1. AMPHIBIANS – A Tetrapod
Delivered By
SHITTU Olalere
Dept of Zoology
University of Ilorin, Nigeria

2. I. Movement Onto Land
Amphibians are vertebrate transition to land; other organisms like plants, gastropods, and arthropods made transition earlier
Since organisms made mostly of water, dangerous transition
Also had to adapt to different oxygen content, density, temperature regulation, and habitat diversity

3. All sorts of “amphibians” in the fossil record

4. II. Evolution of Terrestrial Vertebrates
A. Devonian Origin
Mild temperatures, and periods of flooding or droughts creating unstable sources of freshwater
Fish with lungs were better able to survive
Early fish fossils that could crawl along mud with “walking fins:” Eusthenopteron, Acanthostega, and Ichthyostega.
Land adaptations include: skull, teeth, stronger pectoral and pelvic girdles, jointed limbs, stronger backbone, muscles to support body in air and elevate head, more protective rib cage, ear structure, and longer snout
Many fossils have more than 5 digits

5. Limbs with digits
strengthened limb girdles ?
“Fish”
Tetrapod

6. 1st Terrestrial tetrapods – Ichthyostegans, Labyrinthodonts
† Acanthostega
Early tetrapod trackway

7. Labyrintodonts
Ichthyostega

8. 1st terrestrial tetrapods

9. B. Carboniferous Radiation
Uniformly warm and wet
Tetrapods radiated in swampy, fern areas eating insects, larvae, and invertebrates
Temnospondyls form lineage from which modern amphibians are derived; they have 4 digits on forelimbs
Became better adapted to aquatic life; bodies flattened, some like salamanders developed weaker limbs and stronger tails, and frogs developed webbing on hind limbs for better swimming

10. Internal choanae (nares)

11. III. Modern Amphibians (Class Amphibia)
A. Diversity
Over 4200 species
Ears redesigned
Remain tied to water since eggs are laid in water and larvae have gills
Thin skin loses moisture rapidly restricting them to moist habitats
Ectothermic which also restricts habitat and range

12. B. Caecilians: Order Gymnophiona
160 species live in tropical rainforests of South America, Africa, and Southeast Asia
Elongate, limbless, and burrowing
Some larvae develop in folds of body and in others develop in oviduct, eating it for nourishment

13. C. Salamanders: Order Caudata
Characteristics
360 species living in northern temperate areas
Most are small, under 15 cm, but Japanese giant salamander is 1.5 m long
Limbs are at right angles of body, with fore and hind limbs of equal length
Burrowing and some aquatic species have lost limbs
Carnivorous, eating high fat and protein foods so do not store much fat or glycogen

14. C. Salamanders: Order Caudata
Aquatic:
“Taste” chemicals in water
Vibrations – Retain lateral line
system
Terrestrial:
Smell – Olfactory epithelium (volatile)
Smell – Vomeronasal organ (Non-volatile)

15. C. Salamanders: Order Caudata
Sexually dimorphic (larger in males)
Courtship / Identification (species / sex / individual)
Highly advanced in Plethodontidae
Nasolabial Grooves = Non-ciliated grooves; upper lip to nares
Aids in collection / delivery of chemical cues (capillary action)
Sexually dimorphic (esp. during reproductive season)

16. Eastern United States / SE Europe
Aquatic:
SE United States
Amphiumidae (Amphiums):
Amphibians
terrestrial egg-laying
aestivate
Morphology:
Eel-like; maintain four reduced limbs
Paedomorphic; lack gills (lungs present)
Habitat:
Sluggish streams / rivers; swamps
Reproduction:
Internal fertilization; female nest guarding
Proteidae (Waterdogs):
Aquatic:
Eastern United States / SE Europe
dissection specimen
nocturnal
Morphology:
Paedomorphic; feathery gills / caudal fins
Habitat:
Lakes / streams
Limestone caves (drastic reduction in numbers)
Reproduction:
Internal fertilization; ♂ / ♀ nest guarding

17. North / Central / South America & Europe
Amphibians
Plethodontidae (example = Ensatina escholtzii):
Anatomy:
Constriction at tail base = tail autotomy
Very costly (tail = large fat reserve)
~ 10 – 12% tail regeneration (~ 2 years)
Terrestrial:
North / Central / South America & Europe
Habitat:
Prefers cool forests with litter / dead trees
Tolerates logging better than most plethodons
Reproduction:
Pheromone:
Chemical cue that affects the
behavior and / or physiology
of a conspecific
Mating begins (Nov.) and ends (March) with rains
♂ use hedonic glands / pheromones to attract ♀
Methods of pheromone administration:
Slap ♀ nares with hedonic gland (video)
Innoculate ♀ with sharp teeth
Elaborately patterned courtship “dance”
“Tail straddle-walking” (unique to plethodons)
♂ repeats dance (~ 1 – 5 hours)
Pathway / movement unique to each species

