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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 as in birds.

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Turtles

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Turtles l.jpg

Turtles

Modern Anapsids


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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.


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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.


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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.


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Pleurodira

  • All are southern hemisphere in distribution, and all are aquatic.

  • 2 Families: Chelidae and Pelomedusidae.


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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.

Pleurodira: Chelidae


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Australian Subgroups

Pseudemydura: <15cm 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.

Pleurodira: Chelidae


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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.


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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.


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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.


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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.


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Cryptodira: Cheloniidae Chelonismydas -green sea turtle.


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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.


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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

Cryptodira: Cheloniidae


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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.


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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.


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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.


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Cryptodira: Chelydridae Cheydra serpentinas -snapping turtle.


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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.


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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.


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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.


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Cryptodira: Kinosternidae Sternotherus oderatus


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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.


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Cyclanorbinae

Africa and India.

Femoral flaps on the plastron.

3 genera and 4 species.

Trionychines:

Cosmopolitan.

Lack femoral flaps.

11 genera and 17 species.

Cryptodira: Trionychidae


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Cryptodira: Trionychidae Apalone spiniferus


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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.


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Cryptoddira: Emydidae Chrysemys picta - painted turtle


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Cryptoddira: Emydidae Emydoidea blandingi Blandings turtle


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Cryptoddira: Emydidae Graptemys geographica Map turtle


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Cryptoddira: Emydidae Terrapene carolina 3-toed box turtle


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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.


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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.

Cryptodira: Testudinidae


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Emydids:

angular bone of lower jaw touches meckel’s cartilage.

Narrow basioccipital

Testudinidae:

the opposite.

Cryptodira: Differences between Testudinids and Emydids


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Cryptodira: Testudinidae Gopherus polyphemus


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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. 11:1011) Note: the following hypothesis is not widely accepted, but is supported by recent work in Science by Lee.


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Turtle History


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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.

Turtle History


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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.

Turtle History


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Sclerosaurus and Pareiasaurs have 5 cervical vertebrae and 14 or 15 dorsal vertebrae.

All turtles have 8 cervicals and 10 dorsals.

Turtle History


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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.

Turtle History


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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.

Turtle History


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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.

Turtle History


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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.


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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.


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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.


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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.


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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.


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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?


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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.


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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.


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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.


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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?


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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.


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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?


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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.


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Navigation and Migration

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


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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.


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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.


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Navigation and Migration

  • In lab experiments, you can expose loggerheads to a magnetic field with a 57 degree angle of intersection with the earth’s 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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