Platypus Matters by Jack Ashby

Author:Jack Ashby [Ashby, Jack]
Language: eng
Format: epub
Publisher: HarperCollinsPublishers
Published: 2022-03-23T12:00:00+00:00

8

Roo-production

The marsupial reproductive strategy requires an almost unbelievable feat from their minute newborns. The minuscule babies must climb, arm over arm, the significant distance from their mother’s vaginas (yes, that’s right, plural) to the pouch, unaided, and then fix themselves to an empty teat. This may explain why there are no marsupial bats or whales: the need to climb into the pouch means that they cannot evolve away from having hands with grasping fingers (and hence form wings or flippers[fn1]),[1] and the babies of fully aquatic marsupials would drown in their pouches. (The parachute-like membranes of the various gliders are wonderful evolutionary solutions for becoming airborne without requiring significant modifications to the all-important grasping hands.)

One departure to this model is seen among the bandicoots, whose young don’t crawl to the pouch – the mother curls over and they sort of flop out into the pouch opening. Given that newborn bandicoots don’t start life with a marathon climb, this birthing technique has potentially freed them of the evolutionary constraint that is applied to most other marsupial hands. And indeed, some bandicoots are among the few marsupials to have done something different with their hands. The pig-footed bandicoots have toes that resemble miniature trotters, with long, slender front legs tipped with little hooves. This is intriguing. The evolution of hooves sparked a massive diversification in placental mammals (think of how many species of antelope, deer, cattle, goats, sheep, giraffes, camels, horses, rhinos, tapirs and pigs there are). Could pig-footed bandicoots be the start of a similar explosion in marsupials? Sadly, we will never know, as the only two species disappeared by the 1950s, driven to extinction by introduced cats and foxes. The second of those species – Chaeropus yirratji – was only described from museum specimens in 2019, demonstrating the value of historic collections in understanding the scale of biodiversity loss over recent centuries.[2] We have one of the eighteen known specimens of this new species in the University Museum of Zoology in Cambridge, which I consider a profound responsibility. The eighteen specimens, held across just five museums worldwide, are the only known physical evidence that the species ever existed.

Pig-footed bandicoots are now extinct, but are the only marsupials to have evolved hoof-like digits, as can be seen in this illustration from Museums Victoria by Gerard Krefft, based on specimens from an 1857 expedition to north-west Victoria. Krefft went on to become director of the Australian Museum.

Public Domain. Image sourced from Wikimedia Commons

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