monotremes and marsupials biol 455 mammalogy jan 27, 2005
TRANSCRIPT
Monotremes and Marsupials
Biol 455 Mammalogy
Jan 27, 2005
Monotremata Prototheria, retention of various reptilian
features Two families: Ornithorhynchidae and
Tachyglossidae Monotremata = “one opening”
Cloaca, common opening of fecal, urinary and reproductive tracts
Rubbery-shelled eggs (permeable)
Monotremata con’t
Eggs are small, incubated for 10 to 11 days
Neonates have well developed forelimbs and shoulders
Monotremata con’t
No teats Pectoral girdle has coracoid, precoracoid,
and interclavicle bone (similar to Therapsid reptile)
Homeotherm - low Tb of 32 C Sperm are fiiform (threadlike) and testis
structures similar to reptile
Pectoral girdle
Morphology of monotremes Cranium - indistinct sutures Jugal bone reduced or absent Zygomatic arch made up of maxilla and
squamosal bones Dentary bone reduced Adults are edentate Elongate rostrum, lack of teeth, high-
domed cranium - birdlike
Morphology con’t
Cochlea (semicircular canal of inner ear) are not coiled
Have epipubic bones Males have large medial spur on ankle Males have baculum, permanently
abdominal testes and no scrotum
Epipubic bone
Ornithorhynchidae Duck-billed platypus Semiaquatic, semifossorial Near freshwater lakes and rivers, east coast of
Australia and Tasmania Feed on invert., fish and amphibians Adult male 1.7 kg, female smaller Short dense fur covers all but bill, feet, and underside
of tail Bill is soft and pliable, with nostrils at tip
Has tactile receptors to sense electric field generated by muscle contraction of prey
Ornithorhynchidae con’t
Has small eyes and ears Pentadactyle (five-toed) and manus
(forefoot) is webbed Long claws for digging burrow
Ornithorhynchidae con’t Spur on hind limb connect to venom gland
in thigh Platypus has no pouch, female incubate
eggs in burrow Neonates have molariform teeth, shed
before emerge from burrow Keratinized pads
Milk is secreted onto tufts of hair
Ornithorhynchidae con’t
Tachyglossidae Short-beaked echidna (Tachyglossus)
Australia, New Guinea, and Tasmania 6 kg
Long-beaked echidna (Zaglossus) Forested highland of New Guinea 10 kg
Feed on ants, termites, and insects - ground to paste between tongue and spiny palatal ridge
Have scooplike claws on feet to break anthills and burrows
Ankle spur not venomous
Tachyglossidae con’t Beak contains electroreceptors Guard hairs modified to become spines Mucus that coat tongue to make it sticky No teeth at any stage of development Have a pouch for incubating eggs
Marsupials
Characterized by marsupium Only 50% of species have permanent pouch
Litters that weigh 1% of mother’s body mass Eutherians: litters weigh 50% of mother’s BM
Have well-developed stylar shelf
Marsupials con’t
Lower basal metabolic rate (BMR) - 70% of comparable sized eutherians
Slower postnatal growth Smaller relative brain size No true flight, no fossorial herbivores,
large marsupial carnivores are extinct
Marsupial reproduction
Bifurcated reproductive tract (female) and bifurcated penis (male)
Choriovitilline placenta Limited intrauterine development time and
accelerated development of muscular forelimb Precludes forelimb from becoming hooves,
flippers, or wings
Marsupial reproduction con’t Paired sperm in New World marsupials Marsupium - open anteriorly or
posteriorly, folds of skin Best developed in arboreal species, and
species that burrow or jump Neonate (no more than 1 g) climb to a
teat Once attached, teat swells, keeping neonate
in place
Zoogeography Living marsupials occur in NA, Central and SA,
Australasia Marsupials are thought to have originated in North
America Oldest fossils dating 100 mya
Panamanian land bridge developed 2 to 5 mya, major interchange of fauna
65 mya, marsupials moved from SA through Drake Passage to Antartica and Australasia
Australian marsupials evolved in relative isolation from eutherians
Orders and Families 7 orders and 18 extant families Polyprotodonts - unshortened mandible, lower
