Animal Diversity Exam 3 Study Guide PDF

CHAPTER 23: CHORDATES Chordates: - Name derived from notochord - includes most animals familiar to most people - Features shared w/ other animals: - bilateral symmetry - coelom - complete digestive system ( tube within a tube)...

CHAPTER 23: CHORDATES Chordates: - Name derived from notochord - includes most animals familiar to most people - Features shared w/ other animals: - bilateral symmetry - coelom - complete digestive system ( tube within a tube) - metamerism - cephalization - Deuterostomes - Anus develops from blastopore - radial cleavage - coelom formed by fusion of enterocoelous pouches - Classification: - * many traditional groups no longer used b/c they didn’t satisfy the requirement of cladistics that only MONOPHYLETIC groups are taxonomically valid - Ex: is protochordata monophyletic or paraphyletic ? - Paraphyletic - Ex: Traditionally reptilia (reptiles) did not include Aves (birds). Without including birds reptilia is _____________ - MAJOR GROUPS: - Major group 1 ( VERTEBRATES) - distinct head w/ brain and cranium - paired special sense organs - vertebrae - Major Group 2 ( GNATHOSTOMATA) - Jaws - Major Group 3 (OSTEICHTHYES) - bony endoskeleton - Major Group 4 (TETRAPODA) - paired w/ limbs used for terrestrial locomotion - Major Group 5 (AMNIOTA) - embryo with amnion (fluid filed sac ) - Major Group 6 (REPTILIA ) - skull characteristics - Subphyla: - Cephalochordata: lancelets - Tunicata: tunicates - Vertebrata: vertebrates - Ancestry & Evolution:  - difficult to reconstruct evolutionary history of the earliest chordates because they were probably soft bodied creatures with little chance of being preserved as fossils - instead learned from analysis of early developmental stages - most likely arose some 540 million years ago - ancestors likely free swimming and soft bodied - Characteristics: - 1. Notochord - flexible rod - extends the length of the body - first part of endoskeleton to appear in embryo - hydrostatic organ with fluid in cell vacuoles or in compartments b/w cells - muscles attach to the notochord, & permits undulating movement of the body - persists throughout life in amphioxus and in jawless vertebrates but replaced by bony vertebrae in other groups - 2. Dorsal tubular nerve cord - dorsal to the digestive tract - hollow tube - anterior end becomes enlarged to form brain in vertebrates - 3. Pharyngeal pouches - openings that lead from the pharyngeal cavity to the outside - In Tetrapod vertebrates, pharyngeal pouches give rise to several diff. Structures including the middle ear cavity & tonsils - evolves as a filter feeding apparatus - In fish, capillary network with thin, gas permeable walls improve gas transfer in the pharynx and led to the evolution of internal gills, permitting the pharynx to act as a respiratory organ - 4. Endostyle - secretes mucus that traps small food particles brought into the pharyngeal cavity - some cells in the endostyle secrete iodinated proteins - these cells are homologous with the iodinated hormone - secreting thyroid gland present in adult lampreys & all other vertebrates - in some protochordates and lamprey larvae, the endostyle and perforated pharynx work together to create an efficient filter feeding apparatus - 5. Postnatal tail - provided motility that larval tunicates and amphioxus need for their free swimming existence - clearly evolved for propulsion in water - efficiency increased in fishes with addition of fins - only evident in humans as a vestige ( the coccyx ) but most other mammals have waggable tails as adults - * always found at some embryonic stage; may change or disappear in later stages of life - * all but pharyngeal pouches are unique to chordates: hemochromatosis have them as well Subphylum Tunicata: - ~3,000 species - live in all seas from near the shoreline to great depths  - most sessile as adults - named after tough, nonliving tunic that surrounds the animal and contains cellulose - CLASSES: - Class Ascidiacea - sea squirts - most common, diverse, and best known - all present in larvae - only pharyngeal slits and an endostyle remain in adult forms - Feeding & Digestion: - food particles are brought in with water through the incurrent siphon - they are then trapped on a mucous net secreted by the endostyle - the mucus net is carried into the esophagus - nutrients are absorbed, and indigestible wastes are excreted through the anus - Circulation & Respiration: - ventral heart and two large vessels - connected to a system of smaller vessels and spaces serving the pharyngeal basket, where respiratory exchange occurs and other organs - Unique Feature: heart drives blood first in one direction for a few beats, then pauses, reverses its action, and drives velodrome in opp. Direction - Nervous System: - Nerve ganglion and a plexus of nerves - larval stage has a tubular nerve cord, but is reduced to the other ganglion during metamorphoses - Distinctive sensory organs absent in adult sea squirts - Reproduction: - hermaphroditic - external fertilization - Class Thaliacea - barrel or lemon shaped forms with transparent gelatinous bodies - often bioluminescent - Class Appendicularia - tiny creatures shaped like a bent tadpoles Subphylum Cephalochordata: - lancelets - slender, laterally compressed, translucent - 3-7 