Amphibians to reptiles

Transcription

1 Origins Amphibians to reptiles Devonian mya The Age of Fishes (& First Tetrapods) Carboniferous mya The Age of the Giant Amphibians Permian mya End of the Age of the Giant Amphibians Origins and evolution of the major groups Vertebrate Cladogram The amniotic egg Shared derived character of amniotes Possible only with internal fertilization Shell protects against desiccation Reduces predation Allantois (waste mgmt, gas exchange) 340 mya (Amniotic egg) (Four-limbed vertebrates) (Animals with backbones) Chorion (interface with mother) Credit: Stanislav Traykov Jan 28, 2005 Amnion (protection) Early amniotes Diverged ~ 340 mya Small and lizard-like Enlarged lungs Nails/claws for burrowing Loss of lateral line system Relatively impervious skin to reduce water loss Fundamental Splits among the Amniotes Skull fenestrae are the synapomorphies that distinguish these groups Synapsids Diapsids Anapsids Euryapsids 1

2 Amniote Evolution Amniote Evolution Rhipidistian crossopterygian lobe-finned fish Lepospondyls Anthracosaurs Rhipidistian crossopterygian lobe-finned fish Lepospondyls Anthracosaurs Synapsids Anapsids Diapsids Euryapsids Synapsids Anapsids Diapsids Euryapsids Mammalia Chelonia? Lepidosaurs (tuatara &squamates) Archosaurs (birds & crocs)? Subclass Anapsida stem reptiles Lack fenestrae - Ancestral condition Developed shells and attained huge sizes (one turtle reached 6 m in length) Eventually lead to the modern chelonians ancient reptiles that have not changed much since the Triassic. Includes turtles and their extinct relatives What are turtles? Because the anapsid condition is ancestral, it gives no clue to their relationship with extant reptiles Both morphological and molecular analyses now suggest that turtles may be nested within Diapsida This would mean that the anapsid skulls of turtles may be secondarily derived? Subclass Diapsida Most species-rich group of amniotes (>16,000 spp.) Includes most extant reptiles Enormous radiation of diapsids in the Mesozoic ( mya) Only two groups are extant: Lepidosaurs: Lizards, snakes, tuatara and their extinct relatives Archosaurs: Crocodylians, birds, and their extinct relatives 2

3 Subclass Diapsida Lepidosauria Two living orders: Rhynocephalia (Tuatara) Subclass Diapsida Lepidosauria Defining characters Transverse cloacal slit Hemipenes Ecdysis Squamata (Lizards, snakes, amphisbaenids) Subclass Diapsida Archosauria The Ruling Reptiles Originated ~ 250 mya in the Permian Dominant terrestrial vertebrates in the Mesozoic Era Descendants include crocodiles, birds and dinosaurs Subclass Diapsida Archosauria Modifications of the skeleton allowing for diverse locomotor specializations Adaptations associated with increased predatory efficiency Teeth set in sockets in the jaw bone Forelimbs with sharp claws Microraptor discovered mya Origins of flight Archaeopteryx First known bird ~250 mya The Age of the Reptiles - Mesozoic mya (Triassic Jurassic Cretaceous periods) Reptile-dominated trophic pyramid Explosive radiation of flowering plants, and the insects and small reptiles that fed on them Many medium- to large-sized semiaquatic herbivorous reptiles arose Immense biomass of insect- and plant-eating reptiles Dominated by carnivorous species 3

4 End of the age of Reptiles (~65 mya): The K- T (Cretaceous-Tertiary) event Mass extinctions correlate with the occurrence of a 310-kmwide impact crater on the Yucatan Peninsula 70% of all species on earth went extinct Legacies of the archosaurs. The birds (~9,000 extant species) Archosaurs also gave rise to the Crocodylia Originated ~200 mya in the Triassic Survive today in small numbers Only ~ 23 species Amniote Evolution Rhipidistian crossopterygian lobe-finned fish Lepospondyls Anthracosaurs Synapsids Anapsids Diapsids Euryapsids Mammalia Chelonia? Lepidosaurs (tuatara &squamates) Archosaurs (birds & crocs)? 4

5 Euryapsids With a single dorsal opening on skull Modified from the diapsid condition Polyphyletic group Highly successful and included many highly derived aquatic forms, but none extant Or are they? Actually, one Euryapsid plesiosaur may still be extant Legend of Silver Lake Subclass Synapsida Subclass Synapsida, with a single opening on the side of the skull The proto-mammals or mammal-like reptiles (technically not reptiles) Originated 315 mya in the Carboniferous Eventually lead to the modern mammals Tetraceratops Oldest known therapsid (Permian) First mammals The first mammals appeared only shortly after the dinosaurs (late Triassic). 1 st 2/3 of their history, mammals were numerous but relatively insignificant Mostly nocturnal or arboreal shrew-like animals Did not expand into a wide variety of environments until after the extinction of the dinosaurs 5

