Intro to Mammals Flashcards
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)
Number of Species
Comprised of 4.5K species (1.8K rodents)
Make up around 1/6 of terrestrial vetebrates
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)
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.
Various Skull Structures
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
Mammal Subtaxa
Three (sort of):
Monotremes (5 species)
Marsupials (324)
Eutherians (5010)
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
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
Eutherian Mammals
All other mammals
Closely related to marsupials (probably diverged at least 125 Ma ago)
4 clades:
Afrotheria
Xenarthra
Euarchontoglires
Laurasiatheria
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)
Xenarthra
Means “strange joints” - extra articulation in vertebral joints
reduced/no teeth
Sloths, anteaters, armadillos
Euarchontoglires
Not the most coherent of clades, but evidence against has yet to be uncovered:
Glires:
Rodentia (rodents)
Lagomorpha (rabbits, hares, pikas)
Euarchonta:
Primates
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)
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
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
