Amniote origins and classification The possession of a shelled egg unites the mammals, birds and reptiles into a monophyletic group the amniotes. The

Amniote origins and classificationAmniote origins and classification

The possession of a shelled egg unites the The possession of a shelled egg unites the mammals, birds and reptiles into a mammals, birds and reptiles into a monophyletic group the amniotes. monophyletic group the amniotes.

The shelled egg freed the amniotes from The shelled egg freed the amniotes from the need to reproduce in water that the need to reproduce in water that hampered the amphibians ability to spread hampered the amphibians ability to spread into harsh environments.into harsh environments.

The Amniotic eggThe Amniotic egg

The amniotic egg is hard shelled and is called an The amniotic egg is hard shelled and is called an amniotic egg because the embryo develops within a sac amniotic egg because the embryo develops within a sac called the called the amnionamnion..

The embryo feeds on yolk from a The embryo feeds on yolk from a yolk sacyolk sac and deposits and deposits its waste into another sac called the its waste into another sac called the allantoisallantois. .

The allantois and another membrane the The allantois and another membrane the chorionchorion together lie against the shell, and being richly supplied together lie against the shell, and being richly supplied with blood vessels, exchange gases with the outside with blood vessels, exchange gases with the outside through the pores in the shell.through the pores in the shell.

Figure 26.04


Unlike amphibians amniotes lack a larval stage Unlike amphibians amniotes lack a larval stage and after hatching develop directly into the adult and after hatching develop directly into the adult form.form.

The evolutionary origins of the amniotic egg are The evolutionary origins of the amniotic egg are unclear because early amniote fossils are scarce unclear because early amniote fossils are scarce and eggs especially so. The oldest known eggs and eggs especially so. The oldest known eggs are from the Early Permian and were probably are from the Early Permian and were probably laid by a Pelycosaur (early primitive synapsids laid by a Pelycosaur (early primitive synapsids e.g., e.g., Dimetrodon. Dimetrodon. This lineage ultimately gave This lineage ultimately gave rise to the mammals).rise to the mammals).


It has been suggested that the earliest amniotes It has been suggested that the earliest amniotes were probably amphibious of semi-aquatic as were probably amphibious of semi-aquatic as were their immediate amphibian ancestors.were their immediate amphibian ancestors.

They probably inhabited quite humid They probably inhabited quite humid environments and eggs may have been laid out environments and eggs may have been laid out of water initially perhaps to reduce their risk of of water initially perhaps to reduce their risk of predation. Gradually eggs may evolved to have predation. Gradually eggs may evolved to have become less vulnerable to dessication.become less vulnerable to dessication.


There is considerable disagreement There is considerable disagreement between cladistic and traditional between cladistic and traditional classification of the amniotes.classification of the amniotes.

Traditional classification recognizes three Traditional classification recognizes three classes:classes: Reptilia: reptilesReptilia: reptiles Aves: birdsAves: birds Mammalia: mammalsMammalia: mammals


Because the class Reptilia does not include all Because the class Reptilia does not include all the descendents of their most recent common the descendents of their most recent common ancestor (i.e., the birds) the reptiles are a ancestor (i.e., the birds) the reptiles are a paraphyletic group. paraphyletic group.

Birds and crocodilians share a most recent Birds and crocodilians share a most recent common ancestor and thus form a monophyletic common ancestor and thus form a monophyletic group (the Archosauria), which includes the group (the Archosauria), which includes the extinct dinosaurs, but neither is more closely extinct dinosaurs, but neither is more closely related than the other to the members of the related than the other to the members of the ReptiliaReptilia

18.2

Figure 26.02


Traditional classification considers birds Traditional classification considers birds because of their endothermy and feathers because of their endothermy and feathers to be members of a different to be members of a different gradegrade to the to the crocodilians and reptiles and so places crocodilians and reptiles and so places them in their own class the Aves.them in their own class the Aves.

Cladistic classification in contrast groups Cladistic classification in contrast groups the amniotes on the basis of common the amniotes on the basis of common ancestry.ancestry.


One of the major characteristics used to One of the major characteristics used to classify the amniotes is the structure of the classify the amniotes is the structure of the skull.skull.

The stem group of amniotes diverged into The stem group of amniotes diverged into three lineages in the Carboniferous period three lineages in the Carboniferous period (approximately 350 mya). These were the (approximately 350 mya). These were the synapsids, anapsids and the diapsids.synapsids, anapsids and the diapsids.

Anapsids, synapsids and diapsidsAnapsids, synapsids and diapsids

These three groups are distinguished from These three groups are distinguished from each other by the number of openings in each other by the number of openings in the temporal region of the skull.the temporal region of the skull.

AnapsidsAnapsids (which include the turtles and (which include the turtles and their ancestors) have a solid skull with no their ancestors) have a solid skull with no openings.openings.

Anapsids, synapsids and diapsidsAnapsids, synapsids and diapsids

SynapsidsSynapsids (which include the mammals (which include the mammals and their ancestors) have one pair of and their ancestors) have one pair of openings in the skull associated with the openings in the skull associated with the attachment of jaw muscles.attachment of jaw muscles.

DiapsidsDiapsids (lizards, snakes, crocodilians, (lizards, snakes, crocodilians, birds, and ancestors) have two pairs of birds, and ancestors) have two pairs of openings in the skull roof.openings in the skull roof.

AnapsidsAnapsids

The anapsids are characterized by having The anapsids are characterized by having no temporal opening behind the eye no temporal opening behind the eye sockets. sockets.

They are represented today by the turtles They are represented today by the turtles a group that has changed little since it a group that has changed little since it evolved about 200 mya.evolved about 200 mya.

20.1

Figure 28.01

18.2

Figure 26.02

SynapsidsSynapsids

The synapsids diverged from the The synapsids diverged from the Sauropsida (anapsids and diapsids) and Sauropsida (anapsids and diapsids) and radiated into a diverse group of herbivores radiated into a diverse group of herbivores and carnivores collectively named the and carnivores collectively named the ““Pelycosaurs” Pelycosaurs” (although that’s a (although that’s a paraphyletic group).paraphyletic group).

SynapsidsSynapsids

Pelycosaurs looked lizard-like and include Pelycosaurs looked lizard-like and include DimetrodonDimetrodon (a predatory “dinosaur” you (a predatory “dinosaur” you may be familiar with), which possessed a may be familiar with), which possessed a large sail on its back a characteristic of large sail on its back a characteristic of many pelycosaurs, which probably played many pelycosaurs, which probably played a role in thermoregulation.a role in thermoregulation.

Edaphasaurus (left)an herbivorous pelycosaur

Dimetrodon (below and below left) acarnivorous pelycosaur.About 11 feet long; 280-260 mya)

SynapsidsSynapsids

The pelycosaurs were the dominant group The pelycosaurs were the dominant group of the Permian period, but disappeared in of the Permian period, but disappeared in the Great Permian extinction (approx 245 the Great Permian extinction (approx 245 mya).mya).

During the Permian a synapsid lineage the During the Permian a synapsid lineage the therapsids diverged from the Pelycosaurs. therapsids diverged from the Pelycosaurs. This lineage is the one that gave rise to This lineage is the one that gave rise to the mammals during the Triassic period the mammals during the Triassic period

Fig 18.1

Figure 26.01

Therapsid to mammal transitionTherapsid to mammal transition

A series of evolutionary changes occurred in the A series of evolutionary changes occurred in the therapsids that were passed on to their surviving therapsids that were passed on to their surviving descendants the mammals.descendants the mammals.