18. North / Central / South America & Europe
Amphibians
Plethodontidae (example = Ensatina escholtzii):
Reproduction:
♂ lays down spermatophore; ♀ picks it up (video)
♀ lay 8 – 12 eggs (~ 5 mm)
Terrestrial – in logs; under logs; in burrows
Terrestrial:
North / Central / South America & Europe
Sperm Cap
Gelatinous Base
♀ guards eggs ( predation / fungal infection)
Direct development of eggs (~60 – 120 days)
Growth / Maturation:
Sexual Maturation ~ 4 years
Life Span ~ 10 years (best guess)

19. Amphibians NW United States
Rhyacotritonidae: (example = Rhyacotriton olympicus)
Anatomy:
Full metamorphosis
No operculum / opercular muscle ( hearing)
Highly reduced lungs (cutaneous respiration)
Habitat:
Terrestrial:
NW United States
Cold, clear streams / seepages / waterfalls
Very desiccation intolerant
Low heat tolerance (susceptible to logging)
Reproduction:
Internal fertilization
Spermatophore deposition
Tail-wagging display
Aquatic egg-laying
No nest guarding
Anti-predator Display
Growth / Maturation:
Sexual Maturation ~ 4 years
Life Span ~ 10 years (best guess)

20. Amphibians Larval Anatomical Specializations: Pond Larvae
Stream Larvae
Ambystomatidae
Salamandridae
Dicamptodontidae
Rhyacotritonidae
Plethodontidae
High body profile
broad tail fin extending up to head
long, plume-like gills
Only front legs at hatching
Depressed body profile
Narrow tail fin (not onto trunk)
Short, thread-like / curly gills
All four legs at hatching

21. North America / Europe / NW Africa / Asia
Amphibians
Salamandridae (example = Taricha granulosa):
Habitat:
Prefer older growth forests during “newt” phase
Warning Coloration:
Flashes tail & brightly colored stomach
Terrestrial:
North America / Europe / NW Africa / Asia
Chemical Defense:
Tarichatoxin (non-protein – VERY poisonous)
Neurotoxin – blocks NA+ channels (paralysis)
Small dose lethal to birds / mammals
Large dose lethal to humans
Red-spotted Garter Snake
“The Arms Race”

22. C. Salamanders: Order Caudata
Hearing – limited high frequency (no ear drum); primarily ground vibration
Vision – acute; especially in Plethodontidae

23. SE United States / NE Mexico Amphibians
Sirenidae (sirens):
Aquatic:
SE United States / NE Mexico
Amphibians
Nocturnal
Vocalization
Morphology:
Eel-like; lack hind limbs (lack pelvic girdle)
Paedomorphic; gills present
Habitat:
Swamps / lakes / marshes (slow-moving water)
Reproduction:
External fertilization; female nest guarding
Aquatic:
Central China / Eastern United States
Cryptobranchidae (Hellbenders):
largest individuals
live 50+ years
Morphology:
Dorsal-ventral compressed body (paedomorphic)
Multiple folds in skin (cutaneous respiration)
Habitat:
Clear, cold mountain streams / lakes
Severely reduced ranges (loss of habitat)
Reproduction:
External fertilization; Males = “den masters”

24. Salamanders

25. Breeding Behavior Fertilize eggs internally
Terrestrial species deposit egg clusters under logs or in soft earth; eggs hatch out to mini adults
Most salamanders lay strings of eggs in water; larvae hatch with gills, and then may turn into terrestrial or aquatic adults
Newts have “red eft” stage with a terrestrial juvenile, that then turns into aquatic, breeding adult
Some newts stay entirely aquatic

26. Respiration Thin skin easily exchanges gases; also use mouth cavity
At various stages may also have gills, lungs, both gills and lungs, or neither
If lungs are used, they are present from birth, but only become functional following metamorphosis; hold nostrils above water to breathe
Larvae hatch with gills, and lose them following metamorphosis, along with fin-like tail; if a lineage does not undergo metamorphosis, it retains these characteristics
Those in terrestrial family Plethodontidae have no lungs and use only skin

27. Paedomorphosis Preservation of larval features into adulthood
Trend found in salamanders
Some never metamorphose, like the mudpuppy
Others typically may not, but can change if conditions change (typically in dry conditions)
Another example is Ambystoma tigrinum, which stays in an axolotyl stage; can metamorphose if treated with thyroid hormone
Some have partial paedomorphosis, retaining larval characteristics but switching to lungs

28. D. Frogs and Toads: Order Anura
Characteristics
3450 species
Evolved during Jurassic Period, 150 mya
All have tailed larval stage but are tailless as adults; none retain larval characteristics as adults
21 families
Family Ranidae, larger frogs of North America
Family Hylidae, tree frogs
Family Bufonidae, toads

