Lecture 12 Flashcards
What are the key mammal characteristics that have evolved?
. Circulatory system . Endothermy and hair . Evolution of lactation . Monotremes . Marsupial characteristics . Diversity of forms
What does coexistence if early mammals with ‘ruling reptiles’ in Triassic and Jurassic possibly favour? How can you tell?
Nocturnalism
Can tell because animals that are nocturnal tend to have larger eyes, small size and high activity rate
High activity at night requires what? What do these animals need to reduced the expenditure of body temperature?
Sophisticated senses, leading to a larger relative brain size
Requires more energy and the insulation provided by hair will reduce that expenditure of that body temperature
What is mammal hair made up of? What are the several levels of functions?
Keratin
Insulation, specialised hair e.g. whiskers that are able to sense, as a way of colouration as a warning or to recognise someone in a way of social communication
What does the Harderian gland beside the eye in mammals do?
Produces waterproofing oil applied to hair in extant mammals
What extinct animal had a Harderian gland and what does this suggest?
Morganucodon- an early mammal
Implies that it had hair
Why is it good if you need for teeth in early life is reduced (via lactation)?
The number of complete sets of teeth can be reduced and final set erupts in full-sized jaw for better occlusion)- means all the teeth can appear at the same time
What is the positive of having skin glands in reptiles?
Chemical tagging of young to aid recognition by mother; antibacterial secretion- added immunity
Diffuse sebaceous/ mammary gland secretion provides what?
Fluid nutrition and disease resistance
What does diphyodonty in reptiles facilitate?
Occlusion
What are monotremes? How many species are there? How are they different to mammals?
The oldest evolutionary mammals that are still extant
Only 5 species
Cheek teeth are the difference between monotremes and mammals
Describe monotremes (reproduction, where they are found, examples)
. Egg laying with extended maternal care: incubation followed by lactation from tufts of hair
. Cretaceous fossils (140 mya) from Australia and South America have tribosphenic cheek teeth (molars)
. Platypus (1 species) nests in Burris, 2 eggs from single functional left ovary, 16 weeks of maternal care; young have temporary molars- have them in the early stages but they are then replaced by the bill
. Have a period of extended maternal care where they look after their young. They produce milk from tufts of hair- so they have areas in the body where milk is secreted, but they don’t necessarily have nipples, so the evolution of nipples to secrete milk from mother to young would be to avoid milk getting in there
. Echidna (other example) (2 species; Australia and New Guinea), lays a single egg and incubates it in a pouch (homoplastic/ convergent with marsupial condition, have evolved separately for the same purpose)
How many extant species of marsupials are there? Where are they?
334 extant species; 70% in Australia and rest in South America, few in central and Northern America (1 or 2)
What are the defining characteristics of marsupials?
. Separate anus and urinogenital sinus
. Testes in scrotum outside body wall
. Paired lateral virginal and bifid penis (some have multiple to match the female)
. Placenta (not the same as in mammals), gestation
. Discrete mammary glands with teats
What is the differences between monotremes and marsupials?
. Marsupials have a separate anus and urinogenital sinus whereas monotremes have dual function cloaca
. Have testes in scrotum outside the body wall whereas they are internal in monotremes
. Have placenta and gestation whereas monotremes have shelled egg incubated externally
. Have discrete mammary glands with teats whereas monotremes have diffuse tissue (no nipples)
