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Turtles

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Turtles Modern Anapsids General Characters Evolved at least 200 MYA. All are anapsids. None have teeth - they have a keratinous sheath which grows continuously, just ... – PowerPoint PPT presentation

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Title: Turtles


1
Turtles
  • Modern Anapsids

2
General Characters
  • Evolved at least 200 MYA.
  • All are anapsids.
  • None have teeth - they have a keratinous sheath
    which grows continuously, just as in birds.
  • Carapace is dermal armor which includes neural
    elements. It is an integral part of the
    vertebral column, and is fused w/ the 8 pairs of
    ribs.

3
Turtles General Characters.
  • Plastron isalso dermal armor, and contains some
    elements of the pectoral girdle and sternum.
  • Plastron and Carapace serve an obvious
    anti-predator function.
  • Pectoral girdle is within the rib cage - an
    amazing evolutionary trick.
  • Pelvic girdle is within the shell.

4
Turtles General Characters.
  • 2 head retraction methods side necks and
    S-necks.
  • All are oviparous, with relatively
    undifferentiated embryos in the eggs when they
    are layed.
  • All lay eggs in nests, and all bury their eggs.

5
Pleurodira
  • All are southern hemisphere in distribution, and
    all are aquatic.
  • 2 Families Chelidae and Pelomedusidae.

6
Pleurodira Chelidae
  • 10 genera and 35 species.
  • Occur in Australia and S. America.
  • All are carnivorous.
  • Matamata may stalk prey, uses a sudden thrust of
    neck and rapid opening of mouth to create
    negative presure and capture prey.
  • They are highly aquatic good swimmers.
  • Generally, lack mesoplastral elements.
  • Have cervical scute on carapace.
  • Reduction/loss of neural bone.
  • Nasals vomers usually present.
  • Premax dentaries unfused.

7
Pleurodira Chelidae
  • Australian Subgroups
  • Pseudemydura lt15cm CL
  • Snake necks - Chelodina neck length often
    exceeds length of carapace.
  • Shortnecks - Elseya, Emydura, Rheodytes
  • South American Subgroups.
  • Chelus
  • Hydromedusa - extremely long necks.
  • Phrynops, Acanthochelys, Platemys.

8
Pleurodira Pelomedusidae
  • 5 genera, 25 species.
  • Occur in S. America, Africa, and Madagascar.
  • All species are aquatic, but some are poor
    swimmers - walking on the bottom instead.
  • Tend to be herbivorous.

9
Pleurodira Pelomedusidae
  • Have a pair of mesoplastral elements.
  • Lack a cervical scute on the carapace.
  • Have a full series of neural bones.
  • Nasals usually present, vomers absent.
  • Dentaries and premaxilaries fused.

10
Cryptodira
  • More diverse than Pleurodira. Marine, brackish,
    freshwater, and terrestrial (desert to wet
    forests).
  • Very little overlap with Pleurodira. Where
    overlap occurs, Pleurodira and Cryptodira usually
    occupy different habitats. For example, only
    softshell aquatic Trionychids occur in freshwater
    habitats in S.A. with Pleurodires. South
    American and African tortoises are terrestrial.

11
Cryptodira Cheloniidae
  • Hard shelled sea turtles.
  • Epidermal scutes on carapace are large.
  • Bony elements of plastron are all present, but
    reduced.
  • Body shape is compressed fusiform.
  • Appendages are flipper-like, and used to fly
    through the water, just as penguins do.

12
Cryptodira Cheloniidae Chelonis mydas -green sea
turtle.
13
Cryptodira Cheloniidae
  • Head and neck are not retractable.
  • Long lived, sometimes they require 40 to 50 years
    to reach sexual maturity.
  • Produce clutches evey 2 to 4 years, but lay
    multiple clutches in each laying season.
  • Sex ratios of clutches are temperature dependent.

14
Cryptodira Cheloniidae
  • Carettinae
  • Caretta Loggerhead turtles. Most temperate
    form. Eats moluscs and crabs.
  • Cheloniinae
  • Chelonia Green sea turtles herbivorous - all
    other genera are carnivorous.
  • Eretmochelys eats sponges and other sedentary
    invertebrates.
  • Natator

15
Cryptodira Dermochelyidae
  • Largest living trutles (Leatherbacks -
    Dermochelys coriacea) 1.5 - 2.5m CL, 500-1000kg.
  • Nest in tropics, but often feed in high latitude
    seas, following blooms in jelly fish.
  • Jelly fish constitute virtually al their diet.
  • They are functional endotherms, aided by inertial
    homeothermy, contercurrent heat exchange in the
    limbs, and insulating abilities of oil dense skin.

