Monotremes and Marsupials




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Monotremes and Marsupials
This lab centers on the Monotreme (egg-laying) and Metatherian (marsupial) mammals. Use your text (Chapter 10) to learn about the geographic distribution, habitat, food habits and natural history of these animals. Be able to identify the skulls, skins and slides and note how the skull and body anatomy is related to life history. Throughout this lab, note how convergent evolution has led to similar anatomical solutions for animals occupying similar ecological niches, even when those animals are as distantly related as marsupials and eutherians.
Skeletal features:

Note that Prototherians and Metatherians retain some reptilian bony elements that eutherians lack. These include: epipubic bones attached to the pelvis in both Prototherians and Metatherians, and the coracoids, precoracoids and interclavicle of the pectoral girdle found in Prototherians. See table 10.1 for other Metatherian – Eutherian comparisons and note as many as possible on the specimens available in lab. .


Reproductive tract:

Recall that Metatherians have a bifurcated reproductive tract in males and females. Note that the penis of the male Virginia opossum is forked, and that the testicles are anterior to the penis.


Tooth structure:

Extant prototherians lack teeth, so the ancestral condition of this mammalian lineage is unknown. Some metatherians and some eutherians (insectivores) have teeth that remain very similar to that found in the immediate ancestors of mammals, teeth that are referred to as unmodified tribosphenic teeth (pp50-51, Figure 4.10 1st ed, pp48-49 2nd ed). Note how the lower molar retains the talonid basin into which the protocone of the upper molar fits. Can you see the characteristic stylar shelf that links the upper molars together as in Fig 10.8? Recall that this condition is the anscestral one, and that many lineages have greatly modified it. Do all metatherians show this unmodified tribosphenic cusp pattern?



Prototherians


Order Monotremata “one-hole”

Family Ornithorhynchidae “bird nose” (Or nith’ o rynk’ id ee)

Duck-billed platypus - Page 176 Fig 10.3, 10.4 & 10.5 in Feldhamer

Adapted for life in the water, with webbed hind and fore feet and a venomous spur on the ankle of males! The soft leathery bill is used to search the lake and stream bottoms for invertebrates. The bill is amazingly sensitive to touch and can even detect electrical currents. Muscle contractions of some of its prey (crayfish, insect larvae) generate electrical currents that the platypus’ bill may detect at close range. Touch and electric sense are very important because the small eyes are closed when the platypus swims underwater. Note that there are no teeth in the adult. Teeth develop embryologically, then degenerate and are replaced by the horny crushing plates.


Order Monotremata

Family Tachyglossidae - “swift–tongue” (Tack’ i gloss’ id ee)

Short-beaked echidna Pp 176-177, Fig. 10.3, 10.6 in Feldhamer

With guard hairs modified into protective spines, echidnas, or spiny anteaters as they are also called, converge on the porcupines and hedgehogs in terms of having a very effective protection from predators. In terms of diet, echidnas are convergent on the marsupial numbat and eutherian anteaters, specializing on termites and ants as its major food source. Many ant specialists have elongated rostrums and reduced teeth, but the echidna has taken this to the extreme, with teeth completely absent and the rostrum modified into a tubular “beak” that it uses to stab into the soil or termite mound. Its dentary is reduced to a mere sliver and its tongue long and sticky. It is an excellent burrower, with heavy claws and powerful fore- and hindlimbs and can dig rapidly when threatened, sinking down into the soil like a submerging submarine until only the spines on its back are exposed. In this sense it converges on the armadillo. Note how in both animals the humerus and femur have been modified for supporting the large digging muscles. Note that both animals need extra protection because diggers are not good runners, so the echidna has spines while the armadillo has its bony shell.


