Reptiles

Question 1

Integument

Answer 1

stratum corneum = thick, heavily keratinised = retains water
well developed epidermis scales

The skin of reptiles generally lacks glands apart from a few specialised scent glands. This means that the skin of reptiles is dry, unlike that of amphibians which must be kept moist to facilitate cutaneous respiration.

Question 2

explain scales

Answer 2

ecdysis occurs periodically = moults scales
osteoderms = plates of dermal bone
or fused osteoderms = shell

Question 3

Reptile skeleton

Answer 3

atlas and axis
have distinct vertebrae (cervical, thoracic, lumbar, sacral (2), caudal vertebrae)

caudal autotomy - tail breaks at cartilaginous vertical plank of fracture
. Extensive regeneration, including replacement of the vertebral column with a cartilage rod, will occur after autotomy.

pectoral girdle = scapula, coracoid, clavicle and inter clavicle, in some species clavicle is not present
pelvic girdle = ilium, ischium and pubis.

5 digits each side

Question 4

Vertebrae of snakes

Answer 4

very deep ball-and-socket joints + additional pair of articular surfaces = strengthen joint to prevent excessive rotation of the spine.

Question 5

Reptile skull morphology

Answer 5

The key feature is the presence or absence of temporal fenestrae – openings within the temporal region of the skull, caudal to the orbit – which reflect
differences in the jaw musculature, and so feeding behaviours.

three main types of skulls anapsid, diapsid and synapsid

Question 6

Anapsid skull

Answer 6

anapsid skull lacks fenestrae and is seen in ancestral reptiles and modern turtles and tortoises

Question 7

Diapsid skulls

Answer 7

2 fenestrae; dinosaurs were diapsids, and the more ancestral form of the diapsid skull is seen in the tuatara and crocodilians, while modified forms are seen in snakes, lizards and birds.

Question 8

synapsid skull

Answer 8

Mammals present various modifications of the synapsid skull which possesses only one fenestra.

Question 9

reptile locomotion

Answer 9

usually sprawled with large adductor muscles

can stand up and run bipedal for bit called high walk very fast

Question 10

Explain geckos going up a wall

Answer 10

very fine setae hairs on digital pads which branch and terminate in cups or flattens ends called spatulae which adhere via suction

each gecko has around 1,000,000,000 setae and 100 -1000 spatulae

Question 11

snake locomotion

Answer 11

sinusoidal movement= wave contractions head to tail

force requires resistance from projections on the ground, so this form of locomotion is impossible on a smooth surface. Large bodied snakes, such as pythons and adders, can creep along with their body in a straight line using rectilinear movement: in a series of waves, the broad ventral scales are brought forward, planted down and the body moved forward over them. Spectacularly, the paradise snakes (Chrysopelea spp) of Southeast Asia and Sri Lanka launch themselves from trees and glide to nearby trees or the ground by flattening their body and undulating laterally while airborne. Engineering boffins have calculated that a rock dropped from the same height of 10 metres will „glide‟ 2 metres while the paradise snake glides an average of 14 metres – pretty impressive! The vertebrae of snakes have an additional pair of zygopophyses to prevent torsion of the vertebral column.

Question 12

Kinesis

Answer 12

movement, of the skull is common in lizards and snakes, but is absent in turtles and crocodiles

Kinesis allows the animal to change the size and configuration of the jaw very rapidly in order to catch or devour prey. Different species of snakes and lizards display different models of kinesis, but typically there is increased mobility between the supratemporal, pterygoid, quadrate, maxilla and prefrontal bones. Vipers and adders can mobilise their maxillary bones, which support the venom-injecting fangs, from a resting position along the upper lip to the front of the mouth when ready to attack.

Question 13

Snakes are well-known for their ability to swallow prey several times their own diameter. This is made possible by several features:

Answer 13

The symphysis between the two mandibles consists only of flexible soft tissue which allows for considerable separation.

Swallowing of prey is achieved by a “pterygoid walk” where the pterygoids on the left and right sides of the skull are able to move freely and independently of each other so that the teeth on one side grip the prey while those on the other side are disengaged, moved forward, and sunk in again to gradually draw the prey back into the pharynx. Note that at no point do snakes “disarticulate, or unhinge, their jaw” – this is a myth!

