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