Comparative Vertebrate Anatomy Exam 2

Contour feathers

-cover the body and are used as air foils on the wing. -On the wing they are called flight feathers. -Feathers have a quill, a shaft, and a vane made of barbs, barbules, and hooklets on the barbules that keep feathers together. -Contour feathers lie in feather tracts called pterylae. -Yellow, orange, red, brown, and black feather colors are the result of pigments, white is due to microstructure and light passing through it, blue and green iridescent colors are structural

Feathers

-feather-like filaments are seen on extinct dinosaurs before flattened feathers appeared on aerial extinct protobirds. -These filaments probably evolved for insulation or for sexual display. -Extant birds use feathers for insulation, sexual display, flight, and camouflage. -Feathers are molted and shed once or twice a year and not all feathers are shed at once

Hard Palate

-From amphibians to primitive reptiles, palate was same and air came into the anterior portion of the jaw. -A secondary plate formed by the development of a shelf so that these animals could eat and breath at the same time. -We find this in advanced synapsid therapsid reptiles and from here on. -This became important with development of constant elevated temperature and the related need for simultaneous breathing and eating. -Secondary palates evolved independently several times, crocodilians have a complete one, and some turtles an incomplete one. -The secondary palate also serves to strengthen the rostrum against bending moments when these animals bite on one side of the jaw.

Limbs

-"ostracoderms" had either pectoral spikes or pectoral lobes of dubious origin. -Placoderms had little better (stiff fins, hinged arms or multiple spines). -The Chondrichthyes have changed little, with cartilaginous basal and radial pterygiophores, and horny certotrichia rays supporting the fin. -Bony fishes have bony pterygiophores (radial pterygiophores) and bony lepidotrichia. -It was possibly the habitat of crawling on the bottom or out of swampy areas on to land that facilitated the evolution of limbs. -The lobed "fleshy" fins made their limbs suitable for crawling around on the swampy shores, and these broad limbs had 6-8 digits. -However, these early amphibians still had a caudal fin on the tail, evidence of a partial aquatic life style. -The bony fish pectoral girdle is attached to the skull through dermal bones, the posttemporal, supracleithrum, cleithrum, and postcleithrum. -Elasmobranchs dont attach pectoral girdle to skull, instead it is united at the midline by the coracoid bar. -Therefore, in fishes the pectoral girdle is more firmly attached and important in the tetrapods the pelvic girdle is the more firmly attached one. -The limbs of early amphibians came off at the side of the body making locomotion quite difficult relative to the higher tetrapods (sprawled position). -The limb bones were short and stocky. -They still used lateral undulation when they walked or swam. -Earlier vertebrates apparently had a variable number of digits; earliest amphibians had more than five (polydactyly); pentadactyly may be a derived character; amniotes have stabilized at five digits on each limb; however modern amphibians have four on the anterior limb. -Most reptiles still have limbs coming off the side and still use a great deal of lateral undulation for locomotion. -Snakes lack the pectoral and pelvic appendages, although vestiges of the pelvics (femora) remain in some as anal spurs ex: boid snakes. -Some lizards have become snakelike because of loss of limbs ex: Florida glass lizard -Birds and bats have greatly modified forelimbs in different manners. -Bird hins limbs are modified for upright bipedal locomotion. -In mammals limbs had to move under the animal and rotate so knees and feet point anteriorly. -Forelimbs have to rotate backwards so elbows point posteriorly and the wrists also have to rotate so radius crosses ulna. -This leads to more efficient locomotion. -To increase running speed the posture has gone from a more ancestral plantigrade design to a digitigrade and unguligrade upright posture as running sped increases with limb length. -Pelvic girdles and hind limbs are lacking in whales and sea cows but they have small remnants.

The Jaw and Hearing

-As the jaw articulation shifted anteriorly due to changing direction of muscle forces, the dentary became larger and the articular became smaller. -The squamosal took over more of the jaw bracing and the quadrate became smaller along with the articular, however, the jaw joint is still between the quadrate and articular. -The columella/stapes (former hyomandibula) transfers vibrations from the jaw to the tympanum to the otic (ear) region of the skull.

