Midterm III

Question 1

What are the two types of amniotes? Which groups do they include?

Answer 1

Synapsids (mammals) and sauropsids (turtle, snakes, crocodiles, lizards, birds)

Question 2

What are the characteristics of amniotes?

Answer 2

Amniotic egg, waterproof skin, keratin in skin (which allows for evolution of hair, scales, feathers) and costal ventilation (ventilation occurs in the chest, not the neck), which allows for the evolution of a longer and freer neck, advanced pectoral muscles, and more dexterity

Question 3

What is the amniotic egg? What makes it different from non-amniotic eggs?

Answer 3

Non-amniotic eggs have just 1 layer and cannot exist outside of water. Amniotic eggs have 3 extra-embryonic membranes, which allows for water retention and selective permeability

Question 4

Name the layers of the amniotic egg shown here and describe each

Answer 4

A - Albumin

B - Chorion

C - Eggshell

D - Amnion

E - Yolk sac

F - Allantois

Question 5

What are the advantages of the amniotic egg?

Answer 5

Resistant to dessication and water loss (can survive in dry environments) Bypass vulnerable larval stage Mechanical protection to the young (calcified shell), which also supports its weight Increased respiratory capacity

Question 6

Describe the varying levels of temporal fenestration. What is the function of the fenestrae? What was the evolutionary advantage?

Answer 6

Synapsids - 1 hole, usually fused in mammals as the zygomatic arch. Anapsids - No holes, only occurs in turtles. Diapsids - 2 holes. The advantage of these holes is to allow for more advanced (bulging) jaw muscles, which increases the strength and range of the jaw. A small hole in synapsids gives an edge for the jaw muscles to attach to.

Question 7

What is the difference between cryptodires and the pleurodires?

Answer 7

Cryptodires - Largest group of turtles, which retract the head by bending it in an S shape. There are no cryptodires in Australia. Pleurodires - Retract the head by bending the neck horizontally. Found only in the Southern Hemisphere.

Question 8

Describe turtle ventilation in detail

Answer 8

Inspiration: Abdominal oblique contracts to pull posterior limiting membrane outward and serratus contracts to rotate pectoral girdle outward, increasing the volume of the visceral cavity Expiration: Transverse abdominis contracts and flattens the posterior limiting membrane inward, and the pectoralis draws the pectoral girdle into the shell

Question 9

Describe blood flow through the turtle heart during normal activity

Answer 9

Deoxygenated blood flows into the right atrium, cavum venosum and then to the cavum pulmonale over the muscular ridge. Atrioventricular valve opens, the interventricular canal is closed off and oxygenated blood flows into the cavum arteriosum. Ventricle contracts and deoxygenated blood flows from the cavum pulmonale to the pulmonary artery (to be oxygenated). The atrioventricular valve closes and the oxygenated blood can now flow from the cavum arteriosum, through the interventricular canal, into the cavum venosum and out of the heart via the right and left aortic arches

Question 10

Describe the turtle heart

Answer 10

A. Right aortic arch

B. Left aortic arch

C. Pulmonary artery

D. Right Atrium

E. Left atrium

F. Atrio ventricular valve

G. Cavum pulmonale

H. Cavum venosum

I. Interventricular Canal

J. Cavum arteriosum

Question 11

Describe blood flow through the heart of turtles while diving

Answer 11

Shunting occurs wherein the interventricular canal is opened up and oxygenated blood can mix with deoxygenated blood. This partially oxygenated mixture is distributed around the body

Question 12

What adaptations allow leatherback sea turtles to maintain a higher body temperature than most reptiles?

Answer 12

• Their large size allows for thermal inertia (can hold more heat) - Have a large amount of body fat to retain heat (gigantothermy) - Favourable surface area to volume ratio - Can bask to take in heat - Counter current heat exchange is used in the limbs, the arteries and veins are parallel to each other to allow for keeping heat in the core of the body

Question 13

Describe temperature-dependent sex determination in reptiles. What advantage might there by to such a system?

Answer 13

Higher incubation temperatures often speed of the development of the organism and produce the larger sex (females in turtles and males in crocodiles). The aromatase enzyme converts testosterone to estrogen but this enzyme is temperature dependent. This system is advantageous because the fitness of a sex may be higher at different temperatures.

