Earliest amphibians

1. Earliest amphibians • The earliest are the labyrinthodonts, which included Icthyostega and Acanthostega. • During the Carboniferous a couple of major lineages of labyrinthodonts arose: the Temnospondyls and the Anthracosaurs.

2. Anthracosauria and Temnospondyls • The Anthracosauria and the Temnospndyls were both diverse groups and many were very large being several meters long. • They looked a bit like large, sprawling reptiles with scaly skin and big heads.

3. Seymouria: an Anthracosaur http://www.prism.gatech.edu/ ~gh19/b1510/tetra.gif Poterogyrinus an Anthracosaur http://upload.wikimedia.org/wikipedia/ commons/thumb/2/2c /Proterogyrinus_DB.jpg/260px-Proterogyrinus_DB.jpg

4. A small carboniferous temnospondyl and a scorpion http://www.hmnh.org/galleries/permocarboniferous/temnospondyl.gif Eryops: a temnospondyl http://comenius.susqu. edu/bi/202/ animals/DEUTEROSTOMES/ vertebrata/eryops.jpg

5. Anthracosauria and Temnospondyls • Both groups left modern descendants behind. • The Anthracosauria gave rise to the amniotes in the late Carboniferous, but the rest of the group became extinct in the Permian. • There were diverse temnospondyl groups during the Carboniferous and Permian periods, but except for one lineage (the Lissamphibia: the modern amphibians) became extinct by the end of the Triassic.

6. Lissamphibia • The Lissamphibia includes all three modern groups of amphibians. All three have smooth skin, hence their name (“Liss” means smooth.). • The oldest fossil salamanders date to the Jurassic (about 145 mya). • The oldest true frog fossils date to 190mya, but froglike vertebrates are known from 200 mya. • Caecilian fossils are scarce but the oldest known are from 195 mya. These had well-developed eyes and small functional limbs (unlike modern forms).

7. Callobatrachus sanyanensis: fossil frog from Lower Cretaceous. http://images.google.com/imgres?imgurl=http://www.fossilmuseum.net/Fossil-Pictures/ Frogs/Callobatrachus/Callobatrachus-sanyanensis1024.jpg&imgrefurl= http://www.fossilmuseum.net/Fossil-Pictures/Frogs/Callobatrachus/ Callobatrachus-sanyanensisb.htm&usg=__mJ8yZDNglWYiMrS7kPPE3NHV794=&h= 768&w=1024&sz=146& hl=en&start=6&um=1&tbnid=I7dMno_ZrUhMuM:&tbnh=113&tbnw=150&prev=/ images%3Fq%3Dfossil%2Bfrog%2B%2Bimages%26hl%3Den%26sa%3DG%26um%3D1

8. Lissamphibia • The evolutionary relationships between the three modern groups of the Lissamphibia are not clear and a lack of fossils has hindered an understanding of their relatedness and evolutionary origins.

9. Class Lissamphibia • The amphibians are represented by about 4800 hundred species divided into three orders. • Urodela “tailed ones”: salamanders • Anura: “tailless ones” frogs, toads. • Gymnophiona (“naked snake”; previously Apoda “legless ones”) caecilians.

10. Eastern Mud salamander http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-mud-salamander/ Eastern_Mud_Salamander_Pseudotriton_mlr.jpg

11. http://upload.wikimedia.org/ wikipedia/commons/6/66/ Caecilian_wynaad1.jpg Caecilian http://www.gregboettcher.com/as/science/classification/images/caecilian.jpg

12. Red-eyed Tree frog http://www.frogsite.org/pic/Redeyed_Tree_Frog.jpg

13. Amphibian skin • Amphibians lack scales and are characterized by a moist permeable skin. • This limits the environments in which they typically can live as they are constrained by the threat of water loss. • Typically they inhabit wet or damp habitats where the humidity is high (e.g., ponds. forest floors in leaf litter).

14. Amphibian skin • Many anurans and salamanders absorb moisture from the soil or other substrates through their skin. • A number of anurans have a specialized region of skin on the ventral surface around the pelvis (the “seat patch” or “pelvic patch”) that is highly permeable to water and allows water to flow rapidly into a dehydrated animal. • In dehydrated Giant Toads (Bufomarinus) the pelvic skin is 6X as permeable to water as skin from the pectoral region.

