Jawbone Discovery Suggests Modern Mammals Originated in The Southern Hemisphere - ScienceAlert

It has taken implicit 2 decades and 1 pandemic for paleontologists to unite the fossilized remains of the earliest mammal ancestors and find that their improvement which gave emergence to modern humans, whitethorn person begun successful the Southern Hemisphere – and not successful the northbound arsenic scientists person agelong thought.

The investigation of a tiny postulation of tiny fossilized jawbones bearing distinctive backmost teeth flips our knowing of erstwhile and wherever modern mammals evolved connected its head, according to the squad of researchers who produced it.

Paleontologist Thomas Rich of Museums Victoria co-authored the caller survey and is simply a long-time fossil hunter.

He was portion of the squad who, successful 1997, aft 23 years of searching, announced they had recovered connected an Australian formation a mammal jawbone with unusual teeth, the likes of which had lone been seen successful Europe and North America. The jawbone was from a tiny shrew-like carnal and dated backmost to the Cretaceous play erstwhile dinosaurs besides roamed.

As the years ticked by, much mammal jawbones from the Mesozoic epoch were discovered: successful Madagascar, Argentina, India, and again, astir recently, successful Australia.

Each of these specimens, measuring an inch oregon less, had distinctive backmost teeth. According to the latest investigation which revisits them, the oldest fossil predates those recovered successful the Northern Hemisphere by immoderate 50 cardinal years.

"These astonishing bid of discoveries person wholly changed our long-held mentation of mammal evolution. Indeed, it turns our ideas of mammal improvement connected its head," Rich says.

The teensy teeth successful question are called tribosphenic molars, which interlock apical and bottommost to cut, crush, puncture and grind works nutrient and insect prey.

The tiny tribosphenic molars connected the jaw of an aboriginal mammal from the Cretaceous period, recovered successful Australia. (James Alcock/Australian Museum)

During the pandemic, esteemed paleontologists Tim Flannery and Kris Helgen, main idiosyncratic astatine the Australian Museum, had an thought to revisit the 3 Australian tribosphenic mammal fossils – the astir caller of which Rich described successful 2020 – and started sifting done the technological lit to spot what other they could find.

They realized these unusual teeth agreed the aboriginal mammal fossils recovered crossed the Southern Hemisphere and that the Argentinean specimen was the oldest of the lot, millions of years older than immoderate aboriginal mammal fossils recovered successful the north.

From there, they mapped retired an alternate root communicative for mammals, whose ancestors could person hopped betwixt the confederate continents erstwhile they were joined unneurotic successful a supercontinent called Gondwana immoderate 125 cardinal years agone earlier heading north.

Based connected the property of the fossils, and their anatomical similarities, the squad believes they correspond the earliest ancestors of marsupials (such arsenic Australia's koalas and wombats) and placentals (which includes humans), which are grouped unneurotic arsenic Therian mammals.

"Our probe indicates that Theria evolved successful Gondwana, thriving and diversifying determination for 50 cardinal years earlier migrating to Asia during the aboriginal Cretaceous," explains Heglen. "Once they arrived successful Asia, they diversified rapidly, filling galore ecological niches."

Tribosphenic mammal fossils recovered connected the confederate continents, shown present arsenic Gondwana. (Flannery et al., Alcheringa, 2022)

The researchers suggest the specialized molars of our earliest mammalian ancestors mightiness person been the cardinal to their evolutionary success. But the improvement of aboriginal mammals who outlived the dinosaurs has long fascinated scientists and volition nary uncertainty proceed to pull ongoing scrutiny.

In paleontology, similar immoderate science, the value of grounds speaks volumes. And for implicit 200 years, the diverseness of mammals surviving successful the Northern Hemisphere and the abundance of fossils recovered determination led scientists to judge that the ancestors of placentals and marsupials arose successful the northbound and dispersed south.

However, probe shows the fossil grounds tin beryllium skewed by who is looking where. For now, each we person to situation this long-standing mentation of wherever mammals originated is this tiny postulation of tiny teeth – and it has taken respective decades to find adjacent those 7 specimens.

Reconstructions of Mesozoic tribosphenic mammalian dentaries recovered successful the Southern Hemisphere. (Flannery et al., Alcheringa, 2022/Australian Museum)

"It's the astir important portion of palaeontological research, from a planetary perspective, that I've ever published, but it whitethorn instrumentality immoderate clip to find afloat acceptance among Northern Hemisphere researchers," says Flannery.

It adjacent took him a agelong clip to judge the findings of the analysis. "I resisted the decision arsenic agelong arsenic I could, but the grounds is compelling," Flannery told Australian Geographic's subject and situation editor, Karen McGhee.

Indeed, not each paleontologists are convinced. While Flannery and squad are holding this caller revelation up arsenic a monolithic find that upends our knowing of mammal evolution, Flinders University paleontologist Gavin Prideaux says their conclusions are based connected "the tiniest, shittiest small shards" of fossilized teeth.

As helium told the Sydney Morning Herald, different mentation could beryllium 1 of convergent evolution: that these tribosphenic molar teeth evolved successful a fewer abstracted places astatine akin times. "The assemblage is inactive out," helium says.

The survey was published successful Alcheringa: An Australasian Journal of Palaeontology.