Australian Museum’s Professor Tim Flannery and colleagues argue that the ancestors of Theria (placental and marsupial mammals) advanced within the supercontinent Gondwana 50 million years earlier than migrating to Asia through the Early Cretaceous epoch, some 126 million years in the past.
An artist’s impression of an early mammal-like animal. Picture credit score: Anatomical Society / Wiley.
“For nearly 200 years it has been believed that the placental mammals, and the associated marsupials, had originated within the northern hemisphere, as that’s the place nearly all of mammal range is now discovered, and the place probably the most considerable fossils happen,” Professor Flannery mentioned.
“Nonetheless, our research of the tribosphenic molars of therian mammals present in Early and Center Jurassic sediments from Madagascar, South America and India — that are as much as 180 million years outdated — predate the oldest such stays from the northern hemisphere by 50 million years.”
“Moreover, our new analysis reveals that therian fossils from the Cretaceous of Australia, courting from round 126-110 million years in the past, share traits with each these Jurassic southern hemisphere types and the trendy northern hemisphere therians.”
“The analysis has utterly revised and turned on its head our understanding of early mammal evolution.”
In the course of the Cretaceous interval, Australia, New Zealand, South America, Antarctica, Africa, Madagascar, and the Indian subcontinent have been all joined in a single supercontinent, Gondwana.
Early mammal lineages will need to have existed presently, however proof of their presence within the fossil file, their anatomical options, and their evolutionary relationships have been sluggish to disclose themselves, stopping in-depth assessments till now.
“Our analysis signifies that Theria advanced in Gondwana, thriving and diversifying there for 50 million years earlier than migrating to Asia through the Early Cretaceous epoch,” mentioned Australian Museum’s Professor Kris Helgen.
“As soon as they arrived in Asia they diversified quickly, filling many ecological niches.”
“A key part to the evolutionary success of Theria lies of their enamel. With their refined molars, often called tropospheric molars, they have been capable of crush, puncture, and lower by way of meals concurrently.”
Whereas the Eureka second occurred in comparisons made earlier this yr, the analysis to seek out key mammal fossils has been painstaking.
The paleontologists searched Cretaceous-age rocks for over 20 years earlier than turning up the primary mammal fossil.
“Relationship mammal lineages depends upon each genetic evaluation and the fossil file. We additionally date the rock across the fossil,” mentioned Museums Victoria’s Dr. Thomas Wealthy.
“With our newest analysis we have now succeeded in filling the gaps to attract an in depth portrait of the early evolutionary historical past of Theria.”
“These astonishing sequence of discoveries have utterly modified our long-held principle of mammal evolution. Certainly, it turns our concepts of mammal evolution on its head.”
The analysis is described in a paper within the journal Alcheringa.
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Timothy F. Flannery et al. The Gondwanan Origin of Tribosphenida (Mammalia). Alcheringa, printed on-line November 1, 2022; doi: 10.1080/03115518.2022.2132288
