Metatheria Flashcards
(24 cards)
Metatheria characters
inflected angle of the jaw, large and medially directed epipubic bones alisphenoid auditory bulla different ossifications in middle ear replacement of last premolar only 4 molars up to 5 upper incisors broad navicular ? oblique cuboid facet on calcaneum ? large scaphoid, triquetrum, hamate ?
Sinodelphys szalayi
up until last year, thought to be oldest metatherian, not thought to be eutherian
diastema
supinator crest
4 molars (disputed)
1 premolar
stylar shelf (buccal side) low for M1, but more consistent for other three
M1 replaced, therefore potentially argued to be a pre-molar
doesn’t have reflected angle
appears adapted for climbing- long metacarpals, large triquetrum and hamate
according to larger data set, placed as sister to Ambolestes on eutherian stem
Deltatheridium pretrituberculare
Late Cretaceous, Mongolia evidence for dental replacement has reduced M4 Juvenile specimen- last premolar still erupting mineralised m4 still in crypty
Pucadelphys
Tiupumpa, Bolivia (best Palaeocene locality)
fossils interpreted as in nest, 2 siblings at similar developmental age
Didelphimorpha
“Ameridelphia”
(opposums), 66 species:
Didelphis most widespread marsupial, only with Northern continent widespread
Includes semiaquatic Chironectes- only hind feet webbed
Most others arboreal eg. Marmosa, Caluromys
Paucituberculata
“Ameridelphia”
(shrew opposums), 7 species:
restricted to western south America, terrestrial, can store fat in tails
most basal extant clade
Microbiotheria
“Ameridelphia”
(Monito del Monte), 1-2 species:
restricted to central Chile and adjacent Argentina, small and faunivorous, v important seed dispersers
more closely related to Australian than American
Peramelemorphia
Australidelphia
(bandicoots, bilbies), 22 species:
diverse in size, ranging from 100g Microperoryctes to 5000g Peroycetes
contains closest to hooved- pig footed bandicoot (Chaeropus ecaudatus)
sister to dasyuromoprhs
Notoryctemorphia
Australidelphia
(marsupial moles), 1-2 species:
convergent on African golden mole and Holarctic talpid moles
arid, sandy habitat in central Australia, buries underground
Dasyuromorphia
Australidelphia
(marsupial ‘wolves’, ‘mice’, ‘devils’, quolls and numbats), 64 species:
second most diverse array of niches in a marsupial order
eg. Thylacinus
Dasyurus (quolls), Myrmecobius (Numbats), Sminthopsis, Sarcophilus (Devils)
sister to peramelians
Diprotodontia
Australidelphia
(kangaroos, koala, wombats, cuscuses, possums, gliding possums), 131 species:
largest size range of any mammalian order, 2,000,000g Diprotodon to 15g glider Acrobates
one of the most diverse groups among mammals
eg. Vombatus (wombat), Macropus (kangaroo), Acrobates, Phascolarctos (koala), Thylacoleo, Diprotodon
Thylacoleo
Diprotodont hypercarnivore
lower carnassial tooth from 3rd premolar, and lost teeth behind it
stabbing tooth- incisor
Diprorodon
2 tonnes, rhino like Diprotodont
Microbiotherium tehuelcum
Microbiothere
Micoene, Argentina
w-shaped stylar shelf
Marambiotheroum glacialis
Microbiothere
Eocene, Seymor island, Antarctica
Borhyaenids
fossil carnivorous S. American marsupials
eg. Prothylacinus, Oligo-Miocene, Argentin, canid-like
eg. Thylacosmilus, Mio-Pliocene, Argentina, Felid-like hypercarnivore w lower carnassial formed from multiple teeth and upper canines as stabbing teeth
unsure whether within Paucituberculata or own group
Marsupial reproduction
Short intrauterine gestation (max 3 weeks in Macropus)
Relatively uniform state at birth across body masses
Climb from reproductive tract to teat in pouch/marsupium
Therefore have better developed forelimbs and facial skeleton at birth, compared to placentals (Smith, 2011)
Dependent on lactation for embryonic and fetal growth
Most have choriovitelline placenta
Chorioallantoic for peramelians (eutherian-like placenta), have largest and most developed newborns of all marsupials relative to body weight and per unit time inauterine gestation
Invest less than placentals per unit time, better suited to arid conditions, scarce resources
Marsupial developmental constraints
Have to climb into pouch therefore restricted forelimb diversity (eg. no wings/flippers)
Forelimbs have increased surface area at distal end to aid climbing (Cooper and Steppan, 2010)
Shoulder girdle constrained- must provide strength for climb, range of forms reduced
Diversity of marsupial forelimbs significantly lower than placentals, but not for hindlimbs
Pig-footed bandicoot been able to escape this
Has 2 functional digits on forelimbs and single of hindlimbs
Member of peramelians, unique, remain attached to mother through placental stalk after birth and don’t require the forelimbs to enter marsupium (Cockburn, 1989)
Notoryctids reduced number of forelimb digits and formed apomorphic forelimbs for fossorial
Yapoks, only marsupial that can be considered semi-aquatic, swim w hindlimbs only
Marsupial geographic constraints
Southern hemisphere means species poor
Placentals in South also much less diversity than Northern (Afrotheria and Xenarthra, 2 eutherian crown groups that originated in southern continents, lower diversity than boreoeutherian mammals)
Southern land area lower, and fewer ecological opportunities for radiation (Sanchez-Villagra, 2013)
Syndactyla
Syndactyly = digits 2&3 are one unit
Peramelians and diprotonts
Paraphyletic
Ankle dichotomy
Microbiotheres and Australasian marsupials, common lower ankle joint pattern
calcaneal facets continuous
Rest of America, separate lower ankle joint pattern calcaneal facets separate
Monophyletic groups confirmed with further phylogenetic analysis
Marsupial early birth
Result of own developmental constraints:
Medial position of ureter in females means that each of the two lateral vaginas can’t support parturition of larger offspring (Sharman, 1970).
Eutherians have more lateral ureter and vaginas fused to support larger offspring
Adaptation to environmental conditions
Use resources over longer period, therefore fewer per unit time
Can abort in adverse conditions without losing much investment
Driven by biogeorgraphy
Anatoliadelphys maasae
Marsupialiforme from Middle Eocene of Turkey
Body mass roughly 4kg (relatively large), and filled mesopredator niche on isolated island
Had no eutherian predators, so could reach this niche
Demonstrates that only reach extremes of morphology when no competition (competitively inferior to placentals because developmentally constrained)
Marsupials in Great American Biotic Interchange (GABI)
Fared poorly, few made it to central and North America, and in South many went extinct due to competitive exclusion
eg. borhyaenids Thylacosmilus and Prothylacinus, driven to extinction by placental predators
S America smaller, therefore mammals there experienced reduced evo and so at competitive disadvantage
