Online Study: Phylum Chordata(Vertebrates)

Phylum Chordata: The Vertebrates

Subphylum Vertebrata

Seven extant classes
- First 3 commonly called fishes
- Remaining 4 called tetrapods (4 feet)
- All possess some form of segmented vertebra

Class Agnatha

Commonly known as Jawless Fish

Include hagfish & Lampreys

Lack paired appendages
Lack bony skeleton
Lack jaws
Usually have circular sucking mouthparts
- Lampreys parasitize other fish

Class Chondrichthyes

Include sharks & rays
Very successful class
Called cartilagenous fishes because skeleton is cartilage not bone
Approx. 750 species
Have paired appendages
Many have acute senses
Sharks have a lateral-line system
- Allows shark to detect water pressure changes

Class Osteichthes

Called Bony fish
Most diverse of all fish
Have skeleton made of bone
Have paired fins
- Allowed evolution of 4 limbed amphibians (tetrapods)
Possess scales for protection
Have bony flap called operculum
- Allows water to be drawn over gills by fins

Have Swim bladder
- Gas content can be manipulated allowing for changes in bouyancy

Class Amphibia

First vertebrates to inhabit land

Most are 4 limbed (tetrapods)

Include frogs, salamanders & caecilians

Include 3 orders

Urodela ("tailed ones" - Salamanders)

Apoda ("tail-less ones" - Frogs & toads)

Caecilia ("legless ones")

Lack internal fertilization & amniotic eggs
- Reproduction must occur in H₂O

Most species undergo metamorphosis

Larval stage (tadpole) is usually an aquatic herbavore
Lacks legs, respiration is through gills
Develops into tetrapod adult (usually carnivorous)

Frog Metamorphosis

Gas Exchange is usually through a combination of lungs, gills and skin

Class Reptilia

Includes lizards, snakes, turtles, and crocodilians

Over 7000 species
Possess several advanced features over amphibians
All adaptations towards independence from H₂O
Possess scales containing keratin

Keratin is a waterproofing protein which prevents water loss in an organism

Possess an amniotic egg.

Prevents water loss of embryo. Allows for eggs to be laid on dry land
Combined with internal fertilization, allows reptiles to reproduce independently of water

Reptilian Amniotic Egg

Reptiles are "cold blooded" or ectotherms

Cannot internally regulate body temperatures
Reptiles can regulate body temperatures behaviorally (eg. Basking or swimming)

Nutritional requirements are lower than warm blooded animals

Modern Reptiles
3 Extant orders of reptiles

Order Chelonia (Turtles)

Inhabit aquatic and terrestrial environment.
Are herbavores, carnivores, and omnivores
Characterized by possessing a dorsal hard shell
- Made from bone, extensions of backbone and rib cage

Order Squamata (Lizards & Snakes)

Most numerous & diverse of the reptiles
Most relatively small Although monitors and their relatives can grow to 6' in length
Herbavores, carnivores & omnivores
Most able to exhibit some form of hibernation

Order Crocodilia (Crocodiles, Alligators, & Caimans)

Largest extant reptiles
Primarily aquatic they are true reptiles
Inhabit warm, tropical climates
Order most closely related to the dinosaurs

Class Aves

General Bird Anatomy

Evolved from dinosaurs during Mezozoic era.

Aminotic eggs and scales on legs reminants of reptilian origins

Almost all adaptations of these animals are made for flight.
- Made of keratin

Forelimbs developed into wings

Honeycombed, light bone structure

Types of feathers

Absence of some organs

Females usually have 1 ovary
Absence of teeth lighten head
- Replaced by gizzard in abdomen & beak
Beak made of keratin
Proven very adaptable structure, having a variety of shapes for differing diets

Beak Types

Birds are the first extant endothermic organisms

Regulate body temperature internally

Metabolic rate is therefor increased and is compensated by the following adaptations

Efficient circulatory system with a 4 chambered heart
Efficient lungs
Increased nutritional demands

Birds have well developed senses especially vision

Larger brains than reptiles

Reproduction is through hardened amniotic eggs

Since birds are endothermic, these must be kept warm by parents

This behavior called brooding

Bird amniotic egg

Birds have also adapted feet for varying ecological niche

Modern Birds

Over 8600 species & 20 orders of birds
Classified into 2 general groups
Flightless species including ostrich, emus, & kiwis are known as ratites

Lack sternal keel on breastbone
Lack strong breast muscles needed for flight

Ostrich: a ratite

Other species capable of supporting flight called carinates

60% are "perching birds" called passeriforms

Possess a sternal keel on breastbone

Support strong breast muscles required for flight

The sparrow: A passeriform carinate

Class Mammalia

Approx. 4500 species of mammals
Evolved from mammal-like reptiles called therapsids in the triassic period
Diversified greatly following the extinction of dinosaurs

Mammilian Characteristics

Have Hair
Made of keratin
Aids in maintaining body temperature

Endothermic
Maintain body temperature internally

Have efficient respiratory system including a diaphragm

Efficient circulatory system with a 4-chambered heart
Most possess placentas and give birth to live young
Have mammary glands to produce milk for offspring
All show parental care of offspring
Have largest brains of all vertebrates
Have differentiated teeth
- Unlike earlier vertebrates, several different teeth can exist in mammal jaws
- Eg. The molars & incisors in the human jaw