Lions and diggers and The Bear, oh my!
The evolutionary hits just keep coming as climate change and other factors unearth amazingly well-preserved specimens of prehistoric beasts in Russia's remote, icy regions.
Images released last month of an 18,000-year-old pup baring its milk teeth are just the latest reminder of the buried biological treasures in Siberia, where the icy climate has kept large patches of earth frozen for tens of thousands of years.
That deep freeze has eased as global temperatures and other factors combine to lay bare evolutionary secrets in a region that's normally more synonymous with cold and isolation.
Russia's famously frozen subterranean zone -- sometimes over a kilometer deep -- has been a natural storehouse for carbon, methane, and other greenhouse gases, but also for the carcasses of prehistoric beasts that last roamed its steppes before the end of the last Ice Age.
Finds of the past decade or so -- as permafrost melts, erodes, or is simply plundered for ivory or other valuables -- have included remarkably well-preserved woolly mammoths, woolly rhinos, cryptic dog-wolves, vanished big cats, and other biological wonders.
They are windows on evolutionary and natural history, offering clues to behavioral, physical, and genetic adaptations that might otherwise be lost.
Their biological material -- frozen cells as opposed to fossils in which the building blocks of life have been replaced by, say, minerals -- includes DNA that is furthering efforts to decipher undiscovered genomes and, some say controversially, could one day help clone species that are extinct.
In at least one case, Siberia has yielded the seeds of an experiment that returned plants to life after tens of thousands of years in a deep freeze.
Dogor (above), named for the word "friend" in the local Yakut language, has confounded scientists since the puppy's 18,000-year-old remains were found near Yakutsk last year.
DNA testing by Swedish scientists has been unable to firmly place it within the evolutionary chain, hinting it could fall somewhere between wolves and dogs.
The oldest-known common ancestor of modern wolves and dogs has otherwise been thought to have lived about 40,000 years ago, based on DNA testing.
Dogor and all but one of the prehistoric finds below are from the latter part of the Pleistocene Epoch that started with the spread of northern ice sheets nearly 2.6 million years ago and ended around 12,000 years ago. It's also the epoch that saw Homo sapiens arise and flourish.
Permafrost is long-frozen ground that in most cases unites rocks and sediment in ice that seals out the elements. It is usually topped off by an "active layer" heavy in organic matter that doesn't decompose due to the cold.
It is abundant in the Northern Hemisphere, owing to the amount of land mass in and near the Arctic Circle.
It covers nearly two-thirds of Russia's 17 million square kilometers of territory.
In the case of wide swaths of Siberia, even shallow permafrost has remained frozen for tens of thousands of years.
But like retreating glaciers and weather patterns, it is said to be seeing dramatic effects from man-made climate change.
The resulting thaws and erosion have helped expose a veritable gold mine for paleontologists.
Yuka became a cause celebre in 2010 as the best-preserved woolly mammoth ever to have fallen into the laps of scientists.
She was named for the Yukagir coast where she died, some 39,000 years ago, as a juvenile between 6 and 12 years of age.
Mammoths are getting increasingly controversial with each new find.
The discovery of such well-protected biological material has sparked talk of an effort to use DNA from Yuka's carcass or that of another mammoth to clone them and revive the iconic, Ice Age species.
Many people believe cloning techniques are advanced enough to successfully revive a species like the woolly mammoth with intact DNA, but the damage of cosmic radiation is likely to have sufficiently "shredded" any DNA so as to make it worthless for cloning efforts.
This year, however, researchers announced they'd taken "less-damaged nucleus-like structures from the remains" of Yuka and seen "signs of biological activities" in them after transferring them into mouse cells capable of forming ova, or eggs.
"Our work provides a platform to evaluate the biological activities of nuclei in extinct animal species," they declared.
There is also an extensively chronicled, but still largely untallied, illicit trade in mammoth tusks that critics say undermines bans on the trade in endangered elephant ivory.
A contentious proposal to treat that long-extinct species as endangered under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) was dropped earlier this year.
The first complete carcass of a juvenile woolly rhino -- hair and all -- turned up near the banks of a Siberian river in 2015.
Nicknamed Sasha and nearly a meter tall and 2 meters long at just 7 months of age, she would have towered over her modern peers.
