Modern Amphibians - The Lissamphibia
Anura (frogs)
Caudata (salamanders)
Gymnophiona (caecilians)
Amniote Origins And The Diversification Of "Reptiles"
Outline: Amniote Origins and the Diversity of the "Reptiles"
Phylogenetic Relationships (cladogram)
Amphibian Deficiencies:
Amniote Innovations:
- 4 major advances made for an ‘improved’ terrestrial vertebrate
- Amniotic egg
porous shell + 4 membranes = terrestrial reproduction
- Resistance to desiccation
Scaly, keratinized skin + improved kidneys = less water loss
- Improved skull
lateral compression + larger, longer jaw muscles = greater force.
- Better body support, more upright posture
elongated leg bones + strengthened wrist/ankle bones = greater mobility and speed
Reptiles: The first amniotes
- First true land animals
- 7,000 living species
- Occupy almost all terrestrial and aquatic habitats
- Represent some of the smallest and largest animals to ever
roam the planet.
Reptile Lineages: 3 skull types
Anapsid Reptiles: Order Testudines
- First appear in late Triassic (approx. 200 mybp)
- Very little change in morphology
Shells consist of a carapace (bony plates fused to the thoracic vertebrae/ribs) and a plastron (plates fused with several ventral bones) - Respiration
- Cannot expand their chests to draw air into the lungs
- Use abdominal/pectoral muscles as a ‘diaphragm’
- lack teeth
- jaw equipped with tough, horny plates for gripping food
- most turtles are mute, but
- have a keen sense of smell and excellent color vision
- oviparous (eggs released by female & develop outside the maternal body)
- leathery shells, buried in the ground
- sex of hatchlings determined by temperature of nest
Diapsid Reptiles: Superorder Lepidosauria (snakes,
lizards)
- 6000 species (95% of all living reptiles)
- Big size range: cm à meters (Komodo dragon)
- Retain the primitive lateral undulation of vertebral column
- Lizards appear first (late Permian 225 mybp), snakes come later (late Jurassic)
- Differences in morphology include:
- Lizards have movable eyelids, snake eyes are permanently covered with a transparent cap.
- Lizards have external ears, snakes don’t
- Snakes have no pelvic or pectoral girdle (except boas, which have remnants of pelvic girdle)
- Feeding: the skull has ‘breakaway’ joints that allow:
- better manipulation of prey
- greater closing force of the jaw
- swallowing of prey several times own diameter
- Sensory
- Eyesight = primary mode in lizards
- retinas rich in both cones & rods = keen daylight vision
- Chemo and thermosensory reception in snakes
- ‘smell’ with pit-like Jacobson’s organs in the roof of the mouth
- Some snakes (e.g. pit vipers) use pit organs to sense temperature differences as small as 0.003° C!
Diapsid Reptiles: Superorder Archiosaura (crocodiles,
dinosaurs)
- Several improvements to the basic reptile body plan:
- lighter, narrower skull
- socketed teeth - easier to replace w/ less trauma to tissues
- tendency towards bipedal locomotion
- reduced forelimbs & pectoral girdle
- hindlimbs under body supported by a strengthened pelvic girdle
- no lateral flexure of the vertebral column
Diapsid Reptiles: Order Crocodilia
- Arose in the late Paleozoic era (approx 225 mybp)
- Little morphological change since their beginnings
- long jaw for prey capture
- skull with massive jaw musculature provides a wide gape and rapid, powerful closure
- long body with laterally compressed tail for swimming
- secondarily evolved quadrapedal locomotion
- can be large (Nile crocodile can reach 1000 kg, salt water crocodile in North Australia can reach 20 feet long, very dangerous for humans).
- well developed lungs
- second palate allows breathing when mouth is filled with water or food.
- oviparous (eggs released by female develop outside the body)
- extensive maternal care of eggs, nest, young
- incubation temperature of the nest often determines offspring sex
Diapsid Reptiles: Orders Saurischia & Ornithaurischia
Several additional innovations made these reptiles extremely successful:
- Erect, digitigrade foot posture (faster, more efficient movement)
- Lighter, stronger pelvic girdle (larger, stronger leg muscles)
- Strengthened ankles (withstand strain of high speed locomotion)
- Rigid tail (counterbalance during high speed maneuvering)
The Saurichia had two independent lines of evolution
- Theropods
- mostly carnivorous
- ranged between 3-40 ft.
- included taxa like Tyrannosaurus and Allosaurus
- Sauropodomorphs
- mostly herbivorous
- some were 120 ft. long!
- secondarily evolved quadrapedalism
- included taxa like Brontosaurus and Brachiosaurus
The Ornithaurishians
- Diverse group of ‘beaked’ herbivores
- Included taxa like Stegosaurus and Triceratops
Complex social behavior
The End of Reptile Dominance
BUT …. Are dinosaurs really extinct? (see
cladogram)