16
Cryptodira Dermochelyidae
  • Compressed fusiform body.
  • Large flippers and hydrodynamic shape enable
    speeds of 30km/hr.
  • Carapace structure is unique
  • Dermal armor is replaced by articulating
    osteoderms.
  • Osteoderms are above, but not fused to the ribs.
  • Keratinous scutes are absent, except in
    hatchlings.
  • Carapace surface is covered with smooth, tough
    skin.
  • Bony plastron is present but reduced.
  • Reproduction is similr to that in the Cheloniidae.

17
Cryptodira Chelydridae
  • 3 genera, distributed in N.A. and Asia.
  • All have large heads, very long tails, and
    flattened, tri-ridged carapaces. Carapace is
    nearly rectangular in outline.
  • They are freshwater turtles, feeding on fish,
    crustaceans, molluscs, and worms.
  • Some are strictly aquatic, some forage on shore,
    and some move over ground from pond to pond.

18
Cryptodira Chelydridae Cheydra serpentinas
-snapping turtle.
19
Cryptodira Carettochelyidae
  • 1 species only Carettochelys insculpta (pig
    nosed turtle of New Guinea and N. Australia.
  • Aquatic w/ flipper-like forelimb. Swims via
    aquatic flight.
  • Carapace is high-domed, complete, and ovoid,
    covered by a rugose skin.
  • Pig-like snout. Omnivorous.

20
Cryptodira Dermatemydidae
  • 1 species only Dermatemys mawii (65cm CL), of
    the Yucatan peninsula.
  • Highly Aquatic and herbivorous. Has extreme
    difficulty moving on land.
  • Shell as in Carettochelys, except covered by
    scutes.

21
Cryptodira Kinosternidae
  • New World. 4 genera in 2 old lineages.
  • Kinosterninae Kinosternon and Sternotherus.
  • Staurotypinae Claudius and Staurotypus.
  • Highly aquatic, but poor swimers. Some forage on
    shore.
  • Generally small w/ high domed, oblong shells.
  • Plastrons are hinged and capable of completely
    enclosing the animals.
  • Some forms ccupy temporary desert ponds.

22
Cryptodira Kinosternidae Sternotherus oderatus
23
Cryptodira Trionychidae
  • 14 genera of soft shell turtles.
  • Distributed in Africa, Asia, N. America, and New
    Guinea.
  • Shaped like Pancakes. Plastrons and carapaces
    are reduced. Peripheral bones are lacking.
  • No epidermal scutes, but thick leathery skin.
  • Long pointed snouts and long necks.
  • Webbed feet, good swimmers. Predominantly
    carnivorous.

24
Cryptodira Trionychidae
  • Cyclanorbinae
  • Africa and India.
  • Femoral flaps on the plastron.
  • 3 genera and 4 species.
  • Trionychines
  • Cosmopolitan.
  • Lack femoral flaps.
  • 11 genera and 17 species.

25
Cryptodira Trionychidae Apalone spiniferus
26
Cryptodira Emydidae
  • Includes terrestrial, semiaquatic, freshwater,
    and estuarine forms. With the exception of Emys
    in Europe and southwest Aisa, this group is New
    World.
  • Omnivorous. Diet may depend on size, e.g. large
    females may eat moluscs while smaller males eat
    insects.

27
Cryptoddira Emydidae Chrysemys picta - painted
turtle
28
Cryptoddira Emydidae Emydoidea blandingi
Blandings turtle
29
Cryptoddira Emydidae Graptemys geographica Map
turtle
30
Cryptoddira Emydidae Terrapene carolina 3-toed
box turtle
31
Cryptodira Testudinidae
  • 35 genera and 100 species
  • World wide except Australia
  • Testudinids and Emydids are remarkably similar in
    external morphology, a consequence of their broad
    overlap in ecology.
  • 2 subfamilies.

32
Cryptodira Testudinidae
  • Testudininae -tortoises
  • strictly terrestrial, columnar elephantine
    hindlimbs, high domed carapaces, large plastrons,
    primarily arid.
  • Shell shape and size prevents predation.
  • Batagurinae
  • primarily semiaquatic and aquatic, but some
    terrestrial forms.