Hair

-Characteristic of mammals and its evolutionary origin is unclear. -Some feel it came from reptilian scales or mechanoreceptors. -Typical hair has a shaft, and the root set in a hair follicle. -At it's base, the root is expanded into a small bulb into which projects a dermal papilla carrying nerves and blood vessels. -The dermal papilla has living cells. -As cells become keratinized and die, they push forward forming gate hair, which forms 2-3 layers. -In coarser hair, there is a central medulla of shrunken cells and large air spaces; next, the pigmented cortex makes the bulb of the hair. The outer cuticle is composed of scaly cells. -Sebaceous gland pours sebum onto hair to waterproof it. -Arrector pili smooth muscle controls erection of hair for added insulation. -Straight hairs are circular in cross section and curly is is oval in cross section. -Hairs are constantly shed, but some mammals produce a winter coat and shed most of it during the summer. -Most furred animals have long guard hairs over a denser coat of under hair or underfur. -Hairs take on a variety of shapes and functions: vibrissae or whisker, quills of porcupines, eyelashes, eyebrows

Mammary glands

-Confined to mammals. -The earliest mammals may have provided anti-microbial protection to the young by glands that the young licked; eventually leading to copious milk secretion and added benefit of nutrition. -Mammary glands are modified sweat glands or sebaceous glands that secrete milk, therefore the are epidermal in origin. -Usually there is a nipple, but monotremes have ancestral condition of no nipple but tufts of hair on which milk accumulates. -Mammary glands develop along a milk line in which two or many mammary glands might develop. -The artiodactyl (even toed mammals) teat has an enlarged cistern for copious milk storage and quick release. -The diphyodont dentition of mammals is associated with suckling of milk; the "milk" teeth are not suited for eating hard prey as they are used for suckling.

Evolution of the head skelton

-During the evolution of the head skeleton probably the first supportive structures of the head were a visceral skeleton or splanchocranium that supported the supported the gills. -Its may have been fibrous or cartilaginous, and then later bony. -Following this, a cartilaginous braincase/neurocranium or chondrocranium evolved in addition to the visceral skeleton. -This forms around the brain and the major sense organs. -The chondrocranium forms from a variety of cartilages. -It may fuse into a solid mass, such as in the Chondrichthyes. -Later in evolution, it became ossified. -Thirdly, dermal bony plates appeared. -This dermatocranium covers and protects the deeper elements of the skull. -The chondrocranium usually does not enclose the brain completely, membrane/dermal bone lying over the brain gives it the most protection. -Bones that form in the visceral arches and the ones that form in the chondrocranium are cartilage replacement bones. -The bones that roof the skull are membrane/dermal bones for the most part. -In both the "ostracoderms" and placoderms the chondrocranium was made of hyaline cartilage or ossified cartilage and the dermal armor formed a protective dermatocranium. -The dermal components, however, cannot be homologized to the bones of higher vertebrates. -The gill arches were cartilage. -By the time the crossopterygian fish stage was reached, however, a general bone pattern was established that we can trace throughout the vertebrates. -In crossopterygians the arrangement of bones in the dermal head shield is remarkably like that of tetrapods. -Because of fusions, deletions and additions of bones the skull is exceedingly complex, but we will trace the basic path through the Crossopterygii -- early amphibians -- earliest and theraspid reptiles -- to the mammals.

Reptiles

-Earliest reptile anapsid skulls with a higher and narrower skull than their amphibian relatives, but otherwise there was little difference. -Dermal bones formed the roof f the skull with endochondral bones beneath them. -In later reptiles, one important difference was openings (fenestrae) in the temple and cheek areas. -The functional significance is not clear; most likely has to do with attachment of the jaw adductor muscles. -The number and bones that border the openings is one character used to classify reptiles. -These differences are due to position and size of jaw muscles. -The early reptiles had jaw muscles like fishes and amphibians in a notch on the side of the skull. -As jaw muscles increased in strength, the cranial vault changed in size and shape. -Generally the openings got larger and moved laterally so that the zygomatic arch of mammal remains. -Turtles, like primitive reptiles, have no fenestrae which is not understood to be a derived condition as they were originally diapsid, mammals came from synapsid stock that had one fenestra. -The lizards came from a stock with two fenestrae (diapsid) but the lower bar of the lower fenestra is lost due to the enlargement of the jaw adductor muscles. -Crocodilians still retain two fenestrae.

Skin of Fishes

-Epidermis has little to no regional cellular specialization. -Unicellular mucous glands lie in the epidermis. These may include goblet, granular, or club cells. Club cells release an "alarm substance". -The dermis is composed of an outer stratum laxum and and inner more dense stratum compactum. -The collagen fibers of the stratum compactum form a helical pattern around the body. -Scales, which are dermal derivatives, follow this helical arrangement around the body as well. -Pigment cells are found mostly in the dermis. -Fish can be yellow, orange, red, blue, black, or silvery. Ex: coral reef fishes -Photophores in the skin can produce bacterial or chemical light.

