Lect 20

Question 1

Eutherian characters

Answer 1

• Complex placenta throughout prolonged gestation. Larger they are longer gestation

Loss of epipubic bones (the ones on top and bottom of hips)
- Allows more room for gestating
young
- Allows for more flexible torso

• Morphology of ankle region
- How ankle fits to lower leg
- Expansion of distal ends of tibia and fibula

,maleola— bump on ankle

Question 2

Diversity of Eutherians

Answer 2

• Lower diversity than either Aves or Lepidosauria

• Greater disparity in body sizes and morphological specializations

2 main groups
More ancestral evolved on gowndona continents and the other group evolved on North America, Europe, and Asia

Question 3

Reproductive organs

Males

Answer 3

• Penis carries both urine and sperm
- no cloaca

• External scrotum
- Allows sperm to develop below
endothermic body temperatures
- Less pressure on testes during locomotion

• Vas deferens have to loop around ureters

Urthera already in place when scrotum moving

Question 4

Reproductive organs

Females

Answer 4

• Females have unpaired vagina
- Marsupials have paired lateral vaginas, which correlate with forked penis

• Most eutherians have paired uterine horns, very few have single uterus
- horns, hav.ex more space, hold more offspring

Question 5

Placenta

Answer 5

• Develops from extraembryonic membranes
- Chorion and allantois
- Blood vessels only develop from endoderm, therefore allantois is essential to placenta development (allows to be very vascularized)

• Implantation of embryo in mother’s uterine lining causes inflammation (short gestation b/c have no immune suppression against inflammation for things not uetherian)
- Eutherians developed immune suppression, which allows for the prolonged gestation period

Question 6

Feeding

Teeth

Answer 6

High metabolism = high food requirements

• Break down food before it reaches stomach
- Increases surface area for enzymes to act on
- Accelerates digestion
- due to teeth meet in close inclusion

• Each tooth composed of enamel, dentine, cementum

• Teeth set in sockets (thecodonty), but connected to jaws via ligaments. In place b/c soft tissue not bone

• Heterodont

Question 7

Molar types

Answer 7

• Tribosphenic
- Basal form
- 3 main point, broader in back, better for grinding

• Bunodont (rectangle in shape)
- One additional cusp
- Cusps are low
- short in height ], don’t take up a lot of space in jaw

• Carnassials
- Upper molar and lower premolar
- compressed side to side, good for sheering meat

• Lophodont
- Cusps merge into ridges

• Hypsodont
- Crowns are tall and erupt slowly throughout life
- refers to height overall
- grow very slowly throughout life, why able to get by with only 2 sets of teeth for life
- more teeth grow out to use over time in life

Question 8

Chewing muscles

Answer 8

Temporalis
• Controls closing of front of jaw
• More developed in carnivores
- starts on top of cranium connects back to jaw muscles runs through the temporal fenstrea

Masseter
• Controls movement of back of jaw
• More developed in herbivores
-grinding
-bottom of zygomatic zone, front of face under nose ish to back of jaw

Question 9

Digestive systems

Answer 9

• Carnivores tend to have more simplistic digestive systems
- Meat is easier to digest, more nutrient-rich

• Mammals cannot digest plant matter independently

• Require symbiotic microorganisms
- can’t break down cellulose so need these b/c they make cellulase enzyme

• mammals who eat plant broken down into 2 groups
- Hindgut fermenters
- Foregut fermenters

Question 10

Hindgut fermenters

Answer 10

• Horses, rhinos, rabbits, elephants

• Enlarged cecum and colon for fermentation
- Regions of large intestines

• Less efficient because small intestines perform the most absorption of nutrients (the fermentation occurs in small intestine)

• Rabbits eat their own feces (coprophagy)

Question 11

Foregut fermenters

Answer 11

• Cows, antelope, giraffes, camels, and many others
- Ruminants (name comes from rumen)

• Multichambered stomach
- Food gets partially processed, regurgitated as cud, re-chewed, then returned to the stomach to continue digestion (mechanically break down cell walls before cellulase can break it down)

• More efficient because plant matter is fermented before it reaches the small intestine (more nutrients)

Question 12

Limb proportions

Answer 12

• Long limbs = faster stride

• Short limbs = greater power

• Foot posture relates to limb length
- Less of the foot contacting the ground increases length

Question 13

Cursorial mammals

Answer 13

• Long limbs
- Elongation greater distally

• Reduced mass (require energy required)
- Muscles concentrated proximally
- Tendons control distal limb • Number of toes reduced

• Tend to only move limbs in anterior-posterior plane

Question 14

Digging mammals

Answer 14

• Both on surface and underground

• Limbs shorter, more processes for muscle attachments

• Retain all five digits (rarely see reduction)

• Wider range of motion at the shoulder (see more lateral motion, not trying to maintain high endurance)

Main,y seen in forelimbs
- burrowing or digging

Question 15

Flying mammals

Answer 15

• Chiroptera = cheir “hand” + peton “wing”
-The wing is supported by elongated bones of the hand

• Flight membrane known as patagium

• No keeled sternum
- Flight muscles on both dorsal and ventral sides of body

Question 16

Swimming mammals

Answer 16

• Semi-aquatic forms use limbs for propulsion
- Webbed feet of beavers
- Fins of seals

• Fully aquatic forms use dorso- ventral flexion and horizontal fluke
- Whales and manatees
- this is opp of sharks, fish, aquatics reptiles
- zygopophies changed overtime, flat (allow side to side) to __ (allow up and down)

Few diff groups that have returned to water

Question 17

Conservation

Threats to mammals

Answer 17

• Typical threats like climate change and habitat loss

• Less typical threat is trophy hunting
- Large game fish nearly the only other vertebrates hunted for trophies

Question 18

Costs of trophy hunting

Answer 18

• Trophy hunters prioritize largest overall size, largest horns, largest antler racks

• Faster-growing individuals killed before they’ve reached reproductive maturity
• Genes for large size, fast growth removed from gene pool
• Genes for smaller sizes, slower growth remain

• Sizes can rebound if hunting is stopped

Question 19

Key Concepts

Answer 19

• Eutherians are united by their lack of epipubic bones, complex placentae, and prolonged gestation.

• Eutherians have complex dental characters and molar morphologies that are closely tied to diet.

• Eutherian limb morphologies show a trade-off between speed and power, and species are typically adapted for one or the other.

• Trophy hunting has been changing the gene pool of large mammals, which tend to be growing smaller trophy features.