Comparative Anatomy of Vertebrates PDF

Comparative Anatomy of the Vertebrates An Introduction Definition and Relation to other Disciplines  The study of the structure of vertebrates (descriptive anatomy) and of the functional significance of structure (functional anatomy)  Comparative anatomy also deals with the stud...

Comparative Anatomy of the Vertebrates An Introduction Definition and Relation to other Disciplines  The study of the structure of vertebrates (descriptive anatomy) and of the functional significance of structure (functional anatomy)  Comparative anatomy also deals with the study of history and of animals that no longer inhabit the earth and are known to us by a fossil record  Specialist from the following different fields are involved in the study of comparative anatomy: zoology, physiology, histology, genetics, ecology, developmental biology, evolutionary biology, phylogeny History  From the Greek words ana and tome that means “to cut up” or to dissect  Aristotle- first to produce a large body of writing on comparative anatomy who described about 540 different kinds of animals (300 B.C.)  Galen (165-200 AD)- added some of his own dissections of apes  Leonardo da Vinci (1452-1519)- anatomical observations  Andreas Vesalius (1514-1564)- De Humani Corporis Fabrica  Pierre Balon (1517-1564)- published an illustration of a human and bird skeleton  William Harvey (1578-1657) – studies on the circulation of the blood, dissection of many animals and advocate of comparative anatomy  Nehemiah Grew (1641-1712) – first used the term Comparative Anatomy, published a book in 1681 describing the anatomy of stomachs and intestines in several different species  Carolus Linaeus (1707-1778)- devised the binomial system for naming plants and animals  Louis Jean- Marie Daubenton (18th century)- compared the anatomies of many different animals  Jean-Baptiste de Lamarck (1744-1829)- made the first scientific division of the animal kingdom into Vertebrata and Invertebrata  Inheritance of acquired characteristics  Georges Cuvier (1769-1832)- argued that species are immutable, stating that the efficient design of each animal is evidence that it could not have changed since its creation  Louis Rodolphe Agassiz (1807-1873)- paleontologist, first modern teacher of Comparative Anatomy  Alfred Russel Wallace (1823-1913)- “survival of the fittest”  Charles Darwin (1809-1882) – develop the modern theory of evolution  Richard Owen (1804-1892) – developed the concepts of homology and analogy  Thomas Huxley (1825-1895) – established the modern concept of the evolution of the vertebrate skull  Karl Ernst Von Baer- contribute important understanding on Mammalian egg and Development of Animals  Ernst Haeckel- contribute to the knowledge of the three germ layers that are found in the early embryos of most animals and develop into the organs of adults known as the biogenetic law Significance  Comprehend the structural basis of biology  To Advance human health and technology  To understand principles of form  To study evolution ANATOMICAL AND EVOLUTIONARY CONCEPTS  Homology- refers to the features of two or more organisms sharing common ancestry  Analogy- refers to the features of two or more organisms sharing common function  Refers to the corresponding function of structure in similar or different organs of organ parts  Homoplasy- refers to features of two or more organisms that may are related by similarity of appearance but can be explained by either homology or analogy Development  Ontogenesis – development history of an organism  Phylogeny- evolutionary history of a taxon symmetry and segmentation  Symmetry- describes the way in which the body of animal meets the surrounding environment  Radial symmetry- a body that is laid out equally from a central axis, so that any of several planes passing through the center divides the animal into equal halves  Bilateral symmetry- right and left sides are mirror images  Body Regions:  Anterior/ Posterior  Dorsal/ Ventral  Distal/ Proximal  Principal anatomical planes Cross section/ Transverse Plane Frontal section/ Coronal Plane Sagittal section  Metamerism - Serial repetition of body structures in the longitudinal axis - Clearly manifested in vertebrate embryos and is retained in many adults systems. Evolution and Habitat Adaptation  Adaptation is the evolutionary process of modification of structures in order to become adjusted to mode of life in a particular environment  A hereditary modification of a phenotype that increases the chances of survival  Believed to be the result of environmental pressures that through natural selection, propagate genetic mutations that have survival value  Habitat acts as the selection pressure or screening process for evolution while organisms through its genetic inheritance produce the model  Evolution results from the interplay between changing environments and adapting organisms Phyletic Line  A lineage that is relatively continuous and complete in the fossil record  Usually represented by genera that are related in time by linear and branching evolution (often a single family), and through extinction by progressive change  Species become extinct when they cannot adapt to sudden shifts in their environments or entire assemblages of animals become extinct when the scale of environmental change is extreme Evolutionary Trends/ Morphocline  Gradual adaptive change in the evolution of a feature within a phyletic line  Usually observed for large populations evolving moderate rates Evolutionary Trends  The evolution of horses from the Eocene epoch (57.8 MYA) to the present is a well studied trend.  Body size – increasing  Foot structure – fewer toes  Tooth structure – larger grinding surface  George Gaylord Simpson showed that this trend is compatible with Darwinian evolutionary theory. Parallelism and Convergence  Parallel evolution is the independent evolution of similar traits, starting from a similar ancestral condition  The ancestor is common but both have evolved a primitive trait independently  Convergence is evolutionary change in two or more lineages such that corresponding features that were formerly dissimilar become similar  Divergence refers to a group from a specific population developing into a new species Concepts: Evolutionary Convergence Darwinian Evolutionary Theory: Evidence  Perpetual Change  Common Descent  Multiplication of Species  Gradualism  Natural Selection PERPETUAL CHANGE Perpetual Change  The main premise underlying evolutionary theory is that the living world is always changing.  Perpetual change in form & diversity of organisms over the last 700 million years can be clearly seen in the fossil record. Fossils  Fossils are remnants of past life preserved in the earth.  