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Prehistoric Mammals

punychicken

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New Scientist

When the dinosaurs ruled the world, the mammals hid in the shadows, daring to grow no bigger than shrew-like insectivores that hunted at night. Or so we thought.

Two stunning new fossils from China have overturned this preconception. Not only did large mammals live alongside their giant reptilian cousins, but some were big and bold enough to go dinosaur hunting.

Named Repenomamus giganticus and Repenomamus robustus, the sturdily built mammals lived in China about 130 million years ago, around 65 million years before we thought their kind inherited the Earth. At 1 metre long, R. giganticus was big enough to hunt small dinosaurs, and a newly discovered fossil of its smaller cousin, R. robustus, died with its belly full of young dinosaur.

This totally overturns the notion of dinosaur-age mammals as tiny and nocturnal, says vertebrate palaeontologist Hans-Dieter Sues of the Smithsonian Institution in Washington DC, US. "Apparently some mammals could grow much larger than anyone had thought was possible."

In another role reversal, those comparative mammalian giants may have affected dinosaur evolution by preying on them, adds palaeontologist Anne Weil of Duke University in Durham, North Carolina, US.
Filling niches

Mammals and dinosaurs evolved from different groups of comparable-sized reptiles during the Triassic, which ran from 248 to 206 million years ago. In the conventional picture, dinosaurs filled the niches for large plant-eaters and predators, relegating mammals to the marginal niches that are now home to shrews and rodents. So large mammals could evolve only after the dinosaurs died 65 million years ago.

And while a handful of teeth and other fragmentary remains hinted that a few large mammals may have lived alongside the dinosaurs, little was known about them. No one had found a reasonably complete skeleton of a Cretaceous mammal as large as R. giganticus, says Yaoming Hu at the American Museum of Natural History in New York, US.

R. giganticus and the new fossil of R. robustus come from an area of China's Lianoning province famed for its feathered dinosaurs. R. giganticus was a short-legged but powerful animal with fearsome teeth, similar to a large modern Tasmanian devil or a honey badger. "I wouldn't want it coming after me," Weil told New Scientist.
Ground dweller

Its skull measures 16 centimetres long, its body 52 cm, and the preserved part of its tail 36 cm. The beast probably weighed 12 to 14 kilograms. Hu says R. giganticus's legs suggest it was a ground dweller that could dash to catch prey, but not run long distances. R. robustus was two-thirds as long and weighed between 4 and 6 kg.

The large sharp front teeth and smaller back teeth of both mammals mark them out as carnivores. Their teeth are not designed for heavy chewing, and the relatively unbroken bones in the stomach of R. robustus confirm that it tore chunks from its prey and gulped them down. The bones found in the stomach came from a young psittacosaurus, a common bipedal plant-eater, and evidently the favourite meal of the local carnivores.

Adult psittacosaurs grew to be nearly 2 metres tall, but R. robustus's last meal was just 14 cm long. Modern mammal predators that weigh less than 21.5 kg normally take prey less than half their body mass, so if both species of Repenomamus followed suit then adult psittacosaurs would have been safe. Not so the juveniles.

The discovery suggests there is much we have yet to understand about mammal evolution during the Mesozoic era, which spans the Triassic, Jurassic and Cretaceous periods, from 248 to 65 million years ago. "It's very possible that when people start looking for Mesozoic mammals of this size, they will find them." Weil says.

The Repenomamus species, however, have no living descendants. They were triconodonts, a poorly understood group of primitive raccoon or opossum-like creatures that diverged from modern mammals during the Mesozoic. Triconodonts have faded from the fossil record by the late Cretaceous, and may have died out before the dinosaurs.

Journal reference: Nature (vol 433, p 149)
 
Not sure if this fit here but i could find no thread about new fossil discoveries in general, feel free to move it if there is a more appropriate thread i coundnt find.

The fossil remains of a huge new rhino has been found in China.

"A new species of the ancient giant rhino - among the largest mammals to walk on land - has been discovered in north-western China, researchers say.

The Paraceratherium linxiaense, which lived some 26.5 million years ago, weighed 21 tonnes - the equivalent of four large African elephants.

The hornless creature's head could also reach 23ft (7m) to graze treetops, making it taller than a giraffe.

The new findings were concluded from fossils discovered in Gansu Province.

In a study published in Communications Biologyjournal on Thursday, scientists said that analysis of the fossils - found near the Wangjiachuan village in 2015 - pointed to an entirely new species that was different to other known giant rhinos."

https://www.bbc.com/news/world-asia-china-57522468
 
Not sure if this fit here but i could find no thread about new fossil discoveries in general, feel free to move it if there is a more appropriate thread i coundnt find.

The fossil remains of a huge new rhino has been found in China.

"A new species of the ancient giant rhino - among the largest mammals to walk on land - has been discovered in north-western China, researchers say.

The Paraceratherium linxiaense, which lived some 26.5 million years ago, weighed 21 tonnes - the equivalent of four large African elephants.

The hornless creature's head could also reach 23ft (7m) to graze treetops, making it taller than a giraffe.

The new findings were concluded from fossils discovered in Gansu Province.

In a study published in Communications Biologyjournal on Thursday, scientists said that analysis of the fossils - found near the Wangjiachuan village in 2015 - pointed to an entirely new species that was different to other known giant rhinos."

https://www.bbc.com/news/world-asia-china-57522468
Wow! It's a wonder there were any trees left! Those things must have needed a fair amount of food just to keep themselves upright,
 
The fossil remains of a new species of 4 legged whale have been found in Egypt.

"Scientists in Egypt have identified a new species of four-legged whale that lived around 43 million years ago.

The fossil of the amphibious Phiomicetus anubis was originally discovered in Egypt's Western Desert.

Its skull resembles that of Anubis, the ancient Egyptian jackal-headed god of the dead after which it was named.

The ancestors of modern whales developed from land-dwelling deer-like mammals that lived on land over the course of 10 million years."

https://www.bbc.com/news/world-middle-east-58340807
 
A newly discovered giant wombat that lived 80,000 years ago has been discovered in Queensland, Australia.

giantwombat.jpg

Researchers discover 'true giant wombat' megafauna species fossil in central Queensland​

Scientists have concluded a seven-year study into 130-kilogram giant wombats — comparable in size to "really large sheep" — that lived in central Queensland about 80,000 years ago.

Key points:​

  • Researchers have concluded a seven-year study into an extinct megafauna species of wombat after a skull was found in central Queensland in the early 2000s
  • Ramsayia magna are closely related to modern wombats but were much larger, weighing up to 130 kilograms
  • A fossil of the species is part of the Queensland Museum collection and could one day be put on display

A team led by Griffith University's Australian Research Centre for Human Evolution excavated and studied the extinct megafauna species after a skull was found at Johannsen’s Cave north of Rockhampton in the early 2000s.

Team leader Julien Louys said Ramsayia magna was one of three giant wombats scientists were aware of.

"They're closely related to the modern wombats but they're much larger than the current species," Dr Louys said.

"[There are] about a dozen specimens across the entirety of the continent of Australia, so it's incredibly rare."
https://www.abc.net.au/news/2022-12...a-species-fossil-central-queensland/101761612
 
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