These included:These included: an an efficient upright stanceefficient upright stance with the limbs positioned with the limbs positioned

under the body rather than sprawled to the side.under the body rather than sprawled to the side. HomeothermyHomeothermy: there is fossil evidence that the : there is fossil evidence that the

therapsids evolved homeothermy. Cross sections of therapsids evolved homeothermy. Cross sections of bones show Haversian canals, which are bones show Haversian canals, which are characteristic of fast-growing, warm blooded animals.characteristic of fast-growing, warm blooded animals.


Additional evolutionary changes in the Additional evolutionary changes in the therapsids include:therapsids include: DiaphragmDiaphragm: there is indirect fossil evidence in the rib : there is indirect fossil evidence in the rib

shape of therapsids that suggests they possessed a shape of therapsids that suggests they possessed a diaphragm another unique mammalian characteristic.diaphragm another unique mammalian characteristic.

Heterodont teeth: Heterodont teeth: Differentiation of teeth into Differentiation of teeth into multiple specialized types.multiple specialized types.

Secondary bony palateSecondary bony palate: separating nasal from oral : separating nasal from oral cavities.cavities.

Turbinate bones in nasal cavityTurbinate bones in nasal cavity: increase retention : increase retention of body heat.of body heat.


Additional evolutionary changes in the Additional evolutionary changes in the therapsids include:therapsids include: Three inner ear bones and a single jaw Three inner ear bones and a single jaw

bonebone. An excellent series of fossils over about . An excellent series of fossils over about 40 million years documents the transition from 40 million years documents the transition from the multi-boned jaw of pelycosaurs to the single the multi-boned jaw of pelycosaurs to the single dentary of mammals. dentary of mammals.

During this transition therapsids evolved a During this transition therapsids evolved a double jointed jawdouble jointed jaw and eventually two bones and eventually two bones from the original pelycosaur joint were from the original pelycosaur joint were incorporated into the inner ear.incorporated into the inner ear.

First mammalsFirst mammals

The earliest mammals first appear in the mid-The earliest mammals first appear in the mid-Triassic (about 210 mya) and most were small Triassic (about 210 mya) and most were small mouse-sized animals.mouse-sized animals.

For about 150 million years they lived in a world For about 150 million years they lived in a world dominated by the dinosaurs and underwent dominated by the dinosaurs and underwent large scale diversification only late in the reign large scale diversification only late in the reign and rapid evolution of large body size only after and rapid evolution of large body size only after the disappearance of the dinosaurs in the Great the disappearance of the dinosaurs in the Great Cretaceous extinction 65 mya.Cretaceous extinction 65 mya.

Morganucudonhttp://www3.interscience.wiley.com:8100/legacy/college/levin/0470000201/chap_tutorial/ch12/images/le12_60.jpg

DiapsidsDiapsids

The third lineage derived from the stem The third lineage derived from the stem amniotes was the diapsids.amniotes was the diapsids.

The diapsids split into two major lineages The diapsids split into two major lineages the the LepidosauriaLepidosauria (which includes the (which includes the Tuatara, modern snakes and lizards) and Tuatara, modern snakes and lizards) and the the ArchosauriaArchosauria (which includes the (which includes the extinct dinosaur lineages, crocodilians and extinct dinosaur lineages, crocodilians and birds).birds).

18.2

Figure 26.02

18.1

Figure 26.01

Differences between reptiles and Differences between reptiles and amphibiansamphibians

Reptilian skin is dry and scaly, which limits Reptilian skin is dry and scaly, which limits water loss.water loss.

The reptiles’ amniotic egg frees reptiles The reptiles’ amniotic egg frees reptiles from the need to lay eggs in water. Thus from the need to lay eggs in water. Thus they can occupy much drier habitats.they can occupy much drier habitats.

Differences between reptiles and Differences between reptiles and amphibians: Reptilian jawsamphibians: Reptilian jaws

Reptilian jaws are more powerful and can Reptilian jaws are more powerful and can apply a crushing grip.apply a crushing grip.

The openings in the skull provide The openings in the skull provide additional surface area for muscle additional surface area for muscle attachment allowing greater pressure to be attachment allowing greater pressure to be exerted.exerted.

In snakes, skull and jaw flexibility allows In snakes, skull and jaw flexibility allows very large prey to be swallowed.very large prey to be swallowed.

Differences between reptiles and Differences between reptiles and amphibians: Dentitionamphibians: Dentition

With the exception of turtles which have a With the exception of turtles which have a horny beak (sometime serrated) all reptiles horny beak (sometime serrated) all reptiles possess teeth and many have them on possess teeth and many have them on both the palate and the jaws.both the palate and the jaws.

Python teethhttp://whiteafrican.com/wp-content/snake2.jpg

Most reptiles have homodont dentition, but Most reptiles have homodont dentition, but partial heterodonty occurs in snakes and a partial heterodonty occurs in snakes and a number of lizards.number of lizards.

Monitor lizards have incisors, canine-like Monitor lizards have incisors, canine-like teeth and molars.teeth and molars.

Komodo Dragon http://www.tropicalisland.de/komodo/images/BMU%20Komodo%20Island%20Komodo%20dragon%20gargantuan%20monitor%20lizard%20%209%203008x2000.jpg

Differences between reptiles and Differences between reptiles and amphibians: Orientation of limbsamphibians: Orientation of limbs

In amphibians, such as salamanders, the In amphibians, such as salamanders, the orientation of the limbs is outward from the orientation of the limbs is outward from the main axis of the body. As a result main axis of the body. As a result salamanders sprawl.salamanders sprawl.

In most reptiles, in contrast, the In most reptiles, in contrast, the appendages are rotated towards the body appendages are rotated towards the body and the long axis of the limbs lies more and the long axis of the limbs lies more parallel to the body’s main axis.parallel to the body’s main axis.

Differences between reptiles and Differences between reptiles and amphibians: Orientation of limbsamphibians: Orientation of limbs

In addition, the angle between the upper and In addition, the angle between the upper and lower limbs is reduced so the limbs are overall lower limbs is reduced so the limbs are overall straighter. In the forelimb the elbow is oriented straighter. In the forelimb the elbow is oriented towards the tail.towards the tail.

In combination, these modifications provide In combination, these modifications provide better support for the weight of the body and better support for the weight of the body and raise it higher off the ground. Together these raise it higher off the ground. Together these changes make greater agility and speed changes make greater agility and speed possible.possible.

Differences between reptiles and Differences between reptiles and amphibiansamphibians

Reptiles have internal fertilization and so Reptiles have internal fertilization and so males have a copulatory organ either a males have a copulatory organ either a penis or hemipenes.penis or hemipenes.

Reptiles also have a more efficient Reptiles also have a more efficient nervous system and a more efficient nervous system and a more efficient circulatory system.circulatory system.

Differences between reptiles and Differences between reptiles and amphibians: circulationamphibians: circulation

Reptiles are the first truly terrestrial vertebrates and the Reptiles are the first truly terrestrial vertebrates and the cardiovascular system reflects the loss of gills and the cardiovascular system reflects the loss of gills and the need for efficient pulmonary circulation to bring blood to need for efficient pulmonary circulation to bring blood to and from the lungs.and from the lungs.

In contrast to the situation in amphibians, the ventricle in In contrast to the situation in amphibians, the ventricle in reptiles has developed a septum that partially divides the reptiles has developed a septum that partially divides the ventricle into separate left and right chambers. In ventricle into separate left and right chambers. In crocodilians (and birds) the separation of the ventricles is crocodilians (and birds) the separation of the ventricles is complete.complete.

