Monotremes and Marsupials

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