SUPERVISOR: PROFESSOR MICHAEL ARCHER
Co-supervisors: Dr Marcelo Sánchez-Villagra, Paläontolgisches Institut und Museum der Universität Zürich and Dr Suzanne Hand, UNSW

Australia is home to a diversity of marsupials which is simply amazing, even more so given the fact that these creatures are nearly extinct everywhere else. Kangaroos, Koalas and allies are this continent's most popular natural assets, drawing crowds of tourists into Australia every year. However, there is little awareness that Australian marsupials are a diverse and successful 'alternative' to placental ('non-pouch') mammals, and as such crucial pieces in the puzzle of mammalian evolution. Particularly the marsupial clade of Diprotodontia (kangaroos, possums, wombats) is very conspicuously diverse. Diprotodontia virtually come in all sizes from less-than-mouse sized pygmy possums as light as 5 grams to red kangaroo bucks weighing 85 kg - and if you add some of the recently extinct species such as the giant Diprotodon optatum, the maximum weight goes up to around 2 ½ tons! Of course, this size diversity also coincides with a large range of ecological adaptations within the group - from dumpy, digging wombats via large and small tree-climbing possums to the hopping kangaroos. As such, Diprotodontia surpass nearly all other mammalian orders in terms of size, and rival most in diversity. This, together with their diverse fossil record, makes them great objects for comparative study of anatomical evolution.

 

In my PhD, I focus on the evolution and functional anatomy of the marsupial (particularly diprotodontian) postcranial skeleton, which has to date been little researched. My focus is the functional anatomy of the limbs and the ontogeny of the postcranial skeleton. Three major approaches are taken: 1) A comparative anatomy component to establish baseline knowledge on diversity within extant and extinct diprotodontians. 2) Correlation of anatomical diversity with function, and assessment of convergence within the group and in relation to placentals 3) Assessment of the link between marsupial diversity and early development.

 

Methods include phylogenetic character mapping, statistical phylogenetically corrected analysis of morphometric datasets, lab-based clear-staining procedures, CT-scans, event-pair analysis for developmental sequences, and anatomical analysis of fossil species.

 

My results so far demonstrated a high degree of convergence in anatomy of the wrist between marsupials and placentals (Weisbecker and Sánchez-Villagra, 2006), and also a strong correlation between locomotion and hand proportions (Weisbecker and Schmid, 2007; Weisbecker and Warton, 2006). I also found that certain traits that are characteristic for a terrestrial (as opposed to arboreal) lifestyle have evolved twice within Diprotodontia (Weisbecker and Archer, in prep.). I am now working on the evolution and morphometric characteristics of syndactyly (the functional fusion of the second/third toe unique to Diprotodontia and Peramelemorpha; Weisbecker and Nilsson, in prep.).

 

Since patterns of diversity in marsupial anatomy have been linked to early developmental (ontogentic) processes, the remainder of my PhD will be spent on an interdisciplinary investigation of marsupial pouch young to examine the developmental processes related to postcranial evolution. For this project, I am stepping out of the focus of my PhD on marsupials. I will also research monotremes (Echidnas and platypuses) and incorporate data collected by my co-supervisor Marcelo Sánchez-Villagra to research changes in bone development timing in all mammals. The main analytical tool I am using is computed tomography (CT) because this allows me to non-destructively investigate ossifications in a large number of museum specimens (and make pretty reconstructions - see illustration). Using CT, I was able to nearly triple the number of species available for comparative ossification analysis.

 

However, I am always in search of opportunities to obtain very young (first three months) pouch young of wombats, koalas, and possums for histological sectioning and/or clearstaining studies. Any information with regards to obtaining these is very much appreciated!

 

 

 

 

 

WEISBECKER, V AND SCHMID, S 2007: Autopodial skeletal diversity in hystricognath rodents: Functional and phylogenetic aspects. Mammalian Biology 72: 27-44.
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WEISBECKER, V AND WARTON, D I 2006: Evidence at hand: diversity, functional implications, and locomotory prediction in intrinsic hand proportions of diprotodontian marsupials. Journal of Morphology, 267: 1469-1485.
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WEISBECKER, V AND SÁNCHEZ-VILLAGRA, M R 2006: Carpal evolution in diprotodontian marsupials. Zoological Journal of the Linnean Society 146: 369-384.
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