Chapter 25.6 Vertebrates

This textbook is designed specifically for Kansas State's Biology 198 Class. The course is taught using the studio approach and based on active learning. The studio manual contains all of the learning objectives for each class period and is the record of all student activities. Hence, this textbook is more of a reference tool while the studio manual is the learning tool.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/[e-mail] is licensed under a Creative Commons Attribution License 4.0 license.

Episode Transcript

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Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is Chapter twenty five
point six Vertebrates. All hyperlinks,images and sources can be found at the

(00:22):
link to the book. In thedescription, the development of the vertebrate proceeds
from an axis upward in two layerswhich coalesce at the edges, and also
downward in two layers, which likewisecoalesce at the edges. Thus two main
tubes are formed, one above theother. During the formation of these,
the embryo separates into strata, sothat the two main tubes are composed of

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subordinate tubes which enclose each other asfundamental organs, and are capable of developing
into all the organs. Carl Ernstvon Baer, German Embryologist, eighteen twenty
eight. Vertebrates are the largest andprobably the most recognizable organisms of the animal
kingdom. Figure more than sixty twothousand vertebrate species have been identified. The

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vertebrate species now living represent only asmall portion of the vertebrates that have existed.
The best known extinct vertebrates are thedinosaurs, a unique group of reptiles
reaching sizes not seen before or sinceterrestrial animals. Photois shows a tiger and
cub in the snow. Photobee showsa yell of frog with black spots sitting
on a leaf. Photoca shows aneagle with a white breast, brown wings,

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and gray face. Examples of criticallyendangered vertebrate species include A the Siberian
tiger Panthera Tigris altaica, B thePanamanian golden frog A Tealipis sedache and see
the Philippine eagle Pithecophaga Jeoffrey I.Credit A modification of work by Dave Pape
credit Bee modification of work by BrianGradwick creditc modification of work by Quadric seventy

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seven slash Flicker Fishes. Modern fishesinclude an estimated thirty one thousand species.
Fishes were the earliest vertebrates, andjollous fishes were the earliest of these jollous
fishes, the present day hag fishesand lampreys have a distinct cranium and complex
sense organs, including eyes, distinguishingthem from the invertebrate chordates. The jawed

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fishes evolved later and are extraordinarily diversetoday. These include the cartilaginous fishes each
e rais and sharks with a skeletonmade of cartilage, and the bony fishes,
which have a bony skeleton. Allfishes are active feeders rather than sessile
suspension feeders. Jollous fishes jollus fishes. Photois shows wormlike hagfish clustered in a

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muddy hole. Photobee shows leechlike sealampreys latched onto a large fish. A.
Jollous fishes include sixty seven species ofhag fishes. These pacific hag fishes
are scavengers that live on the oceanfloor. B lampreys are another type of
jollous fish. These parasitic sea lampreysattached to their lake trout host by suction

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and use their rough tongues to raspaway flesh in order to feed on the
trout's blood. Credit a modification ofwork by Linda Snook Noah slash cbnms kredit
bee modification of work by USGS.Jawed fishes cartilaginous fishes. Photo as shows
a shark with a wide snout.Photobee shows a stingray with a long,

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thin body in a circular head restingon the sandy bottom. The jawed fishes
include the clade chondric These fishes withskeletons made of cartilage, and these include
the sharks and rays. A.This hammerhead shark is an example of a
predatory cartilaginous fish. B. Thisstingray blends into the sandy bottom of the
ocean floor when it is feeding orawaiting prey. Credit A modification of work

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by Masashi Sugawara kredit bee modification ofwork by saim one slash flicker. Sharks
reproduce sexually in eggs are fertilized inInternally. Most species are oviviparous bad is.
The fertilized egg is retained in theoviduct of the mother's body, and
the embryo is nourished by the eggyolke. The eggs hatch in the uterus
and young are born alive and fullyfunctional. Some species of sharks are oviparous.

