chapter 29 Vertebrates

Vertebrates

• Derive their name from vertebrae: the series of bones that make up the backbone

• Most recognizable organisms of the Animal Kingdom

• More than 62,000 vertebrate species have been identified

• 3 groups of terrestrial vertebrates alive today: the amphibians, the reptiles (including birds),

and the mammals

• Are members of the phylum Chordata, the chordates

Chordata

1. Subphylum Urochordata

2. Subphylum Cephalochordata

3. Subphylum Vertebrata

Characteristics of Chordates

1. Notochord

• Flexible, rod-shaped structure that runs along nerve chord

• In vertebrates, notochord develops into vertebrae

2. Dorsal hollow nerve cord

• In vertebrates, develops into spinal cord

3. Pharyngeal slits

• Vertebrate fish – develop into gill supports

• In tetrapods (4 limbed vertebrates) –develop into parts of jaws, ears and tonsils

4. Post-anal tail

• Multiple muscle segments

• Undulating locomotion

post-anal tail

Chordates: Cephalochordata

lancelets

Lancelets

-all key chordate features in adult

• burrows tail-in & filter-feeds, cilia draw seawater into the lancelet’s mouth

• gas exchange occurs mainly across the external body surface

Chordates: Urochordata

-Tunicates (“sea squirts”)

Tunicates (“sea squirts”)

• swimming larva has all key chordate features

• Notochord, postanal tail, & dorsal nerve cord absent in adults

• suspension-feeds w/ pharyngeal slits

Chordates : Vertebrate characteristics

• Vertebrae made of cartilage &/or bone enclose spinal cord (dorsal nerve cord).

• Two or more sets of Hox genes

-Endoskeleton:

• Axial Skeleton : skull, vertebrae (backbone), ribs

• Appendicular skeleton : pectoral and pelvic area

-A skeletal system and complex nervous system have

allowed vertebrates efficiency at two essential tasks

• Capturing food

• Evading predators

Vertebrates: Cyclostomes (Jawless)

hagfishes and lamprey

cyclostomes (jawless) characteristics:

• reduced vertebrae

• eel-like bodies & no lateral fins

• no jaw

• keratin teeth

hagfish

• Marine scavengers

• cartilage skull & notochord

• keratinous teeth (aid feeding)

• Defensive slime

lamprey

• jawless parasite on fish

• notochord & cartilaginous skeleton

Vertebrates: Gnathostomes (Jaw)

• Vertebrates w/ hinged jaws

→derived from skeletal rods which supports gill slits

→usually have bony teeth (predation!)

• Larger forebrain (smell & sight)

3 gnathostome “fish” lineages

1. cartilaginous

2. ray-finned

3. lobe-finned

Gnathostomes: Chondrichthyes (cartilaginous)

• All have skeleton of cartilage

• Most diverse group - sharks, rays, skates

• A few ratfishes or chimaeras

• Bone minerals lost to reduce density

- buoyancy raised by liver oils & active swimming

• With bony teeth

• Most are active predators, marine

- but a few filter-feed; some live in fresh water

Reproductive adaptations of Chondrichthyes

• oviparous: eggs “laid” and hatch outside the mother’s body; embryo develops w/in protective egg-case, fed by yolk

• viviparous: the young develop within the uterus; obtain nourishment prior to birth by nutrients from the mother’s blood through a yolk sac placenta; live birth

• ovoviviparous: fertilized egg retained w/in mother; embryo fed by egg yolk; live birth

Gnathostomes: Osteichthyes (bony)

• includes both ray-fin fish & lobe-finned fish

• usually oviparous w/ external fertilization

• skeletons remain mostly ossified (mineralized)

• flat scales & slime protect & reduce drag

• operculum (gill cover) protects & helps pump water over gills

• lungs modified into swim-bladder for buoyancy

ray-fin fish

• thin fins supported by long, flexible rays are modified for maneuvering, defense etc.

• most diverse group of all vertebrates (almost all living bony fish ).

lobe-finned fish

• pelvic & pectoral fins supported w/ bones & muscles

• 3 lineages survive and include coelacanths (Actinistia),

lungfishes (Dipnoi), and tetrapods

tetrapods

• four limbs w/ wrist & digits (key feature)

• neck: head moves independent of body

• pelvic girdle fused to backbone

• lung-breathing as adults (absence of gills: except in some aquatic species)

• ears for detecting airborne sounds

Ancestors of tetrapods

• were lobe-finned, lung-breathing fish

• had many tetrapod features

• Ex: fossil fish Tiktaalik w/ tetrapod features

→Tiktaalik could shuffle in shallow pools & maybe a bit on land.

