Chapter 7

• Among all phyla of terrestrial species (annelids, molluscs, arthropods, vertebrates, etc...), the more simple forms, the less evolved and the most ancient creatures are deeply aquatic animals
• First, life took place and has been diversified in water, and then many lineages have acquired the emerged land
• The terrestrial forms are the products of the evolution. They are never the initial form and are always derived from aquatic ancestrals
• Relicts of the Palaeozoic group of the primary age

  • Cyclostomes
  • Fishes
  • Amphibians
• The reptiles, despite some species that are readapted to live in water (crocodiles, turtles) are provided with the needed tool to meet all the requirements for an aerial mode of life
• The reptiles are more evolved than the fundamentally aquatic animals but are more recent
• Both of them are originated from the primary but the reptiles characterize the secondary age, during which they colonized the emerged land and were diversified into multiple lineages
• The present reptiles are very few if compared to the reptilian forms of the secondary
• Reptiles


  Vertebrates, amniotic tetrapods (lateral legs raise badly their bodies off the ground but more than the amphibian limbs), poikilothermals, and members of the super-class Sauropsida

  
• Modern reptiles inhabit every continent except for Antarctica, although their main distribution comprises the tropics and subtropics
• Most modern species of reptiles do not generate enough energy to maintain a constant body temperature and are thus referred to as "cold-blooded" or ectothermic
• Reptiles rely on gathering and losing heat from the environment to regulate their internal temperature, e.g. by moving between sun and shade
• Lack of adequate heating imposes costs relative to temperature regulation through behavior, but it also provided a large benefit by allowing reptiles to survive on much less food than warm-blooded animals, who urn much of their food for warmth
• Four surviving groups of reptiles today

  • Crocodilia (crocodiles and alligators)
  • Sphenodontia (tuataras from New Zealand)
  • Squamata (lizards and snakes)
  • Testudines (turtles and tortoises)

  
• Reptiles


  • Impermeable glandless dry epidermis with horny scales
  • Limbs five-toed, clawed
  • Breathing by lungs
  • Heart four chambered, ventricular separation usually incomplete
  • One pair of aortic arches
  • 12 pairs of cranial nerves
  • Excretion metanephric
  • Fertilization internal
  • Eggs with extraembryonic membranes and shells
  • Development direct
  • Oviparous, ovoviviparous or viviparous

  
• The heart is four chambered, completely so in crocodiles, nearly so in the other groups
• Lizards


  Reptiles of the order Squamata, which they share with the snakes (Ophidians)
• Lizards are usually four-legged, with external ear openings and movable eyelids
• Lacerta laevis is a common wall lizard in Lebanon found at altitudes from sea level up to 1500 meters or more along the levantine coast and in the Beqaa valley

  
• Skin of lizards


  • Dry and protected from desiccation by horny epidermal scales
  • Shedding of the skin is done by steps (strip off) of desquamation (case of lacertilians) or at once (molt case of serpents)
  • Dermis of some species contains pigment cells (chromatophores) giving the ability to change color according to the background foliage of their arboreal environment
• Head of lizards


  • Terminal mouth
  • Two small nostrils
  • Two eyes each guarded by three eyelids, an upper, a lower, and a nictitating membrane
  • Posterior to each eye there is a shallow pit, the tympanic pit, at the bottom of which lies the tympanic membrane
  • Tongue is generally forked
  • Teeth are fused to the mandibular bones

  
• Trunk of lizards


  • Two pairs of pentadactyle limbs, each with 5 digits which terminate in sharp horny claws
  • Limbs are attached on the side of the body and they can hardly lift the body off the ground; reptiles crawl
  • Snakes are legless (also without sternum)

  
• Tail of lizards


  • Thicker at its base than at its end
  • Can snap off by voluntary muscular action of the animal
  • Lizards are particularly noted for this capacity of autotomy or self-amputation, when a tail becomes trapped
  • No blood is lost here because the muscular contraction strangles the blood vessels
  • Presence of a cracked vertebra at the base of the tail
  • Autotomy occurs only once in the life of the lizard
  • New (but usually smaller) tail then regenerate readily
• Digestive system of lizards

  • Consists of a mouth, short pharynx, long esophagus (because of the presence of a neck region), elongated stomach, duodenum, ileum and rectum
  • At the junction ileum-rectum appears, for the first time in the series of the vertebrates, a rectal caecum
  • Mouth is guarded by two jaws, each carrying one row of small but strong teeth

  
• Respiratory system of lizards

  • Strictly air breathers, with a breathing system constructed like that mammals and birds; tracheal and bronchial tubes pipe air to the lungs
  • Lungs are alveolar but not of parenchyma type as it is the case of homeothermals
  • In Chameleon, the lungs extend two outer air-sacs
• Circulatory system of lizards

