A gigantic rat of eggs with huge tusks that roamed the Earth 184 million years ago has been unearthed in the wastelands of Arizona.
This "rare weird" fossilized animal, about the size of a small dog, was unearthed along with 38 offspring, which experts assume is his.
Finding well-preserved juveniles of the Jurassic period, when dinosaurs dominated the Earth, are particularly unusual as they are often destroyed or eaten after death.
The clutch of young animals contains twice as many offspring as you would expect from a mammal, but it is the standard litter size for a reptile.
Unearthing so many young animals in one place is unprecedented.
Scientists hope the discovery sheds new light on the evolution of mammals and reduces the window when mammals moved from large reptile-like litters to smaller mammalian nests. young people with bigger brains.
The image shows computerized tomographies of the skulls from left to right, a baby tuatara (modern reptile), one of the young Kayentatherium and a 27-day opossum (modern mammal), which are shown with the same magnification. As the class of mammals developed, it grew to favor a large investment in relatively few offspring with larger brains.
The rat, which has been called Kayentatherium wellesi, was a precursor to the first mammals, although it gave birth as a reptile.
Study leader Eva Hoffman, who led the research as a graduate student in geosciences at the University of Texas at Austin, said: "These babies are from a really important point in the evolutionary tree.
"They had many characteristics similar to modern mammals, characteristics that are relevant to understanding the evolution of mammals."
Mammals are essentially defined by reproduction, and almost all of them carry live young (instead of laying eggs) that they then feed with milk.
As the class of mammals developed, it grew to favor offspring with larger brains that required more investment from their parents.
As a result, the size of the litter began to decrease.
However, since the offspring of both mammals and their ancestors are rarely preserved as fossils, much less as newborns or embryos, the timing of this transition remains unclear.
This discovery of the 184 million year old rat narrows the window for change.
According to the study, Kayentatherium wellesi is not a true mammal but one of a group of very early animals similar to mammals, known as tritylodonts.
The youngsters have similar skulls in shape and size to the adult mother, according to the article published in the journal Nature.
This suggests that Kayentatherium wellesi grew as modern-day reptiles, without experiencing the cranial lengthening seen in modern mammals.
The image is a computerized tomography of a part of the sample that shows a maternal vertebra (gray) with the bones of the babies (colors) in their original positions. Finding well-preserved young people from the dinosaur era is particularly unusual, as they are often destroyed or eaten after their death.
The image shows computerized tomographies of the skulls of a tuatara calf (left), which is a New Zealand endemic reptile and a 27-day opossum (right) that is a opossum-like mammal (right). This shows that the brains, and therefore the skulls, of young mammals, such as the opossum, are round and relatively large.
The fossil was collected by Professor Timothy Rowe more than 18 years ago from a rock formation in northeastern Arizona.
Professor Rowe incorrectly believed that he was bringing back a single specimen, but he had no idea of the dozens of babies the adult contained.
Dr. Sebastian Egberts, a former graduate student and fossil trainer, detected the first sign when a speck of tooth enamel the size of a grain caught his attention in 2009 when he was unpacking the fossilized remains.
Now, as an anatomy instructor at the Philadelphia College of Osteopathic Medicine, he explained: "It did not look like a pointed fish tooth or a small tooth from a primitive reptile, it was more like a molar tooth, and that really moved me.
A CT scan revealed a handful of bones inside the rock. But advances in the technique of computerized images were needed to reveal the rest of the babies.
Study leader Eva Hoffman produced 3D visualizations that allowed her to perform an in-depth analysis.
It was this analysis that revealed that the small bones belonged to babies and were of the same species as the adult.
Professor Rowe said: "Only a few million years later, in mammals, they certainly had a large brain, and certainly had a small litter size.
"There are additional deep stories about the evolution of the development and evolution of intelligence and the behavior and physiology of mammals that can be extracted from a remarkable fossil like this now that we have the technology to study it," he said.
In the image are the skulls of the 38 Kayentatherium wellesi babies found next to the adult specimen, which the researchers believe is their mother (in the photo on the left to see the scale)
WHY ARE THE SCIENTISTS INTERESTED IN THE RAT OF MOLE NAKED?
With wrinkled skin and walrus teeth, naked mole rats will never win any beauty contest.
However, these creatures, who live underground in the deserts of East Africa, are one of the medical wonders of the natural world.
If a human had the same life span as a naked mole rat, in relation to its size, they would live up to 600 years.
In addition to being resistant to cancer, they have very low respiratory and metabolic rates, which means that they use little oxygen.
Scientists have devoted considerable effort to sequencing the creatures' genomes in an attempt to understand their secrets.
The machinery that translates its DNA into functional molecules in cells, proteins, has also been found to be highly accurate.
This means that their proteins contain few errors compared to other mammals, which means that there is less chance of something going wrong.