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HERPETOLOGY- Branch of zoology that deals with the study of amphibians and reptile provide significant insight of terrestrial and aquatic ecosystem.
• These were the first class of organisms to adapt to life on land.
• There are about 10000 different species of reptiles on earth. They are cold-blooded animals belonging to the phylum Chordata of Animal kingdom.
• Reptiles were the first animals adapted to life entirely on land.
• Reptiles evolved from amphibians ~ 320 million years ago and displaced amphibians in many environments.
• Reptiles are ectotherms (“cold-blooded”).
Following are the important characteristics of the animals belonging to Class Reptilia:
1. These are creeping and burrowing terrestrial animals with scales on their body.
2. They are cold-blooded animals found in most of the warmer regions of the world.
3. Their skin is dry, and rough, without any glands.
4. The body is divided into head, neck, trunk, and tail.
5. The respiration takes place with the help of the lungs.
6. The skull is monocondylic.
7. Limbs may or may not be present. If they have limbs, they are two pairs of pentadactyl limbs, each bearing claws. Snakes do not have limbs.
8. The heart is 3 chambered. However, crocodiles have a 4-chambered heart.
9. Reptiles do not have external ear openings. Tympanum represents ear
10. Fertilization is internal.
11. They are oviparous and the eggs are very yolky. Development is direct.
12. E.g., Snakes, Turtles, Lizards, Crocodiles.
- Terrestrial turtles also eat a variety of foods, from earthworms, grubs, snails, beetles and caterpillars to grasses, fruit, berries, mushrooms and flowers.
- Both aquatic and land turtles have been known to eat carrion (decaying flesh) when it's available.
• The digestive system of modern reptiles is similar in general plan to that of all higher vertebrates. It includes the mouth and its salivary glands, the esophagus, the stomach, and the intestine and ends in a cloaca.
• Digestive tract is similar to amphibians, however is longer, with a larger J shaped stomach (similar to higher vertebrates such as mammals)
• It includes the mouth and its salivary glands, the esophagus, the stomach, and the intestine and ends in a cloaca.
• One pair of salivary glands evolved to become venom glands in many reptiles.
• As in all vertebrates, the nervous system of reptiles consists of a brain, a spinal nerve cord, nerves running from the brain or spinal cord, and sense organs. When compared with mammals, reptiles have proportionately smaller brains.
• Most reptiles have a three-chambered heart and double loop blood circulation (similar to amphibians)
• However, reptiles have an incomplete septum, or wall dividing the ventricle into two.
• Order Crocodilia (Alligators and crocodiles) have developed four chambered hearts.
• Reptiles are more active than amphibians, so they need more oxygen.
• Reptiles cannot skin breathe; their dry scaly skin is “watertight” to avoid water loss.
• The lungs of reptiles contain a larger surface area
• Oviparous with internal fertilization (lays amniotic eggs)
• Most male reptiles have two sex organs called hemipenes. They are housed internally in males just at the base of the tail, and are everted when needed.
• In many snakes, the hemipenes possesses spines or hooks, in order to anchor the male within the female.
• Unlike many other reptiles, alligators/crocodiles use a penis that is always erect and “pops” out of their bodies to mate
• In some reptiles, nest temperature determines sex of the hatchlings. This is called temperature-dependent sex determination.For example, In turtles, low temperatures during incubation produce males and high temperatures produce females.
Parthenogenesis – reproduction
• Parthenogenesis = reproduction from an ovum without fertilization
• The only vertebrates that show true parthenogenesis are the squamates, with about 50 lizard species and one snake being obligate parthenotes.
• These are unisexual species, all individuals being females that reproduce asexually without the intervention of any male.
• Ex. Tropical Night Lizards
Major Evolutionary Advancement – Amniotic Egg
- Developed from internal fertilization and provides the embryo with atmospheric oxygen, food, and water.
- Egg covered in a mineralized shell – reptiles have leathery eggs
- Removes nitrogenous wastes and protects the embryo from drying out.
- This marks the start of the amniotes (animals with amniotic eggs)
The amniotic egg is different because they have four extra membranes:
- Amnion– thin membrane enclosing the fluid in which the embryo floats/prevents drying out.
- Allantois– stores wastes produced by the embryo.
- Yolk Sac– Surrounds the yolk (nutrients for embryo)
- Chorion– Outermost membrane of the egg – protects embryo and allows gas exchange.
Cotylosauria
Chelonia
No order/ All forms are extinct
Rhynchocephalia
ANAPSIDA
PARAPSIDA
DIAPSIDA
SYNAPSIDA
Lepidosauria
Lacertilia
Squamata
Ophidia
Archosauria
Crocodilia
No order/ All forms are extinct
Anapsids have no openings, synapsids have one opening, and diapsids have two openings.
Sub-class: Anapsida:
This subclass is divided into two orders.
• Cotylosauria
• Chelonia
• These Reptiles are extinct.
• In these Reptiles Jaws and teeth are poorly developed.
• These Reptiles resemble with Labyrinthodont Amphibians.
• They became extinct in the triassic period of Mesozoic era.
• Ex: Seymauria and Lepidosaurus.
Order: Chelonia:
• This order includes Turtles and Tortoises.
• These are Terrestrial or aquatic.
• Body is covered by shell containing dorsal carapace.
• Neck, limbs and tail are covered with scales.
• They show 4 limbs. pentadactyle are, modified into paddles in aquatic forms.
• Jaws without teeth.
• Cloacal opening is longitudinal.
• These are Oviparous.
• Ex: Thonyx (Soft river terrapin), Testudo (Land tortoise). Chelone (Turtle).
• This group includes extinct forms.
• Those forms lived from Triasslac period to cretaceous period.
• Ex: lchthyosaurus, plesiosaurus.
This subclass is divided into two super orders Lëpidosauria and Archosauria
• These are primitive reptiles.
• Teeth are present on the palate jaw margins. They are not present in Sockets.
This super order includes two living orders.
1) Rhynchocephalia 2) Squamata.
Order: Rhinchocephaiia: Ex: Sphenodon (Newzealand)
Order: Squamata:
• This includes Snakes & Lizards.
• Their body is covered by epidermal scales.
• This is divided into two suborders.
Sub Order: Lacertilia:
• These are terrestrial, arboreal or burrowing forms.
• Limbs &re pentadactyl and are usually present.
• Ex: Calotes, Chamaeleon, Draco, Varanus, Gecko.
Sub Order: Ophidia:
• This sub order includes snakes.
• They are terrestrial or aquatic, or arboreal or burrowing forms.
• Temporal vacuities are absent.
• Limbs and limb girdles are absent.
• Tongue is bifid.
• Ex: Python , Lycodon, Naja naja, Hydrophis, Viper.
• This includes advanced reptiles.
• Teeth are on jaw margins and are set in muscular sockets.
• This super order includes a single living order Crocodilia.
Order: Crocodilia:
• These are fresh water and predatory forms.
• Body is covered by an exoskeleton made by horny’ scales & scute.
• Teeth are thecodont.
• Ex: Crocodilus, Alligator, Gavialis
Difference between Crocodile and Alligator
Alligator- have shorter and a more rounder snout.
Crocodile- have a longer and pointier snout.
• This group includes all extinct forms.
• They lived from carboniferous to permen period.
• Their skull shows one pair ot Vacuities.
• Ex: Dimetrodon, Cynognathus.