Lab 7-Order Monotremata

Subclass PROTOTHERIA

Order MONOTREMATA

The order consists of six living species in three genera, one is the platypus (Ornithrhynchus) in the Family Ornithrhynchidae and two are echidnas (Tachyglossus and Zaglossus) in the Family Tachyglossidae. Together these are highly specialized mammals that retain many primitive mammalian or even amniote characteristics (oviparity, shell-covered eggs, mammary glands without a nipple, epipubic bones, coracoid, procoracoid [=epicoracoid], and interclavicle in the shoulder girdle, splayed limb posture, and a cloaca [the basis for the name Monotremata, which means ‘single hole’]). Monotremes are endothermic, but with low metabolic rates compared to eutherian mammals; all either hibernate or are periodically inactive in winter; all are long-lived, with captive echidnas living more than 50 years.

distribution: known only from Australasia (Australia and New Guinea); fossils known from South America and Australia.

from Mcdonald, D. (ed.) 1986. Encyclopedia of Mammals. Facts-on-File.

shared-derived characters:

• pectoral girdle with large procoracoids, coracoids, and interclavicle (bones that are absent from all other mammals)
• females lay eggs (oviparous)

other characters:

1. limbs modified for digging or swimming
2. ankle in males with horny spur
3. no vibrissae
4. epipubic bones present
5. skull bird-like in shape, sutures usually obliterated by fusion of bones in adults
6. no auditory bulla
7. premaxillae separated for at least part of their length
8. jugal reduced or absent
9. no lacrimal
10. palate extending far posteriorly
11. no teeth in adults (adult platypus have horny pads only)
12. cloaca present (absent in other mammals, with few exceptions)
13. penis within cloaca, used only for passage of sperm
14. mammae without pendulous teats (nipples)

Family TACHYGLOSSIDAE

(echidnas)

characters:

1. body covered with thickened, stiff spines

2. feet not webbed, modified for digging, claws large

3. snout slender, long

4. pinna well developed

5. tail very small

6. tongue thin, elongate (worm-like)

7. premaxillae separated except at anterior ends

8. dental formula: no teeth

genera: Tachyglossus - Australia, Tasmania, New Guinea

Zaglossus - New Guinea

Family ORNITHORHYNCHIDAE

(platypus)

characters:

1. pelage of soft hairs, no spines

2. foot webbed, with moderately large claws

3. snout broad, “duck-billed”

4. no pinna

5. tail well developed, flattened

6. tongue flattened

7. premaxillae expanded laterally, and separate anteriorly

8. dental formula: no teeth (only horny plates present on jaws)

genera: Ornithorhynchus - eastern Australia, Tasmania