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Paleoparadoxia Bone Identified By Researchers In Japan

Paleoparadoxia Bone Identified By Researchers In Japan

Six decades after it was first discovered and mislabeled as a dinosaur fossil, the 15.9-million-year-old femur was finally identified as belonging to a Paleoparadoxia aquatic mammal.

An old relic “nearly forgotten” inside a museum cabinet was finally correctly identified and restored to its deserved glory, reports Phys.org.

Initially mislabeled as a dinosaur femur, this rare fossil actually belongs to a long-extinct marine mammal known as Paleoparadoxia — an evocative name that translates to “ancient paradox.”

Dating back to the Miocene epoch 20 to 10 million years ago, these aquatic herbivores once occupied the waters of the now Pacific Ocean and are all the more intriguing considering that we can merely speculate on their exact appearance and behavior since they left no living descendants for us to observe.

Discovered by dam workers in 1955 near the Japanese town of Tsuchiyu Onsen in Fukushima, the Paleoparadoxia fossil was incorrectly cataloged as belonging to a dinosaur and was placed in the care of the University of Tsukuba in the Ibaraki Prefecture. There it remained undisturbed for more than half a century, until Yuri Kimura, from the university’s department of geology and paleontology, brought it back into the light.

The Mystery Of Paleoparadoxia

This enigmatic creature truly lived up to its name and represents a veritable 20-million-year-old puzzle that paleontologists are still trying to solve.

Its unusual and very illustrative name refers to Paleoparadoxia‘s peculiar appearance — a strange mix of physical features that echo different animals and seem to be arbitrarily strung together. While this ancient mammal resembles the modern hippopotamus, its skull looks remotely like that of a horse and its short limbs sport very wide paws.

Belonging to the Desmostylia order — “a fossil group of Japanese iconic mammals,” according to a new study co-authored by Kimura — these extinct aquatic animals had a wide habitat stretching from Alaska to Japan and as far south as Mexico and were initially believed to be amphibious.

Prehistoric Wildlife notes that Paleoparadoxia spent most of their day underwater feeding on aquatic plants and came back on land to rest and sleep.

“The lack of specialized aquatic features such as limbs modified into flippers, means that even though Paleoparadoxia swam in the sea, it probably restricted itself to the shallows,” states the media outlet.

A Paradoxical Journey

According to the new study, Kimura stumbled upon the Paleoparadoxia fossil completely by chance in the spring of 2017. The researcher found the bone in “an old wooden box in the geological collection room” at the university, along with a hand-written note listing the details of the fossil’s discovery.

This precious information played a big part in unraveling the fossil’s true identity, note the study authors — an international team of scientists from several universities in Japan and the New York Institute of Technology College of Osteopathic Medicine in the U.S.

Published today in the journal Royal Society Open Science, the research documents how the Paleoparadoxia bone was found more than 60 years ago and the complicated journey that eventually revealed the fossil’s origin.

After a long investigation that involved traveling back to the site where the bone was unearthed — the right bank of the Higashi Karasugawa River, Tategoshi — and conducting multiple interviews in the field, the specimen was finally identified as the right femur of a Paleoparadoxia mammal.

The study notes that the fossil “shows well-preserved muscle scars on the surface” and has “the best-preserved femoral surface of all Paleoparadoxia specimens.”

A ‘Paleoparadoxia’ skeleton exhibited at the National Museum of Nature and Science in Tokyo, Japan. Momotarou2012 / Wikimedia Commons/Resized (CC BY-SA 3.0)

“Through the interviews, we learned that the fossil was discovered during construction of a debris flow barrier and that it was recognized as a ‘dinosaur’ bone among the locals and displayed in the Village Hall before/until the town experienced a fire disaster in 1954,” the authors wrote in their paper.

Material retrieved from the site enabled the team to date the fossil by analyzing the crystal zircons in the soil samples.

The paleontologists estimate that the Paleoparadoxia femur is 15.9-million-years-old. This places the fossil about 50 million years after the Chicxulub wiped out all non-avian dinosaurs, notes Phys.org.

“This study shows an excellent case that historical and scientific significances could be extracted from long-forgotten uncatalogued specimens as long as the original information is retained with the specimens,” the authors concluded.

Their research also yielded an exquisite 3D model of the live Paleoparadoxia mammal based on the specifics of the fossil. And, since the bone was preserved in excellent conditions, the scientists are confident that this is the most accurate 3D model of a Paleoparadoxia to date.

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