Mammalogy: Lecture 6
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- Describe the skull of a Metatherian
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1. Narrow, sm braincase housing a brain w/relatively sm cerebral hemisphisphres
2. Auditory bullae, if present, formed fm allisphenoid bone
3. Palate w/lg vacuities
4. Angular process of mandible inflected medially - What's the dental formula for Metatherians?
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Primite;
5/4i, 1/1c, 3/3p, 4/4m = 50 - What's unique about the dentition of Metatherians?
- There are never equal numbers of incisors above and below (except in the Vombatidae)
- What type of cheekteeth do the Metatherians have?
- Tribosphenic
- What's the name of the bone that's present on the pelvic girdle and is used to support the marsupium?
- Epipubic bones are present on the pelvic girdle
- Describe the Metatherian female reproductive tract.
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1. Bifid
2. Bicornate vagina
3. Bipartate uterus
4. Lateral vaginal canal recieves forked penis of male and is the sperm pathway
5. Vaginal sinus is bith canal - Is the Metatherian female's Vaginal sinus Macropodidae (remaining open) or is it closed?
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1. Some remain open (Macropodidae)
2. Most marsupials; sealed shut except during parturition - Where is the penis located in relation to the testes?
- Penis is posterior to testes
- Is the gestation period in the Metatherian long or short?
- Short; the young are tiny and rudimentary at birth
- What type placenta is found in the Metatherian? What's the yolk sac like?
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1. Primitive Choriovitelline placenta
2. Yolk sac greatly enlarged; forms placenta - What are the three parts to reproduction in Kangaroos?
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1. Postpartum estrus
2. Embryonic diapause
3. Double suckling - Describe Postpartum estrus
- Mates shortly after giving birth
- Describe Embryonic diapause
- Suckling initiates neural and hormonal responses that induce dormancy of blastocyst, which is then covered by a protective membrane; no implanting or cell division
- What happens when suckling stops?
- Blastocyst development begins again; implanted and cell division initiated
- Describe double suckling
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-newborn on one nipple; recieves milk low in fat for slow growth
-Joey on 2nd nipple; recieves milk high in fat for rapid growth - Due to this unique three part reproduction cycle in Kangaroos, how many young could a mother potentially be nourashing?
- Three; The blastocyst, pouchling attached to nipple, and Joey
- Where and when are Marsupials first known?
- Lower Cretacious in Texas
- What were Cretacecous marsupials like?
- Small, insectivorous and omniverous
- What is the most primitive family in the Infraclass Metatheria?
- Didelphidae; stem group from which most other forms were derived
- When were Didelphidae present in N. America? What of its fossil record?
- Early Cretaceous (no fossil record during Cenozoic)
- When were Didelphidae present in S. American? What of its fossil record?
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-Late Cretaceous
-Early Paleocene: 4 genera
*Nearly a continuous fossil record through the Cenozoic - When were Didelphidae present in Antarctica?
- Late Cretaceous or Early Paleocene
- When were Didelphidae present in Australia? What of fossil records?
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-NO didelphids known
-earliest fossil marsupials Early Eocen - When were Didelphidae present in Africa?
- -Oligocene; same genus as known fm Europe
- When were Didelphidae present in Europe?
- Early Eocene to Middle Miocene; single genus
- Where do marsupials appear to have had their origin? Where did they migrate to and "develope"?
- North America, they seem to have dispersed through the Southern Continents (Gondwanaland) and have had tr major radiations in South America and Australia.
- What's the geographic distribution of the Family Didelphidae?
- Living forms in North and South America; fossil forms more widely distributed
- Contrast Syndactylous and Didactylous
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- Syndactylous: two or more toes fused into common compartments of skin
- Didactylous: toes not fused into common compartments of skin - List 6 representative Genuses (common name) of the Family Didelphidae; Order Didelphimorphia
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1. Wooly opossum
2. Four-eyed opossum
3. Mouse Opossums
4. Yapok (or water opossum)
5. Didelphis (lg American Opossum)
6. Thick-tailed opossum - How many species of Genus Didelphis are there? Are they herbivores, carnivores or omnivores?
- Four species. Opportunistic feeders; omnivores
- Are Didelphis virginiana nocturnal? What is their geographic distribution?
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-yes, they're nocturnal
-Range fm S. Canada along the West Coast and from S. Canada, VT and NH along the East Coast to central Mexico; large hiatus in center of northern range (Rocky Mountains and desert region) - What is the Didelphis virginiana's current habitate expansion direction?
- Expanding range northward into Canada
- How long is the Didelphis virginiana gestation period? What's the litter size? How many Pouchlings?
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-Gestation 13 days
-Litter size at birth: 10-56, average of 21
-Pouchlings (13nipples) 5 to 13, averages 8 to 9 in north US and 6 to 7 in south US - How old before a Didelphis virginiana baby releases the nipple? How long before baby leaves the pouch? How long before it is weaned?
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-Releases nipple: 50 days
-leaves pouch: 70 days
-Rides mom's back until weaned at 90-120 days - What temperature in New England does the Didelphis virginiana stop foraging at?
- 20F
- Of the other Didelphis, which two are virtually impossible to tell apart w/out doing genetic analysis?
- The black-eared opossum (Didelphis marsupialis) and white-eared opossum (Didelphis albiventris)
- What is the single living family of Order Didelphimorphia?
- Family Didelphidae
- What are two examples of extinct South American families of Order Didelphimorphia?
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1. Family Borhyaenidae
2. Family Necrolestidae
3. Family Caroloameghiniidae - What was the basal stock of South American Didelphoids (late Eocene)?
- Family Caroloameghiniidae
- Borhyaena where what? (of the family Borhyaenidae)
- Hyaena-like marsupial
- Thylacosmilus where what? (of the family Borhyaenidae)
- Sabertooth marsupial
- When did the Borhyaenidae Family become extinct and probably why?
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- Pliocene, wn S. America came back in contact w/North America
-Modern ungulates replaced the archaic herbivores of S. Am.
-Eutherian carnivores colonized and outcompeted - What family and order is the Monito del monte in? What else is in this family and order?
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Order Microbiotheria
Family Microbiotheridae
*No other living species or families in this order - The Monito de Monte was originally placed in which family? Why was it moved?
- Originally in Family Didelphidae based on identical dental formulas, then DNA sequencing data placed it in the current Order-family-etc.
- Which taxa did the DNA analysis show the Monito de Monte to be a sister taxa of?
- Sister taxon of the Australian Diportodontidae
- What's the geographic range of the Microbiotheria (Monito de Monte)?
- Restricted to south-central Chile
- Where have fossils of the Microbiotheria (Monito de Monte) been found?
- S. America, Antarctica
- What do natives call the Monito de Monte and what do they consider it?
- Colo-colo: very bad luck
- What's in the Order Paucituberculata?
- Shrew or rat opossums
- How many living families of Order Paucituberculata are there?
- One
- What is a key characteristic of the Paucituberculata marsupials?
- No marsupium!
- What's the range of the Paucituberculata?
- Restricted to the Andes Mountains of norhtwestern S. America
- Where have Paucituberculata fossils been found?
- S. America and Antarctica
- What are the three Genera of Order Paucituberculata?
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1. Common rat opossum or shrew-opossum
2. Incan rat opossum
3. Chilean rat opossum