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They lay eggs that hatch outside ofthe mother's body. Embryos are protected
by a shark egg case or mermaid'spurse. That has the consistency of leather.
The shark egg case has tentacles thatsnag in seaweed and give the newborn
shark cover. A few species ofsharks are viviparous. Bad is the young
developed within the mother's body and shegives live birth. Raisin skates include more

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than five hundred species and are closelyrelated to sharks. They can be distinguished
from sharks by their flattened bodies,pectoral fins that are enlarged and fused to
the head, and gill slits ontheir ventral surface figure ebb. Like sharks,
rays and skates have a cartilaginous skeleton. Most species a marine and live
on the seafloor, with nearly aworldwide distribution. Bony fishes members of the

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clayde ostik. These or bony fishes, are characterized by a bony skeleton.
The vast majority of present day fishesbelong to this group, which consists of
approximately thirty thousand species, making itthe largest class of vertebrates in existence today.
The illustration compares a bright red salmonA and a blue selicanth B,

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both of which are similar in shapeand have fins. The a sakey salmon
and b. Selicanth are both bonyfishes of the ostik these clayde The selicanth,
sometimes called the lobe fin fish,was thought to have gone extinct in
the Late Cretaceous period one hundred millionyears ago until one was discovered in nineteen
thirty eight between Africa and Madagascar.Credit A modification of work by Timothy knapp

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USFWS credit b modification of work byRobbie Cotta. Amphibians Amphibians are vertebrate tetrapods.
Amphibia includes the familiar frogs, toads, and salamanders, as well as
the kisilians, limbless amphibians that superficiallyresemble worms and snakes. The term amphibian
means dual life, which is areference to the metamorphosis that many frogs undergo

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from a tadpole to an adult andthe mixture of aquatic and terrestrial environments in
their life cycle. Amphibians evolved inthe Devonian period and were the earliest terrestrial
tetrapods. Amphibian diversity. Amphibia compriseand estimated six thousand, five hundred extant
species that inhabit tropical and temperate regionsaround the world. Amphibians can be divided

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into three clades uridilla tailed ones thesalamanders and nuts and eura tell less ones,
the frogs and toads, and apodalikeless ones the kisilians, frogs and
salamanders. Photo shows a black salamanderwith bright yellow spots. Photobee shows a
big, bright green frog sitting ona branch. There are about five hundred

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species of salamanders and five thousand speciesof frogs worldwide. A Salamanders are terrestrial
animals, but most are commonly foundonly near water b The Australian green tree
frog is a nocturnal predator that livesin the canopies of trees near a water
source. Credit a modification of workby Valentina Storty credity modification of work by

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Evan Pickett. Keysilians comprise an estimatedone hundred and eighty five species. They
lack external limbs and resemble giant earthworms. They inhabit soil and are found primarily
in the tropics of South America,Africa, and Southern Asia, where they
are adapted for a soil burrowing lifestyleand are nearly blind. Unlike most of

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the other amphibians that breed in ornear water. Reproduction in a drier soil
habitat means that keysilians must utilize internalfertilization and most species give birth to live
young figure. The photo shows alarge wormlike animal in an aquarium. The
body is segmented and it has asmall mouth and very small eyes. Keycilians

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lack external limbs and are well adaptedfor a soil burrowing lifestyle. Credit modification
of work by Cliff ten sixty sixslash flicker Reptiles and birds. The amniotes,
reptiles, birds, and mammals aredistinguished from amphibians by their terrestrially adapted
shelled egg in an embryo protected byamniotic membranes. The evolution of amniotic membranes

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meant that the embryos of amniotes coulddevelop within an aquatic environment inside the egg.
This led to less dependence on awater environment for development and allowed the
amniotes to invade drier areas. Thiswas a significant evolutionary change that distinguished them
from amphibians, which were restricted tomoist environments due to their shell less eggs.

