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At Sci News: Brasilodon is Earliest Known Mammal, New Research Shows

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Paleontologists have examined the fossilized lower jaws of Brasilodon quadrangularis, a mouse-sized creature that lived in Brazil during the Late Triassic epoch, some 225 million years ago. The analysis of the different growth stages showing tooth development in each of the Brasilodon fossils provided evidence that these were the remains of a mammal. Previously, the earliest accepted record in geological time of mammals was 205 million years ago.

Brasilodon quadrangularis was approximately 12 cm (8 inches) long and weighed about 20 grams. The animal existed at the same time as the earliest known dinosaurs and probably lived in burrows like the shrews today. Image credit: Anatomical Society / Wiley.

Mammalian glands, which produce milk and feed the young of mammals today, have not been preserved in any fossils found to date.

Therefore, scientists have had to rely on fossilized bone and teeth for alternative clues.

The dental records date 225 million years ago, 25 million years after the Permian-Triassic mass extinction event that led to the extinction of roughly 70% of terrestrial vertebrate families.

Mass extinction events provided an opportunity for new types of fauna to multiply, but the scientific evidence on the limitations of natural processes indicate that the appearance of new class of animals requires the input of intelligent design.

A tiny animal called Morganucodon is usually considered the first mammal but its oldest fossils, only represented by isolated teeth, date from around 205 million years ago.

“Comparative studies with recent mammal dentitions and tooth replacement modes suggest that Brasilodon was a placental, relatively short-lived animal,” Dr. Richter said.

“Dated at 225.42 million years old, this is the oldest known mammal in the fossil record contributing to our understanding of the ecological landscape of this period and the evolution of modern mammals.”

“The evidence from how the dentition was built over developmental time is crucial and definitive to show that brasilodons were mammals,” added Professor Moya Meredith Smith, a researcher at King’s College London.

“Our paper raises the level of debate about what defines a mammal and shows that it was a much earlier time of origin in the fossil record than previously known.”

The paper appears this week in the Journal of Anatomy.

Full article at Sci News.

Out of curiosity, I found that the little creature was a type of shrew. With a partial skull containing 6 teeth, scientists were able to determine that it was the earliest known mammal because its size and dentition is similar to modern shrews, plus the little suckers are notoriously mammals. Ok, it had two sets of teeth, "baby teeth" and "adult teeth." https://www.researchgate.net/figure/Anterior-portion-of-the-skull-of-Soturnia-caliodon-MCN-PV-2738-in-dorsal-A-and_fig2_285854536 https://onlinelibrary.wiley.com/doi/10.1111/joa.13756 The remains were found napping on a Triassic layer in a riverbed undisturbed for 220 million years or so. Thus, the "odon" suffix was deemed appropriate. However, naming it a "shrewodon" sounded lame, so because it was found in Brazil, it was instead cleverly named "Brasilodon." Not surprisingly, one account stated that "the new discovery is labeled 'very important' by the researchers." Also note that everything in the illustration was an artist's rendition of what it mighta looked like. -Q Querius
Methinks you are right. :) relatd
Methinks it is Like a Weasel. Andrew asauber

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