REPTILES & AMPHIBIANS • The Rise of Amphibians (Devonian Period) A. Amphibians have a body plan and mode reproduction somewhere between “fishes” and “reptiles.” They are vertebrates with a bony endoskeleton and a four-legged aquatic ancestor.
REPTILES & AMPHIBIANS The 4 classes of terrestrial (tetrapods) vertebrates: • Amphibians • Reptiles • Birds • Mammals
REPTILES & AMPHIBIANS • Scientific classification Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Amphibia
REPTILES & AMPHIBIANS • Subclasses and Orders of Amphibians • Order Temnospondyli- extinctSubclass Lepospondyli- extinctSubclass Lissamphibia Orders AnuraCaudataGymnophiona
REPTILES & AMPHIBIANS 1. Life on land presented new challenges to the emerging amphibians. The idea here is that asteroids that hit earth caused the mass extinction of marine life and affected much of the available O2 at the sea’s surface. Since the tetrapods had lungs they could take advantage of gulping air while spending some of their time on land.
REPTILES & AMPHIBIANS Scientists say no significant genetic change would be required to make the transaction from lobed fins to limbs. They contend that even a single mutation in one of the so-called, “master genes” could lead to a big change in morphology.
REPTILES & AMPHIBIANS a. Water availability was not reliable. b. Air temperatures were variable, and air itself was not the strong supporting medium that water was, but it was a richer source of oxygen. Lungs had to be modified in ways that enhanced O2 uptake. Circulatory systems became more efficient in rapidly moving oxygen to cells.
REPTILES & AMPHIBIANS Both of these modifications increase the capacity for aerobic respiration, thus generating more ATP for use in increased activity. c. New habitats, including vast arrays of plants, insects, necessitated keener sensory (vision, hearing, balance) input. As a result, different regions of the brain further developed.
REPTILES & AMPHIBIANS d. Fortunately, climate shifts in the Carboniferous provided an abundance of insects as food for the amphibians.
REPTILES & AMPHIBIANS • Amphibians developed with the characteristics of pharyngeal slits/gills, a dorsal nerve cord, a notochord, and a post-anal tail at different stages of their life. Though early tetrapods (which appeared 390 million years ago in the Devonian period) are often referred to as "amphibians", the first true amphibians appeared during the early Carboniferous period.
REPTILES & AMPHIBIANS • Superorder Salientia • Triadobatrachus (Triassic) • Order Anura (frogs and toads) Jurassic to recent - 5,296 recent species • Order Caudata or Urodela (salamanders): Jurassic to recent - 555 recent species • Order Apoda (caecilians): Jurassic to recent - 171 recent species
REPTILES & AMPHIBIANS 2. Existing amphibians share several common characteristics: a. All have bony endoskeletons and usually four legs. b. Most shed their eggs into water, which is also home to a free- swimming larval stage.
REPTILES & AMPHIBIANS c. Depending on their habitat, amphibians can respire by use of gills, lungs, skin, and pharyngeal lining. d. The skin is usually thin and some- times supplied with glands that produce toxins. We’ll see this shortly.
REPTILES & AMPHIBIANS The word ‘amphibian’ comes from the Greek meaning, “both” (amphi), and bios, meaning, “life”. It describes cold-blooded animals with backbones that spend their lives both in fresh water and on land.
REPTILES & AMPHIBIANS When we say, ‘cold-blooded’ we mean that the amphibians do not hold or regulate their own body temperature. Their internal body temperature depends on the external environment. They must absorb the warmth of the sun or become sluggish at very cold temperature to maintain bodily heat.