This greatly reduces the mixing of oxygenated and This greatly reduces the mixing of oxygenated and deoxygenated blood.deoxygenated blood.

FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillariesLung and skin capillariesGill capillaries

Right Left Right Left Right Left Systemic

circuitSystemic

circuit

Pulmocutaneouscircuit

Pulmonarycircuit

Pulmonarycircuit

SystemiccirculationVein

Atrium (A)

Heart:ventricle (V)

Artery Gillcirculation

A

V VV VV

A A A AALeft Systemicaorta

Right systemicaorta

Vertebrate circulatory systemsVertebrate circulatory systems

Differences between reptiles and Differences between reptiles and amphibians: respirationamphibians: respiration

Reptiles depend almost entirely on lungs to Reptiles depend almost entirely on lungs to oxygenate their blood and reptilian lungs are oxygenate their blood and reptilian lungs are more developed than those of amphibians.more developed than those of amphibians.

In amphibians the lungs are simple sacs, but in In amphibians the lungs are simple sacs, but in reptiles they have divided into chambers and reptiles they have divided into chambers and subchambers (called faveoli), which increases subchambers (called faveoli), which increases the surface area for gas exchange.the surface area for gas exchange.


Most reptiles breathe by expanding and Most reptiles breathe by expanding and compressing the pleurpoperitoneal cavity compressing the pleurpoperitoneal cavity by movements of the ribs produced by by movements of the ribs produced by contracting the intercostal muscles. contracting the intercostal muscles.

Turtles cannot move their ribs and instead Turtles cannot move their ribs and instead use specialized sheets of muscle to use specialized sheets of muscle to expand and contract the lungs.expand and contract the lungs.


Although reptilian respiration primarily Although reptilian respiration primarily depends on lungs, some gas exchange depends on lungs, some gas exchange takes place across the skin, the inside of takes place across the skin, the inside of the mouth and in the cloaca particularly in the mouth and in the cloaca particularly in various turtles.various turtles.

In soft-shelled turtles up to 70% of gas In soft-shelled turtles up to 70% of gas exchange may take place across the exchange may take place across the leathery skin that covers the shellleathery skin that covers the shell

Softshell turtlehttp://www.tortoisetrust.org/articles/3162658.jpg

Modern reptilesModern reptiles

The modern reptiles being a paraphyletic group The modern reptiles being a paraphyletic group include anapsids and diaspids.include anapsids and diaspids.

The anapsid representatives are the turtles The anapsid representatives are the turtles (Order Testudines). Turtles have changed little (Order Testudines). Turtles have changed little from the oldest known fossil forms 210 mya. from the oldest known fossil forms 210 mya.

Turtle fossils from 210 mya are known from Turtle fossils from 210 mya are known from across the globe so the group clearly originated across the globe so the group clearly originated some time before this.some time before this.

TurtlesTurtles

Turtles have a shell that consists of a Turtles have a shell that consists of a dorsal dorsal carapacecarapace and a ventral and a ventral plastronplastron..

Ribs and vertebrae are fused to the shell Ribs and vertebrae are fused to the shell and the head and limbs can be withdrawn and the head and limbs can be withdrawn into it.into it.

18.6

Figure 26.06

TurtlesTurtles

The carapace and plastron are both made of The carapace and plastron are both made of dermal bone overlain by horny scutes.dermal bone overlain by horny scutes.

In the carapace a series of 8 bony plates run In the carapace a series of 8 bony plates run along the dorsal midline and are attached to the along the dorsal midline and are attached to the neural arches of the vertebrae.neural arches of the vertebrae.

On either side of the midline are pairs of costal On either side of the midline are pairs of costal bones that are fused to the ribs and 11 pairs of bones that are fused to the ribs and 11 pairs of peripheral bones lie outside these.peripheral bones lie outside these.

Bones of the turtle carapacehttp://reptilis.net/index4/shell.jpg

TurtlesTurtles

Flexible areas called hinges are found in Flexible areas called hinges are found in the shells of many turtles. the shells of many turtles.

In box turtles the anterior and posterior In box turtles the anterior and posterior ends of the plastron can be raised to close ends of the plastron can be raised to close off the front and rear openings of the shell.off the front and rear openings of the shell.

Box turtle inside its shellhttp://www.dogbreedinfo.com/images21/TurtleBoxTurtle1.jpg

TurtlesTurtles

Soft-shelled turtles lack peripheral Soft-shelled turtles lack peripheral ossifications and epidermal scutes. ossifications and epidermal scutes.

Instead the plastron and carapace are Instead the plastron and carapace are covered with skin.covered with skin.

TurtlesTurtles

Turtles have no teeth and instead have a Turtles have no teeth and instead have a keratinized beak. keratinized beak.

This does not mean they can’t have an This does not mean they can’t have an impressive bite as snapping turtles impressive bite as snapping turtles demonstrate.demonstrate.

Alligator Snapping Turtlehttp://www.dausettrails.com/snapturtle.jpg

Body sizeBody size

Turtles are unusual among the reptiles in Turtles are unusual among the reptiles in having a large number of species that having a large number of species that achieve very large body sizes.achieve very large body sizes.

Large size means thermal stability Large size means thermal stability because larger animals heat and cool because larger animals heat and cool more slowly than smaller ones, but large more slowly than smaller ones, but large size may make temperature regulation size may make temperature regulation difficult in habitats where shade is scarce. difficult in habitats where shade is scarce.

Body sizeBody size

The marine turtles are the largest members of The marine turtles are the largest members of the group and leatherbacks (the largest species) the group and leatherbacks (the largest species) can weigh 1,500 lbs and are more than two can weigh 1,500 lbs and are more than two meters in length (largest ever was just over 3m). meters in length (largest ever was just over 3m). Their large body size plays a major role in Their large body size plays a major role in allowing them to range into very cold ocean allowing them to range into very cold ocean waters yet maintain a body temperature that waters yet maintain a body temperature that may be as much as 18may be as much as 18º C higher than the º C higher than the surrosurrounding water. unding water.

The largest land dwelling members are the Giant The largest land dwelling members are the Giant tortoises of the Galapagos.tortoises of the Galapagos.

Leatherback Turtlehttp://jcote1271.transworld.net/files/2008/11/home-turtle.jpg

18.8

Figure 26.08

Galapagos Giant Tortoises

Ecology and Behavior of TurtlesEcology and Behavior of Turtles

Turtles are very long-lived.Turtles are very long-lived.

Even small species such as the painted turtle do Even small species such as the painted turtle do not mature until aged 7 or 8 and even box turtles not mature until aged 7 or 8 and even box turtles may live to be 50 years old.may live to be 50 years old.

Large tortoises and turtles can live at least as Large tortoises and turtles can live at least as long as humans and perhaps longer, although long as humans and perhaps longer, although accounts of several hundred year old turtles are accounts of several hundred year old turtles are likely exaggerated.likely exaggerated.

Ecology and Behavior of TurtlesEcology and Behavior of Turtles

Not surprisingly, being naturally long-lived, turtle Not surprisingly, being naturally long-lived, turtle populations are vulnerable to increased adult populations are vulnerable to increased adult mortality (as e.g., are sharks). mortality (as e.g., are sharks).

Thus, increased adult mortality in sea turtles as Thus, increased adult mortality in sea turtles as a result of fishing has severely reduced their a result of fishing has severely reduced their populations. populations.

However, the use of turtle excluder devices on However, the use of turtle excluder devices on shrimp nets has reduced mortality.shrimp nets has reduced mortality.