Complete remains – insects in amber.  Petrified skeletal parts infiltrated with silica or other minerals.  Or traces of organisms such as molds, casts, impressions, trackways, or fossilized excrement. Stratigraphic record and inferred evolutionary relationships among alcelaphine (blesboks, hartebeests, wildebeests) and aepycerotine (impalas) antelopes in Africa. Species in this group are identified by characteristic sizes and shapes of horns found in rock strata of various ages. COMMON DESCENT (with Modification) Common Descent  Darwin proposed that all organisms have descended from a single ancestral form.  Life history is shown as a branching tree called a phylogeny.  Haploid Chromosome from each of four ape species: human (Homo sapiens), bonobo (the pygmy chimpanzee, Pan paniscus), gorilla (Gorilla gorilla), and orangutan (Pongo pygmaeus). MULTIPLICATION OF SPECIES Species  Defining a species can be difficult.  Criteria:  Common descent  The smallest distinct groupings of organisms sharing a pattern of descent.  Morphological & molecular techniques  Members of a species must form a reproductive community that excludes other species. Speciation  Speciation refers to the formation of new species.  Occurs in two ways:  Phyletic Speciation  Divergent Speciation  Phyletic Speciation  One species gradually becomes so changed that it must be considered a new species.  Sequential evolution or transformation  Divergent Speciation  Some populations of a species evolve into a new, second species while other populations either continue relatively unchanged as the original, parental species or evolve into a new, third species. Allopatric Speciation  Allopatric (another land) populations occupy separate geographic areas.  Separated geographically, but able to interbreed if brought together.  Over time, reproductive barriers may evolve so that they could not interbreed.  Allopatric speciation Sympatric Speciation  Sympatric (same land) speciation occurs when speciation occurs in one geographic area – a lake for example.  Individuals within the species become specialized on a food type, shelter, part of the lake etc.  Eventually reproductive barriers evolve. Parapatric Speciation  Parapatric Speciation – geographically intermediate between allopatric and sympatric speciation.  Two species are parapatric if their geographic ranges are primarily allopatric but make contact along a borderline that neither species successfully crosses. Adaptive Radiation  Adaptive radiation – the production of ecologically diverse species from a common ancestral stock.  Common in lakes & islands – sources of new evolutionary opportunities.  Usually occurs when the species enters a new habitat where little or no competition or environmental stress exists GRADUALISM Gradualism  Darwin’s theory of gradualism proposes that small differences accumulate over time producing the larger changes we see over geologic time.  Certainly, this process is always at work, but probably does not account for all changes.  P e t e r W i l l i a m s o n ’s Freshwater Snail Evolution in Lake Turkana, Africa  The geology of the Lake Turk ana b as in reveals a history of instability. NATURAL SELECTION Natural Selection  Only a small fraction of all offspring produced by any species actually reach maturity and reproduce.  Natural populations normally remain at a constant size.  Those that survive may have heritable traits that increased their chances of survival.  They will pass those traits on.  The frequency of those traits will increase.  Gives us a natural explanation for the origin of adaptation Natural Selection  When an environment changes, or when individuals move to a new environment, natural selection may result in adaptation to the new conditions.  Sometimes this results in a new species. Natural Selection Organic evolution  Defined as a change in genetics of a population over a period of time  Microevolution- refers to small-scale genetic changes within a population  Macroevolution- refers to the large-scale results of genetic changes in population, including the formation of new species and the evolution of large scale trends seen across species in what traits they have Systematics  The study of phylogenetic relationships among species  Two main ways we learn how different species are related to each other:  Studying fossils  Hierarchical pattern of homology Phylogeny  Evolutionary history of species  Refers to the evolutionary relationships among species or to the family tree of all life, indicating how all living things are related, typically diagrammed as a tree  Dendograms is a summarized graphic representation of the course of evolution and phylogeny  A practical device designed to illustrate the evolutionary history of related groups of organisms  Clade is a natural evolutionary lineage including an ancestor plus all and only its descendants  Placing together organisms belonging to the same clade is called cladistics  Monophyletic clade  Paraphyletic clade  Polypheletic clade Primitive and Derived Traits  Primitive/ Plesiomorphic Traits are characters of organisms that were present in the ancestor of a certain group of related organisms  Symplesiomorphy- if the character is present in the immediate common ancestor, as well as in the earlier ancestor (primitive character)  Derived / Apomorphic Traits are characteristics of organisms that have evolved within the group or related organisms that were not present in the ancestor most important when doing phylogenetic tree  Synapomorphy- a situation in which the character is present in the intermediate common ancestor, but not in the earlier ancestor (derived character). lizard alligator bird feathers, wings presence of gizzard body covered with scales, presence of teeth, a heart with only three chamber, four legs Determining primitive versus derived trait  Outgroup comparison- finding one or more species that are relatives of the group we are studying but outside of it in that they are equally related to all members of the group we are studying  Ingroup and Outgroup  Characteristics found within both ingroup and outgroup species are most likely primitive while characteristics found just within some, but not all, the ingroup species that are not found in the outgroup are most likely derived  Shark Trout Frog Mouse Cartilage skeleton Bone skeleton Bone skeleton Bone skeleton Amphioxus With Notochord With Notochord No skeleton, with notochord With Notochord With Notochord Jaws Jaws Jaws Jaws No jaws No fur Fur No fur No fur No fur Mammalia osteichthyes Natostomes? B Tetrapoda A  In general, sharing a derived characteristic provides evidence for ancestry because it potentially provides evidence about phylogeny, thus phylogenetically