Week 8

Question 1

Cephalochordata

Answer 1

Early ancestors of vertebrates did not have a vertebral column. They had a notochord, this was the first step toward evolution of all vertebrates including humans.

Question 2

Pikaia

Answer 2

One of the earliest ancestors of all vertebrates.

Had a head and a notochord but no vertebral column. Also had myotomes (muscles).

Question 3

Myotomes

Answer 3

Muscles

Question 4

What made a pikaia a cephalochordata?

Answer 4

It had a head.

Question 5

What were earlier ancestors with no head and a notochord called?

Answer 5

Chordates

Question 6

Vertebrata

Answer 6

Animals with a jointed spinal column

Question 7

The first animals to develop a vertebral column did not have jaws. These are called…

Answer 7

jawless fish.

Modern hagfish and lampreys are jawless fish.

Question 8

The first vertebrates had a head and a vertebral column but not

Answer 8

a jaw.

Question 9

Gnathostomes

Answer 9

Animals with jaws. Jaws are a huge evolutionary step.

Early gnathostomes have skeletons made of cartilage.

So gnathostomes have a vertebral column and jaws, but primitive forms have a skeleton made of cartilage.

Question 10

Osteichthyes

Answer 10

After jaws evolved the next step was calcified skeletons: boney fish.

Osteightyes can be split into two groups:

• ray finned fish (typical fish, like Gilgamesh)
• lobe-finned fish or sarcopterygii, this is where the fins of fish start to become fleshy and limb-like.

Question 11

Ray-finned fish

Answer 11

• vertebral column
• jaws
• mineralized skeleton

Question 12

Sarcopterygii

Answer 12

Lobe-finned fish

• vertebral column
• jaws
• mineralized skeleton
• limb-like fins

Question 13

Tiktaalik

Answer 13

Fishapods: Fish with feet

Up until the Tiktaalik all life lived in the water. The Tiktaalik is a lobe-finned fish that represents the next step in vertebrate evolution. It has weight bearing elbows, simple wrist bones, and rays that resemble fingers. It also had gills and lungs.

It spent most of if not all of its life in water, but it had features that made it preadapted to live on land.

Question 14

Tetrapoda

Answer 14

All animals with two arms and two legs.

They have no gills but retained their lungs evolved from Tiktaalik.

They were bound to water to reproduce.

Primitive tetrapods like amphibians are still water bound to reproduce to this day.

Question 15

The evolution of vertebrates can be explained through a cladogram, what evidence do we have for this cladogram?

Answer 15

Homologous structures

Comparing lobe-finned fish and ray-finned fish make it easy to see how features are modified and passed on over time.

The shoulder girdle, humerus, radius, and ulna are present in both animals and thus provide us with homologous structures and an example of evolution.

Question 16

Are mammals amniotes?

Answer 16

Yes, we just retain our eggs internally.

Question 17

The evolution of a membrane called the ____ in eggs allowed the ____ to become fully terrestrial.

Answer 17

The evolution of a membrane called the amnion in eggs allowed the amniotes to become fully terrestrial.

Question 18

What is the next step in evolution after tetrapoda?

Answer 18

Amniotes

Question 19

Amniotes are split into two groups:

Answer 19

1. Synapsids: single pair of openings behind the eyes

2. Diapsids: 2 pairs of openings behind the eyes. Openings are called temporal fenestrae.

Question 20

Clades

Answer 20

Groups of organisms that are descended from a common ancestor

A monophyletic group, meaning that it is a group of organisms that includes a common ancestor and all of its descendants

Question 21

Are dinosaurs synapsids or diapsids?

Answer 21

Diapsids

Question 22

The diapsids can be split into two clades based on differences in the skeleton

Answer 22

1. Lepidosauromorphs: short non-overlapping vertebrae in the neck
2. Archosauromorphs: Longer vertebrae in the neck that tend to overlap and provide neck support for longer necks. This clade includes, birds, dinosaurs, and crocodiles.

Question 23

Archosauria

Answer 23

A subset of archosauromorphs

Antorbital fenestrae: The archosauria have additional openings in front of the eyes

Includes crocodiles, pterosaurs, birds, and dinosaurs.

Question 24

All birds are dinosaurs but

Answer 24

not all dinosaurs are birds.

Question 25

Crocodiles retain a sprawling stance, they belong to the clade called:

Answer 25

Crurotarsi, this is what separates crocodiles from dinosaurs.

Question 26

Pterosaurs, birds, and dinosaurs all have an upright stance and therefore belong to a clade called:

Answer 26

Ornithodira, flight then evolved in birds separately.

Question 27

Diagnostic characters of Archosauria:

Answer 27

1. Antorbital Fenestra
2. Simple ankle joint (motion limited to front and back)
3. Specializations for flight (including elongation of digit IV)

Question 28

Digitigrade Posture

Answer 28

An upright stance that balances primarily on the balls of the feet and allows for a longer stride.

Question 29

The earliest, most primitive dinosauromorphs before the dinosaurs were

Answer 29

small, lightly built, carnivorous, and bipedal.