Chordate Evolution

7/27/2019 Chordate Evolution

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Directional Terms You Must Know

Caudal towards the tail

Ventral towards the belly

Dorsal towards the back

Anterior towards the head

Posterior towards the rear Lateral to the sides

Medial towards the middle


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Distal farther from the core of thebody

Proximal closer to the core of thebody

Buccal mouth region

Pharyngeal muscular swallowingregion of throat

Integumentary the skin system

Respiratory dealing with gasexchange

Cardiovascular dealing with circulationof blood


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Chordate Evolution


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Four defining characteristics of

the phylum Chordata Notochord

Post-anal tail

Pharyngeal gill slitsor pouches

Dorsal hollow nerve

cord


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Advantages of Chordate

Characteristics Notochord provides stabilizing

structure and muscle attachment =

mobility in water Gill slits/pouches efficient oxygen

delivery system in large bodiedorganisms

Post-anal tail propulsion

DHNC No clear hypothesis why dorsalwould be any better than ventral


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Subphyla of the Chordates

Urochordata tunicates (sea squirts)

Cephalochordata Lancelets

(amphioxus)

Vertebrata more accurately called

Craniata, including anything with a

cranium


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Hypotheses on Vertebrate

Evolution Urochordate Ancestor: (1928) proposes larval

tunicates are ancestor; larval forms retained

form into adulthood and gained gonads toreproduce (paedomorphosis)

Cephalochordate Ancestor: (1991) proposes

a lancelet ancestor due to many fossil forms

that show notochord, myomeres, gillstructure, and caudal projections.


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Vertebrata Groups

Agnathans lampreys and hagfish

Gnathostomesjaw opening

cartilaginous fish, bony fish, amphibians,

reptiles, birds, & mammals


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Hagfish vs Lampreys No jaws

Cartilaginous

skeleton No paired or dorsal

fins

No eyes Many mucus glands

No jaws

Cartilaginous

skeleton No paired fins, but

dorsal fin present

Eyes well developed No mucus glands

AGNATHA


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Hagfish


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Lampreys


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GnathostomesAnimals with Jaws

Hinged jaws were the most importantevolutionary development

Jaw structure is thought to be derived fromthe first gill arch

Jaw was probably at first a hingedmechanism that prevented reflux of waterduring breathing

Jaws allowed new sources of food and newniches

MORE FOOD = BETTER SURVIVAL = MOREBABIES = MORE REPRESENTATIVES

WITH THOSE GENES FOR THE GOODTRAIT


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Jaw Development


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Development of Paired Fins

Paired fins include the pectoral and

pelvic fins.

Pectoral fins are used for balancing andturning

Pelvic fins are for stabilizing motion

Both kinds help control pitch, yaw, and

roll


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Pitch, Yaw, and Roll?!?


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Origin of Paired Fins

Paired fins might have evolved from the

most posterior gill arch, folds of the

body wall, or from spiny appendages

along the body.

The fossil record provides no clear

answer to which hypothesis is accurate

or if more than one may be accurate.


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Acanthoidians (spiny sharks)

that support the idea of fins from

spines


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Paired Finscontinued

Once paired fins arose, wide radiation

of fish groups occurred.

Many fish groups are now extinct, butfish are still the most abundant and

widespread vertebrate


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OsteichthyesChondrichthyes


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PlacodermsMean and Extinct


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Class Chondrichthyescartilaginous

fishSharks

Rays Skates

Chimaeras (Ratfish)


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Chondrichthyan characteristics

Cartilaginous skeleton

No bony structures except in the teeth

and scales

Placoid scales (hooked from the side

view)

Approximately 850 living species,

mostly marine


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Subclasses of the Chondrichthyes

Elasmobranchii sharks, skates, rays

Holocephali chimaeras (also called

ratfish)


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Skates vs Rays


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Skates vs Rays

Dorsoventrally

flattened

Hugely enlargedpectoral fins

More muscular tail

Usually 2 dorsal fins

Lay eggs in cases

Pelvic fin is one lobe

Dorsoventrallyflattened

Hugely enlargedpectoral fins

Whip-like tail

Sometimes

poisonous Dorsal fins usually

absent

Pelvic fin is 2 lobed


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Chimaera Facts Males have a single

clasper on the head

used for clenchingthe female during

mating.

The gills are

covered with afleshy flap.

They have grinding

plates rather thanseparate teeth.

Deep-sea dwellers


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Shark Facts Have 5 to 7 gill slits. Range in size from 7 inches long (dwarf

lanternshark) to 39 feet long (whale

shark)


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Birth Patterns

Oviparous laying eggs outside of the body,most often with external fertilization (salmon,

gray nurse shark)

Ovoviviparous eggs are retained in thefemale body but are not connected to her

during development, internal fertilization

(dogfish, hammerheads, coelacanths)

Viviparous egg is fertilized internally andretains a connection to the mother for

nutrients until birth (bull sharks, surf perch,

guppies, mollies)

S U i Fi h h


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Structures Unique to Fish that

Chondrichthyes and Osteichthyes

Share Lateral line system to detect pressure

waves.

Two chambered heart with single atriumand ventricle.

Have a range of birth patterns from

oviparous, ovoviviparous, to viviparousbirth.


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OsteichthyesThe Bony Fish

Bony Fish have skeletons made of

bone.

The two subclasses exist: the-ray finnedfish (Actinopterygii) and the lobe-finned

fish (Sarcopterygii)

The ray-finned fish comprise 97% of allliving species of fish.


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Sarcoptyergii Lobe-finned fish

have fleshy fins with

internal bones.

Lungfish and

coelacanths belong

to this group.


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Lungfish

Lung is a highlyvascularized swimbladder.

They do also have gills. Gulp air at surface

when oxygen levelsdrop.

Can survive droughtsby burying themselvesinto mucus-linedburrows.


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The Ray-Finned Fish

Ray finned means the fins are webs ofmembrane supported by internal bony

spines called fin rays. Have a bony plate covering the gills,

called the operculum.

Have a symmetrical homocercal tail.

Have a swim bladder used for buoyancyand gas exchange.

Documents

Chordate Evolution