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BIOL 305 > LECTURE 23 - Mammalia > Flashcards

LECTURE 23 - Mammalia Flashcards

1
Q

How synapsids distinguished from other tetrapods?

A
  • Synapsids are distinguished from other tetrapods y having a single temporal fenestra
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2
Q

Describe the evolution of Synapsids

A

PHYLOGENETIC TREE OF DECENT
- Synapsids
- Pelycosaurs
- Therapsids
- Early Therapsids
- Cynodonts

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3
Q

(IN SYNAPSIDS) What are Pelycosauria?

A
  • Arose in mid-Carboniferous (~320 MYA)
  • Extensive radiation during the early Permian: half of amniote genera
  • Some herbivorous, most carnivorous
  • Some had a sail: flap of skin supported by projection of the vertebrae
  • Extinct by the end of the Permian (~250 MYA)
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4
Q

(IN SYNAPSIDS) What are Therapsida?

A
  • Appeared in later Permian, flourished during early Triassic
  • Greater diversity of body design, differentiated teeth (feeding specialziations)
  • Legs more directly positioned under the body: more efficient and active locomotion
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5
Q

(IN SYNAPSIDS - IN THERAPSIDA) What are Cynodontia?

A
  • “Advanced therapsids” arose in the late Permian and survived the mass extinction
  • Lineage show evidence of the gradual evolution of many mammalian characters along with transitional fossils
  • Thought to represent the ancestral stock from which modern mammals evolved
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6
Q

What are mammalian characteristics?

A
  • Endothermy
  • Four-chambered hearts
  • Single bone in lower jaw
  • Three bones in middle ear
  • One-time tooth replacement
  • Hair
  • Mammary glands
  • Diaphragms
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7
Q

What is the size-refugium hypothesis fro endothermy?

A
  1. Early therapsids were relatively large ectotherms because selection favoured low surface area to volume (once warm, they retain heat easily and can have a fairly constant body temperature)
  2. In the Triassic, dinosaurs radiated and became dominant, so under this hypothesis, there would have been selection for smaller size to escape competition and/or predation - Cyonodonts from this time were all quite small
  3. As size decreases, thermal inertia is lost and selection would favour animals with the ability to produce their own heat (endothermy)
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8
Q

What are some implications brought in by the evolution of endothermy?

A
  1. Energy requirements (10x energy required as a similar sized ectotherm) would favour selection for increased cardiopulmonary and food processing efficiency
  2. Allows activity during cold nights and thus nocturnality, which would favour selection for improved auditory and olfactory capabilities, as well as hair for insulation
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9
Q

Describe the 4-chambered heart in mammals

A
  • 4-chambered heart makes it possible to send de-oxygenated blood to the lungs and oxygenated blood to fuel muscles without needing to mix them
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10
Q

Describe the evolution of the mammalian skull

A
  • Mammals show highly efficient food processing via specialized dentition and powerful jaws

FROM EARLY SYNAPSID (REPTILE-LIKE JAW) TO MAMMALIAN
- Prcynosuchus (primitive cynodont): quadrate-articular joint only, non-specialized teeth
- Probainognathus (advance cynodont): quadrate-articualr and dentary-squamosal joints (dual articulation), somewhat specialized teeth
- Morganucodon (stem-mammal): dentary-squamosol join, specialized teeth
- Didelphis (mammal): dentary-squamosal joint only, highly specialized teeth

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11
Q

Describe the jaws of mammals

A
  • Powerful
  • Merging of the temporal fenestra with the orbit and evolution of a single large jaw bone (dentary) increased the surface area available for jaw muscle attachment and allows for increased biting force
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12
Q

What do jaw bones have to do with hearing in mammals?

A
  • The quadrate and articular bones involved in early synapsid jaw articulation were incorporated into the middle ear, resulting in more efficient hearing
  • The chan of malleus, incus, and stapes bones create a complex system of levers known as the ossicles which reduce the amplitude of vibrations; increasing the mechanical force of vibrations and improving the efficient transmission of sound energy from the eardrum to inner ear (particularly amplification of high frequency sounds)
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13
Q

Describe tooth specialization in mammals

A
  • HOMODONTY
    • all teeth are functionally and anatomically of the same type, although size may be variable depending on location
  • HETERODONTY
    • “Swiss army” teeth: different teeth specialized for different function, e.g., incisors for cutting, canines for tearing, molars for grinding
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14
Q

What is diastema in mammals?

