phylogeny of class Reptilia vertebrates.pptx

reptiles

1. BIO 203 LESSON 2

2. REPTILIA (REPTILES) CHARACTERISTICS Presence of scales. They produce amniotic eggs They have simple occipital condyle Have single ear They have three chambered heart They are poikilothermic ( i.e. cold blooded)

3. Reptiles are believed to have evolved from amphibians during the carboniferous period, some 300 million years ago (mya). The original stocks were cotylosaurs which were extinct about 150 mya during the Jurassic period. Before this, they radiated during the Mesozoic era before going extinct due to environmental changes. They experienced drastic changes in the environment at the end of the Mesozoic era.

4. E.g. Birds and mammals evolved and preyed on the eggs of the reptiles. There were 15 orders before the Mesozoic era but only 4 orders remain extant (living ). These are; Order Rhynchocephalia : T his comprises a single species called Sphenodont punctata (Tuatara ). Order Crocodilia- 25 species Order Chelonia- Tortoises and turtles

5. (iv) Order Squamata . About 2,000 spp. These are the most dominant. They include the snakes and lizards. Extinct orders include dinosaurs, marine reptiles and therapsids. During the transition from amphibians to reptiles, there were some changes. A . Evolution of water proof skin consisting of dry cornified skin covered with scales for water conservation.

6. B. Improved lungs. The lungs became harder and compact . C. Protection of amniotic egg. This was necessary against desiccation and also as a shock absorber. The allantoid cavity was a store for secreting waste. The allantrochorion was used for respiration. The eggs are covered with leathery scales . D. Improved kidneys. The terrestrial forms and all the squamates produce uric acid through the biochemical pathways.

7. TAXANOMY OF REPTILES SUB-CLASS ANAPSIDA This class has no temporal opening behind the eye and therefore the skull is compact. Orders of this sub-class include: 1. Order Chelonia- Tortoises, turtles and terrapins. In this order: They have a shell of two elements i.e.; the skeletal element, which consists of the vertebral column and the ribs and the horny elements which comprises the scales.

8. ( ii) They have a plastron, which forms the ventral part of the animal. ( iii) The chelonians have no teeth but they have horny-like beak for cropping vegetation. Sub-orders of Chelonia a. Sub-order Pleurodira is different because - the neck folds sideways when withdrawn. - Also, the pelvis is fused with the plastron. eg snaked-necked turtle.

9. b. Sub-order Cryptodira - The neck folds in a vertical plane when withdrawn. - Also the pelvis is not fused but free. SUB-CLASS LEPIDOSAURIA This is either a diapsid or the temporal opening is secondarily lost. They have scales on their body.

10. Order Rhyncocephalia Members in this order are diapsid with a pair of temporal foramen. They are found in New Zealand. E.g. Sphenodont punctata Order Squamata The skin has horny epidermal scales and they have a quadrate bone which is movable.

11. Sub-orders i . Sub-order Lacertilia These are lizards and their mandibles are fused anteriorly. They have movable eye-lids The tongue is usually entire.

12. ii. Sub-order Ophidia (Serpents ) These are the snakes The mandibles are joint anteriorly by a ligament The tongue of ophidians is forked not entire. They have secondarily lost both foramen in the adult; but the juveniles still possess both.

13. The lizards, including agamas, geckos, monitors, stinks are cosmopolitan but not beyond North of Europe. Snakes evolved from burrowing forms of original stock and secondarily radiated to the surface above. They used to be subterranean/ fossorial.

14. FAMILIES OF THE SUB-ORDER OPHIDIA Family Hydrophiidae . They are water snakes They are venomous 2. Family Boridae . These are primitive snakes 3. Family Elapiidae . These are members of green snakes 4. Family Viperiidae . These are rattle snakes.

15. 5. Family Columbriidae . These are cobras. They are venomous . 6. Family Typhlopiidae . They are extinct. They were non-venomous. They were insectivorous. They were fossorial i.e.. They lived underground in holes and burrows 7. Family Leptotyphlopiidae . They are insectivorous. They are non-venomous. They are fossorial. E.g. worm snakes

16. SUB-CLASS ARCHOSAURIA These are diapsids. The only surviving member is the order Crocodilia ( but included dinosaurs and flying reptiles). There are 25 species and are semi-aquatic. They have flattened tail, nose and eyes are raised. The internal nerves of crocodiles are supported by valves . Crocodiles are largest living reptiles. E.g. Crocodilus porosus and it is 25 ft.

17. Some reptiles have invaded the sea and have problem in osmotic balance. They therefore take in water and the problem is to get rid of excess salt in the blood . To solve this problem, the salt is quickly absorbed into the blood. This process is called Extra-renal excretion . (it occurs outside the kidney).

18. E.g . The marine turtle, the Caretta sp uses lachrymal glands for the same purpose of extra-renal excretion . In Iguana spp, the nasal gland in the nose are used for extra-renal excretion. In the sea snakes, the natrial glands are used for extra-renal excretion. Some reptiles have specialized in fish eating and therefore take in less water. E.g. Natrix sp .

19. COMPARISON OF THE EYES OF SNAKES AND LIZARDS LIZARDS SNAKE 1. Presence of fovea 1. Absence of fovea 2. Pigments are present in the retina. 2. Pigments are present in the lens 3. The retina is normal 3. Retina is with double cones 4. The sclera is present 4. Sclera is absent 5. During accommodation, they change the lens by ciliary muscles. 5 . During accommodation, lens is constant in shape but moves forward and backwards by the movement of the iris.