Scientists still know very little about the behavior of woolly rhinos or their timeline on Earth, but early estimates put Sasha's remains at between 10,000 and 34,000 years old.
She was well-enough preserved that her tufty, strawberry-blond remains were reconstructed by a local taxidermist for visitors to her home in Yakutsk.
A woolly rhino whose partial skull was found in Germany in 2008 lived nearly a half million years ago, making it Europe's oldest such find. It was hailed as a major clue to how large, cold-loving species spread across Eurasia during the Ice Age.
The cavernous Batagayka Crater in eastern Russia's taiga surrendered another prehistoric juvenile animal in 2018, this time a gangly foal (above) of the extinct species known as a Lena horse.
It was thought to be roughly 2 months old when it died, some 40,000 years ago.
Internal organs, tail, and hooves are whole, and even eyelashes and nostril hairs are clearly visible.
The prospect of harvesting useful DNA from the foal was high enough that a renowned South Korean pioneer of cloning, Hwang Woo-suk, was brought in as part of the dissection earlier this year.
Hwang, a vocal advocate of cloning techniques to revive woolly mammoths whose false claims earned him the label of "bad-boy geneticist," reportedly took samples of biological fluids like blood and even urine.
Cave lions, a subspecies of today's lion that also inhabited North America, are thought to have become extinct at least 10,000 years ago.
So scientists swooned when two nearly intact cubs, nicknamed Uyan and Dina, were uncovered just below the Arctic Circle in 2015.
They were spotted in an ice lens exposed when a crevice opened after the Uyandina River burst its banks and receded.
They are thought to have lived between 25,000 and 55,000 years ago.
Uyan and Dina were just weeks old when they died, with eyes not fully opened and teeth still embedded, so they never got a chance to roam the Siberian steppes. Instead, a scientist has speculated that a landslide entombed them inside their cave-like hiding place.
One of Russia's foremost authorities on prehistoric-fauna discoveries, Albert Protopopov from the Yakutian Academy of Sciences, told the Siberian Times the cubs were a "sensational" find and noted that even their whiskers were intact.
"Given that the cubs have well-preserved soft tissues, we believe that they can be cloned. But we can speak about the results of this work in two or three years," TASS quoted scientists as saying after the discovery.
Another frozen cub carcass emerged in 2017 from the eastern Siberian permafrost -- this one under 2 months old and possibly dating back tens of thousands of years.
Found near the Tirkhtyakh River by a man who was said to have been searching for mammoth tusks, it is thought to be a cave lion or a Eurasian lynx. In either case, a discovery dating back to the Ice Age would be rare.
Mammoth hunters were said to have found the disembodied head of an ancient subspecies of wolf (above) staring back at them from a bank of the Tirekhtyakh River in 2018.
Its mottled fur, brain, tongue, and other features were said to be the best-preserved of any previous specimens.
Scientists said its size -- about 25 percent larger -- distinguishes it from many modern wolves.
It is thought to have gone extinct in the past 10,000 years or so.
Yukagir tribe members stumbled across the preserved carcass of an ancient relative of the modern bison along a muddy Siberian lakeshore in 2011.
The adult Steppe bison likely to have starved to death 9,000 years ago, judging by the paucity of its digestive tract.
Its heart was complete enough that scientists even performed a CT scan on its brain.
Not all of the remarkable finds in Siberia's melting permafrost have been animals.
Russian scientists announced in 2012 that they had beat the previous plant-regeneration record by 30,000 years.
The seed-bearing fruits of the flowering Silene stenophylla, better known as the campion or catchfly, had been frozen for 32,000 years until they were dug up from "fossil squirrel burrows" 38 meters beneath a bank of the Kolyma River.
Scientists produced healthy, fertile adult plants from regenerated "placental tissue" from unripe fruits. They speculated that placental tissue is special because it is especially active -- it processes and transports not only its own nutrients but also those bound for other tissues. And, they suggested, the unripe fruit is a better vessel for preservation because it's closed off more tightly from the environment -- closer to ideal "hermetic conditions."
"Naturally occurring permanently frozen sediments offer an important opportunity for the discovery of wild plant species, preservation of biological material, studying the conditions for cryopreservation, and developing germplasm collections," said the authors of a Silene study.
"We consider it essential to continue permafrost studies in search of an ancient genetic pool, that of preexisting life, which hypothetically has long since vanished from the Earth's surface."