Metatherians


Order Didelphimorphia (Di delf o morf’ ee a)

Family Didelphidae pp181-182, (Di delf’ id ee)

These marsupials are generalists and their dentition reflects this. What modifications of the dentition do you see that would suggest an omnivorous diet? The Virginia oppossum is the only marsupial in the United States, but in Central and South America this group is quite diverse, as indicated by the other didelphid skins and skulls shown here. Note on the skeleton some of the distinguishing traits of metatherians: epipubic bones, medially inflected angular process, jugal participating in the jaw articulation and the diamond shaped nasal bones. Note: not all marsupials have all of these characteristics, but at least one is usually present.



Order Microbiotheria (Micro bio theer’ ee a) Family Mcrobiotheriidae (Micro bio thuh ree’ id ee) and

and Order Paucituberculata (Posse too burk u lata), Family Caenolestidae (See no less’ ti dee)

are two small South American orders. We have no specimens, only slides of these.
Order Dasyuromorphia (Daisy uro’ morf ee a)

Family Myrmecobiidae (Mur ma co bee’ id ee)– numbat pp 184-185 “ant-eater”

Unfortunately we don’t have a skull or skin of this animal, but it is important because of its convergence on the echidna and eutherian anteaters. Once again, ants and termites are a rich resource, often abundant and widespread, and many mammalian lineages have evolved adaptations to feed on them. Look at the skull drawing and determine which skull characteristics are typical of a myrmecophagous mammal.


Family Thylacinidae - (Thigh la sin’ a dee) The thylacine or Tasmanian tiger. “pouch- dog”

Note the amazing convergence between the thylacine and coyote skull. What skull characteristics typical of a carnivorous mammal do they share? Would such similarity support or refute the idea that competition between dogs and thylacines could have led to the thylacine’s extinction? Is it extinct? Every year reports come out of the wilds of Tasmania that one of these has been sighted. Although many scientific searches have been made, it is unlikely any survive, (but I’d like to think there are one or two wily pairs of these amazing animals out there).


Family Dasyuridae (Daisy ur’ id ee) “hairy tail” pp 184 186

These are predatory marsupials of three sizes.

1) The Tasmanian devil, a thick bodied animal the size of a bull terrier can kill its own prey but is also a great scavenger, feeding on road-killed wallabies and kangaroos. It is said that the bodies of hikers that go missing in the Tasmanian highlands are often never found, in part because these animals are so good at not only scavenging meat, but also of crushing and scattering bones. Note the similarities between the skulls of the marsupial devil and the eutherian badger.

2) The marsupial cats or quolls hunt on the ground and in the trees for their prey of small rodents and marsupials and birds. They are about the same size as a domestic cat. Note the similarity between their skull and that of a Pine marten, a member of the weasel family here in North America that hunts on the ground and in trees for squirrels.

3) The “marsupial shrews”, like this animals in the genus Antechinus, are small mouse-sized energetic predators that take on invertebrates and vertebrates that are often as large or larger than themselves. In this way they are convergent on the North American shrews.
Order Peramelemorphia (Pear o mel a morf’ ee a)

Family Peramelidae (Pear a mel’ id ee) – bandicoots pp185-186 “pouched badger”

Bandicoots are about the size of a cottontail rabbit and are often considered pests by home owners in Australia, because of the conical holes and piles of dirt they leave behind in lawns and gardens after a night foraging for worms and other invertebrates. Are they convergent on any North American mammals?


Order Diprotodontia (Dip ro to don’t’ ee a)

Family Vombatidae (Vom bat’ i dee) – wombats p 188.

These animals are relatively large, about the size of a small sheep. They live in burrow systems that they often share with other wombats. Compare the wombat skull to the beaver. What dental characteristics do they share? Have you noticed any other marsupials with this characteristic? What might be one reason that the skull is so flat and heavy?


Family Phascolarctidae (Fas co larc’ ti dee) – koala pp187-188 = “pouch bear”

Koalas are famous for their dependency upon a single food resource – the leaves of a specific subset of Eucalyptus trees. This low energy-food leads to a low-energy lifestyle, and koalas seem to spend most of their time eating and sleeping. Males can be quite aggressive during the mating season however, and have been known to kill small and medium sized dogs. Ask the instructor and perhaps he will give a demonstration of a male koala’s territorial call. How do you recognize koala dung in the field? Just take a whiff, they smell like eucalyptus too.