Question 14

Compare and contrast true chameleons with igaunids

Answer 14

True chameleons have a prehensile tail, fused toes, independently moving eyes, the ability to change colour, and are insectivorous (also have tongue that they project to grasp prey). They also have keratinized horns. They are found in Africa, the Middle East, India, and Madagascar. Igaunids are mostly new world, and include many species. Most are herbivorous. They have separated toes for walking and hanging on trees.

Question 15

Describe how the morphology of amphisbaenins reflects their lifestyle

Answer 15

The skull has thick bones for burrowing and the brain is encased in frontal bones (to prevent brain damage). The trunk and skin have very few connections, allowing for sliding in tunnels. They have either no legs at all or small, underdeveloped legs (legs get in the way of burrowing). They have skin annuli to allow for segmented movement. And, finally, they have a notched tooth arrangement that helps them bite chunks off of prey

Question 16

Leglessness has evolved several times among tetrapods. Why would that trait develop and what are the evolutionary relationships between these legless forms?

Answer 16

Leglessness is selected for in environments where burrowing can be advantageous. Legs typically get in the way when burrowing so many organisms that are legless (snakes, legless lizards, amphisbaenins) evolved such traits for burrowing. Extant snakes rarely burrow, but it is thought that leglessness was evolved for burrowing in an ancestor of snakes.

Question 17

Discuss locomotion and feeding of boid snakes

Answer 17

Boas and Pythons are both boids. Pythons are the Old World equivalent of boas. Most boids move by slowly inching forward, and kill prey by constricting them. They wrap themselves around a prey item and slowly squeeze the air out of them until they die. Then, the snake swallows them whole.

Question 18

Several methods of venom delivery have evolved among snakes. Describe these and give examples of snakes that use each system

Answer 18

“Rear-fanged snakes” - Opisthoglyphs - Mainly colubrids. Have 2-3 teeth at the back of the maxilla and venom is highly variable in strength. Groove in the teeth called the venom canal delivers venom. “Front fixed fanged snakes” - Proteroglyphs - Includes cobras, coral snakes, sea snakes, kraits. Hollow, venom-filled fangs are at the front of the maxilla, permanently erect. Solenoglyphs - Hollow, retractable fangs (only teeth on maxilla). Includes pit vipers (rattlers) and true vipers (gaboons). Venom kills prey and digests tissues. Aglyphous - Non-Venemous

Question 19

Discuss the colubridae

Answer 19

Colubrids are the most abundant species of snake. They have lost all traces of the pelvic girdle. Many are non-venemous. They are found on all continents except Antarctica and their skulls are highly kinetic.

Question 20

How did venom evolve?

Answer 20

Duvernoy’s gland in the upper jaw of colubrids is homologous to the venom gland of front-fanged snakes. This gland is likely the ancestral venom delivery system, and the venom is not stored anywhere so it must be “chewed” into the victim. In front-fanged snakes this system became much more complex, containing a central lumen for storage, a muscle to push the venom out, and an accessory gland

Question 21

What are the major clinical effects of elapid vs. viperid venom?

Answer 21

Elapid venom is neurotoxic and slowly shuts down the body. Viperid venom is hemolytic and breaks down the flesh

Question 22

How do Galapagos marine iguanas stay on their territory all day long and not suffer from excessive cold or heat?

Answer 22

At night, the iguanas huddle together for warmth. When the sun comes out in the morning, they spread themselves out over the black rocks (gain heat from rocks via conduction), maximizing the surface area that can be used to absorb energy from the sun. They themselves also turn a darker shade to absorb more heat. When they are hot enough, they adjust their posture so that their bellies are no longer touching the hot rocks, and the wind can flow underneath them. They lower the surface area they expose to the sun and they change colours to a lighter shade.

