(ORDO NEWS) — Approximately 14,000 years ago, the first humans crossed the Bering Strait into North America with tusks, domesticated dogs they used for hunting.
But long before the appearance of fangs, predatory canine species lived here, which hunted in the grasslands and forests of America. A rare and nearly complete fossilized skeleton of one of these long-extinct species was recently discovered by paleontologists at the San Diego Museum of Natural History.
This fossil belongs to a group of animals called archeocyons, which means “ancient dog”. It was embedded in two large chunks of sandstone and mudstone discovered in 2019 during construction work in the Otay Ranch area in San Diego County. The fossil belongs to the late Oligocene era and is believed to be between 24 and 28 million years old.
Although the fossils are still awaiting further study and identification by a Canid researcher, their discovery has been a boon to San Diego Museum scientists, including paleontology curator Tom Demere, postdoctoral fellow Ashley Paust, and curator assistant Amanda Lynn.
Because the fossil record in the museum’s collection is incomplete and limited, archeocion fossils will help the paleontological team fill in the gaps in what they know about the ancient dog-like mammals that lived in what we know as San Diego tens of millions of years ago.
Did they walk on their feet like modern dogs? Did they burrow into the ground or live in trees? What food did they get and what animals hunted them?
How did they feel about the extinct dog-like species that came before them? And perhaps it’s a brand new undiscovered species? This new fossil gives SDNHM scientists a few more pieces of the unfinished evolutionary puzzle.
“It’s like finding a branch of a tree, but you need more branches to figure out what kind of tree it is,” says Lynn, who spent almost 120 hours from December to February extracting some of the brittle, and in some places papery -thin skeleton. “Once you open the bones, they start to fall apart… I used a lot of patience and a lot of glue.”
Archeocion fossils have been found in the Pacific Northwest and the Great Plains states, but almost never in Southern California, where glaciers and plate tectonics have scattered, eroded, and buried many fossils from that period of history deep underground.
The main reason the Archeokion fossil was found and put in a museum is California state law, which requires palaeontologists to be present on major construction projects in order to locate and protect potential fossils for later study.
Pat Sena, a paleontologist at the San Diego Museum of Natural History, was monitoring rock heaps at the Otay Project almost three years ago when he saw tiny white bone fragments sticking out of some of the dredged rocks.
He marked the stones with a black Sharpie marker and moved them to the museum, where scientific work soon stopped for almost two years due to the pandemic.
On December 2, Lynn began work on two large stones, using small carving and cutting tools and brushes to gradually remove layers of stone.
“Each time I discovered a new bone, the picture became clearer,” Lynn said. “I said, ‘Look, here this part coincides with this bone, here the spine goes into the legs, here are the rest of the ribs.'”
According to Paust, as soon as the cheekbone and teeth showed out of the breed, it became clear that this was an ancient type of canid. In March, Paust was one of three international paleontologists to announce the discovery of a new cat-like saber-toothed predator, Diegoaelurus, from the Eocene era.
But if ancient cats had only carnivorous teeth, omnivorous canids had both cutting teeth in the front for killing and eating small mammals, and flatter molars in the back of the mouth, used to grind plants, seeds and berries.
This combination of teeth and the shape of the skull helped Demere identify the fossil as an archeocyon.
The new fossil is completely intact except for part of the long tail. Some of the bones were mixed up, possibly as a result of ground movements after the death of the animal, but the skull, teeth, spine, legs, ankles and fingers are completely preserved, which provides a wealth of information about the evolutionary changes of archaeokyons.
According to Paust, the length of the fossil’s ankle bones at their junction with the Achilles tendons suggests that archeocyons have adapted to pursue prey long distances over open pastures.
It is also speculated that its strong, muscular tail may have been used for balance when running and making sharp turns. From his paws, you can judge that he could live or climb trees.
Physically, the archeocion was about the size of a modern gray fox, with long legs and a small head. He walked on his feet and had non-retractable claws.
The more fox-like body shape was significantly different from the extinct species known as Hesperotsion, which was smaller, longer, had shorter legs, and resembled modern weasels.
Although the fossil archeocyons are still being studied and not on public display, the museum’s ground floor has a large exhibit displaying fossils and a large mural depicting animals that inhabited San Diego’s coastal zone in ancient times.
One of the animals in the mural painted by artist William Stout – a fox-like creature standing over a freshly slaughtered rabbit – is close to what the archeocyons might have looked like, Paust said.
As soon as the fossil from the Archeokion was partially identified in February, Demeret asked Lynn to stop working on the fossil, leaving it partially embedded in the rock.
He did not want to risk damaging an intact skull until it was studied by a world-renowned carnivore researcher such as Xiaoming Wang of the Los Angeles County Museum of Natural History.
“Nothing makes a curator happier than inviting researchers to a collection,” Demeret said. “Hopefully some of them will come along. Such an almost complete skeleton could answer all sorts of questions, depending on who’s interested.”
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