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Flashcards in Intro to Mammals Deck (17)
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1

Historical Context

When did mammals first appear?

First appeared Triassic Period (220 Ma), coexisted with dinosaurs through to end of Mesozoic (225 to 135 Ma)

Dominant terrestrial vetebrates since beginning of Cenozoic (63 to 0 Ma)

2

Number of Species

Comprised of 4.5K species (1.8K rodents)

Make up around 1/6 of terrestrial vetebrates

3

The Vertebrate Skull

Composed of 3 main components:

chrondocranium - the brain case

visceral skeleton - the gill arches and jaws

dermal elements - superficial framework (dermal bones)

4

Early Reptile Skull Structure

Form, issues, and how they were resolved...

In the ancestral amniote and early reptiles the chrondocranium and dermal elements were solid & heavy, restricting jaw muscles - known as anapsid

Problem solved by adding holes in side of dermal elements.

 

 

5

Various Skull Structures

6

Mammal Lineages

From what to what? And what on the way?

Split off from reptiles at the start of the Mesozoic - most recent CA was "the ancestral amniote"

AA to mammals by way of:

dimetrodons (large, reptilian synapsids) then

therapsids (mammal-like reptiles)

First "real" mammals appeared during Mesozoic - small and nocturnal, didn't diversify until dinosaur extinction freed up niches

7

Mammal Subtaxa

Three (sort of):

Monotremes (5 species)

Marsupials (324)

Eutherians (5010)

8

Monotremes

Species?

Defining Characteristics?

Only 5 species - 2 subgroups 

Echidnas (AUS & New Guinea)

Platupuses (AUS)

Lay eggs (reptilian)

Have hair (mammalian)

Endothermic (m), but at ~32 C

Produce milk (m) but no nipples - secreted directly through skin

9

Marsupials

Species?

Defining Characteristics?

Found in AUS and Americas

Includes Opossums, Bandicoots, Koalas, etc

Young are born premature and crawl to pouch on mother to develop

Show clear paralells to placental mammals, but outcompeted everywhere except AUS & NG

10

Eutherian Mammals

All other mammals

Closely related to marsupials (probably diverged at least 125 Ma ago)

4 clades:

Afrotheria

Xenarthra

Euarchontoglires

Laurasiatheria

 

11

Afrotheria

Animals in or originally from Africa. Various orders:

Proboscidea (elephants)

Sirenia (manatees and dugongs)

Hyracoidea (hyraxes or dassies)

Macroscelidea (elephant shrews)

Afrosoricida (tenrecs and golden moles)

Tubulidentata  (aardvark)

 

12

Xenarthra

Means "strange joints" - extra articulation in vertebral joints

reduced/no teeth

Sloths, anteaters, armadillos 

13

Euarchontoglires

Not the most coherent of clades, but evidence against has yet to be uncovered:

Glires:

Rodentia (rodents)

Lagomorpha (rabbits, hares, pikas)

Euarchonta:

Primates

14

Laurasiatheria

Mammals believed to have originated on the northern supercontient of Laurasia

Carnivora (dogs, cats, bears, etc)

Cetartiodactyla (sheep, pigs, cows, camels, etc)

Cetacea (whales, dolphins, and porpoises)

Perissodactyla (odd-toed ungulates including horses, tapirs and rhinoceroses)

Chiroptera (bats)

Eulipotyphla (hedgehogs, moles, shrews, etc)

Pholidota (pangolins)

15

Mammalian Characteristics

What makes a mammal?

Vertebrates - internal skeleton made of bone

Skin: hair/fur; nails, hooves, horns; mammary glands

facial muscles: more, and externally placed

diaphragm: efficient breathing

high metabolic rate (also in birds): endothermy

heterodony: adapted, specialised teeth

parasagittal gait: limbs paralell to vertebral column

16

Mammalian Bone

What's so special about it?

Bone: tissue w/ several cell types, innervated and w/ blood supply

Regulator of Ca2+ and PO4 in mammals

Formed and degraded much faster than in other vertebrates

17

Mammalian Skin

"Key to mammal-ness"

Varies in thickness between rodents (<10 cells thick) to humans (20-40) to elephants and rhinos (200-400)

Varies hugely in texture: hairy-furry, smooth-hairless, rough-dry, etc

Hair (keratin): insulation, camoflage, display, defence/tools (horns, nails)

Secretion: cooling/adhesion (eccrine glands), waterproofing/scent (sebaceous glands), volatile scent (apocrine glands), milk (mammary glands)