Rise of the Archosaurs

Question 1

Which two extinction events began and ended the Mesozoic?

Answer 1

Start- end-Permian Extinction- Outpouring of the Siberian Traps (252mya)

Finish- end-Cretaceous Extinction- Chicxulub impact (66mya)

Question 2

What are two other major events that occurred during the Mesozoic?

Answer 2

1. Carnian Pluvial Event (232mya)- interruption of Triassic droughts which increased dinosaur diversity
2. end-Triassic Extinction (202mya)

Question 3

Archosaurs are members of which clade?

Answer 3

Diapsids

Question 4

The Marine Diapsids included which 4 groups?

Answer 4

1. Ichthyosaurs
2. Plesiosaurs
3. Marine turtles
4. Mosasaurs

Question 5

What key convergent trait did ichthyosaurs share with sharks

Answer 5

Heterocercal tail- lobes of tail are of different lengths

Question 6

What key adaptations to marine life did ichthyosaurs and plesiosaurs share?

Answer 6

1. Viviparity

2. Endothermy

Question 7

What two features of modern turtles did Odontochelys, a Triassic testudine, lack?

Answer 7

1. Ossified carapace

2. Horny beak

Question 8

Which part of the shell first ossified in testudines?

Answer 8

The lower shell (plastron), suggesting an ossified shell was used for protecting from attacks from below.

Question 9

Dinosaurs and pterosaurs form which clade?

Answer 9

Avemetatarsalia (All archosaurs more closely related to birds than crocodiles)

Question 10

What trait do only crocodile and birds (archosaurs) possess amongst the modern diapsids?

Answer 10

4-chambered heart, reflecting the active lifestyle of archosaurs

Question 11

What are the diagnostic characteristics of archosaurs?

Answer 11

1. Powerful bite (teeth in sockets, antorbital and mandibular fenestra accommodating large muscles)
2. Modified ankle joint with calcaneal tuber, allowing for more upright gait.

Question 12

How did Mesozoic Crocodylomorphs differ from modern crocodiles?

Answer 12

Much greater diversity of body form, ranging from fully marine, to athletic terrestrial builds.

Question 13

Biomechanics modeling suggests pterosaurs had what form of unique terrestrial locomotion?

Answer 13

Walking with a plantigrade (“flat-footed”) hindlimb and a digitigrade forelimb (walking on the fingers to accommodate the wing).

Question 14

What traits of pterosaur reproduction are indicated by current fossil evidence?

Answer 14

1. Parchment-like egg shells, like snakes
2. Colonial breeding
3. Care for offspring after birth.

Question 15

What were the filamentous integumentary appendages (like downy feathers) coating many pterosaurs called?

Answer 15

pycnofibres

Question 16

What are the defining features of the Dinosauria?

Answer 16

1. Perforate acetabulum forming hip joint
2. in-turned head of femur

(Both associated with upright and bipedal stance.)

Question 17

Which two clades are dinosaurs traditionally believed to fall into?

Answer 17

1. Ornithischia (herbivorous bipeds and quadrupeds)

2. Saurischia (Sauropoda and Theropoda)

Question 18

When did the dinosaurs first appear?

Answer 18

Middle Triassic (c.245mya)

Question 19

How did the splitting of Pangea into Laurasia and Gondwana during the Cretaceous impact the dinosaurs?

Answer 19

Promoted rapid allopatric speciation.

Question 20

What trend can de seen in dinosaur diversity in the last 10 mya of the Cretaceous?

Answer 20

Sharp decline

Question 21

What form of thermoregulation did many large dinosaurs employ?

Answer 21

Gigantothermy- body temperature remains high and relatively constant due to huge size.

Question 22

What were the purposes of air sacs in Sauropod vertebrae?

Answer 22

1. Thermoregulation

2. Regulation

Question 23

How did the growth rates of large and small dinosaurs vary?

Answer 23

1. Large dinosaurs had fast growth rates like modern precocial birds.
2. Small dinosaurs grew slowly, like modern lizards.

Question 24

What maximum walking speed does biomechanics analysis suggest for Tyrannosaurus?

Answer 24

5 m/s

Question 25

What is the purpose of anterior and posterior air sacs in modern birds (and non-avian saurischian dinosaurs)

Answer 25

Unidirectional flow (deoxygenated air does not need to pass back through the lungs.)

Question 26

What characteristic traits of avian reproduction originated in non-avian dinosaurs?

Answer 26

1. Coloniality
2. Brooding
3. Site fidelity
4. Shell pigmentation

Question 27

What was the first non-avian dinosaur with feathers to be discovered?

Answer 27

Sinosauropteryx

Question 28

Why is integument (feather-like appendages) likely to have been an ancestral feature of the clade Avemetarsalia?

Answer 28

Similarities between pycnofibres and simple therapod feathers.

Question 29

Why are non-avian feathered dinosaurs likely to have coexisted with birds?

Answer 29

Many non-avian feathered dinosaurs are younger than Archeopteryx, which is often considered to be the earliest known bird.