Lab 5 Spring 2018 - EEB 111 - Biology of Vertebrates Professor - Caitlin Brown Summary - Reptiles PDF

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EEB 111 - Biology of Vertebrates
Professor - Caitlin Brown
Summary - Reptiles...

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Lab 5: Reptiles - Spring 2018 EEB 111 Week 6

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Introduction

This week, we will start examining terrestrial amniotes, organisms with amniotic eggs. There are three main groups of amniotes: reptiles, birds, and mammals. The common name “reptiles” is a paraphyletic group because birds are excluded. Reptiles, crocodylians and birds are often grouped together as Reptilomorpha or Diapsids Living non-avian reptiles contain three orders: Chelonia, the turtles and tortoises, Squamata, the lizards and snakes, and Crocodilia, the alligators, crocodiles, and caimans. We will look at the first two orders this week. Unlike amphibians, reptiles have adapted to a fully terrestrial lifestyle. Reptiles have thick skin, which is covered by keratinized scales, better developed limbs, and amniotic eggs covered with a thick leathery shell. While their skin no longer houses poisonous glands, reptiles have evolved numerous defenses through modifications of their keratinous scales, dermal bones, and glands contained within the oral cavity. We will focus on these various defenses in the notes this week. Order Chelonia is considered to be the most ancestral lineage of sauropsids. The fossil record for the turtles is somewhat ambiguous because the first fossil turtles look very much like extant species, so there is considerable debate as to when the turtles first arose. Turtle shells are composed of two parts: a dorsal carapace and a ventral plastron. The rib cage and vertebral column are fused to the carapace (turtles are the only group in which the limb girdles are situated within the rib cage!). Make sure that you look at the plastron of each turtle species. Notice that for some of them the plastron is very constricted between the arm and leg. Others have more space around the limbs, allowing for a broader range of motion. The shape fo the plastron can also be used to differentiate males from females. There are two main groups of turtles: the pleurodires (the side-necked turtles), which are confined to the Southern hemisphere, and the cryptodires (turtles that withdraw the head into the shell), which live in the Northern hemisphere. The cryptodires are composed of nine families; all the examples of preserved turtles you will see in lab today are cryptodires. Turtles have anapsid skulls without teeth. The jaws are instead covered with a keratinous beak The remaining orders in lab are all Diapsid, though the bony border of one or both skull fenestra may have been lost in some groups. Order Squamata is the most dominant lineage of extant reptiles. Squamates can be found worldwide, except for Antarctica, and exhibit incredibly diverse morphologies, feeding strategies, behaviors, etc. As you look at the specimens in lab today, ask yourself how the morphological differences you observe are related to the ways in which the organisms make their living. How long are the limbs? Does the lizard rely on speed to evade predators, or does it have other defenses?

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→Why are herbivorous lizards and chelonians generally large? Squamata also contains the snakes. It is easy to discern between lizards and snakes because snakes have elongate limbless bodies, lack movable eyelids, and have a high degree of cranial kinesis, which allows them to do a pterygoid walk as they move large prey into their mouths. The kinetic skull and independantly moving mandibles easily distinguish the snakes from other limbless squamates. →How do snakes breathe while slowly consuming prey with a pterygoid walk? Hint: they adapted a structure made of cartilage. The least speciose order of diapsids is Rhynchocephalia, containing just the tuatara. These reptiles are superficially lizard-like but they maintain the anscetral diapsid skull pattern, have unusual teeth and share skeletal and cardiovascular characters with amphibians, making the tuatara the least derived diapsid. Tuatara are extremely slow growing and long lived (as of 2017 a male named Henry is still breeding at the age of 111). This growth rate and lack of natural predators has lead to their near extinction with the introduction of invasive rats to New Zealand. Not surprisingly, we do not have a specimen of this exceedingly rare creature. There will be many endangered species featured in this lab, many of which are menaced by human activities and slow reproductive rates.

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Specimens

2.1

Turtles: Order Testudines (Chelonia)

2.1.1

Desert tortoise

Family

Testudinidae

Sci. Name Gopherus agassizii Habitat

Deserts

Range

Mojave desert (CA, NV, AZ) to northern Mexico

Notes

The desert tortoise is an endangered species due to human encroachment and predation from wild and domesticated mammals. It is herbivorous, eating small, near-ground grasses and shrubs. This species requires firm ground for burrowing. This is one of three native turtle species in Southern CA.

2.1.2

Western box turtle

Family

Emydidae

Sci. Name Terrapene ornate Habitat:

Prairies and woodlands

Range:

Midwestern US to Texas and northern Mexico

Notes:

Box turtles have hinged plastrons, allowing the animal to fully enclose the body when threatened. This is a common pet store species.

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2.1.3

Spiny softshell turtle

Family

Trionychidae

Sci. Name Apalone spinifera Habitat:

Slow running streams and ponds

Range:

Southeast North America

Notes:

Fast swimming aquatic carnivores. These turtles often lie hidden in the mud and extend their neck so that their snorkel-like nose extends above the water. Note the strongly webbed, oar-like feet. The forefeet bear three claws (Tri = three, onych = claw). →Why is it advantangous for this animal to have a less dense shell than, say, the snapping turtle?