informative  larval form is brought to its adult form Metamorphosis, paedomorphosis  Paedomorphosis: ontogenetic changes whereby certain larval features of the immediate ancestor become the end product of metamorphosis in the descendant species (paedomorphic species) Other terms  Primitive: ancestral  Generalized; connotes potential adaptability  Specialized: adaptive modification  Derived or modified: connotes any state of change from an ancestral condition  Vestigial: a phylogenetic remnant that was better developed in an ancestor eg. tailbone  Rudimentary: e.g. muellerian duct in males eg. in females for developing fallopian tube  - main driver is females, because they choose Sexual Selection - eg lioness choose stronger lion for breeding and mating -  A special case of natural selection  Acts on an organisms ability to obtain or successfully copulate with a mate  Male Competition  Female Selection Examples of Sexual Selection Male elephant seals fight for sexual access to a cluster of females Examples of Sexual Selection A male bird of paradise engages in flashy courtship display to catch the sexual interest of a female Females are choosy; a male mates with any female that accepts him Kin selection  The change in allele frequency depends on both the direct influence of the trait on the individual organism, and on its indirect effect: the increment (or decrement) in fitness that the trait bestows on related individuals that carry other copies of the allele. - mas favorable evolution ang magbantay n 3 pamangkin kaysa mag anak (??) - allele computation shows higher survival of allele when preserved than to reproduce - The Origin of Chordates Lecture 2 Phylum Hemichordata Hemichordates (acorn worms) are marine animals that have gill slits and a rudimentary notochord – however, the notochord is not homologous with the notochord in vertebrates. Phylum Hemichordata Vermiform bottom dwellers, usually in shallow water. Some are colonial living in secreted tubes. Phylum Hemichordata Hemichordates are deuterostomes with radial indeterminate cleavage and enterocoelous coelom development. Larvae are similar to those of echinoderms. Phylum Hemichordata A tubular dorsal nerve cord in the collar zone of acorn worms seems to be homologous to that in chordates. Gill slits in the pharynx serve for filter feeding and secondarily for breathing – another characteristic found in chordates. Phylogeny Hemichordates share characteristics with echinoderms: Early embryogenesis Similar larvae And Chordates: Gill slits Dorsal hollow nerve cord Who are the chordates? Phylum Chordata By the end of the Cambrian period, 540 million years ago, an astonishing variety of animals inhabited Earth’s oceans. One of these types of animals gave rise to vertebrates, one of the most successful groups of animals. Phylum Chordata Chordates are bilaterian animals that belong to the clade of animals known as Deuterostomia. Two groups of invertebrate deuterostomes, the urochordates and cephalochordates are more closely related to vertebrates than to invertebrates. Phylum Chordata Chordates have: Bilateral symmetry A coelom Deuterostome development Radial, indeterminate cleavage Enterocoelous coelom development Metamerism Cephalization. Deuterostomes Deuterostome characteristics: Radial, indeterminate cleavage Formation of the mouth from a second opening Enterocoelous coelom development Phylogenetic Tree of Chordates Phylum Chordata Five distinctive characteristics define the chordates: Notochord Dorsal tubular nerve cord Pharyngeal pouches (gill slits) Endostyle Postanal tail All are found at least at some embryonic stage in all chordates, although they may later be lost. Notochord The notochord is a flexible, rod-like structure derived from mesoderm. The first part of the endoskeleton to appear in an embryo. Place for muscle attachment. In vertebrates, the notochord is replaced by the vertebrae. Remains of the notochord may persist between the vertebrae. Dorsal Tubular Nerve Cord In chordates, the nerve cord is dorsal to the alimentary canal and is a tube. The anterior end becomes enlarged to form the brain. The hollow cord is produced by the infolding of ectodermal cells that are in contact with the mesoderm in the embryo. Protected by the vertebral column in vertebrates. Pharyngeal Pouches and Slits Pharyngeal slits are openings that lead from the pharyngeal cavity to the outside. They are formed when pharyngeal grooves and pharyngeal pouches meet to form an opening. In tetrapods, the pharyngeal pouches give rise to the Eustachian tube, middle ear cavity, tonsils, and parathyroid glands. Pharyngeal Pouches and Slits The perforated pharynx evolved as a filter feeding apparatus. Later, they were modified into internal gills used for respiration. Endostyle or Thyroid Gland The endostyle in the pharyngeal floor, secretes mucus that traps food particles. Found in protochordates and lamprey larvae. Secretes iodinated proteins. Homologous to the iodinated-hormone-secreting thyroid gland in adult lampreys and other vertebrates. Postanal Tail The postanal tail, along with somatic musculature and the stiffening notochord, provides motility in larval tunicates and amphioxus. Evolved for propulsion in water. Reduced to the coccyx (tail bone) in humans. Phylum Chordata Two protochordate subphyla Subphylum Urochordata Subphylum Cephalochordata Subphylum Urochordata Tunicates (subphylum Urochordata) are found in all seas. Most are sessile and highly specialized as adults. Subphylum Urochordata In most species, only the larvae show all of the chordate hallmarks. Tadpole larva Subphylum Urochordata Tunicates filter feed using the pharyngeal slits and a mucous net secreted by the endostyle. Subphylum Urochordata Some tunicates are colonial. Subphylum Urochordata Larvaceans are paedomorphic. Subphylum Cephalochordata Cephalochordates are the lancelets, also called amphioxus. Subphylum Cephalochordata All five chordate characters are present in a simple form. Filter feeding is accomplished using pharyngeal slits and a mucous net secreted by the endostyle. Subphylum Cephalochordata The dorsal, hollow nerve cord lies just above the notochord. The circulatory system is closed, but there is no heart. Blood functions in nutrient transport, not oxygen transport. Segmented trunk musculature is another feature shared with vertebrates. Subphylum Cephalochordata Many zoologists consider amphioxus a living descendant of ancestors that gave rise to both cephalochordates and vertebrates Would make them the living sister group of the vertebrates  Vertebrate Diversity: A Parade of the Different Vertebrate Taxa Lecture 3  Phylum Chordata: Craniata Superclass: Pisces – Superclass: Tetrapoda Class Agnatha – Class Amphibia Class Placodermii – Class Reptilia Class Chondricthyes – Class Aves Class Acanthodii Class Osteichthyes – Class Mammalia  CRANIATA Craniates are chordates that have a head. The origin of a head opened up a completely new way of feeding for chordates: active predation. Craniates share some common characteristics: – A skull, brain, eyes, and other sensory organs.  