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'Tully Monster' Mystery Solved: True Identity Revealed

The Tully monster's classification has perplexed researchers since 1958.

In 1958, amateur fossil collector Francis Tully found a prehistoric creature so strange that even scientists called it a monster. The beast has perplexed researchers ever since, with some calling the so-called "Tully monster" a worm and others classifying it as a shell-less snail.

But now, an analysis of more than 1,200 Tully monster (Tullimonstrum gregarium) fossils has uncovered the monster's true identity. It's a 307-million-year-old jawless fish, a creature in the lineage leading to modern-day lampreys, the researchers found.

Living Fossils: Animals From Another Time: Photos

"It's a very unusual animal," study co-author Scott Lidgard, curator of invertebrate paleontology at the Field Museum of Natural History in Chicago, told Live Science. [See Images of the Bizarre Tully Monster]

The roughly foot-long (0.3 meters) monster had a narrow body with eyes like a hammerhead's on the top of its head and a long, slender snout ending in a toothy jaw.

Scientists formally described it in 1966, and in 1989, Illinois designated it as the official state fossil. But experts still couldn't make heads or tails of it. They couldn't even place it in a phylum, a big-picture category that includes about 30 broad subcategories, and explains the origins of almost every living thing on Earth.

Sea Monsters Real And Imagined: Photos

Researchers have found thousands of Tully monster specimens in Illinois over the years. Many of them were digitally scanned into The Field Museum's electronic database, so scientists had plenty of samples to examine while undertaking the new study.

"Basically, nobody knew what it was," study co-author Derek Briggs, a professor of geology and geophysics at Yale University and a curator of invertebrate paleontology at the Yale Peabody Museum of Natural History, said in a statement. "The fossils are not easy to interpret, and they vary quite a bit. Some people thought it might be this bizarre, swimming mollusk. We decided to throw every possible analytical technique at it."

The researchers combed through the database and also used synchrotron elemental mapping, a technique that uses a powerful light source to determine the chemistry within a fossil.

These Fish Are Oddly Shaped For A Reason: Photos

Although soft-bodied, the Tully monster is a vertebrate that likely used its tail to propel itself forward in the water. Moreover, analyses showed that "the monsters are related to the jawless fishes that are still around today by a unique combination of traits, including primitive gills rows of teeth," Paul Mayer, The Field Museum's fossil invertebrates collections manager, said in the statement.

It also has "traces of a notochord, the flexible rodlike structure along the back that's present in chordate animals - including vertebrates like us," Mayer said.

The big-eyed and pointy-toothed fish was likely a predator, said study lead author Victoria McCoy, who conducted the research as a Yale graduate student and is now at the University of Leicester in the United Kingdom. However, it's unclear when the animal first developed and when it went extinct, she said.

The study was published online today (March 16) in the journal Nature.

More from LiveScience:

Images: Weird Ancient Fish Fossil (Titktaalik)

Image Gallery: 25 Amazing Ancient Beasts Photos: The Freakiest-Looking Fish Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Article originally appeared on Live Science.

The Tully monster likely used its long tail to propel it forward in the water.

We all enjoy a tall tale. Cultures with seafaring traditions are especially ripe in what seem like the tallest sea monster tales of all: hydra, kraken, sirens, scylla, leviathans, assorted serpents and mermaids. Usually the stories are never confirmed and deemed baseless. Then again, some of the tales are based on something. With our skeptical hats on, let's have a look at sea monsters both real and fanciful. We begin with a story that went viral just this week, about a supposed monster that revealed itself during a swim in the Thames River. A

Nessie-like

bump in the water, filmed from overhead, started it all. But you'll have to judge for yourself: Real or fake? Watch the video and read

Ben Radford's take

on the tale.

'Thames Monster' Video: Hoax Or Mammal?

In keeping with our subject of monsters of the deep, we also learned this week that at least

some whales

really can, and will, use their heads for ramming -- just as the fictional Moby Dick did, in the Herman Melville classic of the same name. Did whales perfect the head-butt long before people started banging heads?

Real Moby Dick: Some Whales Ram With Their Heads

Sea monsters are truly global, of course. This one from Japan serves as the villain for the classic maiden in distress, who awaits rescue by her hero. The poor monsters are almost always cast as the bad guys. And so they usually end hacked to pieces; fish food. But is there any truth behind these sea serpent tales?

Ancient Sea Monsters Were Black

Maybe it's the oarfish. It looks too monstrous to be true. It can grow many meters long, has strikingly bright silver scales, scarlet fins and some ornate headgear that more than explains why some call it a roosterfish. If only it were a reptile, it'd be a true sea serpent. Alas. It is a fish. A very weird and beautiful fish, but still a fish.

Is the Loch Ness Monster Dead?

There are also other, newfound "sea serpents" our sea-going ancestors never imagined. This one was spotted by a satellite coiling off the south coast of Japan's Hokkaido island. What do we know about it? 1) It's arguably one of the largest organisms on Earth, 2) It swallows ships, engulfs islands and generally does what it wants, and 3) We're darned lucky it's made of plankton.

Monster Goldfish Found in Lake Tahoe

Research into such massive blooms and the individual plankton cells that comprise them has revealed surprising cooperation among the microorganisms. They appear to operate like more than just floating individual cells. They live and die for the greater good, it seems. So they may be, in fact, a gigantic watery superorganism. Now that's a cool monster for you: You can swim in it and never know you've been in the belly of a beast.

VIDEO: Why Squid Are Terror Monsters Of The Sea

Mermaids and mermen have always been the stuff of fantasy. Where did the fantasies come from? There are some standard answers to this question, which have always seemed rather inadequate. For instance ... (next slide, if you please) ...

Mermaids Exist! And They Are Seismically Sensitive

The manatee has often been called the source of mermaid myths. It's a mammal, so it breathes air. But who would ever mistake a manatee for a sleek and beautiful mermaid? Could it be love-starved sailors with poor eyesight? There was no shortage of these fellows in the days before optometrists.

Make Way For Manatees Month: Photos

Another possibility is that merfolk were inspired by fish with roughly human-looking faces, like this fellow. Some fish can look humanoid. That would be enough to get superstitious sailors started.

First Face? Prehistoric Fish Was a Jaw-Dropper

How about giant, ship-destroying squid and octopi? These monsters were old hat even to the easily freaked-out. Most folks figured they were historical exaggerations. That's until some very large and unusual squids started washing up or being hauled in by marine biologists in recent years. Colossal squid are meters long, pretty amazing beasts. Still, they have never been known to lift ships out of the water. And since were on the topic of squids ...

Giant Squid Photos

Do you remember when this one hit the headlines? It's not so gigantic, at four meters long, but it was observed 3,380 meters down in the Pacific Ocean near Oahu. It's pretty big to have gone unseen before its May 2001 discovery. So what else is out there? It's pretty clear marine biologists have only just begun discovering what lives in the deep sea. The more time they spend searching, the more they will find. But none would dispute that the nastiest sea monster to ever rise out of the sea is ... (drum roll please) ...

You might have guessed it: Human garbage. Yep. It's the ugliest, most alien-looking, fatal and pervasive monster in the seas. Garbage patches have been getting a lot of attention lately. These are areas on the seas where currents and winds tend to concentrate floating garbage.

Life On The Ocean Floor Garbage Patch: Photos