  • Heart is four-chambered: two auricles completely separated from each other (except for snakes), and one ventricle divided by a septum, completely so in crocodiles, nearly so in the other groups
  • It keeps arterial blood separated from venous blood, essentially as in mammals and birds
  • Three arches leave the heart: a right systemic (aortic) arch, and a left systemic (aortic arch, which curve backwards as in the toad and unite to form a median dorsal aorta, and a pulmonary arch
• Excretory system of lizards

  • The adult excretory system is metanephric as in mammals and birds, and is capable of producing highly hypertonic water-conserving urine
  • Secondarily, aquatic turtles and alligators excrete urea like mammals; but all terrestrial reptile including lizards excrete a semisolid urine containing uric acid, as in birds
• Skeleton of reptiles


  • Provides a framework for the head, trunk, and tail
  • Most reptiles have hip and shoulder bones called girdles that support the legs
  • The majority of snakes do not have girdles
  • Reptiles are distinguished taxonomically mainly by the number and location of lateral windows in the skull bones behind the eyes
  • A primitive anapsid skull, without lateral windows, still occurs in turtles
  • All other living reptiles have diapsid skulls, with two pairs of lateral windows

  
• Reptile excretory system


  • Metanephric as in mammals and birds
  • Capable of producing highly hypertonic water-conserving urine
  • Aquatic turtles and alligators excrete urea like mammals
  • All terrestrial reptiles including lizards excrete a semisolid urine containing uric acid, as in birds
• Reptile skeleton


  • Provides a framework for the head, trunk, and tail
  • Most reptiles have hip and shoulder bones called girdles that support the legs
  • Majority of snakes do not have girdles
  • Reptiles are distinguished taxonomically mainly by the number and location of lateral windows in the skull bones behind the eyes
  • Primitive anapsid skull, without lateral windows, still occurs in turtles
  • All other living reptiles have diapsid skulls, with two pairs of lateral windows
  • Extinct mammal-like reptiles have a synapsid skull with one pair of temporal pits

  
• Theropsidian lineage


  Encompasses the Cotylosaurians as well as the Synapsidians, leading to mammals
• Sauropsidian lineage


  Has a finest columella which is independent from the palato-quadrate, found in most reptiles (present and fossils) and in a little bit modified form in Birds
• Birds and Mammals are both descending each from different reptilian phylum
• Reptile scales


  • Dry, scaly skin
  • Helps them hold in moisture and lets them live in dry places
  • Not separate, detachable structures like fish scales
  • Connected in a "sheet", which is the outermost layer of skin
  • Shed and replaced periodically
• Reptile teeth


  • All turtles lack teeth
  • Snakes, lizards, crocodilians, and tuataras all have teeth
  • Teeth vary in form, attachment, and whether they are shed
  • Herbivorous species have broadly flattened teeth with crushing surfaces
  • Carnivorous reptiles have tapered, sharp-pointed teeth
  • Teeth in the front of the mouth often have recurved tips to facilitate prey puncture and reduce escape
  • Some snakes have fangs that deliver venom
  • Teeth may be attached in sockets (thecodont), on the alveolar surface of the jaw (acrodont), or on the inner side of the jaws (pleurodont)
  • Few reptiles as crocodiles have thecodont teeth that are replaced within the same socket
  • Snakes typically have acrodont teeth
  • Most lizards have pleurodont teeth, but there are many exceptions
  • Tuataras also have acrodont tooth attachments
  • Tuatara, crocodilians, and venomous snakes have heterodont dentition with more than one tooth type per arcade

  
• Reptile glands


  • Oral glands (loosely termed salivary glands) include the premaxillary, palatine, nasal, lacrimal, Duvernoy's, Harderian, posterior, sublingual, lingual, infralabial, and mandibular glands
  • Not all oral glands are found in all reptile species
  • Glands produce mucus, lubricate the mouth and eyes, and in venomous snakes, produce venom
  • Oral glands are found in all terrestrial reptiles but are typically lost or very reduced in aquatic species, except for sea snakes and crocodilians
• Reptile locomotion


  • Quadrupedal reptiles keep their stomachs close to the ground with splayed out legs, making it difficult to raise the body off the ground
  • Crocodilians raise their bodies off the ground and make short, fast rushes
  • Quadrupedal mammals have their limbs directly underneath the body, which is more efficient
  • Snakes use several modes of locomotion: serpentine, sidewinding, concertina, and rectilinear
  • Snakes travel best on surfaces with obstructions and roughness, which gives their bellies something to grip
• Snake locomotion types


  • Serpentine
  • Sidewinding
  • Concertina
  • Rectilinear