Amphibians

Physical Characteristics:

·         Adapted for life on land

o   Skeletal strengthening

o   Shifting of special sense priorities from lateral line system to senses of smell and hearing

o   However, most amphibians are still reliant on water for reproduction.

·         Ectothermic with low metabolic rates

·         Circulation is done with 3-chambered hearts

·         Separate sexes: fertilization can be internal or external

·         Eggs are moderately yolky with jellylike membrane coverings

Three Orders:

1. Gymnophiona

·         Elongate, limbless burrowing creatures called caecilians

·         Many vertebrae

·         No limbs

·         Small eyes, many blind

·         Internal fertilization, usually oviparous

2. Caudata

·         Tailed amphibians called salamanders

·         Some forms are wholly aquatic, but most start out as aquatic larvae and metamorphose into terrestrial adults.

·         Limbs set at right angles to the body

·         Carnivorous

·         Respiration may be done via external gills, lungs, both, or neither of these.

o   Vascular nets in skin: serve for respiratory exchange of oxygen and carbon dioxide

o   Some forms loose gills before adulthood and breathe primarily by lungs.

§  Lungs are present from birth in salamanders that have them.

o   Some terrestrial forms completely lack lungs.

§  Cutaneous respiration is increased by increased efficiency of capillary networks.

§  Air is also pumped in and out of mouth across vascularized membranes.

·         Internal fertilization

o   Female picks up previously deposited spermatophores.

§  Terrestrial species deposit eggs in soft most earth.

§  Aquatic species lay eggs in masses in the water, usually fail to metamorphose.

§  Some species retain larval characteristics as sexually mature adults (paedomorphosis).

·         Ex: mud puppies of genus Necturus

·         Tiger salamander (Ambystoma tigrinum)

3. Anura

·         Tailless amphibians known as frogs and toads

·         Larvae metamorphose from tailed, gilled specialized organisms to adults with completely different form.

·         No adult is permanently gilled.

·         Breeding is done during warmer seasons of year (annual cycle) in temperate areas.

o   Males attempt to attract females.

·         Amplexus:

o   Female lays eggs in large masses and are fertilized externally.

·         Eggs develop into tadpoles.

·         Tadpole morphology:

o   Mouth with spiky jaws, ventral adhesive disc behind mouth

o   Swellings on each side of head that become external gills

o   Three pairs of external gills that are transformed into internal gills covered by operculum

o   Operculum fuses with body wall on right side, but a small opening remains on the left side called a spiracle.

o   Hindlegs appear first.

o   Tail is absorbed during metamorphosis, mouth changes, lungs develop, gills are absorbed.

·         Many reproductive strategies exist in tropical anurans.

 

21 Families of Anurans: below are the 3 most common

·         Ranidae: most familiar frogs

o   Most abundant and found in nearly every temperate and tropical region of the world

o   Usually found near water

o   Most are solitary except during breeding season=noisy time for frogs!

o   Defense mechanism: inflating lungs so they are difficult to swallow

o   Many hibernate during winter months in mud

o   Some with the ability to survive prolonged freezing

o   Frogs can survive multiple freeze/thaw events during winter if not more than about 65% of the total body water freezes.

·         Hylidae: tree frogs

·         Bufonidae: true toads

Decline of amphibian populations:

•      Video Clip: In the last two decades, there have been an alarming number of amphibian extinctions.

 

Reptiles

•      Age of the Reptiles

–     Reptiles were the dominant terrestrial animals during the Mesozoic Era (248-65 mya).

–     A large extinction event saw the demise of most reptiles. Those that survived gave rise to today’s living reptiles.

•      Characteristics of Reptiles

–     Tough, dry, scaly skin:

–     Well-developed dermis:

–     Scales:

•      Some remain throughout life

•      Some are shed at intervals

•      Turtles:

–     Shelled amniotic egg:

•      No water required

•      Young hatch as lung-breathing juveniles

–     Modified jaws with larger, longer jaw musculature than is found in fish or amphibians

–     Copulatory organs in males

•      Paired testes produce sperm that are carried by the vas deferens to the copulatory organ

–     Female system

•      Oviducts secrete albumin and shells for eggs

–     Efficient circulatory system with separated right and left atria.

