The first journey of a newborn dunnart, a marsupial smaller than a paper clip, is a remarkable sight. Immediately after birth, each tiny creature, weighing no more than a grain of rice, must navigate across their mother's fur to reach the safety of her pouch--an event that has never been filmed until now.
Researchers in Australia have successfully captured this extraordinary moment on camera, showcasing how these delicate neonates propel themselves with surprising strength and determination. Their findings, published in Royal Society Open Science, reveal that even at just 5 milligrams, these newborns can climb into the pouch independently.
A 20-Second Window
Marsupials are known for birthing extremely underdeveloped young. Unlike placental mammals, whose offspring develop for months in the womb, marsupial babies are born after very short gestation periods and must continue their growth while attached to a teat.
For many small Australian species, observing the exact moment of birth has been nearly impossible. Dunnarts are nocturnal and give birth quickly--sometimes in less than a minute for a litter. This changed when a researcher noticed blood in a breeding enclosure and examined a female dunnart, discovering tiny newborns already wriggling toward the pouch.
"We witnessed the pouch young waving their arms and crawling," said Brandon Menzies from the University of Melbourne. "It resembled a freestyle-swimming crawl or a commando crawl," he added. He managed to film approximately 22 seconds of this incredible event before returning the mother to her natural position, providing the first direct evidence of how this species begins life.
The footage illustrates the newborns moving their heads from side to side while rapidly pumping their forearms at about 120 times per minute. This movement is faster than similar actions observed in other marsupials. Their forelimbs are already well-developed, equipped with tiny claws, indicating that climbing is crucial from the very beginning.
Previous theories suggested different mechanisms for how mothers might assist their newborns in reaching the pouch, such as using fluids or specific positioning during birth. However, this new study shows that dunnarts rely on their own strength to make the climb.
The Fastest Baby Climbers
The crawl may be a vital test of survival. Female fat-tailed dunnarts can produce up to 17 offspring but only have 10 teats for feeding. Consequently, only the fastest and strongest newborns will secure a position to continue their development.
This competitive dynamic is common among carnivorous marsupials. For instance, Tasmanian devils may give birth to around 30 young but typically raise only four. Scientists believe this strategy reflects the low energy cost of producing tiny embryos, coupled with fierce competition post-birth.
These new observations suggest that the ability to crawl could be a determining factor in survival. Once attached to a teat, the vigorous head-swinging and crawling motions cease, indicating that the journey requires significant energy.
Beyond the biological implications, this research holds broader significance. Fat-tailed dunnarts are part of the same carnivorous marsupial group as the extinct Tasmanian tiger, and they are being studied as biological models in research exploring the potential for de-extinction. Understanding their early development could be pivotal for such endeavors.
For now, a brief 20-second video provides the clearest glimpse yet into the beginnings of one of the world's smallest mammals.