cm long - inhabit sandy sediments of coastal waters around the world - Previously Amphioxus now Branchiostoma - 32 species - spend most of their lives with only their anterior end exposed - has all 5 chordate characteristics - Movement: segmented muscled (myomeres) attached to notochord and used for swimming  - Feeding & Digestion: - water enters the mouth - moves into the pharynx and is trapped on the mucus sheet secreted by the endostyle - moved by cilia into the gut - Circulation & Respiration: - Closed circulatory system with no heart - respiration occurs over the surface of the body - Nervous system: - hollow nerve cord above notochord - simple sense organs including an ocellus - anterior end of nerve cord not enlarged as in the vertebrate brain - Reproduction: - separate sexes - external reproduction - direct development from larvae to adults CHAPTER 23 -24 : INTRO TO VERTEBRATES & FISHES Early vertebrate evolution: - the earliest vertebrates were substantially large than protochordates and considerably more active - modification of skeletal structures and muscles permitted increased speed and mobility - the higher activity levels & increased size of vertebrates also required structures specialized in locomotion, capture, and digestion of food and adaptations designed to support a high metabolic rate Musculoskeletal Modifications : - Most vertebrates have an endoskeleton of cartilage or bone - endoskeleton promotes almost unlimited body size - vertebrates have a cranium protecting the brain and vertebrae - disc like centra replace notochord and neural spines proved more area for muscle attachment - segmented muscles (myomeres) are folded into a W-shape allowing powerful control over the body - endoskeleton was likely initially composed of cartilage and later of bone - cartilage grows faster and is more flexible,making it an ideal material for the first skeletal framework of embryos - endoskeleton of living hagfishes, lampreys, sharks , and their kin and even some bony fishes like sturgeons are composed of cartilage - bone formation may have been adaptive for early vertebrates - structural strength of bone i superior to cartilage - makes bone more ideal for muscle attachments areas of high mechanical stress - bone may also have evolved as means of mineral storage and homeostasis - phosphorus and calcium are used for many physiological process in organisms with high metabolic rates - some of the earliest fishes including Ostracoderms and Placoderms were partly covered in a bony dermal armor - Were modified in later fishes as scales - most vertebrates are protected with keratinized structures derived from the epidermis like reptilian scales, hair , feathers , claws, and horns Physiological Upgrades: - Physiological upgrades for vertebrates include - Digestive, respiratory, circulatory, and excretory systems modified to meet increased metabolic demand - Respiratory: - Perforated pharynx evolved as a filter feeding device in early chordates - In vertebrates, the use of pharyngeal muscles created a powerful pump to move water - Role of pharynx shifted from feeding to gas exchange with the development of highly vascularized gills - Digestion: - Shift in the movement of food by ciliary action to muscular action - Addition of distinct digestive glands: the liver and the pancreas - All supports more food intake - Circulatory System: - Chambered, ventral heart - Erythrocytes with hemoglobin - Led to enhanced, transportation of gasses, nutrients and other substances - Excretory System: - Paired kidneys improve the efficiency of metabolic waste removal and the regulation of body fluids and ions New Head, Brain, and Sensory Systems: - Shift from filter feeding to active predation required new sensory motor and integrative controls for locating & capturing larger prey - Anterior end of nerve cord became enlarged as tripartite brain (forebrain,midbrain, and hindbrain) - Paired sense organs adapted for distance recognition evolved: - Specialized eyes - Mechanoreceptors (e.g. paired inner ears ) - Chemical receptors for smell and taste - Lateral line receptors for detecting water vibrations - Electroreceptors for detecting electrical currents Evolution of Vertebrates: - Ostracoderms were armored jawless fishes, which were the earliest known vertebrate fossils found in the late Cambrian deposits - These show many vertebrate characteristics like heart, pair eyes, ear capsules, and rudimentary vertebrae - Earliest Ostracoderms had armor with bone in dermis but lacked paired fins that later fishes used for stability - All jawed vertebrates= Gnathostomes whether living or extinct - Gnathostomes constitute a monophyletic group - Having jaws is a derived character state shared by all jawed fishes and tetrapods - Agnathans= the absence of jaws - Having jaws was one of the most important events in vertebrate evolution - Allowed predation on large and active food  - Additional features from the drastic modification of gill arches include formation of ear ossicles in the mammalian ear - Gnathostomes also developed paired pectoral and pelvic fins for more stable swimming - The combined evolution of jaws and paired appendages that later formed into limbs for locomotion on land - Led to the formation of modern fishes and all tetrapods Fish Overview: - Definition of fish: - Aquatic vertebrate with gills - Appendages ( if present ) arefins - Usually skin with scales - Fish don’t form a monophyletic group - Ancestor of land vertebrates is found within a group of fish - Fish are all vertebrates that are not tetrapods - ~31,000 living species about as many as all other species of vertebrates combined - Adaptations for almost every conceivable aquatic environment - Body streaming for movement through water, a medium 800 times more dense than air - Excellent organs for salt and water exchange —- great at osmoregulation - Gills extract oxygen from water with less than 1/20 as much oxygen as air - Lateral line system for detecting water currents and vibrations - Evolution in water both shaped and constrained the evolution of fish Ancestors & Relationships of Major Groups of Fishes: - 5 major groups of living fishes: - Hagfishes - Lampreys - Cartilaginous fishes - Ray-finned fishes - Lobe-finned fishes - First appeared ~550 million years ago Agnathans: - Earliest vertebrates - Paraphyletic assemblage of jawless fish - include living hagfishes (Myxini) and lampreys (Petromyzontidae) - Extinct Ostracoderms - Scavengers or parasites Gnathostomata: - All remaining fishes and tetrapods - Paired appendages and jaws - Four major groups: - Placoderms - Paraphyletic assembly of armored fishes - Extinct by the end of the Devonian period - Cartilaginous fishes  - Sharks, rays, chimeras - Lost heavy dermal armor - Cartilage for endoskeleton - Active predators - Flourished during Devonian and Carboniferous periods , neared extinction at the end of the Paleozoic era, recovered in the Mesozoic era and diversified to form modern sharks and rays - Acanthodians - Extinct - Fossils known from the Silurian to the early Permian periods - Osteichthyes (body fishes and tetrapods ) - Bony fishes and tetrapods - Two groups: - Actinopterygii (ray finned fishes ) - Sarcopterygii ( lobe = finned fishes ) - Ray-finned fishes includes nearly all of our familiar bony fishes - Lobe finned fishes are represented today by lungfishes and coelacanths Cyclostomata: Living Jawless Fishes - Myxini (hagfishes) and Petromyzontida (lampreys) - Both groups lack: - Jaws - Internal ossification - Scales - Paired fins - Both groups have pore like gill openings and an eel like body form - Class Myxini: Hagfishes: - 78 species, all marine - Scavengers and predators of annelids, molluscs, dead or dying fishes, etc. - Enters a dead or dying animal through an orifice or by digging into the body - Nearly bling, but locates food through acute senses of smell and taste - Secrete enormous quantities of slime - Body in osmotic equilibrium with seawater - Reproductive biology is a mystery - Class Petromyzontida: - Lampreys - Most in North America - Half are parasitic , half are non-parasitic “book lampreys” - Reproduction and Development: - Ascent freshwater streams to breed - Marine forms are therefore anadromous - Larvae drift downstream and burrow into sandy areas - Larvae filter feed until metamorphosing into adults - Change to adult involves many changes, including the eruption of eyes  - Parasitic forms attach themselves with their suckerlike mouth to fish, rasp through the flesh, and consume bodily fluids or flesh - Non parasitic lampreys never feed after metamorphosis; they spawn & die within a few months Chondrichthyes: Cartilaginous Fishes: - 1200 living species - Their impressive combination of well developed sense organs, powerful jaws and swimming musculature, and predaceous habits helps them to survive - These animals have a cartilaginous skeleton, and bone is entirely absent in the endoskeleton - Almost all marine; only 28 species live primarily in freshwater - Two subgroups: - Elasmobranchii (sharks, skates, rays) - 12 orders with a total of ~1150 species - Shark body is fusiform, or streamlined, enabling it to moves smoothly through the water - Paired pectoral and pelvic fins, one or two medians dorsal fins, a median caudal fin, and (often) a median anal fin help them to move through the water - Sharks: - Predatory lifestyle: - Sharks are well equipped for their predatory lifestyle, tracking their prey using highly sensitive senses - Initially detect prey from a kilometer or more away with large olfactory organs - Locate prey from moderate distances by sensing low-frequency water vibrations with mechanoreceptors in the lateral line system - Includes specialized sensory organs called neuromasts - Have excellent vision, event in dimly lit waters - Guided to prey by bioelectric fields through electroreceptors - Other adaptations: - A rectal gland, unique to chondrichthyans, secretes a fluid with a high concentration of sodium chloride, assisting the kidneys in regulating the salt concentration of the blood - Front row of functional teeth is backed by rows of developing teeth that replace worn teeth throughout the shark’s life - Reproduction & Development: - All have internal fertilization - Some species are oviparous, laying eggs which may mature in a “mermaid purse” for up to 2 years in one species - Some are viviparous, retaining young in the uterus, where they are nourished by a yolk sac until born - Some are truly viviparous, with embryos receiving nourishment from the material bloodstream through a placenta  - Rays: - More than