REPTILES & AMPHIBIANS The Class Amphibia contains three orders: • Anura (frogs and toads) • Urodela (salamanders and newts) • Apoda (caecilians)
REPTILES & AMPHIBIANS FROG TOAD SALAMANDER
REPTILES & AMPHIBIANS NEWTS CAECILIANS
REPTILES & AMPHIBIANS Most amphibians share 5 key characteristics: 1. Legs – adapted to living on land (frogs, toads, salamanders, newts all have 4 legs) 2. Lungs – larval amphibians have gills, most adult amphibians breathe with a pair of lungs (salamanders are an exception)
REPTILES & AMPHIBIANS 3. Double-loop circulation – two large veins called Pulmonary veins return oxygen-rich blood from the lungs to the heart. Oxygen-rich blood is then pumped to the tissues. 4. Partially divided heart – the atrium of the heart is divided into left and right sides, but the ventricle is not. A mixture of oxygen- rich and oxygen-poor blood is delivered to the tissues.
REPTILES & AMPHIBIANS 5. Cutaneous respiration - besides breathing with their lungs, amphibians take up oxygen through their skin.
REPTILES & AMPHIBIANS Double-loop circulation in amphibians:
REPTILES & AMPHIBIANS • Life Cycle ‘Metamorphosis” of a Frog (pg. 758-759)
REPTILES & AMPHIBIANS • Frogs and Toads (4,000 species) 1. These animals are distinctive with their long hindlimbs capable of res- ponding to powerful muscles, which allow them to leap into the air. 2. Their success on land is due in part to: the excellent prey-grasping capability of the tongue attached to the front of the mouth.
REPTILES & AMPHIBIANS 3. Frog skin has mucous glands, poison glands & antibiotics that provide protection against pathogens in an aquatic habitat. 4. Scientists have noticed frog populations on the decline due to increases in parasitic attacks, predation, UV radiation, habitat losses & chemical pollution.
REPTILES & AMPHIBIANS Frog versus Toad • Frog has two bulging eyes • strong, long, webbed hind feet that are adapted for leaping and swimming • smooth or slimy skin (generally, frogs tend to like moister environments) • Frogs tend to lay eggs in clusters.
REPTILES & AMPHIBIANS Frogs versus Toads • Toads have stubby bodies with short hind legs (for walking instead of hopping) • warty and dry skin (usually preferring dryer climates) • paratoid (or poison) glands behind the eyes • The chest cartilage of toads is different. • Toads tend to lay eggs in long chains.
REPTILES & AMPHIBIANS • Salamanders 1. Live in temperate zones & in tropical areas of Central and South America numbering about 380 species 2. When they walk, the body bends from side to side, much like a fish moving through water.
REPTILES & AMPHIBIANS 3. Adults may retain larval features including gills and tail. 4. Some larvae may become sexually mature but not reach a true adult stage 5. Both forms, larval & adult, are carnivorous.
REPTILES & AMPHIBIANS • Caecilians 1. As amphibians evolved they lost their limbs & vision, but not their prey-capturing jaws. 2. These unusual creatures live burrowed in the forest floor where they hunt for invertebrate prey. 3. Most of the 160 species burrow through the soil, using touch & smell to pursue insects & earthworms. The few aquatic types use electrical cues.
REPTILES & AMPHIBIANS • Summary of amphibians: • They are vertebrates • they have bony endoskeleton • They have four legs • Their body plan and mode of reproduction is somewhere between “fishes” and “reptiles”
REPTILES & AMPHIBIANS - Their transition to land involved: development of legs more efficient lungs more efficient heart
REPTILES & AMPHIBIANS Because of this transition from water to land: • Amphibians had to contend with a drier habitat. This required a modified way to enhance oxygen uptake through their lungs • This drier habitat required that they go back to a water environment for laying of eggs
REPTILES & AMPHIBIANS • Legs, sufficient to support their body weight, allowed them to move from land to water when necessary. • Their circulatory systems became more efficient to provide oxygen to all cells which, over time, increased the capacity for aerobic respiration and subsequently greater production of ATP – allowing for more activities.