incisors small and unspecialized Diprotodont - shortened mandible with first pair
of lower incisors enlarged to meet upper incisors
Didactylous - unfused toes, each in own skin sheath
Syndactylous - skeletal elements of 2nd and 3rd toes in common skin sheath
Dentition
Digits
Didelphimorphia Single family, Didelphidae New World distribution Terrestrial burrowers, semiarboreal Solitary and opportunistic feeders Most specialized didelphid, water opossum (aquatic,
webbed hind feet, marsupium watertight during dives)
Didelphimorphia morphology Paired spermatozoa Pentadactyly, with primitive metatherian
dental formula 5/4, 1/1, 3/3, 4/4 =50 Polyprotodont and didactylous Have sparsely haired prehensile tails and
opposable pollex (thumb on forefoot) Some have incrassated tail (store fat in
the base)
Paucituberculata
Single family, Caenolestidae “Shrew” or “rat” opossum Dense vegetation of northwestern
Samerica Nocturnal, insectivorous or omnivorous,
and terrestrial Paired spermatozoa
Small, shrewlike Long rostrum, adult weigh 40g No marsupium Didactylous, only New World marsupial that is
diprotodont Lower canine vestigial
Paucituberculata morphology
Microbiotheria
Single family, Microbiotheriidae One species, monito del monte (Dromiciops
gliroides) South central Chile in beech/bamboo forest Small, 16-30g Have prehensile tail and pouch Greatly inflated auditory bullar Called “colocolos” by natives, bad omen
Dasyuromorphia Small to medium sized, incl. carnivorous
species (Tasmanian devil and quoll) Polyprotodont and didactylous Canines well-developed, have carnassial
dentition Tails never prehensile 3 families: Thylacinidae, Myrmecobiidae,
Dasyuridae
Numbat
Dasyuromorphia con’t
Peramelemorphia Bandicoots and bilbies - Australasia 2 families, Peramelidae and Peroryctidae Terrestrial omnivores Have chorioallantoic placenta (no villi) Short compact body with long pointed rostrum Bandicoots have well-developed patella
(kneecap) and no clavicle Polyprotodont Marsupium opens posteriorly
Diprotodontia
8 families, 116 species Diprotodont, syndactylous In arboreal diprotodonts, first two digits of
forefeet oppose the other three digits - schizodactylous Hallux (big toe) opposable (not in terrestrial
species)
Phascolarctidae
Koala
Vombatidae
Wombat - powerful burrower 30 kg Grazing herbivore, dentition open-rooted
Phalangeridae
Brushtail possum, cuscus Long prehensile tail, excellent climbers
Potoroidae
Bettongs, potoroos Weak prehensile tail Upper canine well developed Have embryonic diapause
Macropodidae Kangaroos and wallabies Grazing herbivores Similar to artiodactyls Molar hypsodont, mesial drift of cheekteeth
Burramyidae
Pygmy possum - smallest possum 7-50g Exhibit embryonic diapause
Acrobatidae Feathertailed glider and feather-tailed possum New Guinea Stiff, featherlike hairs on side of tails Feathertailed glider - smallest gliding mammal
(10-14g) Both species nectivorous with brush-tipped
tongue Exhibit embryonic diapause
Pseudocheiridae
Slow-moving, ringtail possum Feed on leaves, aboreal Molars are selenodont Schizodactylous digits Prehensile tail Have marsupium
Petauridae
Striped possums and wrist-winged gliders Petaurus similar to NA gliding squirrels Prehensile tail, opposable hallux Have marsupium Diprotodont but molars bunodont
Tarsipedidae Honey possum 12 g Nectivorous Long pointed rostrum with brush-tipped
tongue, small peglike teeth Prehensile tail, hallux opposable, pads on
digits for gripping branches Delayed implantation
Notoryctemorphia Marsupial mole Secretive, completely fossorial, eats beetles and
larvar Similar to eutherian talpids and chrysochlorids “Swim” through ground, substrate collapse behind, no
permanent tunnels Spend time aboveground too, active both day and
night Fusiform, scooplike claw, thick keratinized nasal
shield (pushing dirt) Cervical vertebrae fused, no pinna, vestigial eye
Notoryctemorphia con’t
Epipubic bone reduced Molars zalambdodont (v-shaped) Eaten by aborigines