half of all elasmobranchs - Specialized for body dwelling - Dorsoventrally flattened body and enlarged pectoral fins are used to propel themselves - Respiratory water enters through spiracles on top of the head, because mouth is often buried in sand - Teeth adapted for crushing prey, including molluscs, crustaceans, and some small fish - Stingrays have a whiplike tail with spines and venom glands - Electric rays have large electric organs on each side of the head - Holocephali (chimaeras) - A.k.a. Ratfishes - Diverged from shark lineage at least 380 million years ago - 48 living species - Instead of distinct teeth, their jaws have large flat plates - Diet is varied, including molluscs, echinoderms, crustaceans, and fishes CHAPTER 24 CONT: FISHES Osteichthyes: - Bony fishes & tetrapods: - In the early to middle Silurian, lineage of fishes with bony endoskeletons gave rise to a clade that contains 96% of living fishes and all living tetrapods - Features uniting bony fishes & tetrapods: - Endochondral bone is present that replaces cartilage developmentally - Endochondral ossification is the process by which the embryonic cartilaginous model of most bones is gradually - A lung or swim bladder is present that was evolved as an extension of the gut - They have several cranial and dental characters unique to this clade - Bony fishes developed into two major lineages - Class Actinopterygii - Ray finned fishes - Radiated to form modern bony fishes - Class Sarcopterygii - 8 species of lobe finned fishes - Include lungfishes and the coelacanth - Land vertebrates ( tetrapods) - Key adaptations & Diversification: - Operculum composed of bony plates covers the gills and helps draw water across the gills - Gas-filled structure off the esophagus helps with gas exchange and buoyancy - Lungs in species where primarily for gas exchange - Swim bladders in species where primarily for buoyancy - Progressive specialized of jaw musculature & skeletal elements involved in feeding - Actinopterygii ( Ray finned fishes ):  - 5 major groups - Paleoniscids - Paraphyletic group - Earliest forms - Small with large eyes - Large, heterocercal caudal fin (unequal upper and lower lobes ) - Single dorsal fin - Interlocking bony, dermal scales - extinct - Bichirs - Clade Cladistia - They have lungs - 14 species in freshwaters of Africa - Chondrosteans - 27 species of freshwater and anadromous sturgeons and paddlefishes - Threatened by dam construction, overfishing, and pollution - Neopterygians - Two surviving early neopterygians are the bowfin and the gars - During the mesozoic, one lineage gave rise to the modern bony fishes, the teleosts - Teleosts - 96% of living fishes, half of all vertebrates - Perhaps 5,000 -10,000 remain undescribed in remote areas, but also in North America - Teleosts range from 10 mm to 17m long, and up to 900 kilograms in weight - They survive extreme altitudes and depths as well as extreme temperatures - Diversification: - Heavy dermal armor of early ray-finned fishes replaced by light, thin, flexible scales - Changes in fins increased maneuverability and speed - Modifications of fins to function in camouflage, social communication, and more - Increasingly fine control of gas resorption and secretion in the slim bladder, improving control of buoyancy - Anatomical modifications to improve feeding efficiency Class Sarcopterygii ( Lobe finned fishes and tetrapods ): - Today clade only included 8 species - 6 species of lungfish and 2 species of coelacanths - Australia lungfishes, unlike close relatives, rely on gill respiration and cant survive long out of water - The South American and African lungfish can live out of water for long periods of time - Tetrapod ancestor is found within a group of extinct sarcopterygian fishes called rhipidistians. The Coelacanth:  - Arose during the Devonian period, radiated, reached a peak in the Mesozoic and dramatically declined - Thought to be extinct 70 mill years ago, a specimen was dredged up in 1938 - Eventually more were caught off the coast of the Comoro islands, and in 1998,in Indonesia - The living coelacanth is a descendant of Devonian freshwater stock Adaptations: Locomotion in Water: - Most fishes swim maximally at ten body lengths per second which is about 10kph - Larger fish swim faster as a general rule: - Trunk & tail musculature propels a fish - Muscles are arranged in zigzag bands called myomeres which are short and have tough connective tissues that separate each unit - Each myomere pulls on several vertebrae - Enables fish to have more power and control - Serpentine movement, with waves of contraction moving backward along the body by alternating contraction of myomeres on either side - Anterior end bends less than the posterior end - Thrust propels the fish towards, while yaw is movement of the head and is minimized in many fish Neutral Buoyancy: - Fish are slightly heavier than water due to skeletons and tissues with heavy materials - To keep from sinking, a shark must continually move forward using heterocercal tail for lift and pectoral fins that keep it “angled up” - Shark also has liver that has a special lipid called squalene, which acts like an oil sack, to keep the shark a little more buoyant - Bony fish swim bladder has a gas-filled space, is the most efficient flotation device - Swim bladder arose from paired lungs primitive Devonian bony fishes - Present in most fishes but absent in tunas, some abyssal fishes, and most bottom dwellers - Fish controls depth by adjusting volume of gas in swim bladder and can remain suspended with no muscular effort Hearing & Weberian Ossicles: - Detect sounds as vibrations in the inner ear - Difficult in water because bodies are nearly same density as surrounding water - One group, the ostariophysi have Weberian ossicles - These small bones allow them to hear faint sounds over a broader range - Sound reception starts at the swim bladder, and is transmitted from the swim bladder to the inner ear by Weberian ossicles Respiration: - Respiration in sharks via gills slits while bony fish have opercular flaps - Gills are inside the pharyngeal cavity and covered with a movable flip, the operculum - Pumping action by operculum helps move water from the mouth and through gills - Water flow is opposite to the blood flow and called countercurrent exchange that maximizes exchange of gasses - Several groups of fishes can live out of water for varying lengths of time - Lungfishes use their lungs to respire in air  - Freshwater eels can wriggle over land during rainy weather and use skin as the major respiratory surface - Electric eel has degenerate gills and gulps air through vascular mouth cavity - Indian climbing perch spends most of its time on land near water edge, breathing air in special chambers above reduced gills Osmotic Regulation: - Freshwater fishes are hyperosmotic regulators, because water tends to enter their bodies osmotically, and salt tends to be lost by diffusion outward - Excess water is pumped out by the kidneys - Special, salt absorbing cells move salt from water to the blood - Marine fishes are hypoosmotic regulators, because water tends to leave their body, while salt tends to enter - To compensate for water loss, they drink seawater - Excess salt is disposed in multiple ways– through salt secretory cells, through feces or excreted by the kidneys Feeding Behavior: - Most fish are carnivores, preying on foods form zooplankton and insect larvae to large vertebrates - A smaller group are herbivores, eating fish and macroalgae - A third groups is comprised of suspension feeders, who eat the abundant microorganisms of the sea - Still others may be scavengers ( hagfishes), detritivores (suckers and minnows) and parasitic fish (lampreys) Migration: - Freshwater eels spend most of their time in freshwater, but migrate to the sea to spawn - Salmon are anadromous, spending their adult lives in the sea but returning to freshwater to spawn, with incredible homing ability Reproduction: - Mostly dioecious with external fertilization and external development of their eggs and embryos (oviparity) - However, some viviparous and some sharks are truly viviparous - Furthermore, there are sequential hermaphrodites, synchronous hermaphrodites, and fish that produce through parthenogenesis CHAPTER 25: Early Tetrapods and Modern Amphibian: Transitioning from Water to Land: - Amphibians transform from aquatic larvae to terrestrial adults through a series of dramatic changes during life - The evolutionary shift from water to land in vertebrates occurred far more slowly and included many major changes - Amphibians are the only extant vertebrate with a shift from water to land both in their ontogeny (development) and in their phylogeny - Tetrapods originated !400 mya and includes two major lineages: amphibians and amniotes ( non-avian reptiles, birds, and mammals) - Life originated in the water, and animals are composed primarily of water, and cellular activities occur in water - Prior to the vertebrate invasion of land, vascular plants, pulmonate snails, and arthropods had already made this transition, generating a food supply for terrestrial vertebrates - Despite the major changes essential to living on land, aquatic and terrestrial vertebrates retain many similarities - Challenges Associated with Transition from Water > Land: - 1. Oxygen content: - 20x more abundant in air and diffuses more rapidly - 2. Density: - `air is 1000x less dense and provides less buoyancy than water - Skeletal structure must provide more support - 3. Temperature Regulation: - Air fluctuates in temperature more readily than water, leading to harsh unpredictable cycles of freezing, drying, and flooding - This requires behavior and physiological strategies to protect themselves from thermal extremes - By ~400 mya, bony fishes had diversified to include many freshwater forms - Characteristics that evolved in aquatic habitats provided access to terrestrial habitats - Characteristics that facilitated a terrestrial invasion: - 1. Air-filled cavity (swim bladder) - 2. Paired internal nares (i.e. nostrils) which functioned as chemoreceptors - On land, these 2 structures would draw oxygen rich air through the nares into the air filled cavity, whose moist surface would exchange carbon dioxide with body fluids - 3. Bony elements of paired fins were modified for support on underwater surface gained sufficient strength to support and move the body on land - Exaptation: a structure that evolved by natural selection for initial utility or row is later recruited or “co opted” for a new role - An air filled cavity, internal