Reptiles Flashcards
When did the reptiles arise?
Palaeozoic era during the Carboniferous period (310 - 320 MYA)
What is the first-known reptile called?
Hylonomus
Reptiles are classified in ____ orders.
___ orders are extinct.
___ orders remain - ~10000 species
(1) 16
(2) 12
(4)
What are the 4 remaining orders?
- Rhynchocephalia (1 species)
- Chelonia (341 species)
- Crocodilia (25 species)
- Squamata (9,671 species) ; Amphisbaenia (188 species); Sauria (lizard - 5,987 species); Serpentes (snake - 3,496 species)
The importance of skull fenestration. What type of animals have:
One skull opening (lateral temporal opening)?
Two openings (dorsal and lateral temporal openings)?
No opening?
(1) Mammals
(2) Reptiles and Birds
(3) Amphibians & Reptile-like amphibians
What is meant by CLADISTIC CLASSIFICATION?
(based on common ancestry)
- Splits the diapsids into three major lineages:
Lepidosauria (Tuatara, modern snakes & lizards)
Archosauria (extinct dinosaur lineages, crocodilians & birds)
______ have lost their skull fenestration and now have an _______ skull.
(1) Chelonians
(2) anapsid
Name at least 3 differences between reptiles and amphibians.
Briefly describe
- Reptilian skin is dry and scaly, limits water loss; Stratum corneum (dead cells) are permanent in reptiles resulting in moulting; Beta-keratin is more rigid
- Amniotic egg: allows embryo to bypass the aquatic stage of amphibians; AMNION: fluid-filled sac that surrounds and cushions the developing embryo. CHORION: outermost layers, allowing gas exchange. ALLANTOIS: excreted wastes from embryo. YOLK SAC: nutrient-rich food supply for the embryo
- Reptilian jaws are more powerful; the openings in the skull (fenestration) provide additional surface area for MUSCLE ATTACHMENT allowing greater pressure to be exerted. With the exception of TURTLES, which have a horny beak (sometimes serrated), all reptiles possess TEETH and many of them have them on both the palate and the jaw.
- Most reptiles have HOMODONT detinition: PARTIAL HETERODONTY occurs in snakes (i.e. fang) and a few lizards
- Orientation of limbs: In most reptiles, the appendages are ROTATED TOWARDS THE BODY; the long axis of the limbs lie MORE PARALLEL to the body’s main axis; the angle between the upper and lower limbs is reduced; LIMBS ARE STRAIGHTER –> provides BETTER SUPPORT FOR THE WEIGHT OF THE BODY and make GREATER AGILITY and SPEED possible
- Reptiles have INTERNAL FERTILISATION and so, males have a COPULATORY ORGAN
- Reptiles REPRODUCTIVE LIFE HISTORIES; most species are OVIPAROUS
Briefly describe the amniotic egg.
- Calcium-impregnated shell that prevents the evaporation of fluids inside but allows gas exchanges
- Large quantities of yolk –> allows embryo to attain a relatively advanced state of development before it hatches; NO METAMORPHOSIS
Briefly describe the characteristics seen in the three different amniote reproductive strategies.
OVIPAROUS: Shell present; Embryo grows OUTSIDE the shell; Food comes from the EGG; Seen in Birds, Reptiles, Few Mammals
OVOVIVIPAROUS: Shell present; embryo growth INSIDE the shell; Food comes from the EGG; Seen in REPTILES
VIVIPAROUS: No shell; embryo grows INSIDE mother; Food comes from the MOTHER; Seen in MAMMALS, few Reptiles
Briefly describe the viviparous squamous cells
Exhibit placentae formed by the appositions of maternal and embryonic tissues
What is parthenogenesis?
TRUE parthenogenesis is the complete absence of male contributions - NO SEXUAL REPRODUCTION
Only 0.1% of all vertebrate species do this - it is VERY RARE
Show the different sexual chromosomes seen. Distinguish which are male and which are female
XY/XX (Male/Female): seen in most reptiles with sexual chromosomes & mammals
WZ/WW (Male/Female) : Few reptiles & birds
Are all offspring that are created through parthenogenesis female?