Agnathans vs. Gnathostomes: semicircular canals – agnathans have 1 or 2 – gnathostomes have 3 jointed, paired lateral appendages – agnathans have none – gnathostomes do jaws – agnathans have none – gnathostomes do  What are the 2 contrasting/general groups of Agnathans? – 1. – 2.  Agnatha 2 contrasting groups: – Ostracoderms (extinct) – Cyclostomes (living)  Which of the 2 is considered as the oldest known vertebrate? – 1.  Ostracoderms (Osteostraci, Anaspida, Heterostraci, & Coelolepid): extinct Paleozoic (Cambrian to Devonian) jawless fish with an external skeleton of bone ('bony dermal armor') oldest known vertebrates many had flattened appearance (some may have been bottom- dwellers) No paired fins  What are the 2 groups of living agnathans? – 1. – 2.  Cyclostomes Include hagfishes and lampreys Prominent notochord No paired fins, no vertebral column, no bony skeleton  Myxiniformes: The Hagfishes primarily marine scavengers have a partial cranium (skull), but no vertebrae, and so they are not truly vertebrates Difference to vertebrates include: – lack of extrinsic eye muscles, lack of eye lens, lack of cardiac Stubby innervation, lack of radial papillae muscles  Petromyzoniformes: The Lampreys parasitic with horny, rasping teeth lack mineralized tissues such as bone a group of jawless fishes found in temperate rivers and coastal seas (but anadromous) have a complete braincase and rudimentary true vertebrae Die shortly after spawning Vertebrate Diversity and Phylogeny  Subphylum Vertebrata Subphylum Vertebrata is a monophyletic group that shares the basic chordate characteristics with the urochordates and cephalochordates.  Subphylum Vertebrata The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone.  Subphylum Vertebrata There are approximately 52,000 species of vertebrates which include the largest organisms ever to live on the Earth. – Fishes – Amphibians – Reptiles – Birds – Mammals  Endoskeleton Vertebrates have an endoskeleton made of cartilage or bone. – All have a cranium to protect the brain. – Almost all have vertebrae to protect the spinal cord. – Important for muscle attachment.  Neural Crest Cells One feature unique to vertebrates is the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryo. Dorsal edges Neural crest Neural tube of neural plate Ectoderm Ectoderm Migrating neural Notochord crest cells (a) The neural crest consists of (b) Neural crest cells migrate to bilateral bands of cells near distant sites in the embryo. the margins of the embryonic folds that form the neural tube.  Neural Crest Cells Neural crest cells give rise to a variety of structures, including some of the bones and cartilage of the skull. The Origin of Vertebrates  The Origin of Vertebrates Vertebrates evolved at least 530 million years ago, during the Cambrian explosion. Pikaia was an early chordate discovered in the Burgess Shale. – Cephalochordate?  The Origin of Vertebrates The most primitive of the early vertebrate fossils are those of the 3-cm-long Haikouella. – Eyes and brain present, but no skull. – It is transitional in morphology between cephalochordates and vertebrates – Some hypothesize Haikouella is the sister taxon of vertebrates.  The Origin of Vertebrates In other Cambrian rocks, paleontologists have found fossils of even more advanced chordates, such as Haikouichthys. – Skull present.  Gnathostomes appearance of the jaw expanded the adaptive range of vertebrates. Used for biting and grasping. Led to more varied and active ways of life, and to new sources of food.  Origin of jaws - two hypotheses: – 1. Modification of a front pair of bone or cartilage gill supports. – 2. More recent hypothesis: Modification of the velum, a structure used in respiration and feeding in lamprey larvae.  What are the 2 groups of earliest known gnathostomes? – 1. – 2.  Acanthodians: earliest known gnathostomes (Devonian Times - Silurian; about 440 mybp) hard spine in front of each of their fins; probably related to modern bony fishes Body is covered by bony armor small (less than 20 cm long) with large eyes Acanthodians most likely died out because of the rapidly increasing number of ray-finned fishes and sharks during the Permian  Placodermii: armored jawed fishes Silurian (about 420 million years before present) probably off the main line of vertebrate evolution many had bony dermal shields some were probably predators named for their heavy armor of dermal bone, which formed large shields on the head and thorax The head and trunk shields of most placoderms were articulated by bony joints  Class Chondrichthyes cartilaginous fishes ancestors had bony skeletons so cartilaginous skeleton is specialized pelvic fins of males are modified as claspers placoid scales numerous today but more abundant in the past Usually have 2 subclasses: – Elasmobranchii – Holocephali  To which subclass does the modern shark belong? – 1.  Class Chondrichthyes Subclass Elasmobranchii  Subclass Holocephali – Cladoselachii - primitive  Chimaeriformes sharks (300-400 mybp) – Selachii - 'modern' sharks (order: Squaliformes) – Batoidea - rays & skates (order: Rajiformes)  Subclass Elasmobranchii most common cartilaginous fishes 1st pharyngeal slit modified as a spiracle – bears a miniature gill-like surface (pseudobranch) naked gill slits (no operculum; usually 5 pairs) mouth located ventrally A ray A clasper A placoid scale  Subclass Holocephali Chimaeriformes Marine gill slits have a fleshy operculum & the spiracle is closed few scales common ancestor with sharks but an independent line From The Marine Flora & Fauna of Norway by Kåre Telnes  Class Osteichthyes bony fishes skeleton is partly or chiefly bone gill slits are covered by a bony operculum skin has scales with, typically, little bone most have a swim bladder 2 subclasses: – Actinopterygii – Sarcopterygii  Which of the 2 groups of subclass Osteichthyes are known as lobe-finned fishes? – 1.  