vertebrates; mammals; monotremes and marsupials Flashcards
aus is only country with all
3 subclasses of mammals
3 subclasses of mammals
eutheria (eutherians)
metatheria (marsupials)
prototheria (monotremes)
monotreme, 5 species but name 2
platypus and short-beaked echidna (both native to aus)
where did monotremes originate
gondwana
monotremes retain several reptilian characteristics such as
- oviparity (eggs)
- meroblastic cleavage of embryo
- produce venom
- electroreception
defining characteristics of monotremes (7)
- absence of calcified teeth
- electroreception
- reptile like stance
- cloaca
- oviparity
- no teats
- venom
crural glands
- venom
- more developed in playtpus than echidna
- sharp keratinous spurs
- medial aspect of tarsal joint
- move independently
- venom evolved independently of reptile venom
- intense pain
- non fatal to humans
electroreception of monotremes
- located within skin of bill/beak
more in platypus - scan for electrical disturbances
- swing head from side to side while swimming
monotreme skull
pre-maxilla forms the bill/beak
monotreme pectoral girdle
- coracoids, epicoracoids and inter-clavicle
- reptilian features
(in eutherians, coracoid fused w scapula to become coracoid process)
monotreme pelvic girdle
epipubic bones
have ilium, ischium and pubis
monotreme limbs
right angle to body
reptilian features but rotate in socked to give mammalian gait
monotremes have multiple
X and Y chromosomes
in the male at meiosis form alternating XY chains, segregate into multiple X and multiple Y bearing sperm
sex determination in monotremes
lack SRY gene on Y chromosomes, unlikes marsupials and eutherians
monotreme system uis link between bird and therian mechanisms
in platypus only ____ ovary is functional
in echidna:
left
in echidna both ovaries functional
describe monotreme eggs
large, yolky, porous leathery shell
platypus; 1-3 eggs incubated in nest
echidna; 1 egg incubated in transient pouch and kicked out when spines start to develop
do monotremes have mammary glands
yes but no teats so young lap milk from specialized hairs
marsupials are named for their
marsupium or pouch (not all marsupial possess a pouch)
marsupials are NOT
primitive mammals
marsupials and eutherians diverged from common ancestor, evolving independently since this time
marsupials are unique in their mode of reproduction:
young born in altricial state
dependence on lactation rather than gestations
marsupial chromosomes compared to eutherians
fewer and larger
what chromosomes necessary for pouch rather than scrotum development
XX
can be
XX: female and pouch
X: female and scrotum
XY: male and scrotum
XXY: male and pouch
explain why genital ducts and ureters are unique in marsupials
- in all mammals embryo has ureters and mallerian ducts
- in eutherians ureters pass laterally to mullarian ducts and distal end of mullerian ducts fuse to form vagina
- in marsupials; ureters pass MEDIALLY to mullerian ducts, and distal ends of mullerian ducts cannot fuse so 2 lateral vaginae from mullerian ducts
the unique way their ureters and ducts are means marsupials have
2 lateral vagina and a median vagina which becomes patent just before parturition, then may regress of remain patent after giving birth
sperm in lateral vagina only
