Tuesday, 25 June 2013

How wombats do it

Rossetti lamenting the death of his wombat

Wombat husbandry has improved since Rossetti's time, but wombats are still difficult to breed in captivity.The northern hairy-nosed wombat Lasiorhinus krefftii is among the rarest species of mammal and a captive breeding program might be needed to save it from extinction. A timely review (here) summarizes what we know and still need to learn about wombat reproduction.

Fetal membranes of the long-nosed bandicoot Perameles
nasuta from Hill (1897) redrawn by Amoroso

Wombats and their close relative the koala Phascolarctos cinereus have a chorioallantoic placenta as well as the yolk sac placenta characteristic of marsupials (previous post). In this respect they resemble the bandicoots. J. P. Hill described placentation in the Southern brown bandicoot in 1895 and two years later published a detailed description for the long-nosed bandicoot (here). As wombats and bandicots are not closely related, this might be an instance of convergent evolution. Although it has also been argued (here) that a chorioallantoic placenta was present in the common ancestor of marsupials and lost in the remaining lineages.

Our knowledge of placentation in wombats relies on specimens of Vombatus ursinus collected by Hill in 1899-1901 and conserved as part of The Hubrecht Collection at Museum für Naturkunde in Berlin. These specimens have been described by Hughes and Green (In: Wells RT, Pridmore PA Wombats Chipping Norton NSW: Surrey Beatty & Sons, 1998).

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