nares, and paired limbs of an aquatic tetrapod ancestor made possible the evolution of terrestrial breathing and support - The instability of freshwater habitats – prone to evaporation or oxygen depletion – created an advantage to terrestrial life - A single transition occurred during the Devonian period (~400 mya) - This lineage evolved several key adaptations: - Increased vascularization of the air filled cavity and a rich capillary network to form efficient lungs - Double circulation to direct deoxygenated blood into the lungs, and oxygenated blood out of the lungs to the other body tissues - Fossils: - The bony elements of the fins of lobe-finned fishes resemble the homologous structures in amphibians - In fossils of Eusthenopteron, a Devonian lobe-fin fish living ~358 mya, we can see an upper arm bone (humerus) and two forearm bones (radius and ulna) as well as other elements homologous with the wrist bones of tetrapods  - This animal could push itself through the bottom of mud pools with its fins - Tiktaalik lived ~375 mill years ago, and is morphologically intermediate between lobe-finned fishes and tetrapods - Such a transitional fossils provide key information about the changes that took place as vertebrates invaded land - Tikaalik may have inhabited shallow,oxygen-depleted streams or swamps, using its appendages to support its body while placing its snout above water to breath air - It may have even traversed land - Ichthyostega: - 365 mill years ; had several adaptations on land - Jointed limbs - Stronger vertebrae and associated muscles to support the body in air - New muscles to elevate the head - Strengthening shoulder and hip girdles - Protective rib cage - Ears modified for hearing airborne sounds - However also retained a tail complete with fin rays and had gill-covering bones - These fossil forms (and others) have several adaptations for life on land, while also sharing many common characteristics with fishes Early Diversification of Tetrapods: - Several extinct lineages and Lissamphibia ( which includes modern amphibians) formed the temnospondyls - Of these, only amphibians survived the end-Cretaceous mass extinction (~66 mya, when dinosaurs went extinct) - ~8,500 extinct amphibian species - Diversified into 3 groups ~250 mya: - Caecilians - Salamanders - Frogs The Ancestral Amphibian: - Eggs are aquatic and hatch to produce an aquatic larval form that uses gills for respiration - Gills lost during metamorphosis - Terrestrial forms use cutaneous respiration- exchanging gasses with the surrounding air through their skin - Dependent on moist environments due to thin skin prone to desiccation - Ectotherms that require cool, wet environments Caecilians: Order Gymnophiona: - 214 species of elongate, limbless, burrowing creatures - Inhabit tropical forests of South America, Africa, India, and southeast Asia - Possess a long, slender body, many vertebrae, long ribs, no limbs, and a terminal anus - Most are blind as adults - Almost entirely burrowing or aquatic - Feed on worms and small underground invertebrates  - Internal fertilization, with eggs deposited near water - Some have aquatic larvae, while larval development occurs within the egg for others - In some species, viviparity occurs Salamanders ( Order Urodela): - ~771 species - Occur in almost all northern temperate regions of the world, but are most abundant and diverse in North America - Most are small, but Japanese giant salamanders sometimes exceed 1.5 m in length, and North American hellbenders can reach up to ~70 cm ( 29 inch) - Burrowing species and some aquatic forms have lost their limbs - Carnivorous as larvae and adults, eating worms, arthropods, and molluscs - Life Cycles: - Ancestral condition: metamorphic w/ aquatic larvae and terrestrial adults - However, some are aquatic or terrestrial throughout their entire life cycle - Fertilization generally internal, with aquatic eggs in most species - Terrestrial species undergo direct development, hatching as miniature adults - Some Northern American newts have aquatic larvae that metamorphose into terrestrial juveniles that again metamorphose into secondarily aquatic, breeding adults - Some newt populations skip the terrestrial “red eft” stage and remain entirely aquatic - Respiration: - Diverse mechanisms - Share ancestral amphibian condition of having extensive vascular nets for exchanging gasses in their skin - May also have external gills, lungs, both , or neither at various stages - Most have an aquatic larval stage with gills that are lost at metamorphoses - Some fail to under metamorphosis and retain gills and a fin like tail - Some aquatic forms breath with lungs, and some terrestrials forms lack lungs - Amphibians are fully aquatic but respire by lungs in adulthood - Plethodontid salamanders are terrestrial and lungless - Likely evolved in cold, highly oxygenated streams where lungs would have been too buoyant and cutaneous respiration was sufficient - Paedomorphosis: - The preservation of pre adult features into adulthood and the consequent elimination of characteristics of ancestral adult morphology - Most dramatic: mature without metamorphosis, retaining their gills and aquatic life habits - Ex: mudpuppy - Some will metamorphose to terrestrial forms under some environmental conditions - Ambystoma may stay in a gilled stage - However, if the pond dries up, they may metamorphose into a terrestrial form Frogs & Toads: Order Anura: - ~7,471 species - Known from the Triassic period and 250 mill years ago - Aquatic reproduction and a water permeable skin mean they must stay near water - Ectothermy bars them from inhabiting polar and subarctic habitats - All have a tailed larval stage and lack tails as adults (except Ascaphus, the tailed frog) - Specialized for jumping - Tadpoles have a long-finned tail, internal and external gills, no legs, specialized mouthparts for herbivorous feeding, and a specialized internal anatomy - Hardly resemble adult frogs - Metamorphosis is thus striking - 56 families of frogs and toads - Family Ranidae contains the common larger frogs in North America - Family Hylidae includes tree frogs - Family Bufonidae contains toads with thicker skins and prominent warts - However, toad is also sometimes used informally to refer to other families - Habitas & Distribution: - Most live near water - Lithobates sylvatica, the wood frog, is found on damp forest floors and breeds in pools - Larger bullfrogs ( Lithobates Catesbeianus) and green frogs ( lithobates clamitans) are near permanent water or swamps - Other frogs, like leopard frogs (lithobates pipiens) occupy a wider variety of habitats - Most frogs in temperate climates hibernate in pools and streams during the winter - Terrestrial frogs will hibernate on the forest floor - Some can even tolerate freezing - Defense: - Many predators - Frogs may defend themselves by hiding - Some feign death - Some inflate their lungs to they are difficult to swallow - Some use potent toxins for defense - Some aggressive - Many can adjust coloration for camouflage - Respiration: - Amphibians use 3 surfaces: - Skin ( cutaneous breathing) - Mouth ( buccal breathing) - Lungs - Frogs depend heavily on lung breathing but skin provides a supplementary mechanism for gas exchange, especially during hibernation - Feeding: - Most are carnivorous as adults, like other amphibians - Use protrusible tongue to catch prey - Reproduction: - In spring, males call loudly to attract females - When eggs mature, females enter water and males clasp them in a process called amplexus - Eggs are then fertilized externally  - After fertilization, eggs are laid in large masses, usually anchored to vegetation - A tadpole hatches and later metamorphoses into an adult with lungs CHAPTER 26: Amniote Origins & Non-Avian Reptiles: Enclosing the Pond: - Amphibians rely on freshwater or moist terrestrial environments due to their shell-less eggs, thin moist skin, and gilled larvae - This limits their success in terrestrial environments - An ancestor of the clade containing: - Turtles - Lizards - Snakes - Tuataras - Crocodilians - Birds - & mammals that evolved a better egg adapted to dry terrestrial conditions - Rather than eliminating “pond-dwelling” stages, this egg encloses these stages within membranes that support embryonic development - Amnion: fluid-filled sac, provides aquatic environment for embryo - Allantois: respiratory surface and chamber for nitrogenous wastes - Chorion: membrane across which oxygen and carbon dioxide freely pass - Shell: protective outer covering - By severing the ties to water required for reproduction, amniotes were able to invade a much wider variety of terrestrial habitats than amphibians - Amniotes diversified into several lineages, giving rise to modern day turtles, snakes, lizards, tuartaras, crocodiles, birds, and mammals. Origin of Amniotes: - Amniotes are a monophyletic group - Arose between 315 and 330 mya - Most closely related to anthracosaurs ( a group of anamniotes – vertebrates lacking an amnion ) - First amniotes were small and lizard like Early Diversification of Amniotes: - Produced three patterns of holes ( fenestrae) in the skull: 1. Anapsid: no openings behind the orbit ( opening for the eye) 2. Diapsid: two openings behind the orbit 3. Synapsid: one opening behind the orbit - Functional Significance of Openings: - Occupied by large muscles that elevate the lower jaw in living forms - Changes in jaw muscular may reflect a shift from suction feeding in aquatic vertebrates to terrestrial feeding - This allows for things like grinding food with posterior teeth - Amriotes have more variation in feeding biology than do anamniotes, and herbivory is common  - Thus, these openings may have facilitate more variation in amniote diets. They are also important for systematics and for amniote habit & function Adaptations of Amniotes: - 7 major adaptations promoting amniote success in terrestrial environments: 1. Amniotic egg - Four extraembryonic membranes: - 1. amnion : encloses embryo in fluid, cushioning it and providing an aqueous medium for growth - 2. Allantois: stores metabolic wastes and is highly vascularized - 3. chorion : highly vascularized and provides an efficient respiratory organ along with the allontois - 4. Yolk sac ( not specific to amniotes ): provides nourishment and sometimes a placenta - Shell provides mechanical support - Shell forms a semipermeable barrier, allowing the passage of gasses but limiting water loss - Evolution: - An amniotic egg can be laid in places too dry for amphibian eggs, facilitating success to land - Permits development