Subclass THERIA

Lab 10 - Infraclass EUTHERIA-

structural characters of eutherians:

1. marsupium not present

2. epipubic bones not present

3. braincase large; cerebral hemispheres large

4. jugal not forming part of mandibular fossa

5. no contribution of alisphenoid to auditory bulla

6. angular process not inflected

7. palatal vacuities usually not present

8. no stylar shelf on upper tribosphenic molars

9. entoconid, hypoconulid, and hypoconid equidistant on talonid

10. single vagina

11. uteri medial to ureters; fused in some groups

12. male phallus not divided

Hypothesis of phylogenetic relationships among eutherian orders (from Novacek, 1993, Reflections on higher mammalian phylogenetics. Journal of Mammalian Evolution 1(1): 3-30).

Order XENARTHRA

(=EDENTATA in earlier classifications)

diagnostic character: extra zygapophyses present on posterior thoracic and lumbar vertebrae.

general characters:

1. size small to medium-large (15-210 cm).

2. body covered with hair or scutes

3. forefoot with two or three principal digits, each bearing long claws; hindfoot with 2-5 digits

4. no incisors or canines

5. cheekteeth absent (Myrmecophagidae), or if present, homodont and wiithout enamel

6. zygomatic arch complete (Dasypodidae) or separate (Bradypodidae, Megalonichidae, Myrmecophagidae)

7. jugal, lacrimal, and interparietal bones present

8. pterygoid bones variable, either separate (sloths, armadillos) or meeting at midline to form part of palate (anteaters)

Family MYRMECOPHAGIDAE

(anteaters)

diagnostic character: no teeth (=edentulous)

general characters:

1. forelimbs and hindlimbs subequal in size

2. tongue very long, protrusible, worm-like

3. skull elongate; rostrum very long and curving downward

4. zygomatic arch incomplete

5. premaxilla very small

6. jugal present but small, articulating with maxilla, not squamosal

7. pterygoids meeting at midline, extending palate posteriorly to auditory bullae

dental formula:

no teeth

three genera: Cyclopes (pygmy or silky anteater), Myrmecophaga (giant anteater), Tamandua (tamandua or collared anteater).

range: Neotropics, from northern Argentina to southern Mexico.

Myrmecophaga tridactyla

Tamandua tetradactyla (banded anteater)

Cyclopes didactylus (silky anteater)

Myrmecophaga tridactyla (giant anteater)

Family MEGALONYCHIDAE

(two-toed sloths)

diagnostic characters: very small tail

blocky skull with blunt snout

two toes (claws) on forefeet

anterior premolars caniniform

general characters:

1. forelimbs much longer than hindlimbs

2. tail very small

3. fur long and shaggy in appearance

4. tongue unspecialized

5. zygomatic arch incomplete

6. first pair of cheekteeth canine-like; all cheekteeth homodont

7. premaxilla very small

8. jugal well developed

9. pterygoids separate, not forming part of palate

10. angular process small, directed posteriorly

dental formula:

0 0 5

0 0 4-5

= 18-20

premolars and molars indistinguishable

genera: the family is monotypic -- Choloepus (two-toed sloth)

range: Neotropical forests, from northern Argentina to Honduras

Choloepus (two-toed sloth)

note caniniform anterior premolar; jugal (with upper and lower

processes on posterior edge) is shaded

Choloepus hoffmanni (Hoffmann’s two-toed sloth)

Family BRADYPODIDAE

(three-toed sloths)

diagnostic characters:

1. very small tail

2. blocky skull with blunt snout

3. three toes (claws) on forefeet

4. anterior premolars not caniniform

general characters:

1. forelimbs much longer than hindlimbs

2. tail very small

3. fur short, feathery in texture

4. tongue unspecialized

5. premaxilla very small

6. jugal well developed

7. zygomatic arch incomplete

8. pterygoids separate, not forming part of palate

9. angular process enlarged, projecting postero-ventrally

10. all cheekteeth homodont; first pair of cheekteeth not canine-like

dental formula:

0 0 5

0 0 4-5

= 18-20

premolars and molars indistinguishable

genera: the family is monotypic -- Bradypus (three-toed sloth)

range: Neotropical forests, from northern Argentina to Honduras

Bradypus variegatus (brown-throated three-toed sloth)

Family DASYPODIDAE

(armadillos)

diagnostic character: body covered with keratin scutes overlaying bony plates

general characters:

1. forelimbs and hindlimbs subequal in size

2. tongue long and protrusible

3. skull elongate, flattened; rostrum elongate

4. zygomatic arch complete

5. cheekteeth homodont

6. premaxilla well developed

7. jugal well developed

8. pterygoids usually separate, not forming part of palate (joined at midline in Dasypus)

dental formula:

0 0 7-25

= 28-100

premolars and molars indistinguishable

genera: Cabassous (naked-tailed armadillos), Chaetophractus (hairy armadillos), Chlamyphorus (fairy armadillos), Dasypus (nine-banded armadillos), Euphractus (yellow armadillos), Priodontes (giant armadillo), Tolypeutes (three-banded armadillo), Zaedyus (pichi)