What term describes the cusp pattern on the koala teeth? What characteristics of jaw and skull are typical of a herbivorous diet?
Family Phalangeridae (Fal an jer’ i dee) – phalangers and brush-tailed possums “web-toed”
This group is in many ways the Australian equivalent of New World oppossums (Family Didelphidae), with many being omnivorous. Compare the skull of this brushtail possum with that of the virginia opposum of North America. Based on skull characteristics, which would be more folivorous and which more omnivorous? Why?
Family Petauridae (Pet tar’ id ee) - gliders
One group of mammals in this family, the sugar gliders and squirrel gliders, show striking convergence on the flying squirrels of North America. Note the long, slender limb bones of this Squirrel Glider and the furred flight membranes of the Sugar Glider. These “wing” membranes allows the animal to glide from tree to tree. NOTE: you won’t have to distinguish between skulls of Petaurids and Phalangerids.
Family Macropodidae (Mac ro po’ di dee) – kangaroos and wallabies pp 189-190 “big-foot”
The niche kangaroos fill in Australia has often been likened to that filled by grazing ungulates (hoofed mammals) in other parts of the world. Compare the skulls of the kangaroo with that of the deer. What similarities are there and how might this relate to similar feeding niches? How would you describe the teeth on the kangaroo in terms of crown height and cusp pattern? Is there any evidence of the mesial drift mentioned in your text on this skull?
Family Tarsipedidae (Tar suh ped’ i dee) – honey possum pp 191 “tarsier – foot”

These animals are most notable because they depend entirely upon pollen and nectar as a food source. In this respect they are convergent on another group of marsupials (pygmy-possums, Family Burramyidae) and nectar-feeding bats. See Figure 10.29 in your text for a diagram of the highly modified skull and tongue. What other animals in today’s lab have shown similar skull adaptations for an entirely different reason? Which would be a more effective pollinator of plants, a honey possum or a bat? Why? The family name is based on similarities between feet of honey possums and those of a primate, the tarsier.


Order Notoryctemorphia (No toe ric ta morf’ ee a)

Family Notoryctidae (No toe ric’ tid ee) – marsupial “moles”

We don’t have a specimen of this animal but you should know it because of its remarkable convergence on the moles of North America and the golden moles of Africa. All three groups show similar adaptations for a fossorial lifestyle; silky hair, reduced eyes, pinna and tails, strong forelimbs with large claws for digging.



Key to Skulls of Monotreme and Marsupial Orders in the NAU Teaching Collection
1A Teeth absent...…Subclass Prototheria….Order Monotremata (platypus & echidna)
1B Teeth present, angular process of the dentary medially inflected, jugal usually

participates in mandibular articulation ……………Subclass Theria, Infraclass Metatheria….………………………………………………………………..2


2A Teeth diprotodont (a)……………………………………… Order Diprotodontia

(koala, wombats, kangaroos, possums, gliders)

2B Teeth polyprotodont (b)………………………...………………………… 3
3A Incisors 5/4 …………………….……………………….. Order Didelphimorphia,

(N and S American opposums)

3B Incisors 5/3 or 4/3-4………………………………………………………….4.
4A Rostrum elongate, upper incisors roughly the same size, upper C widely separated from both incisors and premolars……..………………….Order Peramelemorphia,

(bandicoots)

4B Rostrum may or may not be elongate, first upper I usually larger than rest, upper C not separated from both incisors and premolars………...Order Dasyuromorphia

(Australian marsupial cats, devils, “shrews”)






  1. Diprotodont dentition b. Polyprotodont dentition

Lower mandible is shortened and unshortened mandible,

lower incisors elongated to meet upper incisors lower incisors small,

unspecialized

(wombat, Vombatidae) (marsupial cat Dasyuridae)


Although most orders of marsupials occur in Australia, not all are found there. On the map on the next page, indicate where the Order Monotremata and the marsupial orders are found. What could explain this current distribution? Mark with an “x” the continent on which the earliest marsupial fossil was found.