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Although the shells of various amniotic speciesvery significantly. They all allow retention
of water. The membranes of theamniotic egg also allowed gas exchange and sequestering
of wastes within the enclosure of anegg shell. The shells of bird eggs
are composed of calcium carbonate and arehard and brittle, but possessed pores for
gas and water exchange. The shellsof reptile eggs are more leathery and pliable.

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Most mammals do not lay eggs,however, even with internal gestation,
amniotic membranes are still present. Inthe past, the most common division of
amniotes has been into classes Mammalia,reptilia, and avies. Birds are descended,
however, from dinosaurs, so thisclassical scheme results in groups that are
not true clades. We will discussbirds as a group distinct from reptiles,

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with the understanding that this does notreflect evolutionary history. Reptiles. Reptiles are
tetrapods limbless reptiles. Snakes may havevestigial limbs, and like kecilians are classified
as tetrapods because they are descended fromfour land ancestors. Reptiles lay shell eggs

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on land. Even aquatic reptiles likesea turtles, return to the land to
lay eggs. They usually reproduce sexuallywith internal fertilization. Some species display over
viviparity, with the eggs remaining inthe mother's body until they are ready to
hatch. Other species are viviparous,with the offspring born alive. One of

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the key adaptations that permitted reptiles tolive on land was the development of their
scaly skin containing the protein keratin andwaxy lipids, which prevented water loss from
the skin. This eclusive skin meansthat reptiles cannot use their skin for respiration
like amphibians, and thus all mustbreathe with lungs. In addition, reptiles

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can serve valuable body water by excretingnitrogen in the form of uric acid paste.
These characteristics, along with the shelledamniotic egg, were the major reasons
why reptiles became so successful in colonizinga variety of terrestrial habitats far from water.
Reptiles or ectotherms, that is,animals whose main source of body heat
comes from the environment. Behavioral maneuverslike basking to heat themselves or seeking shade

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or burrows to cool off help themregulate their body temperature. Class Reptilia includes
diverse species classified into four living clates. These are the Crocodilia, Sphenodontia,
squamida, and testudines. The Crocodiliasmall lizard arose approximately eighty four million years
ago and living species include alligators,crocodiles, and caymans. Crocodilians Figuria lived

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aout the tropics of Africa, SouthAmerica, the southeastern United States, Asia,
and Australia. They are found infreshwater habitats such as rivers and lakes,
and spend most of their time inwater. Some species are able to
move on land due to their semierect posture. Photo shows a crocodile sitting

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in the mud. Photobeach shows agreen lizard with its tail curled like a
snail shell. The lizard has twohorns and matches the leaves of the plant
on which it sits. Photoc showsa snake with orange and black bands and
white stripes. Photo D shows avery large tortoise. Crocodilians such as this

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Siamese crocodile provide parental care for theiroffspring b This Tuatara Sphenodon punctatus is one
of only two species in the Sphenodontiaand is found only in New Zealand.
C. The garter snake belongs tothe genus Damnophus, the most widely distributed
reptile genus in North America. D. The African spurred tortoise lives at the

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southern edge of the Sahara Desert.It is the third largest tortoise in the
world. Credit A modification of workby Cache of Mucuan Cantodai. Credit B
courtesy of David A. Ringtoul CreditC modification of work by Steve Jurvitzen.
Credit D modification of work by JimBowen. The Sphenodontia wedge tooth arose in

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the message zoic Era and includes onlyone living genus, the Tuoatara, with
two species that are found in NewZealand. Figure EBB. There are many
fossil species extending back to the Triassicperiod two hundred and fifty to two hundred
million years ago. Although the twoataras resemble lizards, bear anatomically distinct and
share characteristics that are found in birdsand turtles. Squamida scaly burrows in the

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Late Permian, living species include lizardsand snakes, which are the largest extant
clad of reptiles. Lizards differ fromsnakes by having four limbs, eyelids,
and external ears, which are lackingin snakes. Lizard species range in size
from chameleons and geckos that are afew centimeters in length to the Komodo dragon,
which is about three meters in length. Snakes are thought to have descended