15. Mucous gland and poison glands • Amphibian skin often contains mucous glands and granular (poison) glands. • Mucous glands continuously produce mucopolysaccharides, which help keep the skin moist and able to function in gas exchange when the animal is out of water. The mucus may also have anti-predator benefits as it makes the animal slippery and difficult to grip.

16. Poison glands • Granular glands in many amphibians produce noxious and sometimes toxic secretions. • These glands are often grouped together and give the skin a textured appearance. The warts and parotid glands of toads and the dorsolateral ridges of Rana frogs are good examples.

17. Poison glands • Toxin-secreting granular glands are widespread in anurans, but also occur in some salamanders and caecilians. • Toxins include vasoconstrictors, hemolytic substances, neurotoxins and hallucinogens. Their effects range from localized irritation to hypothermia, convulsions, and paralysis.

18. Poison glands • Newts of the genus Taricha produce a neurotoxin that is present in high concentrations and a single individual produces enough toxin to kill 25,000 mice. • The salamander Bolitoglossa rostrata produces skin secretions that may paralyze and sometimes kill garter snakes that attempt to eat them.

19. Poison dart frogs • Several genera of brightly colored Neotropical frogs (Dendrobates, Phyllobates, and Epipedobates) produce highly toxic steroidal alkaloids in their skin. • The alkaloids affect both the muscular and nervous systems causing muscles to remain contracted and blocking nerve transmissions, which can result in cardiac arrest and death.

20. Green and Black Poison Dart Frog http://www.shoarns.com/frog.jpg

21. Poison dart frogs • These frogs are very small (rarely more than 2” long), but just one frog produces enough toxin to kill several people. • Several tribes of Colombian Indians use the toxins of Phyllobates frogs to tip the darts for their blowguns. • The toxin is extracted by impaling the frogs on sticks and holding them over a fire, which causes the toxin to seep out so it can be collected. • The tips of darts are then dipped in the poison, allowed to dry and used to kill birds and small mammals.

22. Medical applications of skin secretions • There have been a variety of investigations into the medical benefits of various amphibian skin secretions. • For example a powerful painkiller called epibatidine (200X more powerful than morphine) has been isolated from a poison dart frog.

23. Medical applications of skin secretions • In addition, a bacteria-killing antibiotic peptide called magainin has been isolated from the skin of the African clawed frog. • This and similar peptides are released to the skin when it is injured and kills a wide range of bacteria as well as parasites, fungi and certain viruses. • Unlike most antibiotics, which disable important bacterial enzymes, these peptides disrupt bacterial membranes punching holes trough them so the contents leak out.

24. Gas exchange • The moist skin is used extensively for gas exchange and some salamanders and one species of caecilian have lost their lungs over evolutionary time and depend exclusively on gas exchange across the skin and oral cavity. • To enhance gas exchange the skin in many species (e.g. hellbenders) is highly folded and heavily vascularized.

25. Eastern Hellbender http://fwie.fw.vt.edu/VHS/amphibians/salamanders/eastern-hellbender/hellbender- MikePinder.jpg

26. Gas exchange • Gas exchange also takes place via lungs and gills (in larvae). • Amphibians use a force pump mechanism to get air into their lungs. Air enters the oral cavity through the nostrils, the nostrils close and the floor of the mouth is raised forcing air into the lungs and prevented from escaping by a sphincter muscle. • Some frogs and toads can repeatedly use this mechanism to inflate their lungs greatly and make themselves appear large and less attractive to a predator.

27. Gills • Larval amphibians breathe using external gills. In anuran tadpoles the gills are concealed behind a flap of tissue and water flows through the mouth across the gills and out of a spiracle. • When anuran tadpoles metamorphose into adults the gills are reabsorbed.

28. Gills • In larval salamanders and caecilians the gills are exposed and project from the sides of the head. • Most species lose their gills when they mature but some retain them into adulthood (neotony). For example, the aquatic salamanders Necturus and Crytobranchus possess both gills and lungs. These species usually air breathe only when oxygen levels in the water are low or when recovering from strenuous activity.

29. Larval Tiger Salamander http://www.axolotl.org/images/tiger/tiger_larva.jpg

30. Feeding • All adult amphibians are carnivorous and amphibians eat anything they can catch and swallow. • Because amphibians generally swallow their prey whole, head size limits prey size. • Frogs of the genera Lepidobatrachus and Ceratophrys which mainly eat other frogs have enormous heads relative to their body size.