Loggerhead turtle escaping through Turtle excluder devicehttp://users.aber.ac.uk/jrd6/ted_loggerhead.jpg

Turtle ReproductionTurtle Reproduction

All turtles are oviparous and the eggs are laid in All turtles are oviparous and the eggs are laid in a nest in sand or soil that the female excavates a nest in sand or soil that the female excavates using her rear limbs. using her rear limbs.

As is true of a number of other reptiles (including As is true of a number of other reptiles (including crocodiles, tuataras and some lizards), crocodiles, tuataras and some lizards), incubation temperature plays a major role in incubation temperature plays a major role in determining the sex of individual turtles. Higher determining the sex of individual turtles. Higher incubation temperatures produce the larger sex, incubation temperatures produce the larger sex, which in turtles is female.which in turtles is female.

Loggerhead Turtle laying eggshttp://www.fws.gov/archiecarr/photos/LOGGER-2.jpg


Young turtles when they hatch are on their Young turtles when they hatch are on their own because adults provide no parental own because adults provide no parental care.care.

Marine turtles lay their 100 or so eggs on Marine turtles lay their 100 or so eggs on sandy beaches. When the young hatch sandy beaches. When the young hatch they must escape a host of waiting they must escape a host of waiting predators to get to the sea and mortality is predators to get to the sea and mortality is high.high.

Green turtle hatchlingshttp://www.naturephoto-cz.com/photos/sevcik/green-turtle--chelonia-mydas-2.jpg


Simultaneous emergence of large Simultaneous emergence of large numbers of young turtles from multiple numbers of young turtles from multiple nests swamps the predators and allows nests swamps the predators and allows some to escape.some to escape.

Turtle ReproductionTurtle Reproduction Where young marine turtles go once they reach Where young marine turtles go once they reach

the sea is a mystery. the sea is a mystery.

Most nesting beaches are upcurrent from Most nesting beaches are upcurrent from feeding grounds so the young likely drift to feeding grounds so the young likely drift to suitable nursery areas. suitable nursery areas.

In areas where currents meet, accumulations of In areas where currents meet, accumulations of weed and other flotsam provide refuge from weed and other flotsam provide refuge from predators and a supply of invertebrate food, and predators and a supply of invertebrate food, and these are likely nursery areas for young turtles.these are likely nursery areas for young turtles.

Movement and NavigationMovement and Navigation

Although where young sea turtles go remains a Although where young sea turtles go remains a mystery we know that adults when ready to nest mystery we know that adults when ready to nest return to the beaches where they hatched.return to the beaches where they hatched.

Given the lack of landmarks in the ocean and Given the lack of landmarks in the ocean and the often huge distances between nesting and the often huge distances between nesting and feeding grounds the navigational success of feeding grounds the navigational success of these animals is remarkable.these animals is remarkable.

Movement and NavigationMovement and Navigation The movements and navigation of green turtles The movements and navigation of green turtles

has been extensively studied for more than 50 has been extensively studied for more than 50 years.years.

Green turtles use four major nesting sites Green turtles use four major nesting sites including Tortuguero on the Caribbean coast of including Tortuguero on the Caribbean coast of Costa Rica and Ascension Island in the mid-Costa Rica and Ascension Island in the mid-Atlantic east of Brazil. Atlantic east of Brazil.

Mating takes place off the nesting beaches Mating takes place off the nesting beaches where males congregate to wait for the females.where males congregate to wait for the females.

Adult Green Turtlehttp://img5.travelblog.org/Photos/1/217471/f/1659239-Green-Turtle-1.jpg


Studies of tagged green turtles at Tortuguero Studies of tagged green turtles at Tortuguero have shown that in a nesting season females have shown that in a nesting season females typically lay three clutches with about 12 days typically lay three clutches with about 12 days between clutches. between clutches.

However, they do not lay every year. One third However, they do not lay every year. One third lay every second year, the remainder every third lay every second year, the remainder every third year.year.

Information from tag recoveries shows that after Information from tag recoveries shows that after breeding the turtle disperse throughout the breeding the turtle disperse throughout the Caribbean.Caribbean.


The ability of female turtles nesting at The ability of female turtles nesting at Tortuguero to return to the same kilometer Tortuguero to return to the same kilometer of nesting beach is impressive, but pales of nesting beach is impressive, but pales in comparison to the challenge of locating in comparison to the challenge of locating Ascension Island, which is 2,200 km east Ascension Island, which is 2,200 km east of Brazil and only 20km in diameter. of Brazil and only 20km in diameter.


In navigating to Ascension it appears that chemosensory In navigating to Ascension it appears that chemosensory cues provide important information.cues provide important information.

The South Atlantic Equatorial current passes Ascension The South Atlantic Equatorial current passes Ascension and flows west towards Brazil. Young turtles that drift on and flows west towards Brazil. Young turtles that drift on this current as hatchlings may learn its odor signature. this current as hatchlings may learn its odor signature.

Satellite-tracking studies of nesting females have shown Satellite-tracking studies of nesting females have shown that they take a quite direct route to Ascension from off that they take a quite direct route to Ascension from off the coast of Brazil and travel much of the way along the the coast of Brazil and travel much of the way along the current apparently working their way up the odor plume.current apparently working their way up the odor plume.


Other studies of marine turtles have Other studies of marine turtles have shown other cues are also important in shown other cues are also important in navigation.navigation.

For example, when initially trying to get to For example, when initially trying to get to sea young loggerhead hatchlings respond sea young loggerhead hatchlings respond first to light and crawl towards the brightest first to light and crawl towards the brightest visible light, which in a natural situation visible light, which in a natural situation would lead them to the sea.would lead them to the sea.

Movement and NavigationMovement and Navigation Once in the water the baby loggerheads swim into the Once in the water the baby loggerheads swim into the

waves and this moves them offshore and ultimately to waves and this moves them offshore and ultimately to the Gulf Stream. the Gulf Stream.

This current carries them up the east coast of the U.S. This current carries them up the east coast of the U.S. and across the Atlantic. Off the coast of Portugal, the and across the Atlantic. Off the coast of Portugal, the Gulf Steam splits into northward and southward Gulf Steam splits into northward and southward branches. branches.

The turtles need to take the southward branch which will The turtles need to take the southward branch which will bring them back across the Atlantic and a lot of evidence bring them back across the Atlantic and a lot of evidence suggests they use the Earth’s magnetic field to orient suggests they use the Earth’s magnetic field to orient themselves correctly.themselves correctly.

Turtle ConservationTurtle Conservation

Turtles and tortoises because of their delayed Turtles and tortoises because of their delayed maturity and slow growth rates are very maturity and slow growth rates are very vulnerable to increased adult mortality or vulnerable to increased adult mortality or reduced juvenile recruitment.reduced juvenile recruitment.

Marine turtles are threatened by coastal Marine turtles are threatened by coastal development that destroys nesting beaches and development that destroys nesting beaches and generates light pollution that fatally disorients generates light pollution that fatally disorients young turtles. In addition, adult mortality caused young turtles. In addition, adult mortality caused by entanglement in fishing nets and long lines by entanglement in fishing nets and long lines has put additional stress on populations.has put additional stress on populations.


Smaller freshwater turtles are also under severe Smaller freshwater turtles are also under severe threat in China and southeast Asia in general.threat in China and southeast Asia in general.

Turtles have traditionally been used for food and Turtles have traditionally been used for food and medicine in China and millions are consumed medicine in China and millions are consumed each year. Chinese populations have been each year. Chinese populations have been severely depleted and as a result China has severely depleted and as a result China has been importing large numbers from neighboring been importing large numbers from neighboring countries.countries.


