Reptiles Flashcards
Name and describe the 4 orders in the reptilia class.
Chelonia – tortoises and turtles
Crocodilian – caimans, crocodiles and alligators
Sphenodonta – tuataras. The most orimitive of the living reptiles. There are only 2 species left alive these days
Squamata – amphisbaenians (worm lizards), lizards and snakes
Distinguish boids and colubrids.
Colubrids are very diverse and 2 thirds of all snake species are in this family. Mostly non-venomous but there are exceptions. Venom of the boomslang, for example, is fatal to humans.
Boids are the constrictor snakes ad include boas and anacondas. Pythons also referred to as boids.
List the features of the snake skull.
Cranial kinesis
Quadrate bone
No mandibular symphysis
Heavily ossified braincase
No external ear/tympanic membrane
What is the advantage to snake skulls having cranial kinesis?
Flexible and mobile bones to allow movement
What is the advantage of snake skulls having quadrate bone?
Allows wide gape, almost 180 degrees. Located very caudally in the skull and articulates with both the mandible and the brain case itself.
What is the advantage of snake skulls having no mandibular symphysis?
Instead the 2 halves of the mandibles are joined by a very flexible elastic ligament, which allows width wise separation of the lower jaw.
What is the advantage of snake skulls having heavily ossified braincases?
Very rigid and protects the brain from damage while the snake is swallowing live prey.
How do snakes hear with no external ear/tympanic membrane?
Hear vibrations via quadrate and columella, equivalent to the stapes in mammals. As the snake moves along the ground, the quadrate bone is more or less in direct contact with the ground and can pick up vibrations and transmit them via the columella to the middle ear.
Describe the skeleton of the snake.
- 400 pre-cloacal vertebra
- All but first 2 cervical have ribs
- No sternum or costal cartilages and ends of the ribs attach via muscle to the inner surface of the ventral scales
- No pelvic girdle or forelimbs but some vestigial part of pelvic girdle may be present in boids in the form of external spurs.
Describe vision and hearing in the snake.
Vision is poor and do not have eyelids.
Hearing – no external ear, but pick up vibrations via quadrate and columella
Describe olfaction in the snake.
Highly developed:
- Vomeronasal organ (of Jacobson)
- Domed cavities lined with sensory epithelium – olfactory nerve
- Tongue acts as sensory organ, protrudes through lingual fossa to collect and bring odours to vomeronasal organ.
- Very sensitive system that blind snakes can use to detect prey.
Describe infrared detection in snakes.
In a pit viper, there is an additional structure between the eye and nostril called the pit organ. It contains specialised infrared receptors that are very sensitive and allow these snakes to detect warm-blooded prey. Boas and pythons have a less sensitive system where they have a series of slits in the same region.
Compare the lizard skull to the snake skull.
Mandibular symphysis present, so has a much narrow gape than the snake.
Describe vision in the lizard.
Large orbit and sclera present. Sclera supported by a ring of small bones called the scleral ossicles. Vision more developed than in snakes.
Describe hearing in the lizard.
No external ear but there is a shallow depression in which the tympanic membrane is present in some lizards. In general, hearing in lizards tends to be better than snakes and chelonia.
Describe olfaction in the lizard.
Vomeronasal organ present in some lizards.
Describe the parietal/3rd eye of lizards.
Present in most lizards and tuatara. Located in dorsal midline of the head between the regular eyes. Sensitive to change in light and dark, and can actually contain a lens and a retina, but does not form images. Associated with pineal gland and is involved in circadian rhythms.
Describe the tortoise skeleton.
- Mandibular symphysis present
- 8 cervical vertebrae and flexible to allow the head to be retracted into the shell
- 10 trunk vertebrae that are fused to the upper part of the shall/carapace
- Pectoral and pelvic gridles and inside ribs are fused to the carapace and are very slender.
- No sternum
- Tripartite shoulder arrangement: scapula fused to the carapace by a ligamentous attachment, an acromion process that projects medially and almost touches its counterpart on the other side, and a coracoid process that projects more caudally.
Describe vision, olfaction and hearing in the tortoise.
Vision – highly developed, more than lizards and snakes. Scleral ossicles present to support the sclera.
Olfaction – modified vomeronasal organ but is not quite as sensitive as snakes or lizards.
Hearing – poor. No external ear
What are the external features of snakes?
- Long tubular body, short tail
- Generally smooth and featureless so as to not impede movement on the ground
- No moveable eyelids
- No external ear
- No limbs, however some boids have vestigial pelvis/spurs
- Arboreal species can have prehensile tail to help grasp tree branches.
Describe snake integument.
- Epidermis thickens and folds to produce scales – allows great expansion when consuming prey
- Transparent spectacle/brille covers eye that protects the cornea
- Single wide scales ventrally gastropeges protect and give support to the ventral surface of the snake and are also important in locomotion.
- Paired subcaudal scales, caudal to vent
What is ecdysis?
Skin shedding. The process allows growth. Snakes will shed their complete skin and the folds in the epidermis allow this.
Describe the process of ecdysis.
- Loosen the skin around its mouth by rubbing the snout against any available surface.
- Lymph builds up between the new and old layers of the epidermis.
- Markings become obscure, and as the spectacle is continuous with the epidermis, the spectacle is shed as well. 4. The spectacle becomes opaque and the snake cannot see very well and can become irritable.
- Shed skin is colourless, as the pigment containing cells/chromatophores are found in the dermis.
- Snake will then crawl out of the shed skin and so the shed skin is inside out.
What is unique about ecdysis in rattle snakes?
The last scales are not shed in this process but are retained to form the rattle. This means at each successive moult, there will be an increase in length of the rattle.