Chapter 34:

Vertebrates

(sea squirtsthrough birds)

Chor

date

Phy

loge

ny

Chordate Characteristics

Subp

hylu

m U

roch

orda

ta

The urochordates include the tunicates, a.k.a., sea

squirts

The tunicates are mostly

sessile, filter feeding animals that look almost

nothing like a chordate

However, their larval form possesses all of

the basic characteristics of a

chordate

Tunicate: Urochordate

Tuni

cate

Lar

va

The notochord serves as a primitive internal support

structure

Subp

hylu

m

Ceph

aloc

hord

ata

Cephalochordates, the lancelets, retain a chordate body plan

throughout life

In addition to the four defining chordate

characteristics, lancelets, as well as

tunicate larvae, have somites

Somites are blocks of musculature arranged in

segments along the bodies of lancelets and fishes (as well as

derivations of this segmentation found in

tetrapods)

Lancelet: Cephalochordate

Clas

s M

yxin

i

Class Myxini are represented in

modern times by the hagfish

Technically hagfish are not fish; they

are more like “sophisticated”

lancelets

Hagfish, a Craniate

Not

ocho

rd, N

erve

Cor

d, E

tc.

In more modern forms, the notochord exists during development but is modified with development, e.g., into the gelatinous material of the intra-vertebral disks

Clas

s Ce

phal

aspi

dom

orph

i

Class cephalaspidomorphi

is represented in extant lineages by

lampreys

Jawless fish were the vertebrate

forerunners of the jawed fish

Lampreys in addition lack paired fins

Lamprey: Jawless Vertebrate

Lamprey have vertebrae (backbones) but no jaw

As vertebrates, lampreys are (just barely) members

of subphylum Vertebrata

Lamprey Larvae are like Lancelets

Lamprey larvae are suspension feeders that resemble lancelets, even burying themselves

in sediment as to lancelets

Early (and armored) Jawless Fish

Supe

rcla

ss G

nath

som

ata

Jawed fish are referred to as gnathostomes

(superclass gnathsomata) for

their defining feature: jaws

Jawed fish also have skulls, vertebrae, and

paired appendages (fins)

Early

Gna

thos

tom

es

Many vertebrate characteristics are

adaptations to vigorous

swimming

Jaws, of course, aid in

eating

Especially carnivorous

eating…

Clas

s Ch

ondr

icht

hyes

Class Chondrichthyes includes the sharks and

rays

Members of this class are named for their

cartilaginous skeletons, i.e., unmineralized (or

less mineralized/ossified) skeletons

Class Chondrichthyes Members

The

Ost

eich

thya

ns

These are bony fish, both ray-

finned and lobe-finned fish

Ost

eich

thya

ns a

re B

ony

Fish The bony fish are all of the fish you are familiar with

except the sharks, rays, and chimaeras The skeleton of bony fish displays ossification, i.e.,

calcium phosphate in addition to the cartilaginous base Bony fish additionally possess flattened scales Bony fish

also secrete mucus onto their skin to aid in reducing their coefficient of drag

Bony fish additionally possess a gas-filled swim bladder that allows them to adjust their buoyancy to match that of the water

• Sharks and rays lack a swim bladder and consequently sink when not moving

Clas

s Ac

tinop

tery

gii

Members of class Actinopterygii are

the ray-finned

The lobe-finned fish are members of

Sarcopterygii

Anatomy of a Ray-Finned Fish

Clas

s Ac

tinis

tia

A Coelacanth

Lobe fins are supported by musculature and a bony skeleton; they may be employed for “walking” upon the bottom and other substrate found within bodies

of water

Clas

s D

ipno

i

Members of class Dipnoi are the lung

fish

The lungfish are named for the lungs they retain and use

for gulping air, especially when air is less readily available

within the freshwaters in which

they reside

Vario

us E

xtan

t Lun

gfish

Clas

s Am

phib

ia

Amphibians are the lineage descended from the earliest

tetrapods: the terrestrial

vertebrates

Vario

us E

xtan

t Am

phib

ians

The amphibians were the dominant terrestrial vertebrates during the

Carboniferous period, i.e., the same time the seed-less, vascular plants dominated

the land

Most amphibians are dependent on the water, minimally for reproduction; this is

because their eggs are not desiccation resistant

In addition, many amphibians employ their skin for gas exchange, thus

requiring that their skin remain moist

Thus, amphibians tend to be not as well-adapted to long term, especially multi-

generational excursions away from moist habitats

Tetr

apod

s The tetrapods are the

terrestrial descendants of

some lobe-finned fish,

starting approximately

with the amphibians

Reconstruction of an Extinct Tetrapod

Clas

s Re

ptilia

Note how the reptiles are indicated as

sister group to the mammals

In fact, the reptiles and mammals

together form a clade known as the

amniotes

The defining features of the amniotes are keratinized

(waterproof) skin and the amniotic

(shelled) egg

Class Reptilia, Examples

Clas

s Re

ptilia

is P

arap

hyle

tic

Class Reptilia, if it excludes the birds, is paraphyletic

The Amniotes

The amniotes were the first fully

terrestrial vertebrates,

achieving true freedom from

water except, of course, for the need to drink

Amniotic Egg

The amniotic egg is shelled, an adaptation to desiccation

prevention

The amniotic egg employs extraembryonic membranes to transfer stored nutrients and water,

exchange gasses, and remove wastes

The

Amni

ote

Phyl

ogen

y

Gia

nt A

quati

c Re

ptile

s

Non-Archosaur Giant Reptiles (i.e., these are

lizards!)

Clas

s Av

es –

Bird

s Members of class Aves (birds) have…• Feathers• Forelimbs modified as wings• Horny bills made of keratin (feathers and hair are

also made of keratin)• No teeth (reduces weight)• Grind their food in a gizzard (since no teeth)• Reduced or absent organs (reduces weight)• Hollow bones (reduces weight)• Acute vision (e.g., high-speed tree-branch avoidance) Some of these adaptations were present in the

dinosaur ancestors of birds (e.g., possessing gizzard, bipedalism, feathers, etc.)

Feathers and Light-Weight Bones

Archaeop

teryx

More primitive extinct birds were more saurischian

dinosaur like