Biological Principles II
Animal Flashcard Activity (Chordates)
1. We have previously divided the animal flashcards as shown below:
METAZOA
(Kingdom Animalia)
EUMETAZOA
(cells organized into true tissues)
Sponges
Diploblasts/Radiates
64, 87
Cnidarians:
66, 94, 100
Ctenophores:
78
Triploblasts/Bilaterians
12
62, 63, 65, 67, 68, 69
70, 71, 72, 73, 74, 75, 76, 77, 79
80, 81, 82, 83, 84, 85, 86, 88, 89
90, 91, 92, 93, 95, 96, 97, 98, 99
101, 102, 103, 104, 105, 106,
107, 108, 109, 110
e bilaterians are broken
down into three clades based
on molecular data.
Lophotrochozoans
68
73, 76, 77
81, 82
97
101
Ecdysozoans
67, 69
83, 84, 85, 86, 89
104
Deuterostomes
12
62, 63, 65
70, 71, 72, 74, 75, 79
80, 88
90, 91, 92, 93, 95, 96, 98, 99
102, 103, 105, 106, 107, 108, 109, 110
ere are two major
deuterostome phyla.
Echinoderms
70, 90
Chordates
12
62, 63, 65
71, 72, 74, 75, 79
80, 88
91, 92, 93, 95, 96, 98, 99
102, 103, 105, 106, 107, 108, 109, 110
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METAZOA > EUMETAZOA > BILATERIA > CHORDATA
2. All chordates, at some point in their lives,
possess four shared derived characters:
a hollow, dorsal nerve cord
a notochord (a firm cartilaginous rod
that is used as the site of muscle
attachment for swimming)
a series of subdivided pouches behind
the mouth called pharyngeal clefts that
can develop into slits that become open
to the outside environment
a muscular post-anal tail
3. Separate out #93 and #91. ese represent the two most basal groups of chordates:
Lancelets
• Named for their bladelike shape
• Retain all four chordate traits
throughout their lives
Tunicates
• Only possess all four chordate
traits as larvae
• Undergo a radical
metamorphosis and become
sessile
4. e remaining chordates will begin to dramatically modify their body plans, resulting in
increasing leaps of complexity.
CRITICAL INNOVATION #1: Craniation
5. e first critical innovation observed in the chordate lineage is the appearance of a head or
cranium.
Craniates possess a brain at one end of their nerve cord.
is brain is encased in a skull and is connected to complex sense organs.
eir brains allow craniates to coordinate more complex movement and feeding patterns.
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6. Separate out flashcard #96.
Hagfish:
• Hagfish are the least derived of the living
craniates.
• ey have a skull made of cartilage, but lack
jaws and vertebrae.
• ey use their notochord to swim in a
snakelike fashion.
• Live mostly as bottom-dwellers where they
scavenge.
CRITICAL INNOVATION #2: Vertebral Columns (Backbones)
7. e next innovation was the appearance of a backbone, called a vertebral column. Chordates
with a backbone are called vertebrates.
Very primitive vertebrates have greatly reduced vertebrae that resemble tiny prongs of
cartilage.
In most vertebrates, however, the vertebral column is composed of bone and encases the
dorsal nerve cord.
8. Separate out flashcard #102.
Lampreys:
• Lampreys are the least derived of the living
vertebrates.
• eir skeletons are made of cartilage.
• ey are mostly parasitic, using their suckerlike mouths to attach to the sides of fish.
CRITICAL INNOVATION #3: Jaws
9. Most vertebrates possess jaws. We refer to these jawed animals as gnathostomes.
Jaws are hinged mouthparts that, along with teeth, help animals tear food into pieces for
ingestion. Prior to the evolution of jaws, animals were forced to eat materials smaller than
their mouths.
Most biologists agree that jaws evolved from bones that supported pharyngeal slits (or
gill slits) directly behind the head. ese thin bony struts became thicker and formed jaw
bones.
In addition to jaws, gnathostomes have enlarged brains and enhanced senses, including a
sense organ called a lateral line system. e lateral line system forms rows along either
side of the body that can sense vibrations in the water.
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10. Separate out flashcards #99 and #103.