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from either burrowing lizards or aquatic lizardsover one hundred million years ago. Figurac
snakes comprise about three thousand species andare found on every continent except in Arctica.
They range in size from ten centimeterlong freads snakes to seven point five
meter long pythons and anacondas. Allsnakes are carnivorous and eat small animals,

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birds, eggs, fish, andinsects. Turtles are members of the Claye
testudines, having a shell. FiguredTurtles are characterized by a bony or cartilaginous
shell made up of the carapace onthe back and the plastron on the ventral
surface, which develops from the ribs. Turtles arose approximately two hundred million years

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ago, predating crocodiles, lizards,and snakes. Turtles lay eggs on land,
although many species live in or nearwater. Turtles range in size from
the speckled pabloper tortoise at eight centimetersthree point one inches to the leather back
sea turtle at two hundred centimeters oversix feet. The term turtle is sometimes

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used to describe only those species oftestudines that live in the sea, with
the terms tortoise and terrapin used torefer to species that live on land and
in fresh water, respectively. Birds. Fossil and genomic data now suggest that
birds belong within the reptile clade,but they display a number of unique adaptations
that set them apart. Unlike thereptiles, birds are endothermic, meaning they

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generate their own body heat through metabolicprocesses. The most distinctive characteristic of birds
is their feathers, which are modifiedreptilian scales. Birds have several different types
of feathers that are specialized for specificfunctions, like contra feathers that streamline the
bird's exterior and loosely structured down feathersthat insulate FIGUREA current thinking is that some

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dinosaurs, the ancestors of modern birds, were also endothermic feathers, not only
permitted the earliest birds to glide andultimately engage in flapping flight, but they
insulated the bird's body, assisting themaintenance of endothermy even in cooler temperatures.
Powering a flying animal requires economizing onthe amount of weight carried. As body

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weight increases, the muscle output andenergetic cost required for flying increase. Birds
have made several modifications to reduce bodyweight, including hollow or pneumatic bones figure
ab with air spaces that may beconnected to air sacks, and cross linked
struts within their bones to provide structuralreinforcement. Parts of the vertebral skeleton and

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brain case are fused to increase itsstrength while lightening its weight. Most species
of bird only possess one ovary ratherthan two, and no living birds have
teeth in their jaw, further reducingbody mass. Illustration as shows a bird's
wing which has two sections of flightfeathers, the long primary feathers toward the
tip of the wing and the secondaryfeathers closer to the body. Illustration bee

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shows a hollow bone with structural supportsproviding reinforcement. A primary feathers are located
at the wing tip and provide thrust. Secondary feathers are located close to the
body and provide lift be Many birdshave hollowneumatic bones, which make flight easier.
Birds possess a system of air sacksbranching from their primary airway that divert

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the path of air so that itpasses unidirectionally through the lung during both inspiration
and expiration, Unlike mammalion lungs,in which air flows in two directions as
it is breathed in and out,air flows continuously through the bird's lung to
provide a more efficient system of gasexchange. Mammals. Mammals are vertebrates that
have hair and mammary glands used toprovide nutrition for their young. Certain features

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of the jaw, skeleton, skin, and internal anatomy are also unique to
mammals. The presence of hair isone of the key characteristics of a mammal,
although it is not very extensive insome groups, such as whales.
Hair has many important functions for mammals. Mammals are endothermic, and hair provides
insulation by trapping a layer of airclose to the body to retain metabolic heat.

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Hair also serves as a sensory mechanismthrough specialized hairs called vibrasi, better
known as whiskers. These attached tonerves that transmit touch information, which is
particularly useful to nocturnal or burrowing mammals. Hair can also provide protective coloration.
The skeletal system of mammals possesses uniquefeatures that differentiate them from other vertebrates.