2.1.4

Snapping turtle

Family

Chelydridae

Sci. Name Chelydra serpentina Habitat

Marshes, ponds lakes, rivers and slow streams with abundant aquatic plants

Range

SW Canada to the equator; Rocky Mountains to Atlantic coast

Notes

These turtles tend to be ill-tempered and prone to bite. Larger specimens are able to bite clean through a person’s finger. Dr. Buth has a live snapping turtle in his office (and all of his fingers) →Compare to the softshell turtle. Is this an actively swimming predator?

2.1.5

Green sea turtle

Family

Cheloniidae

Sci. Name Chelonia mydas Habitat

Young turtles inhabit deep pelagic waters feeding on jellyfish; mature individuals are found near shore associated with reefs and seagrass pastures.

Range

Tropical and subtropical oceans worldwide. In the USA, can be found along the entire Pacific coast and Hawaiian archipelago, and from Texas to Massachusettes.

Notes

This species can travel 1,600mi between feeding and nesting sites and will return to the beach they hatched on to nest. Most turtle mortality occurrs in the egg or hatchling stage. Adults are preyed upon by humans and large sharks. →How does a marine turtle generate thrust in the water?

2.2

A Living Fossil: Order Rhynchocephalia

2.2.1 Family

Tuatara Sphenodontidae

Sci. Name Sphenodon Habitat

Forested areas associated with seabird colonies

Range

New Zealand, primarily on protected offshore islands

Notes

All living tuatara have been relocated to rat-free islands to prevent the extinction of the order. New Zealand had no native mammal species prior to human arrival. 3

2.3

Lepidosaurs, Order Squamata: Lizards and Snakes

2.3.1 Family

Basilisk lizard Iguanidae

Sci. Name Basiliscus vittatus Habitat

Tropical wetlands and rainforest

Range

Central America (Costa Rica to Guatemala)

Notes

The Basilisk lizard is also known as the “Jesus Lizard” due to its ability to run on water. In order to accomplish this feat, the lizard must be running and be of small enough size so as not to break the surface tension of the water.

2.3.2 Family

Collared lizard Iguanidae

Sci. Name Crotaphytus collaris Habitat

Rock-dwelling species in arid and chaparral regions

Range

Great Basin to Baja California and Sonora

Notes

Collard lizards move quickly and are insectivorous. When encountered, they often do “pushups” (a threat display that they use to deter predators).

2.3.3 Family

Desert iguana Iguanidae

Sci. Name Dipsosaurus dorsalis Habitat

Creosote bush desert. Usually found in rocky areas with patches of sand and firm ground.

Range

California, Nevada, Arizona, and Baja California

Notes

The desert iguana is well adapted to desert climates and is able to withstand high temperatures and desiccation. These lizards feed primarily on vegetation, occasionally also eating small insects.

2.3.4 Family

Chuckwalla Iguanidae

Sci. Name Sauromalus obesus Habitat

Creosote desert in rocky areas

Range

California, Nevada, Utah, Arizona, and Sonora (Mexico)

Notes

The Chuckwalla is the largest local species of lizard. When threatened, chuckwallas have a remarkable defense—they run into a rock crevice and wedge themselves in firmly by taking in gulps of air, inflating their body cavities.

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2.3.5 Family

Horned lizard Iguanidae

Sci. Name Phrynosoma coronatum Habitat

Rocky desert regions

Range

SW North America

Notes

Horned lizards are remarkable in having a flattened body covered with thorny scales, which are thought to act as camouflage in the desert. These lizards eat ants, and have a unique defense mechanism to distract predators—when threatened, they are able to rupture blood vessels in the corners of their eyes and squirt blood to startle a predator.

2.3.6 Family

Jackson’s chameleon Chamaeleonidae

Sci. Name Chamaeleo jacksonii Habitat

Arboreal, living in woodland and areas with dense foliage

Range

Madagascar, India, and east Africa

Notes

True chameleons have the ability to change color for camouflage or to signal to conspecifics. They also have eyes that can be independently rotated and fixed on an object. To catch insects, chameleons can eject their tongue to distances up to twice their body length!

2.3.7 Family

Banded gecko Gekkonidae

Sci. Name Coleonyx variegates Habitat

On and around rocks in chaparral or on barren sand dunes

Range

California to New Mexico, south to Sonora and Ba ja California

Notes

Geckoes are only able to live in deserts because of their nocturnal and subterranean habits. Examine the toes of the specimen – note the tine ridges on the ventral surface. When running, these ridges engorge with blood and conform to the fine surface details of the substrate, ensuring a good grip even on glass!

2.3.8 Family

Two-footed mole lizard Amphisbaenidae

Sci. Name Bipes canaliculatus Habitat

Burrows in sandy soils

Range

Rare, found only along the west coast of Baja California.