33
Cryptodira Differences between Testudinids and
Emydids
  • Emydids
  • angular bone of lower jaw touches meckels
    cartilage.
  • Narrow basioccipital
  • Testudinidae
  • the opposite.

34
Cryptodira Testudinidae Gopherus polyphemus
35
Turtle History
  • Controversy exists over who the ancestors to
    turtles are, and over the exact derived
    characters of turtles.
  • Hypothesis for the evolution of the chelonians
    (Watson. 1914. Proc. Zool. Soc. 111011) Note
    the following hypothesis is not widely accepted,
    but is supported by recent work in Science by Lee.

36
Turtle History
37
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38
Turtle History
  • Pareiasaurs have long lateral extending ribs.
    Fossils which are found with undisturbed ribs,
    are always lying belly down, indicating that this
    is the position of a body at rest just as in
    modern turtles.
  • This suggests that the bodies of Pareiasuars are
    broader and flatter than originally thought.

39
Turtle History
  • The pectoral girdle of pareisaurs is narrower
    than the rib cage because the clavicles and
    coracoids do not form broad ventral plates.
    Also, it tends to be anterior to a wide flat
    carapace.
  • Most basal amniotes, including nyctiphruretians
    and procolophonoids have 5 cervical vertebrae and
    20 dorsal vertebrae.

40
Turtle History
  • Sclerosaurus and Pareiasaurs have 5 cervical
    vertebrae and 14 or 15 dorsal vertebrae.
  • All turtles have 8 cervicals and 10 dorsals.

41
Turtle History
  • Thus
  • 5 or 6 dorsals were lost in the lineage leading
    to sclerosaurus, pareiasaurs, and turtles.
  • In the transition to turtles, there was an
    increase in the number of cervicals and a
    reduction in the number of dorsals.
  • This suggests that the pectoral girdle shifted
    posteriorly about 3 vertebrae in turtles, and
    that cervicals 6 to 8 in turtles are modified
    dorsals.

42
Turtle History
  • Support
  • the major line of neck flexion in pleurodires and
    cryptodiran turtles is between cervical 5 and 6
    (perhaps the old cervical/dorsal boundary).
  • Cervicals 6, 7, and 8 usually work as a single
    rigid unit.
  • In pareiasaurs, the transverse processes on the 5
    cervical centra are ventral, on the first 3
    dorsals they gradually assume a more dorsal
    position.
  • In the earliest turtle, proganochelys, this
    change occurs at cervicals 6, 7, and 8.

43
Turtle History
  • The dorsal tip of the scapula liesadjacent to
    cervial 7 in proganochelys, but behind cervical 8
    in later turtles. This change might represent
    the final stage in the posterior migration of the
    scapulocoracoid.
  • A similar pattern is seen with the pelvic girdle
    in pleurodires.

44
Turtle Respiration
  • Ossification around thoracic cavity prevents
    typical ventilation mechanisms.
  • Lungs are suspended right under dome of carapace.
  • Ventrally, lungs are attached to a connective
    tissue sheet which is itself attached to the
    viscera.

45
Turtle Respiration
  • Weight of the viscera pulls down on the
    connective tissue sheet, and thus causes negative
    pressure in the lungs, and therefore inhalation.
  • Other muscles contract and increase the volume of
    the visceral cavity, and thus cause negative
    pressure in the lungs, and thus inhalation also.

46
Turtle Respiration
  • Contraction of musclesthat will force the viscera
    upwards will increase pressure in the lungs, and
    cause an exhalation.
  • Viscera are forced upwards by contraction of the
    Transverse abdominus muscle. This muscle inserts
    on the posterior limiting membrane. When the
    pectoralis contracts, the shoulder girdle is
    drawn back into the shell, and the volume of the
    viscera is reduced further.

47
Turtle Respiration
  • The abdominal oblique also inserts on the
    posterior limiting membrane, but when it
    contracts, it creates negative pressure in the
    lungs. Contraction of the serratus moves the
    pectoral girdle forward, and further reduces
    pressure in the lungs.
  • The cloaca and pharynx can also be used for gas
    exchange in aquatic turtles. In fact, the
    australian turtle, Rheodytes leukops can
    ventilate the cloaca 15 to 60 times a minuts, and
    can take up a significant amount of oxygen in
    this way.