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Most mammals have heterodont teeth, meaningthey have different types and shapes of teeth
that allow them to feed on differentkinds of foods. These different types of
teeth include the incisors, the canines, primolars, and molars. The first
two types are for cutting and tearing, whereas the latter two types are for
crushing and grinding. Different groups havedifferent proportions of each type depending on their

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diet. Most mammals are also diffiodonts, meaning they have two sets of teeth
in their lifetime, deciduous or babyteeth and permanent teeth. In other vertebrates,
the teeth can be replaced throughout life. Modern mammals are divided into three
broad groups monotremes, marsupials, andeutherians mammals with a placenta, the Eutherians

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and the Marsupials collectively are called threein mammals, whereas monotremes are called metatherians.
There are three living species of monotremes, the platypus and two species of
Echidnas or spiny anteaters. Figure.The platypus and one species of Echidna are
found in Australia, whereas the otherspecies of Echidna is found in New Guinea.

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Monotrims are unique among mammals as theylay leathery eggs similar to those of
reptiles, rather than giving birth tolive young. However, the eggs are
retained within the mother's reproductive tract untilthey are almost ready to hatch. Once
the young hatch, the female beginsto secrete milk from pores in a ridge
of mammary tissue along the ventral sideof her body. Like other mammals,

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monotrems are endothermic, but regulate bodytemperatures somewhat lower ninety degrees fahrenheit thirty two
degrees celsius than placental mammals due ninetyeight degrees fahrenheit thirty seven degrees celsius.
The illustration on the left shows twoshort haired platypus with webbed feet, flat
tails, and a flat snout.The photo on the right shows an echidna

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with a long, fleshy snout anda body covered in coarse hair and spines.
The platypus left, a monotreme,possesses a leathery beak and lays eggs
rather than giving birth to live youngand Echidna. Another monotreme, is shown
in the right photo credit Achidna modificationof work by Barry Thomas. Marsupials are
found primarily in Australia and nearby islands, although about one hundred species of possums

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and a few species of two otherfamilies are found in the Americas. Australian
marsupials number over two hundred and thirtyspecies and include the kangaroo, koala,
bandicoot, and Tasmanian devil figure.Most species of marsupials possess a pouch in
which the young reside after birth,receiving milk and continuing to develop. Before

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birth, Marsupials have a less complexplacental connection, and the young are born
much less developed than in placental mammals. The illustration shows an animal resembling a
small bear lying in the grass TheTasmanian devil is one of several marsupials native
to Australia. Credit Wayne McLean Eutheriandiversity for mammals, bat ant eater,

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dolphin cat for Eutherian mammals, Achiropteran, the Mexican longtowned bat Cornictorus mexicana,
feeding on sugar water at a hummingbirdfeeder. These bats pollinate many varieties
of cactuses and agavies, including theblue agavi that is used to make tequila
beat pink river dolphin India geofransis afreshwater cetacean found in the Amazon River and

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its tributaries see as a narthrin.The giant anteater or Tamandua Tamandua tetradactyla hunting
for termites in the pantanol of Brazild a member of the order Carnivora.
The domestic cat Felis catus photocredits davida, ringtoul Eutheria are the most widespread of
the mammals occurring throughout the world.There are several groups of Eutherians, including

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Insectivora, the insect eaters, Zinarthra, the toothless anteaters, Redentia, the
rodents, Chiroptera, the bats,Cetacea, the aquatic mammals including whales,
Carnivora, carnivorous mammals including dogs,cats, and bears, and primates,
which includes humans. Eutherian mammals aresometimes called placental mammals because all species have

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a complex placenta that connects a fetusto the mother, allowing for gas,
fluid, waste, and nutrient exchange. While other mammals may possess a less
complex placenta or briefly have a placenta, all Eutherians have a complex placenta during
gestation. This podcast will be releasedepisodically and follow the sections of the textbook

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in the description For a deeper understanding, We encourage you review the text version
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