Subclass Actinopterygii Ray-fins 2 superorders: – Superorder Chondrostei – Superorder Neopterygii  Chondrosteans most primitive ray-fins; chiefly paleoniscoids chiefly Paleozoic (300-400 mybp) May or may not have ganoid scales include present-day Sturgeons & Paddlefish (no ganoid scales)  Neopterygii Order Semionotiformes Division Teleostei - modern ray-finned fishes  Order Semionotiformes dominant Mesozoic fishes possess ganoid scales two extant genera: – Lepidosteus - predatory; includes present-day gars – Amia - includes present- day bowfins (or dogfish) – Also called Holosteans A gar  Division Teleostei modern ray-finned fishes recent bony fishes 95% of all living fish about 40 living orders well-ossified skeleton cycloid & ctenoid scales (flexible & overlapping) pelvic fins often located far 1 = operculum, 2 = dorsal fin, 3 = caudal peduncle (The narrow section of a fish's forward body directly anterior to the insertion of the tail but before the mid-body.), 4 = no spiracle caudal fin or "tail", 5 = anal fins, 6 = pelvic fins, & 7 = pectoral fins  Subclass Sarcopterygii lobe-finned fishes With bony operculum 2 major taxa: – Crossopterygii – Dipnoi 3 groups (Kent 9th ed) – Actinitians – Rhipidistians – Dipnoi A dipnoi  Which of the 2 Sarcopterygii are considered as ancestors of amphibians? –1 Which of the 2 Sarcopterygii are called the lungfishes? –2  Crossopterygii With true cosmoid scales chiefly Paleozoic except Latimeria resemble early amphibians skeleton of fin lobe corresponds closely to proximal skeletal elements of early tetrapod limbs skull similar to that of early amphibians had swim bladders that may have been used as lungs 2 orders: Rhipidistia; Coelacanthiformes  Dipnoi lungfish (3 living genera; Africa, Protopterus; Australia, Neoceratodus; & South America, Lepidosiren) African & South American species have inefficient gills & will drown if held under water Australian species (Neoceratodus spp.) relies on gills unless oxygen content of water is too low  Phylum Chordata: Subphylum Vertebrata Superclass: Pisces – Superclass: Tetrapoda Class Agnatha – Class Amphibia Class Placodermii – Class Reptilia Class Chondricthyes – Class Aves Class Acanthodii Class Osteichthyes – Class Mammalia  Class Amphibia ectothermic First tetrapods – subclass Labyrinthodontia – Subclass Lepospondyli – Subclass Lissamphibia  Subclass Labyrinthodontia  Oldest known amphibian/tetrapods Fish-like features: small bony scales in the skin fin-rays in the tail (for swimming) a skull similar to that of some Crossopterygians a sensory canal system (like the lateral line system) that indicates a primarily aquatic existence)  Subclass Labyrinthodontia 3 orders: – Ichthyostegalia – oldest; Devonian – Temnospondyli – common in the Permian – Anthracosauria – possibly direct line to the reptiles Ichthyostegali Anthracosaur a ia temnospondyli  Subclass Lepospondyli Abundant during the Carboniferous period ancestry uncertain due to lack of fossil evidence probably on a 'side branch' of vertebrate evolution Perhaps, ancestor to urodeles and apodans  LISSAMPHIBIA – Modern Amphibians Arise with the labyrinthodont Includes the frogs and toads (Anurans), salamander (Urodela), and the caecilians (Gymnophiona) Eggs laid on moist environment External fertilization and internal fertilization Paired lungs but absent to some salamaders Mucous glands  Subclass Lissamphibia Characteristics: – aquatic larval stage with external gills – middle ear cavity with ear ossicle (columella) – no bony scales (except apodans)  Urodela - Caudata Salamanders or Newts Paired limbs with long tails Protrude their tongue to feed Skull more broad and open with no tymapanic membrane Fertilization is external Spermatophores in males  Salientia - Anura Adult frogs without tails Hindlegs important for leaping Except Ascaphus fertilization is external Metamorphosis  Gymnophiona - Apoda Caecilians Legless amphibians Males have copulatory organ, thus fertilization is internal Some lays eggs other produce live youngs  Class Reptilia the first amniotes ectothermic characteristics – scaly – clawed – large, yolk-laden, shell-covered eggs (cleidoic) laid on land First to develop extraembryonic membranes (amnion, chorion, allantois)  Class Reptilia Subclasses Reptile subclasses: – Anapsida – classified in part – Lepidosauria according to presence or absence of temporal – Archosauria openings: – Ichthyopterygia Anapsida – Synapsida Diapsida Parapsida Synapsida Euryapsida  Reptile subclasses based on temporal openings Synapsid type = mammal-like reptiles (one) Anapsid type = stem reptiles & turtles (none) Diapsid type = all living reptiles except turtles: rhynchocephalians, lizards, & snakes (two) Euryapsid type = extinct plesiosaurs. (one) Parapsida= extinct  Anapsida No temporal fossa; primitive condition Orders: Cotylosauria - stem reptiles Chelonia - turtles & tortoises – unchanged for about 175 million years – identified by bony dermal plates to which ribs & trunk vertebrae are fused  Subclass Diapsida All living reptiles except the turtles Two temporal openings. – All other reptile groups and birds. Examples; crocodiles Pterosuars Lepidosauria  Crocodilia Crocodile, alligators, caiman and gavials Interesting note on the Pterosaurs: first vertebrates to evolve true flight were the pterosaurs, flying archosaurian reptiles  Superorder Lepidosauria Rhyncocephalian – primitive lizardlike reptiles (Sphenodon) Squamates – modern lizards, snakes and amphisbaenians  Euryapsida marine reptiles, Orders: includes the plesiosaurs Dorsal temporal fossa on each side  Synapsida Pelycosauria - first stage in evolution to mammals; Therapsid: have 2 occipital condyles like mammals  Paraspida A pair of dorsal openings (fenestrae) in the skull. Most show two pairs of paddle like limbs.  Class Aves - birds may have arisen from an archosaurian reptile, perhaps a small bipedal dinosaur lost several dinosaur characteristics (e.g., long tail & teeth) but retained others (e.g., claws, scales, diapsid skull, single occipital condyle &, perhaps, feathers) Endothermic  Class Aves Subclass Archaeornithes Subclass Neornithes  Subclass Archaeornithes Genera: Archaeopteryx & Archaeornis Characteristics: – solid bones – weakly developed keel &, probably, weakly developed flight muscles – Reptilian tail, thecodont teeth  Subclass Neornithes Superorder Odontognathae Superorder Paleognathae Superorder Neognathae - birds adapted for sustained flight  Superorder Odontognathae Extinct many features of modern birds (e.g., hollow bones & short tail) Toothed marine birds  Superorder Paleognathae Known as Ratites small wings but powerful leg muscles  Superorder Neognathae Modifications to reduce weight include: – loss of some bones – pneumatic bones – reduced tail – loss of teeth – loss of urinary bladder Generally known as carinates  Class MAMMALIA Amniotes with synapsid skull, hair and mammary glands and nipples Single dentary bone on each of the lower jaw Three bones in the middle ear cavity Muscular diaphragm separating the thoracic and abdominal cavity Absence of adult cloaca Heterodont dentition Unnucleated RBCs Pinna Sweat glands Well developed cerebral cortex  Class mammalia Subclass Prototheria Subclass Theria Spotted tailed quoll  Subclass Prototheria - egg-laying mammals Monotremata - platypus + 2 spiny anteaters – lay eggs; with cloaca – testes within the abdominal cavity – no pinna – no corpus callosum – less stable body temperature – only three species, which are found in Australia and New Guinea.  