Skin of Amphibians

-Epidermis lacks distinct layers and is only a few cell layers thick. -Some have a thin layer of keratinized stratum corneum cells on the outside that get shed every few days. -Epidermally derived mucous glands are abundant as are granular or poison glands that secrete toxins. -Because stratum corneum is so thin, they must live in moist habitats. Aquatic species and amphibian larvae generally lack keratinized skin. -Skin is a major respiratory organ in most mammals. -Keratinized or horny teeth are found on tadpoles and the claws of the African clawed toad, Xenopus, are made of keratin. -Fossil amphibians had dermal (bony) ossicles and only legless caecilian have dermal scales embedded in their skin now.

Amphibia

-Gravity, and twisting (torque) on the vertebral column were new forces on the vertebral column as the animals walked on land. -This was resisted by helically wood fibers in the notochord (early species), heavy ossification of the centrum, and the development and strengthening of pre- and postzygapophyses. -In fishes the girdles were not associated with the vertebral column, now they are attached to it for support. -Regional differentiation of the vertebral column amphibians is minimal but more than fishes. -With the loss of the gills and the bony connection between the skull and the pectoral girdle lost (ex: bony fishes), there now is ONE cervical vertebra (the atlas) giving greater mobility to the short neck and head; trunk vertebrae; a SINGLE sacral vertebra that fuses to the pelvic girdle to support it, as most locomotory force is from the hind legs; and finally caudal vertebrae. -Anurans have an atlas, trunk vertebrae, one sacral vertebra, and FUSED caudal vertebrae called the urostyle for jumping, as well as a shorter trunk and fewer vertebrae, elongated ilia, elongated proximal tarsals, reduction of ribs, lengthening of the hind limbs, and no tail. -Apoda ma have up to 285 vertebrae.

Phylogeny and Structure

-In many ancestral living and fossil fishes the notochord remains throughout life, called a persistent notochord, as this is the primitive axial support. -Such a supportive rod is important for the muscles to work around the body. -They mostly have various dorsal cartilaginous arches above and ventral arches below the notochord (except hagfishes which only have a notochord) which provide attachment points and give protection to the nerve cord and blood vessels. -These cartilages probably evolved where tendons inserted on the notochords. -The next stage in evolution involved the formation of two centra (pleurocentrum and intercentrum) from the ventral arches. -The amniote centrum is derived from one of these. -In adult amniote all that remians of the notochord is the nucleus purposes of the intervertebral disc.

Fins

-It is presumed that most ancestral fishes had no fins. -One hypothesis states a median fin fold developed to aid locomotion; this eventually formed the dorsal, caudal, and anal fins. -A ventrolateral fin fold, similar to what we see in the early development of the shark's pectoral and pelvic fins, may have given rise to the paired fins. -Fins no doubt evolved to stabilize fishes during swimming. -Today we see a variety of caudal fin shapes. -In sharks, surgeons, and paddlefish, the vertebral column courses into the upper lobe resulting in the upper lobe most often being larger than the lower lobe. -This is the heterocercal tail. -The resultant force from the heterocercal shark caudal fin is directed anterodorsally. -The large pectoral fins and ventral body surface add life to the anterior end of the body. -Some extinct fishes had the vertebral column passing into the lower lobe, this is the hypocercal tail. -However, most fishes have a homocercal tail, ex: teleosts, with the upper and lower lobes being equal in size and all the fin membrane lying posterior to the bony skeleton. -In these the forces are directed anteriorly. -In these the pairds fins, pectorals mostly, are now used for maneuvering and steering. -Sharks have cartilage pterygiophores (basal and radials) and horny ceratotrichia supporting the fin, bony fishes have bony pterygiophores (radials) as well as bony lepidotrichia.

Epidermal Scales and Structures

-Keratinized scales are found on tails of rat, beaver, mouse and opossum. -Scaly anteater (pangolin) of Asia and Africa has a complete body covering of scales; armadillo has scales over dermal plates. -Baleen in toothless whales is made of keratin and used for filter feeding. -There is an emphasis on DERMAL derivatives more than there is an emphasis on EPIDERMAL derivatives in tetrapods. -From the early bony armor of ostracoderms and placoderms we see the transformation to teeth and scales, dermal bones covering the skull and forming some bones of the pectoral girdle, gastralia in crocodilians, with the gradual reduction of heavy armor and replacement with epidermal derived scales, feathers, and hair.