A
  • Diastema: a space or gap between teeth
  • Most herbivorous mammals have diastema between the incisors and molars, including many rodents, lagomorphs and ungulates
  • Caused by an imbalance in the relationship between the jaw and size of teeth
  • Often associated with enlarged incisors for cutting through tough vegetation
  • In contrast, many carnivores have smaller incisors and enlarged canines for puncturing and tearing into soft flesh
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15
Q

What are the different molar teeth specialization?

A
  • Carnivores
    • Carnassial teeth: slicing soft food
  • Herbivores
    • Hypsodont teeth: grinding fibrous food
  • Primates
    • Compression teeth: pulverizing hard food
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16
Q

What is crown height in mammals?

A
  • Brachydont
    • Low crowned teeth with well-developed roots (e.g., humans)
  • Hypsodont
    • High-crowned teeth with short roots (e.g., ungulates)
17
Q

What are the different cusp shapes on crowns of cheek teeth in mammals?

A
  • MULTICUSPID
    • Bunodont (chimpanzee)
    • Lophodont (horse)
    • Selenodont (deer)
  • UNICUSPID
    • Cone-shaped (dolphin)
    • Peg-shaped (armadillo)
18
Q

What are the two different terms for tooth replacement?

A
  • Polyphyodonty (REPTILES)
    • Continuous replacement of teeth
    • uneven tooth row (replacement is out of phase) make precise occlusion difficult
  • Diphyodonty (MAMMALS)
    • Only two sets of teeth
    • Keeps a full set of teeth in the jaw for complete and precise occlusion and better chewing of food
19
Q

Why is fur a useful adaptation for endothermy in mammals?

A
  • Can trap heated air next to the body
  • Protect the skin from sun or wind
  • Slow escape of sweat in hot conditions
  • Provide waterproofing (using oily secretions of sebaceous glands)
20
Q

What are the specialized glands in the skin of mammals?

A
  • Sweat glands - release water on skin for cooling
  • Apocrine glands - scent, pheromonal signals
  • Sebaceous glands - lubricate hair and protect skin
21
Q

What are mammary glands in mammals?

A
  • Mammals nurse their young with milk produced by mammary glands
  • Modified and enlarged sweat glands consisting of ducts and glandular tissues that secrete milk through nipples
  • Present in both males and females, but in most species mammary glands only fully develop in females
  • Provides young with important proteins, sugars, fats, and vitamins
22
Q

Describe the diaphragm in mammals

A
  • Diaphragm: muscles in the chest that expand and contract lungs
  • To work effectively, require the ribs to no restrict the abdomen so that expansion of the chest can be compensated for by a reduction in volume of the abdomen
  • Mammal rib cages haven greatly reduced lumbar ribs relative to a reptile which allows the diaphragm to work more effectively, facilitating strenuous activity and higher metabolic rate
23
Q

(IN MAMMALIA) What are Monotremata?

A
  • Order
  • Unusually for mammals: egg-laying and do not possess teeth as adults
  • 3 genera, 5 species
  • Australia, Tasmania and New Guinea
  • Subclass Prototheria
    • Order Monotremata
      • Family Ornithorhynchidae
        • duck-billed platypus
      • Family Tachyglossidae
        • Short-beaked echidna
        • Long-beaked echidnas
24
Q

Why is the platypus considered enigmatic?

A
  • First specimen thought to be a hoax
  • Mix of mammalian and reptile traits, plus some very unusual traits
  • Genome reflects this mosaic, e.g.,
    • Shares mammalian genes associated with milk production
    • Half as many odour receptors as other mammals (more similar to a reptile)
    • shares duplication of venom genes with reptiles
25
Q

What is the infraclass Marsupialia (Metatheria)?

A
  • 7 orders, ~280 species (~70% on the Australian continent)
  • Two primary divisions (superorders): American and Australian marsupials
  • Most species give birth to relatively undeveloped young that reside with the moth in a pouch (which contains nipples for nourishment)
  • Early birth puts newborns at greater environmental risk but reduces dangers associated with long pregancies
  • Relatively small skulls, different numbers of incisors in upper and lower jaws
  • Many species have a high number of teeth (`40-50) relative to placental mammals
26
Q

What are in the Superorder Ameridephia?