Subclass Theria Placental mammals Infraclass Metatheria – Marsupialia – poor placenta; pouched mammals; young born alive, but at a very immature stage; yolk sac serves as placenta Infraclass Eutheria – true placental mammals; have chorioallantoic placenta  Marsupialia  do not have long gestation times like placental mammals the young animal, essentially a helpless embryo, climbs from the mother's birth canal to the nipples in a maternal abdominal pouch (marsupium) short gestation time is due to having a yolk-type placenta in the mother marsupial Wallaby Other marsupials Koala, wombat, kangaroo  Eutheria have well developed placentas, longer pregnancies and no pouch. The degree of development at birth varies, some newborn eutherian mammals (cats, dogs and humans, for instance) being helpless, while others (such as the antelopes) are up and running within minutes of birth.  Order Insectivora – moles, shrews, and hedgehogs Order Xenartha – New world insectivorous mammals (armadillos, sloths, S. Am anteaters) Tubulidentata – Aardvarks Pholidota Chiroptera Primates Lagomorpha Rodentia Carnivora  Pinnipedia Perrisodactyla – horses, rhinos Artiodactyla – camels, pigs, hippos, deer, bovines, giraffes Hyracoidea – Hyraxes Proboscidea Sirenia Cetecea Life History and Embryogenesis Gametes and Fertilization  Gametes are the mature sex cells, includes the male sperm and female ovum or egg, each carries a haploid number of chromosomes Sperm Cell smaller animals, bigger sperm - smaller distance to travel Mammalian Egg Cell egg cells choose the sperm cell they want to enter fertilization - (from Gilbert 1988, p. 30) The process where male and female gametes (sex cells) "fuse together to create a new individual with genetic potentials derived from both parents." The fertilized egg is the zygote. Fertilization includes at least four major activities: 1. Contact and recognition between sperm and egg - "quality control" - only sperm of same species may enter 2. Regulation of sperm entry into egg -"quantity control" - only 1 sperm may enter. 3. Fusion of genetic material of both sperm and egg 4. Activation of egg metabolism to start development Penetration of Egg Membrane  Egg  Lecithal = Yolk  Types of Vertebrate Egg with respect to:  amount of yolk: small amt of yolk eg. amphioxus, humans, nutrients from mother instead of yolk  Microlecithal  Mesolecithal  Macrolecithal  Yolk distribution  Isolecithal equal fistribution  Telolecithal unequal Egg: amount of yolk  Microlecithal eggs  Macrolecithal  Small amount of yolk  Large amount of yolk  Amphioxus  Bird and reptiles  Eutherians  Most fish  Mesolecithal  Medium amount of yolk  Amphibians  Egg: yolk Distribution  Isolecithal  Telolecithal  Even yolk distribution  Uneven yolk distribution  In microlecithal eggs  Macrolecithal and Mesolecithal eggs  Vegetal Pole – yolk region  Animal Pole – relatively yolk-free, high metabolic activity/embryo Oviparous  Lay their eggs  Sufficient yolk  Massive yolk: fully formed young  Less yolk: larval state Viviparous: Ovoviviparity  Mother provides only protection and oxygen  Nourishment is from the egg  other squamates python - viviparous cobra, fish that eat their offpring - oviparous boa, vipers - ovoviviparous Viviparous: Euviviparity  Giving birth to offspring  Embryo cannot develop without nourishment being constantly supplied by the mother from maternal tissues - no eggs, except monotremes Key Events in Development  Development describes the changes in an organism from its earliest beginnings through maturity. Cleavage  the series of mitotic divisions that take the large zygote to a mass of smaller cells, the blastula. The individual cells during cleavage are called blastomeres. In early cleavage, the solid ball of cells looks like a blackberry and is called a morula. In later stages, a fluid filled cavity, the blastocoel, forms. In most animals, the cell divisions do not increase the total volume of the cell mass. Instead, the volume remains the same because each generation of daughter cells simply gets smaller and smaller.  Holoblastic cleavage- the cleavage furrows penetrate the entire yolk (Total Cleavage)  Cleavage is equal, all blastomeres are almost the same size at any given time microlecithal  Ex: Amphioxus  Mesolecithal have also total but unequal cleavage, blastomeres near the vegetal pole are larger than those near the animal pole  Ex: Amphibians  Slower development in the vegetal pole  The blastocoel is displaced into the animal hemisphere Cleavage in Birds  Meroblastic cleavage, incomplete division of the egg.  Occurs in species with yolk-rich eggs, such as reptiles and birds.  Blastoderm – cap of cells on top of yolk. Blastula  A fluid filled cavity, the blastocoel, forms within the embryo – a hollow ball of cells now called a blastula. Gastrulation  The morphogenetic process called gastrulation rearranges the cells of a blastula into a three-layered (triploblastic) embryo, called a gastrula, that has a primitive gut. Gastrulation  The three tissue layers produced by gastrulation are called embryonic germ layers.  The ectoderm forms the outer layer of the gastrula.  Outer surfaces, neural tissue  The endoderm lines the embryonic digestive tract.  The mesoderm partly fills the space between the endoderm and ectoderm.  Muscles, reproductive system simple gastrulation, lower forms of chordates like amphioxus Primitive state - invagination and enterocoely in amphioxous  invagination of vegetal pole wall creates archenteron  dorsal wall of archenteron is the notochord rudiment  mesodermal pouches pinch off by a process called enterocoely  ectoderm derived from animal pole cells that now cover the ball Gastrulation - Frog  Result – embryo with gut & 3 germ layers.  More complicated:  Yolk laden cells in vegetal hemisphere.  Blastula wall more than one cell thick. Derived state in amphibians - involution through blastopore  Sheets of cells in wall at junction of vegetal and animal pole begin migrating in along the blastocoel. The site of this involution is the blastopore. anus  the involuting sheets of cells create the archenteron, which displaces the blastocoel  migrating cells on the surface (a process called epiboly) migrate toward the blastopore but many continue past this and cover the vegetal pole, only a small plug of yolk cells (the yolk plug) can be seen at the surface through the bastopore. All of these covering cells become ectoderm  cells in the dorsal wall of the developing archenteron become the notochord -mesadormal in origin  cells migrating through the blastopore laterally become mesoderm Gastrulation - Chick meroblastic  Gastrulation in the chick is affected by the large amounts of yolk in the egg.  