The Chordates

All chordates have:  Dorsal nerve (Spinal) cord  Notochord or backbone/vertebrae  Tail (at some stage of the life cycle)  Gill Slits (at some stage of the life cycle)

General Chordate Body Plan

Vertebrata -Some of the 5 chordate features are evident only during development - Embryonic vertebrates have: - a notochord - dorsal nerve chord - gill slits/pouches (pharyngeal clefts)

Compared to the Invertebrates, the Chordates are: – Smarter – Larger – Faster –More coordinated

Why a spinal cord?  Allows for better nerve conduction to the brain from a longer body.  Messages can travel faster  Organisms can grow larger and still be able to send nerve signals effectively.

Why a backbone (Vertebrae)?  Added strength and rigidity for an elongated body,  Protection for the spinal cord  Muscle attachment sites  Organisms can grow larger and have larger muscles.

Why a Tail?  An adaptation for locomotion,  Improves balance  Improves forward movement (propulsion)

Why Gill Slits?  Greater exchange of respiratory gases is needed for larger organisms.  Also thought to be the structures from which jaws evolved.

7 Classes of Chordata Agnatha Chondrichthyes (cartilaginous fish) Osteichthyes (boney fish) Amphibia Reptilia Aves (bird) Mammalia

The Fish Common Features: Skull Bones (either cartilaginous or calcified) Jaws (which evolved from gill slits) Fins (paired appendages, different from the appendages of the invertebrates)

The first 3 classes are often grouped under the heading “Fish” Agnathans Chondrichthyes Osteichthyes

Agnathans Jawless Cartilaginous skeletons E.g - Lampreys and hagfish

Why Jaws Evolved  Gill openings in the head became enlarged and fitted with teeth  Allowed organisms to consume huge chunks of food, allowing fish to grow to enormous size.

Other Interesting Facts about Fish: Have a 2 chambered heart & a closed circulatory system Are cold blooded (ectotherms) Sexually reproduce, but use external fertilization –Sharks have 2 penises Produce jelly-like eggs that must be laid in water

Chondrichthyes Skulls smaller – lighter weight Skeletons of cartilage – very flexible and light weight – for greater agility and speed Sharks and Rays

Osteichthyes The Bony Fishes Two types: 1) Lobe Finned Fish 2)Teleosts

Lobe Finned Fish Fins in the shape of lobes, allowing them to walk on pond bottom or even on land Also had primitive lungs for breathing – did not have to rely on gills, could be out of water for short periods of time Modern day lung fish and coelocanthes evolved from the lobe finned fish Amphibians likely evolved from lobe finned fish too

Teleosts – Spiny Finned Fish Modern fish - name a fish and it’s probably a teleost !! Fins have spines in them for support Have a swim bladder to help them be buoyant at any depth

Amphibians Frogs, toads, newts and salamanders In addition to the innovations accomplished by fish, amphibians have: Legs that extend sideways – awkward for both swimming and walking – but better than lobes Lungs – (though the lobe finned lung fish also had lungs) 3 chambered heart

Crocodiles & Snakes Reptiles Turtles & Lizards

And Don’t Forget… Dinosaurs were reptiles too!!

Reptile Evolution: Dry scaly skin (prevented drying out of skin, but also prevented breathing through skin) Expandable rib cage (allowed them to inflate their lungs to a large volume) Leather shelled amniote eggs (allowed them to lay their eggs away from water)

Copulatory organs (i.e. a penis - for internal fertilization – the only way for sperms to get to eggs when animals are living on land !!) Legs extending beneath the body (for better locomotion & supporting more weight) 3 & ½ chamber heart (for better separation of oxygenated and deoxygenated blood – richer blood = more energy)

Birds Improvements over reptiles include: Feathers (for insulation and flight) Hollow bones (lighter weight for flight)

Warm blooded (allowing for greater energy production) Air sacs (for greater surface area and gas exchange) 4 chamber heart (for complete separation of oxygenated and deoxyg. blood = richer blood = more energy) Hard shelled amniote egg (more protection from drying out and from predators)

Mammals In addition to warm blood and a 4 chambered heart, mammals also possess: Milk and Mammary glands (to nourish young) Body hair (for insulation) 3 groups: placentals, monotremes, and marsupials

Placentals Possess a placenta which supports the growth of the embryo until birth – better chance of survival

Monotremes Lay leathery eggs (like reptiles) Echidna (spiny ant-eater) platypus

Marsupials Give birth to an immature live young - no larger than a kidney bean Wombats, opossums, kangaroos, koalas

How well do you know your classes of Chordates?

To which class do I belong?

The End!