Question 14

venom glands

Answer 14

modified salivary glands of the serous (i.e. protein secreting) form rather than those that produce mucous

mpties at the level of the mucous membrane sheath at the base of the maxillary fangs.

In most reptiles, there are waves of tooth replacement which minimises the number of teeth missing at any given time. Thus, removal of fangs is NO protection against snake bite in venomous snakes!

Question 15

what does snake venom consist of?

Answer 15

variety of proteins both toxins and digestive enzymes
The digestive enzymes initiate the breakdown of the prey‟s tissues permitting a more rapid digestion of large prey. This is also the reason why some snake bite wounds present with extensive local tissue trauma. Although it is an over-simplification, snake toxins are usually classified as either neurotoxins or cytotoxins based on the major effect of the key toxin produced.

Question 16

Reptile respiration general

Answer 16

paired lungs
can be simple sacs to interconnected chambers and falveoli.

left lung often reduced

The trachea leads to a single central air chamber which extends to the faveoli. Around each faveolus is a cord of smooth muscle which functions much like a purse string to open and close the opening of the faveolus. The walls of the faveoli are enclosed by capillaries.

lungs in pleura-peritoneal cavity and ventilation by intercostal muscles and ribs

caudal portion of lungs in snake is often without faveoli and is avascular

During the ingestion of large prey, this saccular region of the lung/s acts like a set of bellows: inflated by the pumping action of muscles caudal to the prey, it acts to ventilate the respiratory portion of the lung/s when the snake is unable to use its ribs for ventilation.

When swallowing particularly large prey, snakes can protrude the glottis so that the airways are not obstructed by the prey

Question 17

Crocodile ventilation

Answer 17

the liver acts like a piston to facilitate lung ventilation. During inhalation, the ribs rotate forwards and outwards, expanding the thoracic cavity and allowing the lungs to inflate. In addition, diaphragmatic muscles, which are derived from the internal abdominal musculature, draw the liver posteriorly further increasing the volume of the thoracic cavity and assisting in ventilation.

Question 18

Turtle ventilation

Answer 18

the presence of a hard shell prohibits the pumping action of the ribs during ventilation. Typically, the adduction and abduction of the limbs, and the activity of muscles within the visceral cavity, are used to alter the pressure on the lungs.

Question 19

Reptile circulatory system

Answer 19

no typical reptilian heart, conus arteriosus forms the trunks of the three main arteries leaving the ventricle and there is a reduction of the sinus venous

atrials separated
but ventricles show variation, lizards vary from one ventral to a full septum division

The circulatory system of reptiles has a separate pulmonary circulation as a consequence of the development of lungs.

Question 20

blood morphology of reptiles

Answer 20

Reptilian erythrocytes are oval, nucleated and bi-convex. Leukocytes have a similar morphology to those of mammals but are relatively more numerous.

Question 21

Thermoregulation of reptiles

Answer 21

ectothermic –>body temperature conforms to that of their environment

this impacts their behaviour

Question 22

General reptile reproducion

Answer 22

In many species of reptiles, sexual dimorphisms are minimal making the sexes difficult to distinguish. All reptiles depend on internal fertilisation. The gonads of both males and females are located in the abdominal cavity, near the kidneys.

Question 23

General reptile reproduction

Answer 23

In many species of reptiles, sexual dimorphisms are minimal making the sexes difficult to distinguish. All reptiles depend on internal fertilisation. The gonads of both males and females are located in the abdominal cavity, near the kidneys.

Question 24

female ovaries

Answer 24

egges –> paired oviducts –> cloaca (shell membrane and egg shell to the fertilised egg as it passes along the oviduct add albumen

turtles and crocs use calcium from egg shell is used to calcify they skeletons

yolk = food

Question 25

viviparity

Answer 25

Many species of snakes and lizards retain the fertilised eggs within the oviduct and give birth to live young

Extraordinarily, some female reptiles (mainly lizards) can reproduce by parthenogenesis, whereby the diploid embryo is derived solely from the fusion of two of the female‟s eggs - this produces only females, since there has been no contribution of a Y chromosome from a male.

