1. Monotremes and Marsupials
Biol 455 Mammalogy
Jan 27, 2005

2. 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)

3. Monotremata con’t Eggs are small, incubated for 10 to 11 days
Neonates have well developed forelimbs and shoulders

4. 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

5. Pectoral girdle

6. 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

7. 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

8. Epipubic bone

9. 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

10. Ornithorhynchidae con’t
Has small eyes and ears
Pentadactyle (five-toed) and manus (forefoot) is webbed
Long claws for digging burrow

11. 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

12. Ornithorhynchidae con’t

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

21. 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

22. 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

23. Dentition

24. Digits

25. 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)

26. 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)

28. Paucituberculata Single family, Caenolestidae “Shrew” or “rat” opossum
Dense vegetation of northwestern Samerica
Nocturnal, insectivorous or omnivorous, and terrestrial
Paired spermatozoa

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

30. 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

31. 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

33. Numbat

34. Dasyuromorphia con’t

35. 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

37. 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)

38. Phascolarctidae
Koala

39. Vombatidae Wombat - powerful burrower 30 kg
Grazing herbivore, dentition open-rooted

40. Phalangeridae Brushtail possum, cuscus
Long prehensile tail, excellent climbers

41. Potoroidae Bettongs, potoroos Weak prehensile tail
Upper canine well developed
Have embryonic diapause

42. Macropodidae Kangaroos and wallabies Grazing herbivores
Similar to artiodactyls
Molar hypsodont, mesial drift of cheekteeth

43. Burramyidae Pygmy possum - smallest possum 7-50g
Exhibit embryonic diapause

44. 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

45. Pseudocheiridae Slow-moving, ringtail possum Feed on leaves, aboreal
Molars are selenodont
Schizodactylous digits
Prehensile tail
Have marsupium

46. Petauridae Striped possums and wrist-winged gliders
Petaurus similar to NA gliding squirrels
Prehensile tail, opposable hallux
Have marsupium
Diprotodont but molars bunodont

47. 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

48. 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

49. Notoryctemorphia con’t
Epipubic bone reduced
Molars zalambdodont (v-shaped)
Eaten by aborigines