48
Connection between respiration and circulation.
  • Turtles have the ability to contract muscles
    around the pulmonary circulation, thus increasing
    the pressure within this circulatory system.
    This raises the pressure within the pulmonary
    circuit to a level equal to that within the
    systemic circuit.

49
Connection between respiration and circulation
  • When this happens, blood flows out of the Cavum
    Pulmonale and Cavum Venosum at the same time, and
    some deoxygenated blood bypasses the lungs and
    flows into the systemic circuit. This is called
    Right-to-left Intracardiac shunt. This is not
    unique to turtles, it also occurs in squamates.
    But why would turtles do this?

50
Connection between respiration and circulation
  • The answer is Thermoregulation. By increasing
    systemic blood flow as they are warming, they
    increase the transport of heat from the limbs and
    body surface into the core of the body, thereby
    warming more rapidly.
  • Also, since aquatic turtles often exhibit apnea,
    they can limit blood flow to the pulmonary
    circuit and permit more effective use of the
    pulmonary store of oxygen.

51
Turtle Life Histories and Temperature
  • Many turtles have temperature dependent sex
    determination. This means, that at some nest
    temperatures, you get exclusively males, and at
    other temperatures you get females. This is also
    a phenoenon in crocodilians, sphenodon, and some
    lizards.

52
Turtle Life Histories and Temperature
  • The pattern seems to be that the higher
    temperatures favor the larger sex, since in
    crocodilians, the temperature pattern is the
    reverse of that found in turtles. Female turtles
    are larger than males (generally), and warm nests
    produce predominantly females.

53
Turtle Life Histories and Temperature
  • Now, from a life history point of view, why would
    this be?
  • Consider life history theory - allocation of
    resources.
  • How much should you invest in reproduction?
  • When should you reproduce?
  • How often should you reproduce?
  • If environmental fluctuations influence juvenile
    survival, what should your reproductive effort
    be?
  • Is it better to produce sons or daughters?

54
Navigation and Migration
  • Feeding and nesting habitats fur turtles,
    especially sea turtles are usually dramatically
    different. For example, green sea turtles feed
    onturtle grass which grows in shallow water in
    the tropics, the juveniles are carnivorous.

55
Navigation and Migration
  • Sea turtles often migrate over 1000s of km.
    There are 4 major populations of green sea
    turtles. There are several populations which
    feed and nest within the Antilles and the
    Carribean. One population in particular nests on
    Ascension island in the southern Atlantic, and
    feeds on the coast of northern South America.
    How can you manage to migrate consistently
    without any real visual cues?

56
Navigation and Migration
  • There are some visual cues newly emerged sea
    turtles tend to go toward light. This usually
    works, since on a beach at night, the ocean
    appears to be lighter than inland. Of course,
    with modern cities, this is no longer the case,
    and this has played havoc with turtles.

57
Navigation and Migration
  • Green sea turtles also probably detect low
    frequency sound waves, polarized light, the sun
    and stars, and the earths magnetic field.

58
Navigation and Migration
  • Hatching loggerhead turtles use light, wave
    detection, and magnetism. After they hatch on
    the atlantic coast of Florida, they enter the
    Gulf Stream which flows northward off the Florida
    Coast. They drift along the coast of the US, and
    then E. across the Atlantic. Off the coast of
    Portugal, the Gulf Stream splits into 2 branches.
    One goes N. to the figid N. Atlantic, but the
    other goes S. and eventually leads back to the
    coast of tropical America in 5 - 7 years.

59
Navigation and Migration
  • Loggerheads use magnetic orientation to tell when
    to turn right off the coast of Portugal.
  • At the poles, the magnetic field of the earth is
    90 degrees to the surface.
  • At the equator, it is parallel to the surface, or
    at 0 degrees.
  • So, by measuring the angle of the field to the
    surface, the turtles can tell where they are
    relative to the poles or the equator.

60
Navigation and Migration
  • In lab experiments, you can expose loggerheads to
    a magnetic field with a 57 degree angle of
    intersection with the earths surface. When you
    do this, the turtles swim E. If you rotate the
    field 180 degrees, they swim W. Florida nesting
    grounds are at 57 degrees.
  • If you increase the angle to 60 degrees, the
    turtles swim S. This corresponds to the
    lattitude at which the Gulf Stream splits.
  • Clearly, olfaction also plays a role, since
    turtles can home in on specific beaches again and
    again.
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