Cornified Structures

-May be excessive deposition of keratin in skin such as in elephant, hippo, rhino or discrete structures may be formed. -Baleen is made of hairlike keratin fibers

Girdles

-Origin of paired fins in fishes is obscure. -In some "ostracoderms" we see paired spinous projections or remnants of fins in the pectoral region; some spines may have clumped together to form a fin. -Placoderms had pectoral ad pelvic girdles and fins. -As fins became larger the endoskeleton part of the pectoral and pelvic girdles became larger. -These are composed of cartilage replacement bone. -Later on, the dermal elements from the head may have contributed, hence the dermal bones in the pelvic gridle of fishes and its attachment to the cranium.

Jaws

-Primitive jawless vertebrates had braincase/neurocranium and series of visceral arches supporting the gills. -The first one or two visceral arches appear to have been lost although one may still be visible on sharks as the labial cartilage. -What we now call the first visceral arch, the mandibular arch, formed the jaws. -Jaws make their first appearance in placoderms according to some. -The upper element, the palatoquadrate bar formed the upper jaw, and the lower element, Meckal's cartilage, formed the lower jaw. -The adult jaws of Chondrichthyes consist of these elements. -Later on dermal bones play a role in jaw function. -In other fishes along the edge of the mouth dermal bones bear teeth; ex: pre maxilla, maxilla, dentary. -These bones envelop the original palatoquadrate and Meckal's cartilage. -In addition to the mandibular arch and hyoid arch, which are called visceral arches I and II, there are 5 other arches called branchial arches that support the gills. -Thus the third visceral arch is the first branchial arch. -In order to brace the jaw for feeding on hard prey, primitive fishes such as placoderms, had the jaw articulating with the brain case without any other support; this is called primary autostylic jaw suspension. -The second visceral arch, the hyoid arch, is composed of an upper element, the hyomandibula, as well as the ceratohyal and the basilhyal. -The hyomandibula then took on the additional role of jaw support. -In some fishes (Crossopterygii, primitive Chondrichthyes, primitive Osteichthyes) the jaw is supported by the hyomandibula and by the direct connection of upper jaw and braincase. This is termed the amphistylic condition. -In most Osteichthyes and Selachii the upper jaw loses any major connection with the braincase and the jaws are propped only by the hyomandibula, called the hyostylic condition. This provides greater feeding mobility to the jaws. -In tetrapods the hyomandibula no longer supports the jaws, the upper jaw fuses with the braincase and agin the jaws are supported at one point only, the secondary autostylic condition again.

Skin of Mammals

-Relatively thick. -Typically, the deepest layer is the stratum germinativum where mitosis occurs, above this there is a variety of layers. -The outermost layer is the stratum corneum, it is cornifiied because keratin replaces the cytoplasm. -The dermis is composed of elastic, reticular, and collagen fibers and is well supplied with blood vessels, nerves, glands, and sense organs. -It has two layers, the papillary layer is superficial and has dermal papillae and larger dermal ridges that protrude into the epidermis, giving us fingerprints and footprints. -The deeper reticular layer has thicker collagen fibers running in preferred directions called Langer's Lines.

Fishes

-Sarcopterygian crossopterygian fishes have heavily boned skull with a hinge in the inner chondrocranium. -This is represented by the skull of Eusthenopteron. -Dermal bones roof the skull and support the teeth (pre maxilla, maxilla, dentary) and the original cartilaginous mandibular arch (palatoquadrate and Meckal's cartilages) is relatively small and forms other elements (i.e. quadrate and other bones are remnants of the palatoquadrate cartilage. Meckel's cartilage is covered by the membrane bones of the lower jaw, and the articular is a remnant of the Meckel's cartilage). -The hinge between the upper and lower jaw is between two bones, the articular and the quadrate. -The quadrate also has the hyomandibula between it and the auditory portion of the brain case bracing the jaw (the amphistylic jaw). -This had the effect of passing vibrations along the lower jaw, which probably rested on the sea floor, through the hyomandibula and into the inner ear. -So the hyomandibula began to function in hearing. -Elasmobranchs retain a cartilaginous neurocranium/chondrocranium, cartilaginous upper (palatoquadrate cartilage) and lower (Meckel's cartilage) jaw elements, which is propped by the hyomandibula (the hyostylic jaw suspension). -The remainder of the hyoid arch is composed of the ceratohyal and basilhyal. -Modern teleosts have greatly reduced the number and size of the bones in the skull most likely as a way of reducing weight. -Dermal bones form the roof of the skull and endochondral cartilage replacement bones lie below them to form part of the neurocranium. -The hyomandibula primarily supports the jaw (before forming the hyostylic jaw suspension). -This enhances mobility of the upper jaw facilitating numerous feeding opportunities. -In bony fishes, the palatoquadrate cartilage forms the quadrate in part, but is covered by dermal bones (premaxilla and maxilla) during the development so all that remains in adults is the quadrate bone. -The Meckel's/mandibular cartilage forms the articular at the posterior end of the jaws, and during development is covered by dermal bones which include the dentary. -In bony fishes, the plesiomorphic condition is for the premaxilla and maxilla to be the dermal tooth bearing bones of the upper jaw. -In modern bony fishes the maxilla is now excluded from the gape and premaxilla is the tooth bearing bone of the upper jaw. -This permitted the maxilla to drive the premaxilla forward and protrude it when the jaw opened. -This no doubt opened up numerous feeding niches for these fishes allowing them to more efficiently suction feed etc. -Remainder of the hyoid arch and the branchial arches support the tongue and internal gills.