31. Amazon Horned Frog http://www.itsnature.org/wp-content/uploads/2008/02/amazon-horned-frog.jpg

32. Feeding • Most amphibians have small, identical teeth (homodnont dentition), which are found on both the palate and jaw. • The function of the teeth is to grasp and hold prey not to chew it.

33. Tongue protrusion • Most amphibians possess a sticky tongue and many can rapidly evert it to catch prey. • In salamanders of the genus Hydromantes the tongue can be extended 80% of the body length (about 6cm). A ballistic mechanism is used to fire the tongue out and it is retracted by a series of muscles. • When the tongue is everted the whole tongue skeleton leaves the mouth. Hydromantes is the only vertebrate that is known to shoot a part of its skeleton as a missile.

34. Hydromantes salamander shooting its tongue to catch a housefly http://autodax.net/tngphoto.jpg

35. Tongue protrusion • In some anurans, such as Rana and Bufo, the tongue is very protrusible. • It is attached to the front of the mouth and flipped out using muscular action so that the rear upper surface of the retracted tongue becomes the front lower surface of the extended tongue. • Caecilans have rudimentary tongues that cannot be everted.

36. http://www.ourclassweb.com/projects/webquest_frogs_tongue.jpghttp://www.ourclassweb.com/projects/webquest_frogs_tongue.jpg

37. Reproduction • The word amphibian means “two lives” and is a reference to the fact that frogs go through metamorphosis from a tadpole stage. • In most anurans fertilization is external. The male grips the female and fertilizes the soft eggs as the female sheds them from her body.

38. Reproduction • Amphibian eggs do not have a hard shell and dry out quickly if not kept in a moist environment. • Many species lay their eggs directly in water or on the undersides of leaves over water so the larvae fall in when they hatch. • Others show more parental care and brood eggs in (depending on the species) the mouth, stomach or pressed into soft skin on their backs.

40. Reproduction • Eggs in frogs develop into tadpoles that have a fishlike tail and external gills. • As the tadpole develops, often very quickly in a race against time to escape a pool before it dries up, limbs develop, the tail shortens by reabsorption and the gills are lost as the tadpole metamorphoses into a miniature frog.

42. Salamander reproduction • Unlike frogs most salamanders (>90%) use internal fertilization. • An intromittent organ is not used. Instead males produce packets of sperm called spermatophores. • Depending on the group of salamander, males may insert the spermatophore into the female or the female may pick it up with her cloaca and then use the sperm to fertilize eggs as they pass out of her body.

43. Salamander spermatophores http://www.wildlife.state.nh.us/Wildlife/Nongame/salamanders/ salamander_images/spermatophore2-Marchand.jpg

44. Reproduction • Unlike frogs the young of most terrestrial salamanders develop from eggs into a larva that looks like a smaller version of the adult, but which has gills, which are lost at metamorphosis. • The most terrestrial salamanders, the lungless plethodontids, have evolved young that hatch from the egg as miniature versions of the adult and there is no aquatic larval stage.

45. Reproduction • Other salamanders lay their eggs in water. Eggs may be laid singly or in clumps. • These eggs develop into larvae that are miniature versions of the adults, but they have external gills. • In terrestrial species larvae transform into a juvenile stage called an eft and when sexually mature these return to water to breed.

47. Caecilian reproduction • In caecilians fertilization is internal (males possess an intromittent organ) and they employ a variety of developmental strategies. • Some species are oviparous with aquatic larvae, others are oviparous, but the young develop directly into terrestrial young. In many cases, the mother will brood the eggs until they hatch.

48. Many caecilians lay their eggs in the mud near water, but some caecilians brood their eggs in burrows.

49. Caecilian reproduction • However, the majority of caecilians are viviparous (about 75%) and matrotrophic (young obtain nutrition from the mother). • Newborn caecilians are 30-60% of the length of their mother and a litter may include 9 or 10 babies, so mother’s clearly invest heavily in their offspring.

50. Caecilian with young http://www.abdn.ac.uk/~nhi708/ classify/animalia/chordata/amphibia/ apoda/caecilian.jpg