6 Vertebrate Cladogram 340 mya (Amniotic egg) (Four-limbed vertebrates) (Animals with backbones) Credit: Stanislav Traykov Jan 28, 2005 Class Reptilia 4 Orders Testudines (Turtles) (300 spp) Squamata (Lizards and Snakes) (7,900 spp) Crocodylia (Crocodylians) (23 spp) Rhynocephalia (Tuatara)(2 spp) Unifying characteristics Tetrapods - a few have secondarily lost their limbs (snakes and glass lizards) Shelled amniotic egg encases the embryo in a fluid-filled container frees reptiles from locating and using a moist habitat for egg laying Scales of epidermal origin made from keratin - prevents water loss and slows dehydration rates more widespread than the amphibians, which are limited by temperature and moisture Three-chambered heart Atria Ventricle All reptiles except crocodilians have a three-chambered heart Despite having a single ventricle, oxygenated and deoxygenated blood are largely kept separate Because there is no septum, reptiles can adjust the proportion of oxygenated blood that goes to the body versus the lungs (intracardiac blood shunt) Aids in heating and cooling Other unifying characteristics All have internal fertilization accomplished by a copulatory organ penis or hemipenis: outpocketing of the cloaca (tuatara lack a copulatory organ - mate by repressing the cloaca) 6

7 Turtles (Order Chelonia or Testudines) = 260 species Only living anapsids = one of earliest reptile lineages (little changed since the Triassic) Protostega from ~ 60 mya Turtles:Characteristics Shell-associated Demography A bony shell completely encloses internal organs Characterized by a carapace, fused to the vertebrae and ribs, and joined to the plastron. Only head and tail free Limbs, head, and neck can be drawn into shell Extraordinary armor Implications: great longevity, high survival. Other characteristics No teeth, replaced by a keratinous beak as in birds. Other characteristics All turtles are oviparous with longterm sperm storage. No parental care. Dig nests with hind feet on land 7

8 Other characteristics Highly mobile neck follows one of two patterns Hidden necks: Cryptodira (suborder) Side necks: Pleurodira (suborder) Class Reptilia 4 Orders Testudines (Turtles) (300 spp) Squamata (Lizards and Snakes) (7,900 spp) Crocodylia (Crocodylians) (23 spp) Rhynocephalia (Tuatara)(2 spp) Squamates; the scaly reptiles (Order Squamata) Most diverse group of reptiles (with > 7,900 species) Lizards [Suborder Lacertilia] Snakes [Suborders Serpentes or Ophidia] Amphisbaenians [Suborder Amphisbaenia] Squamates - Lizards (Suborder: Lacertilia) ~3,000 species, 25 families Range in size from m Most are small (80% are < 2 g) and insectivorous, larger species are often herbivorous Sphaerodactylus ariasae Squamates - Lizards (Suborder: Lacertilia) Four limbs, but limb reduction or loss in some groups Squamates - Lizards (Suborder: Lacertilia) Most are oviparous, but some are viviparous External ear openings Moveable eyelids (unlike snakes) Two species are venomous (Gila monster, Mexican bearded lizard) 8

9 To help protect your privacy, PowerPoint prevented this external picture from being automatically downloaded. To download and display this picture, click Options in the Message Bar, and then click Enable external content. Squamates Snakes (Suborder: Ophidia, Serpentes) ~2,300 species No limbs, eyelids or external ear (inner ear detects vibrations) Have lost the sternum ribs extend the entire length of the vertebral column Left lung is reduced or absent, organs elongate Snakes and feeding All are carnivorous Most take relatively large prey Subdue by venom and/or constriction Heat sensitive pits Skull and jaws exceedingly mobile Python eating a wallaby Squamates Amphisbaenids (Suborder: Amphisbaenia) Amphisbaena = to go both ways named after a mythical ant-eating serpent with a head at each end ~ 135 species Mostly legless burrow, eat inverts Skin loose, scales in annuli Order Crocodylia (crocodiles = 23 species most are endangered) Survivors (along with birds) of the once-prevalent group Archosauria thrived during the Mesozoic 9

10 Crocodylia Thecodont teeth (teeth set in bony sockets) Teeth are replaced as often as once a month Crocodylia... Bodies armored by sheets of abutting osteoderms (plates of bone under the skin) and covered by thick non-overlapping scales Crocodylia A very advanced Four-chambered heart Cogged valve allows blood to be shunted from the right side of the heart to the systemic circulation, introducing deoxygenated blood Can re-route blood usually pumped into the lungs into other parts of the body Allows crocodiles to dive for several hours without surfacing to breathe When blood rich with carbon dioxide goes to the stomach instead of the lungs, it can aid digestion Secondary palate Allows crocodiles to breathe even when submerged under water Their internal nostrils open in the back of their throat, where a part of the tongue called the "palatal valve" closes off their respiratory system. This way they can open their mouths underwater. Most reptiles lack a secondary palate Crocodylia... All build nests, either as mounds of rotting vegetation (alligators, caimans, and a few crocodiles) or in friable soils (most crocodiles) Females guard nests and assist young Rhynchocephalians (tuatara) Sister group to the Squamates Order: Rhynchocephalia 10

11 To help protect your privacy, PowerPoint prevented this external picture from being automatically downloaded. To download and display this picture, click Options in the Message Bar, and then click Enable external content. Why are Tuatara Unique? Rhyncocephalians Once a widespread group, but now just 2 species of the Genus Sphenodon on small islands off New Zealand. Most Rhynocephalians went extinct 70 mya Rhyncocephalians: Characteristics Chisel-beaked upper jaw overhanging the lower jaw. Teeth fused to the jaw and not replaced throughout life Lizard-like in body form Series of spines on nape and back tuatara = "spines on back in Moari Rhynocephalians: Characteristics Vestigial eye (parietal eye) It has its own lens, cornea, retina with rod-like structures and degenerated nerve connection to the brain, possibly evolved from a real eye Its function is unknown may be used for navigation, thermoregulation, tracking photoperiod Tuatara Long-lived, incubation of a year or more, sexual maturity of a decade or more Do not copulate rub cloacas together Origins of reptiles End 11