Primitive streak – a groove on the surface along the future anterior-posterior axis.  Functionally equivalent to blastopore lip in frog. Gastrulation - Chick  Blastoderm consists of two layers:  Epiblast and hypoblast  Layers separated by a blastocoel  Epiblast forms endoderm and mesoderm.  Cells on surface of embryo form ectoderm. displacing the hypoblast replaces endoderm, area of yolk sac - middle turns into mesoderm  Gastrulation in the chick  In reptiles (as well as in teleost fishes) the blastula is a small disk of cells (blastoderm) on a large yolk. Cells in the blastoderm migrate ventrally to form the hypoblast. The remaining cells in the disk are the epiblast. The blastocoel is the thin space between the epiblast and hypoblast  Cells migrate medially along the epiblast to form a thickened sheet of cells, the primitive streak. A depression that forms in the streak is the primitive groove. At the anterior end of the streak is a local thickening of cells, the primitive knot, or Henson's node, which is effectively the equivalent of the dorsal lip of the amphibian blastopore.  Epiblast cells migrate across and down into the blastocoel through the primitive streak. Initially, the cells migrate anteriorly and ventrally forming the foregut endoderm. These cells moving ventrally forming the foregut displace the hypoblast cells. More epiblast cells ingress and form the head mesoderm and the anterior part of the notochord. Following this, the primitive streak regresses, moving Hensen's node posteriorly. As it moves, the more posterior regions of the notochord develop. More epiblastic cells move in forming the endoderm ventrally and mesoderm in an intermediate position. At its most posterior position, Hensen's node forms the anal region. At the end we have three layers, the endoderm which has displaced the hypoblast, the ectoderm, which is what is left of the epiblast, and lots of mesoderm in between. Note that the gut is not formed yet (no archenteron). The gut forms as a fold of the endoderm during neurulation. reptile-like mice have similar gastrulation process to birds/chicks Gastrulation - Mouse  In mammals the blastula is called a blastocyst.  Inner cell mass will become the embryo while trophoblast becomes part of the placenta.  Notice that the gastrula is similar to that of the chick. placenta The implanting blastula is composed of the external trophoblast and the internal epiblast and hypoblast. During early embryonic development, the epiblast forms a hollow structure containing the amniotic cavity. Similarly, the hypoblast forms a yolk sac. The point where the epiblast and hypoblast meet is called the bilaminar disc. During gastrulation, this bilaminar disc will be converted to a trilaminar disc containing the three germ layers. bilaminar - epiblast and hypoblast trilaminar - germ layers form epiblast endoderm from epiblast, only displaces hypoblast  Aside from the germ layers, the notochordal process is also formed from the primitive node, which is a wider indentation at the end of the primitive streak. This merges with the endoderm to form the notochordal plate which has now direct access to the yolk sac, forming a continuity from the amniotic cavity to the yolk sac through the primitive node and notochordal plate which allows equilibration of pressure in the two compartments of the early embryo. notochordal process merges w the endoderm will eventually form into fluid enters primitive node to the yolk sac notochord there is exchange in fluids in yolk sac Ectoderm, Mesoderm and Endoderm Ectoderm  Nervous System  Sensory structures  Neural crest cells that become melanocytes, adrenal gland…  Epidermis of skin  Epithelium of mouth/nose and anus Endoderm  Lungs & Swim bladders  Digestive viscera  Mesoderm  Chordomesoderm becomes notochord  Mesoderm  Dorsal Mesoderm = Epimere  Segmented bands called somites  Divides into – Dermatome – Myotome – Sclerotome Mesoderm  Lateral plate mesoderm = hypomere  Splits into Somatic and Splanchnic layers  Coelom between these layers Hypomere  Somatic Mesoderm plus Ectoderm =  Somatopleure  Splanchnic Mesoderm plus Endoderm =  Splanchnopleure Mesoderm  Intermediate mesoderm = Mesomere  Kidney tubules and associated ducts Comparative Vertebrate Anatomy: Integument Embryonic Origin  Integument ⚫ Epidermis – derive from the ectoderm ⚫ Dermis - develops from the mesoderm ⚫ Basement Membrane – between the epidermis and dermis ⚫ Hypodermis – transitional subcutaneous region made up of very loose connective tissue ⚫ One of the largest organs of the body making up some of the 15% of the body weight ⚫ Epidermis and dermis may rise up to special forms Function ⚫ Provides as a border between the organism and its environment ⚫ Parts of the exoskeleton and thickens to resist mechanical injury ⚫ Maintenance of suitable water ⚫ Barriers that prevents the entrance of pathogens ⚫ Thermoregulation and respiration ⚫ Protection from harmful sun rays ⚫Storage of calcium and synthesis of Vitamin D ⚫ Production of pheromones ⚫ Receptions ⚫ The multilayered epidermis arises from the single-layered ectoderm ⚫ The deep layer of epidermis, the stratum basale stays on the basement membrane and replenishes the outer Periderm through active cell division ⚫ The epidermis further differentiates into a stratified layer with a mucous coat on the surface ⚫ The dermis arises from several origin: ⚫ Dermatome, an embryonic skin segment derived from the outer wall of the dermomyotome of the segmental epimeres ⚫ The dermatome settles in under the epidermis to differentiate into the connective tissue layer of the dermis ⚫ Some migrating neural crest cells settle between the dermis and the epidermis contributing to bony armor and to skin pigment cells called chromatophores General Feature EPIDERMIS Avascular layer composed of epithelial cells ⚫ Produces mucus ⚫ Keratinized or cornified layer DERMIS ⚫ Vascular inner layer of the integument ⚫ Composed of collagenous connective tissue derived from the mesoderm ⚫ Holds the blood vessels, nerve cells, pigment cells, bases of multicellular glands, and bases of hairs or feathers in place ⚫ Provides tensile strength, and physiological support for the interfacing epidermis Integumentary Structure/Function ⚫ The Structure of the Epidermis Figure 5-2 Integumentary Structure/Function ⚫ Components of the Integumentary System Figure 5-1 Chromatophores - Pr o v i d e c o nc e a l i ng c o l o r a t i o n t o t h e integument Types: Melanophore – melanin Iridophore – which