Question 26

reptile male reproduction

Answer 26

paired internal testes –> epididymis –> ductus deferens –> cloaca

crocs and turtles have a penis (corpus cavernous)

snake and lizards= paired hemipenes are present in base of the tail In many snakes, the head of the hemipene has many spines which help to anchor it within the female cloaca during copulation. In many species sperm can readily survive in the female tract for several months and, in exceptional species, for several years.

Question 27

Nervous system and sense organs reptile

Answer 27

small brains 1.5 metre croc = 5cm long brain.
forebrain
midbrain
hindbrain
12CN are present as in higher vertebrates

Question 28

reptilian ear function

Answer 28

most = tympanic membrane
snakes= stapes is attached via a short ligament to quadrate bone while the other end attaches directly to the oval window of the inner ear

Question 29

eyes reptile

Answer 29

are well-developed in most reptiles which generally have good colour vision. Many turtles and lizards are also able to visualise ultraviolet wavelengths – the significance of this is uncertain. In all reptiles (except snakes), the sclera is cartilaginous and small plates of bone, called scleral ossicles, are often present to help maintain the shape of the sclera. In snakes, near-vision focusing takes place by moving the lens forward by contraction of the iris, increasing pressure on the vitreous humor. In other reptiles, accommodation takes place in a manner similar to that in higher vertebrates, by contraction of the ciliary muscles around the lens.

Question 30

parietal organ

Answer 30

it consists of a single photoreceptor located on the surface of the diencephalon, and underneath a small hole in the parietal bone. It is particularly evident in goannas and Sphenodon. It consists of a cornea, lens, and retina- like tissue that contains photoreceptive cells that form synapses with adjacent ganglion cells to form a nerve that transmits signals to the nervous system. While it is unlikely that the parietal organ can form images it can distinguish light from dark. The parietal organ is an ancestral feature that is also found in lampreys and frogs. It is absent in crocodiles, snakes and geckos.

Question 31

reptile smell

Answer 31

Reptiles generally have a good sense of smell, with olfactory epithelium on a variable number of conchae in the nasal cavity. A second olfactory organ, the vomeronasal organ (Jacobson’s organ), is well-developed in lizards and snakes, but absent in adult crocodiles. In snakes, and lizards with long bifid tongues, scent particles are picked up on the tongue and carried to the vomeronasal organ, located in a pit in the roof of the mouth, where they are sampled by the sensory cells. The vomeronasal organ is present in mammals with the exception of some bats and marine mammals.

Question 32

Boas and pit vipers possess

Answer 32

frared receptors (heat receptors, thermoreceptors) on the margins of the jaw. These are exquisitely sensitive to infrared wavelengths and pit vipers
can detect an increase in temperature of as little as 0.003°C! This change in temperature can be generated by a mouse 30 cm away from the viper!

Question 33

The Australian Reptiles Crocodiles

Answer 33

2 species in Australia.
Crocodiles have a heavy, muscular, well-protected body. The back skin is thick and leathery, supported internally by bony plates (osteoderms). The belly is also protected by “abdominal ribs” (gastralia) not attached to the main skeleton. These are not really true ribs, as they do not form from endochondral ossification like other ribs, but are membrane bones and thus thought to be remnants of an ancestral bony dermal skeleton. Crocodiles are well adapted for amphibious life with a powerful tail for swimming and valves which close the nostrils and the back of the mouth when submerged. Unlike other reptiles the ventricles are completely separated in crocodiles. Blood can bypass the lungs during submersion
Freshwater Crocodile (Crocodylus johnstoni) Narrow snouted, largely fish-eating, in freshwater.
Estuarine Crocodile (C. porosus)
Broad snouted, large (to 7m) sea-going. Feeds on fish, reptiles, birds and mammals.

Question 34

Tortoises and Turtles

Answer 34

22 species in Australia.

Marine turtles (Cheloniidae) have a bony shell and large, heavy paddle-shaped limbs. They come ashore seasonally to lay eggs. Several species occur in Queensland waters including the Green, Loggerhead and Hawksbill.
The Leathery Turtle (Dermochelyidae) has a carapace made up of many small plates embedded in a tough leathery skin.
Freshwater tortoises (Chelidae) have 4- or 5-clawed, webbed feet. All are mainly carnivorous, unlike the herbivorous terrestrial tortoises imported from overseas which are often kept as pets.