Key to Skulls of Monotreme and Marsupial Families in the NAU Teaching Collection
1A Teeth absent ………………………Subclass Prototheria…….Order Monotremata…… 2

1B Teeth present, angular process of the dentary medially, inflected, jugal usually participates in

mandibular articulation ……………Subclass Theria, Infraclass Metatheria….……….. 3
2A Rostrum with flared premaxilla forming a bill…………..….F. Ornithorhynchidae (platypus)

2B Rostrum narrow, thin delicate dentary…………………….……F. Tachyglossidae (echidnas)


3A Teeth diprotodont (first pair lower incisors enlarged and elongated)… Order Diprotodontia ………………………………………………………………………………………..… 7

3B Teeth not diprotodont…………………………………………………………………… 4


4A Incisors 5/4 ……………………………….……………………….. Order Didelphimorphia,

Family Didelphidae, (N and S American opposums)

4B Incisors 5/3 or 4/3-4……………………………………………………………… ……… 5
5A Rostrum elongate, upper incisors roughly the same size, upper C widely separated from

both incisors and premolars……....Order Peramelemorphia, Family Peramelidae (bandicoots)

5B Rostrum may or may not be elongate, first upper I usually larger than rest, upper C not separated

from both incisors and premolars…………………………………..……………………. 6


6A Skull large, greater than 150mm in length, dog-like…………………………F. Thylacinidae

(Australian marsupial wolf)

6B Skull smaller than 150mm in length………………………………………......F. Dasyuridae

(Australian marsupial cats, devils, “shrews”)

7A Dental formula 1/1,0/0,1/1,4/4, …………………………………..…………....F. Vombatidae

(wombats)

7B Dental formula not as above, …………………………………………………….… 8
8A Upper incisors 3/1, equal in size, lower incisors very procumbent, deep masseteric

fossa with large masseteric canal, P’s sometimes bladelike ……..… ……..…F. Macropodidae

(kangaroos, wallabies)

8B Upper incisors not 3/1 or if 3/1, I1 larger than I2-3, slightly procumbent, masseteric

fossa shallow, masseteric canal small if present, P’s not bladelike…………………….. 9
9A Incisors 3/1, molars selenodont………………………………….…..F Phascolarctidae (koala)

9B Incisors 3/2-3, 2nd and 3rd lower I tiny or absent, molars usually with rounded cusps

………………………………………………………………………..F. Phalangeridae

(Australian possums and cuscuses)


A
lso be able to recognize representatives of the Orders Microbiotheria, Paucituberculata, & Notoryctemorphia, and F. Tarsipedidae and Myrmecobiidae from slides.

Key Characteristics of Monotremes and Marsupials Review Sheet

Fill in the following table with key characteristics that will help you recognize each of the following




Group

Size

Skull

Skin

Slide

O. Monotremata













F. Ornithorhynchidae













F. Tachyglossidae













Infraclass Metatheria













O. Didelphmorphia













Didelphis marsupialis













Marmosa sp













O. Dasyuromorphia













F. Thylacinidae













F Dasyuridae

Tasmanian devil















F Dasyuridae

Antechinus













F Dasyuridae

Marsupial cat















F. Myrmecobiidae

Numbat














O. Peramelomorphia













F Peramelidae

bandicoots















O Diprotodontia













F. Phascolarctidae

koala














F. Vombatidae

wombat














F. Macropodidae

kangaroos














F. Petauridae

gliders














F. Phalangeridae

brush-tail possums















F. Tarsipedidae

Honey possum















O. Microbiotheria

F. Microbiotheriidae















O Paucituberculata

F. Caenolestidae
















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