Tortoises are also threatened, but instead of Tortoises are also threatened, but instead of being taken for food they are illegally taken for being taken for food they are illegally taken for the pet trade.the pet trade.

In addition, in the southwestern U.S. deserts In addition, in the southwestern U.S. deserts degradation of desert habitat and bacterial degradation of desert habitat and bacterial disease (likely introduced from pet tortoises disease (likely introduced from pet tortoises released back into the wild) have caused desert released back into the wild) have caused desert tortoise populations to fall by 30-70%.tortoise populations to fall by 30-70%.


All of these threats coupled with All of these threats coupled with widespread habitat degradation and widespread habitat degradation and enormous numbers of road deaths mean enormous numbers of road deaths mean that turtles and tortoises face as severe a that turtles and tortoises face as severe a global crisis as amphibians do.global crisis as amphibians do.

18.2

Figure 26.02

Tuataras: Order SphenodontaTuataras: Order Sphenodonta

The order is represented by two living The order is represented by two living species found only on offshore islands in species found only on offshore islands in New Zealand. New Zealand.

They are the last survivors of a group that They are the last survivors of a group that was much more diverse 200 million years was much more diverse 200 million years ago. ago.

18.23

Figure 26.26

TuatarasTuataras

Tuataras retain many features of their Tuataras retain many features of their distant ancestors including a diapsid skull distant ancestors including a diapsid skull with two openings and associated with two openings and associated complete arches and a well developed complete arches and a well developed parietal “third eye” on the top of its skull. parietal “third eye” on the top of its skull.

TuatarasTuataras

The parietal eye has a lens, cornea, and The parietal eye has a lens, cornea, and retina, but a degenerated nervous retina, but a degenerated nervous connection to the brain. It is not used for connection to the brain. It is not used for vision, but may help regulate day-night vision, but may help regulate day-night cycles or absorb UV rays to manufacture cycles or absorb UV rays to manufacture vitamin D.vitamin D.

TuatarasTuataras

Adult Tuatara are about 2 feet long, nocturnal Adult Tuatara are about 2 feet long, nocturnal and live in seabird burrows.and live in seabird burrows.

Tuatara have two rows of teeth on the upper jaw Tuatara have two rows of teeth on the upper jaw (one on the maxilla, the other on the palatine (one on the maxilla, the other on the palatine bones). bones).

When they bite the single row of teeth on the When they bite the single row of teeth on the lower jaw fits between those on the upper jaw.lower jaw fits between those on the upper jaw.

TuatarasTuataras

The feeding ecology of Tuatara is dictated The feeding ecology of Tuatara is dictated by their association with seabird colonies.by their association with seabird colonies.

They eat seabirds, which are most They eat seabirds, which are most vulnerable to attack at night. In addition, vulnerable to attack at night. In addition, the birds guano, food scraps and dead the birds guano, food scraps and dead bodies attract lots of invertebrates that the bodies attract lots of invertebrates that the Tuatara also eat and in fact invertebrates Tuatara also eat and in fact invertebrates make up most of their diet.make up most of their diet.

Modern reptiles: diapsids Modern reptiles: diapsids SquamataSquamata

Subclass Diapsida: Order Squamata.Subclass Diapsida: Order Squamata.

The Squamata includes about 95% of all The Squamata includes about 95% of all living reptiles including three suborders:living reptiles including three suborders: Sauria: lizards, Sauria: lizards, Serpentes: snakesSerpentes: snakes Amphisbaenia: worm lizards.Amphisbaenia: worm lizards.

Modern reptiles: diapsidsModern reptiles: diapsids

The diapsid skull of squamates has been The diapsid skull of squamates has been modified from the ancestral condition by modified from the ancestral condition by the loss of bone behind and below the the loss of bone behind and below the temporal opening.temporal opening.

Most squamates have a kinetic skull, Most squamates have a kinetic skull, which has movable joints that allow the which has movable joints that allow the snout and upper jaw to be moved against snout and upper jaw to be moved against the skull and raised. the skull and raised.

18.9

Figure 26.11

Kinetic skullKinetic skull

Mobility of the skull allows squamates to Mobility of the skull allows squamates to seize and manipulate prey and also seize and manipulate prey and also increases the force of the bite. increases the force of the bite.

Snakes show the most extreme Snakes show the most extreme development of the kinetic skull and are development of the kinetic skull and are capable of swallowing prey several time capable of swallowing prey several time their own diameter. their own diameter.

18.16

Figure 26.18

Order Squamata: Suborder Order Squamata: Suborder Sauria the lizardsSauria the lizards

Lizards are a very diverse group that Lizards are a very diverse group that includes terrestrial, burrowing, aquatic, includes terrestrial, burrowing, aquatic, arboreal and even gliding members.arboreal and even gliding members.

There are about 4800 species ranging in There are about 4800 species ranging in size from about 3cm to 3m long.size from about 3cm to 3m long.

Most lizards are insectivorous and small Most lizards are insectivorous and small (80% weigh 20 grams or less).(80% weigh 20 grams or less).

LizardsLizards

Lizards have invaded many of the world’s Lizards have invaded many of the world’s hottest areas by evolving a suite of hottest areas by evolving a suite of adaptations that make survival in deserts adaptations that make survival in deserts possible.possible.

These include a thick skin that contains These include a thick skin that contains lipids, which reduce water loss, and the lipids, which reduce water loss, and the excretion of uric acid which minimizes excretion of uric acid which minimizes water loss.water loss.

LizardsLizards

Reptiles are ectothermic and adjust their body Reptiles are ectothermic and adjust their body temperature by moving from one microclimate to temperature by moving from one microclimate to another to bask or cool down. another to bask or cool down.

Cold climates do not suit lizards as there are too Cold climates do not suit lizards as there are too few opportunities to warm up. few opportunities to warm up.

Because they spend relatively little energy Because they spend relatively little energy keeping warm, ectotherms in general do well in keeping warm, ectotherms in general do well in low productivity ecosystems such as tropical low productivity ecosystems such as tropical deserts and grasslands.deserts and grasslands.

LizardsLizards

Lizards are very adaptable and occupy a Lizards are very adaptable and occupy a wide range of habitats. In addition to wide range of habitats. In addition to deserts and grasslands they occur in deserts and grasslands they occur in swamps, along coasts, above timberline swamps, along coasts, above timberline on some mountains and many species are on some mountains and many species are arboreal.arboreal.

LizardsLizards

Lizards have good vision and an external Lizards have good vision and an external ear, which snakes lack. They also have ear, which snakes lack. They also have eyelids, also a trait that snakes lack. eyelids, also a trait that snakes lack.

Most lizards have four limbs, although Most lizards have four limbs, although some species (the Amphisbaenians) are some species (the Amphisbaenians) are completely legless.completely legless.

LizardsLizards

Well known species of lizards include: Well known species of lizards include: chameleons, geckos, iguanas, and chameleons, geckos, iguanas, and monitor lizards, which include the largest monitor lizards, which include the largest species, the Komodo dragon.species, the Komodo dragon.

ChameleonsChameleons Chameleons are the most arboreal lizards.Chameleons are the most arboreal lizards.

Their zygodactylous feet (the toes are fused Their zygodactylous feet (the toes are fused together) allow them to grip branches firmly and together) allow them to grip branches firmly and they have a prehensile tail.they have a prehensile tail.