Snakes and Lizards

-The bars of the upper and lower temporal fenestra are lost so that in snakes (originally diapsid) the entire cheek area is cleared of dermal bones so quadrate hinges loosely against the supra temporal, and both are kinetic providing cranial kinesis for swallowing large prey.

Generalized Amniote Vertebra

-The body is called the centrum, above this is a neural arch protecting the spinal cord, below it may be a hemal arch protecting blood vessels. -Both arches can be extended as a neural and hemal spines. -Prezygapophyses and postzygapophyses link it to other vertebrae. -Lateral traverse process stick out from the sides. -Procoelous centra have concave anterior surface (ex: frog); opisthocoelous have concave posterior surfaces (ex: turtle). -These permit a grater range of motion and resist dislocation. -Amphicoalous are concave on both sides (ex: bony fishes) and platen/acoelous are flat on both (ex: birds and mammals) and these restrict motion.

Birds

-The body skeleton of birds have thinner but denser bones, making them stiffer and stronger relative to their weight. -There are 5 types of vertebrae, although there is great fusion except in the cervical region which has numerous vertebrae (12-25) give them a long flexible neck. -They have partially fused thoracic vertebrae bearing ribs. -A short rigid and lightweight back is adapted for flight and bipedalism. -This is due to FUSED thoracic and lumbar (10-12), TWO sacral, 5-6 caudal vertebrae and ribs to form a synsacrum which supports the pelvic girdle. -After free caudal vertebrae, fusion of the last caudal vertebrae (4-7) forms the pygostyle.

Amphibia

-The early amphibian skull is basically conservative, looking a great deal like that of the crossopterygian skull. -The principal difference lies in the overall proportions of the skull, in particular, the amphibians have considerably increased the length of the snout and tooth row compared to the crossopterygians. -The quadrate and articular still comprise the jaw joint. -The quadrate of the upper jaw articulates with the squamosal without bracing of the hyomandibula. -The upper jaw is now directly fused to the neurocranium to further brace it for feeding on solid food and is referred to as the secondary autosylic jaw suspension. -The old spiracle opening is covered by the tympanic membrane and since the hyomandibula is freed from the jaw function, it forms the columella (stapes) which runs to the inner ear transferring vibrations, especially those from the lower jaw (extinct amphibians) as well as from the tympanum (recent amphibians ex: frogs). -Ventral parts of the hyoid arch still support the tongue, and the branchial arches only serve a respiratory function in larvae and adult gill-breathing amphibians. -In others, the hyoid and branchial arches support the tongue and larynx, and possibly form cartilaginous tracheal rings. -Modern amphibians have diverged, with reduction in dermal bone. -So the neurocranium has dermal bones on the upper surface and endochondral bones deeper. -In the Anura the skull has become flattened probably to aid the respiratory pressure pump of the mouth, and large vacuities (holes) in the skull have developed. -This allows retraction of the eyes into the mouth region to aid swallowing.

