Subclass THERIA
Lab 9-Infraclass METATHERIA
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Simpson, 1945 |
Marshall, 1990 |
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Order Marsupialia Superfamily Didelphoidea Family Didelphidae Superfamily Dacyuroidea Family Dasyuridae Family Notoryctidae Superfamily Perameloidea Family Peramelidae Superfamily Caenolestoidea Family Caenolestidae Superfamily Phalangeroidea Family Phalangeridae Family Pascolomyidae Family Macropodidae |
Cohort Ameridelphia Order Didelphimorphia Family Didelphidae Order Paucituberculata Family Caenolestidae Cohort Australidelphia Order Microbiotheria Family Microbiotheriidae Order Dasyurimorphia Family Myrmecobiidae Family Thylacinidae Order Peramelina (=Peramelemorphia) Family Peramelidae Family Peroryctidae Order Diprotodontia Family Pseudocheiridae Family Phalangeridae Family Burramyidae Family Petauridae Family Potoridae Family Macropodidae Family Phascolarctidae Family Vombatidae Family Tarsipedidae Family Acrobatidae Order Notoryctemorphia Family Notoryctidae |
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A
suggested phylogeny of marsupials (after
Luckett, W. P. 1994. Superfamilial relationships within
Marsupialia: resolution and discordance
from multidisciplinary data. Journal of
Mammalian Evolution 2: 225-283; Woodburne, M. O., and J. A. Case. 1996.
Dispersal, vicariance, and the Late Cretaceous to early Tertiary land
mammal biogeography from South America to Australia. Journal of Mammalian Evolution 3: 121-161).
structural
characters of marsupials:
1.
marsupial
(pouch) usually present, but absent in some forms
2.
epipubic
bones present
3.
braincase
small
4.
jugal forming part of mandibular fossa
5.
alisphenoid large, forming anterior part of the
auditory bulla
6.
angular process of lower jaw inflected
7.
palatine bones with large vacuities (fenestrated)
8.
vaginae
paired
9.
cloaca
absent, or short if present
10. penis external, forked, carrying both urine and
sperm
11. cerebrum relatively small
special
characters:
1.
polyprotodont
versus diprotodont
terms
refer to whether or not the lower incisors are many and equal in size (=
polyprotodont) or whether the medial incisor is greatly enlarged (=
diprotodont). Diprotodont taxa may have
multiple small posterior incisors (e.g., Caenolestidae, Phalanderidae), or only
the enlarged medial pair (e.g., Vombatidae, Macropodidae).
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polyprotodont |
diprotodont |
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Didelphis (Didelphidae) lower jaw – note multiple lower incisors, all of
equal size |
Caenolestes (Caenolestidae) lower jaw –
note enlarged anterior incisor and multiple small posterior ones
Macropus (Macropodidae) lower jaw –
note single, enlarged lower incisor |
2.
polydactyly
versus syndactyly
all
digits of the hind foot are free, and approximately equal in size
(polydactyly), or digits 2 and 3 are distinctly smaller and encased in a common
sheath of skin (syndactyly).
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polydactylous |
syndactylous |
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Didelphis (Didelphidae) |
Sminthopsis (Dasyuridae) |
(Peramelidae) |
(Phascolartidae) |
Macropus (Macropodidae) |
3.
tribosphenic
molar: the basic primitive tribosphenic
molar (both upper and lower) of a metatherian is easily distinguishable from
that of any eutherian tribosphenic molar by the following:
upper
molars: stylar shelf on labial side of
tooth, typically with five distinct cusps present (termed “stylar cusps” A
through E)
lower
molars: entoconid and hypoconulid on
talonid closely appressed and widely distant from hypoconid
Order DIDELPHIMORPHIA
Family DIDELPHIDAE
(American
opossums)
diagnosis: combination of polyprotodonty with 5/4 incisors, polydactyly, and
small, uninflated bullae
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1.
body small
to medium 2.
marsupiam,
if present, opening to anterior 3.
tail long
(shorter than head-body only in Monodelphis),
usually naked, prehensile in some (e.g., Caluromys,
Micoureus) 4.
foot
posture plantigrade 5.
polydactylous; digits 5-5, subequal in length 6.
hallux
well developed, opposable, without claw 7.
cranium
relatively long and slender 8.
bullae relatively uninflated 9.
sagittal
crest often well developed 10.
zygomatic arch
relatively slender 11.
paroccipital
process small 12. polyprotodont;
lower incisors subequal in size, not procumbent 13.
canines
well developed 14.
molars
tritubercular (tribosphenic) |
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5
1 3 4 4
1 3 4 |
= 50 |
common
genera: Caluromys (woolly opossums), Chironectes (water opossum), Didelphis (common opossum), Gracilinanus (murine opossum), Lutreolina (lutrine opossum), Marmosa (murine opossum), Marmosops ((murine opossum), Metachirus (brown 4-eyed opossum), Micoureus (murine woolly opossums), Monodelphis (short-tailed opossums), Philander (gray and black 4-eyed opossums).
range
of family: New World
- one species (Didelphis virginiana) extends into temperate zone of North America, all
others are neotropical (Mexico south to South America); most species occur in
lowland tropical forests, a few extend into the dry high Andes or the
grasslands of southern Argentina and central Brazil.
Didelphis (common opossum)
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Occlusal view of second and
third upper right molars of a murine opossum, Marmosa |
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Chironectes (water opossum)
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Didelphis (common opossum) |
Monodelphis (short-tailed opossum)
Marmosa
(murine, or mouse, opossum) |
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3
0-1 1-2 4 1
0 1-2 4 |
= 30 or 34 |
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