The eyes are raised on small cones that can The eyes are raised on small cones that can rotate independently. This arrangement allows rotate independently. This arrangement allows chameleons to gauge distance accurately, which chameleons to gauge distance accurately, which is very important is prey capture. They catch is very important is prey capture. They catch prey by projecting their long tongueprey by projecting their long tongue

Figure 26.14

Chameleon catching an insect with its sticky extensible tongue.

GeckosGeckos

Geckos are among the smallest lizards Geckos are among the smallest lizards (3cm to 30cm), but they are very (3cm to 30cm), but they are very successful with more than 1,000 species successful with more than 1,000 species and they occur on every continent but and they occur on every continent but Antarctica.Antarctica.

They have modified scales on their feet They have modified scales on their feet (setae) that allow them to cling to vertical (setae) that allow them to cling to vertical surfacessurfaces

Figure 26.12

Gecko (note the flattened pads on the toes. Ridges on these pads enable the geckoto cling to smooth surfaces).

IguanasIguanas

Most large lizards are herbivorous and many iguanas are Most large lizards are herbivorous and many iguanas are arboreal. In areas without mammalian predators (e.g. arboreal. In areas without mammalian predators (e.g. islands in the West Indies) larger species have evolved islands in the West Indies) larger species have evolved that spend much of their time on the ground.that spend much of their time on the ground.

Iguanas occur throughout South and Central America Iguanas occur throughout South and Central America and some species (e.g. the Chuckwalla) occur in the and some species (e.g. the Chuckwalla) occur in the western U.S. western U.S.

The marine iguanas of the Galapagos Islands are The marine iguanas of the Galapagos Islands are behaviorally very specialized and they dive and swim to behaviorally very specialized and they dive and swim to obtain seaweed. obtain seaweed.

Galapagos Marine Iguanahttp://www.bio.davidson.edu/people/midorcas/animalphysiology/websites/2008/Belcher/marine-iguana.jpg

Green Iguanahttp://animals.nationalgeographic.com/staticfiles/NGS/Shared/StaticFiles/animals/images/primary/green-iguana.jpg

Monitor LizardsMonitor Lizards

Unlike other large lizards monitor lizards Unlike other large lizards monitor lizards are active predators and feed on a wide are active predators and feed on a wide variety of prey. variety of prey.

Monitors have evolved a positive pressure Monitors have evolved a positive pressure gular pump to assist the axial muscles in gular pump to assist the axial muscles in lung ventilation. This enhanced lung ventilation. This enhanced respiration enables them to sustain high respiration enables them to sustain high activity levels.activity levels.

Komodo Dragonhttp://blog.turntablelab.com/images/KomodoDragon.jpg

Water Monitor Lizardhttp://www.mongabay.com/images/malaysia/06/malaysia0513.JPG


Monitor Lizards are widely distributed Monitor Lizards are widely distributed throughout the Old World with large throughout the Old World with large species found throughout the range.species found throughout the range.

In Australia and New Guinea a diverse In Australia and New Guinea a diverse array of smaller monitors occur and this array of smaller monitors occur and this appears to be due to a lack of small appears to be due to a lack of small placental mammal carnivores.placental mammal carnivores.


Monitors display complex hunting behavior and Monitors display complex hunting behavior and will adjust their strategies depending on the will adjust their strategies depending on the behavior of their prey.behavior of their prey.

For example, Komodo dragons hunting deer For example, Komodo dragons hunting deer wait in the morning to ambush deer as they wait in the morning to ambush deer as they move along paths between resting and feeding move along paths between resting and feeding areas. If they are unsuccessful, they then switch areas. If they are unsuccessful, they then switch to active stalking for deer in the thicket habitats to active stalking for deer in the thicket habitats where they are most likely to occur.where they are most likely to occur.


Komodo Dragons can dispatch smaller prey Komodo Dragons can dispatch smaller prey easily, but do not have to kill larger prey in their easily, but do not have to kill larger prey in their initial attack.initial attack.

Komodo mouths contain a diverse stew of Komodo mouths contain a diverse stew of bacteria and bites inevitably become infected. A bacteria and bites inevitably become infected. A bitten animal rapidly develops sepsis and dies. bitten animal rapidly develops sepsis and dies. The monitor that bit it merely needs to trail the The monitor that bit it merely needs to trail the victim for a few days until it succumbs to its victim for a few days until it succumbs to its wounds.wounds.

AmphisbaeniansAmphisbaenians

Leglessness has evolved multiple times Leglessness has evolved multiple times among lizards and one large group the among lizards and one large group the Amphisbaenians is exclusively legless Amphisbaenians is exclusively legless (apart from 4 species in one genus that (apart from 4 species in one genus that retain forelimbs).retain forelimbs).

These are tunneling lizards and have a These are tunneling lizards and have a variety of specialized adaptations for variety of specialized adaptations for digging and moving in burrows.digging and moving in burrows.

AmphisbaeniansAmphisbaenians Amphisbaenians burrow using by ramming their Amphisbaenians burrow using by ramming their

heads against the soil and pushing dislodged heads against the soil and pushing dislodged material to the sides. material to the sides.

The head is heavily keratinized and there is The head is heavily keratinized and there is variation in head shape that relates to the variation in head shape that relates to the particular mode of tunneling used. particular mode of tunneling used.

For example, those with shovel-shaped snouts For example, those with shovel-shaped snouts ram their heads into the end of the tunnel and ram their heads into the end of the tunnel and then compress the material into the roof.then compress the material into the roof.

Gray Amphisbaenianhttp://4.bp.blogspot.com/_LbccUVbSRd8/RdteZVPJ4iI/AAAAAAAAAZk/3gDlu3kFXlk/s400/puerto+rican+gray+amphisbaenian_kingsnake1com.JPG

AmphisbaeniansAmphisbaenians Amphisbaenians skin is distinctive and rings Amphisbaenians skin is distinctive and rings

called annuli encircle the body.called annuli encircle the body.

The integument has only a few connections to The integument has only a few connections to the body so that the trunk is free to move within the body so that the trunk is free to move within a tube of skin. a tube of skin.

To move, the animal contracts integumentary To move, the animal contracts integumentary muscles between selected annuli. This bunches muscles between selected annuli. This bunches the skin so it presses against the tunnel and the the skin so it presses against the tunnel and the trunk then slides forward within the tube of skin.trunk then slides forward within the tube of skin.

Order Squamata: Suborder Order Squamata: Suborder Serpentes: the snakesSerpentes: the snakes

There are approximately 2900 species of There are approximately 2900 species of snakes and they range is size from 10cm snakes and they range is size from 10cm long burrowing forms that eat termites to long burrowing forms that eat termites to almost 10m long anacondas and pythons.almost 10m long anacondas and pythons.

SnakesSnakes

Snakes are limbless and usually lack both Snakes are limbless and usually lack both the pectoral and pelvic girdles. the pectoral and pelvic girdles.

They have numerous vertebrae, which are They have numerous vertebrae, which are shorter and wider than those in other shorter and wider than those in other vertebrates and allow them to make vertebrates and allow them to make undulatory movements.undulatory movements.

SnakesSnakes

There are three major lineages of snakes:There are three major lineages of snakes: Scoleophidia: more than 300 species of small Scoleophidia: more than 300 species of small

burrowing (fossorial) snakes.burrowing (fossorial) snakes. Alethinophidia: About 160 species that include Alethinophidia: About 160 species that include

the boas, pythons and a variety of boa-like the boas, pythons and a variety of boa-like snakes.snakes.

Colubroidea: more than 2400 species Colubroidea: more than 2400 species including the Colubridae, Elapidae and including the Colubridae, Elapidae and Viperidae.Viperidae.