fish versus tetrapod characteristics

-fish: scales, fins, gills and llungs

-tetrapod: neck, ribs, fin skeleton, flat skull, and eyes on top of skull

Tetrapods: Amphibia

• thin, moist skin; loses H2O easily

• gas exchange w/ air across moist skin & lungs; gulps air like fish

to fill lungs

• larval stage common aquatic, w/ gills; metamorphosis into

carnivorous adult

• almost all are oviparous (fish-like eggs); reproduction is closely

tied to fresh water

• diverse mating behaviors

Amniote Characteristics

Amniotic egg : reproduction freed from water

• amnion protects embryo w/in watery amniotic sac

• other extraembryonic membranes sustain embryo w/

little water loss

• albumen stores water

• porous egg-shell protects, reduces water loss but allows

O2/CO2 exchange (rigidity varies w/ amt. of CaCO3)

• fertilization MUST be internal (before egg shell is made)

Evolution of Amniotes

-The first amniotes evolved from tetrapod ancestors approximately 340 million years ago during the Carboniferous period

-Mammals are the only species that are classified as synapsids

-Reptiles are classified as diapsids

-Turtles are the only ones with anapsids

-Temporal fenestrae of anapsids, synapsids, and diapsids

(Anapsids have no openings, synapsids have one opening, and diapsids have two openings)

Amniotes: Reptiles

• Tetrapods

• Snakes and legless lizards—are classified as tetrapods -- descended from four-

limbed ancestors

• Scaly skin, containing the protein keratin and waxy lipids -- key adaptations that permitted reptiles to live on land

• Cannot use their skin for respiration, like amphibians -- breathe with lungs

• Negative-pressure breathing by expanding rib cage -- more efficient than

“gulping” air by fish & amphibians (positive-pressure breathing)

Amniotes: Archosaurs: Birds

Origin of birds: diverged from a group of bipedal, feathered

dinosaurs called theropods during late Mesozoic Era

Many adaptations for flight:

1. forelimbs modified into wings w/ keratin contour feathers that provide lift

2. skeleton is lightweight but strong

• decrease in the number of bones

• pneumatization of bones (hollow bones)

3. stubby feathered tail for flight maneuvers

4. no teeth: beak of keratin over bone

5. efficient 4-chambered heart

6. highly efficient respiration system w/ air sacs

(negative-pressure breathing)

7. Urogenital adaptations

• no bladder or urethra

• only one ovary

• sex organs functional only during breeding season

• muscular gizzard grinds up food

Mammal Fossil History

• mammals descended from synapsid amniotes which had

mammal traits

• Cynodonts first appeared in the Late Permian period 260 million years ago, are thought to be the ancestors of modern mammal

Mammals: Unique traits

1. mammary glands secrete milk for feeding young

• Extensive parental care

2. hair or fur, primarily for insulation

• also for camouflage, sensing, protection

3. teeth vary in size, shape & number, adapted to many different food types

4. highly developed brain & complex behavior (the highly convoluted and folded cerebral cortex)

Mammals: Unique traits cont.

5. Efficient respiratory and circulatory systems

• ribcage breathing aided by muscular diaphragm

• improves negative pressure breathing

6. digestive tract adaptations for food types

• herbivores have longer tract than carnivores

• cecum can hold mutualistic microbes that digest cellulose

7. sweat glands secrete 99% water for evaporative cooling

8. Kidneys, which conserve water from wastes

mammals

-monotremes

-marsupials

-eutherians

Mammals: Monotremes

• egg-laying mammals

• lay shelled eggs (oviparous)

• young hatch & lap milk (no nipples)

• only echidnas & platypus

-only 1 species of platypus, 4 species of echidna

Mammals: Marsupials

• w/ maternal pouch

embryo starts growing in uterus w/ placenta

• fetus is born at early stage, crawls to pouch

• latches onto nipple to finish development

-marsupials are viviparous

-great diversity in Australia/New Zealand

Mammals: Eutherians

• “placental mammals”

• better placenta for longer gestation

• young more developed at birth

• viviparous

• most diverse and widespread mammals

Mammals: Primate characteristics

Characteristics, related to arboreal life(live in trees):

• hands & feet adapted for grasping

• flat nails on digits

• large brains

• eyes forward

• flat face

Living Primate Groups

1. lemurs and relatives – arboreal

2. tarsiers – arboreal (one of the smallest primates, 3-6 inches in the Phillippines)

3. anthropoids – monkeys, apes & humans

anthropoids – monkeys, apes & humans

-humans and chimpanzees are most closely related

- last common ancestor ~7 mya ago

-old world monkeys: tails can’t grasp, mostly ground-dwelling (baboons and macaque)

-new world monkeys: prehensile tails, arboreal (spider and white-faced monkey)

Apes & humans

-no tail; trees & ground

-A Hominid - any member of the family Hominidae -

Includes living and extinct great apes, modern humans,

orangutans, gorillas, chimpanzees, and bonobos

Homo sapiens

-very recent (200,000 years ago); only hominin (human & human ancestors) today

-characterized by:

• bipedal locomotion,

• ground-dwelling

• much larger brain

• language, complex

tools

• shorter digestive tract

• reduced jaws