A
  • Didelphimorphia (oppossums)
26
Q

What are in the Superorder Ameridephia?

A
  • Didelphimorphia (oppossums)
    • 103 species in 19 genera
    • semi-arboreal omnivorous generalists that have been successful colonizers across diverse locations and conditions
    • Originated in South America and have spread into North America
    • Prehensile tails aid with climbing
    • When threatened, will mimic the appearance and smell of a dead animal
  • Paucituberculata (shrew oppossums)
    • 7 species in 3 genera
    • as recently as 20 million years ago were 7 genera
    • poorly known due to residing in difficult to access forest and grasslands habitat in the Andes mountains of South America
    • Mostly carnivorous (insects, worms)
    • nocturnal, poor vision, hunt mainly with hearing
    • reside in underground burows
    • no pouch, will often leave young in a burrow
27
Q

What is in the superorder Australidelphia?

A
  • Microbiotheria
    • “little brush monkey”
    • 1 species
    • insectivore supplemented with fruit
    • nocturnal and arboreal (bamboo thickets)
    • perhensile tail
  • Dasyuromorphia
    • Quolls, dunnarts, the numbat, the Tasmanian devil, the thylacine
    • 4 families, ~70 species
    • carnivores
    • primarily nocturnal
    • mostly ground-dwelling
      -territorial
    • threatened
  • Peamelemorphia
    • Bandicoots and bilbies
    • 3 families, 22 species
    • omnivores
    • polyprotodont
    • syndactyly
  • Notoryctemorphia
    • Marsupial moles
    • 1 family, 2 species
    • carnivores
    • mostly subterranean
    • dig tunnel using enlarged claws
    • blind, no external ears, short limbs, tube-like body
  • Diprotodontia
    • kangaroos, wallabies, possums, koalas, wombats
    • 11 families, ~125 species
    • mostly herbivores
    • diprodont
    • Syndactyly
28
Q

What is the Infraclass Placentalia (Eutheria)?

A
  • The fetus is carried in the uterus of the mother and nourished via a placenta until live birth of a well developed offspring
  • Distributed worldwide and highly diverse (21 orders, and 5080 species)
  • Four major clades determined mainly by (much debated) molecular data as opposed to shared anatomical characters
29
Q

What are the four major clades of Placentalia?

A
  • Euarchontoglires: primates, rodents, rabbits
  • Laurasiatheria: whales, bats, dogs, cats, seals, hoofed mammals
  • Xenarthra: armadillos, anteaters, sloths
  • Afrotheria: elephants, manatees, hyraxes, tenrecs, golden moles
30
Q

Describe the mammalian placenta

A
  • The placenta is an organ that develops in females during pregnancy and provides nourishment and oxygen to the fetus
  • Allows live birth of young in a more fully developed state (viviparity), which can improve their chances of survival
31
Q

What is the Magnorder Afrotheria?

A
  • Elephants, manatees, hyraxes, tenrecs, golden moles, aardvarks, sea cows, elephant shrews
  • Taxa are partly or entirely in African in their distribution
  • Probably due to Africa being an island continent during the early Cenozoic
  • Includes largest living land animals (Elephantidae)
32
Q

What is the Magnorder Xenarthra?

A
  • Anteaters, sloths, armadillos
  • Extant lineages only present in the Americas
  • Name means “strange joints” - vertebral joints have extra articulations unlike other mammals
  • No front incisors and poorly developed peg-like molar teeth
  • Some of the lowest metabolic rates among mammals
33
Q

What is the superorder Laurasiatheria?

A
  • Shrews, pangolins, bats, cetaceans, carnivorans, ungulates
  • Originated on the supercontinent of Laurasia 99 MYA
  • Chiroptera (bats) are the only mammals with powered flight
  • Cetaceans (whales, dolphins, porpoises) are fully aquatic
34
Q

What is the superorder Euarchontoglires?

A
  • Rodents, lagomorphs, treeshrews, colugos, primates
  • Split from Laurasiatheria sister group ~90 MYA and developed on the Laurasian island group that later became Europe
  • Primates possess the most advanced brain development in mammals

BIOL 305 (25 decks)

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