Question 23

Explain how snakes can consume prey larger than themselves

Answer 23

In order to catch prey larger than themselves, snakes often use venom that incapacitates them in some way. Some snakes, like the pythons and boas, will constrict prey until they can no longer breathe. Snakes have highly kinetic skulls. The quadrate has movable joints to increase the volume of the oral cavity. The neck and mouth regions are highly elastic so they expand as the skull expands. When a snake takes prey, they do so head first so the legs fold against the body. The glottis sticks out from under the prey so the snake may continue to breathe, and the two sides of the jaw move alternately to “walk” the prey backward down the mouth.

Question 24

Explain the coral snake mimicry system

Answer 24

Coral snakes are brightly coloured snakes consisting of red, yellow, and black banding patterns. They are highly toxic. Because of this, no predator learns from experience to avoid them (predators die), but the innate avoidance may pass down genetically. In this respect perhaps the coral snake benefits from its moderately toxic mimics. There are several other snakes that mimic coral snakes. Some mimic them and are moderately toxic, and others, such as the scarlet kingsnake, are completely harmless but receive the benefit of no predators.

Question 25

Explain the structure and function of pit organs

Answer 25

Vipers have pit organs that are similar to that of boids, but much more sensitive. These organs sense infrared radiation (heat) given off by other organisms and help them locate prey in the dark. They are located just behind the nares and consist of a heat sensitive membrane with air on either side that is connected to branches of the trigeminal nerve

Question 26

Describe the adaptations of derived sea snakes for an aquatic existence

Answer 26

Sea snakes have valvular nerves, an extended lung (which may help in buoyancy), skin respiration, caudal fin, no ventral scutes, and are viviparous. They produce neurotoxic venom that paralyses the respiratory system. They may be slightly laterally flattened to allow for better swimming

Question 27

Why do snakes have a forked tongue? What specific sensory area detects the stimuli brought into the body by the forked tongue?

Answer 27

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Question 28

What is autotomy?

Answer 28

Autotomy occurs when an organism breaks off its tail when it is seized by a predator. This escape mechanism is used by many skinks and lizards. The tail (and accompanying vertebrae) breaks off and the tail is regrown with a cartilaginous rod in place of the old vertebrae.

Question 29

Most reptiles are oviparous but what are some exceptions? What is a common method of reproduction in lizards and snakes that live in cold climates? Explain and give examples

Answer 29

Many boas, all pit vipers and garter snakes are viviparous. So are many skinks. Viviparity is extremely useful in cold climates where the eggs cannot be incubated. Reptiles in colder climates (such as manitoba) may hibernate through the winter and then emerge all at once for a big snake orgy. The males would emerge first mate with a female, and then transfer a pheremone to her, rendering her unattractive. This occurs in Manitoban garter snakes

Question 30

Name and describe the four major types of snake locomotion. When and by which snakes are these methods employed?

Answer 30

1. Lateral undulation - The body is thrown into a series of curves. Most common type of locomotion. 2. Rectilinear locomotion - Used by heavy bodied snakes, performed by contracting and stretching alternating bands of muscle along the bottom of the body 3. Concertina locomotion - Snake moves through burrows by anchoring against the sides and pushing the front part of the body forward 4. Sidewinding - Body is raised in loops with only 2 or 3 points contacting the ground. This method is used by snakes in the desert that cannot gain traction.

Question 31

List and describe five derived archosauran features

Answer 31

1. Antorbital fenestrae 2. Deep skull 3. Teeth laterally compressed 4. Trend toward bipedalism 5. Powerful caudofemoral muscle

Question 32

What is parthenogenesis?

Answer 32

“Virgin” females will give birth to children that are essentially clones of herself

Question 33

What are the three major extant groups of crocodilians? distinguish between them

Answer 33

Alligatoridae - All are new world except the Chinese alligator, most are freshwater and they have a broad snout. Lower teeth are not visible when mouth is closed in alligators. Crocodiles - Have indeterminate growth. valves on the nares they can close when swimming, and most species are endangered. A tooth is visible when their mouth is closed. Gharials - There is only one species, and it is found in the Indo-Pacific. They are critically endangered and have a narrow snout

Question 34

Explain the flow of blood through the crocodilian heart and major vessels surrounding the heart during normal activity, diving, and strenuous activity