contains light reflecting crystalline guanine platelets Xanthophore – yellow pigments Erythrophore - red pigment ⚫ Melanocytes Figure 5-3 Glands ⚫ Formed from the stratum germinativum of the epidermis ⚫ All are exocrine Types of glands 1. Unicellular glands ⚫ Single specialized, and interspersed among the epidermal cells in fishes Types: 1. Club cells – elongated, binucleated unicellular gland - contains chemicals that excite, alarm or fear 2. Granular cells- in Lampreys and other fishes - contribute to mucus cuticle 3. Goblet Cells – in bony and cartilaginous fishes 4. Sacciform cells – hold a large, membrane- bound toxic secretory products used to repel enemies 2.Multicellular glands ⚫ Formed by ingrowths of the stratum germinativum into the dermis ⚫ The branches of multicellular glands are connected to a single duct which opens onto the outer surface  Types 1. Tubular Glands ⚫ Simple tubular glands – ceruminous glands ⚫ Simple coiled tubular glands – sweat glands ⚫ Simple branched tubular glands – sweat in the axillae ⚫ Compound tubular glands- mammary glands of Monotremes 2. Saccular glands ⚫ Simple saccular glands – mucous and poison glands in the skin of amphibians ⚫ Simple branched saccular glands- sebaceous or oil glands ⚫ Compound saccular glands- mammary glands of metatherians and eutherians Scales ⚫ Serve as exoskeleton of vertebrates for protection of the body ⚫ Epidermal (turtles and snakes) ⚫ Dermal scales (fishes) Dermal Scales ⚫ Cosmoid scale is a small, thick scales consisting of a dentine-like material known as cosmine ⚫ in sarcopterygians resides in a double layer of bone, one layer is vascularized and the other is lamellar ⚫ Placoid scale- consists of basal plate embedded in the dermis with a caudally directed spine projecting through the epidermis (Elasmobranchs) ⚫ Rhomboid/ Ganoid scale – rhomboidal in shape and composed of bones ⚫ thick surface coat of enamel, without dentin ⚫ Sturgeons, Paddle fish and Gars ⚫ Cycloid and Ctenoid scale – closely resemble with each other that may occur both on one fish ⚫ Consists of an outer layer of bone and a thin layer of connective tissue ⚫ The bony layer is characterized by concentric ridges representing the growth increments in the fish Feathers ⚫ Are modified reptilian scales formed from the beta keratin layer of the epidermis ⚫ Distinguish birds from all other vertebrates Types 1. Filoplumes or hair feathers consists of long, slender shaft which may bear a few barbs at its distal ends 2. Down feathers/ Plumulae Composed of a short basal hollow quill, embedded in the skin and numerous barbs which arise from the free end of the quill 3. Contour Feathers - arise in pterylae, consists of long shaft and a broad, flat portion called the vane Hairs ⚫ Mammals, composed primarily of alpha keratin of the epidermis ⚫ Consists of a base or root and a shaft ⚫ Fur/ Pelage composed of guard hairs and underfur ⚫ Vibrissae or whiskers – hairs with sensitive nerves ⚫ Hairs – root, shaft (cuticle, cortex, medulla) ⚫ Arrector Pili Fishes: ⚫ Primitive fishes contains bony plates of dermal armor ⚫ Nonkeratinized and covered by a mucus ⚫ Most living fishes there is no prominent superficial layer of dead, keratinized cells ⚫ Microridges – surface cells increases surface area for communication ⚫ Mucous cuticle ⚫ Epidermal cells and specialized unicellular glands Development of Fish Skin Scales Chondrichthyes ⚫ Dermal bone is absent but contains placoid scales ⚫ Numerous secretory cells and stratified epidermis cells are present in the epidermis ⚫ Chromatophores occur in the lower part of epidermis and upper region of the dermis ⚫ Dermis is composed of fibrous CT especially elastic and collagen ⚫ Placoid scales develop from the dermis Osteichthyes ⚫ Larger number of mucous glands especially among Lungfishes and modern fishes ⚫ Epidermal glands (Unicellular glands) and Multicellular glands in few fishes ⚫ Dermis is subdivided into a superficial layer of loose CT and a deeper layer of dense fibrous CT with cycloid or ctenoid scales ⚫ Chromatophores within the dermis ⚫ Scales are located near close to the epidermis Tetrapods - Amphibians ⚫ Scales are absent, multicellular glands (epidermal glands) and epidermis with stratum corneum ⚫ Skin is specialized as respiratory surface across which gas exchange occurs ⚫ Salamanders – Cutaneous respiration ⚫ Leydig cells within the epidermis of larval salamanders secrete substances that resist in entry of bacteria and pathogens ⚫ Nuptial pads in males ⚫ Two multicellular glands: Mucous glands – smaller made up of little cluster of cells Poison glands – larger with stored secretions ⚫ Chromatophores – occasionally in the epidermis but common in the dermis  Reptiles ⚫ Keratinization is much more extensive and skin glands are fewer ⚫ Epidermal origin of scales ⚫ Hinge – junction between the adjacent epidermal scale ⚫ Large scales are termed scutes ⚫ Osteoderms – dermal bones support the epidermis ⚫ The dermis is composed of fibrous connective tissues ⚫ Epidermis is divided into three layers ⚫ Stratum basale ⚫ Stratum granulosum ⚫ Stratum corneum ⚫ Molting or Ecdysis ⚫ Stratum basale duplicates the deeper layers of granulosum ⚫ Stratum intermedium is formed ⚫ WBC promote separation and loss of the old superficial layer of the skin ⚫ Femoral glands – in many lizards, along the underside of the hindlimb in the thigh region ⚫ Scent Glands in turtles and crocodiles  Birds ⚫ Feathers is considered as an elaborate reptilian scales ⚫ Dermis of bird skin is richly supplied with blood vessels – Brood patch, sensory nerve endings and smooth muscles ⚫ Epidermis comprises the stratum basale and the stratum corneum ⚫ Skin is almost entirely free of glands except for Uropygial Gland and Salt Gland ⚫ Feathers as a distinguishable traits of birds among the other vertebrates ⚫ Pterylae vs Apteria ⚫ Feathers follicles Mammals ⚫ Epidermis – specialized as hair, nails or glands ⚫ Keratinocytes that forms the dead, superficial cornified layer of the skin ⚫ Langerhans cells in the stratum spinosum ⚫ Merkel cells ⚫ Chromatophores Dermis ⚫ Double layered – outer papillary layer and inner reticular layer ⚫ Communication with other organ systems ⚫ Cardiovascular ⚫ Lymphatic ⚫ Nervous ⚫ Sensation ⚫ Control of blood flow and secretion Specialization of the Integument ⚫ Nails – tightly, compacted, cornified on the surface on hands ands toes -protection and stabilize the skin at the tips of the fingers and toes ⚫ Claws or Talons – curved, laterally compressed keratinized projections from the tips of digits ⚫ Hooves – enlarged keratinized plates on the tips of the ungulate digits ⚫ Horns and Antlers ⚫ Baleen – strainers to extract krill from the water gulped in the distended mouth ⚫ Scales – for protection