Mammals – Part II VERTEBRATE ZOOLOGY (VZ Lecture30 – Spring 2012 Althoff - reference PJH Chapters 18-20) Bill Horn

Early Mammal groups 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

Early Mammal groups Monotremes (egg-layers) Marsupials (pouched) Eutherians (placentals) Live birth

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 only  spur) Dense fur, eyes and ears covered by flap of skin when submerged, webbed feet  key 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 Anterior Posterior

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

Marsupials: __________________ “big-footed” marsupials: kangaroos, wallabies Found in Australasia (deserts  forests) 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 incisors B) Large diastema C) Pronounced _____________ fossa of the mandible A B 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 mammals 3) marsupials are more diverse and more widely distributed than monotremes 4) marsupials and eutherians (placentals) have more advanced reproductive patterns than monotremes (i.e., live birth) 5) marsupials and eutherians have significant differences in length of gestation and lactation periods…but still have about the same parental investment in production of young up to weaning