Answer 34

At rest: Mixed blood heads through the left aortic arch to the gut, bringing down the pH of the stomach using the CO2 in the blood. When active: Pressure in left ventricle is higher and blood is shunted from left to right and the left aortic arch and right aortic arch carry oxygenated blood. When diving: Pulmonary artery closes off and right to left shunt occurs to reduce heat loss - blood leaves right ventricle through left aortic arch to the body

Question 35

Compare lung ventilation in a crocodile and turtle

Answer 35

Inhalation: Intercostal muscles contract, increasing size of the thoracic cavity, and diaphragmaticus contracts to pull the liver backwards. Pelvic girdle rotates to move the ischiopubis. Exhalation: Intercostals and diaphragmaticus relax, rectus abdominis and transverse abdominis contract. The primary difference in respiration between the crocodile and the turtle is that in the turtle the ribs have no place in respiration so the organs must be moved in order to push against the lung.

Question 36

What possible clues do living archosaurs give us as to how the dinosaurs may have lived?

Answer 36

Crocodiles and birds share nests made with vegetation, parental care of the young, vocal communication, stones in gizzards, and faveolar flow through lungs. These are traits that we can assume were present in some or many dinosaurs

Question 37

Name these parts of the crocodile heart

Answer 37

A - Right atrium

B - Left atrium

C - Right ventricle

D - Left Ventricle

E - Foramen of Panizza

F - Right aortic arch

G - Left aortic arch

H - Pulmonary artery

Question 38

Discuss the pterosaurs with regard to their morphology and lifstyle. Compare and contrast the rhamphoryncoids and pterodactyls

Answer 38

Pterosaurs were flying, bird-like organisms with flaps of skin for wings. They are the sister group to dinosaurs. Rhamphorhynchoids are basal pterosaurs. They had long tails, teeth, and no crest. They were quite small and were likely very awkward on land. They may have had fine bristles on the body (potentially for insulation). Some forms had an extensive membrane on the hind legs further inhibiting land movement. They had heterodont dentition. Pterodacyloids has larger skulls, little or no tails, reduction in teeth (homodont), and were typically quite large (1m - 12 m). Many were coastal fish eaters.

Question 39

How well did pterosaurs fly? Compare wing anatomy in a bird, pterosaur, and bat

Answer 39

Pterosaurs - Wing supported by an enormously elongated fourth digit. Flap called propatagium changes shape and angle of wing. Birds - Forearms and parts of the hand form the wing, and feathers grow off of these parts. Bats - Finger bones form the skeletal support of the wing, running in between membranous flaps

Question 40

Distinguish between the two major radiations of dinosaurs based on pelvic morphology, and locomotion/body stance

Answer 40

Ornithischians - Pubis is rotated backward and is parallel to the ischium. Origin of leg muscles further from insertion, gives technical advantage. Allowed for erect posture. Saurischian - Pelvic girdle looks like that of a lizard’s. Elongation of the pelvis allows for huge muscles and a large femur. Allowed for erect posture.

Question 41

List the derived characteristics of ornithischians

Answer 41

• Derived forms had tendons that ossified and criss-crossed through the vertebrae, locking them together. - All ornithischians were herbivores - Backward-pointing pubis - Beaked pre-dentary bone that bears no teeth - Had teeth on their cheeks for grinding up plant material - Bipeds or quadrupeds

Question 42

Discuss the morphology and inferred lifestyle of the three major groups of ornithischians

Answer 42

Thyreophora - Have rows of dermal ossifications that are free from the axial skeleton. Early forms were small and bipedal and later forms were much larger and quadrupedal, with much larger hind limbs. Ornithopods - Early ones were small and bipedal, and later ones were larger facultative bipeds. They had no premaxillary teeth. Fifth digit was opposable and the second and third digits were flattened into hooves. Some had projections on the back that could have been a sail or even a hump. Marginocephalians - Characterized by the shelf of bone over the skull. Primitive forms were bipedal but some later forms were large obligate quadrupeds.

Question 43

What is a pleurokinetic jaw? Compare and contrast the function of the dental battery of hadrosaurs and ceratopsians.

