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Adaptive radiations in reptiles
What is adaptive radiation?• It is the phenomenon
in which the same genera or different but closely related genera become adapted to different kinds of environment or habitat.
• It is the formation of different species from a common ancestor getting adapted to different kinds of environment i.e. habitats by adopting various modifications.
Flourishing reptiles• End of devonian produces
organisms “amniota”• Mesozoic era = age of
reptiles• first reptile (ancestor of
reptilia)-cotylosauria(stem reptiles)
• Durind late Triassic period arose Dinosaur and Pterosaur belonging to archosauria
• During late cretaceous period all of these giant reptiles disappeared
Reptilian ancestor-Cotylosaur
• Lizard like creature about 2 feet long
• It used to live on other larger animals
• Intermediate characteristics
Early adaptive radiations during Permian period
• Synapsids and Thecodonts evolved
synapsid thecodont
• Synapsids Therapsids Mammals• Thecodonts
Dinosaurs Crocodiles
• Some stem reptiles returned to water
Ichthyosaurs Plesiosaurs
Second major adaptive radiations during Triassic
period• Dinosaurs and Pterosaurs evolved from Thecodonts
DINOSAURS• Largest animals ever• Carnivorous and Herbivorous• They can be divided into Reptile-like(Saurischians eg:-Tyrannosaurus Rex)
and Bird-like(Ornithischians eg:-Camptosaurs)
PTEROSAURS• Small sized flying reptiles• Powerful forelimbs supporting wings• Eg:- Pteranodons
Third major adaptive radiations during Cretaceous period
• Period of mass extinction• Nearly all dinosaurs and many
invertebrates disappeared• Few reptilian groups survived
SquamataCheloniaCrocodilia
Rhynchocephalia
Classification of reptilia• Subclass: anapsida
o Order-cotylosauriao Order-chelonia
• subclass: synaptosauriao Order-sauropterygia
• Subclass: ichthyopterygiao Order-ichthyosauria
• Sublass: lepidosauriao Order-rhynchocephalia
o Order-squamata• Subclass: archosauria
o Order-crocodiliao Order-pterosauriao Order-saurischia
o Order-ornithoschia• Subclass:synapsida
o Order-pelycosauriao Order-therapsida
Adaptive radiations in order-squamata
(lizards and snakes)Lizards
• Various habitats such as forests, grasslands, deserts and even below soil
• Lizards have adapted to various habitats such as
Adaptations to aboreal habitat Adaptations for flying
Adaptations for running Adaptations for fossorial habitat Adaptations for desert habitat
Adaptations to aboreal habitat(living on trees)
• Short limbs• Prehensile tail eg:-
chameleon• Digits with adhesive discs &
pads/claws eg:-gecko
Adaptations for flying(gliding)
• Development of petagia supported by ribs(5-6)
• Slender and tapering tail eg:-draco
Adaptations for running
• Narrow body for least resistance• Well developed hind limbs for upright
posture• Reduced number of digits• Eg:- calotes
Adaptations for fossorial habitat
• Narrow cylindrical body • Limbs absent• Eyes are degenerated (eg:-anguis)
Adaptations for desert habitat• Body covered by numerous spines• Ureotelic• Skin-hygroscopic• Eg:uromastyx and phrynosoma
Snakes• Burrow and also live on land• Vestigial organs• Adapted to various habitats such as trapical and temperate forests,
grasslands, in desserts, in alpine medows and also living underground• Smallest species (brahming blind) and largest species(reticulated python)
Carnivorous snakes show following adaptations:-• Loosely articulated jaws• Presence of Venom apparatus• Python & boas squeeze their prey• Presence of prey is easily detected by vibrations of air and water• Presence of forked tongue
Aboreal snakes show following adaptations:-• Laterally compressed body• Prehensile tail• Exhibit protective colouration• Flying snake can glide from tree to tree
Aquatic snakes show following adaptations:-
• Flat tail• Nostrils on the top of snout• Highly venomous• Feed on fish particularly eel• Protective colouration such as yellow bellied sea snake
and black banded krait• Fresh water snakes are semi-aquatic• They overhang on tree branches on a stream to catch
their prey• they also hunt in water
Adaptive radiations in order- chelonia(turtles and tortoises)
• Oldest living reptiles on the earth evolved from stem-reptiles
• Tortoise = landforms (short limbs with 5 digits each)
• Turtles = aquatic forms (limbs modified to form flippers)
• Outer shell(plastron) fused with ribs called plastron
• Slow metabolic rate• Can remain for long time under water • Reproductive behaviour
Adaptive radiations in order-crocodilia(crocodiles, alligators and gavialis)
• Evolved from thecodonts• Kins of dinosaurs• Only archosaurs surviving• Semi-aquatic Habitats- rivers, lakes, ponds, swamps, estuaries, seas etc… Locomotion- long and powerful tail Breathing:- • development of false palate• Nostrils present in the front of the mouth in
the primitive land dewelling animals• Aquatic forms- nostrils towards the back of
their head• In crocodilians nostrils are on the tip of snout
but underneath lies a partion running along the entire length of the mouth
• Nasal opening are opened by constrictor muscles and closed by dialator muscles
Food habits:-• Feed on insects,
crustaceans, fishes, small frogs, birds, other reptiles and mammals.
• Also developed a method of
crushing and grinding their prey.
Reproduction:-• Oviparous
Adaptive radiations in order-rhynchocephalia (tuatara)
• Rhynchocephalians evolved during permian period of paleozoic era and survived upto jurassic period
• Sphenodon (Tuatara) “living fossil”• Tuatara means lightening back in native Maori language
Survival instincts:-• Crest of large erect spines on their back• Thick tail with spines• Head relatively larger than body proportion• Jaws are “chisel-like”• Third eye on the top of head. This eye has lens, retina,
and also nerve connection to brain.• Habitat- burrows• Penis is absent in males.• Female lays eggs only once in 4 years.
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