Reptiles Flashcards
What does a lower basal metabolic rate mean?
Conversion of biomass is about 10 times more efficient in ectotherms than endotherms. Reptiles can therefore eat less food than a similar sized endotherm, and do so less frequently. Low metabolic rate allows reptiles to live in low energy environments. This potentially opens them to the arid zones of the Earth. To exploit this, reptiles have evolved to achieve the lowest water flux rate of any vertebrate group. Water loss is further reduced by active uptake of urinary salts, which are then excreted at very high concentrations through specialised salt glands. Salt glands have evolved on at least 5 independent occasions in reptiles.
Example of an ectotherm?
Crocodiles. Use ambush predation, for example, balance sticks on their snouts during the birds’ breeding season. Shows a purposeful method. Sit and wait ambush modes of predation are also common among snakes (Juvenile Cantil pit vipers have a lure on its tail, insects come and investigate).
Advantages of venom?
Venomous snakes avoid risk by dealing a lethal venom quickly before waiting. Venom toxins appear to have evolved by gene duplication of digestive enzymes: some venoms actually begin the digestive process. Venom proteins are extremely complex, with various nasty effects. Waiting for envenomed prey to die necessitates following the prey, sensory systems of snakes are well adapted to this. Forked tongue used to transfer chemicals from outside to paired vomeronasal organs in roof of mouth for chemo-sensation, track by recognising the characteristic scent.
How do the reptiles detect prey?
Specialised sensory systems, especially in nocturnal forms. Infrared sensors have evolved several times in snakes, but are most specialised as the pit organs in pit vipers. Measurements of pit organ sensitivity suggest they are on a par with the best cryogenic infrared detectors currently on the open market. Sensory tentacles are present on the head of one highly specialised species – the tentacle snake. Tentacles operate as mechano-sensors detecting water movement, analogous to a scaled up version of the superficial neuromast systems of the fish they predate. - Snake forms a cryptic J-shape, and prefers to strike when the fish is between its head and body. A feint of the body before the strike causes the fish to C-start straight into the snake’s jaws.
Special adaptations for infrequent meals?
Cranial kinesis is the relative movement of parts of skull, exclusive of lower jaw, in a rattlesnake. It is a primitive character of tetrapods, lost in mammals but taken to an extreme in snakes. Some larger snakes feed so infrequently that they must enlarge their digestive system to accommodate large meals. Mass of small intestine increases 40% in Burmese Pythons in the day or two after feeding.
Oxygen requirements in ectotherms?
Low oxygen demands. Most reptiles can hold breath for long periods (apnea). Useful in dividing and a variety of other activities, construction of the heart allows reptiles to increase systemic blood flow during apnea.
Locomotion in ectotherms?
Maximum rate of oxidative metabolism is up to 10 times higher in mammals, which is much better for sustained activity. But, by increasing glycolytic (anaerobic) metabolism reptiles achieves similar total metabolism, in short bursts with a long recovery time.
Example of locomotion in ectotherms?
Tortoise – basal reptilian gait is a sprawling motion (slow and inefficient) but stable and requiring little energy. Snakes – push off the surrounding area. Larger snakes move in a straight line by lifting and lowering their belly. Snakes can move down narrow burrows by pushing off both walls. Sidewinding also allows fast motion. Can also swim & jump fly.
Relationships of living reptiles?
Mesosaurs were small marine reptiles in the Permian, and there are fossils of pregnant females suggesting viviparity. First amniotes to return to water after transition to land.
Diapsids are characterised by the presence of two pairs of temporal fenestrae, but these can be modified/lost in some groups.
How can temporal fenestrae be used?
Can attach larger muscles to the hole. Larger muscles create a large volume when tensing so the holes accomodate a large change in muscle power. Can curve the muscle around the holes. The holes also spread stresses.
Convergence in reptiles?
- viviparity in all major groups of marine reptiles except turtles perhaps because of the shell arrangement
- viviparity has evolved many times in squamates, most commonly in breeding season
- flight, at least 8 separate lineages of gliders, birds and pterosaurs
- marine lifestyles, 7 separate lineages
- venom delivery systems, snakes several times and some lizards
- limblessness, numerous times in lepidosaurs
- slender, elongate body form, snakes, amphisbaenians, skinks