Notes

Amphisbaenids are thought by some to be the ancestors to snakes (although most studies support a varanid ancestry). The skull is shovel-like and used to help these animals dig. Note the similarity between Bipes and the caecilians. This is an example of convergent evolution.

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2.3.9 Family

Green tree monitor Varanidae

Sci. Name Varanus prasinus Habitat

Terrestrial or arboreal, found in a wide variety of habitats including deserts, coastal areas, and mountains

Range

New Guinea and Australia

Notes

Monitor lizards are carnivorous and include the largest known lizard, the Komodo Dragon (Varanus komodoensis). This species, however, is an expertly camoflauged arboreal predator. It has a prehensile tail and large scales on its feet to aid in climbing.

2.3.10 Family

Boa constrictor Boidae

Sci. Name Boa constrictor Habitat

Arboreal in tropics and subtropics

Range

Central and South America

Notes

The boa constrictor is ovoviviparous, meaning that females retain and hatch eggs internally. Females are larger, while males have longer tails in which the hemipenes (paired penis) are housed. These boids are common pets, and are generally quite tame.

2.3.11

Rosy boa

Family

Boidae

Sci. Name Lichanura trivirgata Habitat

Rocky brushland and desert

Range

Death Valley, California to Baja California and Sonora

Notes

As with all members of the Boidae, males can be distinguished from females by the presence of two small spurs next to the urogenital slit. These spurs represent vestigial hind limbs.

2.3.12

Sidewinder

Family

Viperidae

Sci. Name Crotalus cerastes Habitat

A desert species, found among wind-blown sand

Range

California, Nevada, Utah, Arizona, and Sonora

Notes

Venomous and viviparous. Has a distinctive “sidewinding” means of locomotion. Note the pointed supraoculars (horns above the eyes). Many members of family Viperidae have heat-sensitive pits on the rostrum, which they can use to detect warm-blooded prey.

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2.3.13 Family

Western diamondback rattlesnake Viperidae

Sci. Name Crotalus atrox Habitat

Arid and semiarid regions in a variety of habitats

Range

California to Oklahoma, south to southernmost Mexico. Common locally.

Notes

A viviparous (live-bearing) snake that is venomous and dangerous. The cost of antivenin for the bite of a diamondback rattlesnake is approximately $60,000. The fangs are hollow teeth that fold against the palate when not in use.

2.3.14 Family

Saw-scaled viper Viperidae

Sci. Name Echis carinatus Habitat

Burrows in desert sands in arid regions

Range

Middle East and North Africa

Notes

Famous for having the most potent venom of any viper, the saw-scaled viper has a warning system similar to rattlesnakes. When threatened, these vipers rub scaled of different parts of their body together to form a loud rasping sound. This is an example of auditory aposematism.

2.3.15

Corn snake

Family

Colubridae

Sci. Name Pantherophis guttatus (formerly Elaphe guttata) Habitat

Fossorial in forests, grassy forests, grasslands, open rocky areas, and abandoned buildings, in dry or humid regions

Range

Native to the Eastern and Southeastern US

Notes

Corn snakes have a variety of coloration patterns, which varies widely by region. Constrictors that feed mostly on rodents, they are generally nocturnal. Because they are docile and non-venemous they are also popular as pets. Their common name is believed to come from the fact that they are often found in agricultural fields, hunting for prey.

2.3.16 Family

Common king snake Colubridae

Sci. Name Lampropeltis getula Habitat

Forests, woodlands, swamps, prairie, chaparral, and desert

Range

throughout the US and northern Mexico

Notes

King snakes display geographic variation in color patterns. They feed on other snakes, even rattlesnakes, although their bite lacks venom. King snakes are classic examples of Batesian mimicry, as their coloration and patterning closely matches that of the venomous coral snake (see below).

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2.3.17 Family

Arizona coral snake Elapidae

Sci. Name Micruroides euryxanthus Habitat

Arid and semiarid regions in a variety of habitats

Range

Arizona, New Mexico, and Sonora

Notes

As with all elapids, the Arizona coral snake is highly venomous. This snake shows Aposematic coloration. To distinguish between the dangerous coral snake and the innocuous king snake, remember the mnemonic “red touches yellow, you’re a dead fellow; red touches black, it’s okay, Jack.”. Better yet, if you see a red, black and yellow snake just leave it alone.

2.3.18 Family

Yellow-bellied sea snake Elapidae

Sci. Name Pelamis platura (sometimes incorrectly identified as P. platurus) Habitat

Marine, pelagic; warm waters far from reefs and coastal areas

Range

Tropical areas of the Indian and Pacific Oceans

Notes

Most other sea snakes live on or near reefs, but the yellow-bellied sea snake is unusual in that they do not. They feed exclusively on fish which shelter beneath them, mistaking the snake for a piece of driftwood. As completely pelagic animals, they never come on land to drink freshwater. Instead, they will swim to the surface when it rains and drink the less dense layer of freshwater collecting at the surface.

→Now that you are familiar with the characteristics of several families, try and evaluate what group the large snake skeleton on the center table belongs to. →What is the most dangerous snake you are able to encounter in a SoCal desert?

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