Mammals

-The gradation between the therapsid reptiles and mammals was a very gradual one. -The mammalian skull is characterized by loss of some bones, fusion of many, reduction of some, but perhaps no new additions. -Generally the cartilage replacement bones are retained in the rear, floor, and front of the brain case, and the dermal bones covers the top and sides of the skull. -Much of the original dermal roof that lay lateral to the jaw muscles are lost. -In carnivorous mammals, the coronoid process of the lower jaw increased in size from the synapsid skull in order to increase the leverage of the temporals jaw closing muscle. -This became more pronounced in advanced forms. -Concomitantly, the original synapsid fenestra moved posteriorly and ventrally with the changing origin of muscle mass. -The increased jaw leverage may have been beneficial in killing larger struggling prey. -As the synapsid graded into the mammals the temporal opening enlarged to such an extent that it merged with the orbit. -Later the bar was partially or completely rebuilt. -As the adductor muscles became enlarged the zygomatic arch became bowed outward to accommodate them. -Herbivorous mammals that do not rely on such massive jaw forces to hold struggling prey in the anterior end of the mouth instead rely mostly on other jaw muscles (master) to masticate plant material. -The temporal is muscle and the coronoid process that it attaches to, become much smaller such that they have more leverage from the master muscle for chewing and grinding, and a smaller lever arm for the temporals muscle. -The temporal is muscle inserted on the coronoid process of the dentary, so the dentary expanded in size and articular became smaller. -The squamosal at this time was supporting the quadrate which in turn supported the jaw. -With the shift on the direction of the force on the lower jaw, the squamosal got larger and took over this role. -The quadrate then became smaller as well as the articular. -As the tympanic (ear) cavity expanded these two became incorporated into the middle ear cavity. -The quadrate and the articular now form the other two ear ossicles in mammals, so the hyomandibula forms the stapes, quadrate the incus, and the articular the malleus. -This leverage system of three ear ossicles is far more efficient at magnifying vibrations than the piston action of the columella alone. -Therefore the lower jaw consists only of the dentary and it articulates with the squamosal. -The squamosal merges into the temporal -So the early palatoquadrate cartilage of fishes forms the incus (formerly quadrate) in part, and the Meckel's cartilage forms the malleus (formerly the articular) in part. -The mammalian dentition became more heterodont to deal with a grater variety of food items. -In herbivores the snout is elongated for browsing within the foliage and raising the head above the ground, resulting in a larger diastema. -The ancestral hypobranchial skeleton (hyoid and branchial arches) forms the hyoid apparatus, usually embedded in the base of the tongue, the larynx and possibly the tracheal rings. -The secondary palate is present and extended by a soft palate. -The nasal cavity expanded in evolution and comes to house delicate bony scrolls, the turbinates (conchae), used to warm and moisten the air in these homeotherms.

Advanced fishes

-The notochord is partially or totally replaced by cartilaginous or bony centra and the arches and processes are enlarged. -In sharks the centra are made of cartilage that is often calcified in various patterns. -Cartilage intercalary plates fill in the gaps on the dorsal side. -Bony fishes have neural and hemal arches near the tail. -Except for trunk and caudal vertebrae, there is little regional difference of the vertebrae in either group because the body is supported by water. -In fishes, the notochord may remain in the center of the vertebral column. -Zygapophyses may be found on some fishes, bracing adjacent vertebrae.

The Pelvic Girdle

-The pelvic girdle of sharks is composed of scapula processes and coracoid bar (also called the scapulocoracoid), unites at the midline. -It does not attach to the chondrocranium. -Paired pectoral fins in teleosts have migrated up to the midline of the fish to prevent pitching when braking. -In modern teleosts the pectoral girdle is attached to the skull by the post temporal, and the pelvic girdle is wedged within the pectoral girdle. -The paired fins of these advanced fishes are used for stabilization, braking, swimming, and some have strengthened hinged fins which they walk with (mudskippers) -In tetrapods, the pectoral girdle has undergone extensive changes: -1) there has been a steady reduction in the number of bones -2) cartilage replacement bones have become larger -3) dermal bones reduces -4) the bones connecting to the skull have been lost above the cleithrum allowing the head and neck greater mobility. -The peak is reached in the birds and mammals. -Amphibians and reptiles retain the scapula and coracoid, as well as the clavicle, and interclavicle, in some cases. -Birds use the girdle bones, scapula, coracoid, clavicle, interclavicle, particularly the coracoid, to brace the large sternum which is used for attachment of flight muscles. -In mammals only the clavicle (a dermal/endochondral bone) and scapula (endochondral bone) remain. -The coracoid has fused to the scapula to form the coracoid process. -Only attachment with the axial skeleton may be through the clavicle. -In man this adds stability and at the same time allows a great deal of movement. -In quadripeds, the clavicle is not attached to the sternum and is greatly reduced or lost allowing a shock absorber effect and greater reach for faster running. -In the dog and cat for example, the pectoral girdle and forelimb is suspended by a "muscular sling".