Sharks
Rays
Cartilaginous fish (chondrichthyans):
• ese fish have skeletons composed
primarily of cartilage.
• Areas of their skeletons have begun the
process of mineralization (which will result
in the fully-mineralized skeletons that
humans have).
• Most have streamlined bodies for swift
swimming, but cannot maneuver well.
• ese fish are not naturally buoyant; they
will sink if they stop moving.
Separate out flashcards #74 and #105.
Ray-finned fish (osteichthyans):
• ese fish have fins that are supported by thin
bones called rays.
• Most of the fish with which we are familiar are
ray-finned, such as trout, salmon, cod, goldfish,
bass, and swordfish.
• eir skeletons are completely mineralized.
• ey possess a swim bladder that makes them
buoyant, so they can stop swimming without
sinking.
11. e remaining “fish” fall into three lineages.
In all three of these lineages, the fins evolved from thin flaps of tissue with tiny bones into
thick, fleshy, muscular fins supported with more substantial bones.
ese animals are referred to as lobe-finned fish.
Lobe-finned fish use their muscular fins to paddle along the bottom, occasionally making
their way out onto dry land.
One of these lineages—the tetrapods—became terrestrial and evolved into the vast array
of land-dwelling vertebrates.
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12. Separate your flashcards into the three lineages of “lobe-finned fish.”
Coelacanth
Lungfish
Tetrapods
12
62, 65
71, 72, 75, 79
88
92, 95, 98
106, 107, 108, 109, 110
CRITICAL INNOVATION #4: Tetrapod Body Plan
13. Becoming terrestrial for the tetrapods brought with it a series of challenges their ancestors
had not encountered in the water:
they evolved limbs with feet that could support them on land
their senses had to adapt
they had to evolve structures that allowed them to perform gas exchange with air (rather
than in water)
14. e least derived of the terrestrial tetrapods are the amphibians. eir name refers to their
dual life: a larval stage spent in the water and an adult stage spent on land.
15. Adults must return to the water to reproduce. In fact, amphibians stay close to moisture
throughout their lives; they have relatively thin skin, so they are always at risk of drying out.
16. Separate out your amphibian flashcards, as shown below:
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CRITICAL INNOVATION #5: Amniotic Eggs
17. In order for tetrapods to exploit new terrestrial habitats, they had to become less dependent
on water. As a result, two new innovations appeared:
tough skin (made out of the protein keratin) that prevented desiccation (drying out)
an egg that contained fluid inside of it called amniotic fluid
18. e amniotic egg, in particular, is a noticeable improvement on amphibians in that it meant
that reproduction could occur away from water.
19. ere are two groups of animals that produce amniotic eggs. ey are:
Reptiles
12
62
71
88
92
109
Mammals
72, 75, 79
95, 98
106, 108, 110
20. Separate the reptile flashcards as shown below:
Other reptiles:
Birds:
• ese were the first truly terrestrial tetrapods.
• Birds are highly derived reptiles and are
hypothesized to be the descendants of the
dinosaurs.
• ey have a thick, leathery skin made of keratin
that prevents them from drying out.
• In addition, they can lay their amniotic eggs on
dry ground, away from water.
• eir keratin scales have evolved into feathers.
• Birds evolved flight independently of insects and
bats.
• Birds are endothermic (warmblooded), meaning
that they regulate their body temperatures.
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CRITICAL INNOVATION #6: Mammals
21. Arguably, the most derived of the chordates are the mammals. Mammals have four basic
characteristics:
they possess hair and subcutaneous fat that allows them to retain heat
they produce milk for their young with mammary glands
they have a muscle called a diaphragm that they use to draw air into their bodies
they are endothermic (warmblooded), but they evolved this independently of the birds
22. Separate your flashcards into the three groups of mammals, as shown below:
Monotremes:
Marsupials:
• is is the only group of
mammals that lays eggs.
• ese mammals give birth to very
premature young and then raise
them in external pouches.
• Includes the platypus (#108) and
the echidna.
• Includes koalas (#95), kangaroos,
possums, wombats, and wallabies.
• Today, they are only indigenous to
Australia and New Guinea.
Eutherians (placental mammals):
• Includes most mammals.
• ese mammals use a placenta to deliver nutrients
to developing young within the mother’s body.
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