•      Some with complete ventricle separation as well

–     Relatively well developed lungs

•      No cutaneous respiration

•      Suck air into lungs by enlarging pleural cavity (no diaphragm)

–     Water conservation:

•      Kidney excretes nitrogenous wastes as uric acid

–     Relatively complex nervous systems

•      Small brains but enlarged cerebrum

•      Advanced connections to central nervous system

•      Sense organs well developed

•      Jacobson’s organ:

•      Anapsid vs Diapsid Reptiles

–     By the end of the Paleozoic Era, land animals had split into three groups: the anapsids, the diapsids, and synapsids.

•      Anapsids:

•      Dapsids:

•      Synapsids:

–     Classifications are based on the number of openings in the skull besides the eye sockets. Anapsids have no other openings, synapsids have one, and diapsids two.

•      Anapsid Reptiles: Chelonians (turtles/tortoises)

–     Turtles have remained relatively unchanged for the past 200 million years.

–     Physical Traits:

•      Shell

•      Shell fused to thoracic vertebrae and ribs

•      Jaws with tough plates for gripping food (no teeth)

•      Poor sound perception, but good senses of smell and color vision

•      Oviparous with internal fertilization

•      Eggs are buried in ground

•      In some, low temps produce males and high temps produce females

–     Ecologically and physically diverse

•      Diapsid Reptiles

–     Most reptiles fall in this group: lizards, worm lizards, snakes, sphenodons, crocodiles, alligators

–     Lizards

•      Extremely diverse group

•      Most with 4 limbs and relatively short bodies

•      Most with movable eyelids

•      Keen vision

•      Most with external ears

•      Some with desert adaptations

 

 

•      Geckos: small, mostly nocturnal

 

 

•      Iguanas: brightly colored with ornamental crests, frills, throat fans

 

 

•      Skinks: diverse group

 

 

•      Chameleons: arboreal lizards primarily in Madagascar and Africa

 

 

–     Worm Lizards

•      Neither worms nor lizards

•      Found in South America and tropical Africa

•      Specialized reptiles with bodies fit for burrowing

 

 

–     Snakes

•      Entirely limbless lacking both pectoral and pelvic girdles

•      Numerous short, wide vertebrae

•      Highly kinetic skull:

•      No movable eyelids:

•      Poor eyesight

•      No external ears

•      Deaf but can sense low-frequency vibrations conducted through ground

•      Chemical senses are the primary sense used for hunting prey.

•      Enlarged olfactory receptors in nose

•      Pair of pit-like Jacobson’s organs in roof of mouth

•      Lined with olfactory epithelium and richly innervated

 

 

•      Pit Vipers

•      Special heat-sensitive organs on heads between nostrils and eyes

•      Pits supplied with dense packing of nerve endings

•      Extremely sensitive to radiant energy:

 

•      Can hunt as effectively in dark as in light

•      Modified teeth (fangs) in upper jaw bones

•      Lie in membranous sheath when mouth is closed

•      Venom injected through canal in fangs

•      Snake Venom:

•      Neurotoxic: acts mainly on nervous system

•       Hemorrhagic: breaks down red blood cells and blood vessels

 

•      Nonvenomous snakes: kill by constricting or by biting and swallowing

 

•      Reproduction

•      Most snakes are oviparous

•      Pit vipers are ovoviparous

•      A few snakes are viviparous with primitive placentas

–     Sphenodons: Tuatara

•      Single survivor of lineage

•      Lizard-like in form, but lives in burrows

•      Slow-growing with long life (up to 77 years)

•      Unique feature:

–     Crocodilians: crocodiles, alligators, caiman, gharial

•      Crocodiles

•      Elongate, robust skull with massive jaw musculature

•      Teeth set in sockets

•      Secondary palate:

•      Swift and aggressive

•      Can reach large sizes (over 2000 pounds)

•      American Crocodile (Crocodylus acutus):

 

•      Alligators

•      Less aggressive than crocodiles

•      Make definite vocalizations

•      American Alligator (Alligator mississipiensis) is only alligator species in the U.S.

 

•      Alligators and crocodiles are oviparous, laying 20-50 eggs in dead vegetation

•      Mother hears vocalizations and open nest to allow hatchlings to escape

•      Parental care by female during first year of life