Although lengthy useless, fossil skeletons present an unimaginable window into the approach to life and surroundings of an extinct animal.
By analyzing the assorted options of fossil bones we will reveal not solely the general measurement and form of the animal, but in addition what sort of motion the animal was able to, its life-style, and the surroundings during which it lived.
But what if we seemed inside fossil bones? What secrets and techniques would it not reveal in regards to the progress and growth of an extinct animal?
In a newly revealed paper within the Journal of Paleontology, we have now finished simply that, utilizing 15 million-year-old skeletons of a large bear-like marsupial from the world-famous Riversleigh World Heritage Area (Boodjamulla) in Waanyi nation of northwest Queensland.
Tree-dwelling wombat kin
The large tree-dwelling herbivorous marsupials, referred to as Nimbadon, weighed about 70kg, making them the biggest arboreal (tree dwelling) mammals recognized from Australia.
Nimbadon belongs to a various group of long-extinct, large-bodied marsupials referred to as diprotodontoids, the likes of which embrace the biggest marsupial to have ever lived, the two.5-ton megafaunal Diprotodon, and weird trunked marsupials harking back to modern-day tapirs.
Among dwelling animals, Nimbadon is most intently associated to wombats. Yet surprisingly, when it comes to physique measurement and life-style, they’re extra similar to solar bears, which right this moment could be discovered scaling the rainforest canopies of Southeast Asia.
When we first uncovered jawbones of Nimbadon at Riversleigh in 1993, we thought we had been taking a look at very massive leaf-eating marsupials who foraged for meals on the forest ground.
But like lots of the species we have unearthed from Riversleigh, the nearer we take a look at these animals, the more odd and interesting they grow to be.
Nimbadon is now recognized from its full skeleton, together with materials representing developmental ages starting from tiny pouch-young to mature adults. It had robust arms with very cellular shoulder and elbow joints.
Its arms and ft had specifically tailored opposable thumbs with large curved claws for climbing, penetrating bark, and greedy branches.
These animals had been extremely specialised climbers and lived vastly completely different life in comparison with their closest dwelling kin – the land-dwelling, burrowing wombats.
Our preliminary analysis confirmed that Nimbadon was not solely a “tree-hugger”, but in addition a “tree-hanger”, spending a few of its time suspended from tree branches like a sloth.
Nimbadon lived 15 million years in the past within the cover of lowland Australian rainforests. These biodiverse, lush forests had been dwelling to some equally unusual animals: flesh-eating kangaroos, tree-climbing crocodiles, ancestral thylacines, cat- to leopard-sized marsupial lions, large anaconda-like snakes, giant-toothed platypuses, and mysterious marsupials so unusual they’ve been known as “Thingodonta”. It was a really completely different Australia than the one we see right this moment.
Sectioning the bones
Despite the wealth of knowledge we have now gleaned from Nimbadon skeletons, till now we hadn’t absolutely understood the expansion patterns of those historical marsupials.
Were they affected by seasonality? How lengthy did they take to develop to grownup physique measurement within the canopies of the traditional forest? Clues to those questions lay within the bones’ microscopic construction.
To look contained in the fossil bones, we would have liked to pick out the fitting materials. Long bones, such because the bones of the leg, are recognized to protect a very good file of progress, so we analyzed ten lengthy bones of a number of different-sized people.
We started by eradicating a piece from the shaft of the bone and embedded it in resin. Using a diamond-edged blade, we minimize our samples into skinny sections and polished them additional till mild may cross by means of them. These thinned sections had been mounted on glass microscope slides to be studied.
Remarkably, even after hundreds of thousands of years of fossilization, the microscopic construction of the fossil bones had remained intact. We had been amazed to find that Nimbadon grew in periodic spurts. Individuals had quick progress intervals, every adopted by a sluggish progress interval, usually related to a band of arrested progress.
Seasonal growers
Cyclical progress patterns have beforehand been documented for marsupials resembling within the dwelling western gray kangaroo. However, our outcomes point out that, general, the limbs of Nimbadon had a a lot slower, extra extenuated progress than kangaroo limbs.
One particular person recorded a minimum of seven to eight progress cycles, which suggests this arboreal large wanted a minimum of this period of time – and possibly extra – to grow to be a fully-grown, sexually mature grownup.
Based on these alternating cycles of quick and sluggish progress, Nimbadon might have been affected by seasonal circumstances resembling meals availability. However, precisely how lengthy it took for eight progress cycles to develop stays a thriller. If certainly they symbolize annual cycles, it might be a minimum of eight years till sexual maturity, which is uncommon within the trendy marsupial world.
For instance, kangaroos are sexually mature at one to 2 years. That being stated, Nimbadon is an uncommon beast and a really massive one at that, so an prolonged developmental interval (and lifespan) isn’t unlikely.
Real-life drop bears
We have come to consider these unusual arboreal marsupials as actual variations of the legendary “drop bears” of Australian folklore – mysterious tree-dwelling creatures that will drop down on unsuspecting animals beneath.
While shifting in herds by means of the rainforest cover, each younger and grownup Nimbadon would have often misplaced their grip earlier than dropping down from the treetops. Sometimes they might find yourself in forest ground caves, which is the place we have now been discovering their still-articulated skeletons.
Given the fixed surprises that analysis into this extraordinary, extinct Riversleigh mammal has already produced, we’re keen and ready for nonetheless extra.
Currently, we’re trying into put on within the enamel microstructure of Nimbadon‘s tooth to find out this legendary drop bear’s food regimen. We count on that what we discover down the observe will proceed to upend our naïve first presumptions in regards to the life of this and lots of the different unusual inhabitants of the traditional inland rainforests of Riversleigh.
Anusuya Chinsamy-Turan, Professor, Biological Sciences Department, University of Cape Town; Karen Black, Leading Education Professional, UNSW Sydney; Mike Archer, Professor, Pangea Research Centre, UNSW Sydney, and Sue Hand, Professor emeritus, UNSW Sydney
This article is republished from The Conversation below a Creative Commons license. Read the unique article.
