- Jim Morrison American Poet and Singer, 1943-1971

1. I've always liked reptiles. I used to see the universe as a mammoth snake, and I used to see all the people and objects, landscapes, as little pictures in the facets of their scales. I think peristaltic motion is the basic life movement. Swallowing. - Jim Morrison American Poet and Singer, 1943-1971

2. SNAKES

3. Cool Features • Poison/Toxins • Digestive capabilities • Shedding • Coiling Abilities

4. Anatomy & Movement

5. Anatomy of a Snake

6. Anatomy • Skeleton • Digestion • Senses • Scales/Exterior • (Musculature)

7. Skeleton • Skull • Vertebrae • Ribs

8. Skull • Many loosely connected bones • Many elastic ligaments • Brain completely enclosed by bone • Two sides of jaws can be moved separately • !Not dislocating lower jaw!

9. Lower jaw – 2 bones connected at chin by an elastic tissue Loosely attached to upper jaw Teeth bend back in Fangs like syringe Jaws as multibar linkages “quadrate” bonedouble hinge

10. Vertebrae • Distinct units • Many more than in other vertebrates • 150-430 in # • Strong, flexible joints↑movement (ball)

11. Ribs • A set of 2 attached to each vertebra • Not connected on the under-side • Can be extended out (room for stomach)

12. Senses • Can See movement • “Near-sighted” • Internal Ears • “quadrate” bone focuses cochlea • Forked Tongue/Jacobson’s organ • directionality • Body Heat- “pit organs” • Vibrations (along stomach)

13. Digestion • no chewing • Swallow large prey whole • Move one side of jaw forward, then the other • Curved teeth stick into prey-prevent escape • Alt. draw each side of jaws backpull prey towards throat • ↑saliva • Windpipe pushed forward, over tongue, out mouth • Can digest entire prey except for hair, feathers

14. Complete cover (recall insect exoskeleton) Transparent, fused eyelids 2 layers: (recall human skin) Inner layer: living cells that grow, divide Outer layer: dead cells what is shed Expandable skin Often camouflage Scales/Exterior

15. Molting/Shedding • Younger>old • More active>less • More temperate regions>less • Grow cont. throughout life • remove parasites -Rub nose against rough surfacerip in skin -Crawl out; left inside-out in one piece

16. Movement • Lateral Undulation (most common) • Straight-line/rectilinear locomotion • Concertina movement • “Sidewinding”

17. Undulation Edges of curvature push against substratum

18. Rectilinear Used to climb up trees (!)

19. Concertina movement: • Move front part of body forward, coil it-press against surface to anchor • Pull back end forward, coil it • Back end pressed down-provides leverage for repeat • Esp. narrow channels

20. Sidewinding: • Head and tail as supports • Lift trunk of body off ground and move sideways • Move head and tail back into position • Esp. in sand

21. Evolution of Snakes, Their Movement and Biomechanical Behaviors

22. Evolution of Snakes • Diapsids ("two arches“): a group of tetrapod animals -developed 2 holes in each side of skulls- 300 million years ago •  extremely diverse • include all snakes as well as other animals. • some lost either one hole (lizards), or both holes (snakes) • There are 2 distinct clades: • Lepidosauria (includes snakes) • Archosauria • These branched off early from diapsid trunk. • These 2 groups characterized by contrasting patterns in locomotion & posture. • Clade = group of organisms consisting of single common ancestor and all descendants of that ancestor • Representative species of the 3 groups of the Lepidosauria : sphenodontids, lizards, & snakes

24. Order SquamataSuborder Serpentes (Ophidia) The phylogeny of snakes is poorly known since snake skeletons are typically small & fragile This makes fossilization difficult and unlikely General consensus based on morphology: snakes descended from lizard-like ancestors There is no general consensus on the phylogeny of snakes, but here are some examples:

27. Lepidosaurs • Lepidosaurs retained: • sprawling posture • laterally directed movement of limbs found in primitive tetrapods • Lateral undulation of vertebral column was also important method of locomotion for most lepidosaurs • “lateral undulation” reached highest degree of development insnakes • Loosely separated skull bones (allowed prey to be swallowed whole) = another important lepidosaur feature

28. Relation to Lizards • Lizards and snakes are considered to be asingle clade: Squamata (scaled reptiles). • Snakes and lizards share many distinct features in the structure of their skull; • Both lizards and snakes have legless forms with jaw structure that allows them to swallow prey whole • Snakes originated much later in the fossil record than lizards • Based on these similarities  theory: • ancient group of monitor-like lizards began to follow burrowing way of life (tunneling through loose dirt and sand in search of prey) just as some lizards do today.

29. Where do snakes come from? • Over period of MILLIONS of years… • these burrowing lizards lost their limbs & their external ears (helps them burrow more easily) • replaced their eyelids with a clear brille or spectacle to protect their eyes while digging • About the time dinosaurs reached their apex: • one group of these burrowing lizards gave up subterranean lifestyle & emerged to the surface • AND developed a new legless mode of locomotion • AND rapidly diversified to invade a large number of ecological niches • Today we classify the various descendants of these legless lizards as…

30. Snake Ancestors • 4 fossils bear closely on the ancestry of snakes: • Pachyrhachis • Podophis • Lapparentophis • Dinilysia. • The marine squamates Pachyrhachis and Podophis: considered most primitive snakes (because have a well-developed hind-limb skeleton) • Terrestrial snake Lapparentophis (called "oldest snake“) is represented by vertebrae only, but clearly snake vertebrae • Dinilysia: has skull that is “mosaic” of lizard & primitive snake characters, but vertebrae are like those of boa-like snake.

