20Reptile

πŸ“š
CLASS REPTILIA
β–’ General Characters:
❖ Habit: Mostly terrestrial, carnivorous, tetrapod vertebrates
❖ Body Division: Head, neck, trunk and tail
❖ Limbs: Usually two pairs, pentadactyl; digits with horny claws/nails/adhesive pads
❖ Limbs Absent In: Some lizards and all snakes
❖ Exoskeleton: Horny epidermal scales, shields, plates and scutes
❖ Skin: Dry, cornified and devoid of glands
❖ Exception: Femoral glands present in male lizards
❖ Mouth: Terminal
❖ Teeth:

Table 1: Teeth in Reptiles

Animal
Teeth Type
Lizards and snakes
Pleurodont
Crocodiles
Thecodont
Turtles
Teeth absent; replaced by horny beak
❖ Alimentary Canal: Terminates into cloacal aperture
β–’ Skeleton:
❖ Endoskeleton: Bony
❖ Skull: Monocondylic with one occipital condyle
❖ Sacral Vertebrae: Two sacral vertebrae
❖ Vertebrae: All vertebrae procoelous
❖ Interclavicle: T-shaped interclavicle present
❖ Important Point: Reptiles are the first vertebrates with well-developed ribs involved in respiration
β–’ Respiration:
❖ Respiratory Organ: Lungs throughout life
❖ Type: Pulmonary respiration
❖ Ribs: Ribs involved for the first time in respiration
β–’ Circulatory System:
❖ Heart: Usually 3-chambered with incompletely divided ventricle
❖ Exception: Crocodiles, alligators and gavials have 4-chambered heart
❖ Sinus Venosus: Present
❖ Truncus Arteriosus: Absent
❖ Systemic Arches: Two systemic arches present
❖ Hepatic Portal System: Well developed
❖ Renal Portal System: Reduced
❖ Hypophyseal Portal System: First appearance
❖ RBC: Oval and nucleated
β–’ Excretion:
❖ Kidney: Metanephric
❖ Excretory Product: Uric acid
❖ Excretion Type: Uricotelic
β–’ Nervous System and Sense Organs:
❖ Cranial Nerves: 12 pairs
❖ Jacobson Organ: Vomeronasal organ present in roof of buccal cavity
❖ Jacobson Organ Well Developed In: Snakes and lizards
❖ Brain: Cerebral hemispheres and cerebellum poorly developed
❖ Pineal Eye: Well developed in Sphenodon
β–’ Reproduction and Development:
❖ Sex: Sexes separate
❖ Male Copulatory Organ: Usually muscular
❖ Hemipenis: Present in lizards and snakes
❖ Penis: Present in turtles and crocodiles
❖ Females: Mostly oviparous
❖ Fertilization: Internal
❖ Eggs: Cleidoic eggs with leathery shells
❖ Yolk: Macrolecithal and telolecithal
❖ Cleavage: Meroblastic
❖ Extraembryonic Membranes: Present; reptiles are amniotes
❖ Development: Direct; no metamorphosis
❖ Parental Care: Generally absent
❖ Body Temperature: Cold-blooded / poikilothermic
β–’ Classification Based on Temporal Fossa:

Table 1: Reptile Skull Types

Subclass
Temporal Fossa
Examples / Status
Anapsida
Temporal fossa absent
Turtles, tortoises, terrapins
Parapsida
One temporal fossa present
Extinct
Diapsida
Two temporal fossae present
Lizards, snakes, crocodiles, Sphenodon
❖ Anapsida Body: Enclosed in two shell plates: dorsal carapace and ventral plastron
❖ Example: Chelone = green sea turtle / soup turtle
β–’ Orders of Diapsida:

Table 1: Main Orders

Order
Examples
Rhynchocephalia
Sphenodon punctatum
Squamata
Lizards and snakes
Crocodilia
Crocodiles, alligators and gavials
β–’ Order Rhynchocephalia:
❖ Status: All extinct except living species Sphenodon punctatum
❖ Pineal Eye: Interesting feature; also called parietal or third eye
❖ Living Fossil: Sphenodon is called living fossil because it retains many primitive characters
β–’ Order Squamata:
❖ Includes: Lizards and snakes
❖ Saurology: Study of lizards
❖ Serpentology / Ophiology: Study of snakes
❖ Autotomy: Voluntary breaking of tail to confuse enemy
❖ Important Point: Regenerated new tail does not possess vertebrae
β–’ Lizards:
❖ Reproduction: Most lizards are oviparous
❖ Viviparous Lizards: Phrynosoma and Chamaeleon
❖ Draco: Gliding lizard with patagium
❖ Heloderma: Only poisonous lizard; also called beaded lizard
❖ Heloderma Venom: Neurotoxic
❖ Limbless Lizards:
  • β€’
    Ophisaurus
  • β€’
    Anguis
  • β€’
    Rhineura
❖ Calotes: Common garden lizard
❖ Ophiosaurus: Limbless glass snake
❖ Difference From True Snakes: Limbless lizards have movable eyelids and external ear opening, which true snakes lack
❖ Largest Lizard: Ferocious dragon / Komodo dragon
❖ Herbivorous Lizard: Iguana
β–’ Snakes:
❖ General: Most specialized reptiles
❖ Body: Limbless, long and slender
❖ Absent Structures:
  • β€’
    Pectoral girdle
  • β€’
    Sternum
  • β€’
    Tympanum
  • β€’
    Urinary bladder
  • β€’
    Movable eyelids
  • β€’
    Nictitating membrane
  • β€’
    External ear
❖ Vestigial Structures: Python and Boa have vestigial pelvic girdle and hindlimbs
❖ Tongue: Long, slender and bifid; sensitive to odour and vibration
❖ Middle Ear: Absent; sound perceived through skin
❖ Skin Shedding: Ecdysis / moulting
❖ Locomotion: By ribs and large ventral scutes
❖ Types: Poisonous and non-poisonous
❖ Largest Non-poisonous Snake: Python
❖ Largest Species: Python reticulatus
❖ Double-headed Snake: Eryx johnii / Sand boa; tail resembles head
❖ Common Poisonous Snakes:
  • β€’
    Cobra
  • β€’
    Krait
  • β€’
    Viper
  • β€’
    Sea snake
  • β€’
    Coral snake
β–’ Snake Venom:
❖ Venom Glands: Modified superior labial / parotid glands
❖ Fangs: Modified maxillary teeth
❖ Nature: Mixture of enzymes and specific toxins; digestive juice
❖ Fatality: Fatal only when mixed with blood
❖ Types of Venom:
  • β€’
    Neurotoxic
  • β€’
    Haemotoxic
❖ Neurotoxic Venom: Seen in cobras, kraits and sea snakes; causes paralysis of respiratory muscles and asphyxiation
❖ Haemotoxic Venom: Typical of vipers; causes tissue destruction and widespread haemorrhage
❖ Proteolysin: Present in viper venom; affects circulatory system
❖ Best Treatment: Antivenin / antivenom serum
❖ Antivenin Preparation: Prepared by injecting horse with gradually increasing doses of snake venom
β–’ Identification of Snakes:

Table 1: Important Identification Points

Snake
Identification
Krait
Mid-dorsal hexagonal vertebral scales; largest 4th infralabial scale
Cobra
Hood with spectacle mark; third supralabial touches eye and nasal shield
Viper
Triangular pear-shaped head with small cephalic scales
Sea snake
Eel-like body; laterally compressed flat tail; viviparous
Pit viper
Loreal pit between eye and nostril
❖ Loreal Pit: Thermoreceptor
❖ Common Sea Snakes: Hydrophis and Enhydrina
β–’ Order Crocodilia:
❖ Examples: Crocodiles, alligators and gavials
❖ Body: Scaly; body scutes present
❖ Teeth: Numerous, thecodont, lodged in sockets
❖ Heart: Only reptiles with completely 4-chambered heart
❖ Diaphragm: Muscular diaphragm separates lung cavity from rest of body cavity; analogous to mammals
❖ Pineal Gland: Absent in crocodiles
❖ Largest Crocodile: Crocodylus porosus
❖ Respiration: Both crocodiles and alligators have respiratory organs to breathe air
β–’ Dinosaurs:
❖ Meaning: Terrible lizards
❖ Nature: Large and heavy extinct reptiles
❖ Origin: Originated with primitive mammals during Triassic period of Mesozoic era
❖ Extinction: Became extinct during Cretaceous period of Mesozoic era
❖ Mesozoic Era: Golden age of dinosaurs
β–’ Miscellaneous Points:
❖ Snake Skeleton: Snake has both exoskeleton and endoskeleton
❖ Snake Venom: Acidic in nature
❖ Foramen of Panizza: Aperture in heart of lizards and crocodiles where right and left aorta cross each other and remain in contact
❖ Lizard Vertebrae: Gastrocoelous / strongly procoelous
❖ Non-poisonous Snake Clue: Tail cylindrical and ventral scales do not extend entire width of belly
β–’ High-Yield Competitive Points:

Table 1: Must Remember

Question Clue
Answer
Reptile skull
Monocondylic
Sacral vertebrae
Two
Vertebrae
Procoelous
Excretion
Uricotelic
Kidney
Metanephric
Cranial nerves
12 pairs
Heart
3-chambered, except crocodiles
Only reptile with 4-chambered heart
Crocodile
Reptiles are
Amniotes
Fertilization
Internal
Egg
Cleidoic, leathery, macrolecithal, telolecithal
Temporal fossa absent
Anapsida
One temporal fossa
Parapsida
Two temporal fossae
Diapsida
Living fossil reptile
Sphenodon
Only poisonous lizard
Heloderma
Flying / gliding lizard
Draco
Largest lizard
Komodo dragon
Largest non-poisonous snake
Python
Double-headed snake
Eryx johnii
Neurotoxic snakes
Cobra, krait, sea snake
Haemotoxic snake
Viper
Thermoreceptor in pit viper
Loreal pit
Best treatment for snake bite
Antivenin
Golden age of dinosaurs
Mesozoic era
Q1.
Reptiles are mostly
Q2.
The body of reptiles is divided into
Q3.
The exoskeleton of reptiles is made up of
Q4.
Skin of reptiles is generally
Q5.
Teeth of lizards and snakes are usually
Q6.
The teeth of crocodiles are
Q7.
Reptilian skull is
Q8.
Number of sacral vertebrae in reptiles is
Q9.
Vertebrae of reptiles are generally
Q10.
Respiration in reptiles is mainly by
Q11.
The heart of most reptiles is
Q12.
Which reptile group has completely four-chambered heart?
Q13.
The kidney of reptiles is
Q14.
Reptiles are generally
Q15.
The number of cranial nerves in reptiles is
Q16.
Jacobson's organ is best developed in
Q17.
Hemipenis is found in
Q18.
Reptilian eggs are
Q19.
Reptiles are called amniotes because they possess
Q20.
Classification of reptiles is based on
Q21.
Anapsida is characterized by
Q22.
Diapsida is characterized by
Q23.
Sphenodon is regarded as a living fossil because it
Q24.
Study of lizards is called
Q25.
Study of snakes is called
Q26.
Autotomy in lizards means
Q27.
The only poisonous lizard is
Q28.
Draco is known as
Q29.
A limbless lizard can be distinguished from a true snake by presence of
Q30.
Python and Boa retain vestiges of
Q31.
The largest non-poisonous snake is
Q32.
Eryx johnii is commonly called
Q33.
Snake fangs are modified
Q34.
Neurotoxic venom is typical of
Q35.
Haemotoxic venom is typical of
Q36.
Best medicine for snake bite is
Q37.
Loreal pit of pit viper acts as
Q38.
The largest crocodile is
Q39.
Dinosaurs became extinct during
Q40.
Mesozoic era is called