REPTILES & AMPHIBIANS • Scientific Classification of Reptiles Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Sauropsida
REPTILES & AMPHIBIANS • REPTILES • Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders: • Crocodilia (crocodiles, caimans and alligators): 23 species • Rhynchocephalia (tuataras from New Zealand): 2 species • Squamata (lizards, snakes and amphisbaenids ("worm-lizards")): approximately 7,600 species • Testudines (turtles): approximately 300 species
REPTILES & AMPHIBIANS Reptiles are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Though all cellular metabolism produces some heat, modern species of reptiles do not generate enough to maintain a constant body temperature and are thus referred to as "cold-blooded" (ectothermic).
REPTILES & AMPHIBIANS Sea Turtle for an exception: a reptile that elevates its body temperature well above that of its surroundings. Normally they rely on gathering and losing heat from the environment to regulate their internal temperature, e.g, by moving between sun and shade, or by preferential circulation — moving warmed blood into the body core, while pushing cool blood to the periphery
REPTILES & AMPHIBIANS Reptiles evolved from tailed amphibian ancestors. There are nearly 8000 species that are divided into four orders; snakes and lizards, crocodiles and alligators, tortoises and turtles, and tuataras. • A reptile has the following features; cold blooded dry, scaly skin tough shell on eggs eggs are laid on land
REPTILES & AMPHIBIANS • The Rise of Amniotes - Reptiles During the late Carboniferous, amphibians gave rise to the amniotes (birds, reptiles, mammals). A. Four features were critical to amniotes’ escape from water dependency: 1. They produce amniote eggs with internal covering membranes and a shell, which allow the eggs to survive in dry habitats.
REPTILES & AMPHIBIANS • Amniote egg contains a membraneous sac that surrounds and protects the embryo.
REPTILES & AMPHIBIANS • Allantois The word comes from the Greek word for sausage, which the allantois resembles. This sac-like structure is primarily involved in respiration and excretion, and is webbed with blood vessels. It is primarily found in the blastocyst stage of early embryological development, and its purpose is to collect liquid waste from the embryo.
REPTILES & AMPHIBIANS • The structure first evolved in reptiles and birds as a reservoir for nitrogenous waste, but also as a means for oxygenation of the embryo. Oxygen is absorbed by the allantois through the egg shell . The allantois functions similarly in monotremes, which are egg-laying mammals.
REPTILES & AMPHIBIANS • In most marsupials, the allantois is avascular, having no blood vessels, but still serves the purpose of storing nitrogenous waste. Also, most marsupial allantoises do not fuse with the chorion. • In placental mammals, the allantois is the precursor of the mature umbilical cord
REPTILES & AMPHIBIANS 2. First vertebrates to form eggs with internal membranes that conserve H2O and cushion an embryo, and metabolically support it. 3. Amniotes have a toughened, dry or scaly skin that is resistant to drying.
REPTILES & AMPHIBIANS 4. They have a copulatory organ that permits internal fertilization. 5. Their kidneys are good at conserving water. Again, these amniotes (mammals, turtles, lizards, snakes, crocodiles & birds) are the only tetrapods that can reproduce successfully away from aquatic habitats, while having the embryos develop to advanced stage before hatching or being born in a dry habitat.
REPTILES & AMPHIBIANS • “Reptiles” demonstrate certain advantageous features compared to amphibians. 1. Modification of limb bones, teeth, and jaw bones allowed greater exploitation of the insect life emerging in the Late Carboniferous. 2. Development of the cerebral cortex permitted greater integration of sensory input and motor response.
REPTILES & AMPHIBIANS 3. A four-chambered heart fully separated into two halves and more efficient lungs allowed greater activity. Crocodilians were the first to exhibit this feature. Though the reptiles’ brain is small compared to it’s body mass, behavior governed by it is advanced to that seen in Amphibians. 4. Descendants of the surviving dinosaurs became the lineage of reptiles.
REPTILES & AMPHIBIANS 5. Transdermal gas exchange seen in amphibians is abandoned by reptiles because of their well develop- ed lungs.
REPTILES & AMPHIBIANS • Circulatory systems Fish Amphibian Reptile, Bird Mammal