BIOL 111 Lecture 23: Mammal 1

• School: McGill University
• Department: Biology
• Course: BIOL 111
• Professor: Andrew Hendry

Document Summary

Divergence between reptilian and mammalian-like amniotes occurred during carboniferous (around 350 million years ago) ---- before the evolution of birds . Sweat glands: mammary glands ---- milk production, mammalian evolution. Ture mammals evolved 225 million years ago (triassic: early mammals were small, arboreal, shrew-like insectivores, nocturnal, had improvements to middle ear. Elephant-sized (brea tar-pit in los angeles: return to oceans. Early similar to whales, can hear while underwater. Unlike reptiles and fish, mammals also show heterodonty (different teeth specialized for different tasks) ---- specialization in teeth among species reflects varied diets. Sexual dimorphism (when the sexes appear differently in size, color and morphology) Have mammary glands ---- no nipples, young suck milk from fur. Species (found in australia and new guinea: platypus, eastern australia, use bill to dig for crustaceans and worms, build nests in river banks. Lay 2-4 eggs, hatch around 8 days and nurse 5 months. Two species: short and long nose (spiny anteaters)