Skin of birds

-The skin of birds is thin, loosely attached and weakly keratinized, adapting to the movement of underlying muscles. -Epidermal scales are found on the feet and they have heavily keratinized beak and feathers. -The epidermis is generally only a few cell layers thick. -Skin is essentially free of glands, except for a single uropygial or preening gland that secretes oil which birds use for waterproofing the feathers, and a salt gland in marine birds. -Pigment is present in scales, feathers, and beaks but the skin may be weakly pigmented. -Coloration of skin and feather may be structural resulting from light striking collagen fibers within the dermis and the underlying melanin. -Dermis is thin, well vascularized, composed of mostly irregular fibers

Birds

-The skulls are basically the same as the reptilian ancestors except the cranial roof is expanded to house the larger brain. -Superficial dermal bones and deeper end-chordal bones form the brain case, and dermal premaxilla, maxilla, and dentary bones house teeth on extinct birds. -There are also thinner BUT DENSER bones for lightness, fashion of many elements, a movable quadrate like the snakes and lizards, and elongation of the beak bones. -Much of the bar behind the orbit and between the two original fenestrae (diapsid skull) is lost, due to enlarging of the brain and the enlarged orbit. -The jaw joint is still between the quadrate and articular; columella runs from the tympanum to the inner ear. -Some birds have cranial kinesis by dropping the lower jaw and simultaneously raising the upper jaw. -The hyoid supports the tongue. -Some birds such as the woodpecker have a greatly elongated hyoid bone that curves all the way around the skull. -It can pull forward to protrude the long tongue. -The turbinals (conchae) are enlarged like mammals to warm and moisten the air as they are homeothermic endotherms also.

Development

-The vertebrae are derived from they embryonic connective tissue mesenchyme. -They come from the upper part of the segmented somites (the sclerotome) which come to lie around the notochord. -During development the vertebral centra from between adjacent myotomes. -Thus the muscle segments come to lie between adjacent vertebrae allowing for bending of the column when they contract. -Initially cartilage vertebrae are formed, then they ossify.

Nails, Claws, Hoofs

-These are tough keratinized structures of epidermal origin. -Claws are found on few amphibians (these are not true claws), common on reptiles, birds and mammals. -Outer plate or UNGUIS of true claw is hardened by keratin and calcification, beneath this is softer SUBUNGUIS. -Ungulates have a modified claw, the hoof, the unglues is the hoof proper, the subunguis is the softer underlying part. -In primates, the nails replace the claws. -The ungluis is the conspicuous part. -Most felids can protract the claws with muscles, and have "hyper-retractility" by means of an elastic ligament. -The cheetah has an autapomorphic state of reduced retractility. -The claws of digits 2-5 are straighter, thicker and more elongated than other felids, resembling canid claws. -The hind limbs have even less retractility. -This is associated with its predatory behavior of chasing down prey and it presumably gives it better traction, but results in somewhat worn and less sharp claws. -Consequently it cannot hook its prey with its claws as other felids do, it uses its dew claw to hook the hide of its prey as it chases it and throws it off balance. -It then suffocates its prey by biting its throat

Ribs

-These develop dorsally and ventrally between muscle bundles where sheets of connective tissue, myosepta, attach to the vertebrae. -Many fishes therefore have dorsal intermuscular and ventral sub peritoneal ribs (salmon); many advance teleosts only have ventral ribs. -Ribs originally provided muscle attachment for locomotion -They lengthened and came to protect viscera and aid in respiration in later vertebrates. -Ancestral condition is to have short ribs on all vertebrae except the most caudal vertebrae. -Most tetrapods have only one set of ribs, probably dorsal ribs. -Typically tetrapod ribs are bicipital haveing two heads, a tubercular (tubercle) and capitulum (head). -The thoracic ribs remain well differentiated, in other vertebrae the embryonic ribs fuse with their attaching rib processes to help form the transverse processes. -Turtle thoracic ribs are fused to the carapace. -Trunk ribs of snakes have no sternum, and have muscular connections to the scales on the ventral side, assisting in locomotion. -Crocodilians have free ribs on the cervicals and thoracic, and fused ribs on the lumbar and sacral vertebrae. -Many of the bird's ribs are linked by uncinate processes for strength and attachment of respiratory muscles, some to the synsacrum. -Mammals have free ribs in the thoracic region, with ribs fused to the transverse processes of the cervical and lumbar vertebrae. -Mammalian thoracic ribs are classified as vertebrosternal where they attach to the sternum, and vertebrocostal where they attach to costal cartilages. -Vertebral or floating ribs do not attach to either.