NO
Briefly describe temperature dependant sex determination
- Temperature of nest affects rate of embryonic development
- Excessive high/low temperatures can be lethal
- Sex determination by temperature of developing eggs is wide spread in turtles, all crocodilians and many lizards; In turtles HIGH temperatures result in LARGER individuals which are usually FEMALE; In some lizards this is the opposite, High temperature = males
- Viviparous lizard selects sex of embryos; Influence of gestation temperature on the sex ration; Mothers can choose the sex of offspring via basking behaviour.
Briefly describe respiration in reptiles
- Although reptilian respiration primarily depends on lungs, some gas exchange takes place across the inside of the mouth and in the cloaca particularly in various turtles
- Soft-shelled turtles, up to 70% of gas exchange may take place across the leathery skin that covers the shell
- NEGATIVE PRESSURE BREATHING
- Most reptiles breathe by expanding and compressing the body cavity by movements of the ribs produced by contracting the intercostal muscles
- NO DIAPHRAGM
Briefly describe the effects of lateral undulations of walking/running lizards
- As lateral movements to the left, left lung is compressed
- As lateral movements to right, right lung is compressed
- As animal runs, air is pumped between lungs, but little in and out through the trachea
- Lizards that retain this methods of breathing can only run for 1-2 minutes
Briefly describe respiration in snakes
- Single (dominant, left) lung in snakes
- NO DIAPHRAGM, ribs provide movement
- ANTERIOR PART NON-RESPIRATORY –> functions as air sac (gas exchange)
- GLOTTI: help respiration when ingesting large preys
Briefly describe respiration in turtles
- Lungs lie within a protective rigid shell
- Fixed rib cage cannot act to ventilate lungs
- They have specialised sheets of muscle within shell that contract and relax the lungs
- Air pressure in lungs can be changed by moving limbs in and out
In terms of respiration, what is meant by Bidirectional flow?
- Air moves tidally in to and out of terminal gas-exchange structures, which are cul-de-sacs (amphibians, mammals, most reptiles)
In terms of respiration, what is meant by Unidirectional flow?
- Air in only one direction during both inspiration and expiration (birds, some alligators, some reptiles)
Briefly describe the pulmonary circuit
Reptiles: efficient pulmonary circulation to bring blood to and from the lungs
- Developed a septum that partially divides the ventricle into separate left and right chambers (3-CHAMBERED HEART)
- In Crocodilians (and birds) the separation of the ventricles is complete (4-Chambered heart)
- This greatly reduces the mixing of oxygenated and deoxygenated blood
Briefly describe excretion
- The method of NITROGEN EXCRETION depends on the habitat; Aquatic reptiles (i.e. turtles) –> ammonia (possibly urea) as amphibians; Terrestrial reptiles (i.e. lizards, snakes & tortoise) –> uric acid
Urea: helps to conserve water - excreted from the cloaca - Kidneys: no loops of Henle –> unable to produce concentrated urine
- Bladder: present in chelonians (turtles): absent in snakes and some lizards
Briefly describe the nervous system and sensory function in reptiles
- Increased brain size in reptiles, when compared to amphibians –> especially the CEREBRUM and CEREBELLUM
- But brain size still small when compared to birds and mammals
- Reptile bigger brain –> motor skills & hunting strategies (sensory development)
Vision:
Reptiles active in the day: Complex eyes (rods and oil droplets); see colour well
Reptiles active at night: Lizards –> large pupillary and lens aperture; Snakes –> infrared “vision”
Smell:
All reptiles have a VOMERONASAL organ (or Jacobson’s organ) inside the mouth on the palate to detect chemicals via the tongue (found in all vertebrates, but only enhanced in a few)
