Mammals – Part II

VERTEBRATE ZOOLOGY (VZ Lecture30 – Spring 2012 Althoff - reference PJH Chapters 18-20)

Bill Horn

EarlyMammalgroups

Monotremes

(egg-layers)

Marsupials (metatherians)

(pouched)Eutherians

(placentals)

Key “Features” of Mammals

• ____________—marsupials and eutherians

• _________________ —milk production for fairly rapid growth of young….more

focus on raising “a few” that have higher probability to reach adulthood

• ______________—heterodont (as noted before)…diet specializations

• _________—major advantage: thermal regulation

EarlyMammalgroups

Monotremes

(egg-layers)Marsupials

(pouched) Eutherians

(placentals)

Livebirth

Monotremes

• Most primitive—among mammal species

• ______________—lay eggs like birds

• ______________ —like birds

• ______________—like birds “mono” = 1 “trema” = hole Monotremata

(order)

• Do have hair and suckle young

Monotremes: in Australia or New Guinea

• 4 extant species:

duckbilled platypus

short-billed echnida(short-nosed echnida)

long-billed echidna (long-nosed echnida)

w. long-billed echidna

Duckbilled Platypus

• Family: Ornithorhynchidae (rhynchus = beak)

• Only ___________ is functional (like birds!)• Mammary glands but no teats• Toothless (except young)• Venomous (males only, hind foot onlyspur)• Dense fur, eyes and ears covered by flap of skin

when submerged, webbed feetkey adaptations to _______________ existence

• Leathery bill—very “tactile”…important is search of food

Echnidas

• Family: Tachyglossidae (tachy = fast, glossa = tongue)

• Also known as “spiny anteaters”• Poorly developed pouch (“pre-marsupial” feature?)

…lays its single egg in the pouch! …10 day incubation period …in pouch, post-hatch, about 4 weeks

• _____________ (edentate), flicks “sticky” tongue to obtain ants, termites, and earthworms

• Short, sturdy spines (_____) that are hollow and lack barbs (vs. porcupine)

• Limbs adapted for rapid digging (important for securing food)

Marsupials• ~ 6% of mammal species are marsupials

• More primitive reproductive pattern than __________ mammals

• Smaller braincase than same-sized ___________ mammals….no corpus callosum

• Where both exist, marsupials have largely been __________ by placentals (compare North America fauna—1 species “left”--to Australia)…yet marsupials probably originated in North America

Marsupials…distribution/ecology

• Last great stronghold for marsupials: Australian region (no _________ placentals except bats) and Neotropics

• Where placental mammals absent, considerable adaptive radiation and _______________

_______________ a) Tasmanian wolf = North American canids

b) sugar gliders = North American flying squirrels

• All large marsupial carnivores are extinct

Marsupials…con’t

• _______ well-developed auditory bulla (or absent)• _______ teeth than any other orders of mammals

(indicates less specialization)opossum = 50 total (28 premolars & molars)

vs.most rodents = 16 total (0

premolars, 6 molars)• Typically, adapted to arboreal heritage• Most have pouches • Number of nipples varies with species

AnteriorPosterior

Other reproduction-related biology

• _______________ period, little investment in energy compared to lactation period

• Entire litters _______ of mother’s body mass (vs. some placentals…rodents &

insectivores…where litter ~50%)

Other reproduction-related biology

• “Premature” newborn crawl to a teat, which swells keeping the young attached as the mother

moves about. Advantage(s) of short gestation

period & “pouch”? _________________________ _________________________

(From: Feldhamer et al. 2007)

1-week old Virginia opossums

~8-week old rock wallaby© Marie Read

Marsupial (metatherian) vs. Placental (eutherian) embryo & extraembryonic membrances

____________ considerably larger for marsupials than for placental

___________________ for marsupials….so no real anchoring in the uterine wall

vs.

Placentals where it is prominent, “anchored” to the endometrium (more about that during lecture focusing on

mammalian reproduction), and permits for nutrient waste exchange

From Feldhamer et al. 2007

1

1

2

Marsupials: __________________

• “big-footed” marsupials: kangaroos, wallabies• Found in Australasia (desertsforests)• 11 genera, 54 species (~20% of the marsupials)• All are browsing or grazing herbivores

(____________________________)

• _____________ equivalent to eutherian artiodactyls (think North American deer, elk,bison, pronghorn)

• Most have diprotodont dentition and diastema typical of herbivores

A)_____________dentition (shortened mandible with first pair of lower incisors enlarged to meet upper incisorsB) Large diastemaC) Pronounced _____________ fossa of the mandible

AB

C

WALLABY SKULL

Marsupials compared to placentals• Relatively smaller braincase

• No corpus callosum

• Reduced or absent auditory bullae

• Have ____________ basal metabolic rate

• ____________ range of body sizes

• Occupy ____________ range of ecological niches (ex. none occupy niches like bats (air), whales (ocean), or fossorial herbivores

In summary….1) some “links” to birds (the monotremes)2) monotremes are primitive mammals3) marsupials are more diverse and more widely distributed than monotremes4) marsupials and eutherians (placentals) have

more advanced reproductive patterns than monotremes (i.e., live birth)

5) marsupials and eutherians have significantdifferences in length of gestation and

lactation periods…but still have about thesame parental investment in production of young up to weaning