English
It's always been thought that placental mammals originated in the northern hemisphere as that is where most mammal diversity is found.
Now, studies of therian mammals, or placental and marsupial mammals, from the early and middle Jurassic period predate the oldest remains from the Northern Hemisphere by nearly 50 million years.
In fact, these fossils from Australia and elsewhere in the southern hemisphere are up to 180 million years old.
Here is palaeontologist Dr Tom Rich.
"Now what's happened is beginning with discoveries that happened here in 1997 in Australia, followed very soon thereafter with discoveries in South America and Madagascar, it looks like we have even older ones in the southern hemisphere that are ancestral to the marsupials themselves. So it seems like, as opposed to the view that's been prevalent for all that time, they actually evolved in the southern hemisphere and went north."
The mammals resemble a rat, weighing around 100 to 150 grams.
But it's these mammal's large teeth that help to identify them.
The lead author of the research is palaeontologist Professor Tim Flannery.
"The thing that sets the modern mammals apart, because they have these quite complex molars that can do several jobs at once, they're like the swiss army knife of mammal molars. They can puncture, sheer and crush all at the same time, so they're quite sophisticated. And we started tracking the evolution of those animals that had that kind of molar in the fossil record, and we found they appeared 50 million years earlier in the southern hemisphere than they do in the northern hemisphere."
During the Cretaceous period, Australia was joined to various other land masses, including the Antarctic, in what was one southern super continent known as Gondwana.
According to the new research, Theria mammals evolved in Gondwana, adapting and diversifying for 50 million years before migrating to Asia during the early Cretaceous.
The mammals are then believed to have moved to the northern hemisphere, some 126 million years ago.
A team of palaeontologists, including some 700 volunteers, have been digging for 23 years before the first mammal fossil was located.
According to Dr Rich, it hasn't been easy work due to Australia's tough terrain.
"The work here in Australia is very labour intensive, it's due to the nature of the rocks. We have rocks as hard as concrete and the only way we can process them is to physically break them up, look at each fresh break and see if we can find a fossil, and if we do fine and if we don't just break them up again and again until we get down to the size of sugar cubes and then we try another rock. And that's very inelegant but that's the only way that works for us. It takes a lot of patience. I mean, one individual is lucky to find one specimen in a field season and a lot of people never do."
While it's a great discovery story, according to Professor Flannery, it may take time for the findings to be fully embraced.
"I think that these discoveries will be quite challenging for a lot of people. The orthodoxy of where the modern mammals came from has been in place for over 200 years. So and because most of the diversity of the modern mammals is in the northern hemisphere, and most of the fossil records are in the northern hemisphere, these findings from the southern hemisphere will be challenging to some people. So I don't expect we'll get quick acceptance of the findings but I do think they'll stand the test of time and prove to be right in the long term."
Such discoveries of the past can help us understand our present environment, especially when it comes to navigating the effects of climate change.
Australia was found to hold the record for the extinction of the most mammals across the world in the 2022 State of the Environment report.
Professor Flannery explains how understanding ancient environments can offer a picture into the future.
"I suppose what it tells us is that life is pretty tenacious, and that these modern mammals start in the southern hemisphere, they migrate into the north, and then we get this massive evolutionary radiation of everything from mice to elephants to humans and then on to the marsupials which then get back into the southern hemisphere and seem to replace these more ancient forms of modern mammal. So life is persistent and given enough time it will start to adapt, but the problem with climate change is that we don't give things enough time and if change is too fast we see extinction rather than evolution. So it is a bit of a warning in that way."
Italian
Si è sempre creduto che i mammiferi placentali fossero originari dell’emisfero boreale, dato che quello è il luogo in cui è stata trovata la più vasta diversità di mammiferi.
Adesso, studi sui mammiferi Teri, noti anche come mammiferi placentali o marsupiali, dal Giurassico inferiore e medio retrodatano i resti più antichi provenienti dall’Emisfero Nord di quasi 50 milioni di anni.
Di fatto, questi fossili dall’Australia e da altre zone dell’emisfero sud hanno fino a 180 milioni di anni.
Questo è il paleontologo Tom Rich.
"Now what's happened is beginning with discoveries that happened here in 1997 in Australia, followed very soon thereafter with discoveries in South America and Madagascar, it looks like we have even older ones in the southern hemisphere that are ancestral to the marsupials themselves. So it seems like, as opposed to the view that's been prevalent for all that time, they actually evolved in the southern hemisphere and went north."
Questi mammiferi assomigliano a dei topi, e pesavano tra i 100 ed i 150 grammi.
Ma sono stati i grandi denti di questi mammiferi ad aiutare la loro identificazione.
L’artefice principale di questa ricerca è il paleontologo Professor Tim Flannery.
"The thing that sets the modern mammals apart, because they have these quite complex molars that can do several jobs at once, they're like the swiss army knife of mammal molars. They can puncture, sheer and crush all at the same time, so they're quite sophisticated. And we started tracking the evolution of those animals that had that kind of molar in the fossil record, and we found they appeared 50 million years earlier in the southern hemisphere than they do in the northern hemisphere."
Durante l’era del Cretacico, l’Australia era unita ad altre masse terrestri, incluso l’Antartico, in quello che era il super continente del Sud noto come Gondwana.
Secondo questa nuova ricerca, i mammiferi Teri si sono evoluti in Gondwana, e si sono adattati e diversificati per 50 milioni di anni prima di migrare in Asia durante il Critacico inferiore,
Da qui, i mammiferi si sarebbero spostati nell’emisfero nord, circa 126 milioni di anni fa.
Un team di paleontologi, inclusi circa 700 volontari, ha scavato per 23 anni prima che il primo fossile di mammifero venisse localizzato.
Secondo il Dr Rich, non è stato facile lavorare a causa del suolo australiano, molto duro.
"The work here in Australia is very labour intensive, it's due to the nature of the rocks. We have rocks as hard as concrete and the only way we can process them is to physically break them up, look at each fresh break and see if we can find a fossil, and if we do fine and if we don't just break them up again and again until we get down to the size of sugar cubes and then we try another rock. And that's very inelegant but that's the only way that works for us. It takes a lot of patience. I mean, one individual is lucky to find one specimen in a field season and a lot of people never do."
Nonostante sia una grande scoperta, secondo il Professor Flannery ci vorrà del tempo per capirne la portata.
"I think that these discoveries will be quite challenging for a lot of people. The orthodoxy of where the modern mammals came from has been in place for over 200 years. So and because most of the diversity of the modern mammals is in the northern hemisphere, and most of the fossil records are in the northern hemisphere, these findings from the southern hemisphere will be challenging to some people. So I don't expect we'll get quick acceptance of the findings but I do think they'll stand the test of time and prove to be right in the long term."
Scoperte simili del passato possono aiutarci a capire l’ambiente odierno, specialmente quando assistiamo agli effetti del cambiamento climatico.
Nel report sullo stato dell’ambiente del 2022, l’Australia è risultata la detentrice del record di estinzioni di mammiferi.
Il Professor Flannery ha spiegato come la comprensione di ambienti antichi possa offrire un quadro del futuro.
"I suppose what it tells us is that life is pretty tenacious, and that these modern mammals start in the southern hemisphere, they migrate into the north, and then we get this massive evolutionary radiation of everything from mice to elephants to humans and then on to the marsupials which then get back into the southern hemisphere and seem to replace these more ancient forms of modern mammal. So life is persistent and given enough time it will start to adapt, but the problem with climate change is that we don't give things enough time and if change is too fast we see extinction rather than evolution. So it is a bit of a warning in that way."
Report by Catriona Stirrat for SBS News.
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