Three extremely rare fossils of a 10-armed squid-like creature from the Jurassic period were recently unearthed in Germany. Researchers say these ancient sea creatures – scientifically known as Acanthoteuthis, a genus of squid ancestors – were likely swift swimmers.

Paleontologists from the University of Zurich discovered the fossil remains at a site in Solnhofen, Germany. The three new specimens measured between 9.8 and 15.7 inches long. Scientists were surprised by how well-preserved the creature's soft body parts were, including its fins and feeding structures. When analyzing the remains, never-before-seen organs were found, shedding new light on the creature's body structure and how it lived millions of years ago.

Acanthoteuthis belongs to a group of ocean-dwellers known as belemnites, which are members of a larger class known as cephalopods - the group that includes modern octopus, squid and cuttlefish. Although cephalopods have an evolutionary history spanning 500 million years, their soft bodies don't preserve well, so not much is actually known about these rather elusive creatures.

Now extinct, belemnites had tough internal shells capped by hard parts called "rostra," which preserve fairly well, as roughly bullet-shaped fossils. While these fossil bits are plentiful, and certain marks on them even indicate where the belemnites' fins attached to the mantle - the cone-shaped, muscular part of the body that forces water through a siphon for jet-propelled swimming - they only reveal part of the creature's long history.

The new Acanthoteuthis specimens, however, tell researchers a little more about the creature's past because the fossil site they were found at kept them exceptionally well-preserved.

"Solnhofen and its surroundings are world-renowned for exceptionally preserved fossils," Christian Klug, co-author of the new study and a curator at the Paleontological Institute and Museum at the University of Zurich, told Live Science in an email. "These fossils were embedded in fine-grained sediments in more-or-less quiet water lagoons between coral reefs. Additionally, microbial mats stabilized the sediments, guaranteeing perfectly flat bedding."

Rapid burial and certain chemical conditions in the soil would also have played a part in the preservation, Klug added. 

For their study, researchers used ultraviolet (UV) imaging to identify morphological details that were previously invisible to scientists using X-ray techniques. The UV images revealed a hyponome, which is a funnel that directs water jets from Acanthoteuthis' mantle cavity; an esophagus and statocysts, which are sensory organs responsible for maintaining balance and detecting movement and change in direction; and a muscular mantle and collar made from cartilage.

Based on these characteristics and the creature's bullet-shaped body, Klug and his team believe Acanthoteuthis would have been a strong and rapid swimmer, and would not have needed to rely on ocean currents to carry it where it needed to go.

"We are unable, however, to determine more precisely in which water depths they lived," Klug continued in his statement made to Live Science, adding that they probably couldn't have dived deeper than 200 to 300 meters below the ocean surface, or the shell chamber inside their mantles would have imploded.

Their findings were recently published in the journal Biology Letters.

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