AletinophidiaAletinophidia

Alethinophidia: Boidae: Includes the 26 Alethinophidia: Boidae: Includes the 26 species of pythons (Pythoninae) and 33 species of pythons (Pythoninae) and 33 species of boas (Boinae).species of boas (Boinae).

The pythons are Old World constrictors The pythons are Old World constrictors that are large to enormous (approaching that are large to enormous (approaching 10m) in size. The boas are the New World 10m) in size. The boas are the New World equivalent of the pythons and have a equivalent of the pythons and have a similar range of sizes.similar range of sizes.

Emerald Tree boahttp://www.infovisual.info/02/photo/emerald%20tree%20boa.html

Anacondahttp://www.oregonreptileman.com/sitebuildercontent/sitebuilderpictures/anaconda.jpg

SnakesSnakes

The large constrictors primarily use rectilinear The large constrictors primarily use rectilinear motion to move. motion to move.

Alternate sections of the ventral integument are Alternate sections of the ventral integument are raised off the ground and pulled forward by raised off the ground and pulled forward by muscles that connect the ribs and ventral scales.muscles that connect the ribs and ventral scales.

Waves of muscles contraction travel down the Waves of muscles contraction travel down the snake which moves in a straight line.snake which moves in a straight line.

ColubroideaColubroidea

Colubroidea includes most of the living species of Colubroidea includes most of the living species of snakes and the Colubridae alone contains 2/3 of all snakes and the Colubridae alone contains 2/3 of all snakes.snakes.

Many colubroid snakes are venomous and the Elapids Many colubroid snakes are venomous and the Elapids and Viperids possess hollow fangs at the front of the and Viperids possess hollow fangs at the front of the mouth and have highly toxic venom.mouth and have highly toxic venom.

Many colubrids possess venom glands but they do not Many colubrids possess venom glands but they do not have the hollow teeth specialized to inject venom.have the hollow teeth specialized to inject venom.

Colubroid movementColubroid movement

Several different forms of motion are used Several different forms of motion are used by colubroids, but horizontal undulations by colubroids, but horizontal undulations and concertina-like movements are the and concertina-like movements are the most common.most common.

ColubridaeColubridae The group is a bit of a phylogenetic dumping The group is a bit of a phylogenetic dumping

ground and includes more than 1800 species ground and includes more than 1800 species that occur worldwide (except Antarctica).that occur worldwide (except Antarctica).

Most are medium sized, all lack a pelvid girdle, Most are medium sized, all lack a pelvid girdle, have no vestigial hindlimbs and in all the left have no vestigial hindlimbs and in all the left lung is absent or very reduced in size.lung is absent or very reduced in size.

North American colubrids include garter snakes, North American colubrids include garter snakes, kingsnakes, hognose snakes, racers, and corn kingsnakes, hognose snakes, racers, and corn snakes.snakes.

Corn Snakehttp://www.pitt.edu/~mcs2/herp/snake.pics/corn.gif

Common Garter snakehttp://www.pitt.edu/~mcs2/herp/snake.pics/t_sirtalis.jpg

Striped whipsnakehttp://www.pitt.edu/~mcs2/herp/snake.pics/Masticophis_taeniatus.jpg

Prairie Kingsnakehttp://www.pitt.edu/~mcs2/herp/Lc_calligaster.html

ViperidaeViperidae

In members of the Viperidae the long In members of the Viperidae the long fangs rest horizontally when the mouth is fangs rest horizontally when the mouth is closed.closed.

Viperids range in size up to about 2m and Viperids range in size up to about 2m and include both the true vipers, which occur in include both the true vipers, which occur in Eurasia and Africa and the pit vipers, Eurasia and Africa and the pit vipers, which occur in New World and Asia.which occur in New World and Asia.

ViperidaeViperidae

True vipers include the Gaboon Viper and True vipers include the Gaboon Viper and Puff Adder.Puff Adder.

Pit vipers include rattlesnakes. Pit vipers include rattlesnakes.

Gaboon Viperhttp://homepage.mac.com/wildlifeweb/reptile/gaboon_viper/gaboon_viper01tfk.jpg

Gaboon Viper Skull http://www.kostich.com/gaboon_viper_skull.jpg

Puff Adderhttp://kolobe.com/photo_gallery/Anml_Gal/slides/Puff%20Adder.JPG

Rattlesnakehttp://i.pbase.com/v3/29/530429/1/45155303.Rattlesnake.jpg

ElapidaeElapidae

Elapids have functionally hollow fangs (the Elapids have functionally hollow fangs (the tooth is folded over to form a groove that is tooth is folded over to form a groove that is almost closed down which the venom almost closed down which the venom runs) that are shorter than those of the runs) that are shorter than those of the viperids, but they are permanently erect. viperids, but they are permanently erect.

Elapids include the mambas, cobras, Elapids include the mambas, cobras, kraits and sea snakes.kraits and sea snakes.

King Cobrahttp://www.digitalcamerareviews.org.uk/wp-content/uploads/2009/01/a-full-sized-indian-king-cobra.jpg

Black Mambahttp://s3.amazonaws.com/readers/2009/03/26/black20mamba_1.jpg

Sea snakesSea snakes

Sea snakes (members of the Elapidae) are Sea snakes (members of the Elapidae) are morphologically specialized for life in the water.morphologically specialized for life in the water.

The tail is laterally flattened so it can act as an The tail is laterally flattened so it can act as an oar. Nostrils are located dorsally on the snout oar. Nostrils are located dorsally on the snout and are equipped with valves to keep water out. and are equipped with valves to keep water out. More primitive sea snakes lay eggs on the land, More primitive sea snakes lay eggs on the land, but the more derived species give birth to live but the more derived species give birth to live young.young.

Yellow-bellied sea snakehttp://elapidcatcher.com/elapidcatcher.com/images/stories/snakes/yellow%20bellied%20sea%20snake.jpg

SnakesSnakes Snakes are an extremely successful group of Snakes are an extremely successful group of

predators. Although most have poor vision (with predators. Although most have poor vision (with the exception of arboreal species) and limited the exception of arboreal species) and limited hearing ability they use other sense organs to hearing ability they use other sense organs to track prey.track prey.

Snakes have pit-like Snakes have pit-like Jacobson’s organsJacobson’s organs in the in the roof of the mouth, which are olfactory organs. roof of the mouth, which are olfactory organs. The forked tongue when extended samples the The forked tongue when extended samples the air and picks up molecules that are delivered to air and picks up molecules that are delivered to the Jacobson’s organ when the tongue is the Jacobson’s organ when the tongue is withdrawn.withdrawn.

SnakesSnakes

Crotaline vipers (pit vipers such as rattlesnakes) Crotaline vipers (pit vipers such as rattlesnakes) have heat-sensitive pit organs on their heads have heat-sensitive pit organs on their heads between the nostrils and eyes.between the nostrils and eyes.

These are very sensitive to radiant heat and can These are very sensitive to radiant heat and can detect temperature differences as slight as detect temperature differences as slight as 0.0030.003ººC. The vipers use the organ to track prey C. The vipers use the organ to track prey and to aim their strike when biting.and to aim their strike when biting.

18.22

Figure 26.24

PredationPredation

Snakes use one of three methods to catch and Snakes use one of three methods to catch and kill prey. kill prey.

Most catch prey by grabbing it and swallowing it Most catch prey by grabbing it and swallowing it alive. Most such species are quick and alive. Most such species are quick and concentrate on small, easy-to-handle prey.concentrate on small, easy-to-handle prey.