of larger, faster growing embryo - Shell provides better support and movement of oxygen compared to the jellylike layer supporting anamniotic eggs - Calcium deposited in the shell can be used by the growing embryo in skeleton reconstruction - Requirements & Modifications: - Shelled amniotic eggs require internal fertilization, since sperm cannot penetrate the shell - The yolk is replaced by the placenta in some groups, transferring nutrients, gasses, and wastes between the embryo and the mother - Embryonic development occurs in a female’s reproductive tract in some animals, providing even greater protection 2. Thicker and more waterproof skin - Amphibians must have a thin, moist skin to permit effective gas exchange - However, this skin also makes amphibians vulnerable to dehydration and physical harm - A shift away from a respiratory function of the skin is associated with change in skin morphology in amniotes - Amniote skin tends to be thicker, more keratinized, and less permeable to water  - Keratin structures ( e.g., scales, hair, feathers) provide protection from trauma - Hydrophobic lipids limit water loss through the skin - Keratin and lipids limit the skins usefulness in gas exchange - Amniote gas exchange occurs primarily in the lungs 3. Rib ventilation of the lungs - Amniote lungs are larger, have more surface area, and are ventilated by a different mechanism compared to amphibians - These changes reflect: - Increased metabolic demands of amniotes - The reduced ability of their skin to serve as a gas exchange organ - Amphibians fill their lungs by pushing air from the oral and pharyngeal cavities into the lungs - Amniotes draw air into their lungs (aspiration) by expanding the thoracic cavity using rib muscles or bulling the diaphragm or liver posterior 4. Stronger jaws - The skeleton and jaw muscles became adapted to seize prey - Jaw musculature provides mechanical advantage 5. High pressure cardiovascular system - The right side of the heart received deoxygenated blood, while the left side of the heart received oxygenated blood from the lungs - In mammals, birds, and crocodilians, these circuits are separated into left and right ventricles - Other reptiles have a single ventricle incompletely partitioned but mixing between oxygen rich and oxygen poor blood is minimized - Permits higher blood pressure, ideal for active terrestrial organisms because they have high metabolic needs and their heart needs to pump blood uphill to overcome gravity - Incomplete separation is adaptive in other vertebrates, as it allows blood to bypass the lungs when pulmonary respiration is not occurring 6. Water conserving nitrogen excretion - Amphibians excrete waste as ammonia or urea - Ammonia is toxic at low concentrations and must be removed in a dilute solution, requiring water - This isn;t adaptive for vertebrates living in dry terrestrial habitats - Mammals excrete nitrogenous waste as urea, which is concentrated in the kidneys, reducing water loss through excretion - Birds and other reptiles excrete wastes as uric acid, which is nontoxic and can be concentrated, requiring very little water ( semi-solid waste)  - Since birds and other reptiles have limited ability to concentrate wastes in kidneys, the urinary bladder resorbs water and many salts 7. Expanded brain and sensory organs - Large cerebrum and cerebellum especially in birds and mammals - Enlargement of cerebrum correlated with integration of sensory information and control of muscles during locomotion - Amniotes especially birds have excellent vision - Olfaction is highly developed in mammals, snakes, and lizards Changes in Reptiles: - Traditionally reptiles including snakes, lizards, tuataras, crocodilians, turtles, and several extinct groups, such as dinosaurs, plesiosaurs, and pterosaurs, and many other early amniotes - This leads to a paraphyletic group - Reptilia is monophyletic by inclusion of birds and exclusion of the clade. - Synapsida ( a group including mammals and some extinct amniotes) - Archosauria: birds, crocodilians, extinct dinosaurs, and pterosaurs - Reptilia: Archosaurs, lepidosaurs ( tuartars, lizards, and snakes ) and turtles - Nonavion reptiles: informally used to refer to a paraphyletic group including living turtles, snakes, lizards, tuataras, crocodilians, and several extinct groups - Four clades of living nonavian reptiles: 1. Testudines, turtles ( Chelonia ) a. Fossils appear starting 240 million years ago b. Earliest turtles had teeth and a reduced shell c. Modern turtles lack teeth, and have tough, keratinized plates for biting food d. Enclosed in shells consisting of a dorsal carapace and a ventral plastron e. Shell is made of bone, overlain by enlarged keratin scales f. Bony part formed from an expansion and fusion of ribs, vertebrae, and many other elements g. Respiration: i. Because its ribs are fused to the shell, a turtle can’t expand its chest to breath like other amniotes ii. Instead they employ some abdominal and pectoral muscles as a diaphragm iii. Exhalation is accomplished by drawing limbs back into the shell, compressing the viscera and forcing air out of the lungs iv. Some aquatic turtles can get oxygen by pumping water in and out of a vascularized mouth cavity or cloaca h. Brain & Nervous System: i. Turtles have small brains (