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

Paucituberculata morphology Small, shrewlike Long rostrum, adult weigh 40g No marsupium Didactylous, only New World marsupial that is diprotodont Lower canine vestigial

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