snakes and turtles

Snakes

• snakes have a cryptic low risk lifestyle of large infrequent meals and use of chemical cues
• snake morphology consists of a lack of ears, and eyelids, nostrils used for respiration, vomeronasal organ used for smelling, cloacal scent glands, and staggered long organs
  • because of their morphology they have poor hearing, poor eyesight, and will scent you if disturbed
  • some boas do have a pelvic girdle
• the boidae family is made up of snakes with pelvic girdles that are constrictors, and have pits around the mouth
  • made up of two groups, an old world group called hte pythonidae, and the boniae which are new world
  • boinae are ovoviparous while pythonidae are oviparous
• the viperidae family is made up of vipers adders and pitvipers where all new world vipers are pitvipers and they tend to be hemotoxic
• the elapidae family is made up of venemous, neurotoxic snakes and consists of coral snakes, cobras and seasnakes
  • the seasnakes are the most successful marine reptiles because they are preadapted to swimming due to movement, and long lung. They are laterally compressed, and have nostrils on top of their head.  they have salt glands in the mouth and can easily shed skin
• snake feeding consists of eating large prey infrequently through a series of  steps
  • first they have to find food which they do using the vomeronasal organ and can be achieved either by active foraging or sit and wait
    • sit and wait is special because it can use caudal lures
  • then they have to catch and kill it by either grabbing it or constricting or using venom
    • constricting occurs by squeezing the heart until it stops
  • next they have to swallow it which is helped by their flexible skull, teeth pointing backwards, the jaw's ability to separate, super lubricated saliva, and stretchy skin
    • they cannot breath while feeding so they will use oxygen stored in lung to help until the glottis can stick out underneath prey to aid in breathing
    • the jaw is also connected out to the side of the brain case which allows it to be larger to eat larger prey, this is aided by the quadrate bone
    • the jaw is also connected to the back of the brain case making it easier to eat larger prey
  • finally they have to digest it which is important because the stomach is turned on and off to save energy when not eating since they eat so infrequently
    • the stomach is turned back on by having the blood become super alkaline which pushes all acids to the stomach, and having the heart and organs increase in size to increase metabolic activity
• thermy
  • most snakes are homeothermic where they can become a certain temperature by going out in the sun and then cool themselves off by sitting in the shade
  • a few like the seasnake and underground snakes are osmoconformers which makes sense because it takes more energy to maintain body temperature underground or underwater where it is much colder and will suck out all that
• venom
  • use of venom to stop prey 
  • venom glands exist in the head and make venom using the gene that makes pancreatic enzymes.  this gland is sometimes protected with a black stripe to prevent UV radiation
  • venom is made up of protein
  • dry bites are used to protect fangs, by only injecting a small amount of venom, it also prevents waste of venom and is used when snakes aren't planning on eating the thing they are biting
  • venom is delivered by fangs
    • aglyphous snakes are snakes with no fangs, and instead have lots of teeth, it is common in boidae
    • opistoglyphous snakes are snakes with fangs in the back of their mouth and are used to chew venom into the victim and is common in colubrids
    • proteroglyphous snakes are snakes with erect short fangs where they grab and hold onto prey and is found in elapids
    • solenoglyphous snakes are snakes with movable long front fangs, that are moved by the pterygoid bone, where they bite injecting venom and backing off they are found in viperinae 
• vipers 
  • vipers tend to be terrestrial and heay body so they tend to not climb
  • vipers move via sidewinding
  • vipers are sit and wait predators that hit their prey and track later using vomeronasal organ and go after the largest prey of any snake group
  • viperinae are old world vipers that don't have pits
  • crotalinae are mostly new world vipers that do have pits
  • a pit is a heat sensing tissue around the lips that acts like an eye and allows for nocturnal hunting and promotes confrontational behavior because they can use the pits to assess predators
    • this is proven by the fact that pitvipers are the only confrontational vipers, pitvipers stay with newborns to protect them and fangs aren't bared when confronting predators because the fangs would block the pit
• snake locomotion
  • concertina movement is similar to an accordion or inchworm where the back of the tail anchors itself and the head is sent to grab something and pull forward
  • serpentine movement is similar to eels where 3 irregularities in the ground are used to push forward
  • sidewinding movement is when the snake pushes down to move sideways
  • rectilinear movement is slow linear movement using belly scales to push forward
  • climbing snakes are special because they have prehensile tails, the heart located close to the head, and long stiff necks
• snake defense
  • first they will try to get away, then they will bluff, then they will engage
  • they hide using blotched coloring however that coloring makes it harder to thermoregulate
  • they use anal glands to scent things
  • they will roll into.a ball to protect their head which is the most vulnerable
  • some snakes have a hood that they can spread to look bigger and more intimidating
  • snakes can use both their glottis and scales to hiss
  • some snakes will have toxins they get from prey they eat concentrated in glands 
  • some snakes can use rattles which warn predators, however if there are no predators in the area snakes will lose their rattle over time
  • some snakes can spit through holes in their teeth that contain rifling
  • mimicry is super easy for snakes because of their tube shape
• snake reproduction 
  • snakes will use pheromones to court other snakes, there is a special form called a copulatory plug which is used to seal the cloaca directly after mating which warns males to stay away
  • some snakes will also perform ritualized combat which is low stakes competition to assert dominance over other male snakes
  • some snakes will perform a mating ball which will force convenience polyandry where the female will go ahead and mate with a less desirable snake to stop the mating ball and later will choose her own
  • snakes have hemipenes that are used for copulation which can last anywhere form a few minutes to all day
  • snakes can store sperm
  • obligate parthogenesis is found in triploid snakes that cannot mate with haploid snakes
  • facultative parthogenesis is used in a pinch where female will use her polar body gametes to fertilize the egg
  • snakes do anything from ovipary to vivipary
  • some snakes will show parental care through incubation

Turtles

• turtles don't have teeth, instead they have a keratinized beak around the skull
  • since they don't have teeth they don't have to worry about wear and tear which allows them to live so long
• turtles have a shell made up of a top piece, carpace, a bottom piece, plastron, and pieces of shell, scutes
  • the shell serves as an extended ribcage where everything is contained inside the shell
  • the shell is great because it provides protection from predators which allows them to live for a long time
  • the shell is limited because it delays reproduction, and leads to a lack of diversity
  • odontochelys are the origin of turtles because they had a plastron which could later develop into a turtle shell
    • fossils show the process of the pectoral girdle getting inside the shell, because the girdle gradually shrunk until it could slip under ribs and relengthen
  • high domes indicate a highly terrestrial turtle
  • flat domes indicate an aquatic turtle 
  • shell reduction is found in both aquatic and large turtles
  • hinges are located on the plastron of some turtles which allows the turtle to pull everything inside the shell and close up keeping everything else out
• feeding
  • turtles go after easy prey such as invertebrates and plants because they are so slow and have no venom
• respiration
  • turtles use buccal pumping to breath
  • lungs are contracted by using muscles to push the stomach up and into the lungs, and lungs are relaxed by using muscles to pull the stomach down
  • aquatic turtles can also use skin, pharynx and cloaca that has high capillary density allowing for gas exchange
  • circulation is accomplished through an incomplete ventricular system where deoxygenated blood mixes with oxygenated blood