Answer 43

A pleurokinetic jaw is a jaw that has independently moving parts. Hadrosaurs had two tooth-bearing parts to their maxilla that could slide against the bottom teeth (dental battery) at an angle to grind up plant material. The teeth of ceratopsians were located at the back of the jaw and consisted of knifelike edges used to “shear” food in a scissor like action.

Question 44

What evidence exists that Thyreophorans may have been able to regulate their body temperature by behavioural/anatomical means?

Answer 44

It was found that the plates of stegosaurus were highly vascularized (lots of capillaries) so the plates would have made excellent surfaces for raising or lowering the temperature of the organism (likely used for lowering, considering the worldwide temperatures at the time).

Question 45

Discuss the reproductive and social behaviour of hadrosaurs and ceratopsians inferred from fossil evidence.

Answer 45

Hadrosaurs likely provided a large amount of parental care to young. They have been found fossilized in nests, with young of varying ages. The crests of some hadrosaurs may have served in sexual signalling, and the ones with hollow crests may have called using them. Trackways have been found for some hadrosaurs suggesting that they travelled in large herds. It is thought that the horns of ceratopsians were not used for combat between males, but potentially used to fend off predators (likely as a group). One ceratopsid nest has been found with juveniles in it.

Question 46

Discuss the marine reptiles that inhabited the epicontinental seas of Manitoba during the Cretaceous. Distinguish between plesiosaurs and pliosaurs.

Answer 46

Placodonts had a covering of dermal armour. Ichthyosaurs were dolphin-like predators which became more specialized and streamlined over time. Plesiosaurs had small skulls, long necks, and a large amount of bones in the fin. They swam through the water by “rowing”. They were fish eaters. Pliosaurs were more streamlined with a shorter neck and larger fins. They likely ambushed prey and were fast swimmers.

Question 47

Briefly describe sauropod lifestyles and anatomy. How do scientists think they keep their necks up?

Answer 47

Sauropods were herbivores. They had teeth optimized for cutting vegetation. They had extremely long necks and grew very large in size. In order to keep their necks up they required small skulls and a canal through the top of the vertebrae to hold a massive Nuchal ligament (which would support the neck)

Question 48

True or false, theropods are carnivores

Answer 48

True

Question 49

Why is it thought that tyrannosaurids got to be so large?

Answer 49

The prey items that they often caught (ornithischians) were getting larger and larger, so the average size of them increased over time

Question 50

What is the evidence for and against dinosaur endothermy?

Answer 50

For: 1. Bones have been found in Alaska and southern Australia, suggesting that they lived in cold climates (however, it was much warmer at the poles back then than it is now) 2. There were less predators in the Cretaceous, indicating endothermy because endotherms require more energy from food. 3. Some think the erect stance of dinosaurs is evidence for endothermy since living endotherms are erect (lolwut. Correlation/causation?) 4. Large sauropods must have had a four chambered heart, like birds and mammals, so they must be endothermic (wrong, because crocodilians also have a four chambered heart 5. Bone histology - there are systems in the bones of many dinosaurs that are found most birds and mammals. However, these systems are likely a reflection of size. 6. The presence of feathers may imply a degree of endothermy 7. Analysis of oxygen isotope ratios between core and extremities are thought to be an indicator of temperature. It was found that dinosaur cores and extremities do not vary much in temperature (endotherm!) 8. Turbinate bones, which are used to warm air coming into the body are characteristic of endotherms and not found in dinosaurs. 9. Gigantothermy - Large dinosaurs would be able to regulate temperature regardless of endothermy/ectothermy. Conclusion: smaller dinosaurs may have been endothermic, but large dinosaurs were likely inertial Homeotherms.

Question 51

What caused the extinction of the dinosaurs?

Answer 51

There are many theories about the extinction of dinosaurs, but they all boil down to two options: was there a single cause, or multiple causes? No one is sure what the single cause could be, but multiple causes could be marine regression (less water putting strain on both terrestrial and marine ecosystems), volcanism (materials from this cooled and dried parts of the globe), and an impact event (large meteor hits the earth and the particles in the sky affect photosynthetic output).

Question 52

What is a trait that is common to all crocodilomorphs?

Answer 52

Unique ankle joint that allows for rotation at the joint