Question 35

Geckos

Answer 35

Geckos (Gekkonidae)
60 species in Australia.
Geckos are nocturnal with a thin skin and non-overlapping scales. Their vertical pupils dilate at night providing good vision. The eyes are without moveable eyelids but are covered by a transparent scale which is cleaned with the tongue.
There are two groups:
- Ground dwelling species which have long, slender toes with claws.
~ 41 ~
- Arboreal species which have flattened toes with adhesive pads.
Some may exude a toxic fluid from pores on the body and tail. Voluntary tail loss (autotomy) is common and a new tail is easily regenerated.

Question 36

Snake Lizards (Pygopodidae)

Answer 36

30 species in Australia and PNG.
Forelegs are totally lost, and the hind limbs are reduced to flaps. Distinct ear openings and a short tongue distinguish them from snakes.

Question 37

Dragons (Agamidae)

Answer 37

50 species in Australia.
Dragons have dull rough scales, often with spines or knobs on them. They are active and diurnal with strong limbs and claws. All are oviparous, laying 2-20 eggs. Most feed on insects, but some will take larger animals and some plant material. The expanded collars of the Frilled Lizard and Bearded Dragon are supported by hyoid bones.

Question 38

Goannas/Monitor Lizards (Varanidae)

Answer 38

20 species in Australia.
This group includes goannas and Australia’s largest lizard, the Perentie. They are powerfully built with strong limbs and sharp claws. When running fast, they become bipedal. Their teeth are long, sharp and backwardly curved and they are carnivorous or carrion feeders. They have a long, deeply forked tongue.
This group also includes the world’s largest lizard, the Komodo Dragon of Indonesia.

Question 39

Skinks (Scincidae)

Answer 39

150 species in Australia.
Skinks form a very diverse group - most have smooth shiny scales and are sun-loving. Most skinks are insectivorous but the larger species are omnivorous. Some lay eggs, but the majority are viviparous, often with a well-developed chorio-allantoic placenta (e.g. Blue-tongued Skink). In some species, the eyelid is fused with a transparent scale in the lower eyelid.

Question 40

Blind Snakes (Typhlopidae)

Answer 40

20 species in Australia.
These are small worm-like snakes which have thickened scales on the snout allowing them to push through the soil. They have vestigial eyes, small darkly pigmented spots under the skin which can probably only distinguish different light intensities. The belly scales are small and the tail ends in a spike which provides anchorage. They are harmless and feed mainly on termites and other insects.

Question 41

Pythons (Boidae)

Answer 41

10 species in Australia.
This family includes the largest snakes in the world; the largest in Australia is the Rock Python, growing to over 8m. The belly scales are relatively small. Small claws are present on either side of the cloaca which are vestiges of hind limbs. These are larger in males. All Australian pythons lay eggs and incubate the eggs by coiling around them until they hatch. They are non-venomous and kill their prey by constriction. The Carpet Snake is a common member of this family.

Question 42

Colubrid Snakes (Colubridae)

Answer 42

11 species in Australia (all in Queensland!).
This is the largest family in the world but has few Australian representatives, probably having recently arrived from the north. All but one of the Australian species are characterised by a loreal scale.
They include both solid-fanged (non-venomous) and rear-fanged (venomous) species, but are not considered dangerous to humans. They include the Green and Brown Tree Snakes and the Freshwater Snake.

Question 43

Elapid Snakes (Elapidae)

Answer 43

60+ species in Australia.
These all lack the loreal scale and have hollow fangs at the front of the upper jaw leading to the poison glands. Only a few species are considered dangerous to humans and domestic mammals. The venom consists largely of neurotoxins (death is by asphyxiation following paralysis of the heart and lungs), but other components of the venom may also be important such as the procoagulants found in Brown Snake venom that put victims at risk of major haemorrhage. The Taipan and Brown Snake lay eggs, while many others are live-bearing.

Question 44

Sea Snakes (Hydrophiidae)

Answer 44

32 species in Australia.
These snakes are closely related to the Elapids but show many adaptations to a marine life - paddle-shaped tail and valves in the nostrils. They have very potent venom but comparatively short fangs and so unless you deliberately put your finger in their mouth, you are probably not at risk…