Reptiles

-These have 5 divisions of the vertebral column: cervical, thoracic, lumbar, sacral, and caudal. -As the neck became longer and more mobile the two most anterior cervical vertebrae developed modifications to allow pivoting and rotation of the head, these are the atlas and axis (there are more cervicals than just these two). -Part of the atlas forms the odontoid process or dens of the axis, limiting twisting movement. -Thoracic vertebrae bear ribs, lumbar vertebrae have fused ribs, and there are now TWO sacral vertebrae for firmer fusion of the pelvic girdle. -Caudal vertebrae support the tail. -Snakes and legless lizards only have trunk and caudal vertebrae. -Turtles have cervical, thoracic, TWO sacral, and caudal vertebrae but LACK lumbar vertebrae. -The thoracic vertebrae are fused to the carapace. -Reptiles have strong zygapophyses (except in caudal region) to further support the body against gravity.

Mammals

-These usually have 7 cervical vertebrae including atlas and axis, thoracic vertebrae with large ribs, and even fused lumbar ribs on the lumbar vertebrae, the support of the propulsory pelvic girdle is braced against the vertebral column with generally 3-5 sacral vertebrae fused as a sacrum to support the lower limbs; lastly there are 3 or 5 caudal vertebrae in man (typically 4) forming the coccyx, to 50 in others. -Zygapophyses are well developed in terrestrial mammals to support the weight of the body against gravity.

Horns, Antlers

-Used in reproduction, protection, and offense. -Horns first found in dinosaurs. -Rhino horn -- epidermal keratin fibers glued by horny cells and is not shed. It has continuous growth and sits on a small bony prominence. -Giraffe horn -- bony projection covered by skin. -True horns of cattle, sheep, gazelles, goat, antelope, bison, and wildebeest is composed of a hollow bony core with keratin fibers over it. They are perminent and cap is shed annually. -Antlers of deer, elk, moose, and caribou have a projection of bone covered by skin during development (velvet), skin dries and sheds when mature before mating season, and later antler is shed. New antler is formed each breeding season.

Epidermal Derivatives

-Various glands develop as down growths from the epidermis. -Sweat glands are either eccrine glands, which secrete sweat and cool the body, or apocrine glands (located in axilla, around the anus, scrotum, and labia majora) these are important in sex smells. -Sweat glands are unique to mammals although some animals, such as whales, do not have them. -Sebaceous glands are also limited to mammals and drain into hair follicles. -Their oily secretion, sebum, waterproofs the hair. -Scent glands are modified apocrine glands found in many mammals, such as the anal glands in dogs and cats. -Ceruminous wax glands in the ear canal produce cerumen.

Skin of Reptiles

-With adaptation to terrestrial life, the skin of reptiles has a complete body covering of keratinized scales. -This gives protection against desiccation, gives mechanical protection, and is used for locomotion. -Epidermis is now thicker with a stratum germinativum and a thicker stratum core. -There are only a few epidermal derived glands. -In lizards and snakes there is an inner and outer epidermal generation of the epidermis. -Molting and shedding in the skin of lizards and snakes occurs between the latter two regions. - Reptiles have two general types of epidermal scales: snakes and lizards have scales arranged in longitudinal rows, each overlapping. -The hinge between the scales is thinner keratin. -Turtles and crocodiles have scales that do not shed; In turtles, the scales arise on top of bony armor -Stratum germinativum produces scales and they "pile up" if they are not worn away. Because each successive scale is larger, they form the appearance of growth rings. -These scales are not shed in crocodilians and some turtles; the Florida Slider irregularly sheds its scales. -These large, plate-like epidermal scales, such as the ones found on crocodilians, turtles, and on the ventral scales of snakes, are called scutes. -Mucous glands are absent, however there are some glands that are involved in reproductive behavior. These are found on the lower jaw of crocodilians and in the inner thigh or some lizards. -The dermis is thin and composed of two layers.

The Pelvic Girdle

-has gone from a small, weakly supported element as most weight was borne by water, to a larger one for more locomotory muscle attachment, with more firm attachment for weight bearing on land. -From early amphibians to mammals it is composed only of the endochondral bones: ilium, ischium, and pubis. -The ilia in particular are expanded to bear greater locomotor muscles, and enlargement of the girdle resulted in it connecting to one sacral vertebra in amphibians, two sacral vertebrae in reptiles, and 3-5 in mammals. -Birds have lost the pelvic symphysis to allow for egg laying.

Down Feathers

-have little, or no shaft and no hooklets. -These are small feathers that lie all over the body for insulation

Bristles or Filoplumes (hair feathers)

-lie around the mouth, around the nostrils, and over the eyes.

Beaks

-made of thickened, keratinized and compact epidermal cells -Teeth are not present in adults but can make an appearance in development. Ex: parrots