ![](media/image25.jpeg) - **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: - **S. corneum**: Outermost layer. - **S. lucidum**: Clear, thin layer. - **S. granulosum**: Granular layer. - **S. spinosum**: Prickle-cell layer. - **S. germinativum/basale**: Deepest, germinative layer. - **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** 1. **Merocrine Secretion** 2. **Apocrine Secretion** 3. **Holocrine Secretion** **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.

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