29. Habitat and Distribution
260 species of genus Rana found in temperate and tropical areas
Frogs and toads are found in damp forested floors, although in tropical rainforests may live entire life in 1 tree
Swamps, ponds, streams
Frogs and toads are declining worldwide and becoming patchy in distribution; cause is unknown

30. Life Cycle Solitary except during breeding season
Spend breeding season swimming around in water
During winter, burrow into mud to hibernate, using energy from stored fat and glycogen
Also accumulate glucose and glycerol in tissues to create an “antifreeze” to prevent tissues from forming ice crystals
Easy prey; protects themselves by concealment, poison glands, and aggression

31. Integument and Coloration
Thin, moist, and attached to body in several points
Epidermis contains keratin; this is thicker in more terrestrial ones
Inner dermal layer has mucous glands, which secrete waterproofing agents, and serous glands, which secrete poisons
Dendrobatid frogs from South America secrete highly toxic poisons

32. Integument and Coloration
Chromatophores are pigment cells that produce skin color
Xanthophores are upper pigments with yellow, orange, and red
Iridophores are middle layer with silvery light-reflecting pigment that gives iridescent quality
Melanophores are deepest layer with brown or black melanin
Green color is produced by interactions among all of these pigments
Frogs can adjust color to camouflage themselves

33. Skin Pigmentation

35. Skeletal and Muscular Systems
Well developed endoskeleton of bone and cartilage with changes to allow for jumping and swimming
Front of skull is light weight and flattened
Limbs have 3 joints: hip, knee, ankle
Foot has 5 rays on hind limb, and 4 on front limb; digits jointed

36. Respiration
Use skin, mouth, and lungs with skin being critical during hibernation
CO2 is mainly lost across skin whereas O2 is mainly absorbed through lungs
The movement of air into lungs is somewhat passive, depending on movement of throat

37. Vocalization
As air enters and leaves lungs, passes over vocal cords, on way to vocal sacs
Both males and females have vocal cords but males have a more developed larynx
Songs are unique and characteristic of the species

38. Circulation
6th aortic arch present in gills was converted into pulmonary artery to lungs
Frog heart has 2 atria and 1 single ventricle
Blood from body enters right atrium and blood from lungs enters left atrium; both deoxygenated and oxygenated blood mix in ventricle
Valves do control blood though so mainly deoxygenated blood goes to lungs and oxygenated goes to body

39. Feeding and Digestion Carnivorous
Catch prey with tongue that is hinged at front of mouth
Free end is glandular with sticky secretions that cause prey to adhere
Teeth are used to hold prey, not to chew or bite
Digestive tract produces enzymes to break down carbohydrates, proteins, and fats
Tadpoles are herbivorous and have longer tracts to digest plant material

40. Nervous System and Senses
a. Brain
Consists of 3 parts: forebrain (sense of smell), midbrain (vision), and hindbrain (hearing and balance)
Forebrain has cerebrum, but not really used. Olfactory lobe most important part
Midbrain has optic lobe
Hindbrain has anterior cerebellum (not used) and posterior medulla which controls auditory reflexes, respiration, swallowing, and circulatory system

41. b. Vision Dominant sense in many amphibians (except caecilians)
Eyelids keep eyes moist, protected, and free of dust; upper is fixed and lower has clear nictitating membrane
Cornea and lens bend light to focus image on retina, with both rods and cones for color vision
Iris changes to adjust to different light levels
At rest, frog focuses on distant objects
b. Vision

42. c. Other Senses
Pressure sensitive lateral line is only found in larvae and aquatic adults
Ear is sensitive to airborne sounds; tympanic membrane passes vibrations to structure similar to cochlea
Chemical receptors in skin, on tongue, and in nasal cavity

43. Reproduction and Development
a. Egg
In spring, males migrate to same pond or stream and call females
This is dependent on temperature, humidity, and hormonal changes
Male clasps female in water and as she releases eggs, male discharges sperm over them
Eggs usually laid in masses
Eggs absorb water and swell; development begins immediately
Tadpoles hatch in 6-9 days

44. Frog Life Cycle

45. b. Tadpoles
Tadpole has horny jaws for grazing and a ventral adhesive disc for clinging to objects
3 pairs of external gills develop into internal gills covered by flap on right side fused to body wall and a spiracle on left side
Water flows through mouth, over gills, and out spiracle

46. c. Metamorphosis
Hind legs appear first; forelimbs are temporarily hidden by operculum
Tail is reabsorbed
Intestine becomes shorter
Mouth transforms into adult version
Lungs develop and gills reabsorbed

47. Metamorphosis

48. Problems with Terrestrial Living
Solutions

49. Solutions
Senses
Olfaction and hearing

50. Solutions
Senses
Hearing

51. Solutions
Respiration
lungs and skin

52. Solutions
Circulation

53. Circulation
Fishes
Single pump / single circuit system

54. Circulation Tetrapods - primitive
lungs
Separate respiratory and systemic circuits
body