The other two group kill their prey either by The other two group kill their prey either by constriction or with venom.constriction or with venom.

ConstrictorsConstrictors A variety of snakes including pythons and boas A variety of snakes including pythons and boas

kill by constriction.kill by constriction.

They coil around their prey and every time the They coil around their prey and every time the prey breathes out they tighten their coils a little prey breathes out they tighten their coils a little more until the prey can no longer breathe and more until the prey can no longer breathe and suffocates. suffocates.

Most constrictors are large, slow-moving Most constrictors are large, slow-moving ambush predators and the largest snakes, the ambush predators and the largest snakes, the anaconda, boas and pythons are all constrictors.anaconda, boas and pythons are all constrictors.

Venomous snakesVenomous snakes

About 20% of all snakes are venomous (although in About 20% of all snakes are venomous (although in Australia 80% of snakes are venomous). About 50,000-Australia 80% of snakes are venomous). About 50,000-60,000 people die annually worldwide from snake bite, 60,000 people die annually worldwide from snake bite, most of them in the Indian subcontinent.most of them in the Indian subcontinent.

Snakes with venom lethal to humans include theSnakes with venom lethal to humans include the vipers (including the American pit vipers) which have vipers (including the American pit vipers) which have

large movable tubular fangs at the front of the mouth;large movable tubular fangs at the front of the mouth; elapids (cobras, mambas, coral snakes, kraits, sea elapids (cobras, mambas, coral snakes, kraits, sea

snakes) which have shorter, but permanently erect snakes) which have shorter, but permanently erect fangs in the front of the mouth;fangs in the front of the mouth;

18.20

Figure 26.25

Venomous snakesVenomous snakes

Snake venoms are highly modified salivas and Snake venoms are highly modified salivas and complex in constitution including a variety of complex in constitution including a variety of proteins and enzymes.proteins and enzymes.

Elapid venom is neurotoxic and works by Elapid venom is neurotoxic and works by shutting down the respiratory system whereas shutting down the respiratory system whereas viper venom is more painful and attacks the viper venom is more painful and attacks the vascular system bringing about coagulation of vascular system bringing about coagulation of blood and clotting of arteries as well as often blood and clotting of arteries as well as often severe tissue damage.severe tissue damage.

Result of a rattlesnake bitehttp://images.townnews.com/helenair.com/content/articles/2008/05/25/top/80na_080525_rattlesnakes.jpg

Crocodiles and Alligators: Order Crocodiles and Alligators: Order CrocodiliaCrocodilia

Modern crocodiles and birds are the only Modern crocodiles and birds are the only survivors of the Archosaurian lineage that survivors of the Archosaurian lineage that included the dinosaurs.included the dinosaurs.

Crocodiles have changed little in almost Crocodiles have changed little in almost 200 million years a testament to the 200 million years a testament to the success of their design. success of their design.

CrocodilesCrocodiles

All crocodiles have their teeth set in sockets a All crocodiles have their teeth set in sockets a trait found otherwise only in mammals and fossil trait found otherwise only in mammals and fossil birds and also like mammals have a complete birds and also like mammals have a complete palate which enables them to breathe even if the palate which enables them to breathe even if the mouth is filled with water or food.mouth is filled with water or food.

They alos possess a four chambered heart as They alos possess a four chambered heart as do the only other extant members of the do the only other extant members of the Archosauria, the birdsArchosauria, the birds


Crocodiles are ambush predators that kill Crocodiles are ambush predators that kill by grabbing and drowning their prey. The by grabbing and drowning their prey. The largest Nile and Estuarine crocodiles largest Nile and Estuarine crocodiles (called “salties” in Australia) can exceed (called “salties” in Australia) can exceed 1000 kgs in weight and can attack and kill 1000 kgs in weight and can attack and kill almost anything.almost anything.


The muscles used to open a crocodile’s mouth are quite The muscles used to open a crocodile’s mouth are quite weak, but those used to close the jaws are massive and weak, but those used to close the jaws are massive and powerful.powerful.

Broad nosed crocodiles can for example crush an adult Broad nosed crocodiles can for example crush an adult turtle.turtle.

A crocodile’s snout contains large numbers of touch and A crocodile’s snout contains large numbers of touch and pressure receptors. These enable the animal to lunge at pressure receptors. These enable the animal to lunge at a prey animal in darkness or immediately snap the jaws a prey animal in darkness or immediately snap the jaws closed on a fish or other animal that brushes against the closed on a fish or other animal that brushes against the animal’s open mouth.animal’s open mouth.


Crocodiles do not chew their prey. Crocodiles do not chew their prey. Smaller prey animals are swallowed Smaller prey animals are swallowed whole, but larger animals are eaten whole, but larger animals are eaten piecemeal. piecemeal.

Crocodiles often allow the animal to Crocodiles often allow the animal to decompose for several days to make it decompose for several days to make it easier to tear chunks off.easier to tear chunks off.

ClassificationClassification

There are 23 species of crocodile divided There are 23 species of crocodile divided into three lineages: into three lineages: Alligatoridae, Alligatoridae, Crocodilidae Crocodilidae Gavialidae.Gavialidae.

AlligatoridaeAlligatoridae

The Alligatoridae includes the alligators The Alligatoridae includes the alligators and caimans and, with the exception of the and caimans and, with the exception of the Chinese alligator, is solely a New World Chinese alligator, is solely a New World group. group.

Alligators and caimans are exclusively Alligators and caimans are exclusively found in freshwater and, in general, they found in freshwater and, in general, they have broader snouts than crocodiles.have broader snouts than crocodiles.

AlligatorsAlligators

The American Alligator is found throughout the The American Alligator is found throughout the Gulf states and caimans occur in Central Gulf states and caimans occur in Central America, South America and the Caribbean.America, South America and the Caribbean.

Alligator populations in the U.S. had declined Alligator populations in the U.S. had declined enormously as a result of hunting for meat and enormously as a result of hunting for meat and especially skins, but Federal protection has especially skins, but Federal protection has caused their numbers to rebound so that they caused their numbers to rebound so that they are again common.are again common.

American Alligatorhttp://www.wildanimalfightclub.com/Portals/41405/images//gex-american-alligator_jpg.jpg

CrocdilesCrocdiles

In contrast to alligators, crocodiles occur in In contrast to alligators, crocodiles occur in both freshwater and salt water and readily both freshwater and salt water and readily move from one to the other.move from one to the other.


The saltwater crocodile is probably the The saltwater crocodile is probably the largest living crocodile and may be largest living crocodile and may be capable of reaching 7m in length although capable of reaching 7m in length although hunting pressure in recent history means hunting pressure in recent history means there may not be old enough individuals there may not be old enough individuals around for maximum size to have yet been around for maximum size to have yet been attained.attained.

Australian saltwater Crocodile with a hooked Barramundihttp://www.ntnews.com.au/images/uploadedfiles/editorial/pictures/2008/04/29/barra_croc.jpg

GharialGharial

There is only a single species in the There is only a single species in the Gavialidae: the gharial.Gavialidae: the gharial.

Gharials were once widespread in large Gharials were once widespread in large rivers in India and Burma but are now rivers in India and Burma but are now threatened species.threatened species.

It has a very narrow snout and is a It has a very narrow snout and is a specialist fish predator.specialist fish predator.

Gharial picture

Gharialhttp://homepage.mac.com/wildlifeweb/reptile/gharial/gharial01tfk.jpg

Documents

Amniote origins and classification The possession of a shelled egg unites the mammals, birds and reptiles into a monophyletic group the amniotes. The