Some snakes (Vipers, Pythons & Boas) have a pit organ for infrared “vision”
Hearing:
Some reptiles have an external ear structure –> visible tympanic membrane; Airborne vibrations go to the tympanic membrane; Substrate (ground) –> quadrate
Reptiles quadrate forms part of the jaw joint
Briefly describe the Jacobson’s Organ
- Smell rerouted from the nose to the tongue
- Tongue extension: Odour particles are captured from the air by the tongue; Odour particles are delivered by the tongue to the openings of the VOMERONASAL organ
- The degree of the fork indicated the use of the organ
Briefly describe the Pit Organ
- Molecular basis of infrared detection by snakes
- Pit organ –> detection (“smell”) of infrared radiation (>0.001’C)
- Transient receptor potential (TRP) channels (TRAP1) –> thermosensors in the vertebrate nervous system
Briefly describe thermoregulation
Modern reptiles are ECTOTHERMS
- Different adaptations to regulate body temperature:
- Morphology: Skin colouration; crest…
- Behaviour: Basking
- Physiology: Heart rates
Briefly describe Rhynchocepalia
1 Species: TUATARA
- Found on a few islands in New Zealand
- Adult tuatara up to 80cm and 1.3kg
- Only surviving members of their order, which flourished around 200 million years ago
- No external ears, primitive scales, mode of locomotion and heart closer to amphibians
- “third eye” (PARIETAL EYE) –> lens, cornea & retina but degenerated nervous connection to the brain
- Not used for vision (may regulate day-night cycles or absorb UV to obtain Vitamin D)
Briefly describe Chelonia
- Turtles & Tortoises
- 3% of reptiles species
- 341 species
- 14 families
- The monophyly of turtles has never been questioned
- Two part-shell built in the skeleton ; Dorsal part - CARAPACE; Ventral part - PLASTRON
- Skull: no fenestration
- Beak instead of teeth (omnivorous)
- Different habitat: Marine; Freshwater; Terrestrial
Briefly describe Crocodilia
- Crocodiles, alligators, caimans & gharials
- > 1% of reptile species
- 25 species
- 4 families
- Modern crocodiles and birds are the only survivors of the Archosaurian lineage
- Have changed little in almost 200 million years… living fossils
- 4 chambered heart
- Unidirectional respiration found in alligators
- Diapsid skull - powerful jaw, on close, not open
Briefly describe Squamata
- Lizards, snakes, worm lizards
- 9,671 species
- 96%
- 3 sub-orders: Amphisbaenia; Sauria; Serpents
Briefly describe the sub-order Amphisbaenia
- Worm-like lizards
- Exclusively legless (apart from 4 species in one genus that retain forelimbs)
- Tunnelling lizards –> variety of specialised adaptations for digging and moving in burrows
- Head heavily keratinised
- Skin distinctive & rings (annuli) encircle body
- Widely distributed (America, Europe, Africa)
Briefly describe the sub-order Sauria
- Lizards
- Large variation in size and body form
- Infraorder: Iguania (14 families)
- Infraorder: Gekkota (7 families)
- Infraorder: Scincomorpha (7 families)
- Infraorder: Platynota (Varanoidea) (3 families)
- Most lizards are nonvenomous: But best known is Gila monster –> long though of as being the only venomous lizard; recent evidence pointing to new species
Briefly describe the sub-order serpentes
- Snakes
- Can be distinguished from legless lizards by their lack of eyelids and external ears.
- COLUBROIDEA: includes most of the living species of snakes; the family along contain 2/3 of all snakes
- Many Colubrid snakes are VENOMOUS
- Elapids and Viperids possess hollow FANGS at the front of the mouth and have highly toxic venom
What is meant by Aglyphous?
A snake without fangs
What is meant by Opisthoglyphous?
A snake with fangs at the rear of the maxilla
What is meant by Solenoglyphous?
A snake with fangs on a rotating maxilla
What is meant by Proteroglyphous?
A snake with permanently erect fangs at the front of the maxilla