31. Pythons & Boas • 1st of modern terrestrial snakes to appear were relatives of the living boids, or boas and pythons • large heavy-bodied snakes with a rather primitive and heavy skull structure

32. Colubrids • About 36 million years ago: a group of smaller, faster snakes appeared which competed with boids for food & living space • colubrids, or "typical snakes” • enlarged belly scales, enlarged head scales, reduced left lung, no traces of pelvis or hind limbs • Includes flying snakes and some water snakes

33. Opisthoglyphs • About 15 million years ago, snakes began appearing which had a number of greatly enlarged teeth at the rear of their jaw (referred to as opisthoglyphs or "rear-fanged" snakes) • Sandsnake is example

34. Proteoglyphs • Shortly after, another group of snakes developed more refined venom apparatus. (proteroglyphs) • Proteroglyphs have short fixed fangs which have migrated (by reducing the size of the maxillary bone) to front of mouth • Cobra is example

35. Solenoglyphs • By about 10 million years ago, most highly specialized of snakes appeared in fossil record • Vipers-characterized by extremely long fangs

36. Rattlesnake • A few million years ago: a group of pit vipers developed structure at end of tail, made up of interlocking pieces of unshed skin, which could be loudly rattled and used as warning device against predators. • Rattlesnakes: thought to be most specialized of all the living snakes.

37. WARNING: “the whole picture of early snake evolution has been muddled by jargon-filled, convoluted arguments, the problem, as always, being the basic similarity of snakes and lizards.” - J. Alan Holman

38. Swimming Snakes

39. Swimming Snakes • Largest group of sea snakes (hydrophiids) evolved from Australian terrestrial elapids that returned to the marine environment around 30 million years ago. • approximately 70 species of sea snakes live in our modern oceans (account for 86% of marine reptile species alive today) • Sea snakes have specialized flattened tails for swimming and have valves over their nostrils which are closed underwater • Differ from eels --don't have gill slits & have scales • Need to breathe air, so usually found in shallow water where they swim about the bottom feeding on fish, fish eggs and eels. • Persistent myths about sea snakes: they can't bite very effectively. • However: their short fangs (2.5-4.5mm) are adequate to penetrate the skin • They can open their small mouths wide enough to bite a table top.

40. How do they do it? • Snakes elongated bodies = pre-adapted for efficient swimming • most sea snake species developed paddle shaped tail that further enhances ability to move in water • Sea snakes can spend: 30 minutes - 2 hours diving between breaths. • They have 2 major adaptations that allows them to do this: • 1: they have 1 elongated cylindrical lung that extends for almost the entire length of body ( very efficient for gas exchange) • They are able to carry out cutaneous respiration (oxygen diffuses from sea water across snake’s skin into tiny blood vessels & carbon dioxide diffuses out) • 2: Sea snakes have nostril valves that prevent air entering lung while underwater. • Nostril valves open inwards & are held shut from behind by erectile tissue engorged with blood (like a penis)

41. “Explaining what it takes for a snake to glide sounds a bit like an episode of Sesame Street: today's program is brought to you by the letters J, S, and C.” - Socha

42. Flying Snakes • found only in South and Southeast Asia, • Roughly circular in cross-section • aren't actually able to fly BUT can glide or parachute (like flying squirrel) • Socha worked with paradise tree snake,Chrysopelea paradisi(what we will examine) • When flying snake prepares to jump: dangles like letter Jfrom branch • Then flings itself upward & away from branch  fall at steep angle that could be described as “plummet” • After falling less than 10 FEET, it flattens entire body (but not tail) & undulates through air in anS shapeby moving head from side to side, as if on land (but more lateral movement) • Snake uses its ribs to change body shape- flattens from head to vent. • S-shaped undulation keeps body parallel to the ground and allows for stability as snake falls • While gliding, these snakes make turns up to 90 degrees and always seemed to land without injury • flares its ribs so far outward that its belly becomes concave • With its body molded into a highly flattened C, the area of the snake's ventral silhouette-silhouette when seen from below-NEARLY DOUBLES

43. Why do they do it? • One of most important factors in snake's midair shift from free fall to glide: •  dramatic increase in width of animal's body. • flattening of snake  animal into an airfoil: increase in body width effectively halves ratio of snake's body weight to area of its underside, • a measure known as wing loading/a crucial indicator of aerobatic talent • Experts in aerodynamics suggest: snake's tight S-bends make its entire body act like a highly slotted wing (like in airplane) • because of the way air flows through gaps, such wings develop more lift at low speeds. • gaps between the bends of the S-shaped snake in flight could produce more lift than snake would have if it shot, arrow-like, through the air. • Any extra lift is crucial for maneuvering while gliding.

44. "Snakes are part body and part tail, and they have ribs up until the tail. They flatten their ribs and make themselves Frisbee-like in form. This gets them aerodynamically fit for gliding. ” - Socha, LiveScience

45. ADVANTAGES • Moving through air from tree to tree bypasses a host of earth-bound predators • Flying snake threatened by an arboreal animal can just launch itself out of tree • Saves energy and time

46. PREDATION

47. Via Constriction (not suffocation)

48. Former Hypothesis: Constriction leads to death by suffocation and collapse of the lungs of the snake’s prey (minutes) • New Hypothesis: Constriction arrests the circulation of prey and thus leads to death faster than would suffocation alone (seconds)

49. Brad Moon Experiments • Small boa constrictors can squeeze with pressures up to 4 PSI (pounds per square inch). This is strong enough to squeeze blood vessels closed in mice and kill them by circulatory arrest…imagine what kind of pressures a 30 foot anaconda might exert!!

50. PRESSURE • Pressure responses to simulated limb and body movements (a) and ventilatory movements (b) during constriction of a dead mouse by Pituophis melanoleucus (pine snake). Coil was loosened at point (c); at peak (d), the snake pulled the mouse out of the coil to start swallowing it. T I M E